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。在多处被龙卷破坏的地区，建筑物、房屋、塔、塔、杆和招牌的破坏程度往往有很大差异，这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、木材和砾石等投掷物的散布方式几乎没有规律性。这是旋转风暴和波动速度的结果，这是tatsumakis的特征。当tatsumaki经过时，风速和风向会不断变化，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变化。由非定常流引起的物体上的风力必然不同于由恒定速度的定常流引起的风力。因此， 关于我们 结构物上的荷载应不同于台风或季风引起的荷载，因为两者都可以近似为定常流。在本研究中，我们假设tatsumaki的旋转运动是以恒定速度移动的Rankine涡，并分析了tatsumaki路径沿着任意点处的非定常水平流。在非定常/加速流的作用下，惯性力是物体上产生的，它可以由以前的实验数据估算，也可以用无粘流的速度势进行理论计算。将惯性力和与流体速度平方成正比的拖曳力合并到Morison方程中，从而能够表达总的流体力。数值计算了涡卷通过任意位置结构时产生的脉动流体力，涡卷内任意点的速度和加速度随时间连续变化，在涡核处达到最大值。加速度与涡的平移速度无关，并且指向涡的中心，作用于结构物的总风力在涡的背风核心处达到最大。由于流体的加速度的惯性力是从流体速度的平方获得的阻力的约30%。物体被龙卷吹落的方向在涡中心路径的不同侧可能是相反的。这与对实际辰卷损害的实地调查结果一致。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