UNSTEADY WIND FORCES IN TATSUMAKI

“tatsumaki”这个词在日本被用来指龙卷风和水龙卷等气象现象。在遭受辰火破坏的郊区，通常可以观察到建筑物、房屋、塔、塔塔、电线杆和招牌的损坏程度有很大差异，这取决于这些建筑物相对于辰火路径的位置。一般来说，这些建筑物被拆除的方向或屋顶瓦片、木材和砾石等导弹的散布方式几乎没有规律性。这些都是旋转风暴和波动速度的结果，这是tatsumakis的特征。当“辰火”经过时，风的速度和方向会不断变化，在时间和空间上，它所遇到的结构上的风荷载的大小和方向都会发生快速的变化。非定常流动对物体所产生的风力不可避免地与定常等速流动所产生的风力不同。因此，对建筑物的更多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的流动。在本研究中，我们将tatsumaki的旋转运动假设为一个等速运动的Rankine涡，并分析了沿tatsumaki路径任意点的非定常水平流动。在非定常/加速流动的作用下，对物体产生惯性力，惯性力可以用以往的实验数据或用无粘流动的速度势进行理论计算来估计。惯性力和与流体速度平方成正比的阻力被合并到莫里森方程中，从而可以表示总的流体力。用数值方法估计了辰火在任意位置的结构上通过时所产生的波动流体力。在辰卷内任意点的速度和加速度随时间连续变化，并在涡核处达到最大值。加速度不依赖于tatsumaki的平移速度，而是指向漩涡的中心。结果表明，作用在构筑物上的总风力在垂垣涡的背风核心处最大。由流体加速度引起的惯性力约为流体速度平方所产生的阻力的30%。在涡旋中心路径的不同侧面，尸体被龙卷风吹落的方向可能是相反的。这与实地调查的结果是一致的。少

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