Masahiro Matsui

An analytical model for simulation of the wind field in a typhoon boundary layer

An analytical model has been developed for calculating the wind field in a moving typhoon boundary layer. The present model has an upper inviscid layer of cyclostrophic balance and a lower friction layer controlled by a surface drag coefficient and eddy viscosity. Velocity in the inviscid region is described first, using the assumption that the wind field moves with the translation velocity of the typhoon. Perturbation analysis is then performed to obtain the tangential and radial boundary layer velocity in the friction region. Wind speeds and directions predicted by the present model agree favorably with observations obtained at a 100 m height tower during three typhoons in 1991. Rapid variations in wind speed due to surface roughness and topography around the tower are also amply demonstrated. In the final section of this paper, a case study is presented to examine the wind field associated with a typhoon, as well as the characteristics of the ratio of surface to gradient wind speeds G(r) and the inflow angle 7. The results indicate that previous observation data obtained at coastal areas during typhoons can be explained satisfactorily by this model.

A numerical study of the wind field in a typhoon boundary layer

The wind field in a typhoon boundary layer (TBL) has been investigated by a numerical model. The results show that vertical profiles of wind speed in the TBL can be satisfactorily stated by conventional power-law expressions. To describe the structure of strong wind in the TBL, two parameters have been suggested: one is a dimensional parameter, fa , approximately representing the absolute vorticity in the wind field, and the other is a non-dimensional parameter, ~, characterizing the heterogeneity of vorticity in the radial direction of a typhoon. Substituting the parameterfx by Coriolis parameter f, the gradient height zg during typhoons can be predicted by the same formula as that used during non-typhoon climates. The ratio of surface to gradient wind speeds G(r) and the inflow angle 7~ in the TBL are also examined using the present numerical results, and the formulae for predicting them are presented.

Influence of Swirl Ratio and Incident Flow Conditions on Generation of Tornado-Like Vortex

When evaluating occurrences of strong wind disasters, it is necessary to clarify the characteristics of tornado wind fields near the ground, such as whether or not there are differences from usual atmospheric boundary layer flow. A tornado simulator of the same type as Word (1971) has been developed to examine the characteristics of tornado flow fields. Visualization experiments have been conducted for various inflow conditions of the confluence layer and shapes of tornado-like flows have been observed. Two cases have been studied regarding supply circulation to the confluence layer, using guide vanes and applying shear flows. Wind speed measurement experiments have been conducted for different floor roughnesses and their effects have been studied.

Directional characteristics of probability distribution of extreme wind speeds by typhoon simulation

Abstract Wind directional fluctuations under typhoon condition was studied on the basis of its effect on the directional probability of annual maximum wind speed. A typhoon model that accurately models the average field observations, underestimates the maximum wind speed. Thus, a probability method is proposed for accurately evaluating the maximum wind speed probability distribution. This probability method is extended to corporate wind directional fluctuations. Before modeling is carried out, uncertainties are divided into physical and other conditions. The physical variation of wind direction is modeled probabilistically as directional fluctuations, and its formula is shown. Other uncertainties include statistical uncertainty (e.g., sampling error), modeling uncertainty and measurement error. These uncertainties are modeled considering two general situations: the maximum uncertain situation, where wind speed is used regardless of its direction, and minimum uncertain (definite), where wind direction is accurately evaluated. Taking these situations into account, a directional wind speed evaluation was formulated. Effects of physical wind directional fluctuations and wind directional uncertainties are indicated as a small increase in wind speeds for long-term wind speed recurrence. More effects were shown in the shorter return period range.

Mean Wind Pressure Coefficients on Surfaces of Gable-Roofed Low-Rise Buildings

To build an aerodynamic database for low-rise buildings, a series of pressure measurement wind tunnel tests were carried out on flat-, gable- and hip-roofed low-rise buildings in a simulated suburban wind field. Contours of statistics of point wind pressure coefficients on surfaces of the buildings were then drawn and disclosed on a website. The present study focuses on the mean wind pressure coefficients on roofs and walls of gable-roofed low-rise buildings for wind parallel or perpendicular to the roof ridges. The effects of building geometric parameters, height/breadth ratios, depth/breadth ratios and roof pitches, on the mean wind pressure coefficients on the building surfaces, which were sorted into four kinds of surfaces, upwind & downwind roof surfaces, crosswind surface, windward surface and leeward surface, are discussed. Based on these discussions, some new equations of the mean wind pressure coefficients are fitted as functions of building geometric parameters and the veracity of these fitted equations are compared with present test results and literatures.

