| 1. |
池谷 直樹, 萩島 理, 谷本 潤, 成田 健一, 末永 啓, 前田 一行, 40450 複雑形状都市におけるバルク輸送係数モデル化のための風洞実験 : 第2報 粗度高さが不均一な場合(風洞実験,環境工学I), 学術講演梗概集. D-1, 環境工学I, 室内音響・音環境, 騒音・固体音, 環境振動, 光・色, 給排水・水環境, 都市設備・環境管理, 環境心理生理, 環境設計, 電磁環境, 2008, 941-942, 2008.07. |
| 2. |
池谷 直樹, 萩島 理, 谷本 潤, 41389 立方体粗度群床面-大気間のスカラー輸送現象に関するLarge Eddy Simulation(選抜梗概,都市の通風・換気(2),オーガナイズドセッション,環境工学II), 学術講演梗概集. D-2, 環境工学II, 熱, 湿気, 温熱感, 自然エネルギー, 気流・換気・排煙, 数値流体, 空気清浄, 暖冷房・空調, 熱源設備, 設備応用, 2010, 785-788, 2010.07. |
| 3. |
池谷 直樹, 萩島 理, 谷本 潤, 田中 雄大, 成田 健一, 40334 複雑都市形状における濃度プロファイル測定に基づく運動量・スカラー粗度の相似性(都市気候シミュレーション(1),環境工学I), 学術講演梗概集. D-1, 環境工学I, 室内音響・音環境, 騒音・固体音, 環境振動, 光・色, 給排水・水環境, 都市設備・環境管理, 環境心理生理, 環境設計, 電磁環境, 2011, 707-708, 2011.07. |
| 4. |
池谷 直樹, 萩島 理, 谷本 潤, 古賀 康彦, 41366 都市キャノピー上空に形成される低速流体塊の統計的分析(地形風・都市キャノピー,環境工学II,2012年度大会(東海)学術講演会・建築デザイン発表会プログラム), 学術講演梗概集, 2012, 739-740, 2012.09. |
| 5. |
波多野 円, 萩島 理, 谷本 潤, 池谷 直樹, 松本 健太郎, 41365 直方体粗度群の壁面風圧に及ぼすアスペクト比の影響に関する風洞模型実験(地形風・都市キャノピー,環境工学II,2012年度大会(東海)学術講演会・建築デザイン発表会プログラム), 学術講演梗概集, 2012, 737-738, 2012.09. |
| 6. |
Sato Tsuyoshi, Hagishima Aya, Ikegaya Naoki, Tanimoto Jun, Particle Image Velocimetry Measurement of Unsteady Turbulent Flow around Regularly Arranged High-Rise Building Models, International Journal of High-Rise Buildings, 2, 2, 105-113, 2013.06, Recent studies proved turbulent flow properties in high-rise building models differ from those in low-rise building models by comparing turbulent statistics. Although it is important to understand the flow characteristics within and above high-rise building models in the study of urban environment, it is still unknown and under investigation. For this reason, we performed wind tunnel experiment using Particle Image Velocimetry (PIV) to investigate and identify the turbulent flow properties and characteristic flow patterns in high-rise building models. In particular, we focus on instantaneous flow field near the canopy and extracted flow field when homogeneous flow field were observed. As a result, six characteristic flow patterns were identified and the relationship between these flow patterns and turbulent organized structure were shown.. |
| 7. |
池谷 直樹, 萩島 理, 谷本 潤, 41388 都市粗度群空気力学パラメータの同定方法に関する考察(都市キャノピー・LES,環境工学II,2013 年度日本建築学会大会(北海道)学術講演会・建築デザイン発表会), 学術講演梗概集, 2013, 775-776, 2013.08. |
| 8. |
佐藤 幹, 萩島 理, 谷本 潤, 池谷 直樹, 41382 高アスペクト比模型群周囲の非定常乱流場に関するPIV計測(建物周辺の気流と拡散,環境工学II,2013 年度日本建築学会大会(北海道)学術講演会・建築デザイン発表会), 学術講演梗概集, 2013, 763-764, 2013.08. |
| 9. |
Naoki Ikegaya, Aya Hagishima, Jun Tanimoto, A consideration on the effects of drag force acting on roughness element - The relationship between drag coefficient and dissipation rate, Journal of Environmental Engineering (Japan), 10.3130/aije.79.297, 79, 697, 297-304, 2014.03, 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.. |
| 10. |
池谷 直樹, 萩島 理, 谷本 潤, 41315 都市境界層を模擬した粗面上の速度・湿度プロファイル相似性に関する考察(都市気流・風洞実験,環境工学II,2014年度日本建築学会大会(近畿)学術講演会・建築デザイン発表会), 学術講演梗概集, 2014, 653-654, 2014.09. |
| 11. |
鄭 朱娟, 萩島 理, 池谷 直樹, 谷本 潤, 41361 都市表面のスカラーソース偏在と粗度がスカラーバルク係数に及ぼす影響の解明 : 第二報 バルク係数のソースサイズ依存性及びスカラー粗度長(都市キャノピー流れのモデル化,環境工学II,学術講演会・建築デザイン発表会), 学術講演梗概集, 2015, 759-760, 2015.09. |
| 12. |
萩島 理, 鄭 朱娟, 池谷 直樹, 谷本 潤, 41360 都市表面のスカラーソース偏在と粗度がスカラーバルク係数に及ぼす影響 : 第一報 実験概要及びバルク係数の測定結果(都市キャノピー流れのモデル化,環境工学II,学術講演会・建築デザイン発表会), 学術講演梗概集, 2015, 757-758, 2015.09. |
| 13. |
佐藤 幹, 萩島 理, 池谷 直樹, 谷本 潤, 41358 庇を有する2次元ストリートキャニオン周囲の気流場に関するPIV計測(都市キャノピー流れのモデル化,環境工学II,学術講演会・建築デザイン発表会), 学術講演梗概集, 2015, 753-754, 2015.09. |
| 14. |
池谷 直樹, 廣瀬 智陽子, 萩島 理, 谷本 潤, 41336 立方体粗度の壁面風圧に対する非定常気流場の影響に関する数値流体解析(自然換気・風圧係数,環境工学II,学術講演会・建築デザイン発表会), 学術講演梗概集, 2015, 689-690, 2015.09. |
| 15. |
深見 亮介, 萩島 理, 谷本 潤, 池谷 直樹, 40409 住宅における冷房使用行動の確率性状に関する考察(住宅のエネルギー,環境工学I,学術講演会・建築デザイン発表会), 学術講演梗概集, 2015, 851-852, 2015.09. |
