We are developing a unified analysis method for the surrounding airflow field and volcanic ejecta during eruptions to predict and forecast the dispersal and diffusion of volcanic ejecta by numerical simulation. In order to obtain data on the flow velocity field for performance and accuracy verification of the created calculation program, a water tank experiment apparatus was built up to reproduce the density flow around a topographic model of the volcano. Using the tank, density flow mixed with tracer particles was reproduced around the volcano model to confirm that the velocity field can be measured using the PIV measurement system.

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This study investigated a method for obtaining the input wind speed time history to reproduce the target wind speed time history in a dome-shaped wind tunnel using a machine learning model. In particular, in this report, the effects of various parameters used to set up the LSTM model on the prediction accuracy were investigated when the input wind speed is set at only one surface and the output wind speed is set at only the horizontal wind direction component. Then, the CFD input wind speed to reproduce the target wind speed was predicted using the machine learning model, and the CFD output wind speed obtained with the CFD input wind speed was compared with the target wind speed. The results showed that the prediction accuracy was relatively good for the parts of the time history where the wind speed changes slowly, but tended to be less accurate for the parts where the wind speed changes rapidly in a short period of time and for the peaks and troughs of the time history.

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Wind velocity field measurements around buildings are essential for wind-resistant design and wind risk evaluation of buildings. However, current technology to measure wind velocity field around buildings are limited in senses that either it is hard to measure wind speeds at multiple locations simultaneously or wind speed near surface with high resolution. To overcome these difficulties, the group by authors has developed a methodology for wind field estimation based on raindrop tracking using PTV technology. This summary reports the way we conduct raindrop tracking, i.e. steps and measurement jigs. The core idea is, fixing two cameras on a rigid jig, to obtain photos that target calibration board on ground. Then, in actual raindrop tracking, the rigid jig with two cameras is tilted up to target the volume where raindrops are tracked; i.e., wind velocity field is measured. The jigs for this were developed, and it was confirmed in our test laboratory that the images required for PTV analysis can be obtained.

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We conducted a wind tunnel experiment to clarify the heat transfer coefficient when a hightemperature cinder with a size of several centimeters to several tens of centimeters is scattered in the air. The variation of surface temperature of heated cinders exposed to the airflow in a wind tunnel and the residual heat amount was measured by using a thermal pot.

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Optimizing grid spacing is critical for accurately capturing turbulent flow dynamics in Large Eddy Simulations (LES). This study examines the relationship between grid spacing and integral length scale using the Kolmogorov energy spectrum in various range of turbulence Reynold number. A quick estimation graph for grid spacing in LES analysis at the laboratory scale is provided. Verification simulation using ANSYS is conducted to confirm the adequacy of grid spacing estimations in three cases, with resolved kinetic energy ratios of 80%, 90%, and 95%. The results demonstrate that grid spacing can be estimated from the integral length scale and the ratio of resolved kinetic energy. Furthermore, the study recommends that the resolved kinetic energy should exceed 80% to ensure accurate flow resolution.

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A typhoon is one of the natural disasters to often give heavy damage to human life and a building. There are various laws and standards to reduce the damage in the natural disaster. For secure severe with the important building for a natural disaster, it is necessary to perform the typhoon strong wind hazard evaluation by the long-term reproduction period. In reference to a guide of the American Nuclear Regulatory Commission, we develop a typhoon hazard evaluation system using the Monte Carlo method. The developed evaluation system, including moving model, the intensity evaluation model, the wind field model is almost appropriate, but we understood the improvement in each model.

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Clarifying the transport mechanism of sensible and latent heat by sea breezes is important for effectively utilizing the cooling effect of sea breezes in urban space. Firstly, qualitative characteristics of sea breezes were extracted based on Doppler lidar observations. Then, the following results were obtained by sensible and latent heat balance analysis based on WRF results. The region where the negative advection value of sensible heat, i.e. the cooling effect by the sea breezes, and the positive advection value of latent heat, i.e. the effect of increasing humidity by the sea breezes, appeared was progressing inland over time. In addition, the sensible heat supplied by advection and turbulent diffusion was transported vertically upwards to about 800 m above the ground by the effect of strong updraft, which heated the upper atmosphere. Also, latent heat supplied by advection and turbulent diffusion at the natural cover surface flowed out into the upper air and humidified above due to strong vertical upward advection at the sea breeze front.

