In this study, we reproduced the results of the wind tunnel experiments on a greenhouse with wing-like cross-section (Uematsu 2004) by CFD. We examined the appropriate analytical conditions for the boundary layer turbulence and compared the results with the experimental ones. From the comparison we confirmed the validity of the analytical model. Based on the results of a parametric study in which the heights of windward and leeward walls, curvature of the roof etc. were changed over a wide range. We propose on optimum cross section on of the wing-shaped greenhouse. This cross-section reduces the drag force significantly compared with the conventional ones.

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The purpose of this study is to gather wind response data of a base-isolated building for calculating wind response by an equivalent linear response method. This paper describes wind response characteristics of an isolated layer, which are obtained from analyzing wind response time series by the rain-flow method. Peak displacements and shear forces of the isolated layer occurring at the same time as peak displacement are selected by the rain-flow method. The results obtained in this study are as follows: 1) The relationship between the displacement and shear force amplitudes agrees with the restoring force characteristics. 2) The probability density of shear forces with periods larger than 1.5 seconds agrees with the Rayleigh distribution. The probability density of displacement amplitudes is obtained from that of shear force by transformation of variable. 3) The average values of minimum peak and maximum peak displacement obtained by the rain-flow method (center displacement) presents the variation of the average displacement momentarily produced by plasticity of the isolated layer.

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In order to realize a strait crossing, a super long-span bridge with excellent economic efficiency and aerodynamic performance is required. Utmost concern for such super long-span is aerodynamic stability. The Third Bosporus Bridge currently under construction has a new composite form of cable-stayed bridge and suspension bridge. It’ll be the first application of the cable-stayed suspension bridge. A cable-stayed suspension bridge has advantages of both cable-stayed and suspension bridges, and is suitable for super long-span bridges. In this study, aerodynamic characteristics, in particular flutter of super long-span cable-stayed suspension bridges with different configuration and span length are analyzed and compared with that of ordinary suspension bridges.

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A feedback control is applied to amplify the flow-induced vibration of a circular cylinder. In this control, a flat plate located upstream of the circular cylinder is driven by linear actuator in real time with the flow-induced vibration of the cylinder. Then the fluctuating flow generated by the excitation with translational motion of the flat plate controls the vibration response of the cylinder. The cylinder response was amplified effectively when the flat plate was driven by the feedback with the time delay of 0.7T ~ 0.9T, where T is the vibration period. Although the feedback control characteristics with the flat plate excitation are totally similar to the conventional circular cylinder excitation, the flat plate excitation is less effective to amplify the flow-induced vibration than the circular cylinder excitation.

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A feedback control is applied to amplify the flow-induced vibration of a circular cylinder. In this control, a flat plate located upstream of the circular cylinder is driven by rotary actuator in real time with the flow-induced vibration of the cylinder. Then the fluctuating flow generated by the excitation with the rotational motion of the flat plate controls the vibration response of the cylinder. The control effect changed depending on the distance C between the trailing edge of the flat plate and the leading edge of the cylinder. The cylinder response was amplified effectively when the flat plate was driven by the feedback with the time delay of 0.1T ~ 0.2T for C ≤ 0.50D and 0.5T ~ 0.6T for C > 0.50D, where T is the vibration period and D is the diameter of the cylinder. The cylinder response was efficiently amplified with the low feedback gain in the case of C ≤ 0.50D.

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In recent years, damaged transmission lines were found out, and the behavior of gust and the flying objects by the tornado are clarified. In this paper, we carried out the three-dimensional elastic large deformation analysis using tower-and-conductor interaction model and clarified basic response characteristics of the tower for the wind velocity field caused by the tornado. We modelled the wind velocity field by two-dimensional Rankine vortex and set the path of the tornado for the transmission line as a parameter. When the tornado is passing at the left hand side of the tower at the maximum wind velocity radius around, the axial force in the tower reached the maximum value. The response level caused by the tornado of the F2 exceeds some response levels of the tower by the current design method.