| 16. |
小野 哲嗣, 萩島 理, 谷本 潤, 池谷 直樹, 大規模集合住戸のエアコンの電力使用量の時系列データに基づく統計分析, 空気調和・衛生工学会論文集, 239, 1-9, 2017.02. |
| 17. |
Muhd Azhar bin Zainol, Naoki Ikegaya, Mohd Faizal Mohamad, Stochastic and statistical characteristics of artificially generated turbulent flow following karman spectrum in a wind-tunnel experiment, Journal of Wind Engineering and Industrial Aerodynamics, 10.1016/j.jweia.2022.105148, 229, 105148-105148, 2022.10. |
| 18. |
Wei Wang, Koki Seta, Naoki Ikegaya, Modelling probability density functions based on the Gram–Charlier series with higher-order statistics: Theoretical derivation and application, Journal of Wind Engineering and Industrial Aerodynamics, 10.1016/j.jweia.2022.105227, 231, 105227-105227, 2022.12. |
| 19. |
W. Wang, N. Ikegaya, C. Hirose, M.F. Mohamad, Indoor flow datasets of two-layered cross-ventilation models by particle image velocimetry and hot wire anemometry, Data in Brief, 10.1016/j.dib.2023.109856, 52, 109856-109856, 2024.02. |
| 20. |
Fei Li, Chiyoko Hirose, Wei Wang, Chun-Ho Liu, Naoki Ikegaya, Correlations among high-order statistics and low-occurrence wind speeds within a simplified urban canopy based on particle image velocimetry datasets, Building and Environment, 10.1016/j.buildenv.2023.111050, 247, 111050-111050, 2024.01. |
| 21. |
N. Ikegaya, K. Nagata, C. Hirose, J. Tanimoto, Effect of artificial speed of sound in ACM, EDACM, and EMV for two-dimensional cavity flow, Computers & Fluids, 10.1016/j.compfluid.2023.105985, 264, 105985-105985, 2023.10. |
| 22. |
N.M. Ali, M.F. Mohamad, W. Wang, C. Hirose, R. Yoshie, N. Ikegaya, Quantifying natural cross-ventilation flow of a two-layered model used for terraced houses in tropical zones by particle image velocimetry, Building and Environment, 10.1016/j.buildenv.2023.110829, 244, 110829-110829, 2023.10. |
| 23. |
Toshiki Sanemitsu, Naoki Ikegaya, Tsubasa Okaze, John J. Finnigan, Appropriate Momentum Provision for Numerical Simulations of Horizontally Homogeneous Urban Canopies Using Periodic Boundary Conditions, Boundary-Layer Meteorology, 10.1007/s10546-023-00823-z, 188, 3, 485-522, 2023.08. |
| 24. |
Leila Mahmoudi, Naoki Ikegaya, Identifying the Distribution and Frequency of Dust Storms in Iran Based on Long-Term Observations from over 400 Weather Stations, Sustainability, 10.3390/su151612294, 15, 16, 12294-12294, 2023.08, 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.. |
| 25. |
Koki Seta, Wei Wang, Naoki Ikegaya, Modeling probability density functions of instantaneous velocity components at the pedestrian levels of a building array by Gram–Charlier series, Journal of Wind Engineering and Industrial Aerodynamics, 10.1016/j.jweia.2023.105427, 239, 105427-105427, 2023.08. |
| 26. |
Toshiki SANEMITSU, Naoki IKEGAYA, 単純都市キャノピーを対象とした周期境界条件を用いた数値流体解析における流れの駆動方法による速度確率性状への影響, Journal of Environmental Engineering (Transactions of AIJ), 10.3130/aije.88.609, 88, 809, 609-618, 2023.07. |
| 27. |
Wei Wang, Naoki Ikegaya, Tsubasa Okaze, Comparing Weibull distribution method and Gram–Charlier series method within the context of estimating low-occurrence strong wind speed of idealized building cases, Journal of Wind Engineering and Industrial Aerodynamics, 10.1016/j.jweia.2023.105401, 236, 105401-105401, 2023.05. |
| 28. |
Abdillah Alwi, Mohd Faizal Mohamad, Naoki Ikegaya, Azli Abd Razak, Effect of protruding eave on the turbulence structures over two-dimensional semi-open street canyon, Building and Environment, 10.1016/j.buildenv.2022.109921, 228, 109921-109921, 2023.01. |
| 29. |
Muhammad Fatih Ibrahim, Mohd Faizal Mohamad, Naoki Ikegaya, Azli Abd Razak, Numerical Investigation of Flow and Dispersion over Two-Dimensional Semi-Open Street Canyon, CFD Letters, 10.37934/cfdl.15.2.5370, 15, 2, 53-70, 2023.01, 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.. |
