The Japan Meteorological Agency (JMA) has started routine operation of an observing network of 1.3 GHz wind profiler in April 2001. The system named as WINDAS (Wind Profiler Network and Data Aquisition System) is composed by 25 wind profilers through the Japan Islands and the Control Center at Tokyo. The outlines of the system, data control methods, reliability of the system and examples of data analysis are presented and discussed.

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The correction factors for various anemometers are proposed and their accuracy was examined. As a result, the change in the averaged annual maximum speeds almost disappears and the variation of 100-year wind with the statistical period decreases. Comparing the sampling errors in 100-year wind, it was found that the proposed correction factors are more accurate than conventional ones. In this study, a new method for estimating design wind speed is proposed to account for effect of unsteadiness in the natural wind. Design wind speeds evaluated by this method are consistent with those obtained by the conventional method at the meteorological stations where wind observation started before 1948, and give larger values at the stations where observation started after 1961.

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Using Digital Surface Model measured with remote sensing technology, some estimations of surface roughness were carried out in urban areas. Roughness density, total space and total volume of the surface roughness were estimated for each area of 3 terrains; Kanda-Marunouchi, Yokohama-Kouhoku, Meguro-Himonya. As the results of the estimations, Digital Surface Model has enough accuracy for the quantitative estimation of the surface roughness in urban areas and can be used for the estimation of the surface roughness.

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It is well known that some topography causes a wind increase and unexpected gust factors. To examine the characteristics of the gust factors by every wind direction throughout Kyushu area, the authors have organized a database of strong wind data classified into non-typhoon and typhoon. The authors have confirmed the different tendencies of gust factors according to the wind direction at several terrains using the database. The database shows that the gust factors of winds by typhoons are generally higher than by non-typhoons even when the wind speed is high. And the authors have found that the gust factor at Imajuku, the western part of Fukuoka City, is much higher in southern wind direction. Such a database on the gust factors is useful to estimate a peak gust in strong winds.

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The wind structures in the lower atmosphere has been investigated by Doppler sodar in Okinawa since 1994 associated with the wind resistant design of high-rise buildings. The measurements were carried out under strong wind conditions on both typhoon and non-typhoon days. It is suggested that the significant influence of the surface topography on the vertical distribution of the observed mean wind speed is limited in the lowest 100m above the ground at the observation site. In order to investigate the characteristics of the variations of wind profiles in typhoon and non-typhoon conditions, principal component analysis are applied to the observed data. The first principal components of typhoon and non-typhoon winds are found to be quite different from each other. According to the analysis, the vertical profiles of the non-typhoon winds seem to be mainly determined by the surface roughness, while the turbulence of the atmosphere aloft seems to contribute in a large degree in the formation of the typhoon wind profile. The latter is considered to be responsible for the decent of the layer with a constant wind speed of gradient wind to low altitudes often observed in typhoon conditions.

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In order to investigate effects of the increase of sea-surface temperature due to the global warming on typhoon intensity, Typhoon Simulation was carried out statistically incorporating the sea-surface temperature. The incorporation model of the sea-surface temperature represented typhoon statistics better than a non-incorporation model. The Typhoon Simulation showed that the number of typhoons approaching to Japan decreased while their intensities increased due to the increase of the sea-surface temperature as a result of the global warming effects.

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The objectives of this study are to estimate how wind speed and direction of typhoon change time depending on irregular ground and the thermal dynamics. Governing equations are conservation of mass, momentum, heat and moisture. Physical models are based on the typhoon pressure model proposed by Schloemer, the cloud model by Mellow and Yamada, and the vegetation model by Deadorff. Boundary conditions are based on the radiation for the vertical direction by Klemp, and the open boundary model for the lateral boundary by Orlanski. Using the calculated pressure, the center pressure and the typhoon scale are evaluated. The motion of typhoon is based on the momentum equations. The coordinate origin is always at the center of typhoon. The ground data are allowed to change and the physical values are interpolated at every step. These equations and the scheme are applied to Typhoon T9119, which occurred in Sep.1991. Calculated wind speed and direction agreed with the measured data.

