九州大学 研究者情報
論文一覧
内田 孝紀(うちだ たかのり) データ更新日:2019.06.14

准教授 /  応用力学研究所 新エネルギー力学部門


原著論文
1. Takanori Uchida, Susumu Takakuwa, A Large-Eddy Simulation-Based Assessment of the Risk of Wind Turbine Failures Due to Terrain -Induced Turbulence over a Wind Farim inComplex Terrain, Energies, 10.3390/en12101925, 19pages, 2019.05, The first part of the present study investigated the relationship among the number of yaw gear and motor failures and turbulence intensity (TI) at all the wind turbines under investigation with the use of in situ data. The investigation revealed that wind turbine #7 (T7), which experienced a large number of failures, was affected by terrain-induced turbulence with TI that exceeded the TI presumed for the wind turbine design class to which T7 belongs. Subsequently, a computational fluid dynamics (CFD) simulation was performed to examine if the abovementioned observed wind flow characteristics could be successfully simulated. The CFD software package that was used in the present study was RIAM-COMPACT, which was developed by the first author of the present paper. RIAM-COMPACT is a nonlinear, unsteady wind prediction model that uses large-eddy simulation (LES) for the turbulence model. RIAM-COMPACT is capable of simulating flow collision, separation, and reattachment and also various unsteady turbulence–eddy phenomena that are caused by flow collision, separation, and reattachment. A close examination of computer animations of the streamwise (x) wind velocity revealed the following findings: As we predicted, wind flow that was separated from a micro-topographical feature (micro-scale terrain undulations) upstream of T7 generated large vortices. These vortices were shed downstream in a nearly periodic manner, which in turn generated terrain-induced turbulence, affecting T7 directly. Finally, the temporal change of the streamwise (x) wind velocity (a non-dimensional quantity) at the hub-height of T7 in the period from 600 to 800 in non-dimensional time was re-scaled in such a way that the average value of the streamwise (x) wind velocity for this period was 8.0 m/s, and the results of the analysis of the re-scaled data were discussed. With the re-scaled full-scale streamwise wind velocity (m/s) data (total number of data points: approximately 50,000; time interval: 0.3 s), the time-averaged streamwise (x) wind velocity and TI were evaluated using a common statistical processing procedure adopted for in situ data. Specifically, 10-min moving averaging (number of sample data points: 1932) was performed on the re-scaled data. Comparisons of the evaluated TI values to the TI values from the normal turbulence model in IEC61400-1 Ed.3 (2005) revealed the following: Although the evaluated TI values were not as large as those observed in situ, some of the evaluated TI values exceeded the values for turbulence class A, suggesting that the influence of terrain-induced turbulence on the wind turbine was well simulated. .
2. Takanori Uchida, Kenji Araki, Reproduction of Local Strong Wind Area Induced in the Downstream of Small‐scale Terrain by Computational Fluid Dynamic (CFD) Approach, Preprint, doi: 10.20944/preprints201904.0041.v1, 15pages, 2019.04, In this research, the computational fluid dynamic (CFD) approach that has been used in wind power generation field was applied for the solution of the problems of local strong wind areas in railway fields, and the mechanism of wind generation was discussed. At the same time, the affectivity of the application of computational fluid dynamic approach to railway field was discussed. The problem of local wind that occurs on the railway line in winter was taken up in this research. A computational simulation for the prediction of wind conditions by LES was implemented and it was clarified that the local strong wind area is mainly caused by separated flows originating from the small‐scale terrain positioned at its upstream (at approximately 180.0 m above sea level). Meanwhile, the effects of the size of calculation area and spatial grid resolution on the result of calculation and the effect of atmospheric stability were also discussed. It was clarified that when the air flow characteristic of the separated flow originating from the small‐scale terrain (at altitude of approximately 180.0 m) targeted in this research is reproduced at high accuracy by computational simulation of wind conditions, approximately 10.0 m of spatial resolution of computational grid in horizontal direction is required. As a result of the computational simulation of wind conditions of stably stratified flow (Fr = 1.0), lee waves were excited at the downstream of the terrain over time. As a result, the reverse‐flow region lying behind the terrain that had been observed at a neutral time was inhibited. Consequently, local strong wind area was generated at the downstream of the terrain and the strong wind area passing through the observation mast was observed. By investigating the speed increasing rate of local strong wind area induced at the time of stable stratification, it was found that the wind was approximately 1.2 times stronger than what was generated at a neutral time..
3. Kenji Ono, Takanori Uchida, High-Performance Parallel Simulation of Airflow for Complex Terrain Surface, Modelling and Simulation in Engineering, 10.1155/2019/5231839, 2019, Article ID 5231839, 10 pages, 2019.02, [URL], It is important to develop a reliable and high-throughput simulation method for predicting airflows in the installation planning phase of windmill power plants. This study proposes a two-stage mesh generation approach to reduce the meshing cost and introduces a hybrid parallelization scheme for atmospheric fluid simulations. The meshing approach splits mesh generation into two stages: in the first stage, the meshing parameters that uniquely determine the mesh distribution are extracted, and in the second stage, a mesh system is generated in parallel via an in situ approach using the parameters obtained in the initialization phase of the simulation. The proposed two-stage approach is flexible since an arbitrary number of processes can be selected at run time. An efficient OpenMP-MPI hybrid parallelization scheme using a middleware that provides a framework of parallel codes based on the domain decomposition method is also developed. The preliminary results of the meshing and computing performance show excellent scalability in the strong scaling test..
4. Takanori Uchida, Large-Eddy Simulation of Airflow over a Steep,Three-Dimensional Isolated Hill with Multi-GPUs Computing, Open Journal of Fluid Dynamics, 10.4236/ojfd.2018.84027, 8, 4, 416-434, 2018.11, The present research attempted a Large-Eddy Simulation (LES) of airflow over a steep, three-dimensional isolated hill by using the latest multi-cores multi-CPUs systems. As a result, it was found that 1) turbulence simulations using approximately 50 million grid points are feasible and 2) the use of this system resulted in the achievement of a high computation speed, which exceeded the speed of parallel computation attained by a single CPU on one of the latest supercomputers. Furthermore, LES was conducted by using the multi-GPUs systems. The results of these simulations revealed the following findings: 1) the multi-GPUs environment which used the NVDIA Tesla M2090 or the M2075 could simulate turbulence in a model with as many as approximately 50 million grid points. 2) The computation speed achieved by the multi-GPUs environments exceeded that by parallel computation which
used four to six CPUs of one of the latest supercomputers..
5. Takanori Uchida, Numerical Investigation of Terrain-induced Turbulence in Complex Terrain by Large-eddy Simulation (LES) Technique, Energies, 10.3390/en11061530, 11(10), 2638, 15pages, 2018.10, In the present study, field observation wind data from the time of the wind turbine blade damage accident on Shiratakiyama Wind Farm were analyzed in detail. In parallel, high-resolution large-eddy simulation (LES) turbulence simulations were performed in order to examine the model’s ability to numerically reproduce terrain-induced turbulence (turbulence intensity) under strong wind conditions (8.0–9.0 m/s at wind turbine hub height). Since the wind velocity and time acquired from the numerical simulation are dimensionless, they are converted to full scale. As a consequence, both the standard deviation of the horizontal wind speed (m/s) and turbulence intensity evaluated from the field observation and simulated wind data are successfully in close agreement. To investigate the cause of the wind turbine blade damage accident on Shiratakiyama Wind Farm, a power spectral analysis was performed on the fluctuating components of the observed time series data of wind speed (1 s average values) for a 10 min period (total of 600 data) by using a fast Fourier transform (FFT). It was suggested that the terrain-induced turbulence which caused the wind turbine blade damage accident on Shiratakiyama Wind Farm was attributable to rapid wind speed and direction fluctuations which were caused by vortex shedding from Tenjogadake (elevation: 691.1 m) located upstream of the wind farm..
6. Takanori UCHIDA, Graham Li, Comparison of RANS and LES in the Prediction of Airflow Field over Steep Complex Terrain, Open Journal of Fluid Dynamics, 10.4236/ojfd.2018.83018, 08, 286-307, Article ID:87086,22 pages, 2018.09, The present study compared the prediction accuracy of the three CFD software packages for simulating airflow around a three-dimensional, isolated hill with a steep slope: 1) WindSim (turbulence model: RNG k-ε RANS), 2) Meteodyn WT (turbulence model: k-L RANS), which are the leading commercially available CFD software packages in the wind power industry and 3) RIAM-COMPACT (turbulence model: standard Smagorinsky LES), which has been developed by the lead author of the present paper. Distinct differences in the airflow patterns were identified in the vicinity of the isolated hill (especially downstream of the hill) between the RANS results and the LES results. No reverse flow region (vortex region) characterized by negative wind velocities was identified downstream of the isolated hill in the result from the simulation with WindSim (RNG k-ε RANS) and Meteodyn WT (k-L RANS). In the case of the simulation with RIAM-COMPACT natural terrain version (standard Smagorinsky LES), a reverse flow region (vortex region) characterized by negative wind velocities clearly forms. Next, an example of wind risk (terrain-induced turbulence) diagnostics was presented for a large-scale wind farm in China. The vertical profiles of the streamwise (x) wind velocity do not follow the so-called power law wind profile; a large velocity deficit can be seen between the hub center and the lower end of the swept area in the case of the LES calculation (RIAM-COMPACT)..
7. Takanori Uchida, Computational Investigation of the Causes of Wind Turbine Blade Damage at Japan's Wind Farm in Complex Terrain, Journal of Flow Control, Measurement & Visualization, 10.4236/jfcmv.2018.63013, 6, 3, 152-167, 2018.07, During the passage of Typhoon 0918 (Melor) over southern Honshu in Japan on 7 and 8 October 2009, strong winds with extremely high turbulence fluctuations were observed over Shirataki Mountain and the surrounding mountains in Shimonoseki, Yamaguchi Prefecture, Japan. These strong winds caused damage to wind turbine blades at the Shiratakiyama Wind Farm owned by Kinden Corporation. In order to investigate the causes of the blade damage, the airflow characteristics from the time of the incidences are first simulated in detail with the combined use of the WRF-ARW mesoscale meteorological model and the RIAM-COMPACT LES turbulence model (CFD model). Subsequently, in order to evaluate the wind pressure acting on the wind turbine blades, an airflow analysis is separately performed for the vicinity of the blades with the RANS turbulence model. Finally, the stress on the blades is investigated using the FEM with the RANS analysis results as the boundary conditions..
8. Takanori Uchida, Designed Wind Speed Evaluation Technique in Wind Turbine Installation Point by Using the Meteorological Model and CFD Model, Journal of Flow Control, Measurement & Visualization, 10.4236/jfcmv.2018.63014, 06, 03(2018), Article ID:85916,17 pages, 2018.07, It is highly important in Japan to choose a good site for wind turbines, becausethe spatial distribution of wind speed is quite complicated over steepcomplex terrain. We have been developing the unsteady numerical model called the RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, Computational Prediction of Airflow over Complex Terrain).The RIAM-COMPACT is based on the LES (Large-Eddy Simulation).The object domain of the RIAM-COMPACT is from several m to several km,and can predict the airflow and gas diffusion over complex terrain with highprecision. In the present paper, the design wind speed evaluation technique inwind turbine installation point by using the mesoscale meteorological modeland RIAM-COMPACT CFD model was proposed. The design wind speed tobe used for designing WTGs can be calculated by multiplying the ratio of the mean wind speed at the hub-height to the mean upper-air wind speed at the inflow boundary, i.e. , the fractional increase of the mean hub-height wind speed, by the reduction ratio, R. The fractional increase of the mean hub-height wind speed was evaluated using the CFD simulation results. This method was proposed as Approach 1 in the present paper. A value of 61.9 m/s was obtained for the final design wind speed, Uh, in Approach 1. In the evaluation procedure of the design wind speed in Approach 2, neither the above-mentioned reduction rate, R, nor an upper-air wind speed of 1.7 Vo, where Vo is the reference wind speed, was used. Instead, the value of the maximum wind speed which was obtained from the typhoon simulation for
each of the investigated wind directions was adopted. When the design wind speed was evaluated using the 50-year recurrence value, the design wind speed was 48.3 m/s. When a somewhat conservative safety factor was applied, that is, when the 100 year recurrence value was used instead, the design wind speed was 52.9 m/s..
