Tornado-like vortex was calculated by numerical simulation. The LES was used for turbulent modeling.

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LES analysis on spatio-temporal structures of vertical vortices in the natural convection

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The flow and temperature characteristics within an urban canopy layer that simulate the urban area were determined using a hot-wire anemometer and a cold-wire thermometer. The thermally stratified wind tunnel of Tokyo Polytechnic University was used. Five gross building coverage ratios were set: 11, 15, 20, 25 and 31%. Results of experiments showed that there was no difference in spectrum configuration due to difference in building coverage ratio. For the power spectrum density of the u and theta components, peak frequency varied with height. A uniform urban area influences temperature and wind velocity when the height reaches about 1.5 times the building height.

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Turbulence characteristics of boundary layer in wind tunnel generated by active turbulence grid have been experimentally investigated. Through the measurement with an x-type how wire, the experimental data of turbulence statistics, including higher-order moment, was accumulated, and it was found that the Reynolds shear stress of boundary layer significantly increases with the active turbulence grid. Then, the skewness and flatness factors of velocity fluctuations revealed that large-scale fluid motions in the outer layer played a predominant role in the generation of turbulence of boundary layer.

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To revise train operational control rule under gales, it needs to show that the safety under the rule is equal or higher than that of rule applied currently. Therefore, it needs to evaluate the probability "When train operation is conducted, severe wind that is higher than the critical wind velocity for overturning appear in the section under applying the train operation control rule", quantitatively. To do this, it needs to consider not only the probability of wind velocity occurrence but also the probability of wind time fluctuations. In order to evaluate the probability, we calculated the probability that gales occur at a section during train operations using functions of distribution of wind velocity occurrence and wind time fluctuations approximated by observed wind data. The authors assumed a section where wind velocity observed, and compared some train operational methods by calculating the probability.

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The fluctuating wind velocity characteristic around the limited part geographical features in the mountain etc. becomes the one that was greatly different from same boundary turbulent flow spatially. The examination of a wind that considers the influence of geographical features in the surrounding enough is needed because there is a possibility that the big response that cannot be explained by a usual Gust response analysis is caused when the large and big structure is constructed in such a place. The wind around the limited part geographical features tried the characteristic grasp of the change velocity of the wind to cause large horizontal response in overhang mounted impeller beam bridge model in the wake of the hill as the first stage to clarify the influence that caused it for the response of the structure in this study.

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A series of field measurement was conducted in order to investigate the effect of wind on sound propagation. Two sound level meters and a speaker are aligned on a straight line. The distances of each sound level meter from the speaker are 60m and 100m. The frequencies of the sound sources are 100Hz, 400Hz, 1000Hz and 4000Hz. An aerovane anemometer is deployed in the vicinity of the speaker. From the measured data, it is recognized that: the gap of the sound pressure levels of the two observation points become large as the wind velocity become high; the gap become larger as the sound level meters become far from the speaker; and the higher frequency sound reveals larger gap rate.

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A fundamental experiment was conducted to study the effects of a train draft on passengers on a railway station platform. The train draft is a transient wind at stationary place, such as a platform, due to a train passing there. This experiment examines the relationship between the transient wind similar to the train draft, the psychological response and the postural stability of an individual. A psychological tolerance and tolerance of a postural stability to a wind speed were discussed.

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To operate trains safety under strong wind conditions, it is important to install anemometers at effectual point along the railways. We suggest a method to calculate occurrence wind velocities along the railways by numerical simulations. First, we performed weather numerical simulation to reproduce a lot of weather conditions that brought strong winds occurred in the past. Using these results, we calculate occurrence mean wind velocities in 3km mesh. Next, we calculate wind velocity distributions in smaller 200m mesh for 3km every direction area including railway, using a flow numerical simulation. Finally we obtain a detailed mean occurrence wind velocity distributions using results of both numerical simulations. These distributions will become the objective bases in the case of examination for arrangement of anemometers.