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During the passage of Typhoon Seth(T9429) over the Sakishima Islands, it had formed an extremely large elliptical eye whose horizontal extent reached as much as 100km by 80km in diameter. It rotated cyclonically with a period of 180min, and followed strong gusts of wind exceeding 50m/s. We tried to analyze its detailed structure by comparing surface meteorological data and radar composites obtained during its passage. As a result, we can obtain the azimuthally wave number two structure in pressure perturbation field with elliptically elongated rainfall distribution corresponding to the elliptical eyewall. Aerological data just outside of the elliptical eyewall indicates a warm core structure with convective unstable stratification at lower 3km.

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In Japan, there are three famous local high winds, called “Kiyokawa-dashi”, “Hiroto-kaze” and “Yamaji-kaze”. They are mechanically induced local high winds due to the topography. Last two winds are known as “downslope-wind” caused by upwind high mountains. In the present study, “Hiroto-kaze” and “Yamaji-kaze” were analyzed based on in-situ measurements including mountain-top data. It is found that typical downslope wind appears as “step-wise” time series, which suggests a critical meteorological condition. During the local high winds, potential temperatures of foot and top of the mountain shows almost same values, which supports the downslope-wind. Local surface pressure depression at the foot of the mountain was observed, which suggests the hydraulic jump.

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Field measurement of outdoor wind and thermal environments were carried out in the last summer at the Haramachi City of Fukusima Prefecture. The aim of the study is to investigate the present outdoor thermal environment condition of urban area and the heat mitigation by means of using the effects of trees, ponds and river. Measurements obtained for cold north-east wind (or Yamase, name in Japanese) and air temperature showed that the records were not so high. Water temperatures from river and sea were also measured, and the readings both showed higher than air temperature in surroundings. Air temperatures measured from the river area showed cooler than around residential and urban areas. It is because river played an important role as a passage of cold air from sea.

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The low-altitude inversion layer above the ocean prevents the diffusion of the aircontaminants released in the coastal area. Additionally, it is known that the vertical gradient of water vapor pressure increases due to the suppressed diffusion in the inversion layer and the duct propagation phenomenon of the microwave arises under the layer. Therefore, the inversion layer affects the radar operation. Observations of vertical profiles of temperature and humidity in the lower atmosphere off the south coast of Kanto were carried out on 12 May 1999 (helicopter-borne) and 3 July 2000 (shipboard) in order to clarify the structure of an inversion layer above the ocean. The inversion layer was found out at the height near several hundred meters in both observations. Aerological data enclosing the area of shipboard observation indicate that environmental downward air motion seems to have some crucial role on the forming of the stable layer. On the other hand, aerological data indicate upward air motion in helicopter-bome observation. Sea surface temperature and surface wind distribution show the existence of the Stable Thermal Internal Boundary Layer. The observed layer seems to be the top layer of the boundary layer.

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Flow and pollutant diffusion in an urban environment have been studied in a wind tunnel under three atmospheric conditions: stable, neutral and unstable by using Laser Doppler Velocimetry (LDV), thermocouples and a hydrocarbon analyzer detector (FID). The flow and diffusion fields in the boundary layer in an urban environment were investigated in three flow obstacle cases: i) without flow obstacles, ii) after 2-D fence, and iii) after 3-D cubic building model. Ethylene, C₂H₄, is used as tracer gas. Gaseous pollutant is discharged in the simulated boundary layer over the flat area. The effluent velocity of the pollutant is set to be negligible. The results obtained are as the following: a) the inner boundary layer produced by flow obstacles is very thick around the wake region due to the turbulence mixing, b) All turbulent velocities is reduced by the stable stratification, c) the maximums concentration appears around the wake region of the obstacles. The concentration spreads measured in the experiment may be used for the evaluation of numerical models and expert estimating of air quality in the urban environment

