Publisher：Journal of Wind Engineering and Industrial Aerodynamics  

Wind speed probability distribution functions (PDFs) are crucial for evaluating urban wind environments. While previous studies have used unimodal distribution functions to model PDFs, bimodal patterns are also observed in urban areas. To more accurately model unimodal and bimodal PDFs, this study assessed the applicability of the mixture Weibull distribution (2W2W). The performance of the two-parameter Weibull distribution (2W) was also analyzed for comparison. Three parameter estimation methods (method of moments (MM), method of L-moments (LM), and maximum likelihood method (ML)) were applied to wind speed data of an isolated building case from a LES database. It was found that L-moments show non-linear relationships with moments, but with smaller magnitudes. 2W2W outperforms 2W in estimating both moments and L-moments, especially for higher-order statistics. 2W2W has the potential to better capture both unimodal and bimodal distributions compared to 2W. While 2W2W generally outperforms 2W under MM, noticeable oscillations were observed at some points. Although ML is the most accurate method at most points, LM still outperforms ML at specific locations based on both 2W and 2W2W. This study is expected to offer valuable insights into modeling PDFs for urban wind environments.

DOI： 10.1016/j.jweia.2024.106001

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Publishing type：Research paper (scientific journal)   Publisher：Building and Environment  

Accurate prediction of low-occurrence wind speeds around urban structures is crucial for safe building design. Although Large-eddy simulation (LES) is commonly used as a high-fidelity model as compared with the Reynolds-Averaged Navier–Stokes (RANS) simulations, the present validation process relies on the comparison of fundamental statistics of the mean and standard deviations. The discrepancies in LESs and wind-tunnel experiments (WTEs) are unclear in terms of physical quantities characterizing the unsteadiness of the simulated turbulent flow such as probability density and power spectral densities, and low-occurrence winds speeds. Therefore, this study aims to evaluate the effectiveness of LES in predicting unsteady wind behavior around a 1:1:2 block model. The study identifies prominent differences to improve the accuracy of unsteady numerical simulations especially for the purpose of predicting low-occurrence wind speeds. Various advection schemes in LESs were investigated, including first-order upwind, second-order linear, and dynamic interpolation schemes. The results show significant discrepancies, particularly in higher-order statistics and low-occurrence wind speeds, with WTE consistently exhibiting higher energy levels across all frequencies. These findings highlight the need to refine advection schemes to enhance their predictive accuracy. LESs with minimal numerical errors from discretization schemes can substantially improve urban wind assessments and contribute to the design of safer structures.

DOI： 10.1016/j.buildenv.2024.112201

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Publisher：Building and Environment  

There is an increase in reliance on large-eddy simulations (LES) over traditional Reynolds-Averaged Navier–Stokes (RANS) simulations for conducting urban wind studies because of their potential to capture detailed flow characteristics and unsteady flow phenomena. Validation remains a crucial aspect of computational fluid dynamics (CFD) analysis. Yet, LES validation often relies on traditional RANS-based metrics that focus on mean quantities, despite LES providing richer flow details. With adequate LES validation guidelines lacking in the computational wind engineering literature, this paper introduces a new validation metric tailored for LES in urban wind studies. This study uses the ”Michelstadt” test case, a semi-idealized model of a generic European city, to demonstrate the metric's evaluation. It begins by assessing the importance of mesh sensitivity and inflow generation techniques in achieving high-fidelity LES results. Then, the proposed metric, called the overall area metric (OAM), improves the evaluation of LES results by quantitatively comparing the cumulative density functions (CDFs) of the velocity time series of LES with experiments. The LES results for mean velocity and Reynolds stresses align well with the experimental data based on traditional hit rate and factor of two metrics both within and above the urban canopy layer (UCL). The OAM reveals poor results above the building compared to the results within the UCL for the mean streamwise velocity. Therefore, the OAM metric accurately represents velocity distributions, allowing validation of a wider range of wind speeds, unlike previous metrics. This is important in recent LES studies on rare high-wind events, such as gusts.

DOI： 10.1016/j.buildenv.2024.112285

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Publishing type：Research paper (scientific journal)   Publisher：Building and Environment  

The dissimilarity of dynamics and turbulence structures between the roughness and inertial sublayers (RSL, ISL) over roughness elements show that ISL turbulence is much more homogeneous. Conventional logarithmic law of the wall is merely applicable for the RSL mean-wind-speed profiles. To characterize the turbulence scales and elucidate the mechanism, the flows in the atmospheric surface layer (ASL) over real urban morphology are measured in wind tunnel experiments fabricated by 3D-printing, reduced-scale model of downtown Kowloon Peninsula, Hong Kong. Elevated dispersive flux at urban canopy signifies the influence from individual buildings and inhomogeneous RSL flows. A positive momentum contribution appears in the low-frequency regime. The large-scale turbulence in RSL thus enhances the mixing and transport, resulting in inhomogeneous flows. The contribution from ejection Q2 and sweep Q4 increases and decreases, respectively, with increasing RSL motion strength. The conventional −5/3 law is observed by empirical mode decomposition (EMD) and the largest amplitude fluctuation occurs more often when the turbulence length scale is comparable to the turbulent boundary layer (TBL) thickness. The single-point amplitude modulation (AM) shows that the large- and small-scale turbulence correlates tightly at the bottom of RSL. Besides, the joint probability density function (JPDF) illustrates that accelerating large scales often occur with decelerating small scales, and they are intensified with increasing wall-normal distance. As a result, large-scale turbulence influences substantially the flow structures over urban areas and the small-scale turbulence (even) in RSLs in the vicinity of building obstacles.

DOI： 10.1016/j.buildenv.2024.112193

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Publishing type：Research paper (scientific journal)   Publisher：Building and Environment  

Within urban boundary layers, the safety of pedestrians is markedly affected by wind speed, particularly in urban areas. The characteristics of turbulence above the canopy layers can lead to unpredictable changes in wind speed at the pedestrian level. Therefore, this study analyzes low-occurrence wind speed phenomena above canopy heights for uniform and nonuniform block configurations using wind tunnel experiments (WTE) to understand the background turbulence characteristics which the wind profile is generated by the boundary layer above the canopy. The urban canopy arrays were reproduced using solid blocks arranged in 30 rows in a streamwise direction with a packing density of 25 % at three different heights. An x-type hot-wire anemometer was used to measure the streamwise and vertical velocity components. The low-occurrence values were classified based on wind speed percentiles of 0.1 %, 1.0 %, 99.0 %, and 99.9 % wind speeds. The results demonstrated that above the canopy, there were minor influences of block height variations on the low occurrence factor. The peak factor demonstrated a comparable value between the uniform and nonuniform cases, regardless of the block arrangement. Statistical models based on the Weibull distribution and Gram–Charlier series demonstrating good agreement with the WTE data in predicting the low occurrence and peak factors. This study found that variations in block height have a minor influence on the low occurrence and peak factors within the turbulent boundary layers, implying that we can separate the effect of background turbulence from the local turbulent generation within the urban canopy layers.

DOI： 10.1016/j.buildenv.2024.112138

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Architectural Institute of Japan  

<p>This study examines the peak wind speed statistics and their uncertainty at the pedestrian level around an isolated building model using Large-Eddy Simulation (LES). Understanding pedestrian-level wind conditions is crucial for building design focused on comfort and safety. Traditional methods, often limited by the inability to directly assess peak speeds through wind tunnel experiments or computational fluid dynamics, rely on lower-order statistical measures combined with gust and peak factors. Our approach allows for a more direct and reliable estimation of these wind statistics, providing insights into the complexities of building-induced winds and their impact on pedestrian-level environments.</p>

DOI： 10.3130/aije.90.35

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Publishing type：Research paper (scientific journal)   Publisher：Building and Environment  

The effect of urban geometries on the peak wind speed at the pedestrian level was investigated using simplified urban-like arrays in wind tunnel experiments. To scrutinize the turbulent flow's spatial and temporal characteristics, large-eddy simulations (LESs) were adopted to simulate suitable experimental conditions using an external force accelerating the flow with the periodic boundary condition. Although previous studies have revealed that conventional LESs use a constant pressure gradient as a momentum source, driving the flow differs from those in developing boundary layers in experiments, and the effect of the momentum source on peak wind speeds at the pedestrian level remains unknown. Therefore, this study used a series of LESs based on the three driving methods to investigate the impact of the momentum provision on the relevant statistics and peak values. The turbulent statistics showed good agreement among the cases driven by the momentum sources regardless of the shape of the profiles of the momentum source. Peak wind speeds, quantified by percentiles, were estimated using statistical models based on the Weibull distribution. Overall, the results showed a good agreement between the LESs and statistical model estimations when higher-order moments were adopted as the estimation parameters.

DOI： 10.1016/j.buildenv.2024.112244

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Publisher：Sustainable Cities and Society  

Since the indoor ventilation significantly influences human health and comfort, there has been a huge demand for realizing a sustainable air conditioning system by utilizing natural ventilation. Although there are numerous experimental studies on wind-induced natural ventilation, these experiments were unable to determine the genuine ventilation rate based on the velocity component normal to opening because of the methodological limitations. In this study, therefore, stereoscopic particle image velocimetry was progressively employed to determine three velocity components within a lateral opening of an isolated cubic building in single-sided and cross ventilation conditions. As a result, the mean, variance and covariance of velocity components at lateral opening of the single-sided-ventilation model are comparable to those of the cross-ventilation model. On the other hand, after the flow goes into the building, the velocity fluctuations are significantly reduced in the single-sided ventilation condition, while it decays more slowly in the cross-ventilation condition. In addition, the mean and instantaneous ventilation rates were experimentally determined to quantify the contribution of the turbulent flow passing to the ventilation rates. This study clarifies the ventilation mechanism by turbulence and provides reliable database of ventilation flow for numerical validation.

DOI： 10.1016/j.scs.2024.106049

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Publishing type：Research paper (scientific journal)   Publisher：Sustainable Cities and Society  

Predicting low-occurrence strong wind speeds in urban areas is crucial for enhancing the comfort and ensuring the safety of residents. Artificial neural network (ANN) models outperform traditional statistical methods in accurately estimating low-occurrence wind distributions. However, generalizing trained models to be applicable to various datasets remains a significant challenge. Therefore, three ANN models with different input variables, trained by a single turbulent dataset of a building array case, were applied to four types of datasets to evaluate the models’ generalization ability for predicting low-occurrence strong wind speeds in urban areas. It found that the ANN model, which uses the mean, standard deviation, and skewness of the turbulent flow, shows the best generalization ability among the three ANN models for all types of datasets. In addition, for the four datasets, the results calculated by this model show that the majority of points have an error of less than 20% compared to the true values. It is advisable to construct models using more extensive training data that encompasses a broad range of mean and skewness of wind speeds. This study contributes to the development of more effective and adaptable ANN models for urban wind safety in building engineering.

DOI： 10.1016/j.scs.2024.105837

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Publishing type：Research paper (scientific journal)   Publisher：Sustainable Cities and Society  

Promoting urban sustainability requires a comprehensive understanding of the interaction between built and surrounding environments. Low-occurrence wind is a key factor affecting building performance, urban breathability, and human comfort and safety. This study proposes artificial neural network (ANN) models to estimate low-occurrence wind speeds using wind speed statistics from field measurements, and to investigate the relationship between these statistics and pedestrian-level low-occurrence wind speeds. The performance of ANN models was compared with traditional statistical methods, including Gram–Charlier series (GCS) and Weibull models (2W and 3W). It was found that ANN models estimate percentile values more accurately due to their data-driven capabilities. The proportion of negative outliers for 0.1 % percentile wind speeds decreased by approximately 70 % compared to the GCS models and 40 % compared to the 3W model. The accuracy for 99.9 % percentile wind speeds in ANN models and traditional statistical methods with input orders higher than the second order improved by approximately 30 % compared to the Gaussian and 2W models. Additionally, the estimation accuracy of ANN models improved with data clustering. This study highlights the potential of ANN models in advancing urban sustainability by accurately estimating pedestrian-level low-occurrence wind speeds from fundamental statistics, contributing to sustainable urban development.

DOI： 10.1016/j.scs.2024.105828

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Language：English   Publisher：International Exchange and Innovation Conference on Engineering & Sciences  

Turbulent structures are intermittent and spatially correlated above the canopy. These structures play a crucial role in enhancing the momentum exchange inside the urban boundary layer. While various studies have explored these structures numerically and experimentally, the structures dynamics over extremely rough surfaces remain substantially less understood. Hence, this study applies Proper orthogonal decomposition (POD) to high temporal and spatial resolution data for the streamwise velocity component derived from large eddy simulation. The results reveal that the first four POD modes account for over 40% to the turbulent kinetic energy. Furthermore, the first POD pair exhibits a wider coherent structure compared to the second POD pair (mode 3 and mode 4). Interestingly, POD mode 1 and mode 2 oscillate at approximately the same frequency. This study provides deeper insights into the coherent structure’s dynamics above the canopy, thereby contributing to a better understanding of the momentum exchange mechanism.

DOI： 10.5109/7323365

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CiNii Research

Language：English   Publisher：International Exchange and Innovation Conference on Engineering & Sciences  

Accurately predicting low-occurrence wind speeds around urban structures is vital for proper building design as well as pedestrian safety. Although Large-eddy simulation (LES) is often used as a high-fidelity model compared to Reynolds-averaged Navier–Stokes (RANS) simulation, current validation processes mainly compare fundamental statistics of the mean and standard deviations of the wind speed. Discrepancies between LESs and wind-tunnel experiments (WTE) remain unclear, particularly regarding physical quantities that characterize the unsteadiness of turbulent flows, such as probability densities, power spectral densities, and high-order moments of the wind speed. This study evaluates LES's results in predicting unsteady wind behavior around a 1:1:2 block model. Two advection schemes in LESs, including first-order upwind and second-order linear were investigated. The results show notable discrepancies, particularly in high-order statistics with WTE consistently exhibiting higher energy levels across all frequencies. These findings underscore the need to refine numerical models to improve their predictive accuracy.