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The criteria for assessment of pedestrian wind environment based on probabilities of exceedance of daily maximum gust speeds are commonly used in Japan. We usually use gust factors to estimate the daily maximum gust speeds from daily maximum mean wind speeds, but it still remains an unsettled problem of how to determine the appropriate gust factors A Working Group for Urban Wind Environment Assessment, Japan Association for Wind Engineering, has been studying to establish rational wind environment assessment method. The Part1 in continued two papers presents a model equation of the gust factors based on field observations at 152 sites. Further, this paper describes the verification methods for applicability of the model equations to wind environment assessment.

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Part 2 validated the applicability of the model equation of the gust factor presented in Part 1 by two different methods. First method compares the exceedance of daily maximum guest speeds and ranks of wind environment between observed daily maximum gust speeds and predictions obtained by the model equation and corresponding mean speeds. Second method compares observations with the predicted values using wind speed ratio, Weibul parameters and the model equation. The result indicates that the model equation, which consists of the mean plus 1 standard deviation of scattering gust factors, most reflects measurements at entire sites.

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In this study, we investigated characteristics of air ventilation and air temperature in a built-up area with closely-packed high-rise buildings by wind tunnel tests and numerical simulations. The objectives of this study were (1) to grasp the situation of ventilations in extremely dense cities, and (2) to assess the influence of height variation of buildings on ventilation. As the experimental results, spatial average of wind velocity ratios at pedestrian level could be expressed by the gross building coverage ratio, and the height variation of buildings was very effective for the ventilation and temperature in this dense area.

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In our past research, ventilation performances in densely built-up areas had been investigated and evaluated with the application of a simplified rectangular 2D model and periodical geometric 3D model respectively. Furthermore, the tendencies of ventilation performances for 3 degrees of city density in other 3-D models had been studied. In this paper we continuously evaluated the performances of natural drafts and ventilation for a street canyon under the ground level, called "dry area" space. The annual probabilities of exceedance were used as the evaluation method, taken wind distributions of 16 directions into consideration. Two new probabilities of exceedance based on CFD calculated indices, Local Air Change Rate and Average Kinetic Energy respectively, were firstly proposed and the detailed calculation procedures were also given. Additionally, relationships between width of the dry area and performances of a region assuming the first floor were also studied for the three-story "dry area" model.

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In the light of the definition and evaluation method of exceedance probabilities for ventilation performance proposed in the Part 1, this paper took the "dry area" model of Part 1 as a concrete example to illustrate the calculation procedure of exceedance probabilities. The "dry area" was supposed to be located in Tokyo and the published Weibull distribution data of Tokyo Meteorological Observatory were utilized. Two exceedance probabilities based on the Local Air Change Rate in range of 0-1000h-1 and Average Kinetic Energy in range of 0-1m2/s2, were calculated separately. The results indicated that both of the two exceedance probabilities changed a lot with different orientations and different widths of the "dry area". For the example case in this paper, the biggest exceedance probabilities appeared in East (West), while the lowest is in South (North), and when the width was over 4 meters, the exceedance probabilities showed a saturation tendency.

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In order to apply Computational Fluid Dynamics (CFD) to the environmental assessment aiming at relief of an air pollution or the heat-island phenomenon, it is important to reinforce the verification example applied to the non-isothermal flow influenced by the buoyancy. However, there are few detailed databases by wind tunnel test with heat flux and concentration flux. In this study, we aim to provide experimental data required to validate CFD simulations of pollutant diffusion around a building in non-isothermal flow. We developed a simultaneous measurement system of fluctuating concentration, velocity and temperature. In order to measure concentration simultaneously with the wind velocity and the temperature, we used a high-speed flame ionization detector.

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LES analysis on spatial structures of maxium wind gust in actual urban area

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The aim of this study is to develop a simulation method to predict the turbulent diffusion process and the thermal environment, which are affected by various small obstacles, within the real situation of urban street canyons based on the methodology of canopy models. This study extends the previous researches of canopy models conducted by the present authors to reproduce the effects generated from various small obstacles, including moving objects such as automobiles, in actual urban space. Three test cases of computations were carried out by using the new developed 'Vehicle Canopy Model'. In the cases without automobiles, k values were largely underpredicted, but the prediction accuracy of k values was greatly improved in the case with moving automobiles.

