不同激励下双层底振动传递特性研究

摘要

为了控制结构振动引起的船舶辐射噪声,截取某型舰艇的机舱双层底并按比例缩减,建立双层底结构的有限元模型,以舱室辅机设备离心泵机脚振动加速度作为单激励,离心泵与激振机激振力代表多激励,在20 Hz～400 Hz频段内对单激励与多激励下双层底结构的频率响应进行分析,并计算底桁和实肋板的结构声强,根据各实肋板和底桁的声强贡献度及声强矢量图对峰值频率的主要传递路径进行辨识排序;以此为基础在主要传递路径上布置阻振质量块,用声学边界元方法计算双层底结构的远场辐射声,以研究频段内合成辐射声功率级为评价指标验证减振措施的可行性.研究发现双层底结构在单激励和多激励下的主要传递路径都位于激励侧下方,单激励变成多激励后系统的最大响应峰值频率由33 Hz变成87 Hz,底桁和实肋板的Y向结构声强和增大一个数量级;在主要振动传递路径布置阻振质量使双层底结构的声辐射减少了8.2 dB.%In order to control the radiated noise of ships caused by structural vibration, the double layer bottom of the engine room of a certain type of ships is extracted and proportionally contracted for finite element analysis. Vibration acceleration of the marine centrifugal pump is used as a single stimulus, and the centrifugal pump and exciting machine excitation forces represent the multi-excitation. In the 20 Hz - 400 Hz frequency range, the frequency responses of the double layer bottom under single excitation and multiple excitations are analyzed and the structural sound intensities of the bottom girder and the plate floor are calculated. The main transmission paths of the peak frequency are identified according to the contributions of the structural sound intensities and the structural sound intensity vector diagrams of each plate floor and bottom girder. On this basis, vibration isolation mass is arranged on the main transmission path, the far-field radiated sound of the double layer bottom is calculated by the acoustic boundary element method. The feasibility of the vibration reduction measures according to synthetic noise power level in the frequency band is evaluated. It is found that the main transmission paths of the double-layer bottom structure under single excitation and multiple excitations are located beneath the excitation side. The peak response frequency of the system changes from 33 Hz to 87 Hz after the single excitation turns to multi-excitation. The structure sound intensity in the Y-direction of the bottom girder and the plate floor is increased by nearly 10 times; By arranging vibration damping mass in the main vibration transmission path, the acoustic radiation of the structure is reduced by 8.2 dB.