9. Takanori Uchida, LES Investigation of Terrain-Induced Turbulence in Complex Terrain and Economic Effects of Wind Turbine Control, Energies, 10.3390/en11061530, 11(6), 1530, 15pages, 2018.06, In the present study, numerical wind simulation was conducted by reproducing the realistic topography near wind turbine sites with high spatial resolutions and using the Large-Eddy Simulation (LES) technique. The topography near wind turbine sites serves as the origin of the terrain-induced turbulence. The obtained numerical simulation results showed that the terrain-induced turbulence is generated at a small terrain feature located upstream of the wind turbine. The generated terrain-induced turbulence affects the wind turbine directly. The wind speed and wind direction at the wind turbine site are significantly changed with time. In the present study, a combination of the series of wind simulation results and on-site operation experience led to a decision to adopt an “automatic shutdown program”. Here, an “automatic shutdown program” means the automatic suspension of wind turbine operation based on the wind speed and wind direction meeting the conditions associated with significant effects of terrain-induced turbulence at a wind turbine site. The adoption of the “automatic shutdown program” has successfully led to a large reduction in the number of occurrences of wind turbine damage, thus, creating major positive economic effects..
10. Takanori Uchida, Computational Fluid Dynamics Approach to Predict the Actual Wind Speed over Complex Terrain, Energies, 10.3390/en11071694, 11(7), 1694, 13pages, 2018.06, This paper proposes a procedure for predicting the actual wind speed for flow over complex terrain with CFD. It converts a time-series of wind speed data acquired from field observations into a time-series data of actual scalar wind speed by using non-dimensional wind speed parameters, which are determined beforehand with the use of CFD output. The accuracy and reproducibility of the prediction procedure were investigated by simulating the flow with CFD with the use of high spatial resolution (5 m) surface elevation data for the Noma Wind Park in Kagoshima Prefecture, Japan. The errors of the predicted average monthly wind speeds relative to the observed values were less than approximately 20%..
11. Takanori Uchida, Computational Fluid Dynamics (CFD) Investigation of Wind Turbine Nacelle Separation Accident over Complex Terrain in Japan, Energies, 10.3390/en11061485, 11(6), 1485, 13pages, 2018.06, We have developed an unsteady and non-linear wind synopsis simulator called RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, COMputational Prediction of Airflow over Complex Terrain) to simulate the airflow on a micro scale, i.e., a few tens of km or less. In RIAM-COMPACT, the large-eddy simulation (LES) has been adopted for turbulence modeling. LES is a technique in which the structures of relatively large eddies are directly simulated and smaller eddies are modeled using a sub-grid scale model. In the present study, we conducted numerical wind diagnoses for the Taikoyama Wind Farm nacelle separation accident in Japan. The simulation results suggest that all six wind turbines at Taikoyama Wind Farm are subject to significant influence from separated flow (terrain-induced turbulence) which is generated due to the topographic irregularities in the vicinity of the wind turbines. A proposal was also made on reconstruction of the wind farm..
12. Takanori UCHIDA, A New Proposal for Vertical Extrapolation of Offshore Wind Speed and an Assessment of Offshore Wind Energy Potential for the Hibikinada Area, Kitakyushu, Japan, Energy and Power Engineering, 10.4236/epe.2018.104011, 10, 04, 11pages, 2018.04, The author’s research group has been conducting research on applications of various meteorological Grid Point Value (GPV) data offered by the Japan Meteorological Agency (JMA) to the field of wind power generation. In particular, the group’s research has been focusing on the following areas: 1) the use of GPV data from the JMA Meso-Scale Model (MSM-S; horizontal resolution: 5 km) and the JMA Local Forecast Model (LFM-S; horizontal resolution: 2 km), and 2) examinations of the prediction accuracy of local wind assessment with the use of these data. In both the MSM-S and the LFM-S, grid points are fixed at 10 m above the sea (ground) surface. The purpose of the present study is to establish a method in which the values of the MSM-S and LFM-S wind speed data from the 10 m height are used as the reference wind speed and are, using a power law, vertically extrapolated to 80 to 90 m heights, typical hub-heights of offshore wind turbines. For this purpose, the present study examined time-averaged vertical profiles of wind speed over the ocean based on the MSM-S data and in-situ data in the Hibikinada area, Kitakyushu City, Fukuoka Prefecture, Japan. As a result, it was revealed that a strong wind shear existed close to the sea surface, between the 10 and 30 m heights. In order to address the above-mentioned wind shear, a two-step vertical extrapolation method was proposed in the present study. In this method, two values of N, specifically for low and high altitudes (below and above approximately 30 m, respectively), were calculated and used. The data were created for the five years between 2012 and 2016. Similarly to previous analyses, the analysis of the created data set indicated that the potential of offshore wind power generation in the Hibikinada area, Kitakyushu City is quite high..
13. Takanori UCHIDA, Large-Eddy Simulation and Wind Tunnel Experiment of Airflow over Bolund Hill, Open Journal of Fluid Dynamics, 10.4236/ojfd.2018.81003, 8, 30-43, 2018.03.
14. Yasushi KAWASHIMA, Takanori UCHIDA, Effects of Terrain-Induced Turbulence on Wind Turbine Blade Fatigue Loads, Energy and Power Engineering, 10.4236/epe.2017.913053, 9, 843-857, 2017.12.
15. Takanori UCHIDA, Three-Dimensional Numerical Simulation of Stably Stratified Flows over a Two-Dimensional Hill, Open Journal of Fluid Dynamics, https://doi.org/10.4236/ojfd.2017.74039, 7, 579-595, 2017.12.
16. Takanori UCHIDA, High-Resolution LES of Terrain-Induced Turbulence around Wind Turbine Generators, by Using Turbulent Inflow Boundary Conditions, Open Journal of Fluid Dynamics, https://doi.org/10.4236/ojfd.2017.74035, 7, 511-524, 2017.12.
17. Takanori UCHIDA, CFD Prediction of the Airflow at a Large-Scale Wind Farm above a Steep, Three-Dimensional Escarpment, Energy and Power Engineering, https://doi.org/10.4236/epe.2017.913052, 9, 829-842, 2017.12.
18. Takanori UCHIDA, High-Resolution Micro-Siting Technique for Large Scale Wind Farm Outside of Japan Using LES Turbulence Model, Energy and Power Engineering, https://doi.org/10.4236/epe.2017.912050, 9, 802-813, 2017.12.
19. 川島 泰史, 内田 孝紀, 清木 荘一郎, 近藤 勝俊, 地形性乱流が風車構造強度に与える影響に関する研究(非定常乱流モデルLESによる地形性乱流診断), 日本風力エネルギー学会論文集, 41, 2, 17-24, 2017.08.
20. 内田孝紀, 風車ウエイクのラージ・エディ・シミュレーション(LES), 計算工学, 22, 3, 3613-3617, 2017.05.
21. Koichi Watanabe, Yuji Ohya, Takanori Uchida, Tomoyuki Nagai, Numerical Prediction and Field Verification Test of Wind-Power Generation Potential in Nearshore Area Using a Moored Floating Platform, Journal of Flow Control, Measurement & Visualization, 10.4236/jfcmv.2017.52002, 5, 2, 2017.04.
22. Yuji Ohya, Masaki Wataka, Koichi Watanabe, Takanori Uchida, Laboratory experiment and numerical analysis of a new type of solar tower efficiently generating a thermal updraft, energies, 10.3390/en9121077, 9, 12, 2016.12, [URL], A new type of solar tower was developed through laboratory experiments and numerical analyses. The solar tower mainly consists of three components. The transparent collector area is an aboveground glass roof, with increasing height toward the center. Attached to the center of the inside of the collector is a vertical tower within which a wind turbine is mounted at the lower entry to the tower. When solar radiation heats the ground through the glass roof, ascending warm air is guided to the center and into the tower. A solar tower that can generate electricity using a simple structure that enables easy and less costly maintenance has considerable advantages. However, conversion efficiency from sunshine energy to mechanical turbine energy is very low. Aiming to improve this efficiency, the research project developed a diffuser-type tower instead of a cylindrical tower, and investigated a suitable diffuser shape for practical use. After changing the tower height and diffuser open angle, with a temperature difference between the ambient air aloft and within the collector, various diffuser tower shapes were tested by laboratory experiments and numerical analyses. As a result, it was found that a diffuser tower with a semi-open angle of 4° is an optimal shape, producing the fastest updraft at each temperature difference in both the laboratory experiments and numerical analyses. The relationships between thermal updraft speed and temperature difference and/or tower height were confirmed. It was found that the thermal updraft velocity is proportional to the square root of the tower height and/or temperature difference..
23. 大城善郎, 伊藤芳樹, 内田孝紀, 高桑 晋, 勝呂幸男, 松澤幸一, 相原雅彦, 太田健一郎, 複雑地形における超音波風向風速計を用いた高精度風況解析(青森県下北地方岩屋ウィンドファームにおける2高度観測), 日本風力エネルギー学会論文集, 40, 2, 7-12, 2016.08.
24. 内田孝紀, LESによる陸上および洋上ウィンドファームの数値風況予測, ターボ機械, 44, 7, 15-22, 2016.07.
25. Takanori Uchida, Reproducibility of Complex Turbulent Flow Using Commercially-Available CFD Software
―Report 1: For the Case of a Three-Dimensional Isolated-Hill With Steep Slopes―, Reports of Research Institute for Applied Mechanics, Kyushu University, 150, 47-59, 2016.03.
26. Takanori Uchida, Reproducibility of Complex Turbulent Flow Using Commercially-Available CFD Software
―Report 2: For the Case of a Two-Dimensional Ridge With Steep Slopes―, Reports of Research Institute for Applied Mechanics, Kyushu University, 150, 67-70, 2016.03.
27. Takanori Uchida, Reproducibility of Complex Turbulent Flow Using Commercially-Available CFD Software
―Report 3: For the Case of a Three-dimensional Cube―, Reports of Research Institute for Applied Mechanics, Kyushu University, 150, 71-83, 2016.03.
28. 内田 孝紀, 風車ウエイクの「ゆらぎ」に関するアクチュエータラインモデルを用いた高解像度LES, 九州大学応用力学研究所所報, 150, 25-33, 2016.03.
29. 内田孝紀, 青柳達郎, 渡邊文人, 見上伸, 市販CFDソフトウエアによる実地形を対象とした年間平均風速および年間発電電量の予測, 九州大学応用力学研究所所報, 150, 34-39, 2016.03.
30. 内田 孝紀, 「みなと100年公園」において2014年12月1日に発生した小型風車の破損事故に関する風況調査, 九州大学応用力学研究所所報, 150, 40-46, 2016.03.
31. 内田 孝紀, 非定常乱流モデルLESによる地形性乱流の数値的再現性, 日本風力エネルギー学会論文集, 39, 4, 53-60, 2016.02.
32. 内田 孝紀, LESによる数値風況診断に基づいた風車制御とその経済効果, 日本風力エネルギー学会論文集, 39, 4, 61-68, 2016.02.
33. Shinsuke Okada, Takanori Uchida, Takashi Karasudani, Yuji Ohya, Improvement in Solar Chimney Power Generation by Using a Diffuser Tower, Journal of Solar Energy Engineering, Transactions of the ASME, 138, 1, 2016.02.
34. 川島 泰史, 内田 孝紀, 複雑地形における気象庁局地数値予報モデルデータ(LFM)を用いた簡易風況推定法の試み-串木野れいめい風力発電所を例として-, 九州大学応用力学研究所所報, 149, 51-63, 2015.09.
35. 内田 孝紀, 風車および小規模地形の周辺流れに対する温度成層の効果-その1:流れ場の可視化-, 九州大学応用力学研究所所報, 149, 85-90, 2015.09.
