A long-term observations of gusts were carried out on the Shonai Plain using X-band Doppler radar and surface weather stations from 2007. Based on the 76 cases of the detected gusts, the features of gusts were revealed. Based on the 1-minute maximum instantaneous wind speed, 4 % of them exceeded 15 m/s and 0.7 % exceeded 20 m/s, respectively. About 50 % of the detected gusts exceeded the wind speed of 20 m/s. 80 % of the gusts were accompanied with radar echoes.

View full abstract

We observed wind velocity with 12 supersonic anemometers in the Shonai plane. We conditionally sampled gusty winds whose instantaneous velocity were more than 20 m/s and examined statistical features of them. Most of the gust events concentrated in winter and their main wind direction was from Northwest to West. The frequency of the gust events increased daytimes. Mean velocity increments and mean duration of the gust were 16 m/s and 7 min, respectively. The horizontal scale of the gusts were less than several hundreds meter.

View full abstract

The spatial correlation of wind velocities and temporal fluctuations were investigated based on the wind data observed at 26 weather stations installed on the Shonai plain. It is found out that the coefficient of correlation between wind velocities at two stations including inland station is the smaller than that of the other two stations. As for the temporal wind fluctuations,the frequency of large increment of wind velocities was almost the same as that of downslope winds observed in the mountain area.

View full abstract

Knowledge of wind speed variation is important for response of small wind turbines. In order to investigate the characteristics of speed variation of natural wind in the time domain of several seconds, a method of detecting specific wind speed patterns by using both correlation coefficient and root mean square (RMS) has been proposed. Threshold of correlation coefficient was determined as 0.98 and that of RMS as 0.35. Wind speed data in the year 2007 was analyzed using the method; and parts that resemble up-ramp patterns or down-ramp patterns were detected. The results showed that natural wind tends to increase in relatively short time but decrease in longer time and that probability of up-ramp patterns with short rise time (about 1 s) becomes higher when wind speed level is high.

View full abstract

Wind tunnel experiments were carried out to understand turbulence structures of the neutral atmospheric surface layer with larger-scale disturbances. The boundary layer was developed along a smooth flat plate in the measurement area. The movement of the active turbulence grid was controlled and the turbulence statistics in the logarithmic layer agreed with observations. Two dimensional wind fields obtained with PIV measurements revealed the existence of coherence structures, correspoinding to the eddy models.

View full abstract

In order to see the validity of the application of JMA MSM-GPV forecast data to the determination of appropriate ways of providing reference winds, which are used in the wind environment assessments, the accuracies of the MSM-GPV 33-hour forecast wind were investigated. Comparisons of the GPV with the JMA operational wind profiler were made for the wind data at the height of 400m above the ground. The results show rather high correlations of the wind speeds between GPV and wind profilers. The frequencies of the occurrence of the wind direction of GPV are also found to be well correlated with those of the wind profiler. It is indicated from this study that, as long as the annual statistics are concerned, the MSM-GPV reproduces the upper level wind conditions reasonably well.

View full abstract

Statistical properties of the MSM-GPV surface wind forecasts and the characteristics of the model-produced diurnal variations of wind in the boundary layer are investigated for the Kanto district, Japan. The annual mean surface wind roses and the wind speed roses of GPV are found to have the statistical properties relevant to those from the surface observations of JMA for both the inland and the coastal stations. The difference of the way of diurnal variations of the wind speeds between the surface and the upper boudary layer are also investigated and compared with wind profilers. The results suggest that much attention should be paid when one derives the reference wind for use in wind environment assessments from the three- dimensional output of meteorological models.

View full abstract

In order to assure the train safety under construction of Amarube Bridge, we' ve been conducting wind observation at the site since November 2007. In this paper, wind characteristics of the north-northwest wind are analyzed. The coherences of main stream component and vertical component are well approximated by the exponential function proposed by Davenport but decay factors are much larger than usual, so the influence of this difference on gust response should be examined precisely in the future. In addition, we calculate the wind of the site using MM5 and LES, and compare the results with the observation. As a result, wind directions show well agreement with the observation, and wind speeds are well calculated on the whole.

View full abstract

The importance of air ventilation in urban areas is now broadly recognized as a countermeasure to urban heat island phenomenon and air pollution problem, so it is becoming extremely important to ensure air ventilation in weak wind regions. In order to apply CFD to the estimation of air ventilation, thermal diffusion and pollutant diffusion in urban areas, it is important to assess the performance of turbulence models for these problems. For this reason, a new working group was organized by the Architectural Institute of Japan (AIJ) to do this. As the first step of the work, we carried out wind tunnel experiments and CFD simulations for gas and thermal diffusion behind a high rise building in unstable non-isothermal turbulent flow.