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To explain the galloping suppression mechanism of a loose spacer, the authors performed wind tunnel tests using a sector model of four-bundled conductors with or without rotatable sub-conductors. When the rotatable sub-conductors revolved due to wind, a large moment acted on the entire four-bundled conductors in the opposite direction to that of the angle of attack. Thus, whereas galloping occurs with a certain amount of angle of attack, the angle of transmission lines with loose spacers is hard to enlarge the range of galloping. Even when the angle of attack reaches the range of galloping, the amplitude of the galloping decreases.

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This study aims to propose the warning system for preventing overturning accidents. By considering the overturning mechanism, this study shows three parameters, crosswind velocity, direction and vehicle velocity, are necessary for preventing accidents. Predicted value for crosswind can be obtained by using the short-term prediction method. With this value and the correcting method of wind fluctuation characteristics using up-crossing rate, the system can judge whether accidents may occur. Finally this system will provide the warning information about decreasing vehicle velocity for drivers before passing strong crosswind area.

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Wind-tunnel investigation for a long-span cable-stayed bridge with a 1/150-scaled aeroelastic full model showed a different result from that with a 1/70-scaled section model. Vertical vortex-induced vibration was observed in the full-model test but not observed in the section-model test. In order to investigate the difference, a wind-tunnel test study with an extracted 1/150 section-model test pointed out the possibility of Reynolds number dependence of vortex-induced vibration due to the different model scale and model details. In this study, by conducting the measurement of Strouhal number of wake flow for both 1/70 and 1/150 section models, further study on the Reynolds number dependence of vortex-induced vibration of box-girder cross section is carried out.

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In this study, the tower loading of wind turbine and the fatigue load of high tension bolt during operation are evaluated and validated in Taikoyama wind power plant in which the same type wind turbine was collapsed due to fatigue failure. Measurements of acceleration and strain are carried out and control parameters are identified using the measurement data. The average stress on tower top is found to be in the tension side for all design wind speed. The relationship between the stress of tower wall and high tension bolt in flange joints is obtained by using the three dimensional FEM analysis. Fatigue load analysis of high tension bolt is evaluated and shows that the decrease in the initial tension of bolt causes the fatigue failure. 

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In the field of small wind turbines, effects from wind direction fluctuation has long been a difficult problem for researchers. Particularly the lack of large scale variable direction wind tunnels made it difficult for researchers to obtain actual scale data and to confirm the accuracy of calculations. In this paper, a new type of variable wind direction revolving type wind tunnel is developed and verified. Compared with previously developed wind direction fluctuation wind tunnels, this revolving type of wind tunnel showed outstanding cost performance and a significant increase in speed of wind direction fluctuation. Initially the inherent design resulted in non-linear performance in regard to lateral offset from the center of the wind tunnel due to the variation in relative air velocity, however this was effectively corrected by providing a simple system of vertical variable air intake louvers.

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To establish an efficient driving method for generating high-Reynolds number homogeneous turbulence, a random-phase method was applied. In previous studies using this method, the input disturbance composed of forty frequencies could induce rapid development of high-Reynolds number homogeneous turbulence. Here, we attempted to determine the least number of frequency components for efficient turbulence generation.We used an input signal composed of two frequencies, and investigated characteristics of the turbulence.

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We have been using Split-Film-Probes (SFP ) to measure wind velocity in our thermally stratified wind tunnel. However it takes long time to calibrate the SFPs. It is necessary to calibrate them in several air temperatures because their output voltages change not only with wind velocity but also with air temperature. On the other hand, if we use Particle Image Velocimetry (PIV), it is not necessary to calibrate them with air temperatures. It also reduces the test durations drastically since they can measure many points at one time. In this research, we aim to find out appropriate measuring method of PIV and confirm the measurement accuracy of it so that we can utilize them to measure wind velocity in our thermally stratified wind tunnel. We examined the measurement accuracy of PIV for flow fields around buildings in unstable turbulent boundary layer by comparing measurement results of SFPs. By appropriate particle seeding, camera setting, and image processing, the measurement results of mean wind velocity by PIV and SFPs matched well with each other.

