MgSO4弛豫吸收对水下强声波脉冲传播的影响分析

对水下等离子体放电强声波脉冲实验测量波形进行FFT变换发现,其能量主要集中在100kHz以下的频段内,在这个频段内,海水中存在的一种盐类——MgSO4(硫酸镁)化学弛豫会造成声波的逾量吸收.本文从包含海水中MgSO4弛豫吸收的修正物质状态方程出发,推导了强声波脉冲传播的新的波动方程,并结合具体的数值算法,对强声波脉冲的传播进行了数值模拟,分析了MgSO4弛豫吸收对脉冲波形的传播及频谱的影响.研究表明,MgSO4弛豫吸收对陡峭的冲击脉冲波形具有平滑和展宽作用,使得脉冲的能量更靠近低频.这种效应与球面波阵面的几何扩散相结合,造成了强声波脉冲能量的逾量损失.

Analysis of the effects of MgSO4relaxation on the propagation of underwater intensive acoustic pulse

Based on the spectrum analysis of the experimental intensive acoustic pulse waveform using FFT,the current research found that the dominating energy of the spectrum is below 100 kHz.It is well known that one of the chemical compositions in sea water,MgSO4,will cause excessive absorption of acoustic energy due to its chemical relaxation.Starting from a modified equation of state,with special consideration of the relaxation absorption of MgSO4 in seawater,a new wave propagation equation of intensive acoustic pulse was deduced.Combined with the numerical algorithm,the propagation process of the pulse was simulated and the effects of MgSO4 relaxation on waveform and spectrum were analyzed.The results indicate that relaxation process will flatten and smooth the steep pulse waveform,and reduce the acoustic energy to low frequency end.The chemical relaxation effects will cause extra loss of the pulse energy,in addition to the geometric spreading effects of pulse wavefront.