Design of Ultrasound-Field in Liquid in Materials Processing

为了有效利用液体中的超声外力在材料加工中的作用，对液体中的声场进行了数值分析和测量。在设计的超声驻波作用下，对复合材料中热对流的抑制、悬浮颗粒的凝聚分离和增强纤维的方向控制进行了模型实验。主要研究成果如下：（1）建立了一种基于特征曲线法的一维声场数值计算方法。计算和分析的字段以及观察之间的密切协议表明该计划的有效性。该方案允许分析导致驻波的波的瞬态传播。(2)为了科普更复杂的声场，发展了一种基于波动方程有限差分解的二维数值格式。该方法允许考虑容器的构造和材料、液浴的深度和性质以及超声振动器的频率和布置来设计声场。(3)水模型实验研究了超声对热对流的影响，结果表明，超声可以抑制声节点附近的加热液体单元。在低能量密度情况下，作用于液体元件上的主要超声力可能是辐射压力，而在高能量密度情况下，由于声压的时间平均梯度而产生的体积力。(4)实验结果表明，悬浮夹杂物在凝固成平面状后，可能从液池中分离出来。(5)本文提出了一种有效控制复合材料中细纤维增强方向的超声波方法，并对实验结果和机理进行了讨论。

For an effective utilization of ultrasonic external force in liquid in materials processing, numerical analysis and measurement has been made on the sound field. Under designed standing wave of ultrasound, model experiments have bee carried out on suppression of thermal convection, coagulated separation of suspended particles, and directional control of reinforcing fibers in composite. The results are summarized as follows :(1) A numerical scheme based on the characteristic curve method has been developed to analyze one-dimensional sound field. A close agreement between calculated and analytical fields as well as observed ones indicated validity of the scheme. The scheme allows to analyze transient propagation of a wave to result in a standing wave. (2) A two-dimensional numerical scheme based on the finite difference solution of the wave equation has been developed to cope with more complicated sound field. This method allows to design sound field taking configuration and materials of a vessel, depth and properties of liquid bath, and frequency and arrangement of ultrasonic vibrators into consideration. (3) Water model experiments to investigate the effect of ultrasound on thermal convection showed that heated liquid element can be suppressed around sound nodes. Major ultrasonic force acting on a liquid element could be radiation pressure in low energy density case and a body force due to time-averaged gradient of sound pressure in high energy density case. (4) An experiment showed a possible separation of suspended inclusions from liquid bath after their coagulation in plane-like nodes. (5) An effective ultrasonic method for directional control of reinforcing fine fibers in composite has been newly proposed and results of supporting experiments and its mechanism has been discussed.