| 30. |
N. Ikegaya, H. Kikumoto, K. Sasaki, S. Yamada, M. Matsui, Applications of wide-ranging PIV measurements for various turbulent statistics in artificial atmospheric turbulent flow in a wind tunnel, Building and Environment, 10.1016/j.buildenv.2022.109590, 225, 109590-109590, 2022.11. |
| 31. |
C. HIROSE, N. IKEGAYA, A. HAGISHIMA, J. TANIMOTO, Computational Fluid Dynamics for Cross-Ventilated Airflow in an Urban Building, Japan Architectural Review, 10.1002/2475-8876.12312, 00, 1-9, 2022.11, 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.. |
| 32. |
Ryosuke Fukami, Aya Hagishima, Jun Tanimoto, Naoki Ikegaya, Stochastic nature of occupants' behavior toward air-conditioning operation in residential buildings, Japan Architectural Review, 10.1002/2475-8876.12293, 5, 4, 649-660, 2022.10, 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.. |
| 33. |
C. Hirose, T. Nomichi, N. Ikegaya, Distributions of gust and peak factors at a pedestrian level in a simplified urban canopy obtained by particle image velocimetry, Building and Environment, 10.1016/j.buildenv.2022.109350, 222, 2022.08. |
| 34. |
真光俊樹, 池谷直樹, 廣瀬智陽子, 谷本潤, 萩島理, 都市乱流境界層を対象とした数値流体解析の運動量供給方法による乱流統計量への影響, 日本建築学会環境系論文集, 10.3130/aije.87.145, 第87巻, 第792号, 145-156, 2022.02. |
| 35. |
Yin Mun H'ng, Naoki Ikegaya, Sheikh Ahmad Zaki, Aya Hagishima, Ahmad Faiz Mohammad, Wind-tunnel estimation of mean and turbulent wind speeds within canopy layer for urban campus, Urban Climate, 10.1016/j.uclim.2021.101064, 41, 2022.01, 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.. |
| 36. |
廣瀬智陽子, 池谷直樹, 萩島理, 谷本潤, 通風換気時における都市内建物の室内気流性状把握のための数値流体解析, 日本建築学会環境系論文集, 10.3130/aije.87.19, 第87巻, 第791号, 19-28, 2022.01. |
| 37. |
K. Nagata, N. Ikegaya, J. Tanimoto, Consideration of artificial compressibility for explicit computational fluid dynamics simulation, Journal of Computational Physics, 10.1016/j.jcp.2021.110524, 443, 2021.10, 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..  |
| 38. |
C. Hirose, N. Ikegaya, A. Hagishima, J. Tanimoto, Indoor airflow and thermal comfort in a cross-ventilated building within an urban-like block array using large-eddy simulations, Building and Environment, 10.1016/j.buildenv.2021.107811, 196, 2021.06, 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.. |
| 39. |
Tsubasa Okaze, Hideki Kikumoto, Hiroki Ono, Masashi Imano, Naoki Ikegaya, Takamasa Hasama, Keisuke Nakao, Takeshi Kishida, Yuichi Tabata, Keigo Nakajima, Ryuichiro Yoshie, Yoshihide Tominaga, Large-eddy simulation of flow around an isolated building: A step-by-step analysis of influencing factors on turbulent statistics, Building and Environment, 10.1016/j.buildenv.2021.108021, 202, 108021-108021, 2021.06, 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.. |
| 40. |
Ahmad Faiz Mohammad, Naoki Ikegaya, Ryo Hikizu, Sheikh Ahmad Zaki, Turbulence effect of urban-canopy flow on indoor velocity fields under sheltered and cross-ventilation conditions, Sustainability (Switzerland), 10.3390/su13020586, 13, 2, 1-11, 2021.01, © 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.. |
| 41. |
Y. Adachi, N. Ikegaya, H. Satonaka, A. Hagishima, Numerical simulation for cross-ventilation flow of generic block sheltered by urban-like block array, Building and Environment, 10.1016/j.buildenv.2020.107174, 185, 2020.11, © 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.. |
| 42. |
