基于固-气-液耦合的气垫船水下辐射噪声数值分析

Numerical analysis of underwater radiation noise of air cushion vehicles considering structure-air-water interaction

气垫船水下声辐射是复杂的船体结构-气垫-周围水体三类介质声振耦合过程,其声传递特性是气垫船声学分析中的难点。本文以某全垫升气垫船为研究对象,结合声固耦合有限元法与解析法,探究气垫船水下辐射噪声传递特性。通过建立固-气-液声固耦合有限元模型,计算机械激励与垫升风机声激励,并以试验固有频率修正数值模型;通过声透射解析公式计算空气螺旋桨、燃气轮机等设备声激励辐射的水下噪声。采用距离左、右舷1 m处线上各点的总声压级作为评价指标。结果表明:气垫船水下辐射噪声为宽带噪声;有限元法计算的水下辐射噪声在低频时集中分布于气垫-周围水体耦合面附近,随着频率的升高,水下噪声增大并逐渐呈不规则干涉状分布;空气螺旋桨等声激励直接辐射水下噪声主要为近场低频噪声,在设备声激励辐射范围内声压平均占比约为40%。本文揭示的水下辐射噪声传递特性对气垫船减振降噪具有重要指导意义。

The underwater acoustic radiation of air cushion vehicles(ACVs)is a complex process consider-ing hull structure-aircushion-water three-phase interaction and vibro-acoustic coupling,which has complex transmission characteristics and is the key and difficult issue in the ACV acoustic analysis.With an ACV tak-en as a computational example,the vibro-acoustic finite element method(FEM)and the analytical method were used to analyze the transmission characteristics of the underwater radiation noise of the ACV.To calcu-late the underwater acoustic field for mechanical noise sources and airborne sources of lift fans,a vibro-acoustic FEM numerical model considering structure-air-water interaction was established and calibrated by the natural frequency of the hull obtained from the tests.The analytical formulas were used to calculate the underwater acoustic field for airborne sources of other equipment.The overall sound pressure level(OASPL)at points 1 m from the port and starboard sides was adopted as an evaluation index.The research shows that the underwater radiation noise of the ACV is broadband noise.The underwater acoustic pressure calculated by the FEM increases with the increase of frequency,and the pressure is concentrated on the aircushion-wa-ter interaction surface at low frequencies.With the increase of frequency,the underwater acoustic field calcu-lated by the FEM gradually presents an irregular interference distribution.The underwater radiation noise caused by the acoustic excitation of equipment like air propellers is mainly near-field and low-frequency noise,accounting averagely for 40%of that of the ACV within the sound radiation range of the equipment.The transmission characteristics of underwater radiation noise of ACVs revealed in this paper has important guiding significance for the vibration and noise reduction of ACVs.