DOI： 10.5109/7323337

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CiNii Research

Publishing type：Research paper (scientific journal)   Publisher：Building and Environment  

Iran has been experiencing severe dust storms due to strong wind speeds that cause sand erosion. This erosion is particularly pronounced in the semi-arid and arid zones. Wind speed predictions using numerical weather forecasting (NWF) are indispensable; however, the applicability of NWF for predicting extreme annual wind speeds is not well known. To validate the NWF model, this study compared NWF-model-predicted 3-hour averaged wind speeds over one year and those observed at 390 weather stations. In addition, a statistical model was employed to estimate the probability densities of wind speeds for both the observational data and the NWF output. As an NWF model, the mesoscale Weather Research and Forecasting (WRF) model was utilized to simulate wind speeds. The results indicate that the observation data are consistent with the modeled datasets regarding the relationships among the mean, standard deviation, and skewness, whereas the WRF model tends to overestimate the mean wind speeds. In addition, the predictability of annual extreme wind speeds was determined using the peak factor. Moreover, skewness has emerged as an influential parameter for predicting extreme winds. Finally, the Gram-Charlier series model was utilized to estimate probability density functions of the wind speeds, demonstrating its effectiveness in capturing positively skewed distributions. The present analyses broaden the use of both NWF outputs and statistical methods to predict extreme wind speeds in Iran.

DOI： 10.1016/j.buildenv.2024.111726

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Publishing type：Research paper (scientific journal)   Publisher：Building and Environment  

Natural ventilation offers significant advantages, especially in terms of energy conservation. However, most published articles have focused on the ventilation flow rate to determine the average contaminant concentration, while few have examined local ventilation distributions. Therefore, isothermal steady-state Reynolds-averaged Navier–Stokes simulations were conducted to analyze the airflow and scalar concentration fields of a cross-ventilation model sheltered by buildings. Based on these fields, we generated the spatial distributions of ventilation indices, namely, the net escape velocity (NEV), point-to-point indices transfer probability (TP), and travel time (TT), to discuss the dispersion of scalars emitted from local points in a room with natural ventilation. The NEV, which indicates the direction of the scalar discharge from each cell, exhibited a distribution distinct from the advection velocity because of concentration gradient effect. Higher TPs were observed when evaluated from a contaminant source to a target point following the NEV streamlines. Meanwhile, lower TTs were observed when evaluated in a point near the source and also from a contaminant source to a target point following the NEV streamlines. Although TP and TT are independent ventilation indices, a negative correlation between them was observed. Instead of the ventilation flow rate, the detailed structure of scalar dispersion can now be described by simultaneously analyzing the ventilation efficiency indices, which provide information on the general contaminant transport direction, and the probability and duration of transfer from a source to a target point. This potentially helps in the design of ventilation system especially in room lay-out to avoid cross-contamination.

DOI： 10.1016/j.buildenv.2024.111668

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Publishing type：Research paper (scientific journal)   Publisher：Journal of Wind Engineering and Industrial Aerodynamics  

Pedestrian-level wind environment is a key aspect in sustainable urban planning. Especially, evaluating extreme wind speed in urban areas is important, since strong winds increase the risk of accidents and injuries of pedestrians. Although several statistical methods were developed to estimate extreme wind speed using statistics in previous studies, their robustness and accuracy remain unclear for the applications on the entire pedestrian level of urban areas. This study validated the effectiveness of the Weibull distribution (KB, 2W, and 3W) method and the Gram–Charlier series (GCS) method in four scenarios: three idealized urban cases and one actual urban case, all at the pedestrian level. The validation was performed using time-series data from the large-eddy simulations (LESs). It was found that for the extreme wind speed with exceedance probability q = 10%, 1%, and 0.1%, the adaptive GCS method (GCS-A) and 3W method (the third-order Weibull distribution method) were found to be robust and accurate. The sixth-order GCS method (GCS-6th) shows high estimation accuracy at most regions, except several regions with large high-order statistics. The outcomes of this study are anticipated to make a valuable contribution to urban planning and design, particularly in the context of wind environment considerations.

DOI： 10.1016/j.jweia.2024.105778

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

The use of RANS (Reynolds-Averaged Navier-Stokes) simulations to study airflow over cross-ventilated buildings has been widely performed under both isolated and sheltered conditions. For a sheltered environment, great efforts still need to be made as few studies have been conducted on cross-ventilated buildings, located far downstream of the urban morphology. Therefore, in this study, a series of simulations with different turbulence models were conducted to determine the performance in predicting the external and internal airflows of a cross-ventilated building under sheltered conditions and to evaluate the ventilation performance. Two urban building dispositions were considered, namely square (SQ) and staggered (ST) layouts. The evaluation of the velocity profiles was performed in the vertical and horizontal planes of the target building to systematically determine the accuracy of each model. The qualitative results showed that several RANS models are able to generate the main features of the external (in-canyon) and internal flows. In addition, the quantitative evaluations of the internal flow showed that the vertical velocity in the vertical plane and the lateral velocity in the horizontal plane are poorly predicted in the SQ array. Furthermore, the prediction of the streamwise velocity in the horizontal plane of the ST array is not satisfactory. The RANS ventilation rates are comparable to the large-eddy simulation (LES) results for certain models in the SQ array, but the deviations are large for all models in the case of the ST array, with the highest predicted ventilation rate being 40% lower compared to LES.

DOI： 10.1016/j.buildenv.2024.111402

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Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Low-occurrence wind speed in urban areas has a profound impact on the daily activities of people. Although several statistical methods were developed for estimating the low-occurrence wind speeds, their accuracy and flexibility still need improvements. Based on the inference from the favorable outcomes of statistical models in which low-occurrence wind speeds can be estimated by the statistics including high-order moments, in this study, the artificial neural network (ANN) models were designed to estimate the low-occurrence wind speeds based on the moments. After the sensitivity tests for the dimensions, hidden layers, epochs and training data ratios of the ANN models, the optimal setting was applied to predict the low-occurrence wind speeds of two building array cases including square and staggered layouts. The applicability of the ANN models was also evaluated for the extrapolation method between two building array cases and compared with the traditional statistical methods. It was found that the ANN models with the higher-order statistic input showed better performance than those with the second-order statistic input. The results obtained from the interpolation method are more accurate than those from the extrapolation method. Compared with traditional statistical methods, the ANN models show greater superiority in the prediction accuracy. According to the comprehensive evaluation of the ANN models, although they require ample training datasets connecting the statistics and low-occurrence wind speeds, it is proved to be a promising approach for estimating the low-occurrence wind speeds in urban wind environment.

DOI： 10.1016/j.buildenv.2024.111171

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

DOI： 10.1016/j.dib.2023.109856

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Predicting infrequent and extreme wind speeds in a built environment is essential for ensuring comfortable and safe pedestrian spaces. Recent studies have employed statistical methods that assume a distribution function for wind speeds at pedestrian levels. Fundamental studies on the relationship between canopy flow and statistics are required to further develop statistical models. Therefore, this study aimed to understand the characteristics of strong and weak wind events within a simplified urban canopy and to scrutinize the relationship between high-order moments and extreme wind events. Particle image velocimetry (PIV) was employed to capture the velocities within a canopy consisting of cubes arranged in a staggered layout with a packing density of 25 %. The probability density functions (PDFs) of the velocity components classified by the mean flow patterns revealed that the PDF shapes were altered by the reverse and spanwise flows. In addition, strong correlations were verified between the gust or peak factor (PF) and high-order moments such as skewness, kurtosis, fifth-order, and sixth-order moments. Accordingly, the PF of the velocity components and wind speed were compared with the predictions by statistical methods based on the Weibull and Gram–Charlier series (GCS). These observations validate the previous statistical methods based on Weibull or GCS distributions. Although the physical interpretation of these statistics is ambiguous, the present analyses indicate that PF can be predicted by high-order moments, especially in particular, by skewness and kurtosis.

DOI： 10.1016/j.buildenv.2023.111050

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Language：Japanese   Publisher：Japan Association for Wind Engineering  

The effect of urban geometries of simplified urban-like arrays on the turbulent airflow at the pedestrian level has been investigated by wind tunnel experiments and computational fluid dynamics. In these experiments, there are the limitations of the spatial and temporal sizes of stored datasets due to the high spatial and temporal resolutions. Therefore, in the present study, the airflow over simplified urban-like arrays is determined by large-eddy simulations using external force accelerating the flow with the periodic boundary conditions and the principal component analysis based on the singular value decomposition is conducted. The characteristics of the singular modes are compared using different sizes of the original datasets to clarify the effect of the sizes of the datasets on the resolvable turbulent properties. Additionally, low-rank approximation analysis was performed on the wind speed fields at pedestrian level to understand the dominant singular modes on the gusty phenomena.

DOI： 10.14887/natsympwindengproc.28.0_90

CiNii Research

Language：English   Publisher：Japan Association for Wind Engineering  

Accurate prediction of the low-occurrence wind speeds around urban structures is critical for secure building design and pedestrian safety. In general, Large-eddy simulations (LESs) are preferred over Reynolds-Averaged Navier-Stokes (RANS) simulations for the prediction accuracy in the turbulent statistics. However, previous validations focus mainly on fundamental statistics such as the mean and standard deviations of velocity components, leaving discrepancies in other statistics characterizing the unsteadiness of the flow unclear. Therefore, this study evaluates the accuracy and reliability of LESs in forecasting unsteady wind patterns around a 1:1:2 block model. By comparing the statistics determined by various advection schemes in LESs with those by wind-tunnel experiment (WTE), significant discrepancies were found, particularly in high-order statistics of the wind speeds. These findings underscore the necessity of to refine the procedure to employ LESs for better predictive accuracy, especially for the prediction of the low-occurrence wind speeds impacting urban wind environment and safer building designs.

DOI： 10.14887/natsympwindengproc.28.0_75

CiNii Research

Language：English   Publisher：Japan Association for Wind Engineering  

Indoor ventilation significantly influences human health and comfort. Although there are experimental studies on wind-induced natural ventilations, these experiments were unable to determine the genuine ventilation rate based on the velocity component normal to the opening. In this study, stereoscopic particle image velocimetry experiments were conducted for the
lateral single-sided ventilation condition of an isolated cubic building to determine three velocity components within the openings. The mean and turbulent flow patterns within the opening and those at the half building height were analyzed. At the opening, the stronger turbulence can be observed for the inlet flow, while it is weaker for the outlet flow. After the flow goes into the building, the velocity fluctuations are significantly damped. Accordingly, the mean and instantaneous ventilation rates were experimentally determined to quantify the contribution of the turbulent fluctuating ventilation flow. This study is an informative supplement for understanding the ventilation mechanism and effective database for numerical validation.

DOI： 10.14887/natsympwindengproc.28.0_83

CiNii Research

Language：English   Publisher：Japan Association for Wind Engineering  

The pedestrian-level wind environment plays an important role for human safety and comfort. Although previous studies proposed several statistical models to determine probability distribution function (PDF) of wind speed based on statistics, the accuracy still needs to be improved. This study proposed an updated framework for modelling the PDF based on the mixture distribution function. The database of an isolated building case was generated by large-eddy simulations (LES) and validated with wind tunnel experiment. Three empirical distribution functions (i.e., two-parameter and three-parameter Weibull distribution (2W and 3W), and a mixture of two 2W (2W2W)) were analyzed. Two distribution parameter estimation methods (i.e., moment method (MM) and maximum likelihood method (ML)) were evaluated. It was found ML and MM methods within the 2W2W framework closely match the probability density functions obtained from LES, while the 2W and 3W methods provide useful insights but with slightly less accuracy. Both ML and MM methods achieve high accuracy at most locations, but the ML method is more stable. Conversely, if feasibility and lightweight implementation are prioritized, the MM method is recommended over the ML method within the 2W2W framework due to the extensive time-series data required by the ML method. These findings offer valuable insights for improving building design and urban planning to better handle and mitigate wind-related hazards.

DOI： 10.14887/natsympwindengproc.28.0_65

CiNii Research

Language：English   Publisher：Japan Association for Wind Engineering  

Wind-tunnel experiments with generic block arrays with the packing density of 25% were performed. Two velocity components in the streamwise and vertical directions were measured using an x-type hot-wire anemometer. The arrays were designed as those with a uniform cubic block with edges of 0.1 m and a combination of the blocks with the heights of 0.05 m and 0.15 m to investigate the effect of the height variation on the gusty wind phenomena. The result demonstrated that, above the canopy, there is little influence of block configurations on the turbulence statistic, extreme and peak factors. In addition, statistical models can predict well the extreme and peak factors for uniform and non-uniform height cases. Additional research on the influences of height variation is needed to fully understand the wind flow characteristics above the urban canopy.