N. Ikegaya, S. Morishige, Y. Matsukura, N. Onishi, A. Hagishima, Experimental study on the interaction between turbulent boundary layer and wake behind various types of two-dimensional cylinders, Journal of Wind Engineering and Industrial Aerodynamics, 10.1016/j.jweia.2020.104250, 204, 2020.09, © 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.. |
| 43. |
Sheikh Ahmad Zaki Shaikh Salim, Mohamad Nor Hafidz Arif Razali, Naoki Ikegaya, Ahmad Faiz Mohammad, Mohamed Sukri Mat Ali, Numerical simulation of the effects of secondary roughness in the form of extension to arrays of terraced houses on pedestrian wind, Science and Technology for the Built Environment, 10.1080/23744731.2020.1735860, 26, 7, 928-940, 2020.08, © 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.. |
| 44. |
N. Ikegaya, T. Kawaminami, T. Okaze, A. Hagishima, Evaluation of exceeding wind speed at a pedestrian level around a 1:1:2 isolated block model, Journal of Wind Engineering and Industrial Aerodynamics, 10.1016/j.jweia.2020.104193, 201, 2020.06, © 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.. |
| 45. |
C. Hirose, N. Ikegaya, A. Hagishima, Outdoor measurements of relationship between canopy flow and wall pressure distributions of a block within urban-like block array, Building and Environment, 10.1016/j.buildenv.2020.106881, 176, 2020.06, © 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.. |
| 46. |
Tsubasa Okaze, Hideki Kikumoto, Hiroki Ono, Masashi Imano, Naoki Ikegaya, Takamasa Hasama, Keisuke Nakao, Takeshi Kishida, Yuichi Tabata, Keigo Nakajima, Ryuichiro Yoshie, Yoshihide Tominaga, Benchmark test of flow field around a 1:1:2 shaped building model using les: Influences of various calculation conditions on simulation result, AIJ Journal of Technology and Design, 10.3130/aijt.26.179, 26, 62, 179-184, 2020.02, © 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.. |
| 47. |
N. Ikegaya, T. Okaze, H. Kikumoto, M. Imano, H. Ono, Y. Tominaga, Effect of the numerical viscosity on reproduction of mean and turbulent flow fields in the case of a 1:1:2 single block model, Journal of Wind Engineering and Industrial Aerodynamics, 10.1016/j.jweia.2019.06.013, 191, 279-296, 2019.08, © 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.. |
| 48. |
C. Hirose, N. Ikegaya, A. Hagishima, J. Tanimoto, Outdoor measurement of wall pressure on cubical scale model affected by atmospheric turbulent flow, Building and Environment, 10.1016/j.buildenv.2019.106170, 160, 2019.08, © 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.. |
| 49. |
N. Ikegaya, S. Hasegawa, A. Hagishima, Time-resolved particle image velocimetry for cross-ventilation flow of generic block sheltered by urban-like block arrays, Building and Environment, 10.1016/j.buildenv.2018.10.015, 147, 132-145, 2019.01, © 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.. |
| 50. |
T. Kawaminami, N. Ikegaya, A. Hagishima, J. Tanimoto, Velocity and scalar concentrations with low occurrence frequencies within urban canopy regions in a neutrally stable shear flow over simplified urban arrays, Journal of Wind Engineering and Industrial Aerodynamics, 10.1016/j.jweia.2018.09.024, 182, 286-294, 2018.11, © 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.. |
| 51. |
Ahmad Faiz Mohammad, Sheikh Ahmad Zaki, Naoki Ikegaya, Aya Hagishima, Mohamed Sukri Mat Ali, A new semi-empirical model for estimating the drag coefficient of the vertical random staggered arrays using LES, Journal of Wind Engineering and Industrial Aerodynamics, 10.1016/j.jweia.2018.08.003, 180, 191-200, 2018.09, © 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.. |
| 52. |
Sheikh Ahmad Zaki, Nur Farhana Mohamad Kasim, Naoki Ikegaya, Aya Hagishima, Mohamed Sukri Mat Ali, Numerical simulation on wind-driven cross ventilation in square arrays of urban buildings with different opening positions, Journal of Advanced Research in Fluid Mechanics and Thermal Sciences, 49, 2, 101-114, 2018.09, © 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.. |
