透射边界条件在点声源海底地震波数值计算中的应用

Application of transmitting artificial boundary in the numerical calculation of seabed seismic wave caused by a point sound source

航行舰船在海底岩土层中引起的弹性波被称为舰船地震波,主要由舰船低频辐射噪声引起,可用于识别舰船目标。本文采用大型有限元软件ANSYS中的流固耦合计算模块,结合多次透射公式(MTF)人工边界条件,对较为简单的水平分层海洋环境下低频点声源海底地震波进行了数值计算,并为了分析数值计算方法的精度,将数值计算结果与波数积分方法结果进行了比较。频率较低时两种方法的声传播损失曲线符合较好,频率较高时结果存在一定差别;两种计算方法所得声传播频率特性曲线的形式有所不同,但曲线总体变化趋势基本一致;而海底表面竖直位移、水平位移、竖直加速度和水平加速度的频率特性曲线基本符合。由此认为,基于多次透射公式人工边界,采用大型有限元软件ANSYS中的流固耦合模块,对较复杂环境下低频点声源海底地震波问题进行数值计算是基本可行的。

The elastic wave in seabed caused by the low frequency noise of a sailing vessel is often called ship seismic wave that can be used to identify ship target. A numerical calculation of seismic wave in seabed caused by a low frequency point sound source is carried out in this paper by applying the liquid-solid coupled calculating module of ANSYS in combination with the multi-transmitting formula artificial boundary. The results of numerical calculating method are compared with those of the wave-number integration technique in order to evaluate the accuracy of the numerical calculating method. The transmission losses of sound pressure vs. range are well agreed in the two methods when the frequency is relatively lower. Small differences are presented while the frequency is relatively higher. The characteristic curves of acoustic pressure vs. frequency are consistent on the whole in the two methods.Further more, the characteristic curves of displacement and acceleration on the surface of seabed in the frequency domain both in the vertical and the horizontal directions are basically accordant in the two methods. Use of numerical calculating method for simulation of seismic wave in seabed caused by low frequency point sound source is thus reasonable on the basis of the above comparison.