36. 内田 孝紀, 福岡市博多湾を対象にした気象GPVデータによる洋上風況解析, 九州大学応用力学研究所所報, 149, 64-71, 2015.09.
37. 内田 孝紀, 渡邊 文人, 見上 伸, 市販CFDソフトウエアによる急峻な3次元孤立峰を対象とした気流場解析(第2報), 九州大学応用力学研究所所報, 149, 72-77, 2015.09.
38. 内田 孝紀, 鵜沢 憲, 大規模な崖状地形に建設された大型ウインドファームを対象とした気流場解析, 九州大学応用力学研究所所報, 149, 78-84, 2015.09.
39. Takanori Uchida, Fumihito Watanabe, Shin Mikami, Analysis of the Airflow Field around a Steep, Three-dimensional Isolated Hill with Commercially Available CFD Software, Reports of Research Institute for Applied Mechanics, Kyushu University, 149, 91-98, 2015.09.
40. Fumihito Watanabe, Takanori Uchida, Micro-siting of Wind Turbine in Complex Terrain:Simplified Fatigue Life Prediction of Main Bearing in Direct Drive Wind Turbines, WIND ENGINEERING, http://dx.doi.org/10.1260/0309-524X.39.4.349, 39, 4, 349-368, 2015.07, In Japan, 1,516 wind turbine accidents have been recorded between year 2004 and 2012, and 84% of them were for turbines in complex terrains. The longest downtime was associated with damage to main shafts or bearings with an average downtime of 5.7 months. Careful micro-siting in complex terrains can prevent these accidents from happening.

The objective of the paper is to provide an intermediate step that allows consultants, developers, and wind farm owners to further evaluate micro-siting of wind turbines in complex terrains, prior to load simulations by manufacturers. The author developed a simplified method to predict fatigue life of a main rear bearing in direct drive wind turbines. The method uses hub-height 10 minutes wind data as an input. The validation with an actual accident showed practically good agreement of 12.0 years of the predicted life against 12.7 years of the actual life. The method was also applied to quantify the effect of a curtailment. The proposed curtailment increased the predicted life to 35.5 years with a relatively small range of wind speed at a direction of only 1 % frequency distribution.

With the proposed method, it is possible to layout turbines where fatigue life of a main rear bearing is longer than its design life. The method can also be applied to existing turbines in order to spot turbines that require careful maintenance, and to consider an installation of condition monitoring system on a bearing..
41. 内田 孝紀, 太鼓山風力発電所のナセル落下事故に対する数値流体力学的アプローチによる一考察, 日本風力エネルギー学会論文集, 39, 1, 6-13, 2015.05, [URL], Because a significant portion of the topography in Japan is characterized by steep, complex terrain, which results in a complex spatial distribution of wind speed, great care is necessary for selecting a site for the construction of Wind Turbine Generators (WTGs). We have developed a Computational Fluid Dynamics (CFD) model for unsteady flow called Research Institute for Applied Mechanics, Kyushu University, COMputational Prediction of Airflow over Complex Terrain (RIAM-COMPACT®). The RIAM-COMPACT® CFD model is based on Large-Eddy Simulation (LES) technique. In this paper, the numerical wind simulation over the Taikoyama wind farm was executed using the high resolution elevation data. As a result, the numerical results obtained suggest that all the six WTGs in the Taikoyama wind farm are subject to significant influence from separated flow (terrain-induced turbulence) which is due to the topographical irregularity in front of WTGs. The new reproduction proposal was also done..
42. Kenji Kitagawa, Shintaro Iwama, Sho Fukui, Yuuki Sunaoka, Hayato Yazawa, Atsushi Usami, Masaaki Naramoto, Takanori Uchida, Satoshi Saito, Hiromi Mizunaga, Effects of Components of the Leaf Area Distribution on Drag Relations for Cryptomeria Japonica and Chamaecyparis Obtusa, European Journal of Forest Research, https://doi.org/10.1007/s10342-014-0859-6, 134, 3, 403-414, 2015.05, The objectives of this study were to clarify the effects of components of the leaf area distribution on the drag coefficient of crowns and streamlining (e.g., leaf area index; LAI, outline of the crown shape, and clumpiness) and to contribute to the accumulation of data on drag relations by quantifying data for Chamaecyparis obtusa and Cryptomeria japonica. We conducted drag experiments while simultaneously capturing dynamic crown images for 28 Ch. obtusa crowns and 13 Cr. japonica crowns to analyze the relationships between the leaf area distribution components and drag coefficient or streamlining. The static drag coefficient increased with the LAI for Ch. obtusa and with decreasing clumpiness for Cr. japonica. The reduction rate of the static drag coefficient decreased with increasing clumpiness for Ch. obtusa and with a combination of increasing LAI and decreasing clumpiness for Cr. japonica. The reduction rate of the static drag coefficient had a clear relationship with the decreasing rate of the dynamic crown projected area of obstacles (foliage elements, branches, and stems) calculated from captured video images under windy conditions for Cr. japonica, while Ch. obtusa did not show clear relationship between them. The drag coefficients assuming non-porous crown; Cmax estimated by simple model combining LAI and clumpiness were approximately 1.0 in Ch. obtusa and 0.5 in Cr. japonica and were equivalent to the dynamic drag coefficients from video image under windy condition. The combination of LAI and clumpiness provided simple estimation for drag relations and enable to link crown structure to wind damage easier..
43. 川島泰史, 内田孝紀, 風車の運転方法の検討を目的としたリアムコンパクトによる数値風況診断-串木野れいめい風力発電所を例として-, 九州大学応用力学研究所所報, 148.0, 59.0-65.0, 2015.03, [URL], Recently to become, in wind farm, which was built on the complex terrain, the operation rate is less than the initial expectations, ie, power generation output and significantly bad windmill, failure of windmill inside and outside (for example, failure of the yaw motor and Yogia, windmill blades cracks, etc.) of the problem of is actualized. The main cause is a change in the windmill most recent slight terrain relief becomes origin, I considered to be a disorder of the wind (terrain turbulence) generated from there. In response to this situation, in our group, precise numerical wind diagnosis by real terrain version RIAM-COMPACT® software (the window risk assessment) was performed, has conducted studies safe windmill operating method 1) . In this paper, under the cooperation of Kyudenko new energy Co., Ltd., Numerical wind conditions diagnosis for the purpose of examination of windmill 10 Unit method of operation of the kushikinoreimei wind farm (start the operation from November 2012) since the was carried out, we report on the results..
44. 内田孝紀, 渡邊文人, 見上 伸, 市販CFDソフトウエアによる急峻な3次元孤立峰を対象とした気流場解析, 九州大学応用力学研究所所報, 148.0, 35.0-41.0, 2015.03, [URL], The present study compared the prediction accuracy of two CFD software packages for simulating a flow around a three-dimensional, isolated hill with a steep slope: 1) Meteodyn WT (turbulence model: k-L RANS), which is one of the leading commercially available CFD software packages in the wind power industry and 2) RIAM-COMPACT® (turbulence model: the standard Smagorinsky LES), which has been developed by the lead author of the present paper. Although the Reynolds number settings differed between the simulation with Meteodyn WT and that with RIAM-COMPACT®, distinct differences in the flow patterns were identified in the vicinity of the isolated hill (especially downstream of the isolated hill) between the flows simulated by the two CFD software packages..
45. 内田孝紀, 福岡市内における陸上と洋上の風況特性, 九州大学応用力学研究所所報, 148.0, 51.0-58.0, 2015.03, [URL], In this report, we explain the outline of the weather GPV data such as MSM. Next, the onshore and offshore wind characteristics in Fukuoka-shi are reported through comparison between the actual measurement data (observed value) and the weather GPV data..
46. 内田孝紀, 福岡市内における冬季の風況特性, 九州大学応用力学研究所所報, 148.0, 43.0-49.0, 2015.03, [URL], In this report, we explain the outline of the weather GPV data such as MSM. Next, the flow characteristics of winter in Fukuoka-shi are reported through comparison between the actual measurement data (observed value) and the weather GPV data..
47. Takanori Uchida, An Examination of the Taikoyama Wind Farm Nacelle Separation Accident Using a CFD Approach, Reports of Research Institute for Applied Mechanics, Kyushu University, 148.0, 15.0-24.0, 2015.03, [URL], Because a significant portion of the topography of Japan is characterized by steep, complex terrain, which results in a complex spatial distribution of wind speed, great care is necessary for selecting a site for the construction of wind turbines. We have developed a computational fluid dynamics (CFD) model for unsteady flow called Research Institute for Applied Mechanics, Kyushu University, COMputational Prediction of Airflow over Complex Terrain (RIAM-COMPACT®). The RIAM-COMPACT® CFD model is based on the large-eddy simulation (LES) technique. In this paper, a numerical wind simulation for the Taikoyama Wind Farm is performed using high-resolution terrain elevation data. The results suggest that all six wind turbines at the Taikoyama Wind Farm are subject to significant influence from separated flow (terrain-induced turbulence) which is generated due to the topographical irregularities in the vicinity of the wind turbines. A proposal has been also made on reconstruction of the wind farm..
48. Shinsuke Okada, Takanori Uchida, Takashi Karasudani, Yuji Ohya, Improvement in solar chimney power generation by using a diffuser tower, Journal of Solar Energy Engineering, Transactions of the ASME, 10.1115/1.4029377, 137, 3, 2015.01, [URL], The solar chimney prototype, operated in Spain from 1982 to 1989, verified the concept of the solar chimney. The power generation mechanism in this system is to turn the wind turbine placed inside a high rise cylindrical hollow tower by an induced thermal updraft. As long as the thermal updraft is induced inside the tower by the solar radiation, this system can produce electricity. The disadvantage of this system is the low power generation efficiency compared to other solar energy power generation systems. To overcome this disadvantage, we improved the mechanism in order to augment the velocity of the air which flows into the wind turbine. By applying a diffuser tower instead of a cylindrical one, the efficiency of the systems power generation is increased. The mechanism that we investigated was the effect of the diffuser on the solar chimney structure. The inner diameter of the tower expands as the height increases so that the static pressure recovery effect of the diffuser causes a low static pressure region to form at the bottom of the tower. This effect induces greater airflow within the tower. The laboratory experiment, as does the computational fluid dynamics (CFD) analysis of the laboratory sized model, shows that the proposed diffuser type tower induces a velocity approximately 1.38-1.44 times greater than the conventional cylindrical type. The wind power generation output is proportional to the cube of the incoming wind velocity into the wind turbine; therefore, approximately 2.6-3.0 times greater power output can be expected from using the diffuser type tower..
49. Fumihito Watanabe, Takanori Uchida, Micro-siting of wind turbine in complex terrain Simplified fatigue life prediction of main bearing in direct drive wind turbines, Wind Engineering, 10.1260/0309-524X.39.4.349, 39, 4, 349-368, 2015.01, [URL], In Japan, 1,516 wind turbine accidents have been recorded between year 2004 and 2012, and 84% of them were for turbines in complex terrains. The longest downtime was associated with damage to main shafts or bearings with an average downtime of 5.7 months. Careful micro-siting in complex terrains can prevent these accidents from happening. The objective of the paper is to provide an intermediate step that allows consultants, developers, and wind farm owners to further evaluate micro-siting of wind turbines in complex terrains, prior to load simulations by manufacturers. The author developed a simplified method to predict fatigue life of a main rear bearing in direct drive wind turbines. The method uses hub-height 10 minutes wind data as an input. The validation with an actual accident showed practically good agreement of 12.0 years of the predicted life against 12.7 years of the actual life. The method was also applied to quantify the effect of a curtailment. The proposed curtailment increased the predicted life to 35.5 years with a relatively small range of wind speed at a direction of only I % frequency distribution. With the proposed method, it is possible to layout turbines where fatigue life of a main rear bearing is longer than its design life. The method can also be applied to existing turbines in order to spot turbines that require careful maintenance, and to consider an installation of condition monitoring system on a bearing..
50. Takanori Uchida, Validation Testing of the Prediction Accuracy of the Numerical Wind Synopsis Prediction Technique RIAM-COMPACT for the Case of the Bolund Experiment-Comparison against a Wind-Tunnel Experiment-, Reports of Research Institute for Applied Mechanics, Kyushu University, 147, 7-14, 2014.09.