| 53. |
Yuki Murakami, Naoki Ikegaya, Aya Hagishima, Jun Tanimoto, Coupled simulations of indoor-outdoor flow fields for cross-ventilation of a building in a simplified urban array, Atmosphere, 10.3390/atmos9060217, 9, 6, 2018.06, © 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.. |
| 54. |
Nurizzatul Atikha Rahmat, Aya Hagishima, Naoki Ikegaya, Jun Tanimoto, Experimental study on effect of spires on the lateral nonuniformity of mean flow in a wind tunnel, Evergreen, 10.5109/1929670, 5, 1, 1-15, 2018.03, © 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.. |
| 55. |
N. Ikegaya, Y. Ikeda, A. Hagishima, J. Tanimoto, Evaluation of rare velocity at a pedestrian level due to turbulence in a neutrally stable shear flow over simplified urban arrays, Journal of Wind Engineering and Industrial Aerodynamics, 10.1016/j.jweia.2017.10.002, 171, 137-147, 2017.12, © 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.. |
| 56. |
Tsuyoshi Sato, Aya Hagishima, Naoki Ikegaya, Jun Tanimoto, A study on accuracy of particle image velocimetry in a wind tunnel simulating airflow around building scale model, AIJ Journal of Technology and Design, 10.3130/aijt.23.567, 23, 54, 567-572, 2017.06, 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.. |
| 57. |
N. Ikegaya, Y. Ikeda, A. Hagishima, A. A. Razak, J. Tanimoto, A prediction model for wind speed ratios at pedestrian level with simplified urban canopies, Theoretical and Applied Climatology, 10.1007/s00704-015-1655-z, 127, 3-4, 655-665, 2017.02, © 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 |
| 58. |
小野 哲嗣, 萩島 理, 谷本 潤, 池谷 直樹, 大規模集合住戸のエアコンの電力使用量の時系列データに基づく統計分析, 空気調和・衛生工学会論文集, 239, 1-9, 2017.02. |
| 59. |
Naoki Ikegaya, Chiyoko Hirose, Aya Hagishima, Jun Tanimoto, Effect of turbulent flows generated by simplified roughness blocks on instantaneous wall pressure based on large-eddy simulation, Journal of Wind Engineering, 10.5359/jwe.42.22, 42, 1, 22-35, 2017.01, 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.. |
| 60. |
Naoki Ikegaya, Yasuaki Ikeda, Aya Hagishima, Jun Tanimoto, Statistical analysis of wind speeds at a pedestrian level of urban-like roughness, Journal of Wind Engineering, 10.5359/jwe.42.1, 42, 1, 1-8, 2017.01, 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.. |
| 61. |
N. Ikegaya, C. Hirose, A. Hagishima, J. Tanimoto, Effect of turbulent flow on wall pressure coefficients of block arrays within urban boundary layer, Building and Environment, 10.1016/j.buildenv.2016.02.005, 100, 28-39, 2016.05, © 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.. |
| 62. |
Tsuyoshi Sato, Aya Hagishima, Naoki Ikegaya, Jun Tanimoto, Wind tunnel experiment on turbulent flow field around 2D street canyon with eaves, Journal of Environmental Engineering (Japan), 10.3130/aije.81.467, 81, 723, 467-476, 2016.05, 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.. |
| 63. |
Rahnat Nurizzatul Atikha, Hagishima Aya, Ikegaya Naoki, Tanimoto Jun, Omar Abd Rahman, An experimental study on aerodynamic interaction between a boundary layer generated by a smooth and rough wall and a wake behind a spire, 九州大学大学院総合理工学報告, 10.15017/1560669, 37, 2, 19-26, 2016.02, A wind tunnel experiment to assess the flow characteristics of the wake behind a spire mounted normal to the wind tunnel floor was conducted to clarify the interaction between the wake flow and the wall shear boundary layer. To reproduce the contrasting boundary layer depth, two types of walls-a smooth wall and a regular cube array-were adopted; for