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For the mitigation of heat island effects on coastal cities, it is sometimes expected that the sea breeze come into the inland area of a city, where its cold air mingles with the hotter air over and inside the urban canopies. But now it is becoming a big problem that the densely-arrayed tall buildings at the Siodome in costal area interrupts the sea breeze coming from the Tokyo Bay, and so temperature at the inland area of Tokyo increase compared to the costal one. To solve this issue, in this study, we have to formulate the LES numerical model which represents correctly aspect of the ground surface condition consisting of buildings, structures and surface temperature. First, we use meso-meteorological model (MM5) and observational data to set the boundary condition, and next, show the wind flow and temperature field characteristics around tall buildings at the Shiodome area. Finally, based on the results obtained from the LES at the Shiodome area, we investigate the environmental aspects at the urban heat island due to densely-arrayed tall buildings.

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Large-eddy simulation is applied to the problem of atmospheric dispersion in stable boundary layer for oncoming turbulence, which is time-sequentially generated by unsteady numerical simulation of spatially-developing boundary layer in the driver unit as another computational domain. We investigate the characteristics of plume dispersion in stable boundary layer based on that of plume dispersion in neutral boundary layer.

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The numerical simulations have been studied in order to give an assessment and to make a prediction of gas diffusion field. It is highly expected to predict time variation of gas diffusion field when the wind direction is fluctuating. In our laboratory, the RIAM-COMPACT, the numerical model based on LES, has been developed for the prediction of airflows over real complex terrain. This research included two purposes: (1) to examine the accuracy in gas diffusion analysis using by the RIAM-COMPACT, and (2) to establish a gas diffusion analysis method in changes in wind direction. This paper described (1), the accuracy validation on gas diffusion field over an isolated hill and real complex terrain. The numerical results agreed with wind tunnel experimental results. It showed that the RIAM-COMPACT is useful to a numerical analysis on gas diffusion.

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In this study, the numerical simulation based on LES model of gas diffusion over real complex terrain were carried out to compare to the field observation performed near Mt. Tsukuba. Simulation conditions were chosen in two methods. One is numerical simulation with the averaged wind direction and the other is considered wind direction change. In addition, this study is intended to develop a more realistic prediction method for gas diffusion field. As a result, numerical simulation with the averaged wind direction condition shows a good agreement for wind field but it does not for gas diffusion field. In contrast, numerical simulation with wind direction change condition shows a good agreement for time change in the concentration distribution, area of the high concentration and the extension of gas diffusion. These results show the way to develop the more accurate prediction method for gas diffusion field.

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Wind power is one of promising natural energy resources in order to counter and mitigate the global warming due to fossil energy consumption. Therefore, the accurate estimates of local wind characteristics are required. This study investigates the spatial and temporal variabilities of microscale winds over the Nemuro Peninsula by conducting very-high resolution simulations with a mesoscale meteorological model. By reducing the horizontal grid spacing down to 111 m, the small-scale features of local terrain are well represented. Wind characteristics under various meteorological conditions are examined.

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Terrain model was made by 3D NC modeler. Effects of terrain on local wind climate was studied with wind tunnel test. NC program was edited from digital altitude data directly. Mean wind profile and turbulence intensity profile were measured on a point of terrain model of Izu-Ohshima. Effects of terrain was not confirmed because angle of slope is small, 7 degree.

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Advances made in CFD technologies, coupled with the phenomenal growth in the speed and memory of computers in the last decade, have made it possible to investigate the characteristics of wind load of moving vehicle. Our objective is to study the characteristics of wind load of moving vehicle.

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The post disaster investigation is conducted when severe wind damage is caused by Typhoon or Tornado. Usually, to estimate the wind speed from damaged objects is needed, but it is not easy to estimate wind speed at site. In this paper, the basic study for wind speed estimation based on damaged road sign was reported.