View full abstract

This study aims to clarify the effect of the variation of building height on urban ventilation at pedestrian level and wind environment in downstream area. LES was applied to 2 types of urban flowfields; with uniform and non-uniform building heights, and kinetic energy balances in the cities based on LES data were examined.

View full abstract

This study aims to clarify the effect of the variation of building height on urban ventilation at pedestrian level and wind environment in downstream area. LES was applied to 2 types of urban flowfields; with uniform and non-uniform building heights, and kinetic energy balances in the cities based on LES data were examined.

View full abstract

This study performs the prediction of strong wind in actual urban area by using the LES and meso-meteorological model (MM5). We investigate the applicability and issues of the method of numerical analysis on the strong wind.

View full abstract

We have conducted LES (Large Eddy Simulation) simulation, focusing on local heat environment in the urban area. For estimating the reference absolute values (wind velocity and temperature) of LES, we proposed the computational model for hybrid method of LES and meso-scale meteorological model (MM5), and this computational model was validated by comparing the results of LES with field measurement data. Also, we clarified that the heat convection as a result of mixing is active vertically and the high temperature region is recognized even at a high position in a large cavity formed behind dense tall buildings, and we showed that the hybrid method is a powerful tool for predicting of the wind turbulence and the heat environment in the urban area.

View full abstract

In this study, a generalized canopy model based on the drag force model is proposed. It can express the fluid force of different kinds of obstacles, i.e., porous media, vegetation and buildings. A wind prediction system is developed with the proposed model. As a application of that system, the annual average wind speed at Shinkiba meteorological station is predicted. The results shows good agreement with the measured wind speed reasonably.

View full abstract

Wind observations around the building in Building Research Institute are carried out to investigate wind flow around a real building. 5 ultrasonic anemometers are set around the building. One of them is on the top of the building as a reference point. As a result of observation, the pattern of a feature flow around a rectangular building was obtained that were reverse flow and separation flow near leading edge.

View full abstract

Recently, on the estimation of wind environment for human field, the prediction of strong-wind occurrence frequency based on occurrence probability of strong wind is conducted. However, it is undeniable that present assessment method is not enough to estimate the influence of the instantaneous-strong wind properly. In this study, the adequate method is explored by the data of meteorological station, actual measurement, and wind tunnel test.

View full abstract

For measuring the wind environment such as maximum wind velocity, the actual measurement system is built. In this paper, the out line of the long-term-observation system in CIT Okubo Campus is introduced. This system consists of the 7 sonic anemometers. So the estimation of the instantaneous strong wind is able to estimate.

View full abstract

The overshoot phenomenon of unsteady drag exerted on a square cylinder by gust wind is revised from the viewpoint of the non-dimensional rise time of the wind history. The overshoot coefficient which is the ratio of the maximum drag to the steady drag is obtained through wind tunnel experiment and numerical flow analysis. It is also shown that the overshoot phenomenon is well described by means of the Morison formula. A formula to predict the overshoot coefficient as a function of the non-dimensional rise time is derived. The formula is well predicting the overshoot coefficients of the referred experiment and numerical analysis.

View full abstract

A sudden severe storm destroyed a large tent structure connected to some concrete weight cubes, at near coast in Tsuruga City, Fukui Prefecture. High wind accompanied with the gust-front in the storm killed a man and injured nine persons. While the tent structure had an opening faced to sea, it was covered on remained walls with canvas. In this situation, when wind attacked toward the open face, the tent would be easily lifted up, even though some weights might fairly resist to the lift caused by wind. This investigation describes the observation of damage to the tent.

View full abstract

In this paper, the wind forces acting on inflatable amusement products were investigated. And the critical wind speed causing accidents were estimated based on the wind forces by wind tunnel tests.

View full abstract

It is known that wind damage to houses is more strongly affected by peak gust speed than maximum wind speed. And wind damage is strongly affected by numerous conditions of construction. In this paper, the authors propose a new damage analysis procedure for estimating residential damage rate corresponding to an actual damage rate using wind-resistant performance. As an example, residential damage rates in Kyushu, Japan as a result of Typhoon Songda (2004) were analyzed. We estimated residential damage rate using not only a wind speed but a structural condition of houses in municipalities. This procedure can estimate damage rate corresponding to the actual damage compared with a conventional procedure using only wind speed.

View full abstract

Virtual anemometer forecasting wind field calculated by mesoscale climate model. With the use of data base of geographical and statistical data of cities damage to buildings and houses from strong winds was estimated and shown on the popup display of virtual anemometer.

