DX (efforts to improve operations using digital technology) is gaining momentum. In design and analysis operations at the design study stage, the following issues exist, and there is much room for improvement through DX. (1) Difficulty in linking geometry for design and geometry for analysis. (2) Manual work for pre/solver/post-processing is complicated. (3) Difficulty in acquiring engineering analysis know-how. (4) Increased analysis time due to higher accuracy. To solve these problems, I have been developing a system that fully automates a series of operations required for wind environment analysis in the cloud by linking with databases such as the 3D city model “PLATEAU” and weather data. The developing system is capable of AI (surrogate model)-training and AI-inference as well as analysis.

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Urban airflow has strong turbulence characteristics, and its distribution varies with time. Strong winds in the urban area may harm pedestrians. Calculating the urban airflow distribution quickly can protect pedestrians from danger. In this study, a machine learning based method, Generative Adversarial Network (GAN), was used to rapidly estimate the high spatial resolution distribution of instantaneous airflow field in the cubic building group model using velocity measurement obtained from sensors as inputs. We compared the results with large-eddy simulation data as true values and with the results of the Proper Orthogonal Decomposition-Linear Stochastic Estimation (POD-LSE) method which has been validated for rapid prediction of airflow distribution. GAN can estimate instantaneous airflow distribution and streamlines, and the reproduction accuracy of GAN is higher than that of POD-LSE. The probability density function of instantaneous velocity obtained from the GAN at representative points is consistent with that of the true value.

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

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The final goal of this study is to elucidate the causal factors of the thermal environment in urban space by analyzing the horizontally and vertically decomposed advection and turbulent diffusion components of the sensible and latent heat balances. In this paper, the advection component of the sensible heat balance was evaluated by decomposing it into horizontal and vertical components. It was found that even on sea-breeze days, the influence of the vertical component in the advection was also significant, together with the influence of the horizontal component.

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Several heat sources can be considered to improve the living environment in cold conditions such as winter in north area. For example, air conditioning using convection heat transfer, floor heating using conduction heat transfer, heaters using radiation heat transfer, and solar radiation from windows on sunny days can be assumed. While it is important to evaluate each heat source from a composite perspective based on its energy consumption and other factors, this report presents a process for understanding the impact of various heat sources on human comfort, which is one factor in the evaluation. In this report, a thermal fluid analysis based on the Lattice Boltzmann Method is used to reproduce airflow behavior (convection), and coupled with a heat transfer analysis (conduction, radiation, solar radiation), an unsteady thermal environment is reproduced. Then, by combining the Berkeley model-based human body heat transfer extension, a physiology-based-thermal-comfort-evaluation results for living-room environments is presented.

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Since the Great East Japan Earthquake, the number of high-rise base-isolated buildings has been increased. However, with the increase of the height of the building, the influence of wind acting on the base-isolated layer will also increase, which will lead to the plasticization of the steel damper, resulting in residual deformation. In the existing wind resistant design, the commonly used 10-minute wind force with the wind speed and direction fixed is not enough to evaluate the residual deformation of the base-isolated layer. Compared with the wind force considering the change of wind speed and direction, the 10-minute wind force cannot take the occurrence of the wind force in the opposite direction to the deformation of the base-isolated layer into account, so there is a possibility that the residual deformation of the base-isolated layer may be overestimated. Therefore, based on the typhoon simulation, this paper will analyze the residual deformation of the base-isolated layer of the multi-degree-of-freedom model to discuss the design information that is closer to the actual situation.

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Noise barrier panels are often installed on the scaffoldings of building demolition works in order to cope with the environmental problem caused by noise and dust. However, the panels are difficult to remove and often left even when strong wind is forecasted. A current technical guideline can estimate wind load on the scaffoldings with solid panels. Still, the wind force distributions with various shape of scaffoldings corresponding to the demolition steps are not clear yet. In this study, wind tunnel tests were conducted to get the wind force coefficient distributions on the noise barrier panels for various steps of a building demolition work. Larger wind force coefficients than the technical guideline were obtained with a model with an opening on one side under a particular wind direction. The possible cause of such a large wind load was discussed. An appropriate design of wall connectors may be necessary based on the larger wind force in these cases.

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A steep decline of atmospheric pressure by a tornado causes a difference between the internal and external pressure of the building, exerting a significant force on the roof or exterior walls of the building. Previous studies have proposed experimental methods in which the model is subjected only to a sudden drop in air pressure under a calm, using a gust wind tunnel. In this study, we attempted to reproduce the experimental method of examining differential pressure by a computational fluid dynamics (CFD) simulation. As a result, the following findings were obtained. 1) To reproduce internal pressure fluctuations caused by a sudden drop in atmospheric pressure by numerical fluid dynamics simulations, it is necessary to perform the CFD simulation using a compressible fluid. 2) The sign and magnitude of the static pressure fluctuations depend on the position of the pressure reference point. 3) The internal building pressure obtained from the analysis results can be reproduced by the internal pressure response equation used in previous studies.

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

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Climate change has led to an increase in floods caused by heavy rain. One of the measures to reduce damages due to the flood is the use of piloti-type buildings. In this study, LES was conducted to analyze the influences of a piloti-type building on the surrounding wind environment and the wind pressure on the building located on the leeward side of the pilotitype building. It was found that good ventilation was obtained in the piloti space, but at the same time, some local high wind speed areas occurred. It was also found that large positive peak wind pressure coefficients appeared on a windward side wall of the building located on the leeward side of the piloti-type building.