51. 内田 孝紀, 川島 泰史, 沿岸部における気象GPVデータを用いた簡易風況推定法の試み-鹿児島県内の風力発電所を例として-, 九州大学応用力学研究所所報, 第147号, pp.15-29, 2014.09.
52. 内田 孝紀, 川島 泰史, 山間部における気象GPVデータを用いた簡易風況推定法の試み-阿蘇車帰風力発電所を例として-, 九州大学応用力学研究所所報, 第147号, pp.31-43, 2014.09.
53. 内田 孝紀, 京都府太鼓山風力発電所で起きたナセル落下事故に対する数値風況面からの一考察, 九州大学応用力学研究所所報, 第147号, pp.45-50, 2014.09.
54. 内田 孝紀, 市販CFDソフトウェアによる複雑乱流場の再現性-第2報 急峻な傾斜角度を有する2次元峰地形を対象として-
, 九州大学応用力学研究所所報, 第146号, pp.147-155, 2014.03.
55. 内田 孝紀, 市販CFDソフトウェアによる複雑乱流場の再現性-第3報 3次元立方体を対象として-, 九州大学応用力学研究所所報, 第146号, pp.157-167, 2014.03.
56. Yuji Ohya, Takanori Uchida, Tomoyuki Nagai, Near Wake of a Horizontal Circular Cylinder in Stably Stratified Flows, Open Journal of Fluid Dynamics, Vol.3, 311-320, 2013.12.
57. Kana Kamimura, Satoshi Saito, Hiroko Kinoshita, Kenji Kitagawa, Takanori Uchida, Hiromi Mizunaga, Analysis of wind damage caused by multiple tropical storm events in Japanese Cryptomeria japonica forests, Forestry, 10.1093/forestry/cpt011, 86, 4, 411-420, 2013.10, [URL], This study analyzed wind damage caused by tropical storms from 1991 to 2007 to Japanese forests mainly consisting of Cryptomeria japonica. Statistical analyses based on logistic regression and Cox regression models were conducted in relation to conditions at the forest and stand level. Known damage to forests managed by Kyusyu Rinsan Corporation (KR forests), located on the Kyushu Island, was analyzed at the forest level, using tropical storm characteristics such as air pressure, precipitation and periods when the forests were within the storm zone as predictors. Wind damage was also examined at the stand level (150 analysis points) using Cox regression models, according to stand age, site index, terrain conditions, management practices and wind velocity indicators (horizontal and vertical velocity vectors). The results indicated that at the forest level, higher maximum hourly wind speed and longer periods of >15 m s-1 of wind speed were significantly correlated to damage occurrence. At the stand level, indicators of upward vertical velocity, thinning treatments and site index were positively associated with the probability of wind damage. For instance, stands receiving higher upward vertical velocities and thinning treatment within 2 years were more likely to have reduced stability against tropical storms. Stands with higher and lower site index than average also showed lower stability in our analysis..
58. 内田 孝紀, Graham Li, 市販CFDソフトウェアによる複雑乱流場の再現性-急峻な傾斜角度を有する3次元孤立地形を対象として-, 九州大学応用力学研究所所報, 第145号, pp.107-119, 2013.09.
59. 齊藤 俊哉, 内田 孝紀, 荒屋 亮, ロケット発射時における地上風の数値風況予測の試行, 九州大学応用力学研究所所報, 第145号, pp.121-126, 2013.09.
60. Kana Kamimura, Satoshi Saito, Hiroko Kinoshita, Kenji Kitagawa, 内田 孝紀, Hiromi Mizunaga, Analysis of wind damage caused by multiple tropical storm events in Japanese Cryptomeria japonica forests, Forestry, 10.1093/forestry/cpt011, 0, pp.1-10, 2013.04.
61. 内田 孝紀, 川島 泰史, 荒屋 亮, 気象GPVデータの風力発電分野への活用に関する検討, 九州大学応用力学研究所所報, 第144号, pp.33-40, 2013.03.
62. 内田 孝紀, 辰己 賢一, 川島 泰史, 荒屋 亮, メソ気象モデルWRF-ARWを用いた複雑地形上の数値風況予測, 九州大学応用力学研究所所報, 第144号, pp.41-47, 2013.03.
63. 内田 孝紀,高橋 幸平,大屋 裕二, レンズ風車の相互干渉に関する数値的研究, 風工学シンポジウム論文集, pp.401-406, 2012.12.
64. 高橋 周平,上野 祥彦,大屋 裕二,烏谷 隆,内田 孝紀, 鍔付きディフューザ風車の性能に対する支持構造の後流の影響, 風工学シンポジウム論文集, pp.407-412, 2012.12.
65. Yuji Ohya, Takanori Uchida, Takashi Karasudani, Masaru Hasegawa, Hiroshi Kume, Numerical studies of flow around a wind turbine equipped with a flanged-diffuser shroud using an actuator-disk model, Wind Engineering, 10.1260/0309-524X.36.4.455, 36, 4, 455-472, 2012.08, [URL], Unsteady 3-D direct numerical simulations based on the finite-difference method (FDM) were performed for flow fields around a wind turbine equipped with a flanged-diffuser shroud. Generally, it is difficult to numerically simulate the flow around rotating bodies such as the blades of wind turbines because of the unsteady flow generated by moving bodies with complex geometry. Therefore, we have devised an actuator-disk model for a wind turbine for simulating the drag and rotational forces exerted on the fluid by the wind turbine. By incorporating the body forces derived from the actuator-disk model into the external terms in the Navier-Stokes equations, the unsteady flow around a wind turbine can be simulated. The results of numerical simulations were compared with the results from wind tunnel experiments and showed good agreement for the velocity and pressure fields..
66. 内田 孝紀,荒屋 亮, 福岡市街地を対象とした大規模数値風況予測, 九州大学応用力学研究所所報, 第142号, pp.55-62, 2012.03.
67. 内田 孝紀,荒屋 亮, 実在市街地における浮力効果を考慮したガス拡散の大規模数値予測, 九州大学応用力学研究所所報, 第142号, pp.63-70, 2012.03.
68. 岡林 一木,永山 圭憲,原 智宏,堀 英一,大屋 裕二,内田 孝紀, 複雑地形へ適用可能な非定常乱流拡散数値シミュレーション技術の開発
-風洞実験代替に向けて-, 三菱重工技報, Vol.49 No.1, pp.75-81, 2012.01.
69. Shuhei Takahashi, Yuya Hata, Yuji Ohya, Takashi Karasudani, Takanori Uchida, Behavior of the blade tip vortices of a wind turbine equipped with a brimmed-diffuser shroud, Energies, 10.3390/en5125229, 5, 12, 5229-5242, 2012.01, [URL], To clarify the behavior of the blade tip vortices of a wind turbine equipped with a brimmed-diffuser shroud, called a "Wind-Lens turbine", we conducted a three-dimensional numerical simulation using a large eddy simulation (LES). Since this unique wind turbine consists of not only rotating blades but also a diffuser shroud with a broad-ring brim at the exit periphery, the flow field around the turbine is highly complex and unsteady. Previously, our research group conducted numerical simulations using an actuator-disc approximation, in which the rotating blades were simply modeled as an externalforce on the fluid. Therefore, the detailed flow patterns around the rotating blades and the shroud, including the blade tip vortices, could not be simulated. Instead of an actuator-disc approximation, we used a moving boundary technique in the present CFD simulation to simulate the flow around a rotating blade in order to focus especially on blade tip vortices. The simulation results showed a pair ofvortices consisting of a blade tip vortex and a counter-rotating vortex which was generated between the blade tip and the inner surface of the diffuser. Since these vortices interacted with each other, the blade tip vortex was weakened by the counter-rotating vortex. The results showed good agreement with past wind tunnel experiments..
70. 内田 孝紀,丸山 敬,大屋 裕二, 流体工学CFDモデルを用いた連続的な風向変化の再現性について, 日本風力エネルギー学会論文集, Vol.35,通巻99, pp.7-13, 2011.11.
71. Takanori UCHIDA, Takashi MARUYAMA, Tetsuya TAKEMI, Yuichiro OKU, Yuji OHYA and Graham Li , Proposal of Designed Wind Speed Evaluation Technique in WTG Installation Point by Using the Meteorological Model and CFD Model
, 九州大学応用力学研究所所報, 第141号, pp.1-12, 2011.10.
72. Takanori UCHIDA, Takashi MARUYAMA, Hirohiko ISHIKAWA, Masaru ZAKO and Akira DEGUCHI , Investigation of the Causes of Wind Turbine Blade Damage at Shiratakiyama Wind Farm in Japan-A Computer Simulation Based Approach-, 九州大学応用力学研究所所報, 第141号, pp.13-25, 2011.10.
73. 内田孝紀,大屋裕二, LES技術を用いたウインドファーム風況診断―熊本県阿蘇車帰風力発電所を例として―, 土木学会論文集A2(応用力学)Vol.67 特集号, 2011.09.
74. Takanori Uchida, Takashi Maruyama, Yuji Ohya, New evaluation technique for WTG design wind speed using a CFD-model-based unsteady flow simulation with wind direction changes, Modelling and Simulation in Engineering, 10.1155/2011/941870, 2011, 2011.09, [URL], Because a significant portion of the topography in Japan is characterized by steep, complex terrain, which results in a complex spatial distribution of wind speed, great care is necessary for selecting a site for the construction of wind turbine generators (WTG). We have developed a CFD model for unsteady flow called RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, computational prediction of airflow over complex terrain). The RIAM-COMPACT CFD model is based on large eddy simulation (LES). The computational domain of RIAM-COMPACT can extend from several meters to several kilometers, and RIAM-COMPACT can predict airflow and gas diffusion over complex terrain with high accuracy. The present paper proposes a technique for evaluating the deployment location of a WTG. The proposed technique employs the RIAM-COMPACT CFD model and simulates a continuous wind direction change over 360 degrees..
75. Takanori Uchida, Yuji Ohya, Kenichiro Sugitani, Comparisons between the wake of a wind turbine generator operated at optimal tip speed ratio and the wake of a stationary disk, Modelling and Simulation in Engineering, 10.1155/2011/749421, 2011, 2011.06, [URL], The wake of a wind turbine generator (WTG) operated at the optimal tip speed ratio is compared to the wake of a WTG with its rotor replaced by a stationary disk. Numerical simulations are conducted with a large eddy simulation (LES) model using a nonuniform staggered Cartesian grid. The results from the numerical simulations are compared to those from wind-tunnel experiments. The characteristics of the wake of the stationary disk are significantly different from those of the WTG. The velocity deficit at a downstream distance of 10 D (D: rotor diameter) behind the WTG is approximately 30 to 40 of the inflow velocity. In contrast, flow separation is observed immediately behind the stationary disk (≤2D), and the velocity deficit in the far wake (10 D) of the stationary disk is smaller than that of the WTG..
76. Takanori Uchida, Takashi Maruyama and Yuji Ohya, New Evaluation Technique for WTG Design Wind Speed using a CFD-model-based Unsteady Flow Simulation with Wind Direction Changes, Modelling and Simulation in Engineering, Volume 2011 (2011), 2011.03.
77. Takanori Uchida, Yuji Ohya and Kenichiro Sugitani, Comparisons Between The Wake Of A Wind Turbine Generator Operated At Optimal Tip Speed Ratio And The Wake Of A Stationary Disk, Modelling and Simulation in Engineering, Volume 2011 (2011), 2011.03.
78. Takanori Uchida and Yuji Ohya, Latest Developments in Numerical Wind Synopsis Prediction Using the RIAM-COMPACT® CFD Model—Design Wind Speed Evaluation and Wind Risk (Terrain-Induced Turbulence) Diagnostics in Japan, Energies, 4(3), pp.458-474, 2011.03.
79. 内田 孝紀,丸山 敬,大屋 裕二, 連続的な風向変化を考慮した非定常数値風況予測による
風車設置地点における設計風速評価手法の提案, 風力エネルギー協会誌, Vol.34,通巻96, pp.129-134, 2011.02.