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The mechanism for composing air temperature field in an outdoor space is explained with new concepts. Here, all heat factors in the outdoor space are treated simply as real or virtual heat sources and sinks. The technique of numerical simulation is used to derive those new concepts. We propose the scales for assessing the contribution of each heat source or sink to air temperature distribution in the outdoor space as CRO (Contribution Ratio of Outdoor Climate) l, 2, 3 and 3.5 according to the concept of CRI (Contribution Ratio of Indoor Climate). These scales quantitatively indicate the capacity of one single heat source in the outdoor space for diffusion and how much that heat source will raise the temperature at a point in question. The scales are applied to assessment of outdoor thermal environment.

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The authors have proposed CRO (Contribution Ratio of Outdoor Climate) according to the concept of CRI (Contribution Ratio of Indoor Climate) in order to estimate outdoor thermal environment. However, there are many different points between indoor and outdoor environment. For example open space is treated in outdoor environment while closed space is treated in indoor environment. The environmental control parameters are also different between indoor and outdoor environments. Thus, we propose NCRO (New Contribution Ratio of Outdoor Climate) for the more practical use in outdoor environment. This index stands for contribution ratio of factors influencing to convection field and radiation field. The effects of surface temperature change of composition elements of outdoor space and artificial heat releases on outdoor thermal environments were estimated using this new index.

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This paper investigates the method for controlling the airflow in and around a building in order to improve the indoor thermal comfort by utilizing cross-ventilation. In the first part of the paper, field measurement was carried out to evaluate the effects of cross-ventilation on indoor thermal comfort. It was confirmed that the comfortable indoor thermal environment could be attained in a considerable part over summer period by controlling the window opening in order to maintain PMV value within the range -0.5<PMV<+0.5. The latter part of this paper reports on the CFD predictions of flow in and around a building. Here, the effects of the planted trees arrangements around the building, the openings locations and the size of openings on the building were numerically investigated.

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Large scale sound propagation through the atmosphere is influenced by the local wind conditions. The wind prevents straight paths of the sound waves and may result in “abnormal sounds”. The objective of the present study is to simulate this class of sound propagation problems, in which the ambient medium is moving. The basic wave equations are derived from the governing equations of the compressible inviscid fluid for the cases of steady wind profiles. The wave equation is transformed to a Helmholtz type equation with respect to the complex pressure amplitude. The present paper focuses on the availability of these basic equations. The standard Galerkin finite element method is applied to solve the Helmholtz type equation. The complex acoustic pressure amplitude, the solution variable, is discretized by the linear triangular elements. An infinite element is employed for the radiation boundary condition. Two cases of numerical examples, in one case the wind profile is uniform and in the other case the wind profile is exponential, are presented in order to demonstrate the effect of wind conditions on sound propagation.

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An increasing number of high-rise buildings are being constructed with unique designs and/or with various facings or components, to improve the quality of life style. This has created the problem of aerodynamic wind noise around buildings, and this problem needs to be addressed. Aerodynamic wind noise occurs at many parts such as rooftop louver sets, veranda frames, etc. Several causes of aerodynamic-noise phenomena have been proposed. This paper considers the cases of vortex sound, called Eolian tones, from respective rectangular frames. This occurs under both separated flow and reattachment flow conditions, and creates a large sound pressure level. Therefore, we first examined the characteristics of pressure on the surface of a rectangular model and the sound condition under a laminar wind tunnel flow. Next, we verified the propriety of Curle’s prediction method for predicting vortex sound from wind force information. Finally, we checked the applicability of Howe’s prediction method for predicting vortex sound from vortices simulated by CFD.

