Study on the bubble sound induced by the impact of a water drop on a liquid surface and exploration of possibility of sound control

通过改变水滴直径d_D和落点高度H（即冲击速度V_<imp>），研究了水滴撞击水面引起的表面变形和气泡形成。对与水精鼓声条件密切相关的不规则气泡夹带区域进行了详细的实验。结果总结如下：(1)在不规则气泡夹带区，我们发现了三种气泡形成机制。特别是可用的声音是由以下机制产生的气泡振荡引起的。第一种情况是由卫星液滴与上升的水面碰撞而产生气泡。第二种气泡形成模式与水柱下落过程中的表面闭合有关。(2)即使在不规则气泡夹带群中，也存在一些区域（d_D-V_<imp>）的条件，即气泡受随空腔表面底部上升的卫星落差的影响而被有规则地夹带。另一方面，水柱在下落过程中会随机产生气泡，从而产生各种各样的水下声音。这些声音的频率范围通常很广。

By changing the drop diameter d_D and dropping height H (i.e.impact velocity V_<imp>), we investigated the surface deformation and air bubble formation induced by the impact of a water drop on a water surface. A detailed experiment was carried out for the irregular bubble entrainment region which is closely related to the sound condition of Suikinkutsu. The results are summarized in the followings.(1)In the irregular bubble entrainment region, we found three types of mechanisms for air bubble formations. Especially available sounds are caused by the oscillation of air bubbles generated by the following mechanisms. The first one is the case where an air bubble is generated by the impact of a satellite droplet with a rising water surface. The second pattern of air bubble formation is associated with the surface closure during the falling process of the water column.(2)Even in the irregular bubble entrainment legion, there is some area of the (d_D-V_<imp>) condition where an air bubble is regularly entrained due to the impact of a satellite drop with the rising bottom of the cavity surface. On the other hand, during the falling process of the water column air bubbles can be generated randomly, resulting in a variety of underwater sounds. These sounds often have a wide range of frequencies.