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Recently, compact weather sensors (CWSs) become commonly available. However, we have little knowledge about the data quality of CWSs, especially the effect of the integrated design of sensors. To evaluate five CWSs, we made wind tunnel experiments.The data by some CWSs shows flow distortion by the pillars near the receiver-transmitters of sonic anemometer.We also made field observations for two months, mean values of each meteorological element by CWSs are compared with reference values measured by the conventional meteorological instruments. The difference of the mean values falls within the specification errors of CWS. 

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It is well known that tornadoes are visualized by funnel clouds and flying debris. If the relationships among the size and strength of tornadoes, the shape and size of funnel clouds and behaviors of flying debris become clear, it may be possible to evaluate the size and strength of a tornado directly from photos and videos. Therefore, funnel clouds and debris clouds formed in tornado-like flow generated by LES were investigated in this study. As the result of this study, the height of funnel clouds is controlled by the strength of the tornado; the width of funnel clouds is controlled by the humidity and the pattern of flying debris were controlled by Tachikawa number and swirl ratio.

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Permeable materials such as louver and punching metal are used as an outer skin attached to the outside of building walls. However, the wind loads acting on such a permeable material have not been clarified. In the present study, a wind tunnel test is performed to investigate the wind loads on permeable panels attached along the perimeter of the rooftop of a high-rise building. The permeable outer skin is modeled by a thin metal plate with rectangular holes. The porosity and size of the openings are changed in the test. The effects of those parameters on the wind loads acting on the outer skin are understood through the test.

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The cladding and components of high-rise buildings are always exposed to dynamic wind forces. The wind forces are characterized by a long duration compared with seismic forces. In many cases, the cladding and components are designed based on the short-term allowable stress for the design wind load with a return period of 50 years. Therefore, they may be damaged by fatigue during the building’s lifetime. In this study, the characteristics of fatigue accumulation in the cladding and components of high-rise buildings are investigated based on the results of a wind tunnel test and the observation data about 50 years at 14 meteorological observatories in Japan.

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Wall systems of low-rise buildings have commonly failed during extreme wind events, such as typhoons and tornadoes. In order to understand the failure mechanism of wall systems in detail, full-scale experiments have been conducted using wall specimens with metal sidings assembled in the same way as actual walls. Two types of loadings, i.e., step-up loading and realistic wind loading generated from wind tunnel data, have been employed. The results indicate that there is no significant difference in wall capacity obtained from different loadings, although failure mode progressions of the wall systems under different loading types exhibit a clear difference.

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The present study investigates the buckling behavior of open-topped oil storage tanks based on a finite element analysis. The distribution of wind force coefficients on two to three tank models in various arrangements are measured in a wind tunnel. The results on the mean wind force coefficients are used for the buckling analysis. First, the fundamental characteristics of buckling behavior are discussed with isolated models. Then, the effects of flexural rigidity of wind girder at the top on the buckling load and mode of tank shells are investigated based on a parametric study. Finally, the effect of wind force distribution on the buckling load is investigated. The results indicate that the distribution of positive wind force coefficients affects the buckling behavior significantly. The buckling load decreases for some arrangements.

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The number of the high-rise buildings with hysteretic dampers are increasing in Japan.  When the hysteretic damper is yielded against the wind force, the consideration based on energy is useful.  In that case, it is important to examine the energy absorption caused by structural damping as well as hysteretic damping.  In this paper, the energy absorption characteristic of the structural damping is discussed based on the time history analytical results that use the multi-degrees of freedom models with the hysteretic damper models.

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Modeling of wind-induced torsional moments on tall buildings is discussed in this study. In this study, fluctuating torsional moment coefficient and power spectral density are estimated from experimental results for aerodynamic forces on tall buildings with various side ratios, and then mathematical formulas are proposed to fit them. The formula of the power spectral density is composed of three components, which are turbulence produced by oncoming flow and the building itself, Karman vortex shedding and re-attached flow on the side face. Torsional response calculated from the proposed formulas shows good agreement with the analytical result using the experimental values.