80. Takanori Uchida, Yuji Ohya, Latest developments in numerical wind synopsis prediction using the RIAM-COMPACT® CFD model-design wind speed evaluation and wind risk (terrain-induced turbulence) diagnostics in Japan, Energies, 10.3390/en4030458, 4, 3, 458-474, 2011.01, [URL], Because a significant portion of the topography in Japan is characterized by steep, complex terrain, which results in a complex spatial distribution of wind speed, great care is necessary for selecting a site for the construction of Wind Turbine Generators (WTGs). We have developed a CFD model for unsteady flow called Research Institute for Applied Mechanics, Kyushu University, COMputational Prediction of Airflow over Complex Terrain (RIAM-COMPACT®). The RIAM-COMPACT® CFD model is based on Large-Eddy Simulation (LES) technique. The computational domain of RIAM-COMPACT® can extend from several meters to several kilometers, and RIAM-COMPACT® can predict airflow and gas diffusion over complex terrains with high accuracy. First, the present paper proposes a technique for evaluating the deployment location of WTGs. Next, wind simulation of an actual wind farm was executed using the high resolution elevation data. As a result, an appropriate point and an inappropriate point for locating WTGs were shown based on the numerical results obtained. This cause was found to be a topographical irregularity in front of WTGs..
81. 内田孝紀,水永博己,齊藤哲,上村佳奈,木下裕子,丸山敬, 森林・林業分野における風害シミュレーション-数値風況予測技術(CFD)によるアプローチ-, 森林立地学会誌,森林立地, 52(2),pp.67-77, 2010.12.
82. 秦祐也,上野祥彦,大屋裕二,烏谷隆,内田孝紀, 鍔つきディフューザ風車まわりの流れ場の渦構造に関する数値的研究, 第21回風工学シンポジウム論文集, pp.227-232, 2010.12.
83. 内田孝紀,大屋裕二, 最適周速比における風車後流のラージ・エディ・シミュレーション
-第2報 格子乱流により生成した流入変動風の影響-, 第21回風工学シンポジウム論文集, pp.233-238, 2010.12.
84. 秦祐也,永井修平,大屋裕二,辻美奈子,内田孝紀,烏谷隆, ポーラス状の外側部をもつ円柱まわりの流れの数値シミュレーション, 第21回風工学シンポジウム論文集, pp.257-262, 2010.12.
85. 丸山敬,石川裕彦,内田孝紀,出口啓, メソスケールモデルとLESを用いたウインドファーム周辺の気流解析, 第21回風工学シンポジウム論文集, pp.209-214, 2010.12.
86. 川島 泰史,内田 孝紀,荒屋 亮,藤本 弘明, 海外サイトにおける標高データ生成と
流体工学モデルRIAM-COMPACT®を用いた風力発電のマイクロサイティング, 風力エネルギー協会誌, Vol.34,通巻.95, pp.97-101, 2010.12.
87. 内田孝紀,大屋裕二, Three-Dimensional Numerical Simulation of Stably Stratified Flows Over a Two-Dimensional Hill
-Effect of Stratification on the Non-Periodic Separation and Reattachment of the Flow-, 九州大学応用力学研究所所報, 第139号, pp.57-68, 2010.09.
88. 内田孝紀,烏谷隆,大屋裕二, 九州大学伊都キャンパスにおける流体工学モデルRIAM-COMPACT®を用いた100kW級風レンズ風車のマイクロサイティング
-第2報 土地造成を考慮した場合-, 九州大学応用力学研究所所報, 第139号, pp.131-139, 2010.09.
89. Takanori UCHIDA, Yuji OHYA, Challenge to Huge Computation of Airflow around Urban Area by using RIAM-COMPACT® CFD Model, Proceedings of EAEP2010/The 4th International Symposium on the Asian Environmental Problems, pp.191-194, 2010.09.
90. Hirotaka HANO, Takanori UCHIDA, Yuji OHYA, Wake Structure Behind Wind Turbine Generator in Turbulent Boundary Layer, Proceedings of EAEP2010/The 4th International Symposium on the Asian Environmental Problems, pp.195-200, 2010.09.
91. 内田 孝紀,丸山 敬,竹見 哲也,奥 勇一郎,大屋 裕二,李 貫行, 気象モデルと流体工学モデルを用いた
風車設置地点における設計風速評価手法の提案, 風力エネルギー協会誌, 第34巻, 第2号, pp.118-124, Vol.34,通巻94, pp.118-124, 2010.08, 本研究では,最新の研究成果を取り入れ,より現実に近い強風性状を取り込み,かつ,安全性を確保したものとして風車設置地点における耐風設計用の基準風速を求める一手法を提案したものである..
92. Takanori Uchida and Yuji Ohya, Large-Eddy Simulation of Topography-Induced Turbulence around WTG by using the RIAM-COMPACT® CFD Model, Proceedings of RENEWABLE ENERGY 2010 (RE2010), 2010.06.
93. 内田 孝紀,大屋 裕二,李 貫行, 風車立地点近傍に発生する地形乱流の高解像度LES, 風力エネルギー協会誌, Vol.34,通巻.93, pp.121-126, 2010.05.
94. Yuji Ohya, Takanori Uchida, Near Wake of a Horizontal Circular Cylinder in Stably Stratified Flows, 九州大学応用力学研究所所報, 第138号, pp.13-22, 2010.03.
95. 内田孝紀,烏谷隆,大屋裕二, 九州大学伊都キャンパスにおける流体工学モデルRIAM-COMPACT®を用いた100kW級風レンズ風車のマイクロサイティング, 九州大学応用力学研究所所報, 第138号, pp.41-54, 2010.03.
96. Takanori Uchida and Yuji Ohya, HIGH RESOLUTION LES OF TURBULENT AIRFLOW OVER COMPLEX TERRAIN, Proceedings of Seventh Asia-Pacific Conference on Wind Engineering (APCWE-VII), pp.405-408, 2009.11.
97. Tomohiro Hara, Yuji Ohya, Takanori Uchida, Ryohji Ohba, Wind-Tunnel and Numerical Simulations of the Coastal Thermal Internal Boundary Layer, Boundary-Layer Meteorology, Vol.130, pp.365-381, 2009.02.
98. Tomohiro Hara, Yuji Ohya, Takanori Uchida, Ryohji Ohba, Wind-tunnel and numerical simulations of the coastal thermal internal boundary layer, Boundary-Layer Meteorology, 10.1007/s10546-008-9343-5, 130, 3, 365-381, 2009.02, [URL], Wind-tunnel experiments in a thermally stratified wind tunnel and direct numerical simulations were performed to simulate the thermal internal boundary layer (TIBL) that developed over a coastal area in a sea-breeze flow. The results of the simulations were analyzed to investigate turbulence structure in the TIBL. To study the effects of the atmospheric stability over the sea on the TIBL, two vertical profiles of temperature were created in the upstream portion of the wind-tunnel experiment and the direct numerical simulation. Turbulence statistics of the TIBL changed significantly according to the temperature profile over the sea, indicating that the stability of the flow over the sea has a significant effect on the structure and turbulence characteristics of the TIBL. Furthermore, the TIBL heights were estimated from the vertical profiles of the local Richardson number. The estimated TIBL heights agreed with those predicted by a pre-existing relation, suggesting that both the wind-tunnel experiment and the direct numerical simulation accurately reproduced the growth of the TIBL..
99. 内田 孝紀,丸山 敬,竹見 哲也,大屋 裕二,道下 和明, 複雑地形上の風車ハブ高さ風速に与える流入気流性状と標高データの影響, 第20回風工学シンポジウム論文集, pp.139-144, 2008.12.
100. 内田孝紀,大屋裕二, 非定常・非線形風況シミュレータRIAM-COMPACTによる野間ウィンドパークを対象とした年間発電電力量の推定精度検証, 風力エネルギー協会誌, Vol.32,No.3, pp.122-131, 2008.11.
101. Takanori Uchida, Yuji Ohya, The wind risk management in the wind farm by using the RIAM-COMPACT CFD code, Proceedings of China Wind Power 2008 & Global Wind Power 2008, 2008.10.
102. Yuji Ohya, Takanori Uchida, Laboratory and numerical studies of the atmospheric stable boundary layers, Journal of Industrial Aerodynamics, 10.1016/j.jweia.2008.02.037, 96, 10-11, 2150-2160, 2008.10, [URL], We have investigated the turbulence phenomena of SBLs for a wide range of stability, particularly focusing on the effects of strong stratification on turbulent boundary layers, using a thermally stratified wind tunnel. In parallel with wind tunnel experiments, to understand the turbulence features and fluid dynamics in detail, we have also performed numerical simulations of SBLs under the boundary conditions similar to those in the wind tunnel experiments. The numerical studies based on a finite-difference method (FDM) are direct Navier-Stokes simulations without any turbulence model (DNS). Under the Boussinesq approximation, the governing equations consist of the Navier-Stokes, continuity and energy equations for 3D incompressible stratified flows. Stable stratification rapidly suppresses the fluctuations of streamwise velocity and temperature as well as the vertical velocity fluctuation. Momentum and heat fluxes are also significantly decreased with increasing stability and become nearly zero over the whole boundary depth of the boundary layer with very strong stability. From the flow visualization in both wind tunnel experiment and DNS, wave-like motions driven by buoyancy and waves due to the Kelvin-Helmholtz instability can be observed locally and intermittently in a SBL flow with strong stability..
103. Takanori Uchida, Yuji Ohya, Micro-siting technique for wind turbine generators by using large-eddy simulation, Journal of Industrial Aerodynamics, 10.1016/j.jweia.2008.02.047, 96, 10-11, 2121-2138, 2008.10, [URL], It is highly important in Japan to choose a good site for wind turbines, because the spatial distribution of wind speed is quite complicated over steep complex terrain. We are developing the unsteady numerical model called the Research Institute for Applied Mechanics, Kyushu University, COMputational Prediction of Airflow over Complex Terrain (RIAM-COMPACT). The RIAM-COMPACT is based on the large-eddy simulation (LES). The object domain of the RIAM-COMPACT is from several m to several km. First, to test the accuracy of the RIAM-COMPACT we have performed an experimental and a numerical simulation of a non-stratified airflow past a two-dimensional ridge and a three-dimensional hill in a uniform flow. Attention is focused on airflow characteristics in a wake region. For this purpose, the velocity components were measured with a split-film probe (SFP) in the wind tunnel experiment. Through comparison of the experimental and numerical results, they showed a good agreement. The accuracy of both of the wind tunnel experiment by the SFP and also numerical simulation by the RIAM-COMPACT were confirmed. Next, we have applied the RIAM-COMPACT to the airflow over real complex terrain. The numerical results obtained by the RIAM-COMPACT demonstrated that the changes induced on the wind field by the topographic effect, such as the local wind acceleration and the flow separation, were successfully simulated. Furthermore, the forecast accuracy of an actual wind speed is examined..
104. 内田孝紀,杉谷賢一郎,大屋裕二, 縮尺模型を用いた風洞実験における幾つかの知見, 応用力学論文集, Vol.11,pp.789-798, 2008.08.
105. Takanori Uchida, Yuji Ohya, Numerical Simulation of Airflow around Urban Area by using the RIAM-COMPACT CFD Model, Proceedings of Sino-Japan International Symposium on The East Asian Environmental Problems (EAEP2008), pp.51-53, 2008.08.
106. Yuji Ohya, Takanori Uchida, Laboratory and numerical studies of the atmospheric stable boundary layers, Journal of Wind Engineering & Industrial Aerodynamics, Vol.96, pp.2150-2160, 2008.07.
