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UNSTEADY WIND FORCES IN TATSUMAKI

龙卷不稳定的风力

基本信息

批准号：
06452288
负责人：
TANIIKE Yoshihito
金额：
$ 3.97万
依托单位：
Osaka City University (1995)Kyoto University (1994)
依托单位国家：
日本
项目类别：
Grant-in-Aid for General Scientific Research (B)
财政年份：
1994
资助国家：
日本
起止时间：
1994 至 1995
项目状态：
已结题

来源：
https://kaken.nii.ac.jp/en/grant/KAKENHI-PROJECT-06452288/
关键词：
Tatsumaki Unsteady Wind Force Rankine Vortex Added Mass Velocity Potential Morison's Equation Wind Tunnel Experiment 渦構造物被害加速度ランキン

项目摘要

The word 'tatsumaki' is used in Japan to designate meteorological phenomena as tornadoes and waterspounts. In surbeys of tatsumaki damage, great differences are often observed in the magnitude of damage to buildings, housings, towers, pylons, poles and signboards, depending on where these structures were located relative to the path of the tatsumaki. Generally, there is little regularity in the direction these structures are torn down or in which way missiles such as roofing tiles, timbers and gravels are scattered. These are results of rotational windstorms and fluctuational velocities, that are characteristic of tatsumakis. As a tatsumaki passes over, the speed and direction of wind will change constantly, creating rapid transitions in the magnitude and direction of wind loads on structures it encounters, both in time and space. Wind forces on bodies induced by unsteady flows are inevitably different from those by steady flows with constant velocity. Therefore, tatsumaki-induced wind … More loads on structures should be different from those induced by typhoons or monsoons, as both can be approximated as steady flows.In the present study, we assumed the swirling motion of tatsumakis as a Rankine vortex that moves with a constant velocity, and analyzed the unsteady horizontal flow at arbitrary points along the tatsumaki path. By the action of unsteady/accelerating flow, the inertial force is generated on bodies and it can be estimated by the previous experimental data or by the theoretical calculation using the velocity potential of inviscid flow. The inertial force and the drag force which is proportional to the square of fluid velocity were combined and incorporated into the Morison's equation, which was then able to express the total fluid force. The fluctuating fluid forces generated during the passage of a tatsumaki on arbitrary located structures were numerically estimated.The velocity and acceleration at arbitrary points in the tatsumaki varied continuously with time and both reached maximum at the core of the vortex. The acceleration did not depend on the translation velocity of the tatsumaki and was directed towards the center of the vortex.It was found that the total wind force acting on structures became maximum at the leeward core of the tatsumaki vortex. The inertial force due to the acceleration of fluid was about 30% of the drag obtained from the square of fluid velocity. The directions in which the bodies are blown down by a tatsumaki may be reversed on the different sides of the path of the vortex center. This was shown to be consistent with the results of a field survey on actual tatsumaki damage. Less

在日本，“tatsumaki”一词用于指代龙卷风和水龙卷等气象现象。在龙卷损坏调查中，经常观察到建筑物、房屋、塔楼、塔架、电线杆和招牌的损坏程度存在很大差异，具体取决于这些结构相对于龙卷路径的位置。一般来说，这些建筑物被拆除的方向或屋顶瓦片、木材和碎石等导弹的散布方式几乎没有规律性。这些是旋转风暴和波动速度的结果，这是龙卷的特征。当龙卷经过时，风速和风向会不断变化，导致其遇到的结构上的风荷载大小和方向在时间和空间上发生快速转变。非定常流引起的物体上的风力不可避免地不同于恒速稳定流引起的风力。因此，龙卷引起的风荷载应该不同于台风或季风引起的荷载，因为两者都可以近似为稳定流。在本研究中，我们将龙卷的旋转运动假设为恒速运动的兰金涡，并分析了龙卷路径上任意点处的非定常水平流。通过非定常/加速流的作用，物体上会产生惯性力，可以通过先前的实验数据或利用无粘流的速度势进行理论计算来估计。将惯性力和与流体速度的平方成正比的阻力合并并代入莫里森方程，从而能够表达总流体力。对龙卷通过任意位置结构时产生的脉动流体力进行了数值估计。龙卷中任意点的速度和加速度随时间连续变化，并在涡旋核心处达到最大值。加速度不依赖于tatsumaki的平移速度，而是指向涡旋的中心。发现作用在结构上的总风力在tatsumaki涡旋的背风核心处变得最大。由流体加速度引起的惯性力大约是由流体速度的平方获得的阻力的30%。龙卷将尸体吹落的方向可能会在漩涡中心路径的不同侧反转。这与对龙卷实际损失的现场调查结果一致。较少的