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Full-scale measurements of mean wind speed and wind directions have been carried out in Kashiwa Campus, The University of Tokyo from the middle of 2000. In this paper, some of data are analyzed and compared with past measurement results at the Hongo Campus. From the comparison, it can be seen that the strong wind occurrence wind directions are almost same in two sites and those tendencies are thought as a characteristics of seasonal wind in Kanto plane. And also, a series of wind tunnel experiments are conducted to estimate mean wind speed characteristics in arbitrary site having no available information and an estimation procedure is shown with a comparison example.

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Simulation of the planetary boundary layer was conducted in a wind tunnel of multi-fan type. The wind tunnel was driven by an array of 99 (11 vertical × 9 horizontal) fans whose velocities were individually controlled through a laboratory computer. With the help of a barrier and surface roughness, a turbulent boundary layer was naturally generated as a target. Different methods were applied to reproduce the target boundary layer, and the resulting flow characteristics were compared with those of the target.

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In an attempt to simulate turbulence of the planetary boundary layer, an innovative wind tunnel is developed, which has enormous potentialities for the studies on wind engineering. The airflow is driven by an array of fans settled on a plane at the upstream end of the wind tunnel, each of which is independently controlled by a computer. A typical static method for generating turbulence is quasi-grid method, where a set of grid-like distributed fans are steadily driven with the rest of the fans inactivated. Attention was paid to intermittency of the generated turbulent flow.

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The non-stationary properties of wind velocity fluctuations were investigated with the information entropy of wavelet coefficients. Many time histories of wind fluctuations were artificially generated and the gust response analyses in time domain were carried out using these data. The relationship between the peak factor and the entropy of the wavelet coefficients showed that the non-stationary wind fluctuations, whose frequencies were nearly equal to the natural frequency of the structure, tended to enlarge the peak factor.

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A number of simulation methods have been proposed and applied to estimate extreme pressure acting on structure and cladding components. However, those methods have some limitations and some procedures are not qualified. In this study, a simulation method based on the translation method is investigated, especially from the viewpoint of appropriateness of nonlinear translation function and spectral distortion correction methods. As a result, Cornish-Fisher expansion for theoretical nonnormal random variables, and Edgeworth’s 3^rd order polynomial for empirical data can be recommended as an appropriate nonlinear translation function. And also, usefulness of Yamazaki-Shinozuka’s algorithm for spectral distortion correction is confirmed. Meanwhile, in the case of autocorrelation correction procedure, accuracy of the correction procedure strongly depends on the Gaussianity of simulated normal random variates.

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A visual study has been made of the stably stratified flows over a ridge or a ridge with a valley. The experiments were performed by towing models through linearly stratified saline-water solutions. The Froude number Fr (=U₀/NH) was changed from 0.05 to 1.67 ( and ∞), where U₀ is the towing speed, N the Brunt-Väisälä frequency and H the height of models. Flow patterns around models were visualized and the velocity fields at several vertical cross sections were measured by PIV method. In the case of a ridge with a valley, the flow has converged to the valley and a strong flow has been generated leeward along the slope of the valley at low values of Fr. When Fr>0.8, however, the flow converging to the valley could not been observed.

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This paper describes the effects of inflow turbulence on the flow around a three-dimensional isolated-hill, having a cosine-squared cross-section and a steep slope. For this purpose, two cases of large-eddy simulation (LES) are carried out: one is a numerical condition in which the hill is immersed in a fully-developed turbulent boundary layer; the other is a numerical condition in which a same mean-velocity profile, obtained from the former case, with no turbulence is imposed (i.e., non-turbulent inflow). For the former case, in order to generate instantaneous velocity fluctuations in an approaching flow to the hill, a turbulent flow field in a driver unit set upstream of the hill is calculated directly. Through comparisons between two cases, the significant change in the flow characteristics is not confirmed in both the near- and far-wake region behind the hill.