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This paper illustrates comprehensive framework for evaluation of functional loss after wind damage. Based on the past examples of building damage observed in post disaster investigation, it may be necessary to make clear the degree of the functional loss after wind-induced damage, especially for commercial buildings and facilities whose importance level are relatively high. This paper shows the evaluation of estimated functional loss in the low-rise building with clay tile roof as the example of the proposed framework.

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Fragility curve for electric poles was constructed by damage ratio in 1km mesh analyzed the damage data from T0314 and predicted wind field covered Miyakojima by the numerical simulation.

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Optimum design wind speed for electric poles was decided by using minimization method of expected total cost, based on the wind hazard from typhoon simulation and fragility curves from the damage data.

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The investigation data of tornado generated from 1997 to 2006 in Japan was totaled, and the characteristics of the tornado generation was examined about the incidence, strength, and the relationship the location of tornado and the cyclonic scale. The average generation of tornado was 20.5, and the number of tornadoes generated in 2006 was more than forty. Tornado strength on F-scale was the same ratio as the investigation of the United States excluding the F0 scale. Tornadoes because of typhoon existed in the area within the five times of the maximum wind speed radius when the location of tornado occurrence was standardized by it. Tornadoes because of the cyclone were generated around the cold front, and the generation proportion in the Frontal region of the cold front neighborhood and the warm sector of Pre-frontal region was 4:6.

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Characteristics of damage to buildings and houses caused by strong wind in 2006 was discussed. Disaster prevention and mitigation methods were presented.

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A questionnaire survey has been made of the Tornado Disaster in Saroma Town, Hokkaido on November 7, 2006. The present paper describes the outline of the questionnaire and the damage to residential houses.

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The tornado disaster in Saroma town, Hokkaido on November 7 2006 caused extensive damage to buildings and people in the town. The authors examined characteristics of tornado, phenomena of the tornado occurred, damage to buildings and structures, and recovery of the damage. We carried out questionnaire investigation to the people in that town. In this paper, Part.2, describes condition of the tornado occurred, human behavior, damage to lifelines.

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A F3 tornado hit Saroma Town in Nov.7,2007, and caused severe damages on human beings and properties. We conducted a site survey during Nov.8-9, 2007 on the damages of buildings. In this paper, the building damages and their characteristics are summarized.

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Damage characteristics of Saroma tornado on November 7, 2006 were revealed from ground survey and helocopter observation.

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Numerical experiments on the strong wind associated with the passage of typhoon 0423, which brought about localized wind damages in OGI city, Saga prefecture, are performed by using a meso-scale meteorological model. With the initial conditions based on the upper air sounding at nearby meteorological stations, the distribution of the surface wind relevant to that of the areal extent of wind damages was obtained. Vertical structures of the calculated flows over Mt.Tenzan are also investigated. It is indicated highly possible from the experimants that the strong wind was a kind of downslope wind from Mt.Tenzan.

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The associated wind distributions with Typhoon Shanshan in the Kyushu region were analyzed using NeWMeK data. And the associated wind distributions with several tornados and gusts which broke out along the east coast of Kyushu are discussed focusing on the associated wind damage area. Moreover, the big difference of wind records at two adjoining NeWMeK sites was confirmed due to the terrain effects of a hilltop and a valley sloping down from it.

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Strong wind disasters has not yet been fully recognized, but they has very higy instantaneous wind speed and bring the heavily damage. The purpose of this paper is to show the necessity for improving recognition level of strong wind disasters including tornado. We examined the response and rehabilitation for the tornado disaster at SAGA Prefecture in 2004. The study has shown the importance of two features. The first is the necessity of early warning system which can communicate to people in another area with Emergency call immedeately after tornado disasters. The second is the importance of "no damage for the pubic facilities at strong wind disasters".