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The near-surface meteorological observation network has been established, which provides local observations to improve local objective analysis data using data assimilations. The development of high-resolution meteorological analysis data provides complementary data for predicting wind speed above urban areas. However, high-precision meteorological data requires observation data assimilation to correct the accumulated errors in weather forecast models, which means that meteorological analysis data are released with a delay. Therefore, this study suggests the Proper Orthogonal Decomposition with Linear Stochastic Estimation as a data fusion method to monitor upper-air wind speed by fusing meteorological near-surface observation data and high-resolution local objective analysis data. By comparing the predicted wind speed with Doppler lidar observations, the results show that the correlation coefficients between predicted and observed wind speed are approximately 0.84 at about 100 m and 0.86 at 200 m. RMSE of predicted wind speeds compared to observations is about 1.8 m/s in both observed heights.

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This study examined applicability of the two-equation turbulence model for two types of urban form in wind environment assessment. The study was based on two benchmark tests. The first was Case E in a benchmark test by Architectural Institute of Japan. The second was a benchmark test based on a wind tunnel test using the 3D city model "PLATEAU" (Tokyo Metropolitan Government Building and surrounding buildings). Based on these two benchmark tests, we compared the accuracy with CFD using four two-equation turbulence models. For the accuracy evaluation, four metrics were used: the COST732 validation metrics (FAC2, NMSE, and FB) plus MAPE. The results showed that RNGkEpsilon or kEpslion was highly accurate for AIJ Case E, and kOmegaSST or RNGkEpsilon was highly accurate for Case PLATEAU. Furthermore, given the wind comfort ranks, it was considered RNGkEpsilon suitable for the case of selecting a single turbulence model for two types of urban form.

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

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Windbreak fences have been used to reduce wind damage in urban areas and transportation. Fence performance may vary depending on the arrangement of openings, but evaluations have often been conducted assuming a uniform arrangement of openings. In this study, the effect of windbreak fences' opening patterns on their wake flow was evaluated by using computational fluid dynamics (CFD). A fence that is uniform in spanwise direction was divided vertically into 10 or 20 sections, and wake flow under various opening ratios and opening patterns were analyzed according to the sections' openings and non-openings. The results showed that, in general, the lower the opening rate, the more effective the wind kinetic energy reduction. However, the placement of the openings also greatly impacted the wind reduction. While a uniform arrangement of openings was most effective in fences divided into 10 sections, some non-uniform opening arrangements had smaller wind kinetic energy than the uniform one in fences divided into 20 sections.

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

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

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

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

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Neural network models in deep learning have represented expectable predictive performance as surrogate models for accelerating numerical fluid dynamics applications. However, existing neural network models still face challenges in accurately capturing the details of unsteady velocity fields, particularly when dealing with high Reynolds number airflow. Therefore, we address this problem to predict Large-Eddy Simulation (LES) results for the three-dimensional velocity field around a building using the emerging Fourier Neural Operator (FNO). The FNO can effectively learn the solutions to partial differential equations and predict them in a purely data-driven manner with high generalization ability. In task predicting the three-dimensional unsteady velocity magnitude over ten consecutive time steps, we found that FNO significantly outperformed the traditional Deep Neural Network (DNN), and the more training data volume used, the higher the FNO accuracy. We compared key FNO parameters such as training data volume, and the numbers of Fourier modes and Fourier layers to summarize their influence on model performance. Results show that the default Fourier mode number 12 can be enlarged to 18 as more training data is applied, thus increasing FNO accuracy. In addition, the default Fourier layer number four can be decreased to one, avoiding overfitting.

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Wind tunnel experiments can be conducted as a precise method for measuring airflow and pressure around buildings. However, the inherent measurement limitations and cost make it challenging to capture detailed distributions. In this study, we implement a physics-informed neural network (PINN) to estimate the average flow field and surface pressure in a twodimensional urban street canyon from sparse velocity information which is assumed to be provided by wind tunnel experiments. High-resolution datasets from a large-eddy simulation provide simulated velocity measurement data for various sensor configurations. As part of the governing equations for the PINN model, a forcing vector method is employed to replace Reynolds stress, thereby reducing computational costs. As a result, the PINN demonstrated high prediction accuracy for the entire detailed flow field. Additionally, the wind pressure on the surfaces was estimated without any pressure measurements. However, regions near building surfaces and shear layers, which exhibit large velocity gradients, still present relatively large errors. To address this issue, supplementary sensors improved performance and increased prediction accuracy. The proposed method shows promising potential in facilitating efficient assessments within wind tunnel experimentation settings.