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Computational domain size required for the numerical prediction of flow over two dimensional ridge and three dimensional hill was investigated by changing the computational domain heights and widths and the distances between the terrain and inlet boundary. It was found that the computational domain heights should be decided so that the blockage is less than 5%, the width of the computational domain should be wider than the length ten times as long as the hill height and inlet boundary should be set so that the distances between the inlet boundary and the terrain center is longer than the length twenty times as long as the terrain height for the two dimensional ridge and ten times for the three dimensional hill. For the analysis of flow over continuous terrain, new boundary treatments were proposed in which the volume of the terrain is maintained. This method shows better result than the conventional one. An additional domain was also introduced at the windward of the analytical domain so that the effect of the upwind terrain was taken into account.

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Wind characteristics over local topography after a wind turbine are studied through Wind Tunnel Experiment. Results are used for validating data for the CFD prediction of the airflow through a wind turbine. The major results are as follows. 1. Characteristics of leeward wind velocity of a single wind turbine model show the characteristics of wake flow after the flow obstacle. 2. The influences of the wind turbine model become smaller with distance from the wind turbine to the downward direction. 3. Significant differences were observed in the drag coefficient of wind turbine model, when the various arrangements of wind turbines were set before the objective model.

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Usually, the wind-characteristics investigation for constructing wind turbines is made by using an observation tower of 30m high and it cannot directly measure the wind speed at the height where the hub of recent high-power wind turbines locates. The present field experiment aims to estimate adequateness in predicting high altitude wind characteristics from the data obtained by the lower observation tower. The observations were made using the tall tower of 70 m high and a Mini Doppler Sodar in Hojo Sand dune, Tottori. Though the observation point locates in relatively flat terrain, the resultant velocity profiles were different from the power-law profile predicted from the data at Z=20 and 30 m. Especially, the wind from The Sea of Japan is strongly affected by a windbreak and the velocity profile showed the flow separation in Z<20 m. possibility of wind power generation was confirmed at the hub height. The wind velocities measured by the Mini Doppler Sodar were well correlated by those by the tower. The mini Doppler Sodar is found to be a promising instrument though the effort improving reliability is still required.

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Hourly data of the wind speed for the period of 1991-2000 have been analyzed in order to find how much the wind is accelerated by the effect of local topography. It has been shown that the wind is accelerated when it blows along a cape or through a narrow gap, or when it crosses a mountain pass (saddle point). This may be because the wind is converged horizontally and/or vertically owing to the effect of local topography. Field observation of wind speed has been made at a mountain pass in the middle of Shimokita Peninsula, Aomori Prefecture. It has been found that the westerly winds increase in speed by 2.7 times as compared with a plain station, whereas the easterly winds 1.5 times. It has also been observed that the acceleration is concentrated within a lower layer of the mountain pass.

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A three-dimensional, computational fluid dynamic model (CFD) model written in the generalized curve-linear coordinate system is developed for use in the prediction of wind potential distribution over complex terrain in limited areas. The CFD model is operated with a meso-scale meteorological model, which is written in the terrain following coordinate system. An iso-parametric coordinate transformation method is applied to prepare the initial and the time-dependent lateral boundary conditions of the CFD model from the product of the meso-scale meteorological model. Some case studies with the nested model were performed and the vertical distributions of the wind velocities produced by the model were compared with those obtained from Doppler sodar observations and the upper air soundings at the nearby meteorological station. Through the comparison, it is found that the nested model can reproduce essential feature of the observed vertical wind profiles well. This indicates that the data transfer from the meteorological model to CFD model is done adequately by the present method.

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In order to study safety in refuge spaces and measures for preventing the spread of urban fires, it is important to predict the temperature distributions in thermal plumes generated by the fires. The objective of this study is to acquire knowledge of temperature distributions in fire-induced flows to serve as a base for the research. In past studies by the authors, their derived relational expressions for temperature distributions in thermal plumes under windy conditions treated the fire region, such as a burning house, as a square heat source through a series of wind tunnel experiments simulating urban fire scenarios. This paper describes a study on the above by larger-scale experiments for the expressions generally used.