107. Takanori Uchida and Yuji Ohya, Micro-siting Technique for Wind Turbine Generators by Using Large-Eddy Simulation, Journal of Wind Engineering & Industrial Aerodynamics, Vol.96, pp.2121-2138, 2008.07, 風力業界で未解決課題であった風車に対する風の乱れ(ウィンドリスク)に対して,NEDO技術開発機構の産業技術研究助成事業(若手研究グラント)に採択され,研究代表者として3年間の研究開発を実施した.本研究を通じ,先端的数値風況予測モデル「RIAM-COMPACT®(リアムコンパクト)」を駆使し,世界で初めてウィンドリスクの存在を視覚的に特定することに成功し,その力学的機構を解明した.一連の成果に対し,2010年科学技術分野の文部科学大臣表彰・若手科学者賞を受賞した..
108. T.Uchida and Y.Ohya, Verification of the Prediction Accuracy of Annual Energy Output at Noma Wind Park by the Non-Stationary and Non-Linear Wind Synopsis Simulator, RIAM-COMPACT, Journal of Fluid Science and Technology, Vol.3, No.3, pp.344-358, 2008.06.
109. Yuji Ohya, Reina Nakamura, Takanori Uchida, Intermittent bursting of turbulence in a stable boundary layer with low-level jet, Boundary-Layer Meteorology, 10.1007/s10546-007-9245-y, 126, 3, 349-363, 2008.03, [URL], The atmospheric stable boundary layer (SBL) with a low-level jet is simulated experimentally using a thermally stratified wind tunnel. The turbulence structure and flow characteristics are investigated by simultaneous measurements of velocity and temperature fluctuations and by flow visualization. Attention is focused on the effect of strong wind shear due to a low-level jet on stratified boundary layers with strong stability. Occasional bursting of turbulence in the lower portion of the boundary layer can be found in the SBL with strong stability. This bursting originates aloft away from the surface and transports fluid with relatively low velocity and temperature upward and fluid with relatively high velocity and temperature downward. Furthermore, the relationship between the occurrence of turbulence bursting and the local gradient Richardson number (Ri) is investigated. The Ri becomes larger than the critical Ri, Ricr = 0.25, in quiescent periods. On the other hand, the Ri number becomes smaller than Ricr during bursting events..
110. Yuji Ohya, Reina Nakamura, Takanori Uchida, Intermittent Bursting of Turbulence in a Stable Boundary Layer with Low-Level Jet,Boundary-Layer Meteorology, Boundary-Layer Meteorology, vol.26, No.3, pp.349-363, 2008.01.
111. Takanori Uchida, High Resolution LES of Airflow over Complex Terrain, Proceedings of APCOM'07-EPMESC XI, 2007.12.
112. 内田孝紀,大屋裕二, CFDを用いた複雑地形上の実風速推定法の提案, 応用力学論文集, Vol.10,pp.733-740, 2007.08.
113. 内田孝紀,杉谷賢一郎,大屋裕二, 九州大学伊都キャンパスにおける風観測
—第二報 乱流強度分布と発電電力量の試算について—, 九州大学応用力学研究所所報, 第131号,pp.13-24, 2006.12.
114. Takanori Uchida, Yuji Ohya, Application of LES technique to diagnosis of wind farm by using high resolution elevation data, JSME International Journal, Series B: Fluids and Thermal Engineering, 10.1299/jsmeb.49.567, 49, 3, 567-575, 2006.12, [URL], We are developing the numerical model called the RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, Computational Prediction of Airflow over Complex Terrain). The object domain of this numerical model is from several m to several km, and can predict the airflow and the gas diffusion over complex terrain with high precision. The RIAM-COMPACT has already been marketed by certain tie-up companies. The estimation of the annual electrical power output is also possible now based on the field observation data. In the present study, wind simulation of an actual wind farm was executed using the high resolution elevation data. As a result, an appropriate point and an inappropriate point for locating a wind turbine generator were shown based on the numerical results obtained. This cause was found to be a topographical irregularity in front of the wind turbine generator..
115. 友清衣利子,内田孝紀,前田潤滋, 台風0423号通過時における佐賀県小城市周辺風況のCFD解析—風況に及ぼす大気安定度の影響—, 第19回風工学シンポジウム論文集, pp.205-210, 2006.11.
116. 岡田臣右,大屋裕二,内田孝紀,烏谷隆,杉谷賢一郎, 垂直型集風構造体の集風性能評価, 第19回風工学シンポジウム論文集, pp.145-150, 2006.11.
117. 内田孝紀,大屋裕二,杉谷賢一郎, 最適周速比における風車後流と静止円盤後流の比較, 第19回風工学シンポジウム論文集, pp.187-192, 2006.11.
118. Takanori Uchida, Yuji Ohya, Diagnosis of Airflow Characteristics in Wind Farm by Using the Unsteady Numerical Model RIAM-COMPACT, Proceedings of Renewable Energy 2006, 2006.10.
119. 内田孝紀,大屋裕二,諏訪部哲也,李貫行, 非定常・非線形風況シミュレータRIAM-COMPACTによるウィンドファーム風況診断の提案, 日本風力エネルギー協会誌, Vol.30,No.2,通巻78,pp.101-108, 2006.09.
120. T.Uchida and Y.Ohya, Application of LES Technique to Diagnosis of Wind Farm by Using High Resolution Elevation Data, JSME International Journal, 「Environmental Flows」, Series B, Vol.49, No.3, pp.567-575, 2006.09.
121. 内田孝紀,大屋裕二,友清衣利子,前田潤滋, 地形性強風の数値予測と格子解像度の影響, 応用力学論文集, Vol.9,pp.795-802, 2006.08.
122. 丸山 敬,石川裕彦,内田孝紀,河井宏允,大屋裕二, 台風0418号通過時の宮島周辺の強風場に関する数値シミュレーション, 日本風工学会論文集, Vol.31,No.3,pp.95-104, 2006.07.
123. 友清衣利子,喜多村美保,内田孝紀,前田潤滋, 台風0423号通過時における佐賀県小城市周辺風況のCFD解析, 九州大学大学院人間環境学研究院紀要, 第10号,pp.49-56, 2006.07.
124. 内田孝紀,大屋裕二, 安定成層流体中の地形効果とその可視化, 可視化情報学会誌, 2006.07.
125. Takashi Maruyama, Hirohiko Ishikawa, Takanori Uchida, Hiromasa Kawai, Yuji Ohya, Numerical simulation of strong wind fields around Miyajima during Typhoon Songda in 2004, Journal of Wind Engineering, 10.5359/jwe.31.95, 31, 3, 95-104, 2006.07, [URL], The strong wind fields around Miyajima in Hiroshima Bay were simulated numerically during Typhoon Songda in 2004. The PSU/MM5 model was used for the calculation of meso-scale regions. The strong wind that passed over the sea and blew into the Hiroshima Bay was simulated. The predicted wind fields were examined comparing with the observed records and the field investigation of damage to the houses and buildings. The calculated maximum wind speed map was well correlated to the distribution of damage rate by strong wind in Hiroshima Prefecture. Unsteady wind fields were also computed by Large Eddy Simulation in the fine region around Miyajima. The local wind characteristics caused by the topography around Itsukushima Shrine were investigated by using the calculated results. The down flow along the valley to the south of the shrine was simulated in the neutral atmospheric condition. The local wind flows around the shrine were discussed..
126. 内田孝紀, PC1台で動く,風が見える,風力発電適地選定ソフトRIAM-COMPACT(リアムコンパクト)の紹介, 日本機械学会論文集, Vol.109,No.1050,pp.411(トピックス記事), 2006.05.
127. 丸山敬,石川裕彦,内田孝紀,河井宏允,大屋裕二, 台風0418号通過時の厳島神社周辺における地形性の強風を再現する試み, 京都大学防災研究所年報, 第49号B, 2006.04.
128. 内田孝紀,杉谷賢一郎,大屋裕二, 一様流中に置かれた急峻な単純地形まわりの気流性状の評価—3次元孤立峰モデルの場合—, 日本風工学会論文集, Vol.31,No.2,pp.63-74, 2006.04.
129. Takanori Uchida, Kenichirou Sugitani, Yuji Ohya, Evaluation on wind characteristics around a steep simple terrain in a uniform flow-case of a three-dimensional isolated-hill model-, Journal of Wind Engineering, 10.5359/jwe.31.63, 31, 2, 63-74, 2006.04, [URL], The purpose of this research is to construct a database of a non-stratified airflow past a steep simple terrain under an imposition of a uniform flow, and, in addition, is to do the accuracy inspection of the numerical model under development at present. This numerical model is referred to as the RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, Computational Prediction of Airflow over Complex Terrain), and is for the purpose of the prediction of airflow over complex terrain with several m to several km. This paper describes the experimental and numerical study of a non-stratified airflow past a three-dimensional isolated-hill in a uniform flow as the second phase. The Reynolds number, based on the uniform flow and the height of the hill, is about 104. Airflows around the hill include the unsteady vortex shedding. Attention is focused on airflow characteristics in a wake region. For this purpose, the velocity components in the streamwise direction were measured with a SFP (Split-Film Probe) in the wind tunnel experiment. In addition, the flow visualization was performed by using the smoke-wire technique. Through comparison of the experimental and numerical results, they showed a good agreement. The accuracy of both of the wind tunnel experiment by the SFP and also numerical simulation by the RIAM-COMPACT were confirmed as the result..
130. 内田孝紀,大屋裕二, ナセル搭載の風向・風速計で測定された複雑地形上の風況特性—岬の場合—, 九州大学応用力学研究所所報, 第130号,pp.35-52, 2006.03.
131. 内田孝紀,大屋裕二,荒屋亮,田辺正孝,川島泰史, 非定常・非線形風況シミュレータRIAM-COMPACTを用いたウィンドファーム風況診断, 九州大学応用力学研究所所報, 第130号,pp.53-60, 2006.03.
132. Toshiyuki SANADA, Masatoshi FUJINO, Daisuke MATSUSHITA, Takanori UCHIDA, Hikaru MATSUMIYA, Masao WATANABE, Yoshinori HARA, Minori SHIROTA, Numerical Site Calibration on a Complex Terrain and its Application for Wind Turbine Performance Measurements, 2006 European Wind Energy Conference Proceedings, 2006.02.
133. 内田孝紀,大屋裕二, 種々の安定成層場における三宅島火山ガスの挙動の数値シミュレーション, 第19回数値流体力学シンポジウム講演論文集(CD-ROM), 2005.12.
134. 弓本桂也,吉田保衡,鵜野伊津志,内田孝紀,大屋裕二, メソスケール気象モデルを用いた高解像度風況シミュレーション
—野間岬風力発電サイトを対象として—, 日本気象学会 機関誌「天気」, VOL.52,NO.11,pp.11-17, 2005.11.
135. 内田孝紀,大屋裕二, 風車単体後流の渦構造解明に向けた基礎的研究, 九州大学応用力学研究所所報, 第129号,pp.123-128, 2005.09.
136. 内田孝紀,大屋裕二, 複雑地形上の非定常風況シミュレーションにおける流出境界断面の取扱いについて, 九州大学応用力学研究所所報, 第129号,pp.129-133, 2005.09.
137. 内田孝紀,大屋裕二,荒屋亮,田辺正孝,川島泰史, 風況シミュレーションのための紙地図からの高解像度地形データの構築, 九州大学応用力学研究所所報, 第129号,pp.135-141, 2005.09.
138. T. Uchida and Y. Ohya, Micro-siting Technique for Wind Turbine Generator by Using One PC
-Introduction of the RIAM-COMPACT based on LES-, EXPO WCWRF 2005(CD-ROM), 2005.09.
139. 内田孝紀,大屋裕二, 風車単体後流の渦構造解明に向けた基礎的研究, 日本流体力学会年会2005講演論文集(CD-ROM), 2005.09.
140. 内田孝紀,大屋裕二, 一様流中の2次元崖状地形まわりの気流性状に関する数値的研究, 応用力学論文集, Vol.8,pp.831-838, 2005.08.
141. 内田孝紀,杉谷賢一郎,大屋裕二, 九州大学元岡キャンパスにおける風観測
—第一報 平均的な風況特性について—, 九州大学応用力学研究所所報, 第128号,pp.37-51, 2005.03.
142. 弓本桂也,吉田保衡,鵜野伊津志,内田孝紀,大屋裕二, 野間岬風力発電サイトを対象とした風況シミュレーション, 九州大学大学院総合理工学報告, Vol.26,No.1,pp.9-14, 2004.12.