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This study investigates the peak wind pressure coefficients on the roof and walls of the lowrise buildings surrounding a high-rise building by wind tunnel experiments. A total of 72 wind directions were considered from 0 to 355 degrees by 5 degrees, and the influence of the wind direction on the peak wind pressure coefficients of surrounding buildings was evaluated. At a wind direction angle of 30 degrees, both the positive and negative peak wind pressure coefficients occurred in a low-rise building located leeward side of a high-rise building. The positive peak pressure appeared at the windward corner on the front wall of a low-rise building and the value was about 1.5 times as large as that in the case of no high-rise building, and the negative peak value was observed at the windward edge on the roof of a low-rise building and the value was about 3 times as large as that in the case of no high-rise building.

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This study investigated the risks of disasters from strong winds in urban districts under global warming by conducting pseudo-global warming (PGW) experiments with a regional meteorological model and large eddy simulations (LESs) as well as by using urban geometrical features. Both the Weather Research and Forecasting (WRF) model and a simplified axisymmetric model were used to conduct PGW experiments on typhoons, while LESs were conducted for airflows in an urban district of Osaka City. Urban geometrical features were derived from a high-resolution digital surface model dataset. From the LES analysis, statistical relationships between wind gustiness and urban geometrical features under various stability conditions were obtained. The PGW experiments indicated how the external forcing of intense typhoons changed in a future climate. A combination of the meteorological, LES, and urban geometrical feature analyses demonstrated that risk of wind disasters in urban districts would increase by 10 % under +4K global warming scenario.

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This paper verifies the accuracy of the meteorological local analysis data and investigates the influence of the atmospheric stability and urban substrate on the power-law index of wind profile in Tokyo. The spatial distribution of the power law index also is shown taking advantage of local analysis data. The comparison of local analysis data and observation data by Doppler lidar has been conducted. The atmospheric stability has been analyzed in the Tokyo area utilizing local analysis data and the virtual potential temperature method. After stability classification, the influence of atmospheric stability and urban substrate on the power law index α of wind profile has been investigated. The variation of the power law index of local observation location and spatial distribution of the power law index in the Tokyo region from 2018 to 2020 has been examined. The results indicate that the atmospheric instability in the Tokyo area is more frequent than in Chiba in a year. The α gradually increases with changes in atmospheric stability from unstable, neutral to stable and the roughness length of upwind fetch has an obvious influence on the α . In addition, the α of some local areas has obvious fluctuation from 2018 to 2020.

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Using data at 724 stations for 12 years in Japan, the climatological characteristics of diurnal variation in surface wind speed were examined. Wind speed reaches a maximum in early afternoon at most sites. The relative amplitude with respect to the daily mean is larger for winds in lower percentiles, while the 99.9_th percentile winds also have a peak in early afternoon as an average for all stations. The amplitude and phase of the first harmonics of temperature and wind speed are positively correlated among stations, but their variability is larger for wind speed than for temperature. The amplitude and phase of wind speed are correlated with geographical factors such as the percentage of water surface, topographic convexity, and population density, with urban stations tending to show later phase. The amplitude of diurnal variation is small at some stations where nighttime wind speed is comparable to that in the daytime, possibly due to dominant mountain breezes.

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Meteorological simulations were conducted using Weather Research and Forecasting (WRF) in the 2000s and 2050s. The simulation for the future climate was conducted using a pseudo global warming method. The initial and boundary data for future climates were generated by adding the difference between the current and the future climates to the current climate. Firstly, the validation was performed by comparing the observed data by the Japanese Meteorological Agency at Tokyo District Meteorological Observatory with the simulated results for the 2000s at the exact location. It was confirmed that the occurrence frequencies of wind velocity could be generally reproduced by WRF. Secondly, changes in occurrence frequency and Weibull parameters of wind velocity between the 2000s and the 2050s simulated by WRF were evaluated at points in several cities. In a city located in the coastal area, the occurrence frequency of weak wind was increased and Weibull parameters were smaller in the 2050s, while in cities located in the relatively inland area, the occurrence frequency of wind velocity in the 2050s was almost the same as that in the 2000s.

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A multi-span cable-stayed bridge is planned for the Osaka Wangan Expressway Western Extension. The main tower of this bridge has an “A” shape in the direction of the bridge axis in order to improve the rigidity, and has a height of over 200 meters, so ensuring wind resistance stability is important. In this paper, a part of the wind tunnel experiment conducted to confirm the wind resistance stability of the tower is reported. First, in order to select a cross-sectional shape with high wind resistance stability, a two-dimensional cross-sectional partial model test was conducted to confirm trends such as the size and angle of chamfering and corner cutting, and the presence or absence of slits. Next, considering this tendency, a wind tunnel experiment was conducted by a three-dimensional locking model, and the cross section with the highest wind resistance stability was selected.

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The effects of detail sections such as handrails on the vibration response of bridges have not been sufficiently clarified. In addition, accurately modeling the detail section of the handrail members in CFD requires a large computational cost. In this study, handrails modeled partially with porous media were installed on a box girder cross-section, and the aerodynamic force coefficients and flutter derivatives obtained from sinusoidal forced vibration were calculated using LES. Based on the obtained flutter derivatives, the steady-state vortex-induced vibration (VIV) amplitude in the vertical one-degree-of-freedom for each reduce wind speed was obtained by calculating the amplitude where the structural damping and negative aerodynamic damping were balanced. The obtained VIV amplitude is good agreement with the results of spring-supported free vibration wind tunnel tests.

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The side openings of bridges affect the aerodynamic characteristics of bridges, but the detailed mechanism is not completely clear. To investigate the effect of side openings on galloping instability, wind tunnel tests were conducted to measure the aerodynamic forces and surface pressures on a model of a rectangular cylinder with two types of side openings and a side ratio is 2. As a result, it was clarified that the onset wind velocity of galloping was controlled by the flow exiting the model which was affected by the shape of the side opening, and that the excitation force of galloping was controlled by the distance between the separating flow and the model.

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