Design of Ultrasound-Field in Liquid in Materials Processing

为了在材料加工中有效地利用液体中的超声波外力，对其声场进行了数值分析和测量。在设计的驻波超声作用下，对复合材料中热对流的抑制、悬浮颗粒的混凝分离和增强纤维的定向控制进行了模型实验。主要研究成果如下：(1)提出了一种基于特征曲线法的一维声场数值分析方法。计算场、解析场和观测场的高度一致表明了该方案的有效性。该方案允许分析波的瞬时传播以产生驻波。(2)发展了一种基于波动方程有限差分解的二维数值格式，以处理更复杂的声场。这种方法可以考虑容器的结构和材料、液浴的深度和性质以及超声波振子的频率和布置来设计声场。(3)研究超声波对热对流影响的水模型实验表明，加热的液体元素可以在声节点附近被抑制。在低能量密度情况下，作用在液体单元上的主要超声力可能是辐射压力，而在高能量密度情况下，作用在液体单元上的主要超声波作用力可能是由于声压的时间平均梯度引起的体力。(4)实验表明，悬浮夹杂物在平面状结节中凝结后，可能从液浴中分离出来。(5)提出了一种有效的超声定向控制复合材料中增强细纤维的方法，并对支撑实验的结果及其机理进行了讨论。

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.