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When a building suffered from it by a disaster, is evaluated such as complete destruction, half destruction, partial destruction. This evaluates the damage that occurred by natural disaster by a notice of the Prime Minister office with a unified standard without depending on classification of a disaster, and system is such that it is based on this evaluation now, and various damage support systems are applied. Therefore a self-governing body visits a local suffering household from the suffering direct back and evaluates the damage every 1 household and is to report the result in Cabinet Office. However, this evaluation standard assumed the earthquake damage mainly; that there is the case that estrangement is seen in between the real strong wind damage situation and evaluation results is pointed out so that is done. When I apply this evaluation standard to match the present conditions of the damage, even in the case of Nobeoka tornado, Nobeoka-city that evaluated the damage performs a device in use. This report intended for the damage such as buildings of Nobeoka tornado and weighed an evaluation result by the evaluation standard mentioned above.

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A tornado attacked and caused damage from Tatsukushi area to Misaki area in Tosashimizu city at about 15:40 on November 26, 2006, due to the passage of a low pressure. As the results of field investigation, Fujita-Pearson scale was found to be F1-PL0-PL2. Moving velocity of the tornado was about 4 m/s, relatively slow. And, last harf of the trajectory of the tornado was bended southward. This fact may caused by a downburst occurred at the northside of the trajectory.

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At 19:14JST on December 25th, 2005, a JR limited express "Inaho No.14" of 6 cars was over-turned and derailed by a strong gust. Fatalities numbered 5, and 33 people were injured. The train was running from north to south under strong wind conditions with 10min-mean wind speeds of around 20m/s. The accident site was in open flat country covered by snow around 50cm deep. The footprint of the wind-induced damage to trees, green houses and wooden residential houses extended over an area 12km long and 20 - 40m wide, starting at the Sea of Japan coast and heading ENE. The damage scale was estimated at F1. A low pressure area had developed in the Sea of Japan accompanied by southward movement of a cold air mass. A cold front had extended from this low pressure area. The convection current was very strong, and the wind damage area corresponded to a pre-frontal line of cumulonimbus that had formed on the south side of the cold front. A strong and developed radar echo was observed just above the damaged area. This was a typical type of tornado observed in winter in Japan, especially in the west coast region facing the Sea of Japan. An anemometer at the seashore recorded a peak gust of 36.9m/s at 19:06 on December 25. Steel snow fences 5km inland were damaged at 19:08, and the train accident occurred at 19:14 10.5km inland. The Meteorological Agency has not concluded whether the strong wind event was due to a tornado or a downburst. However, the pattern of damage to a farm appliance shed located just upstream of the train accident point suggested that it was a tornado rather than a downburst.

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A gust occurred in Ogata-mura and Kotooka-machi, Akita Prefecture, causing collapse of a wooden house, scattering of roofs and damage to agricultural facilities etc. on November 8th, 2005. Wind speed records in Ogata, the Automated Meteorological Data Acquisition System (AMEDAS) observation point, 7 to 8 km, which were not remarkable speeds. The meteorological conditions including rader-echo maps and the distribution of damaging points were shown. Wind speeds were evaluated under a simple assumption.

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The branch switch characteristics of coupled flutter are clarified by use of Step-by-Step flutter analysis. In the case of typical coupled flutter instability, the branch switch characteristic from Torsional Branch to Heaving Branch is observed. In this paper, a revised Step-by-Step analysis method is proposed and new strategies for flutter control are investigated. The branch switching phenomena for the coupled flutter is confirmed through Step-by-Step analysis and wind tunnel tests for fundamental structural sections. However, small numerical differences exist between solutions of complex eigen-value analysis and Step-by-Step analysis. Therefore, Step-by-Step analysis is revised considering the logarithmic damping characteristics in the process and the results of revised Step-by-Step analysis show completely good agreement with those of Complex Eigen-Value analysis. Then, basing upon revised Step-by-Step analysis, the mechanism of coupled flutter is investigated and flutter stabilization method is proposed from view point of the effect of the aerodynamic derivatives.