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Wind loads on cladding fins attached to a high-rise building vary depending on the building shape, wind direction, the position of the fins, and so on. This paper discusses experimental results of peak wind forces acting on fins with various arrays. The influence of aspect ratio and side ratio of the building on wind forces acting on fins are also discussed based on experimental data for building models without fins. The nearer to the corner, the fin locates, the higher the wind force becomes, and the wind force acting on the closest fin to the corner shows the largest value. The effects of the aspect ratio and the side ratio of the building are not significant.

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Our goal is to estimate structural safety under strong wind force with long duration due to mature typhoon. For this purpose, dynamic response analysis is one of effective tools and requires external force time series of strong wind. This paper proposes a method to produce strong wind time series under mature typhoon, in order to supply severe wind force for dynamic response analysis. The maximum potential intensity (MPI) of typhoon as a lower limit of central pressure is estimated over the southern sea of Tokyo, Japan, and reaches 900hPa at 500km offshore from Tokyo. The maximum surface wind speed due to severe typhoon with 900hPa of central pressure as MPI is 34.8m/sec at Tokyo.

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The occurrence of tornado, it needs the large-scaled instability and convective flow field. Tornado some time comes from meso-cyclone which contains two flow patterns such as upward flow and rotational flow. Also down draft occurs under the meso-cyclone, we need to add the asymmetrical flow pattern in modeling of tornado. According to the previous studies about modeling of tornado such as tornado simulator, there is no model containing those phenomena. The motivation of this study is propose the new type of flow pattern which contains instability, convective flow, upward and rotational flow, asymmetrical flow pattern.

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Windbreak nets are usually used as wind resistant devices. Estimations
of effect of windbreak nets are empirical, so the objectively and accurately estimation
method has been needed. One of the methods is a computational fluid
dynamics technique. However pressure loss coefficients of windbreak nets
are not clarified. In this study, pressure loss coefficients for CFD are
measured by wind tunnel tests, and the relation between pressure loss
coefficients and porosity ratio quantified by the Fourier transform of
images of windbreak nets were investigated. As the results of this
investigation, it was clarified that pressure loss coefficients of wind
break nets are decided by porosity ratio and diameter of fiber.
Moreover, PIV test showed that flow fields behind those windbreak nets
were reproduced by CFD including those pressure loss coefficients.

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Large eddy simulation of flow past a rectangular cylinder using the non-inertial coordinate system fixed on the movable cylinder is described. It is well known that treatment of conditions at outer boundary is very important for efficient calculations, particularly non-inertial coordinate system with rotation, in which situations the velocity in region far from the origin are rather different. In this paper, boundary conditions of outer boundaries are also treated properly. Then, unsteady wind forces and the unforced vibration responses of rectangular cylinder (B/D=2) in heaving and torsional mode were calculated using the provided system. It is found that, computations predict the aero-elastic instabilities well, and the validities of this calculate system are confirmed.

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Prediction of location and time of occurrence of a tornado is very difficult,so directly observation of tornado is almost impossible.In order to understand the characteristics of tornadoes,researchers have investigated tornado-like flows generated by experimental tornado simulator devices and numerical fluid simulations.In this study,a moving tornado-like flow simulator was reproduced by LES analysis,and effects of boundary conditions of inlet,vanes and outer fields on tornado-like flows were investigated.Moreover,3D-PIV method showed the three-dimensional flow structure of tornado-like flow generated by the moving tornado-like flow simulator.

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Large negative pressures are observed experimentally on the sidewall of a building with a setback in local pressure zone. Numerical simulations using two types of SGS models, Standard Smagorinsky model and Coherent Structure Smagorinsky model (CSM model) for LES with meshes in different resolutions are carried in low-turbulence uniform flow. Both models show good agreement with experimental results in case of the higher mesh resolution, which can reproduce the large negative peak pressure. CSM model shows more accuracy results than the Standard Smagorinsky model even by the low mesh resolution.