DOI： 10.14887/natsympwindengproc.28.0_54

CiNii Research

Language：Japanese   Publisher：Japan Association for Wind Engineering  

DOI： 10.5359/jawe.49.222

CiNii Research

Language：Japanese   Publisher：Japan Association for Wind Engineering  

DOI： 10.5359/jawe.49.37

CiNii Research

Language：Japanese   Publisher：Japan Association for Wind Engineering  

DOI： 10.5359/jawe.49.387

CiNii Research

Language：English   Publisher：International Exchange and Innovation Conference on Engineering & Sciences  

Understanding the turbulent flow feature over building arrays are essential because the flow distribution is determined by the interaction between the atmospheric boundary layer and building array. The present study investigated the turbulent statistics over roughness elements arranged in a staggered array using large eddy simulation. Unlike a conventional method to drive the flow by the constant pressure gradient, the current simulation method employed a vertical profile of the streamwise pressure gradient determined by the experimental data of the Reynolds stress obtained in a wind tunnel. The time series data were analyzed to determine the fundamental statistics and probabilistic characteristics. The results revealed that the probability density function of the streamwise velocity component followed the gaussian distribution curve behind the building model. However, the probability density function of the vertical component showed a positive skewed results owing to the reverse flow back to the roughness element.

DOI： 10.5109/7158035

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CiNii Research

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

This study compared various numerical schemes that have been reported with the assumption that artificial compressibility aids in the realization of explicit fluid dynamics simulations for a two-dimensional cavity flow. Four artificial compressible schemes, the artificial compressible method (ACM), entropically dumped ACM (EDACM), explicit method with virtual particles (EMV), were compared with a conventional incompressible scheme (simplified marker and cell, SMAC). The purpose of the comparisons is clarifying the validity of EMV in which the artificial speed of sound can be theoretically determined. In addition, the effect of the artificial speed of sound was investigated for ACM and compared with EMV. Moreover, three conditions of Reynolds numbers, Re=100, 1000, and 5000, were employed. Under steady-state conditions, the velocity and pressure distributions were found to be consistent among the EMV, ACM, EDACM, and SMAC. Further, the comparisons of the horizontal and vertical profiles indicated that these artificial compressible schemes reproduced the velocities using the incompressible scheme at three Reynolds numbers. In contrast, the temporal development of the velocity fields in the three artificial compressible schemes clearly exhibited small fluctuations in the velocity and pressure around the overall trends determined by SMAC. Further, the power spectral densities demonstrated that such fluctuations were due to compression-wave propagations with the artificial speed of sound. Although no clear differences were observed among EMV, ACM, and EDACM at these Reynolds numbers, EMV was determined to be advantageous in terms of theoretically determining the unique value of the artificial speed of sound once the lattice-grid system was fixed, whereas ACM and EDACM require sensitivity studies to select suitable values.

DOI： 10.1016/j.compfluid.2023.105985

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Wind-induced natural ventilation is a sustainable approach for improving the indoor thermal comfort, air quality, and energy consumption. Although numerous ventilation studies have addressed generic ventilation models, the cross-ventilation flow of a multilayered model (widely ingrained in a tropical climate zone such as Malaysia as a typical terraced house with a deep-plan layout) has not been studied well. Therefore, this study aims to investigate the flow patterns inside a simplified two-layered model separated by a second floor at the middle height with an opening using wind tunnel experiments. Two cases are considered based on the positions of the inlet and outlet openings on each floor. Two velocity components are measured using particle image velocimetry (PIV) and hot-wire anemometry (HWA). This study provides high-quality experimental datasets, which enables us to understand turbulent characteristics of indoor airflow, obtained using PIV and HWA for a generic two-layered cross-ventilation model. In addition, the results show that the ventilation performance of two-layered stratified buildings is significantly affected by the inlet opening positions. Moreover, the indoor flow direction is considerably changed owing to the multi-zoning of the indoor space. Although we employed only a generic two-layered model, this study clearly highlights the importance of considering multi-layered buildings for a better understanding of the ventilation performance.

DOI： 10.1016/j.buildenv.2023.110829

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Springer Science and Business Media LLC  

Turbulent flow over urban-like roughness has been numerically studied for various purposes, such as the clarification of turbulent characteristics over rough walls, visualization of turbulent structures around block arrays, and evaluation of urban ventilation and pedestrian winds. In such simulations, a portion of the developing boundary layer is extracted as a numerical domain, assuming periodic boundary conditions in the horizontal direction to reproduce laterally homogeneous rough surfaces. However, the conditions required to drive the airflow by an artificial momentum source uniquely determine the turbulent statistics, which are different from those in developing boundary layers. Therefore, this study presents a new approach for driving the airflow over urban-like block arrays. The new method is based on spatially averaged Navier–Stokes equations to prove the necessity of height-dependent momentum provision. The turbulent flow over a cubical-block array is determined using large-eddy simulations driven by four different momentum sources. Regardless of the driving force, the vertical profiles of the streamwise velocity components are identical. In contrast, slight differences in the vertical Reynolds stress, variances in the velocity components, and turbulence kinetic energy are appropriately reproduced in the new approach. In addition, the budget equations of the turbulent statistics reveal that a change in the vertical Reynolds stress affects the energy production and its redistribution into variance components. The proposed method can contribute to the reproduction of a realistic turbulent flow and provide a theoretical understanding of the momentum provision.

DOI： 10.1007/s10546-023-00823-z

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Other Link： https://link.springer.com/article/10.1007/s10546-023-00823-z/fulltext.html

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Probability density distributions (PDFs) of wind speeds at pedestrian levels are required to predict gusts for wind environment assessments. However, the time-series data are extremely large in data volume for calculating the PDFs. Therefore, we applied the Gram–Charlier series (GCS) to the dataset of the flow fields at the pedestrian level around a simplified block array obtained by a large-eddy simulation to analyze the probability density and low-occurrence strong wind speeds. PDFs are predicted using the GCS-nth model, in which the distribution is modified from the Gaussian distribution by incorporating third to nth-order moments. The GCS can estimate the skewed PDFs of pedestrian winds and more accurately predict the percentile values compared to a Gaussian distribution. In addition, at most locations, the higher-order GCS estimates the probability densities and percentiles more accurately than the lower-order models. In contrast, the accuracy of GCS-6th is not always better than that of GCS-5th or lower models in some locations because of the large values of the coefficient in the polynomial function that modifies a Gaussian distribution. This study proves that using GCS to predict PDFs from statistics is a newly discovered and useful approach for wind environmental assessment.

DOI： 10.1016/j.jweia.2023.105427

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：MDPI AG  

Middle Eastern countries suffer from dust events due to extended arid areas. Among them, Iran is a country experiencing a high record of dust events each year causing major environmental challenges. Although there are previous studies of the present situations of dust storm occurrences in Iran, most studies have analyzed the meteorological dataset in limited weather stations and areas in Iran. To understand the nationwide trends of the distributions and frequencies of dust storm events, comprehensive statistical evaluations of dust storm events, based on different dust categories, are required. Therefore, this study analyzes 12-year meteorological databases obtained at 427 stations in Iran to clarify the distribution of dust events and occurrence frequencies of the dust in a recent decade by classifying the dust events into suspended dust, rising dust, and dust storm. The highest record of the days belongs to rising dust, which surpassed 150 days per year, followed by suspended dust with over 100 days per year, and, finally, dust storms with a frequency of 30 days per year as annual statistics of dust events. In contrast, there were some stations that recorded minimal occurrences of dust events during the observation periods. To prove the spatial nonuniformity of the dust events, suspended dust events showed a distinct concentration in the western regions of the country, while rising dust tended to occur more frequently in the southern, eastern, and central parts of Iran. Accordingly, seasonal analyses indicate that the highest number of dust events occurred during the spring season, with the number of stations experiencing dust events being greater than during other seasons in all three categories. Nonetheless, annual analyses of dust events do not demonstrate any significant trends, with only 2012 having the highest record of dust events across all three categories. In terms of monthly analyses, dust events tended to increase from late spring to early summer in the suspended dust and rising dust categories. These analyses demonstrate the importance of studying numerous weather station datasets to clarify spatial trends of dust events with long-term variations.

DOI： 10.3390/su151612294

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Architectural Institute of Japan  

<p>Wind environment at a pedestrian level has been evaluated based on probability density functions and percentile wind speeds. The purpose of this paper is to clarify the effect of the driving force on the probabilistic cha racteristics of the airflow around a simplified urban like array using large eddy simulation. The vertical profiles of skewness and kurtosis as well as probabilistic density functions of velocity compon ents are clearly affected by the driving method above the roughness sublayer. In contrast, they showed similar trends regardless of the driving force in the roughness sublayer, although subtle local differences in the probability density functions are observed.</p>

DOI： 10.3130/aije.88.609

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Publisher：E3S Web of Conferences  

We conducted isothermal large-eddy simulations to generate the velocity and concentration distributions to investigate the air pollution transport from outside to inside of a space surrounded by urban-like block arrays. Contrary to previous study, we assumed that the pollution in the form of scalars are generated outdoors and not indoors which we placed at: 1) middle of window, 2) near window wall, 3) middle of street canyon at ground level, and 4) middle of street canyon at window level. Results showed that regardless of scalar source location, the scalars accumulated inside the indoor space which can be explained by the downdraft effect that are typically found in urban environments. The downdraft effect produced vortices outside and inside the indoor space. For scalars near window, indoor vortex drove the concentration to indoors. On the other hand, outdoor vortex transported the scalars located at street canyon to reach the window where they were eventually transported to indoors also due to indoor vortex. The average normalized indoor concentrations found in this study are 1.25 -1.50, 1.00 -1.75, 0.25 -0.50, and 0.0 -0.25 for scalars C1, C2, C3, and C4, respectively. Our study suggests that for natural ventilation studies of urban environments where air pollution is significant, outdoor effects should also be carefully considered.

DOI： 10.1051/e3sconf/202339602004

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Understanding low-occurrence strong wind speed (LOSWS) distributions at the pedestrian level is important. However, the robustness of the statistical methods for estimating LOSWSs under different conditions remains uncertain. In this study, the performances of the Weibull distribution method and Gram–Charlier series (GCS) method were compared. Their accuracies for isolated building and building array cases were analyzed. It was found that the constant peak factor (PF) of the Gaussian distribution showed acceptable accuracy only when the exceedance probability q = 10%. For q = 0.1%, the PF of the three-parameter Weibull distribution (3W) was more accurate than that of GCS-3rd. For fitting probability density functions, GCS-6th exhibited better flexibility than the two-parameter Weibull distribution (2W) and 3W. However, large leading terms leaded to oscillations at several points in GCS-6th. Regarding the estimation accuracy of LOSWSs, the 2W and 3W methods are superior to the GCS methods when the available orders of statistics are equal. Although the GCS methods showed higher accuracy than the 3W method in some regions, the oscillations at specific points in the GCS methods may lead to lower accuracy on average. The present findings can serve as an illuminating reference for further applications of these statistical methods.

DOI： 10.1016/j.jweia.2023.105401

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

The semi-open configuration of canyons is often associated with elevated structures such as eaves, awnings, balconies and arcades. Although numerous researchers have investigated the influence of these structures on canyon ventilation, detail investigations on the flow fields over two-dimensional (2D) semi-open street canyon with protruding eaves at the building level have not been studied adequately. Therefore, in this study, a series of large eddy simulation (LES) was performed to investigate the effect of various eave designs on the modification of flow structure and turbulent characteristics within and above 2D semi-open street canyon. The size of the vortices changes significantly with increasing length of the eaves as well as with the positioning of the eaves on the windward or leeward side or on both building facades, as the detachment and impingement points of the flow change. Spatial distribution of the turbulence statistics depicts a strong dependency on the eave dimension and position. The turbulence intensities and Reynolds stress were systemically reduced as the presence of eaves attenuate the penetration of the above flow into the street canyon. However, spatially-averaged profiles showed a clear dependence of turbulence statistics on the total length of eaves instead of the position of individual eave. The spatio-temporal of the mean wind speed showed an S-shaped profile in all cases instead of the different eave configurations. Furthermore, the occurrence frequency of ejections was dominant within the canyon, while above the building height sweeps was greater.

DOI： 10.1016/j.buildenv.2022.109921

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Akademia Baru Publishing  

A semi-open street canyon is able to protect pedestrians from unpleasant situations such as direct sunlight and rain. However, the protruding elements of the two opposite building facades that form the semi-open configuration can affect the air quality of the urban canopy layer (UCL). Therefore, this paper investigated the influence of the eave structures on the flow and pollutant dispersion over an idealized 2D street canyon with a unity aspect ratio. The length of the eaves was varied into 0.25H and 0.5H (H is the building height) and placed either on the leeward wall, the windward wall, or on both building facades located at the same elevation as the street canyon. Numerical simulations were performed using the steady-state Reynolds-averaged Navier-Stokes (RANS) equations in conjunction with Re-Normalization Group (RNG) k-ε as the turbulence closure model. The pollutant was released from a line source in the center of the bottom of the target canyon with uniform flow rate. Six different eave configurations were simulated in the wind direction perpendicular to the canyon axis, representing the worst condition of canyon ventilation. The evolution of the primary vortex, which occupied the entire canyon with the characteristic of skimming flow, showed less dependence on the length and position of the eave, except for the longest eave on the windward wall. However, the position of the vortex center depicted opposite results. The pollutant concentration is always higher near the leeward wall, but for the eave that protrudes from the windward wall with a length of 0.5H, the pollutant accumulates near the windward region. The ratio of pollutant concentration showed higher concentration in the semi-open configurations compared to the fully open layout as a result of limited penetration of shear flow into the canyon, which leads to deterioration of pollutant removal.