143. 内田孝紀,大屋裕二,鵜野伊津志, 急峻な岬まわりの気流場シミュレーション
—気象力学モデルCSU-RAMSと流体力学モデルRIAM-COMPACTの適用性について—, 第18回風工学シンポジウム論文集, pp.35-40, 2004.12.
144. 河内昭紀,岡林一木,吉門洋,小林恵三,北林興二,大屋裕二,内田孝紀,井手靖雄, 複雑地形へ適用可能な拡散モデル開発の概要, 環境管理, Vol.40,No.10,pp.50-61, 2004.10.
145. 内田孝紀,大屋裕二, 人工的に生成された流入変動風を用いた建物周辺流れのラージ・エディ・シミュレーション, 九州大学応用力学研究所所報, 第127号,pp.95-107, 2004.09.
146. 内田孝紀,大屋裕二, 非定常風況・拡散シミュレータRIAM-COMPACTを用いた
Intel Itanium2プロセッサとAMD Opteronプロセッサの性能評価
—自動並列計算の有効性について—, 九州大学応用力学研究所所報, 第127号,pp.87-94, 2004.09.
147. 内田孝紀,大屋裕二,田辺正孝,葛生和人,橋本晃慈, 実地形を対象に非定常風況・拡散シミュレータRIAM-COMPACTの紹介
—最新のインテルPentium4プロセッサ搭載Windows PCの製作と性能評価—, 九州大学応用力学研究所所報, 第127号,pp.75-86, 2004.09.
148. 内田孝紀,大屋裕二,田辺正孝,葛生和人,橋本晃慈, 風力タービン適地選定のためのコンピュータによるマイクロサイティング技術
—実地形を対象にした非定常風況・拡散シミュレータRIAM-COMPACTの紹介—, 日本風力エネルギー協会誌, Vol.28,No.2,pp.46-51, 2004.09.
149. 内田孝紀,大屋裕二,田辺正孝,葛生和人,橋本晃慈, 風力タービン適地選定のためのコンピュータによるマイクロサイティング技術
—実地形を対象にした非定常風況・拡散シミュレータRIAM-COMPACT—, 土木施工, Vol.45,No.8,pp.49-55, 2004.08.
150. Y. Ohya and T. Uchida, Laboratory and Numerical Studies of the Convective Boundary Layer Capped by a Strong Inversion, Boundary Layer Meteorology, 10.1023/B:BOUN.0000027913.22130.73, 112, 2, 223-240, Vol.112, pp.223-240, 2004.08.
151. Yuji Ohya, Takanori Uchida, Laboratory and numerical studies of the convective boundary layer capped by a strong inversion, Boundary-Layer Meteorology, 10.1023/B:BOUN.0000027913.22130.73, 112, 2, 223-240, 2004.08, [URL], The convective boundary layer (CBL) with a wide range of stability is simulated experimentally using a thermally stratified wind tunnel, and numerically by direct numerical simulation (DNS). The turbulence structures and flow characteristics of various CBL flows, capped by a strong temperature inversion and affected by surface shear, are investigated. The various vertical profiles of turbulence statistics similar to those from the observed CBL in the field are successfully simulated in both the wind-tunnel experiment and in DNS. The comparison of the wind-tunnel data and DNS results with those of atmospheric observations and water-tank studies shows the crucial dependence of the turbulence statistics in the upper part of the layer on the strength of the inversion layer, as well as the modification of the CBL turbulence regime by the surface shear..
152. Takanori Uchida, Kenichirou Sugitani, Yuji Ohya, Evaluation on wind characteristics around a steep simple terrain in a uniform flow-case of a two-dimensional ridge model, Journal of Wind Engineering, 10.5359/jwe.29.35, 29, 3, 35-43, 2004.07, [URL], The purpose of this research is to construct a database of a non-stratified airflow past a steep simple terrain under an imposition of a uniform flow, and, in addition, is to do the accuracy inspection of the numerical model under development at present. This numerical model is referred to as the RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, Computational Prediction of Airflow over Complex Terrain), and is for the purpose of the prediction of airflow over complex terrain with several m to several km. This paper describes the experimental and numerical study of a non-stratified airflow past a two-dimensional ridge in a uniform flow as the first phase. The Reynolds number, based on the uniform flow and the height of the ridge, is about 10 4. Airflows around the ridge include the unsteady vortex shedding. Attention is focused on airflow characteristics in a wake region. For this purpose, the velocity components in the streamwise direction were measured with a SFP (Split-Film Probe) in the wind tunnel experiment. In addition, the flow visualization was performed by using the smoke-wire technique. Through comparison of the experimental and numerical results, they showed a good agreement. The accuracy of both of the wind tunnel experiment by the SFP and also numerical simulation by the RIAM-COMPACT were confirmed as the result..
153. 内田孝紀,杉谷賢一郎,大屋裕二, 一様流中に置かれた急峻な単純地形まわりの気流性状の評価—2次元尾根モデルの場合—, 日本風工学会論文集, No.100,pp.35-43, 2004.06.
154. 内田孝紀,大屋裕二, 風況シミュレータRIAM-COMPACTによる拡散場シミュレーション
—その2.安定時の場合—, 九州大学応用力学研究所所報, 第126号,pp.17-22, 2004.03.
155. 内田孝紀,大屋裕二, 風況シミュレータRIAM-COMPACTによる拡散場シミュレーション
—その1.不安定時の場合—, 九州大学応用力学研究所所報, 第126号,pp.9-15, 2004.03.
156. 内田孝紀,大屋裕二, PCクラスタを用いた風況予測シミュレータRIAM-COMPACTの開発
—その2.スカラー並列計算機における経過時間の比較—, 九州大学応用力学研究所所報, 第126号,pp.1-8, 2004.03.
157. 内田孝紀,大屋裕二, 風況シミュレータRIAM-COMPACTによる
インテルプロセッサ搭載ハイパフォーマンスコンピュータの性能評価, 九州大学情報基盤センター広報, Vol.4,No.1,pp.1-14, 2004.03.
158. 内田孝紀,大屋裕二, 小規模なスカラー並列計算機を用いた風況予測シミュレータRIAM-COMPACTの実用化へ向けた開発, 九州大学情報基盤センター年報, 第4号,pp.19-30, 2004.03.
159. 内田孝紀, 大屋裕二, PCクラスタを用いた風況予測シミュレータRIAM-COMPACTの実用化へ向けた検討, 日本風力エネルギー協会誌, Vol.27,No.4,pp.8-11, 2003.10.
160. 内田孝紀,大屋裕二, 風況予測シミュレータRIAM-COMPACTの開発
—風況精査とリアルタイムシミュレーション—, 日本流体力学会誌「ながれ」, Vol.22,pp.417-428, 2003.10.
161. 内田孝紀, 大屋裕二, PCクラスタを用いた風況予測シミュレータRIAM-COMPACTの開発
—その1.種々の計算機におけるCPU時間の比較—, 九州大学応用力学研究所所報, 第125号,pp.5-20, 2003.09.
162. 内田孝紀, 大屋裕二, 乱流境界層に埋没した急峻な孤立峰まわりの風況シミュレーション
—大きな乱れ強さを伴う流入風の場合—, 応用力学論文集, Vol.6,pp.819-826, 2003.08.
163. 内田孝紀,大屋裕二, パッシブ粒子法による三宅島火山ガス挙動の可視化, 可視化情報学会論文集, Vol.23, No.7, pp.58-65, 2003.07.
164. 内田孝紀, ブラフボディまわりの数値流体シミュレーションとその可視化
—マイクロスケールからメソスケールまで—, 九州大学情報基盤センター広報, Vol.3, No.2,pp.135-148, 2003.07.
165. Yuji Ohya, Takanori Uchida, Turbulence structure of stable boundary layers with a near-linear temperature profile, Boundary-Layer Meteorology, 10.1023/A:1023069316164, 108, 1, 19-38, 2003.07, [URL], By using a thermally stratified wind tunnel, we have successfully simulated stably stratified boundary layers (SBL), in which the mean temperature increases upward almost linearly. We have investigated the flow structure and the effects of near-linear stable stratification on the transfer of momentum and heat. The vertical profiles of turbulence quantities exhibit different behaviour in two distinct stability regimes of the SBL flows with weak and strong stability. For weak stability cases, the turbulent transfer of momentum and heat is basically similar to that for neutral turbulent boundary layers, although it is weakened with increasing stability. For strong stability cases, on the other hand, the time-mean transfer is almost zero over the whole boundary-layer depth. However, the instantaneous turbulent transfer frequently occurs in both gradient and counter-gradient directions in the lower part of the boundary layer. This is due to the Kelvin-Helmholtz (K-H) shear instability and the rolling up and breaking of K-H waves. Moreover, the internal gravity waves are observed in the middle and upper parts of all stable boundary layers..
166. 内田孝紀, 杉谷賢一郎,大屋裕二, 一様流中の2次元崖状地形まわりの気流性状に関する実験的研究, 日本風工学会論文集, No.95,pp.233-244, 2003.04.
167. Takanori Uchida, Kenichiro Sugitani, Yuji Ohya, Experimental study on wind characteristics around a two-dimension escapement in a uniform flow, Journal of Wind Engineering, 28, 2, 233-244, 2003.04, This paper describes the experimental study of a non-stratified airflow past a two-dimensional escarpment in a uniform flow. The Reynolds number, based on the uniform flow and the height of the escarpment, is about 104. The slope gradient of the escarpment is 25, 35 and 45 degree. Airflows around the escarpment include the unsteady separated and reattaching flow (hereafter called a "separation bubble"), where the separation occurs from a sharp comer. Attention is focused on an influence of a surface roughness on airflow characteristics in a wake region. For this purpose, the velocity components were measured with the X-wire probe and the split-film probe. In addition, the flow visualization was performed by using the smoke-wire technique. Through comparison between the experimental results with the surface roughness and those without it, the significant difference in the airflow characteristics is confirmed in the separation bubble. This is mainly due to the size in the separation bubble. The size in the separation bubble with the surface roughness is much larger than the one without it. In the case under an imposition of the surface roughness, the velocity is strongly defected near the slope surface. As a result, the production of the vorticity in the separated shear layer is also inhibited, leading to the elongation in the separation bubble..
168. 内田孝紀, 杉谷賢一郎,大屋裕二, 3次元数値モデルによる九大新キャンパスの風況予測シミュレーション
—第2報建物群まわりの風環境予測—, 九州大学情報基盤センター年報, 第3号,pp.57-66, 2003.03.
169. T. Uchida, Y. Ohya, Stable stratification effect on the separated and reattaching flow behind two-dimensional topography, 九州大学応用力学研究所所報, 第124号,pp.17-24, 2003.03.
170. 内田孝紀, 大屋裕二, 安定成層流体中の地形効果に関する数値的研究
—急峻な孤立峰の場合—, 九州大学応用力学研究所所報, 第124号,pp.9-16, 2003.03.
171. 内田孝紀, 大屋裕二, 安定成層場における山越え気流の三次元数値シミュレーション
—非定常な剥離—再付着流れに対する安定成層の効果—, 日本流体力学会誌「ながれ」, Vol.22,pp.65-78, 2003.02.
172. Takanori Uchida, Yuji Ohya, Large-eddy simulation of turbulent airflow over complex terrain, Journal of Industrial Aerodynamics, 10.1016/S0167-6105(02)00347-1, 91, 1-2, 219-229, 2003.01, [URL], In order to develop an overall efficient and accurate method of predicting an unsteady three-dimensional airflow over a complex terrain with characteristic length scales on the order of kilometers, we recently developed the CFD codes referred to as the RIAM-COMPACT (Research Institute for Applied Mechanics, Kyushu University, Computational Prediction of Airflow over Complex Terrain). In this paper, we carried out the calculation of turbulent airflow over a real complex terrain in a horizontal region of 9.5km × 5km with a relatively fine spatial resolution of 50 m. This area covers the new campus of Kyushu University. In order to generate instantaneous velocity fluctuations in an approaching flow, an unsteady flow field in the driver unit is directly calculated. The numerical results obtained by RIAM-COMPACT demonstrated that the changes induced on the wind field by the topographic effect, such as the local wind acceleration and the flow separation, were successfully simulated. We emphasized the following features as regards the wind field over the new campus area under the influence of the west wind. The wind field in the central region of the new campus area is strongly influenced by the wake region generated behind Mt. Hiyama (244m). The airflows moving around the side of Mt. Hiyama exhibit relatively small fluctuations. When these winds reach Mt. Ishigateke (99m), they are locally accelerated at the peak. Consequently, a local speed-up effect is confirmed in the southern part of the new campus area..