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As a measure for giving adequate inlet boundary conditions in LES of spatially developing turbulent flows, attention was paid on ‘linear forcing’, a method for generating isotropic turbulence, and a specification method of turbulence length scale using the linear forcing was proposed in this research.  The applicability of the linear forcing to LES and the validity of the specification method of turbulence length scale were evaluated using LES results of isotropic turbulent flows.  As a result, it was found that the basic characteristics of isotropic turbulence which should be generated by the linear forcing is reproduced under the grid conditions satisfying that the ratio of the subgrid-scale energy dissipation to the total dissipation is less than 0.6. Moreover, it was confirmed that the time-averaging length introduced in this linear forcing could vary low-frequency power spectra of velocity to control turbulence length scale.

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In the present study, the new Source Term Estimation(STE) method was developed to be applied operationally for the emergency response system of nuclear power stations. It is a residual method to minimize the error between the observed and the calculated data of dispersion model, named a Transfer Coefficient Matrix (TCM) based on the assumption of unit release rate. Our developed STE method uses the modified Gaussian plume model to be fitted with the concentration data of wind tunnel experiments conducted for the nuclear safety assessment. We validated our developed model with the concentration data of wind tunnel experiment of Tokai-Daini nuclear power station.

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In order to predict the flying behavior of debris through wind, a fluid-structure interaction method is developed. The main idea is that the domain of the flow simulation is deployed over the limited area around the flying body which is wide enough to evaluate the aerodynamic forces, and the computational domain moves with the flying body. The numerical flow simulation method employed is the finite element method. The ALE method is applied to handle the moving mesh. In order to examine the fundamental featureof the present method, a falling sphere in still air and in horizontal flow are calculated.

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In order to evaluate the impact of missiles caused by tornado, a study on the velocity prediction of flying debris in a tornado-like vortex was carried out by numerical simulation. A series of unsteady flow fields of a tornado-like vortex was generated by Large Eddy Simulation. The aerodynamics of debris was examined and the range of aerodynamic parameters of debris resulting building damage was investigated. The trajectories of flying debris and the statistical distributions of the maximum speed of debris were obtained in various conditions i.e. the release height and the aerodynamic parameter of debris, the maximum tangential wind speed, the radius of maximum tangential wind speed and the traveling speed of tornado. Relation between the maximum ground speed of debris and the maximum wind and traveling speed of tornado was obtained as a function of aerodynamic parameter of debris.

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Recently, it becomes possible to estimate wind flows over complex terrain using the numerical model which is directly represented by terrain features. A lot of previous study, wind flows is predicted by standard k-ε model. When wind flows over steep complex terrain is estimated by standard k-εmodel, it is expected that predictive accuracy falls. This study examines the applicability of modified RANS model of wind over various complex terrain. Firstly, we elucidate the applicability of modified RANS model for the prediction of the wind velocity profiles over a 3D simple hill-shaped terrain, comparing the wind tunnel results. Next, modified RANS model is applied to estimate complex flow field over steep two-dimensional 2D slope which has influence of wind direction. Finally, we investigate applicability of estimation of wind flows over two kinds of complex terrain.

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In order to generate a rough-wall turbulent boundary layer, LES with pseudo-periodic boundary conditions and artificial fluctuation on inflow surface is carried out.  Karman-type spectrum density function of atmospheric boundary layer with large turbulence scale can be simulated as same as the property of wind tunnel tests.  As the result, the windward overturning moment in the along-wind direction can be simulated in lower frequency part.

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In order to examine how accurately the Weather Research and Forecasting model (WRF) and JMA Meso-ANALysis (MANAL) can estimate wind speed fields in coastal waters, one-year WRF simulation is conducted for the coastal area off Shirahama, Wakayama Prefecture, and the accuracy is verified using in-situ measurements from two offshore sites. It is found that WRF can estimate coastal wind speed fields much more accurately than MANAL, with a bias of less 0.3m/s (about 5% of annual mean wind speed) and a RMSE of less than 1.9m/s (35%).