DOI： 10.37934/cfdl.15.2.5370

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Language：Japanese   Publisher：Japan Association for Wind Engineering  

DOI： 10.14887/jaweam.2023.0_137

CiNii Research

Language：Japanese   Publisher：Japan Association for Wind Engineering  

DOI： 10.14887/jaweam.2023.0_109

CiNii Research

Language：Japanese   Publisher：Japan Association for Wind Engineering  

DOI： 10.14887/jaweam.2023.0_127

CiNii Research

Publisher：Healthy Buildings 2023: Asia and Pacific Rim  

We performed large-eddy simulation (LES) of airflow within an urban building to estimate net escape velocity (NEV) distribution - a velocity scale that describes contaminant transport integrating both convection and diffusion effects, which we superimposed on contaminant concentration distribution. Results showed that at different flow times, contaminant accumulations may appear in local domains of indoor space that were higher than the mean contaminant concentration. These instantaneous accumulations, though happen in short periods, should be infomative in optimized indoor environmental design to avoid cross-contamination.

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Language：Japanese   Publisher：Japan Association for Wind Engineering  

DOI： 10.5359/jawe.48.376

CiNii Research

Language：Japanese   Publisher：Japan Association for Wind Engineering  

DOI： 10.14887/jaweam.2023.0_131

CiNii Research

Language：Japanese   Publisher：Japan Association for Wind Engineering  

DOI： 10.14887/jaweam.2023.0_133

CiNii Research

Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

This study focused on the low-occurrence wind events at pedestrian levels. The probability density functions (PDFs) are reliable statistical information. However, instantaneous velocity datasets are required to determine PDFs. In this study, theoretical methods were derived to model PDFs, based on the Gram–Charlier series (GCS methods) and higher-order statistics. The time-series data of the wind velocity components and speed at the pedestrian level around an isolated building from a large-eddy simulation (LES) database were used to validate GCS methods. Results showed that all GCS methods showed enhanced flexibility than the Gaussian distribution for modelling PDFs. For the low-occurrence values, the estimation accuracy of the GCS method gradually increased as the modelling order increased, at most probe points. The GCS-A method was developed to adaptively remove the large-error points based on thresholds of the fifth- and sixth-order moments. For global accuracy, the GCS-4th and GCS-A methods have higher estimation accuracy than other methods. The present model provides a new framework to estimate the low-occurrence wind events at pedestrian levels using only turbulence statistics, yielding to the expansion of the application of LESs for pedestrian-level wind assessments.

DOI： 10.1016/j.jweia.2022.105227

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Publisher：Building and Environment  

Although ventilation effectiveness varies in different sections of indoor spaces owing to imperfect mixing condition, previous studies on cross-ventilation in a model sheltered by urban-like arrays were limited to the computation of boundary-based volume flow rates and air exchange rate. To evaluate the local ventilation efficiency in the cross-ventilation model, we conducted large-eddy simulations (LESs) to generate the velocity and concentration fields of an indoor space surrounded by blocks arranged in a staggered manner to compute local ventilation using the age of air, purging flow rate, and net escape velocity (NEV*). We solved the distributions of seven scalars with corresponding sources positioned at the inlet of the indoor space (flow fluctuation is intermittent), indoor corners (flow stagnation is present), and downwind location, for two window-opening cases: parallel and perpendicular to the flow direction. The results indicated that the location of scalar sources significantly affects the ventilation of the scalar, resulting in different concentration fields, even when the sources are near each other. Additionally, we pioneered the use of NEV* for an unsteady simulation using LES and the decomposition of NEV* into two components: advection (NEVA) and turbulent diffusion (NEVT). The NEVA field appeared to be the velocity field, whereas the NEVT field appeared to be the induced or equivalent velocity field owing to turbulent diffusion. NEVT significantly affected local ventilation and even surpassed the effect of advection in regions with low mean velocities. This study reinforced the use of ventilation indices over boundary-based ventilation rates when analyzing the sheltering effect.

DOI： 10.1016/j.buildenv.2022.109759

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Particle image velocimetry (PIV) is currently the only method which can experimentally quantify the spatial distributions of velocity with high sampling frequencies without causing intrusions into the airflow of the measuring devices. To extend the use of PIV systems for determining the distributions of velocity for wind environmental and engineering purposes, this study showed various applications of wide-ranging PIV systems for an artificially created turbulent flow at the wind-tunnel scale. Various turbulent statistics, which are commonly employed for evaluating the wind structures and environments, were compared among three conditions of the measurement areas covered by PIV systems and a hot-wire anemometry (HWA). The largest measurement covering 500 × 500 mm2 can capture the turbulent motions extending to 40% of the entire boundary layer. In addition, the discrepancies on two-length scales could be discussed using spatial and temporal correlation functions owing to the wide-ranging PIV. Moreover, the limitations of the wide-ranging PIV systems were clarified. While the turbulent statistics compared among three PIV conditions and HWA demonstrated adequate agreement, the PIV with the largest measurement area failed to capture the small-scale turbulent structures due to the coarse grid resolutions. Moreover, the measurement resolutions of PIV systems demonstrated sensitivity in determining the spectrum and probability density functions, whereas a wide-ranging PIV system can cover wide-ranging measurement areas.

DOI： 10.1016/j.buildenv.2022.109590

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY  

In this study, the velocity field in a naturally ventilated building within an urban-like array was explored using large-eddy simulations. Reduced-scale building models were used to examine the impacts of the geometric conditions in the surrounding buildings and cross-ventilating windows on the flow statistics and instantaneous velocity fields in the sheltered building. The instantaneous velocity components averaged in the opening area were calculated for each condition of the building arrays and openings. The results indicate that the surrounding urban geometry significantly affects the turbulent opening velocities. Additionally, the three-dimensional instantaneous velocity distributions within the target building clearly demonstrate considerable differences under the different building and opening conditions. Such differences also affect the mean, maximum, and minimum wind speeds within the indoor regions. Moreover, the distributions of the two-point correlation coefficient (defined by the velocities normal to the windows at the center of the windward opening and inside the building) were compared for each condition. The strong correlations near the two openings indicate that the instantaneous velocity generated by the surrounding buildings is an important factor in determining the statistical and instantaneous features of indoor ventilating airflows.

DOI： 10.1002/2475-8876.12312

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Language：English   Publisher：Interdisciplinary Graduate School of Engineering Sciences, Kyushu University  

Dust storms originate from drylands and bring hazards and dramatic socio-economic impacts. This paper reviews the impacts of this phenomenon on human health, pollution of air, and socio-economic situations by focusing on susceptible areas to dust and sandstorms in Iran. It provides a short review of the dust and sandstorm phenomenon and the process of dust emissions. In addition, it reviews possible sources of dust and sandstorms inside Iran's borders and concludes that it originates from dried bed lakes which are located inside Iran. To consider the countermeasures of the hazardous effects of the dust storms, accurate prediction methods are required to be developed with plausible physical models describing the sand transport phenomenon with the association of mesoscale atmospheric predictions models. Accordingly, case studies employing atmospheric numerical simulation models were discussed. This study highlights the importance of the numerical predictions of dust storms that frequently occur in Iran.

DOI： 10.5109/5909116

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Wind gusts at the pedestrian level around buildings are caused by both effects of turbulent flow generated by surrounding buildings and the turbulent characteristic of the approaching flow. Although numerous researchers have stochastically investigated the contribution of buildings to gusts, the probabilistic characteristics of approaching flow have not been studied adequately. Therefore, the aim of this study was to investigate the statistical quantities such as high-order statistics, extreme wind speeds, and probability density functions (PDFs) of an artificially generated flow according to typical empirical equations. The approaching flow was generated by wind-tunnel experiments. In addition, we propose a PDF based on the Gram–Charlier series (GCS) to describe approaching flow. The determination of high-order statistics showed that these can be used as indices to validate whether the GCS can be applied to the PDFs of the approaching flow. Moreover, the current approaching flow was described effectively by the PDFs based on the GCS by considering the mean, standard deviation, skewness, and kurtosis. Furthermore, the mean, skewness, and kurtosis were correlated strongly with the percentile velocity components. This study demonstrates the importance of considering stochastic information of approaching flow when characterizing urban wind environments.

DOI： 10.1016/j.jweia.2022.105148

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Japan Architectural Review  

Occupants' behaviors (OBs) toward air conditioning (AC) usage in residential buildings have a strong influence on diverse time patterns of load profiles; thus, various stochastic OB modeling has been proposed. However, the validity of such models has not been fully assessed with metered data, particularly for modeling AC switching-off actions. In this study, the AC operation behavior of 20 dwellings in Japan was observed during the summer. The occurrence of AC-use events identified from the measured data was analyzed in relation to the time slot of an event, thermal conditions, and frequency of AC usage in each dwelling. The results exhibited a difference between switch-on and switch-off actions; the former is primarily dominated by indoor temperature because of thermal adaptation behavior, while the latter is more habitual. Based on this analysis, this study proposed a revised algorithm to synthesize AC operation schedules, which expresses the switch-off action as the probability of the duration of an AC-use event rather than a state transition probability function. The proposed algorithm can be incorporated into dynamic building energy simulations. The validity of the revised algorithm was also demonstrated through comparison with the measured data.

DOI： 10.1002/2475-8876.12293

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Language：English   Publisher：Building and Environment  

The complex velocity fields within an urban canopy affect the occurrence of rare weak and strong wind-speed phenomena at the pedestrian level. Although particle image velocimetry (PIV) is widely used to determine velocity components, it has not been applied to pedestrian spaces for rare wind events, owing to the surrounding buildings. Therefore, in this study, two velocity components within a simplified urban canopy layer were measured using time-resolved PIV by inserting a laser optics system into a focal block. We determined the turbulent statistics, probability densities, gust factor (GF), and peak factor (PF) at the pedestrian level within the canopy layer. The probability density functions of the velocity components at positions with a lower mean wind speed tend to be negatively skewed, whereas those at positions with a higher mean wind speed tend to become closer to the Gaussian distribution. The GF values are small in the regions where a larger velocity is observed. However, the PF shows less distribution than the GF, regardless of the measurement position. Owing to the importance of strong gusts, the PF could be a more useful index for evaluating strong winds speed within the urban canopy layer.

DOI： 10.1016/j.buildenv.2022.109350

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Language：English   Publisher：Indoor Air  

Net escape velocity (NEV) and net escape probability (NEP) are concepts that describe that scalar quantity discharged from a source in an indoor air environment is expressed by the unique velocity scales of the returning and escaping populations. Despite the conceptual description and applications of several numerical simulations, the definitions were not precisely explained using a mathematical formula. Here, we derive rigorous mathematical formulations of the NEV and NEP. These formulations provide us with the physical interpretation of NEV, clarify the sufficient condition of perfect escape, and lead to a further formulation of the transfer probability of the scalar. To justify and apply the derived relationships, two simple problems were numerically solved: One was a diffusion equation, and the other was an advection–diffusion equation. The results of the diffusion problem clearly demonstrate that only the outgoing scalar flux exists on the surface of the control volume, covering the source at any location. In contrast, the advection–diffusion problem reveals that there is a returning population of the scalar in most locations, despite both diffusion and turbulent parts working to remove the scalar. This rigorous formulation contributes to apply NEV as an appropriate air quality index with the clear physical interpretation to determine the local scalar concentration.

DOI： 10.1111/ina.13072

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PubMed

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Architectural Institute of Japan  

EFFECT OF MOMENTUM PROVISION IN COMPUTATIONAL FLUID DYNAMICS ON TURBULENT STATISTICS IN URBAN BOUNDARY LAYER
To reproduce homogeneous flow fields above urban-like turbulent boundary layers in computational fluid dynamics (CFD), numerous CFDs with a limited numerical domain employ periodic boundary conditions in both lateral directions with artificial momentum provision to maintain airflows. Although such artificial momentum sources are clearly different from the momentum provision in windtunnel experiments, the effects of these numerical conditions on the airflow in the boundary layer are not well studied. In this paper, therefore, we investigate how the momentum provision differentiates the vertical Reynolds stress and turbulent kinetic energy profiles using large-eddy simulations of airflows over cubical block arrays.

DOI： 10.3130/aije.87.145

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Publisher：Boundary-Layer Meteorology  

Integral equations for the vertical velocity component and momentum flux within boundary layers with sufficient fetch under neutral stratifications are derived by extending von Kármán’s integral equation. To simplify the equations, a self-similar profile for the streamwise velocity component and a zero-pressure gradient are assumed. The integral equations enable the following calculations. The vertical velocity component and momentum flux are calculated by the integral of the streamwise change in the streamwise velocity component. The vertical velocity component at the boundary-layer top is determined by the drag coefficient and shape factor. The advective flux at the boundary-layer top is of the same order as the turbulent momentum flux near the surface. Accordingly, the derived integral equations are applied to various types of boundary layers with sufficient fetch. For laminar boundary layers, profiles determined by the equations perfectly agree with the profiles determined by the analytical Blasius solution. For turbulent boundary layers, the comparison of the momentum flux between the proposed equations and experimental data verifies that the equations predict the turbulent momentum flux very well. Finally, we employ a power-law approximation for determining both the velocities and the momentum flux. As the streamwise velocity component can be approximated by the power law for both smooth and rough surfaces, the resulting turbulent flux agrees well with that obtained in experiments and numerical simulations.