each wall, the spanwise distribution of the streamwise velocity was measured at two downwind positions and seven heights within and above the wall boundary layer with and without a spire. The span wise distribution of the wake generated by the spire far above the wall boundary layer with low turbulence agreed with the well-known function for two-dimensional (2D) wake flow, derived theoretically from the gradient-diffusion model, despite the weak asymmetry of the inflow. In contrast, the spanwise distribution of the wake within or near the outer edge of the wall boundary layer showed different trends from that of the 2D wake flow. In the former, the expansion of the wake width is compressed in the lateral direction by the turbulence of the wall boundary layer and the velocity deficit of the wake is sustained far from the spire.. |
| 64. |
Juyeon Chung, Aya Hagishima, Naoki Ikegaya, Jun Tanimoto, Wind-Tunnel Study of Scalar Transfer Phenomena for Surfaces of Block Arrays and Smooth Walls with Dry Patches, Boundary-Layer Meteorology, 10.1007/s10546-015-0063-3, 157, 2, 219-236, 2015.11, © 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 CEwet for an underlying wet street surface of dry block arrays show a convex trend against the block density λp. Comparison with past data, and results for wet smooth surfaces including dry patches, reveal that the positive peak of CEwet with increasing λp 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 CElot 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 CEwet 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.. |
| 65. |
Mohamad Mohd Faizal, Hagishima Aya, Ikegaya Naoki, Tanimoto Jun, Omar Abd Rahman, Aerodynamic effect of overhang on a turbulent flow field within a two-dimensional street canyon, 九州大学大学院総合理工学報告, 10.15017/1525830, 37, 1, 1-7, 2015.09, This paper reports the results of flow field analysis within and above a two-dimensional street canyon with various overhang lengths using large-eddy simulation (LES). Simulations were conducted for a constant canyon aspect ratio of W/H = 3, where W is the street width and H is the building height. Three different overhang lengths were simulated with P = 0H, 0.5H, and 1H in order to derive the mean and instantaneous flow characteristics. The results are compared with wind tunnel experiments for validation. The LES results of the mean flow with the P = 0H condition agree fairly well with the wind tunnel data. However, profiles of the standard deviation for the streamwise and vertical velocity components show large discrepancies at all measured locations. In addition, an increase in overhang length on both building façades significantly modifies the in-canyon flow pattern by limiting the penetration of the bulk flow into the canyon layer.. |
| 66. |
Jun Tanimoto, Takuya Fujiki, Shinji Kukida, Naoki Ikegaya, Aya Hagishima, Acquisition of the field measurement data relating to lane change actions, International Journal of Modern Physics C, 10.1142/S0129183115500722, 26, 7, 2015.07, © 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.. |
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Takashi Ogasawara, Jun Tanimoto, Eriko Fukuda, Aya Hagishima, Naoki Ikegaya, Effect of a large gaming neighborhood and a strategy adaptation neighborhood for bolstering network reciprocity in a prisoner's dilemma game, Journal of Statistical Mechanics: Theory and Experiment, 10.1088/1742-5468/2014/12/P12024, 2014, 12, 2014.12, © 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.. |