View full abstract

An air-cannon missile-propulsion device is made for the impact test of claddings. Missile impact resistant tests for laminated glasses were performed according to ISO 16932. The test results are judged whether the glass is remaining without damage or the glass is penetrated by the missile. The glasses that are cracked and are opened by a small hole without penetrating by the missile, were subjected to an pressure-cycle test.

View full abstract

The downburst emerges in urban area is numerically simulated. A 10km x 10km square area in Tokyo metropolitan is chosen as a target domain. The aerodynamic effects caused by buildings are treated by an urban canopy model. Comparing those computed results obtained with or without using the canopy model, how the bulings affect strong wind velocitry distributions is shown.

View full abstract

This study aims to develop a rational simulation method of wind-tunnel turbulence by investigating effects of small-scale turbulence on flow patterns around a bluff body. Base pressure coefficient and Karman-vortex intensity were investigated in previous studies. Characteristics of aerostatic force coefficients such as drag coefficient and slope of lift force coefficient were examined in this study.

View full abstract

When wind velocity is a step function, the drag forces show overshoots exceeding the quasi-steady level with a short time interval. It is called overshoot phenomena. In this study, overshoot phenomena is investigated by wind tunnel experiments and analyses. By wind tunnel experiments, time history of drag forces on a 2-D cylindrical model is measured under suddenly changed wind velocity. The wind velocity in the working section is controlled by opening the shutter suddenly and 2-D rectangular cylinders and circular cylinder are used in wind tunnel experiments. So we tried to compare drag force with calculation model. Since inertia forces have strong effects on overshoot phenomena under sudden increase of wind velocity. Also, we focused on them in addition to vortex shedding.

View full abstract

In this method, the spatial correlation of fluctuating wind force so called coherence function is one of the most important parameter. However this correlation is considered the same as the correlation of fluctuating vertical wind velocity even some recent researches have shown that the first is quite higher than the second. The purpose of this research is finding out a more accurate gust response analysis method based on the correlation of fluctuating wind force. The surface pressure of 12 types of rectangular cylinder models setting on 4 type of approaching flow has been measured. The gust response analysis based on this pressure has been also compared with the result of 1 heaving degree of freedom free vibration test to confirm the compatibility of the analysis process.

View full abstract

Characteristics of dry galloping of a stay cable with the indented surface treatment were experimentally investigated. Wind-induced response, surface pressures and axial flow speed were measured in a wind tunnel. It was found that dry galloping occurred in the critical Reynolds region when Karman vortices were suppressed by strong axial flow.

View full abstract

The measurement of the flow field around two square cylinders in tandem arrangement is conducted by means of a split-film probe. The time-averaging and the phase averaging techniques are applied to recorded data. According to the time-averaged field, The streamwise component of the time-averaged velocity around the upper surface of the downstream cylinder is smaller than that around the upper surface of the upstream cylinder. The thickness of the boundary layer around the downstream cylinder is twice larger than that around the upstream cylinder. According to the phase-averaged field, a vortex whose diameter is about twice larger than the width of the square cylinder is formed.

View full abstract

This paper's purpose is that vortex excitation characteristic are calculated by using computational fluied dynamics (CFD). As conclusions, the excitation mechanism of three areas are examined. Furthermore, aerodynamic instability vibration is examined.

View full abstract

In this study, unsteady aerodynamic lift forces of rectangular cylinders of side ratio B/D=1 and 2 were measured under the forced vibration condition, and the relation between the Karman vortex and galloping are discussed. As a result, for the B/D=1 section, the Karman vortex-induced vibration and galloping must occur continuously and the onset velocity of galloping should be 1/St. But the conventional Karman vortex-induced vibration may occur only at very small vibration amplitude region. On the other hand, for the B/D=2 section, it seems that the conventional Karman vortex-induced vibration never occurs and the onset velocity of galloping is higher than 1/St. And also, the onset of galloping seems to be related to certain vortex effects, and then further investigations must be needed.

View full abstract

According to the recent trend of building verticalization the dynamic responses under considering the interaction between buildings becomes important in the wind resistant design. The characteristics of the side-by-side structures are still uncertain, though some studies pointed out that the aerodynamic characteristic and the pattern of the flow are changed significantly by the relative gap distance. In this study, aerodynamic characteristics and dynamic response of two side-by-side square cylinders were investigated by the 2D computational fluid dynamics. The pressure distribution surrounding the two stationary cylinders was found to be symmetry and the interaction is small. However, the interaction becomes remarkable and the responses tend to be increased in the self-induced vibration.