DOI： 10.1007/s10546-021-00651-z

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Language：Others   Publishing type：Research paper (scientific journal)   Publisher：Urban Climate  

The aim of this study was to clarify the effects of high-rise buildings on the mean and turbulent wind speeds within the canopy layer of an urban university campus in Malaysia. We investigated the characteristics of both mean and exceeding wind speeds by deriving probability density functions of wind speed at a selected canopy height. First, mean wind speeds were compared with those predicted by several existing models as a function of building morphological parameters. Although all empirical models predicted wind speed decreases with an increase in building density, the predicted values and our experimental data did not agree. These results imply that existing prediction models exhibit limitations in specific urban morphologies. Second, the derived probability density functions approached the normal distribution when mean wind speeds increased. In addition, peak factors of wind speeds within the canopy layer approached the values determined by the normal distribution when the mean wind speed ratios were larger than 0.5. These results indicated that strong wind speeds can be predicted by the peak factor of the normal distribution regardless of the location or wind direction using the provided mean wind speed and standard deviations of the mean when wind ratios are larger than 0.5.

DOI： 10.1016/j.uclim.2021.101064

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Architectural Institute of Japan  

COMPUTATIONAL FLUID DYNAMICS for CROSS-VENTILATED AIRFLOW in AN URBAN BUILDING
The velocity field in a naturally ventilated building within urban-like arrays was explored by means of large-eddy simulations. The reduced-scale building models were utilized to examine the impact of the geometric conditions in surrounding buildings and cross-ventilating windows on flow statistics as well as instantaneous velocity fields in a sheltered building. The obtained results indicated how the incoming flow was propagated in the target building. Although simplified conditions were employed, the present findings of the features of cross-ventilation are valuable to consider the effect of outdoor turbulent flow to indoor wind environment.

DOI： 10.3130/aije.87.19

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Language：Japanese   Publisher：Japan Association for Wind Engineering  

The rare weak and strong wind-speed phenomena at the pedestrian level are mostly unpredictable because of the complex velocity fields within an urban canopy. In this study, therefore, two velocity components within a simplified urban canopy layer were measured using time-resolved particle image velocimetry (PIV) to scrutinize the instantaneous and statistical characteristics of pedestrian-level winds (PLWs). The new laser-camera system
realized by inserting a laser optics system into a focal block could successfully capture the flow fields within an urban-like array, which enabled us to understand the aerodynamic effects of simplified block arrays on the PLWs.

DOI： 10.14887/natsympwindengproc.27.0_19

CiNii Research

Language：Japanese   Publisher：Japan Association for Wind Engineering  

Probability density distributions of each velocity component at pedestrian levels are required to predict extremely rare and strong wind events. Therefore, in this study, the PDFs were compared between the Gaussian and modified Gaussian distributions with the third-order and fourth-order statistics, as known as the Gram-Charlier Series (GCS), for the velocity components around a simplified urban array determined by a large-eddy simulation. The GCS with the third-order and fourth-order moments could predict the PDFs and percentile values of each velocity component more accurately than those determined by the Gaussian distributions. In addition, the comparison shows that it can be judged whether the PDFs are represented by the Gaussian distributions or not by confirming the third and fourth order statistics.

DOI： 10.14887/windengresearch.27.0_9

CiNii Research

Language：English   Publisher：Japan Association for Wind Engineering  

This study compared the accuracies of the Weibull distribution method (two-parameter Weibull and three-parameter Weibull methods, i.e., 2W and 3W methods) and Gram.Charlier series (GCS) method for estimating the low-occurrence wind speed at the pedestrian level around an isolated building. The wind speed data analyzed in this study is taken from an LES database. For the advantage of the models to predict the probability density function (PDF) of the wind speed data, the 2W, 3W and GCS methods more accurately modelled the unimodal distribution than the bimodal distribution. In addition, the highest-order GCS method in this study (i.e., GCS-6th method) exhibited better flexibility in modelling PDFs than the 2W and 3W. For estimating the low-occurrence wind speed, the 2W, 3W and i-th-order GCS methods require the mean and standard deviation, these two statistics plus the skewness, and the first-order to i-th-order statistics, respectively. For the estimation accuracy, the 2W method is better than the second-order GCS method and the 3W method is better than the third-order GCS method although the GCS-6th method is regarded as the most accuracy method in this study owing to incorporating the higher-order statistics.

DOI： 10.14887/windengresearch.27.0_28

CiNii Research

Language：English   Publisher：Japan Association for Wind Engineering  

Turbulent characteristics of the pedestrian-level winds around buildings are determined by both aerodynamic effects due to surrounding buildings and the innate turbulent characteristic of the approaching flow. Although previous research has stochastically investigated the probability density function of the pedestrian-level winds altered by the surrounding buildings, those of an approaching flow have not been studied adequately. Therefore, this study aims at investigating the relationship between high-order statistics and probability density functions of a typical approaching flow following the power-law and Karman-type power spectrum density. First, we discussed the theoretical relationship between the statistics and the probability density functions for Gaussian and modified Gaussian distributions. It showed that the high order statistics can be indices to consider an appropriate model for describing the probability density function of the approaching flow. Second, we demonstrated that the modified Gaussian distribution can well describe the probability of the approaching flow. This study contributes to the framework for illustrating and considering stochastic information of approaching flow while addressing wind environments based on stochastic analyses.

DOI： 10.14887/natsympwindengproc.27.0_61

CiNii Research

Language：Japanese   Publishing type：Research paper (scientific journal)  

In this paper, we discuss the theoretical interpretation of the artificial compressibility method (ACM) to propose a new explicit method for the unsteady numerical simulation of fluid flow. The proposed method employs the compressible continuity and Navier–Stokes equations, which facilitates the replacement of pressure as one of the major variables with density, theoretically backed by virtual particle concept. This new concept justifies the theoretical treatment assuming the speed of sound in ACM as a model parameter determined by the grid system. More importantly, the present method realizes, in a fully explicit manner, the solving of a set of equations, which prevents the solving of the Poisson equation of pressure. The new method was validated and proven by comparing the results of two-dimensional cavity flow between the proposed method, conventional incompressible method, and the Lattice–Boltzmann method with varying Reynolds numbers (100, 1000, and 10000). The results of the proposed method agree well with conventional and reference data for both steady-state and unsteady-state conditions, although slight numerical oscillations were observed for the proposed method at a Reynolds number of 10000. Thus, the numerical validation assures that the proposed method is an explicit method based on a solid theoretical ground to be a new efficient simulation framework.

DOI： 10.1016/j.jcp.2021.110524

Repository Public URL： http://hdl.handle.net/2324/4751322

Language：Others   Publishing type：Research paper (scientific journal)  

This study characterizes the indoor airflow and occupants’ thermal sensations in a cross-ventilated building model sheltered by generic cube arrays based on large-eddy simulations (LESs). Four ventilation models, which comprise different cross-ventilating openings, streamwise (STR) and lateral (LAT) windows, and block arrangements, lattice-type square (SQ) and staggered (ST) patterns, were examined to understand the following geometry-oriented features: i) the temporal and spatial deviations of wind speed at openings and inside the ventilation models, ii) effects of time and space resolutions for the velocity data on the estimation accuracy of the ventilation rate, and iii) predicted mean vote (PMV) and predicted percentage of dissatisfied (PPD) indices calculated with elaborately simulated velocity data. The difference in distribution of fluctuating normal velocity at openings was more significant when varying the conditions of the opening locations than that observed when varying the building arrangements. Therefore, the ventilation rates in the STR conditions were reasonably estimated using only the time-averaged flow rate at the center position of the windward opening; meanwhile, when the contributions of reverse flow were ignored at the openings, the ventilation rates in the LAT conditions were drastically underestimated using highly resolved velocity data at openings. Based on the thermal comfort assessment at an air temperature of 26°C, the discrepancies of area-averaged PMV values between STR and LAT cases were within 0.7 and 0.9 at the lower and middle heights of naturally ventilated buildings, resulting in a 5% difference in the PPD values.

DOI： 10.1016/j.buildenv.2021.107811

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We designed and exclusively performed a wind tunnel experiment to obtain high-quality and high-resolution measurement results for three components of mean and fluctuating velocities around a 1: 1: 2 isolated building to establish a benchmark case for large-eddy simulation (LES) as a part of the activities of the Architectural Institute of Japan. Subsequently, we conducted LES to investigate the effect of computational grid arrangement on turbulent statistics by changing three grid arrangements. Finally, we performed a comparison by changing spatial discretization schemes, sub-grid scale (SGS) turbulence models, and convergence criteria. A grid in which the width of a building was discretized into 20 grids yielded sufficient resolution to reproduce the mean flow and second-order turbulent statistics. Under this appropriate grid arrangement, in the condition that the blending ratio of the first-order upwind interpolation scheme with the second-order linear interpolation scheme from 5 to 10%, the appropriate second-order statistics of wind velocity around the isolated building was obtained and numerical oscillation was effectively removed. Then, with this grid, any SGS model yielded appropriate results. In addition, the convergence criteria had little effects on the LES results if stable solution was obtained. Because the convergence criteria greatly affect the total calculation cost, weaker appropriate criteria should be set.

DOI： 10.1016/j.buildenv.2021.108021

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© 2021 by the authors. Licensee MDPI, Basel, Switzerland. Understanding the characteristics of natural, wind-induced ventilation of buildings is essential for accurate predictions of ventilation flow rates; however, indoor ventilation is significantly influenced by surrounding buildings. Therefore, a series of wind-tunnel experiments were performed to clarify the relationship between outdoor and indoor air flows around and within a target cube model with several openings. Two surrounding building arrangements, namely square (SQ) and staggered (ST), were placed under the condition of a building coverage ratio of 25%. The results indicated that the wind speed near the windward openings on the streamwise faces showed 0.3 to the reference wind speed, whereas those on the lateral faces were less than 0.1; these numbers indicate that the opening positions significantly affect the mean indoor wind speed. Furthermore, the temporal fluctuations of velocities near the opening demonstrated that the introduction of the flow is significantly affected by turbulent flow due to the surrounding buildings. In addition, correlation between the outdoor and indoor air flows was observed. The highest correlations were obtained for both opening conditions with a certain temporal delay. This result indicates that indoor air flows become turbulent because of the turbulent flows generated by the surrounding outdoor buildings; however, slight temporal delays could occur between indoor and outdoor air flows. Although the present study focuses on the fundamental turbulent characteristics of indoor and outdoor air flows, such findings are essential for accurately predicting the ventilation flow rate due to turbulent air flows for sheltered buildings.

DOI： 10.3390/su13020586

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© 2020 Elsevier Ltd This study reports the results of large eddy simulations with the standard Smagorinsky model of the velocity fields within a cross-ventilation model sheltered by block arrays. A very fine resolution of 1/100 of the building height was adopted. The objectives are to understand the sheltering effect of the surrounding building array and quantify the ventilation rate in the cross-ventilation model. Two types of block arrays and opening positions were simulated. Comparisons of the numerical and experimental results justify that the present simulations reproduced the characteristics of the mean as well as turbulent flows introduced in the ventilation model. In addition, the simultaneous observations of the outdoor and indoor velocities enabled us to conclude that the change in the outdoor flow patterns caused a dramatic change in the indoor velocity distributions, although the opening position was identical in all such cases. Using these detailed flow fields, we compared three types of ventilation rates: the net, gross, and instantaneous ventilation rates. Moreover, we estimated the instantaneous ventilation rate using a random variable following the Gaussian distribution. The ventilation due to the turbulent inflow was crucial in the model with its opening on the lateral side of the block, whereas the mean flow primarily determined the ventilation rate for the block with its opening on the streamwise walls. In both cases, the estimation model could predict the instantaneous ventilation rate well with a maximum overestimation of only 3%. This means that the model was justified for all the present array and opening conditions.

DOI： 10.1016/j.buildenv.2020.107174

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© 2020 Elsevier Ltd The interaction between the turbulent boundary layer and wake behind various types of two-dimensional cylinders is examined based on the velocity measurements by hot-wire anemometry and particle image velocimetry. Three types of cylinders, such as circular, square, and 1:5 rectangular cylinders, of two different diameters of 5 ​mm and 10 ​mm were employed in this study. The streamwise velocity distributions of the wake flow showed that its width is sustained in the streamwise direction within the boundary layer because of its interaction with the turbulent boundary layer flow. Interestingly, this phenomenon was observed regardless of the cylinder shapes. The momentum exchange in both spanwise and vertical directions showed that the advective momentum flux considerably contributes to momentum budget in the wake flow owing to the weak vertical flow formed within the boundary layer. Consequently, the spanwise width of the wake does not expand in the streamwise direction due to the alternation of the momentum budget. The results of this study can contribute to clarifying the effect of interaction between the wake and the turbulent boundary layer, as well as explain the sustaining mechanics of the low speed streaks formed within the turbulent boundary layer, even for different origins of the low-speed regions.

DOI： 10.1016/j.jweia.2020.104250

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© 2020, © 2020 ASHRAE. The present study used large eddy simulations (LES) to examine the pedestrian wind velocity distribution for several cases of terraced houses with extensions. Two simulation cases of idealized terraced houses were performed with extension elements in square (E-SQ) and staggered (E-ST) arrangements. These extension elements were treated as secondary roughness. A simulation of the terraced houses without extension (NE) was also performed to provide a baseline comparison. The mean velocity distribution from LES showed that the secondary roughness strictly limited the flow penetration in both cases, which reduced the turbulent kinetic energy (TKE) inside the canyon. In comparison, E-ST had a stronger effect on TKE than E-SQ with a maximum difference of 19%. Downwind extension elements severely reduced the wind speed at the street and neighbors’ houses by about 40% to 50%. However, upwind extension elements increased the wind speed at neighbors’ houses about threefold compared to NE. The weak pedestrian wind speed at upwind houses was improved about twelve times with E-SQ and eight times with E-ST when neighbors extended their houses. This indicates that the secondary roughness significantly influences the wind distribution around buildings. Selecting the extension area is important for providing effective outdoor flow conditions.