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Jun Tanimoto, Takuya Fujiki, Zhen Wang, Aya Hagishima, Naoki Ikegaya, Dangerous drivers foster social dilemma structures hidden behind a traffic flow with lane changes, Journal of Statistical Mechanics: Theory and Experiment, 10.1088/1742-5468/2014/11/P11027, 2014, 11, 2014.11, © 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.. |
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Eriko Fukuda, Satoshi Kokubo, Jun Tanimoto, Zhen Wang, Aya Hagishima, Naoki Ikegaya, Risk assessment for infectious disease and its impact on voluntary vaccination behavior in social networks, Chaos, Solitons and Fractals, 10.1016/j.chaos.2014.07.004, 68, 1-9, 2014.11, 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.. |
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Naoki Ikegaya, Aya Hagishima, Jun Tanimoto, A consideration on the effects of drag force acting on roughness element - The relationship between drag coefficient and dissipation rate, Journal of Environmental Engineering (Japan), 10.3130/aije.79.297, 79, 697, 297-304, 2014.03, 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.. |
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Kohei Miyaji, Jun Tanimoto, Aya Hagishima, Naoki Ikegaya, Influence of stochastic perturbation of both action updating and strategy updating in mixed-strategy 2 × 2 games on evolution of cooperation, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.88.062149, 88, 6, 2013.12, 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.. |
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Kohei Miyaji, Jun Tanimoto, Zhen Wang, Aya Hagishima, Naoki Ikegaya, Direct Reciprocity in Spatial Populations Enhances R-Reciprocity As Well As ST-Reciprocity, PLoS ONE, 10.1371/journal.pone.0071961, 8, 8, 2013.08, 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.. |
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Sato Tsuyoshi, Hagishima Aya, Ikegaya Naoki, Tanimoto Jun, Particle Image Velocimetry Measurement of Unsteady Turbulent Flow around Regularly Arranged High-Rise Building Models, International Journal of High-Rise Buildings, 2, 2, 105-113, 2013.06, Recent studies proved turbulent flow properties in high-rise building models differ from those in low-rise building models by comparing turbulent statistics. Although it is important to understand the flow characteristics within and above high-rise building models in the study of urban environment, it is still unknown and under investigation. For this reason, we performed wind tunnel experiment using Particle Image Velocimetry (PIV) to investigate and identify the turbulent flow properties and characteristic flow patterns in high-rise building models. In particular, we focus on instantaneous flow field near the canopy and extracted flow field when homogeneous flow field were observed. As a result, six characteristic flow patterns were identified and the relationship between these flow patterns and turbulent organized structure were shown.. |
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Azli Abd Razak, Aya Hagishima, Naoki Ikegaya, Jun Tanimoto, Analysis of airflow over building arrays for assessment of urban wind environment, Building and Environment, 10.1016/j.buildenv.2012.08.007, 59, 56-65, 2013.01, 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.. |
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Naoki Ikegaya, Aya Hagishima, Jun Tanimoto, Yu Dai Tanaka, A study on the similarity of the momentum and scalar roughness lengths over urban-like roughness, Journal of Environmental Engineering (Japan), 10.3130/aije.77.917, 77, 681, 917-923, 2012.11, 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.. |