View full abstract

This paper describes analysis of aerodynamic vibration of a square prism in two-dimensional flow,The simulation in conducted by means of New Hybrid Aerodynamic Vibration Technique.The analysis focuces the relation between the density ratio and oscillation velocity.The phenomenon of aerodynamic vibration in air flow depends on Scruton number that in formulated by the product of density ratio and damping parameter.However,the oscillation velocity is getting smaller with the density ratio getting smaller even though the Scruton numbers are similar.In this simulation,similar result was oftained,and the peak response frequency gets smaller than the natural frequency.

View full abstract

This paper aims to clarify the relationships between the density ratio and the oscillation velocity.The analysis of the result in the part1 is conducted based on Added-mass effect as a result,the phenomenon,which the oscillation velocity is getting smaller with the density ratio getting smaller and the peak response frequency gets smaller than the natural frequency,can be explained by the Added-mass effect and the relationship between the density ratio and the ascillation verocity can be clarified.

View full abstract

The flow past a circular cylinder surrounded by a porous body was numerically investigated by using a 2D DNS code for various porosity Ct. We find strange wake structures of the cylinder-porous body. The wake flows are classified into three regimes. Regime I (Ct ≤ 1.0) : Karman vortex street from the inside solid cylinder is clearly formed. A pair of separated shear layers from the outside porous body surround the inside vortex street and form the vortex street in the far downstream. Regime II (1.5 ≤ Ct ≤ 10) : The inside Karman vortex street disappear. Regime III (15 ≤ Ct ) : The Karman vortex street from the outside porous body is dominant. In this report, the characteristics of these three wake structure are investigated in detail.

View full abstract

Many researches on reducing wind-induced excitations of tall buildings have been carried out. One way to reduce the excitations is an aerodynamic modification of sectional shapes with height through tapering or set-back. In this paper, to investigate the mechanism of aerodynamic force reduction, high-frequency force-balance test was conducted. Two types of tapered models with different tapering ratios, a set-backed model and a prototype model of a square cross-section, were employed under two typical boundary layers. From the results, changing cross section helps to reduce the mean drag force and the fluctuating lift force. And the power spectra of tapered and set-backed models are wider than that of square prism.

View full abstract

The flow ground of various object rotations has been examined by the development or spread of CFD and PIV. However, the flow around a three-dimensional object represented by a building is complicated, and it cannot always become clear about the details. On the unsteady interference of the flows from the top and the sides of the prism, it cannot be said in particular that it is elucidated though various trials have been accomplished till now. In this report, based on measurement results of a 3 dimensional square prism model of aspect ratio 2.7 by PIV, we examined an average flow in part 1.

View full abstract

The flow ground of various object rotations has been examined by the development or spread of CFD and PIV. However, the flow around a three-dimensional object represented by a building is complicated, and it cannot always become clear about the details. On the unsteady interference of the flows from the top and the sides of the prism, it cannot be said in particular that it is elucidated though various trials have been accomplished till now. In this report, based on measurement results of a 3 dimensional square prism model of aspect ratio 2.7 by PIV, we examined the three dimensional structure of the Karman vortices with the interference of unsteady flows from sides and top of a prism in part 2.

View full abstract

This study investigates the effects of inclination angle and yaw angle for wind forces acting on inclined circular cylinders. In this paper, the experimental method and characteristics of modal wind forces on inclined circular cylinders are described. The modal mean wind along-wind force coefficient and the modal fluctuating across-wind force coefficient on an inclined circular cylinder is characterized by the effective yaw angle calculated by the inclination angle and the yaw angle.

View full abstract

This study investigates the effects of inclination angle and yaw angle for wind forces on inclined circular cylinders.In this paper, the characteristic of power spectral density and axial phase shift of fluctuating across-wind forces. Strouhal number obtained from across wind force on a inclined circular cylinder is characterized by the effective yaw angle calculated by the inclination angle and the yaw angle. The fluctuating across wind force is transmitted at uniform velocity from upwind side to downwind side of the cylinder, and the transmit velocity is approximated by a liner function of the effective yaw angle.

View full abstract

In order to know the aerodynamic behavior of a bridge, a wind tunnel test is usually conducted by a scaled full model. For the scaled full model, the scale of the model must be larger according to the size of a wind tunnel facility. Then a smaller model is used than a section model in 2-dimensional wind tunnel test. The accuracy of the result of the scaled full model test becomes lesser than that of the sectional model test depending on the scale of model. Therefore, it is focused to establish an estimation method of aerodynamic behavior of the full bridge by a time trace response analysis which is developed in the present research, through the results in the section model test which has higher accuracy than the scaled full model test. The method is developed by the authors and patented.