DOI： 10.1080/23744731.2020.1735860

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© 2020 Elsevier Ltd We analyzed the datasets of the flow fields at a pedestrian level around a 1:1:2 isolated block model obtained by a large eddy simulation. The purpose was to understand the effect of the block on the probability density distributions of each velocity component and wind speed, and to propose a reasonable model to predict the percentile values of wind speed (exceeding wind speeds) for the pedestrian level. The probability density distributions were skewed, especially near the block side, whereas other vicinities of the front and wake of the block did not cause significant change in the distributions. Consequently, the probability density distributions were standardized using mean and standard deviations to compare with the normal distribution. Clearly, rare wind events had an occurrence frequency of less than 10%, which shows large discrepancies from the normal distribution. Accordingly, the exceeding wind speeds for each velocity component and magnitude were determined. The exceeding wind speeds of each velocity component were poorly estimated by the mean wind speed. Nonetheless, better prediction of the exceeding wind speed of each velocity component is possible by using the peak factor. By contrast, the exceeding wind speed of the velocity magnitude is clearly proportional to the mean wind speed.

DOI： 10.1016/j.jweia.2020.104193

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© 2020 Elsevier Ltd Research on indoor ventilation is mainly conducted utilizing wind-tunnel experiments and computational fluid dynamics simulations under controlled flow conditions. However, with these techniques, the effects of the actual urban boundary-layer flow with variable wind directions and turbulence on the ventilation performance of a building surrounded by various buildings remain unresolved. Therefore, we conducted outdoor experiments at the Comprehensive Outdoor Scale Model experiment site to evaluate the mutual relationships between wall pressure of a building within a square array, in which cubical blocks are aligned in same spanwise position in a row, and atmospheric urban boundary-layer flow. The dataset consisting of the simultaneous measurements of the wall pressure acting on a target block and the air flow around it was analyzed statistically. The results demonstrate that the distributions of wind pressure coefficient significantly change with the approaching wind direction, while similar cavity flow patterns such as the downward flow at windward wall and the upward flow at leeward wall are observed regardless of the wind direction. Additionally, the pressure coefficient is more sensitive to the approaching wind direction at the side-edge than at the center of the block surface. Moreover, the temporal and spatial distributions of wall pressure are highly correlated with the fluctuating flow above the canopy rather than the turbulence generated within the canopy.

DOI： 10.1016/j.buildenv.2020.106881

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© 2020 Architectural Institute of Japan. All rights reserved. Appropriate large-eddy simulation (LES) guidelines for pedestrian wind environments are being established by the working group of the Architectural Institute of Japan. We conducted LESs for a flow field around an isolated building to clarify the influence of computational conditions on turbulent statistics. We performed a cross-comparison study by examining both experimental and LES results for various computational conditions such as grid arrangements, subgrid scale models, spatial derivation schemes for convection term, and convergence criterion for a coupling algorithm of flow and pressure fields. Results can be used to provide LES guidelines for predicting the pedestrian wind environment.

DOI： 10.3130/aijt.26.179

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© 2019 Elsevier Ltd Large-eddy simulations were performed for the velocity fields around a 1:1:2 single block model to clarify the effect of the numerical viscosity in different advection schemes. Six types of advection schemes with different numerical viscosities were employed: second-order central, first-order upwind, and blending schemes with ratios of 95:5, 90:10, 80:20, and 60:40. The central scheme alone or the blending schemes predicted values of the mean and turbulent kinetic energy that were comparable with those of the experiments, whereas the upwind scheme significantly underestimated the experimental values. In addition to the comparison with the experimental data, the turbulent flow fields among the schemes were compared by deriving the probability and power spectral densities. Blending of the upwind scheme indeed reduced the turbulence energy contribution at high frequency. However, such a reduction in energy became influential to the reproduction of the turbulent flows only when damping of the peak spectral energy occurred. The reduction of the statistical values became ∼10% when blending the upwind scheme by 20%. In contrast, a strong or weak velocity, evaluated by the percentile velocities, was more sensitive to the selection of the advection scheme than the mean velocities.

DOI： 10.1016/j.jweia.2019.06.013

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© 2019 Elsevier Ltd Most studies on indoor ventilation have utilized wind-tunnel experiments (WTEs) or computational fluid dynamics based approaches under well-controlled flow conditions. However, the effects of urban boundary layer flow with variable wind directions and various turbulence scales on the ventilation driven by the pressure differences between the upwind and downwind sides of a building within a block array is still under discussion. Therefore, we conducted outdoor experiments at comprehensive outdoor scale model (COSMO) experiment sites in an urban climate to clarify the relationships between the building wall pressure differences and the approaching flow. The pressure coefficients for the outdoor site were comparable with those obtained during previous WTEs. Accordingly, temporal variations in the wind speed and pressure coefficient on the target block were investigated in detail using low-pass filtering operations. The relationships between the filtered wind speed and the pressure differences indicate that the slower temporal variations in the wall pressure showed good agreement with the filtered approaching flow. In addition, the correlation coefficient between the filtered wind speed and the wall pressure differences quantified the apparent coherence between the turbulent flow and the ventilation rate. Furthermore, the statistics of the ventilation rate were determined based on the conventional model to clarify the effects of the turbulent flow on the natural ventilation rate. The ratios between the mean and short-term ventilation rates imply that the short-term ventilation rate presented dramatic temporal fluctuations owing to the various scale turbulence generated by the atmospheric flow.

DOI： 10.1016/j.buildenv.2019.106170

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© 2018 Elsevier Ltd In this work, time-resolved particle image velocimetry is used for indoor velocity determination of cross-ventilation flow sheltered by urban-like arrays, to elucidate the instantaneous and statistical characteristics of the velocity fields. Combinations of two opening positions relative to the main stream flow and two surrounding array types are considered, yielding four cross-ventilation flow cases for comparison. For the streamwise window condition, the instantaneous velocity distributions differ significantly according to the outdoor block arrangement. Intermittency of the flow introduction through the windward opening and the indoor flow distributions are also confirmed based on temporal variation of the velocities. These differences in flow distribution are statistically correct according to the temporally averaged flow distributions. For the lateral window condition, instantaneous flow introduction is found to occur intermittently and alternately through each opening. Moreover, the flow introduction angle differs according to the outdoor arrangement, for both the instantaneous and mean flow distributions, indicating the importance of the surrounding-block sheltering effects on the indoor flow distributions. In addition to this elucidation of the indoor flow characteristics, the datasets obtained in this work are valuable for validating future numerical analyses of the cross-ventilation flow of a generic block under sheltered conditions.

DOI： 10.1016/j.buildenv.2018.10.015

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© 2018 Elsevier Ltd The unsteadiness of urban airflow influences rare events of high wind speeds or high scalar concentrations. Therefore, this study uses large-eddy simulations to investigate the geometrical impact of generic block arrays on the statistical features of wind speeds and scalar concentrations within urban canopy regions. Six types of urban-like arrays with uniform and non-uniform block heights are considered, and probability density functions of wind speeds and scalar concentrations are derived based on the flow and concentration distributions within urban canopy regions. Exceeding wind speeds and scalar concentrations are determined through cumulative probability densities. The non-uniform spatial distribution of scalar concentrations is found to be correlated with the velocity magnitude distribution. In particular, airflows with strong wind speeds near tall blocks contribute to a reduction in the scalar concentration in that region. The probability density functions of velocity magnitude for arrays with height variations become long-tailed as the horizontally averaged wind speeds increase. Accordingly, the probability density at high scalar concentrations is lower for arrays with height variations. Finally, the exceeding wind speeds and scalar concentrations for arrays with height variation can be expressed as linear functions of the mean wind speed.

DOI： 10.1016/j.jweia.2018.09.024

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© 2018 Elsevier Ltd Sheltering of buildings has a significant impact on the total drag of an urban surface. This study performs large eddy simulations (LESs) of flows over vertical random arrays (comprised of buildings with height variability) in staggered layout to estimate the drag coefficient, CD. The vertical random arrays are configured in several frontal area densities, λF (ratio of buildings’ frontal area to total surface area) ranging from 0.09 to 0.81. The sheltering effect is parameterized using the individual building's wind pressure coefficient, Cp(t) normalized with that of the isolated building, Cp(iso). The ratio Cp(t)/Cp(iso) is well correlated with the target building's frontal area density, λf(t). Subsequently, the relationship between Cp(t) and λf(t) is expressed using power law equations for three building categories based on the height-to-width ratio, αp(t): tall (2.64 ≤ αp(t) ≤ 3.76), medium-rise (1.32 ≤ αp(t) ≤ 2.00), and low-rise (0.36 ≤ αp(t) ≤ 0.84). Based on the Cp(t), an equation of the CD is formulated, yielding the following outcomes. Firstly, the predicted CD values are mostly within 10% of the previous experimental results. Secondly, a semi-empirical model is derived, whereby the predicted CD values are generally consistent for various vertical random arrays.

DOI： 10.1016/j.jweia.2018.08.003

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© 2018 Penerbit Akademia Baru. Effective wind-driven cross ventilation requires a well-designed opening, such as a window, to allow sufficient exchange between indoor and outdoor air, especially when the building is surrounded by other buildings. Using computational fluid dynamics, the present study investigated the effect of different opening positions on wind-driven ventilation in a building in an area with a packing density of 25%. The renormalizationgroup κ-ε turbulence model, a type of Reynolds-averaged Navier-Stokes (RANS) model, was used to characterize the airflow in cubical building blocks arranged in a square array. Nine different configurations of aligned cross openings and nine configurations with non-aligned outlet positions were tested. The ventilation rates obtained for the aligned cross openings showed that openings positioned at the uppermost of the windward and leeward façade provided highest ventilation rate. The ventilation rate was reduced by 75% when the openings were positioned at the bottom of the façade. As for the fixed inlet in the centre, the ventilation rate was 100% higher when the outlet is at the top of the leeward façade compared to the bottom of the façade. The outcomes of this study show that opening position is imperative in providing effective wind-driven cross ventilation in urban areas.

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© 2018 by the authors. Computational fluid dynamics simulations with a Reynolds-averaged Navier-Stokes model were performed for flow fields over a building array and inside a building in the array with different building opening positions. Ten combinations of opening locations were selected to investigate the effect of the locations on indoor cross-ventilation rates. The results of these simulations show that the exterior distributions of mean wind speed and turbulence kinetic energy hardly differ even though building openings exist. Although similar patterns of outdoor flow fields were observed, the opening positions produced two different types of ventilations: one-way and two-way. In one-way ventilation, the wind flows through the opening are unidirectional: diagonally downward at the windward wall. In two-way ventilation, both inflow and outflow simultaneously occur through the same opening. Determination of ventilation rates showed that the ventilation types can explain what type of ventilation rate may be significant for each opening location.

DOI： 10.3390/atmos9060217

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© 2018, Novel Carbon Resource Sciences. All rights reserved. The present work discusses in detail the experimental settings to establish a thick artificially generated urban-like atmospheric boundary layer in a short-fetch-length wind tunnel. It summarizes the comprehensive review of past studies on the flow behind quarter-elliptic-wedge spires, and clarifies the current issue of the spire setting in a wind tunnel experiment. This study investigates the persistent spanwise heterogeneity, the spatial structures of the flow past a row of quarter-elliptic-wedge spires, the streamwise distance required for a wake of elliptic-wedge spires to naturally recover, and how the mean flow changes farther downstream. Two experimental conditions were implemented in the present work (without and with spires) to analyse the effect of mean flow heterogeneity both within and above boundary layer height (BLH) regions, developing over a smooth wall that was produced by the installation of a flat plate on the wind tunnel floor.

DOI： 10.5109/1929670

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© 2017 Elsevier Ltd The geometric dependency of the wind environment at a pedestrian level is an important issue that influences human comfort and safety in urban outdoor spaces. As such, this paper proposes to investigate the statistical features of wind speeds at the pedestrian level by calculating wind speed probability density functions based on flow field data from large-eddy simulations of simplified urban arrays, aiming to clarify the effects of urban geometry on rare velocity events such as strong gusts or extremely weak air flow. Though strong wind events occur infrequently, a positive correlation was demonstrated between percentile and mean wind speeds, indicating that the risk of gusty events increases with the increase of mean wind speeds. Conversely, the frequency of weak wind events shows an inverse correlation with mean wind speeds, showing that better ventilated urban arrays will retain higher wind speeds. Furthermore, these percentiles and occurrence frequencies are clearly expressed by the frontal area indices of urban block arrays. These results imply a trade-off between the following two objectives for urban area wind environments characterized by the urban geometry: enhancing air ventilation in urban areas and preventing strong wind gust events at a pedestrian level.

DOI： 10.1016/j.jweia.2017.10.002

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PIV is an attractive experimental method for investigating turbulent flow around building model in a wind tunnel. However, it is difficult to obtain data with high accuracy in large size wind tunnel. In this paper, first we give an overview of PIV technique and organize the experimental conditions of past PIV in urban climatology. Then, we consider a technological problem which is called peak locking. We explain the mechanism of the generation of peak locking and how it affects the final output. Avoiding peak locking is difficult in general experimental condition, but it is mitigated by a simple image processing.