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Keizo Shigaki, Jun Tanimoto, Zhen Wang, Satoshi Kokubo, Aya Hagishima, Naoki Ikegaya, Referring to the social performance promotes cooperation in spatial prisoner's dilemma games, Physical Review E - Statistical, Nonlinear, and Soft Matter Physics, 10.1103/PhysRevE.86.031141, 86, 3, 2012.09, 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.. |
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K. Shigaki, S. Kokubo, J. Tanimoto, A. Hagishima, N. Ikegaya, Does copy-resistance enhance cooperation in spatial prisoner's dilemma?, EPL, 10.1209/0295-5075/98/40008, 98, 4, 2012.05, 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.. |
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Naoki Ikegaya, Aya Hagishima, Jun Tanimoto, Yudai Tanaka, Ken Ichi Narita, Sheikh Ahmad Zaki, Geometric Dependence of the Scalar Transfer Efficiency over Rough Surfaces, Boundary-Layer Meteorology, 10.1007/s10546-012-9698-5, 143, 2, 357-377, 2012.05, 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.. |
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Jun Tanimoto, Makoto Nakata, Aya Hagishima, Naoki Ikegaya, Spatially correlated heterogeneous aspirations to enhance network reciprocity, Physica A: Statistical Mechanics and its Applications, 10.1016/j.physa.2011.08.039, 391, 3, 680-685, 2012.02, 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.. |
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Jun Tanimoto, Aya Hagishima, Takeshi Iwai, Naoki Ikegaya, Total utility demand prediction for multi-dwelling sites by a bottom-up approach considering variations of inhabitants' behaviour schedules, Journal of Building Performance Simulation, 10.1080/19401493.2012.680498, 6, 1, 53-64, 2012.01, 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.. |
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Naoki Ikegaya, Aya Hagishimaand, Jun Tanimoto, Large-eddy simulation large-eddysimulation onscalartransferphenomena betweenurbansurfaceandatmosphere, Journal of Environmental Engineering, 10.3130/aije.76.943, 76, 668, 943-951, 2011.10, 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.. |
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Aya Hagishima, Jun Tanimoto, Satoru Suenaga, Naoki Ikegaya, Kazuyuki Maeda, Ken Ichi Narita, Wind tunnel experiment on bulk scalar coefficient of urban-like roughness, Journal of Environmental Engineering, 10.3130/aije.73.1225, 73, 632, 1225-1231, 2008.10, 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 |
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Naoki Ikegaya, Jun Tanimoto, Aya Hagishima, Hiroki Sagara, A study on multi-agent simulation model for transient dynamics and distribution of the population in an urban area, AIJ Journal of Technology and Design, 10.3130/aijt.13.845, 13, 26, 845-848, 2007.12, 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.. |
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Man Yong Jeong, Kohei Suzuki, Naoki Ikegaya, Rocking of rigid block under minute fluctuation of system parameter (1st report, minute fluctuation of friction coefficients), Nihon Kikai Gakkai Ronbunshu, C Hen/Transactions of the Japan Society of Mechanical Engineers, Part C, 10.1299/kikaic.73.2662, 73, 10, 2662-2669, 2007.10, 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.. |
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Man Yong Jeong, Kohei Suzuki, Naoki Ikegaya, Rocking of rigid block under minute fluctuation of system/excitation parameter (2nd report, minute fluctuation of restitution coefficient), Nihon Kikai Gakkai Ronbunshu, C Hen/Transactions of the Japan Society of Mechanical Engineers, Part C, 10.1299/kikaic.73.1955, 73, 7, 1955-1962, 2007.07, 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.. |