View full abstract

A series of wind tunnel tests was conducted using a circular cylinder with various skew angles, so that the characteristics of the large-amplitude vibration of stay cables at high wind speed can be clarified. Cases with skew angles of 0, 40, 45, 50, and 60 degrees were tested where the aspect ratio was between 10.4 and 20.7. Response with large amplitude beyound 2D and strong negative aerodynamic damping was observed with skew angles 40, 45, and 50 degrees. It was thought to be the point to reproduce the vibration that the flow particularly around the windward end of the model is not disturbed. At the wind speed in critical Reynolds number, random vibration was observed probably due to asymmetric separation from the model.

View full abstract

In the current bridge design, aerodynamic stability of bridge has been investigated for almost bridges after a structural section shape was determined. In these cases, aerodynamic stability of bridge has been secured by installing additional members such as fairing, flap and horizontal plate as suppression device of aerodynamic vibration. In the present study, our attentions are focused on a horizontal plate effect. The horizontal plate has some advantages for suppression of aerodynamic vibration. However, detail mechanism is not yet elucidated on suppressing aerodynamic vibration. The objective of the present study is to investigate the suppression effect of the horizontal plate by changing both the length and the installation position of the horizontal plate.

View full abstract

A hanging-jumper beam of a transmission tower is adopted as a countermeasure against a short fault of jumper conductors under strong winds. However it is thought that the hanging-jumper beam may cause the vibration of transmission tower members due to its weight when the hanging-jumper beam starts to vibrate under strong winds. The authors have conducted an excitation test of a strain transmission tower with the hanging-jumper beam to comprehend the dynamic behaviors of the hanging jumper beam. In this paper the effects of the oscillation of hanging-jumper beam on side members were investigated based on the excitation test data, and the information for estimating the vibration of the hanging-jumper beam under a string wind was organized.

View full abstract

Some basic data to predict wind responses of a tower-cable coupling system including hanging jumper beams are acquired by some excitation tests under calm as report No.1. However few investigations of the response based on the data measured under strong winds with an actual tower are reported. The authors try to comprehend the responses under strong winds. So this paper discusses the responses under light winds based on the some data measured at this time, which is a basic data to comprehend the responses under strong winds. As a result, it became evident that the cable vibrations had much effect on the oscillations of the tower and the hanging jumper beams and the effects of the cable vibrations on the both were different.

View full abstract

The authors have examined the reliability and stability of acquisition data required of a new instrumentation system, which enables response measurement of a power transmission tower by a minimum cable installation, using the data transmission by wireless LAN, and advanced the improvement of the system. This paper clarified basic performance of the wireless transmission instrumentation system using measurement data of a steel tower vibration test. And it was found that the system can acquire same quality data as measurement by a cable system and has been close to practical use.

View full abstract

This paper is examined the upper limit value of the acceleration for wind response for the execution work from questionary survey and hearing to be based on two vibration bodily sensation experiments.

View full abstract

The purpose of this study is the response estimation of multi-mass system under fluctuating wind force in elast-plastic range. In part1, the research evaluates Dispersing Ensemble Average of wind wave form and the effects of higher-vibration modes. In part2, the study investigates the modal parameter identification technique of elast-plastic structure under fluctuating wind force. From the analytical results of part1, it is recognized that the appropriate number of wind wave forms for ensemble average is 30 or more waves. In addition, it is necessary to consider not only 1st but also 2nd or 3rd mode in modal analysis when input energy of fluctuating wind force and response of structure are evaluated.

View full abstract

The objects of part2 are to evaluate the modal identification technique of the elast-plastic structure by using Frequency Domain Decomposition (FDD) method, and to estimate multi-mass system to fluctuating wind force in elast-plastic range. From the analytical results, it is validated that FDD is very effective method to identify the modal parameter not only elastic range but also elast-plastic range response.

View full abstract

This paper discusses the properties of viscoelastic damper during long duration random vibration. Experiment is carried out to evaluate viscoelastic damper properties such as temperature dependence, stiffness etc. Experimental results show that temperature inside the viscoelastic material body become stable by effect of heat conduction & heat transfer even if the damper is vibrating randomly. Moreover, They show that the influence on the temperature history by heat transfer coefficient is large. In addition, these experiments adopt a simplified evaluation method using sinusoidal-wave to substitute for random time history data properties. Accuracy of evaluation method is validated by comparing with experiment result using random time history data.

View full abstract