DOI： 10.3130/aijt.23.567

Language：Japanese  

Statistical Analysis of Time-Series Data of Electricity Consumption of Air Conditioners Observed in Multiple Dwellings

Language：Japanese  

Statistical Analysis of Time-Series Data of Electricity Consumption of Air Conditioners Observed in Multiple Dwellings

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© 2015, Springer-Verlag Wien. The purpose of this study is to review and improve prediction models for wind speed ratios at pedestrian level with simplified urban canopies. We adopted an extensive database of velocity fields under various conditions for arrays consisting of cubes, slender or flattened rectangles, and rectangles with varying roughness heights. Conclusions are summarized as follows: first, a new geometric parameter is introduced as a function of the plan area index and the aspect ratio so as to express the increase in virtual density that causes wind speed reduction. Second, the estimated wind speed ratios in the range 0.05 < z/h < 0.3, where h is the building height, are consistent with those derived from the database to within an error of ±25%. Lastly, the effects of the spatial distribution of the flow were investigated by classifying the regions near building models into areas in front of, to the side of, or behind the building. The correlation coefficients between the wind speeds averaged over the entire region, and the front or side region values are larger than 0.8. In contrast, in areas where the influence of roughness elements is significant, such as behind a building, the wind speeds are weakly correlated.

DOI： 10.1007/s00704-015-1655-z

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We have performed Large-Eddy Simulation of flow and pressure fields over two types of urban-like block arrays in order to investigate the relationships between instantaneous building wall pressure and surrounding flow fields. The adopted block arrays are: lattice-type square and staggered pattern. The analysis on the distributions of statistics for wall pressure shows that the large values of the statistics are observed along with the top and side edges of the wall for the square array, whereas they are shown on an upper half region of the wall for the staggered array. These large values are due to air flow introduction from both above and side of the target block for square array; in contrast, strong flows introduced into canopy area cause large pressures of the upper half of the wall for staggered array.

DOI： 10.5359/jwe.42.22

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We have performed Large-Eddy Simulation of turbulent boundary layer over simplified urban like roughness. Totally six types of arrays are adopted with several roughness densities and roughness aspect ratios. The turbulent flow fields at a pedestrian level are investigated to identify probability characteristics of unsteady flows. Conclusions are summarized as follows. First, the probability density functions of wind speeds at a pedestrian level show long-tail shape with positive skewness for all arrays and well explained by dimensionless probability variable defined by the mean and standard deviation of wind speeds. On the other hands, the discrepancies of the probability between arrays become considerable for events with wind speeds larger than triple of the standard deviations. Second, such events with large wind speed rarely happen; the cumulative probability shows approximately 1%. Lastly, linear relationships are confirmed between the mean and percentile wind speeds. These findings will help the understanding of the unsteadiness nature of turbulent flow in urban boundary layer especially when evaluating very rare events such as gusts or extreme low winds.

DOI： 10.5359/jwe.42.1

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© 2016 Elsevier Ltd. Various numerical simulations have been developed to evaluate the mean ventilation rates of a target building; however, the manner in which turbulent flow generated by buildings and surrounding conditions affects the mean and fluctuating ventilation rates is not well understood. Therefore, we have performed large-eddy simulation of flow and pressure fields above two types of block arrays (lattice-type square and staggered pattern) to clarify the turbulent characteristics of estimated ventilation rates based on pressure coefficient distribution on the block faces. The concept of short-term ventilation rates, which are estimated from filtered pressure coefficients, is introduced to investigate the temporal variation in the estimated ventilation rates for different locations of the block faces and arrangements. First, mean and second-order turbulent statistics agree well with previous results obtained from both wind-tunnel experiments and numerical simulations, indicating that the turbulent characteristics of the flow above urban-like arrays are well reproduced. Second, short-term ventilation rates are found to vary temporally and spatially. Therefore, these values instantaneously become larger or smaller than the mean ventilation rates. In addition, complex fluctuation patterns of pressure coefficient distribution are found to be caused by air flow introduction from the block arrays into gaps between the blocks as well as by small-scale turbulence generated by surrounding buildings themselves. Lastly, the temporal statistics of filtered pressure coefficients show that the short-term ventilation rates can possibly become stronger or weaker than the mean ventilation rates, whereas the accumulated fluctuating ventilation rates are almost comparable to those estimated by mean pressure coefficients.

DOI： 10.1016/j.buildenv.2016.02.005

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In this study, the influence of the complexity of shape of roughness on turbulent flow fields in a 2D street canyon was investigated using a wind tunnel experiment (WTE). Time-resolved particle image velocimetry (TR-PIV) was employed to investigate temporally averaged flow fields, the spatial distributions of turbulent statistics, canyon ventilation rates, and the flow exchange mechanism between the regions above and inside a canyon. The measurements revealed that the temporally averaged flow fields and the spatial distributions of turbulent statistics are drastically changed by the complexity of roughness, especially when the canyon aspect ratio is small. Moreover, the ventilation rate is reduced by the eaves attached to roofs. However, the decreasing rate of the ventilation strongly depends on the canyon aspect ratio.

DOI： 10.3130/aije.81.467

Language：English  

An experimental study on aerodynamic interaction between a boundary layer generated by a smooth and rough wall and a wake behind a spire

DOI： 10.15017/1560669

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© 2015, Springer Science+Business Media Dordrecht. We report the result of a wind-tunnel experiment to measure the scalar transfer efficiency of three types of surfaces, wet street surfaces of cube arrays, wet smooth surfaces with dry patches, and fully wet smooth surfaces, to examine the effects of roughness topography and scalar source allocation. Scalar transfer coefficients defined by the source area C<inf>Ewet</inf> for an underlying wet street surface of dry block arrays show a convex trend against the block density λ<inf>p</inf>. Comparison with past data, and results for wet smooth surfaces including dry patches, reveal that the positive peak of C<inf>Ewet</inf> with increasing λ<inf>p</inf> is caused by reduced horizontal advection due to block roughness and enhanced evaporation due to a heterogeneous scalar source distribution. In contrast, scalar transfer coefficients defined by a lot-area including wet and dry areas C<inf>Elot</inf> for smooth surfaces with dry patches indicate enhanced evaporation compared to the fully wet smooth surface (the oasis effect) for all three conditions of dry plan-area ratio up to 31 %. Relationships between the local Sherwood and Reynolds numbers derived from experimental data suggest that attenuation of C<inf>Ewet</inf> for a wet street of cube arrays against streamwise distance is weaker than for a wet smooth surface because of canopy flow around the blocks. Relevant parameters of ratio of roughness length for momentum to scalar B^-1 were calculated from observational data. The result implies that B^-1 possibly increases with block roughness, and decreases with the partitioning of the scalar boundary layer because of dry patches.

DOI： 10.1007/s10546-015-0063-3

Language：English  

Aerodynamic effect of overhang on a turbulent flow field within a two-dimensional street canyon

DOI： 10.15017/1525830

Language：Japanese  

40409 A study on the probability characteristics of occupant behavior for using air-conditioner in residential buildings

Language：Japanese  

41336 Numerical study on the effect of turbulent field generated by simple cubical arrays on the wall pressure

Language：Japanese  

41358 Particle Image Velocimetry Measurement of Unsteady Turbulent : Flow around Regularly Arranged High-Rise Building Models

Language：Japanese  

41360 Effects of heterogeneity of scalar source distribution and roughness on scalar transfer coefficients of urban surfaces : Part 1. Experimental setting and measured transfer coefficients

Language：Japanese  

41361 Effects of heterogeneity of scalar source distribution and roughness on scalar transfer coefficients of urban surfaces : Part 2 Effect of scalar source size on scalar transfer coefficient and scalar roughness length

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© 2015 World Scientific Publishing Company. As a data set for validation of microscopic simulation models, we obtained the fundamental diagram (flux versus density relation), and the relations of velocity versus density, lane usage ratio versus density and lane-changing frequency versus density derived from a single field measurement campaign held at a Japanese urban expressway. The results were drawn from image analysis of video camera data obtained at the site.

DOI： 10.1142/S0129183115500722

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© 2014 IOP Publishing Ltd and SISSA Medialab srl. In 22 prisoner's dilemma (PD) games, network reciprocity is one mechanism for adding social viscosity, leading to a cooperative equilibrium. In this paper, we explain how gaming neighborhoods and strategy-adaptation neighborhoods affect network reciprocity independently in spatial PD games. We explore an appropriate range of strategy adaptation neighborhoods as opposed to the conventional method of making the gaming and strategy adaptation neighborhoods coincide to enhance the level of cooperation. In cases of expanding gaming neighborhoods, network reciprocity falls to a low level relative to the conventional setting. In the discussion below, which is based on the results of our simulation, we explore how these enhancements come about. Essentially, varying the range of the neighborhoods influences how cooperative clusters form and expand in the evolutionary process.

DOI： 10.1088/1742-5468/2014/12/P12024

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© 2014 IOP Publishing Ltd and SISSA Medialab srl. Motivated by the fact that there are quite a few ill-mannered drivers who disregard traffic rules concerning lane-changing and maximum speed, we investigated an interesting question: whether or not social dilemma structures can be formed from a frequent dangerous lane-changing attitude in a typical traffic flow without any explicit bottlenecks. In our model system, two classes of driver-agents coexist: C agents (cooperative strategy) always keep to traffic regulations with respect to lane-changing and speed, while D agents (defective strategy) disregard them to move ahead. In relatively high-density flows, such as the metastable and high-density phases, we found structures that correspond to either n-person Prisoner's Dilemma (n-PD) games or to quasi-PD games. In these situations, existing ill-mannered drivers create heavy traffic jams that reduce social efficiency.

DOI： 10.1088/1742-5468/2014/11/P11027

Language：Others   Publishing type：Research paper (scientific journal)  

Achievement of the herd immunity is essential for preventing the periodic spreading of an infectious disease such as the flu. If vaccination is voluntary, as vaccination coverage approaches the critical level required for herd immunity, there is less incentive for individuals to be vaccinated; this results in an increase in the number of so-called "free-riders" who craftily avoid infection via the herd immunity and avoid paying any cost. We use a framework originating in evolutionary game theory to investigate this type of social dilemma with respect to epidemiology and the decision of whether to be vaccinated. For each individual in a population, the decision on vaccination is associated with how one assesses the risk of infection. In this study, we propose a new risk-assessment model in a vaccination game when an individual updates her strategy, she compares her own payoff to a net payoff obtained by averaging a collective payoff over individuals who adopt the same strategy as that of a randomly selected neighbor. In previous studies of vaccination games, when an individual updates her strategy, she typically compares her payoff to the payoff of a randomly selected neighbor, indicating that the risk for changing her strategy is largely based on the behavior of one other individual, i.e., this is an individual-based risk assessment. However, in our proposed model, risk assessment by any individual is based on the collective success of a strategy and not on the behavior of any one other individual. For strategy adaptation, each individual always takes a survey of the degree of success of a certain strategy that one of her neighbors has adopted, i.e., this is a strategy-based risk assessment. Using computer simulations, we determine how these two different risk-assessment methods affect the spread of an infectious disease over a social network. The proposed model is found to benefit the population, depending on the structure of the social network and cost of vaccination. Our results suggest that individuals (or governments) should understand the structure of their social networks at the regional level, and accordingly, they should adopt an appropriate risk-assessment methodology as per the demands of the situation. © 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.chaos.2014.07.004

Language：Japanese  

41315 A study on similarity of profiles between velocity and scalar concentration in an urban boundary layer

Language：Others  

Momentum and energy budgets on an urban surface are investigated based on theoretical approach by deriving the budget equations. Firstly, we have introduced the integral equation for energy, which corresponds to the equation as known as Karman's integral law for momentum. These equations can explain the effect of drag force acting on roughness elements on the budgets of momentum and energy. Secondly, it is shown that the additional term appears to explain for the drag force to be able to directly absorb momentum provided out of boundary layer. Although the corresponding term does not exist in the energy budget equations, the drag force may work to increase the turbulence energy through the additional turbulence production terms. Thirdly, the relationship between drag coefficient and dissipation rate have been discussed. These quantities have positive correlation and can be an index to explain the wind velocity deficit.

DOI： 10.3130/aije.79.297

Language：Others  

Momentum and energy budgets on an urban surface are investigated based on theoretical approach by deriving the budget equations. Firstly, we have introduced the integral equation for energy, which corresponds to the equation as known as Karman's integral law for momentum. These equations can explain the effect of drag force acting on roughness elements on the budgets of momentum and energy. Secondly, it is shown that the additional term appears to explain for the drag force to be able to directly absorb momentum provided out of boundary layer. Although the corresponding term does not exist in the energy budget equations, the drag force may work to increase the turbulence energy through the additional turbulence production terms. Thirdly, the relationship between drag coefficient and dissipation rate have been discussed. These quantities have positive correlation and can be an index to explain the wind velocity deficit.

DOI： 10.3130/aije.79.297

Language：Others   Publishing type：Research paper (scientific journal)  

In a mixed-strategy game framework, each agent's strategy is defined by a real number; on the other hand, in a discrete strategy game framework, only binary strategies, either cooperation or defection, are allowed. In a spatial mixed-strategy game, with respect to the process for updating action (offer), either a synchronous or an asynchronous strategy update should be presumed. This study elucidates how stochastic perturbation that results from a synchronous or an asynchronous process for updating action significantly affects the enhancement of cooperation in an evolutionary process. Especially, when a synchronous process for updating action is assumed, the extent of cooperation increases with an increase in degree. © 2013 American Physical Society.

