考虑结构损耗时水中圆柱壳的振动声辐射特性研究

Vibration and Sound Radiation by a Cylindrical Shell with Structural Loss in Water

基于圆柱壳的振动方程以及壳与流体边界上振速连续条件,推导了简支在刚性圆管上的有限长圆柱壳的低频声辐射的自辐射阻抗和互辐射阻抗计算公式,在考虑结构损耗情况下求解了圆柱壳的机械阻抗、表面振速、辐射声功率、辐射效率以及辐射声场的分布特征。结果表明:低阶模态自辐射阻抗大于互辐射阻抗,且自辐射阻随模态阶次增大迅速减小;当p、m同为偶数或奇数时模态辐射阻系数rpmqq大于零,反之小于零。模态辐射抗系数xpmqq在零值附近波动并当ka趋于无穷大时xpmqq都趋向零;p与m相差越大,rpmqq和xpmqq越小。当激励力频率较低时圆柱壳辐射声场指向性为"∞"和"8"叠加的形状;随频率增高,轴向模态和周向模态综合效果导致辐射声场指向性趋于复杂。计算简支圆柱壳的声辐射特征,必须要考虑结构的损耗。

Based upon the vibratory equation of cylindrical shells and continuous condition of vibratory velocity on the shell-fluid interface,the expressions for low frequency self-modal radiation impedance and cross-modal radiation impedance of a finite cylindrical shell simply-supported at two infinite rigid cylindrical shells are resolved.Under the consideration of the structural,loss the mechanical impedance,vibratory velocity,sound radiation power,sound radiation efficiency and the distribution of sound field of the shell are determined.It is sumarized that When the modal order is not high,self-modal radiation resistance and reactance are larger than cross-modal radiation resistance and reactance,and self-modal radiation resistance decreases rapidly with the increase of modal order;When modal order p and m get both even or odd,radiation resistance is larger than zero,otherwise it is less than zero;Radiation reactance oscillates around zero and approaches zero when ka approaches infinite;radiation resistance and reactance coefficients become small when the difference of p and m increases;When the frequency of the driving force is low,the sound field shapes as '∞'and '8'superposeition directivity pattern;When the frequency of the driving force grows higher the sound directivity pattern becomes complex due to the superposition of axial modes and circumferential modes.It looks necessary to consider structural loss for a finite simply supported cylindrical shell.