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Most previous studies have clarified the interference effects between only two or three buildings, and very few have assessed the effects of a high-rise building within an urban district on its surrounding buildings. In our previous studies, wind tunnel experiments were conducted to analyze the effect of a high-rise building on the wind pressure acting on surrounding low-rise buildings, and it was found that a large negative pressure is generated locally on the roof of a low-rise building located immediately leeward side of the high-rise building. However, there has been no discussion regarding the degree to which exterior material damages can occur under strong wind conditions, and the risk of structural damage has not been shown. This study analyzed the properties of negative peak wind pressure and wind loads acting on the roof surface of low-rise buildings located near a high-rise building. The analysis is based on wind tunnel experiment results with various densities of low-rise buildings and various shapes of a high-rise building. Then, the risk of structural damage based on wind loads acting on the roof surface of the low-rise building was evaluated by comparing them with the bearing capacity of the metal roof.

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The present study focused on the characteristics of dispersing peak wind pressure coefficients acting on a square cylinder with an aspect ratio of three, which were obtained in wind tunnel tests. The experiments were carried out at a wind direction angle of 0 degrees, and 18369 waves of time history of wind pressure coefficients, which are equivalent to ten minutes of real time, were obtained. The peak wind pressure coefficients show a wide dispersion range near the leading and trailing edges on the side surface. Furthermore, it was confirmed that the range is larger in the lower part of the square cylinder. The convergence curve to the expected value with respect to the number of ensemble averages indicates that the rate of convergence follows a logarithmic function when the number of averages exceeds 5～30. Fluctuations of wind pressure coefficients when absolute value of the peak wind pressure coefficient is high were discussed using power spectral density functions. A significant difference was confirmed in the lower part of the square cylinder in case that the dispersion range is large. Additionally, a large difference was observed at non-dimensional frequencies of 10^-3 for the front surface and 10^-1 for the leading edge on the side surface in the lower part, and this suggests that the dispersion of the peak wind pressure is caused by the flow fluctuations at these frequencies.

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The unsteady aerodynamic properties of a large-span cantilevered roof were studied by means of 2D forced oscillation simulations with the k-ω SST model. The roof was assumed to be rigid with a rotational degree of freedom. The effect of roof shape and downburst wind were analyzed and discussed. The result shows that 1) curved roofs were subjected to greater wind loads though their critical velocity for instability was higher than the plate roof in ABL wind or with a pitch angle of 20°, 2) the moment loads became greater and the critical velocity decreased in the downburst wind, especially for the case with a pitch angle of 20°, 3) the curved roof shape can affect the flow pattern and change the dynamic property of wind load.

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A viscoelastic (VE) damper is an effective device for dissipating vibrations in buildings, with a broad range of applications that can effectively mitigate vibrations caused by earthquakes and strong winds. When VE materials are subjected to shear vibrations, their properties change complexly due to their frequency-, temperature-, and strain-level-sensitivities, and primarily in the thickness direction. Many one-dimensional (1D) analytical methods have been extensively studied to understand property changes in this direction, particularly for different conditions such as random loads, long-duration loadings, and multilayer configurations of VE materials. However, these methods involve very detailed and complex calculations that lead to great computation times. Pursuant to these, this study proposes a simplified 1D analytical method with high computational efficiency. This method considers the 1D modeling of each layer in multi-layer dampers and employs a constitutive model that can reproduce the temperature-, frequency- and strain-level- sensitivities of VE materials to calculate the properties of VE dampers. However, this method has not yet been applied to simulate the response of VE dampers under wind-induced vibrations. Thus, this study uses this method to simulate a wind-induced vibration experiment on a six-layer VE damper. The analytical results show a good agreement with the experimental results.

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In recent years, the combination of base isolation and active structural control (active base isolation) has been extensively studied. Conventional design approaches for control systems rely on trial-and-error methods and numerical simulations, which are time-consuming. To propose a simple design method for active base isolations, this paper validates the effectiveness of the peak factor from the Japanese design code in estimating the maximum response and maximum control force as the first stage. We considered different superstructure heights, isolation natural periods, and numbers of hysteretic dampers for validations. Numerical results indicate that the peak factor proposed by Japanese design code accurately estimates the maximum control force in all cases. However, it can only be used to estimate the maximum response for active base isolations within the elastic range.