Recent topics in wind engineering focusing on monitoring techniques

Publisher Summary This chapter provides an overview of wind speed monitoring, wind pressure monitoring, and wind response monitoring techniques and methods. In wind tunnel experiments, wind speed is usually measured by Pitot static tubes and hot-wire anemometers. However, optical techniques are playing important roles in comprehending complex flow fields. There are two main optical techniques available. One uses the optical Doppler shift and the interference effect and other obtains the loci of particles from two successive images. Doppler radar, GPS drop-sondes, and Doppler sodars are powerful devices for measuring atmospheric boundary layer wind profiles. Although the height and land use pattern of the ground surface are digitized and have been utilized as the geological information system, the aerodynamic effects of roughness including buildings and trees are most important in wind engineering. Recently, a laser profiler mounted on an aircraft with a GPS and an Inertial Navigation System has been developed. This technique enables monitoring of the displacement between the ground surfaces including obstacles, and then evaluation of the terrain roughness. The measured results are obtained in the form that can be handled by a computer as a digital terrain model, and is utilized for the shadow evaluation of a building condensed urban area.

Fluctuating Pressures on Cube Faces and Simulator Floor Intornado-Like Flow

Extreme local weather disturbances like tornadoes involve very complex interaction between wind and structure, making real time evaluation difficult. A tornado simulator was developed in the Wind Engineering Research Centre at Tokyo Polytechnic University and wind speeds and pressure distributions on a cubic model in tornado-like flow were measured. The present investigation focuses on fluctuations of pressure on the cube faces and the neighboring floor under a tornado-like flow. The pressure on the floor was distributed cylindrically and the curve best fitted to Rankine-type showed its core size to be of the same size as one from the wind speed distributions. The pressure was expressed as a wind pressure coefficient based on the central pressure depth. The wind pressures around the cube also showed the effect of swirl flow. A statistical analysis of the pressure coefficients was carried out and the results show the distribution of pressures on the faces of the cube and on the simulator floor. The results are compared with those obtained from a boundary-layer flow for the same cube over a range of incidence angles.

Mean wind pressure coefficients on gable roof of low-rise buildings

Publisher Summary The chapter discusses mean wind pressure coefficients on the cable roof of low-rise buildings. To comprehend wind effects on low-rise buildings, a series of pressure measurement wind tunnel tests for gable or hipped houses with roof pitches of 0°∼ 45°, height/breadth ratios of 3/8 ∼ 18/8, and depth/breadth ratios of 1.0 ∼ 4.0 are taken in the chapter. Based on these wind tunnel tests, mean values of wind pressure coefficients on gable roofs are calculated and compared with those in literatures. Effects of roof pitch, height/breadth ratio, and depth/breadth ratio of the gable house on the mean wind pressure coefficients for wind direction angle of 0° and 90° are analyzed in the chapter. Then new equations of the mean wind pressure coefficients are fitted with those test data.

From Load Estimation to Performance Estimation—From Model-Scale Test to Full-Scale Test: With Special Interest in Asian Region

This paper first discusses the current status of natural-hazard-induced disasters, with special focus on devastating wind-related disasters in the Asian region. The importance of the combined effects of wind and water hazards, the importance of performance of cladding and components in wind resistant design of buildings, and deterioration of metal roofing systems of long-span structures mainly caused by fatigue of fixing joints due to daily solar heating effects are demonstrated. Some human errors caused by lack of attention to aerodynamic and structural behaviors are also indicated. Then, psychological impacts and social impacts are discussed, and common underestimation of social impacts of wind-induced disasters on society is pointed out. The main reason for repeated wind-induced damage is lack of information on the real performance of claddings, components and main frames under wind actions. The demand and necessity for full-scale tests are emphasized, aiming to check the performance of building and structural systems under realistic and controlled conditions of extremely strong actions of wind, rain, snow, fire, solar heating and so on. Finally, the academic and social significance of the full-scale storm simulator is discussed.

Shielding Effects of Surrounding Buildings on Wind Loads on Low-Rise Building Roofs

Low-rise buildings are often built in groups, and their wind loads differ from those on isolated buildings. In this study, the wind pressures on flat roofs of low-rise buildings surrounded by similar buildings were measured with a series of wind tunnel tests. The general properties of the shielding effects of surrounding buildings were discussed. The effects of area density, relative height, and arrangement patterns of the surrounding buildings on the shielding factors of the smallest minimum negative extreme wind pressure coefficients and of the largest peak uplift force coefficients on the whole roof of the shielded building for all wind directions were analyzed. For practical purposes, both shielding factors were expressed as equations of the building area density and the relative height of the surrounding buildings based on the wind tunnel test data, which can cover most of the test results.