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The purpose of this study is to investigate the properties of flames formed around a building under external wind. An experimental study is described using a small-scale enclosure having a prescribed fire source to investigate the behavior of flames emerging from an opening and ceiling of the enclosure at steady state conditions. The fire source in the enclosure was a propane porous gas burner and wood crib. In the experiment, the width and height of the opening, the discharge rate of propane gas supplied to the gas burner, wind velocity and direction to compartment were varied. The modeling of flame length, vertical height and angle are proposed to judge risk fire spread between buildings under the wind condition.

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Experimental study was carried out to understand the characteristics of the high temperature field behind a fire in a turbulent boundary layer and to obtain the verification data for the numerical simulations. The temperature fluctuation was measured by a cold wire behind a two dimensional flame placed on the floor in wind tunnel. The frequency response of the wire was compensated analytically based on the heat conduction equations for the sensor. We evaluate the temperature fluctuation and discuss the characteristics of high temperature field behind a flame.

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Many studies have been conducted to evaluate the strong wind damages to buildings and the relationships between the maximum instantaneous wind speeds and the building damage ratios during typhoons. To evaluate the strong wind damage to a building, a strong wind hazard curve and a fragility curve of a building should be modeled. However, very few studies have been done to investigate those stochastic values and accessed the strong wind risk of the buildings. Hence, the standardization of the structural performance assessment for the buildings will be expected. This study has been conducted to develop the common database and standardized tools for the structural performance assessment for the buildings. Everyone can use this system in the web site of http://ssweb.k.u-tokyo.ac.jp.

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For the recent several years, East Japan Railway Company has been developing an intelligent high wind alert system called ‘WINDAS’. This system is designed to protect trains from extreme crosswind hazard. This system works with continuous wind velocity data measured by anemometers located along the right-of-way. A forecasting model to make short-term prediction of peak winds uses these measurements. If the gusts are predicted with wind velocities above the permissible level, the system issues an alert for the relevant trains to stop or reduce the speed of operation.

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The flowfields around a front-step and a cubic shaped building model placed within the surface boundary layer were analyzed by using various k-ε models; namely standard k-ε, Durbin’s revised k-ε and revised k-ε with mixed time-scale concept. The calculated results are compared with those of wind tunnel experiment. Turbulent kinetic energy k around the windward corner is overestimated by the standard k-ε and the Ω type revised k-ε models, while it is improved by the S type model and the model proposed by Durbin. However, all revised k-ε models overestimate the reattachment length behind the building in comparison with the experimental data.

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In this study, aerodynamic properties of square prism with respect to various angles of attack were predicted utilizing computational fluid dynamics in which LES turbulence model was employed. The results met well with experiments in time average aerodynamics properties, drag force coefficients, lift force coefficients, and surface pressure coefficients for all cases examined here. Regarding fluctuations, which is important when aeroacoustics is of interest, predictions were quantitatively comparable with experiments in the vicinity of 0 degree attack angle, however, the predictions were overestimated for the rest of the cases though qualitative agreement can be observed to some extent. In conclusion, this numerical approach successfully predicts mean aerodynamic properties of square prism, but, further investigation is necessary for predicting fluctuation properties.

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The appearance of a temporal irregularity of aerodynamic force of a rectangular cylinder with the critical depth (D/H=0.6), seems to be such startling phenomenon that is well worth investigating further. In this paper, turbulent flow around a stationary rectangular cylinder with the side ratio D/H of 0.2 to 1.0, has been computed by the LES method at high Reynolds number of 2.2×10⁴. The main objectives of this work are to predict and evaluate characteristics of flows for a stationary cylinder. The computational results of force coefficients such as mean and fluctuating values of drag and lift forces, Strouhal number and flow-configurations correspond well with experimental data. We confirm that the abrupt changes of the aerodynamic force appear irregularly with the time for the cylinder with a critical section. The temporal variation of a drag force between low and high values is certified to be accompanied with the corresponding change of instantenious frequency of lift force, by using of a wavelet transform method and an analysis of frequency histogram. The time history of drag force CD agrees well with variation of the intensity of the wavelet transform coefficients or Strauhal number from the wavelet analysis results of lift force CL.

