声介质对有限潜深圆柱壳自振特性的影响机理分析

Influence of Acoustic Media on Vibration of Submerged Cylindrical Shell with Finite Depth

计及流体静压和自由液面的影响,建立有限潜深状态下有限长圆柱壳-声场耦合振动模型,从声固耦合角度出发提出了模态附连水质量概念,进而揭示自由液面对水下圆柱壳振动特性的影响机理,并通过分析结构等效弯曲刚度的变化解释了流体静压的影响机理。研究表明:自由液面的存在将导致结构模态附连水质量减小,致使结构模态频率相应增大;随着潜深的增大,自由液面的影响逐渐减小;在薄壳振动范围内,当潜深大于4倍壳体半径时,自由液面的影响可以忽略,该结论具有普适性,不受壳体长度和半径的影响;计及流体静压将导致结构等效弯曲刚度减小,最终致使结构模态频率相应减小;随着潜深的增大,流体静压的影响程度逐渐增大。为满足工程计算精度要求,当潜深大于18m时,考虑流体静压的影响不可忽略,而当潜深足够大时,结构将面临失稳。

From the view of sound-structure interaction,a dynamic model is built for a finite cylindrical shell submerged with finite depth below the free surface.With consideration of free surface and hydrostatic pressure,mdoal added mass concept is proposed to reveal influence of the free surface and hydrostatic pressure on the structural vibration.Some conclusions are made:presence of the free surface will make negative contribution to the modal added mass and results in the increase of coupled modal frequency;the free surface effect will be reduced and finally negligible if the immersion depth is more than 4R;account of hydrostatic pressure will reduce flexural stiffness of submerged structures;effect of hydrostatic pressure will be important and the shell will be instability,if the immersion depth is big enough.When the immersion depth is more than 18 meters,the effect of hydrostatic pressure cannot be neglected.