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The number of bridges that needs rehabilitation maintenance due to structural deterioration has been increasing rapidly in Japan. The prediction of deterioration of structure is one of the major subjects of aging atructures. Especially for structures located on coastal areas, deterioration due to corrosion and chloride attack to steel structures and reinforcing steel bars in concrete is an urgent proble. In order to operate efficient maintenance and management, it is important to predict the amount of air borne sea salt adhered to each member of structural surface. In this srudy, the mechanism of the deposition to a structural is to be discussed based on field observation and numerical calculation.

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This paper studied the generation mechanism of a unique downslope wind in the west coast
of  Lake  Biwa,  Shiga,  Japan.  This  strong  downslope  wind,  feared  as  “Hira-Oroshi”  for
millennial years shows the narrow gust of a few kilometers in the various location within 10
km width area.  
This  feature  cannot  be  explained  by  the  conventional  mechanism  of  previous  studies:  the
location of downslope wind is strongly restricted by the location of valley in mountain range.
Due  to  such  distinct  characteristic,  the  numerical  prediction  of  this  gust  wind  is  too
inaccurate to use operationally.    
Considering strong demands to the prediction of this gust wind, this study aims to elucidate
the mechanism via very fine numerical forecast model with the horizontal resolution of 50 m.
The  results  successfully  represented  the  narrow  gust  wind  structure  in  the  edge  of  the
mountain range. 

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In 2004, 10 typhoons made landfall in Japan, which recorded the largest number since the Japanese meteorological observations began. Among them, Typhoons 0416 and 0418 caused a severe damage by the storm surge to coastal regions around the Seto Inland Sea. We combined the atmospheric meteorological model (WRF) and the ocean model (POM) to reproduce the storm surge occurred in the Seto Inland Sea due to Typhoons 0416 and 0418, both of which followed the same path. In the present study, drifting effects causing storm surges were focused, and the differences in regions damaged by the two typhoons were investigated. Comparisons of the observed and calculated tidal values at Takamatsu, Uno, Matsuyama, and Kobe sites showed that for Typhoon 0416, the calculated value for the tidal-level deviation was overestimated at Takamatsu after the typhoon had passed and at Uno before the typhoon approached. Moreover, for another typhoons following a similar path, we found that the wind directions differed depending on whether the typhoon passed most closely was on land or on the sea, and that there was difference in sea areas where large tidal-level deviations occurred due to influence of these winds.

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On the basis of CFD for air flow and a blowing and drifting snow simulation model, we developed a technique to reproduce roof snow shapes for the purpose of constructing and operating a roof-snow hazard assessment system. As a turbulent flow model, we used the Durbin-type k-ε model. We also measured the actual data of roof snow to improve the accuracy of the model by comparison. The study periods consisted of a short-term snow accumulation (a span of approx. 5-10 days) and a long-term snow accumulation (several months). We compared the different methods of calculating friction velocities u_* and dealing with snow blowoff phenomena. The method of finding u_* from the logarithmic law showed the best reproducibility for short-term snow accumulation, and the method of finding u_* from the turbulence energy showed the best reproducibility for long-term snow accumulation. In addition, giving meteorological conditions to many split events of blowing snow improved reproducibility for both short-term and long-term snow accumulations.

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Numerical flow computations and wind-tunnel experiments are conducted for evaluating the wind flows within an urban canopy.  Computations are done by LES.  Their time-depending inflow boundary conditions are provided by SEM with considering anisotropy of the Reynolds stress components.  The computed results are verified with the wind-tunnel experimental results.  The time-averaged velocity profiles of LES coincide well with the experiments.  The LES results, however, show larger magnitude of the Reynolds stress properties.  The cause of this excess estimation is due to the discrepancy of shape of building models among experiments and LES.

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