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This study has focused on aerodynamics for the wind-resistance design about the single and tandem box girder sections to realize a super-long span bridge in the near future. Three-dimensional static analyses of flows around the fundamental three types of single and tandem box girder sections with fairings are carried out by means of the IBTD/FS finite element technique with LES turbulence model. As the results of the analyses, computations have verified aerodynamic characteristics of three types of sections by the histories of aerodynamic forces, the separation and reattachment flow patterns and the surface pressure distributions. The relationship between the shapes and the aerodynamics is also investigated in three types of sections. And the mechanism about the generation of fluctuating aerodynamic forces is discussed.

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Every arbitrary vector field can be expressed by using scalar and vector potentials based on Helmholtz’ theorem. We have proposed a FEM using the potentials for basis function. In the scheme, we previously applied only solenoidal component for incompressible fluid. One of the objectives of this paper is to propose a scheme for abstraction and conservation of the incompressible irrotational component. In the previous study, the solenoidal was abstracted by applying Galerkin method, a MWR, that allows to minimize the variance of residuals of the navier-stokes equation and to adjust the mean value of whole system to zero. The sub-domain method is also one of MWRs and it adjusts the mean value of the residual in individual sub-domain to zero. The latter one provides a weak solution more correctly than the former one. The other objective of this paper is to propose a scheme, which could allow us simultaneously both to conserve vorticity in individual sub-domain and to minimize the variance.

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This study describes the wind force and the pressure characteristics on several D-sectioned cylinders of which section was composed of a plane and an arc at the crossing angular position α. Models of α≤53° have a small drag coefficient, because of the flow separated from the leading edge re-attached on the after body. On the other hand, models of α≥60° have a large drag coefficient due to the complete separation of the flow. When a oblique wind attacks to a D-sectioned model, the strong negative pressure was observed near the leading edge. Galloping on the model of α=53° will occur so that the lateral force of the model has the obvious negative gradient.

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Since an aerodynamic behavior of main towers in tandem arrangement of long-span bridges is very complicated, it has not been completely examined. In this study, torsional vortex-induced vibrations of tandem rectangular prisms with corner-cut are examined by means of wind tunnel experiment. As parametric study, the effects of spacing ratio of tandem arrangement, shapes of corner-cut and turbulent characteristics such as turbulent intensity and scale on torsional responses of the models are investigated. In addition, vortex-onset frequency in the wake of the models is measured, and flow around the tandem prisms is visualized to consider the occurrence cause of torsional response.

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The aim of this study is to clarify the reason why the span-wise coherence of fluctuating pressures on two-dimensional bluff sections is larger than that of fluctuating wind velocities. The surface pressure and the velocity fluctuation around a 2-D model with rectangular section of B/D=5 (B: chord length, D: depth of the section) were measured in grid turbulence and in the artificially generated 3-D fluctuating flow. In conclusion, it is considered that vortex is formed around leading edge and the strong fluctuation of surface pressure by external pulsation is produced by the change of the size of the separation bubble.

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Gust force by across wind fluctuation, which is affected by separated flow from leading edge, cannot be theoretically derived. Therefore, gust force on bridge deck is estimated by experimental aeroelastic response function. However, the formation mechanism of gust force is not known precisely. In this study, to investigate pressure fluctuation of rectangular cylinders, simultaneous surface pressure measurements were carried out in two-dimensional and grid turbulent flows. The results showed that the separated flow from the leading edge of a rectangular cylinder dominantly forms the gust force.

