跃移砂粒起跳的受力机制

Force Mechanism of Lifting Off Saltstion Sand Particles

根据作者拍摄的高速电影摄影实验发现,沙粒起跳后垂直加速度均为负值,亦即沙粒跳离地面后再无大于重力的、向上的外力作用于其上,从而排除了八种起跳学说中的五种有关非接触力的起动学说,即:升力起动说、压差起动说、湍流起动说,负压起动说和涡旋起动说。在余下的三种有关接触力的起动学说中,作者估算后认为:跃移起跳是斜面飞升与冲击碰撞相结合作用的结果。在凸凹不平的地面上滚动的沙粒只需很小的速度(厘米/秒量级)就可离地而去,并从风中获取更多的能量。在地面上滚动或在空中飞行的沙粒,以不同的角度冲击其它颗粒,能以锐角和钝角反弹飞开。运动沙粒的动能只需有1/10转换为转动动能,就可使沙粒获得数百以至上千转/秒的转速。

According to experiement of high speed photography, we found that the vertical acceleration is al- ?ways negative value after san particle leaving ground surf ace, there is no upward external force smaller than gravity acting on the sand particle. Thus five out of eight lifting-off hypotheses of npncontacting force were precluded, such as buoyance force hypotheses, differential pressure hypotheses, turbulence hypotheses, negative pressure hypotheses and vortex hypotheses. Of the other three lif ting-off hypotheses of contacting forces, the author considered the saltant lifting off as an interactive result between bevel flying and impact. The rolling sand particle which move om uneven surface can detach from ground surface with low velocity (cm/sec)and get more energy from wind. Those sand particles which roll on the surface or fly in the air impact other particles from different angles,and bounce back at a-cute or obtuse angle. If the 10% of kinetic energy of moving sand particles transformed into rotative energy, sand particles could obtain hundreds or more than thousand of rotations/second of rotative velocity.