173. 内田孝紀, 大屋裕二, 急峻な孤立地形まわりの複雑乱流場に対するLES
—流入気流の乱れの影響について—, 第17回風工学シンポジウム論文集, pp.137-142, 2002.12.
174. R. Ohba, T. Hara, S. Nakamura, Y. Ohya, Takanori Uchida, Gas diffusion over an isolated hill under neutral, stable and unstable conditions, Atmospheric Environment, 10.1016/S1352-2310(02)00642-8, 36, 36-37, 5697-5707, 2002.12, [URL], Wind tunnel experiments of gas diffusion were performed over flat terrain and over an isolated three-dimensional hill under neutral, stable and unstable (sea breeze) conditions. Conditions of airflow in the wind tunnel were determined so as to satisfy the similarity rule for the bulk Richardson number, by controlling temperature profiles and wind velocity of the thermally stratified wind tunnel. Typical characteristics were observed under each condition of atmospheric stability; reversed vortex behind the hill in neutral condition, downward slope wind in stable one and convective motion in unstable one. We compared these experiments with the results of a Direct Numerical Simulation (DNS) model for the wind velocity over the hill under neutral conditions. The numerical results showed good agreement with the experimental results..
175. 内田孝紀, 大屋裕二, 急峻な2次元山からの非定常な渦放出に対する数値的考察, 応用力学論文集, Vol.5,pp.735-742, 2002.08.
176. 内田孝紀, 大屋裕二, ネストグリッドを用いた複雑地形上の風況予測シミュレーション, 日本風工学会論文集, No.92,pp.135-144, 2002.07.
177. Takanori Uchida, Yuji Ohya, Numerical simulation on wind fields over complex terrain using nested grids, Journal of Wind Engineering, 27, 3, 135-144, 2002.07, In order to develop an overall efficient and accurate model of simulating an unsteady three-dimensional airflow over complex terrain with characteristic length scales on the order of kilometers, we have been examining the large-eddy simulation (LES) technique using a finite-difference method (FDM). These LES codes are referred to as the RIAM-COMPACT (Research institute for Applied Mechanics, Kyushu University, Computational JPrediction of Airflow over Complex Terrain), and are based on two grid systems and corresponding variable arrangement: one is an orthogonal staggered grid; the other is a generalized curvilinear collocated grid. In this paper, using the RIAM-COMPACT based on a generalized curvilinear collocated grid, we have performed the calculations of a non-stratified airflow over real complex terrain. This area covers the new campus of Kyushu University. To investigate more clearly the influence of topography on the airflow over the new campus area, we employed nested grids: the outer grid domain is 9.75km × 4.65km × 1.46km with horizontal grid spacing of 50m and the inner grid domain is 5km × 2.7km × 1.46km with horizontal grid spacing of 25m. The numerical results were compared with the wind tunnel experiment, and airflow characteristics due to the topographic effect, such as the wind speed-up and the separated flow, were successively simulated..
178. 内田孝紀, 大屋裕二, 3次元数値モデルによる九大新キャンパスの風況シミュレーション, 九州大学情報基盤センター年報, 第2号,pp.99-106, 2002.03.
179. Takanori Uchida, Yuji Ohya, Numerical study of stably stratified flows over a two-dimensional hill in a channel of finite depth, Fluid Dynamics Research, 10.1016/S0169-5983(01)00025-9 , 29, 4, 227-250, 2001.10, [URL], Stably stratified flows over a two-dimensional hill in a channel of finite depth are investigated numerically at a Reynolds number of 2000, which is based on the uniform upstream velocity U and the hill height h. As a first step, we assume a free-slip condition on the ground, both upstream and downstream of the hill, and impose a no-slip condition only on the hill surface. Such a configuration corresponds to that of the previous towing tank experiments and numerical studies. For strong stratification (1 < K = NH/πU ≤ 2), the present numerical results confirmed that the flow around the hill is intrinsically unsteady, which is manifested very clearly as periodic oscillations in the drag coefficient Cd on the hill, and emphasize the following features, where N is the buoyancy frequency and H is the channel depth. For 1.1 ≤ K ≤ 1.7, columnar disturbances with mode n = 1 are dominant so that the flow around the hill shows a persistent periodic unsteadiness. This flow unsteadiness is mainly due to the periodic shedding of upstream advancing columnar disturbances with mode n = 1 with a clockwise circulation. For 1.8 ≤ K ≤ 2, as columnar disturbances with mode n = 2 become dominant, the flow around the hill rapidly reaches an almost steady state. In addition, through the calculations with the blockage ratio H/h = 6, 10 and corresponding Re=20, 100 and 2000, it is found that the normalized periods of Cd oscillations have a strong dependence on both the H/h and Re. As a next step, to investigate the flow around the hill under real atmospheric situations, we have performed calculations under imposition of a no-slip condition on the ground, particularly focusing on the effect of stable stratifications on the unsteady separated-reattached flow behind the hill. The flow around the hill exhibits different behavior over the whole range 0 ≤ K ≤ 2, corresponding to the difference in the boundary condition on the ground. For 0 ≤ K ≤ 0.9, the vortex shedding from the separation bubble behind the hill occurs. For K = 1 and 1.1, the vortex shedding is strongly suppressed so that the flow around the hill rapidly reaches an almost steady state. Under strong stratification (1 < K ≤ 2), although lee waves are excited downstream of the hill, the vortex shedding clearly exists. For 1.2 ≤ K ≤ 1.5, the flow field with a vortex shedding shows an approximately steady state, corresponding to the stationary Ice wave. It is much more likely that there is no significant change in the approaching flow just ahead of the hill, because the change in the columnar disturbances with mode n = 1 is very small. Only when 1.6 ≤ K ≤ 2 does the flow around the hill become unsteady. However, the rate of the periodic change in the separation bubble is very small. These flow mechanisms for 1.6 ≤ K ≤ 2 are almost the same as those discussed in the prior numerical results..
180. 内田孝紀, 大屋裕二, 九州大学新キャンパス移転地上の風況場に関する数値シミュレーションと風洞実験, 九州大学応用力学研究所所報, 第121号,pp.59-72, 2001.09.
181. 内田孝紀, 大屋裕二, ラージ・エディ・シミュレーションによる局地的風況予測モデルRIAM-COMPACTの評価
—その2.壁面せん断乱流場による計算精度の検証と実地形上の風況場解析への適用—, 九州大学応用力学研究所所報, 第121号,pp.73-85, 2001.09.
182. 内田孝紀, 大屋裕二, 安定成層場で風下波の砕波により発生する局地強風の数値的考察, 応用力学論文集, Vol.4,pp.655-664, 2001.08.
183. 内田孝紀, 大屋裕二, ラージ・エディ・シミュレーションによる局地的風況予測モデルの評価, 九州大学応用力学研究所所報, 第120号,pp.29-34, 2001.02.
184. 内田孝紀, 大屋裕二, 局地的風況予測に対するLESの適用, 第16回風工学シンポジウム論文集, pp.59-64, 2000.11.
185. 内田孝紀, 大屋裕二, 風工学における数値シミュレーションのための流入変動風の生成法に関する研究
その1. 一定圧力勾配により駆動される十分に発達した境界層流のLES, 九州大学応用力学研究所所報, 第119号,pp.75-81, 2000.09.
186. 内田孝紀, 大屋裕二, 丘陵地形を過ぎる安定成層流の2次元数値シミュレーション
—格子分解能と数値計算法の影響について—, 応用力学論文集, Vol.3,pp.729-736, 2000.08.
187. 内田孝紀,大屋裕二, 有限深さ流路内の2次元丘陵地形を過ぎる安定成層流の非定常性
—第2報 非定常な剥離・再付着流れに対する安定成層の効果—, 日本流体力学会誌「ながれ」, Vol.18,pp.308-320, 1999.11.
188. 内田孝紀,大屋裕二, 定成層場で地形効果により発生する局地強風の数値的検討, 応用力学論文集, Vol.2,pp.583-592, 1999.08.
189. Takanori Uchida, Yuji Ohya, Numerical simulation of atmospheric flow over complex terrain, Journal of Industrial Aerodynamics, 10.1016/S0167-6105(99)00024-0, 81, 283-293, 1999.05, In order to develop an overall efficient and accurate method of simulating an unsteady three-dimensional atmospheric flow over topography, we examined two grid systems and corresponding variable arrangements: one is a body-fitted coordinate (BFC) grid system based on a collocated variable arrangement; the other is an orthogonal grid system based on a staggered variable arrangement. Using these codes, we calculated the wind system over topography such as an isolated hill and real complex terrain. Both codes remarkably removed the numerical difficulties such as the convergence of the SOR method in solving the pressure Poisson equation, resulting in numerical results with much higher accuracy. Despite the differences in the grid system and in variable arrangement, no significant differences in the flow pattern between the both numerical results were found. Compared with the previous studies, the numerical results obtained are very satisfactory in the sense that overall characteristic flows are successfully simulated irrespective of the simulation codes..
190. 内田孝紀,大屋裕二, 安定成層した非粘性流体中に地形効果により励起された内部重力波の数値解析, 九州大学応用力学研究所所報, 第85号,pp.13-22, 1999.02.
191. 内田孝紀,大屋裕二, 山越え成層流の差分解析—地形形状と格子分解能の影響—, 九州大学応用力学研究所所報, 第85号,pp.1-12, 1999.02.
192. 内田孝紀,大屋裕二, 一般曲線座標系・コロケート格子を用いた複雑地形上の安定成層流に関する風況予測, 第15回風工学シンポジウム論文集, pp.131-136, 1998.12.
193. 内田孝紀,大屋裕二, 差分法における幾つかの知見, 九州大学応用力学研究所所報, 第84号,pp.29-43, 1998.10.
194. 内田孝紀,大屋裕二, 有限流路内の2次元丘陵地形を過ぎる安定成層流のLES, 応用力学論文集, Vol.1,pp.615-624, 1998.08.
195. 内田孝紀,大屋裕二, 有限流路内の2次元丘陵地形を過ぎる安定成層流の非定常性, 日本流体力学会誌「ながれ」, Vol.17,pp.45-56, 1998.02.
196. 内田孝紀,大屋裕二, DNSによる複雑地形を過ぎる安定成層流の風況予測
—矩形格子系と一般曲線格子系との比較—, 九州大学応用力学研究所所報, 第82号,pp.113-126, 1997.11.
197. 内田孝紀,大屋裕二,小園茂平, 3次元複雑地形を過ぎる安定成層流の数値シミュレーション, 第14回風工学シンポジウム論文集, pp.91-96, 1996.12.
198. Takanori Uchida, Y. Ohya, A numerical study of stably stratified flows over a two-dimensional hill - Part I. Free-slip condition on the ground, Journal of Industrial Aerodynamics, 10.1016/S0167-6105(97)00096-2, 67-68, 493-506, 1997.01, [URL], Stably stratified flows over a two-dimensional hill in a channel of finite depth are analyzed numerically by using a newly-developed multi-directional finite-difference method at a Reynolds number Re = 2000. To simplify the phenomena occurring in the flow around the hill, the free-slip condition for the velocity is assumed on the ground, and the nonslip condition is imposed only on the hill surface. Attention is focused on the unsteadiness in the flow around the hill for the cases of K( = NH/πU) > 1 where N and U are the buoyancy frequency and free-stream velocity and H is the domain depth. The flow unsteadiness is discussed, being associated with shedding of the upstream advancing columnar disturbance..

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