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This paper describes examination on aerodynamic stability of 4-span continuous steel deck box girder bridge with 144m main span length crossing class A river with a width of 145m and a national route. This bridge is in an open area where typhoons pass through well, and flexible. Moreover, this bridge has the ratio of width B to height d is B/d=2.67, the possibility of galloping and vortex-induced vibration is predicted. So, wind tunnel tests are conducted to investigate the aerodynamic devices. From the spring supported model wind tunnel tests, galloping and vortex-induced vibration occurred in case of without aerodynamic devices, and it is concluded horizontal plates and double flaps are necessary to suppress galloping and vortex induced vibration. However, structural safety is ensured by horizontal plates. Therefore, take account of the cost, it was decided to attach double flaps if any usability issues occur after the bridge is constructed.

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In recent years, the number of super high-rise buildings adopting seismic isolation structures has increased. On the other hand, wind forces increase as buildings become taller, and the possibility that the seismic isolation layer will exceed its elastic limit and exhibit elasticplastic behavior increases. In addition, in current wind-resistant designs, a time history response analysis is required when the seismic isolation layer exhibits elastic-plastic behavior. However, this is impractical as it requires huge calculation processing. The Recommendation for Loads on Building (RLB) of AIJ allows for a simple calculation of wind response parameters without using time history analysis. The RLB also considers the simultaneity of wind forces and stipulates a method for combined of wind loads. However, there are few cases where the shearing force of a seismic isolation layer under combined loads has been evaluated. Therefore, in this study, we target a super high-rise seismically isolated building with elastic sliding bearings and evaluate the combined loads based on the RLB.

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With the increasing height of base-isolated buildings, it is necessary to considering their wind resistance performance in design. Specifically, for base-isolated buildings with elastic sliding bearings, there is a concern that, under along-wind forces with a mean component, the windinduced shear force might cause sliding even if it is lower than the sliding load set calculated in seismic-resistant design, potentially leading to the displacement response larger than the design value. Previous studies have demonstrated the relationship between the friction coefficient of sliding materials and the increment of the displacement response. However, these studies used to involve forced displacement method to carry out the experiments, which differ from actual wind loads. In this study, we conducted load-controlled excitation experiments to simulate the real along-wind force with a mean component. From the experiment results, the effects of the maximum wind force and the gust factor of wind force on displacement is investigated.

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This study presents a statistical analysis of the spatial distribution of the hourly variations in the wind-direction angle in Japan (including the offshore areas) using the local objective analysis data. The spatial distribution of the year-round average indicated that the variations over the land areas were larger than those over the surrounding sea areas; notably, the variations over offshore areas were smaller farther away from the coastline. In winter (January), the variations in the wind-direction angle were large near the Japan-sea Polar airmass Convergence Zone (JPCZ) and the local discontinuity line. In summer (July), the variations in the wind-direction angle in the Pacific Ocean were smaller than those in the Japan Sea. In the coastal areas, the variations increased temporarily during certain periods; this could be attributed to the periods of transition between the land and sea breezes. The results suggested that the variations in the wind direction were seasonal and diurnal and were primarily affected by the regional climatic conditions.

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In previous reports, the authors have investigated the characteristics of winds focusing on the coastal area of Aomori Prefecture using various methods. Specifically, in addition to longterm observations at lighthouses, we have conducted observations using anemometers mounted on ferries that regularly operate on the ocean, and vertical Doppler lidar on land along the coast. In this paper, we compare the observation results obtained with the wind model used for design and consider the risks of offshore wind, which will be introduced in the future.

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The introduction of offshore wind power generation is accelerating in response to the Japanese government's 2030 renewable energy ratio target. In this study, meteorological and oceanographic data were refined to evaluate the effects of meteorological and oceanographic conditions on the construction process of the foundation and wind turbine. A multi-agent simulation (MAS) was used to simulate the foundation and windmill construction process, and an evaluation of process delays was conducted based on data from ERA5 (ECMWF), MSM, and CWM (Japan Meteorological Agency). The results show that the number of construction days increases by a factor of up to 1.3 compared to the case using MSM/CWM data and ERA5 data.

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