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It is well known that the spatial correlation of fluctuating life force, R_L′, is important to estimate the vertical gust response in frequency domain. Generally, the spatial correlation of approaching flow fluctuation, R_W′, is used for the estimation, instead of R_L′, because the measurement of R_L′ is very difficult. However, R_W′ and R_L′ are not necessarily equal. This difference affects the result of gust response analysis. In this study, the relation of the spatial correlation between the approaching flow fluctuation and the fluctuating lift force were investigated by wind tunnel test. Furthermore, the formation process of the spatial correlation of the fluctuating force was investigated by generating the periodic disturbance near the stagnation point. As results of this study, the transmission process from the flow fluctuation to the fluctuating force with spreading the spatial correlation was clarified.

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The wake dynamics behind a circular cylinder (diameter d) was investigated using a water tank at Re=7.4 × 10³. Deflectors were inserted in the wake as an interference element. Here the deflectors used were a circular cylinder of an equal diameter and a long splitter plate with a chord length of 6d. Attention was made to a discontinuity of the wake dynamics, when the deflectors were traversed upstream horizontally at several levels. As the deflectors were shifted upstream, the base suction coefficient increased gradually, until it fell critically in a similar manner to the previous results using a wind tunnel. An additional wind tunnel experiment performed at the same Reynolds number as in the water tank experiment supported this result, and the increase was found to be due to a Reynolds number effect. Details of the vortex formation process and its correspondence to the change in base pressure were addressed by a particle image velocimetry.

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The characteristics of a flow around a cubic model are experimentally studied by a wind tunnel test. The flow around the model was measured by PIV method. And simultaneous multi-pressure measurements on the model surface were also performed. By using this two method synchronously, simultaneous data set of the flow and the wind pressure on model were obtained. As a result of the measurements, instantaneous reattachment was observed on the roof surface of the cubic model.

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Many papers have been reported the arch-type separating shear layer and Karman vortices formed around a cubic building in a smooth flow. And so various vortices except aforesaid vortices, for example “trailing vortices”, has been formed when flow attacks at a front side of the building. In this report we studied the phenomenon of these vortices by flow visualization and tried to inspect the relation to the fluctuating pressures in a wind tunnel. As a result, the fluctuating pressures reflect the phenomenon of flow visualization. That is, the Karman vortices affect the windward flow and the switching of trailing vortices on the ridgeline between the roof and the side affect the leeward flow.

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Three-dimensional fluid flow around two circular cylinders in tandem arrangement is computed by finite difference method without any turbulence model. The overlapped grid technique is employed in order to catch the flow interference between two tandem cylinders. As the result, the numerical abrupt change of drag coefficients is good agreement with the previous experimental ones.

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Nowadays suspension bridges tend to be long-spanned with the background of the development on wind-resistant engineering. But so many physical problems are still left in the design, and especially, flutter phenomena are the major and serious ones because they are classified into divergent oscillations. Therefore, it is essential to classify flutter instabilities associated to the geometrical shapes of the bridge girders. In this paper, heaving branch coupled flutter for fundamental girders with center barriers is discussed from the point of its generating mechanisms.

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In this paper, flutter analysis of rectangular cross-sections based on k-ε model is discussed. Recently, some successful application of the computational fluid dynamics to the simulation of flutter has been reported. It is noteworthy to mention here that almost all of the aeroelastic application has been performed so far by means of two-dimensional analysis. These good performances of 2D analysis is due to the turbulence viscosity which acts as the mimic spanwise momentum diffusion. However, two-dimensional analysis is essentially an approximation and thus it is necessary to examine physical consistency of the obtained results. In this paper, the authors have followed Matsumoto (1994, 2001), who have investigated flutter characteristics of generic rectangular cross-sections, by means of k-ε model and physical consistency of the obtained numerical result is examined. As a result, good agreement was obtained for B/D=5 and 10 cross-sections, however, for B/D=20 cross-section, flutter analysis indicated a conservative prediction in flutter speed.

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