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Precise evaluation of the aerodynamic admittance and the joint mode acceptance is essential to develop advanced analytical methods of gust response of large scale structures. Flow around structures, surface pressures and induced aerodynamic forces depending on geometry of structures should be taken into account. To investigate the influence of the flow around rectangular cylinder upon the span-wise coherence of fluctuating forces, the surface pressures around 2-D model with rectangular sections of B/D=5 (B:chord length, D:depth of the section),and the random responses of the model were measured in turbulent flow generated by grid. In addition, frequency-time domain analysis was carried out to evaluate spatial correlation about unsteady buffeting forces, and predicted responses were compared with the measured ones to observe the effects of the approximation of the joint mode acceptance on gust response

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Time history of drag force on a 2-D cylindrical model is measured under suddenly changed wind velocity by wind tunnel experiments. Wind velocity in a working section is controlled by opening the shutter suddenly. 2-D rectangular cylinders with side ratio B/D=0.5, 1.0, 2.0, 2.75 and 4.0 as well as a 2-D circular cylinder are used in wind tunnel experiments. Indicial functions of drag forces produced by an idealized step change of wind velocity are evaluated analytically by use of the measured data. The evaluated indicial functions show overshoots exceeding the quasi-steady level with a short time interval. Fluctuating drag forces are also measured in longitudinally perturbed flow to compare with frequency transfer functions which are obtained from indicial functions by the mathematical transformation.

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Turbulence effects on wind-induced vibration of a structure were investigated by a wind-tunnel test where base pressure of a rectangular section model in turbulent flows was measured. Base pressure was simulated in turbulence with the same spectral intensity at small-eddy region rather than the same turbulence intensity.

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In this report, three-dimensional computational fluid dynamics for around a circular cylinder are carried out by the finite element method. Concretely, by paying attention to the drag coefficient, the Strouhal number, and the location of exfoliation point, how the estrangement with the experiment data can be decreased by taking thought of three dimensions of the flow is examined. and when analising it, the direct method that did not use the turbulence model was adopted, because it was the first stage of the research in this report.

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The tandem cables rarely cause a phenomenon of complicated vibration called wake-galloping as cables interfere each other. This phenomenon of vibration can get fatigue destruction on a part of fixation. The purpose of this study is to grasp the characteristics of wake-galloping phenomenon on tandem cables of cable-stayed bridge using the computational fluid dynamics which is based on finite element method. In addition, with comparing an analysis result with an experiment result, examine applicability of this analytical method. As a result, by the two-dimensional static analysis that performed a circular cylinder interval and an attack angle as a parameter, we understood that we could grasp mechanism of a flow of around tandem circular cylinder.

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There are two kinds of shot balls in soccer game. One is well known curved ball, which is explained by air force of Magnus effects with ball rotation. The other is so called middle shot, which was to be famous in 2006 FIFA world cup. This ball flights in less spinning, but aerodynamic mechanism of this erratic ball is not clarified in this stage. In this study, we conducted this problem by free fall examination, image processing using TV sine and wind tunnel experiments. The Strouhal number in flight of soccer ball was near around 0.012, which value is smaller than smooth sphere 0.2 in sub-critical Reynolds number. The magnitude of unsteady air force measured by the wind tunnel experiments explained qualitatively as same as the real movements in flight. Flow around soccer ball is near around super-critical Reynolds number flow of smooth sphere by the seam existence of the ball surface. In this flow region, a horseshoe-shaped vortex on the rear surface of the sphere and a pair of stream wise line vortices ranging to far wake. This flow was explained by Taneda (1978), and successfully adopted of this soccer ball erratic behavior by this research.

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This paper describes the characteristics of wind-turbine airfoil M-F073 aerodynamics. The aerodynamics were investigated using wind tunnel tests. The test parameters were Reynolds number and turbulence intensity. As a result, when there is not the value of the turbulence intensity, the lift coefficient changed in the vicinity of the stall angle, in ranges from 100,000 to 200,000 of Reynolds number. In addition, it was confirmed that the turbulence intensity makes Reynolds number effect small.

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The flow around tandem arrangement structures is known that a separated shear flow from a front structure impinges a rear structure by the interval of structures. However, the study of flow around tandem circular cylinders is investigated wider than that around tandem bluff bodies. Therefore, the flow characteristic around square cylinders is investigated in the present study. As a result, the drastic change of the flow around the cylinders is confirmed in case of the particular non-dimensional distances of the cylinders

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