DOI： 10.1103/PhysRevE.88.062149

Language：Others   Publishing type：Research paper (scientific journal)  

As is well-known, spatial reciprocity plays an important role in facilitating the emergence of cooperative traits, and the effect of direct reciprocity is also obvious for explaining the cooperation dynamics. However, how the combination of these two scenarios influences cooperation is still unclear. In the present work, we study the evolution of cooperation in 2×2 games via considering both spatial structured populations and direct reciprocity driven by the strategy with 1-memory length. Our results show that cooperation can be significantly facilitated on the whole parameter plane. For prisoner's dilemma game, cooperation dominates the system even at strong dilemma, where maximal social payoff is still realized. In this sense, R-reciprocity forms and it is robust to the extremely strong dilemma. Interestingly, when turning to chicken game, we find that ST-reciprocity is also guaranteed, through which social average payoff and cooperation is greatly enhanced. This reciprocity mechanism is supported by mean-field analysis and different interaction topologies. Thus, our study indicates that direct reciprocity in structured populations can be regarded as a more powerful factor for the sustainability of cooperation. © 2013 Miyaji et al.

DOI： 10.1371/journal.pone.0071961

Language：Japanese  

41382 Particle Image Velocimetry Measurement of Unsteady Turbulent Flow around Regularly Arranged High-Rise Building Models

Language：Japanese  

41388 Analysis on optimization for the aerodynamic parameters of urban-like rough surfaces.

Language：English  

Particle Image Velocimetry Measurement of Unsteady Turbulent Flow around Regularly Arranged High-Rise Building Models

Language：English  

Particle Image Velocimetry Measurement of Unsteady Turbulent Flow around Regularly Arranged High-Rise Building Models

Language：Others   Publishing type：Research paper (scientific journal)  

Large eddy simulation (LES) of the airflows around various types of block arrays was performed to estimate the pedestrian wind environment. Five types of uniform staggered block arrays with different aspect ratios and an array with a nonuniform height were selected for the simulations. The simulation accuracy was validated by comparing the drag coefficient and wind profiles with those of previous work. The characteristics of the spatially averaged mean wind profiles of the arrays were analyzed on the basis of the calculation results. This study reveals that the frontal area ratio, which is the product of the plan area ratio and building aspect ratio, is the most important parameter in estimating the pedestrian wind environment. In addition, a simple exponential equation was derived for predicting the pedestrian wind speed as a function of the frontal area ratio, which is applicable to various building aspect ratios and amounts of height variability. © 2012 Elsevier Ltd.

DOI： 10.1016/j.buildenv.2012.08.007

Language：Others   Publishing type：Research paper (scientific journal)  

We have performed a series of wind-tunnel experiments to measure scalar concentration profiles over urban-like roughness arrays. The concentration measurements revealed two features of scalar distribution. First, the high concentration filed was observed in the leeward region of each roughness element. Secondly, the averaged concentration became high up to the roughness height due to the updraft along the element and the boundary layer thickness drastically reach to the height in spite of the short length of scalar source area. In addition to the concentration measurements, we determined the roughness length of scalar based on the preliminary performed comprehensive study on scalar transfer coefficients, momentum transfer coefficients and wind profiles and discussed the similarity between momentum and scalar transfer phenomena by applying the relation between the Dalton number and the roughness Reynolds number.

DOI： 10.3130/aije.77.917

Language：Japanese  

41366 Statistical analysis on low speed streaks organized above urban-like arrays

Language：Others   Publishing type：Research paper (scientific journal)  

We propose a new pairwise Fermi updating rule by considering a social average payoff when an agent copies a neighbor's strategy. In the update rule, a focal agent compares her payoff with the social average payoff of the same strategy that her pairwise opponent has. This concept might be justified by the fact that people reference global and, somehow, statistical information, not local information when imitating social behaviors. We presume several possible ways for the social average. Simulation results prove that the social average of some limited agents realizes more significant cooperation than that of the entire population. © 2012 American Physical Society.

DOI： 10.1103/PhysRevE.86.031141

Language：Japanese  

41365 A study on the effects of different aspect-ratio blocks on the form drag by using wind tunnel experiments

Language：Others   Publishing type：Research paper (scientific journal)  

We propose a novel idea for the so-called pairwise-Fermi process by considering copy-resistance when an agent copies a neighbor's strategy, which implies that the focal agent with relatively affluent payoff vis-à-vis social average might be negative to copy her neighbor's strategy even if her payoff is less than the neighbor's payoff. Simulation results reveal that this idea with a revised strategy adaptation process significantly enhances cooperation for prisoner's dilemma games played on time-constant networks. © 2012 Europhysics Letters Association.

DOI： 10.1209/0295-5075/98/40008

Language：Others   Publishing type：Research paper (scientific journal)  

We performed a series of wind-tunnel experiments under neutral conditions in order to create a comprehensive database of scalar transfer coefficients for street surfaces using regular block arrays representing an urban environment. The objective is to clarify the geometric dependence of scalar transfer phenomena on rough surfaces. In addition, the datasets we have obtained are necessary to improve the modelling of scalar transfer used for computational simulations of urban environments; further, we can validate the results obtained by numerical simulations. We estimated the scalar transfer coefficients using the salinity method. The various configurations of the block arrays were designed to be similar to those used in a previous experiment to determine the total drag force acting on arrays. Our results are summarized as follows: first, the results for cubical arrays showed that the transfer coefficients for staggered and square layouts varied with the roughness packing density. The results for the staggered layout showed the possibility that the mixing effect of air can be enhanced for the mid-range values of the packing density. Secondly, the transfer coefficients for arrays with blocks of non-uniform heights were smaller than those for arrays with blocks of uniform height under conditions of low packing density; however, as the packing density increased, the opposite tendency was observed. Thirdly, the randomness of rotation angles of the blocks in the array led to increasing values of the transfer coefficients under sparse packing density conditions when compared with those for cubical arrays. © 2012 Springer Science+Business Media B.V.

DOI： 10.1007/s10546-012-9698-5

Language：Others   Publishing type：Research paper (scientific journal)  

Perc & Wang demonstrated that aspiring to be the fittest under conditions of pairwise strategy updating enhances network reciprocity in structured populations playing 2×2 Prisoner's Dilemma games (Z. Wang, M. Perc, Aspiring to the fittest and promoted of cooperation in the Prisoner's Dilemma game, Physical Review E 82 (2010) 021115; M. Perc, Z. Wang, Heterogeneous aspiration promotes cooperation in the Prisoner's Dilemma game, PLOS one 5 (12) (2010) e15117). Through numerical simulations, this paper shows that network reciprocity is even greater if heterogeneous aspirations are imposed. We also suggest why heterogeneous aspiration fosters network reciprocity. It distributes strategy updating speed among agents in a manner that fortifies the initially allocated cooperators' clusters against invasion. This finding prompted us to further enhance the usual heterogeneous aspiration cases for heterogeneous network topologies. We find that a negative correlation between degree and aspiration level does extend cooperation among heterogeneously structured agents. © 2011 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physa.2011.08.039

Language：Others   Publishing type：Research paper (scientific journal)  

This article reports systematic case studies based on a Total Utility Demand Prediction System presented in the authors' previous works, in which one can follow a bottom-up approach to accurately calculate the time series utility loads (energy, power, city water, hot water, etc.) for multi-dwelling systems, including residential buildings, residential block areas and even an entire city. This calculation considers the behavioural variations of the inhabitants of the dwellings. In the case studies, we assumed a residential building consisting of 100 independent dwellings to accurately predict various peak demands and seasonal or annual demands. A series of simulations reveals that considering time-varying inhabitant behaviour schedules significantly affects the peak loads. Hence, HVAC COP, inhabitants' age and their family type significantly influence the peak loads and their accurate time-series. © 2013 Copyright Taylor and Francis Group, LLC.

DOI： 10.1080/19401493.2012.680498

Language：Others   Publishing type：Research paper (scientific journal)  

The authors performed a numerical simulation of scalar transfer phenomena between an urban surface and atmosphere. A parallelized large-eddy simulation model was adopted for the simulation. Two types of regular block arrays, a square array and staggered array, were arranged on the floor of computational domains. It was assumed that area scalar source was installed on the floor of arrays and scalar fluxes were estimated by using a wall function based on a logarithmic law. The results are summarized as follows. (l) The flow statistics of the normalized wind speed and turbulence intensity above a canopy showed good agreement with that obtained experimentally. (2) Scalar profiles shows self-similarity after 3rd rows. (3) Scalar boundary layer develops rapidly especially the edge of the scalar source area because of upward wind due to roughness.

DOI： 10.3130/aije.76.943

Language：Japanese  

40334 A study on the similarity between a momentum and scalar roughness length based on scalar profile measurements by means of wind tunnel experiments.

Language：Japanese  

41389 Large-eddy simulation on scalar transfer phenomena between urban surface and atmosphere

Language：Others   Publishing type：Research paper (scientific journal)  

The authors investigated bulk scalar coefficient (CE) of the street in the 3-D canopy with various conditions of arrangement, plan area density (λp), frontal area index (λf), and variability of model height in a wind tunnel using salinity method. The results can be summarized as follows. 1) The relationships between CE and lf of both staggered and normal arrayed canopy with uniform height shows different tendency. The CE of 3-D canopy of staggered and normal pattern have similar value under the sparse (λf) and dense conditions, in contrast, CE of staggered canopy is higher than that of normal canopy under the condition of λf = 17.4%. 2) CE of uniform canopy is larger than that of canopy with height variation under the condition of λf < 17.4%. In contrast, CE of uniform canopy is smaller than that of canopy with height variation under the condition of λf = 30.9%. Such a tendency is opposite to the result of drag force coefficient.

DOI： 10.3130/aije.73.1225

Language：Japanese  

40450 A study on wind tunnel experiment for modeling of the bulk scalar transfer coefficients of complex urban array : Part 2 Result on roughness with non-uniform heights

Language：Others   Publishing type：Research paper (scientific journal)  

In order to reproduce both transient dynamics and space distribution of an urban population only derived from a simple self-organism principle, a multi-agent simulation model is established. A resident agent tries to move to a cell so as to maximize his own utility that is defined by both effects of distance from the urban central and population density. The so-called "doughnut phenomenon" as well as growing Densely Inhabited District (DID) can be emulated qualitatively, even though the model bases on a simple self-organism rule.

DOI： 10.3130/aijt.13.845

Language：Others   Publishing type：Research paper (scientific journal)  

This investigation deals with the rocking response of a rigid block subjected to 1 dimensional harmonic excitations with the minute changes of the system parameters, such as the frictional coefficient. This paper is part one of the examination about the effects by those minute changes and is related with the minute change of friction coefficients. The numerical analysis program is developed to solve the nonlinear equations of motion governing the rocking motion of a rigid block subjected to horizontal base excitation. Natural change of the frictional coefficient is realized by the random numbers with normal probability distribution. The analytical results showed that the rocking responses are very sensitive to small changes of the friction condition between the block and the base and their effect is also large. The minute change of the friction coefficients makes the rocking response unstable and the distribution shape of rocking response change massively. Those effects by the dynamic change of the friction coefficients become a testimony of the non-reappearance on the experimental rocking responses.

DOI： 10.1299/kikaic.73.2662

Language：Others   Publishing type：Research paper (scientific journal)  

This investigation deals with the rocking response of a rigid block subjected to 1-dimensional harmonic excitations with minute changes of the system parameter, namely, the restitution coefficient, and excitation parameters, such as frequency, amplitude and phase. This paper is the part two of the examination about the effects by those minute changes and is related with the minute change of the restitution coefficient. The numerical analysis is carried out by solving the nonlinear equations of motion governing the rocking motion of a rigid block subjected to the horizontal base harmonic excitation. Natural changes of not only the restitution coefficient but also the excitation are realized by the random numbers with normal probability distribution. The analytical results showed that the rocking responses are very sensitive to small changes of the restitution coefficient and the base excitation, and their effect is also large. Minute change of the restitution coefficient or the excitation phase makes the rocking response unstable and the distribution shape of rocking response change massively.

DOI： 10.1299/kikaic.73.1955

Event date： 2018.3

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Country：Japan  

Event date： 2017.9

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Event date： 2017.9

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Event date： 2017.9

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Event date： 2017.3

Language：English   Presentation type：Oral presentation (general)  

Venue：Kansai University, Osaka   Country：Japan  

Event date： 2016.12

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Venue：タワーホール船堀   Country：Japan  

Event date： 2016.8

Language：Japanese   Presentation type：Symposium, workshop panel (public)  

Venue：九州大学 筑紫キャンパス   Country：Japan  

Event date： 2016.8

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：福岡大学 七隈キャンパス   Country：Japan  

Event date： 2015.9

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Venue：東海大学湘南キャンパス   Country：Japan  

Event date： 2015.9

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Venue：東海大学湘南キャンパス   Country：Japan  

Event date： 2015.9

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Venue：東海大学湘南キャンパス   Country：Japan  

Event date： 2015.9

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Venue：東海大学湘南キャンパス   Country：Japan  

Event date： 2015.9

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Venue：東海大学湘南キャンパス   Country：Japan  

Event date： 2015.6

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Venue：Toulouse   Country：France  

Event date： 2015.5

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Venue：徳島大学   Country：Japan  

Event date： 2014.9

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Presentation type：Oral presentation (general)  

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Type：Peer review 

Number of peer-reviewed articles in foreign language journals：10

Number of peer-reviewed articles in Japanese journals：0

Proceedings of International Conference Number of peer-reviewed papers：0

Proceedings of domestic conference Number of peer-reviewed papers：3

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Peer review 

Number of peer-reviewed articles in foreign language journals：8

Number of peer-reviewed articles in Japanese journals：2

Proceedings of International Conference Number of peer-reviewed papers：0

Proceedings of domestic conference Number of peer-reviewed papers：0

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc. 

Type：Competition, symposium, etc.