Research On The Calculation Method Of Underwater Acoustic And Vibration Response Of Cabin Segment Based On Onshore Vibration Test

As the main underwater combat platform,concealment is the most remarkable characteristic of submarine,and also the guarantee of its safety and combat effectiveness.Mechanical vibration caused by power plant is one of the main noise sources of submarine,and vibration acoustic radiation test is an important means to obtain its vibration acoustic radiation characteristics.Considering the high cost and difficulty of underwater vibration and sound radiation test,it is of great engineering significance and application value to replace underwater whole boat vibration and sound radiation test by predicting underwater whole boat vibration performance based on onshore cabin vibration test.Firstly,according to the vibration test of land cabin under the condition of elastic support,the influence laws of elastic support on the vibration characteristics of land cabin is studied,so as to establish the correction method of elastic support to free boundary.Through the modal space transformation,the influence of the elastic support on the modal parameters of the structure is deduced,and the modification method of the modal parameters on the elastic support boundary is established.In this paper,the accurate cabin finite element model is condensed to the radial degree of freedom to simulate the measured data and verify the applicability of the modified method.Numerical examples show that the modified method based on the measured modal parameters and vibration response of the structure can be well converted into the modal parameters and vibration response of the structure in free state.Secondly,the conversion method of acoustic vibration characteristics between onshore and underwater cabin structures is studied.The axisymmetric boundary element method(BEM)is introduced to describe the radiated acoustic field,and the acoustic radiation impedance matrix of the outer surface of the shell is constructed by solving the integral equation of BEM.Based on the assumption that the low order mode of underwater cabin structure is the same as that of onshore cabin,combined with the boundary element theory and structural modal theory,the modal added mass and modal added damping are calculated,and the conversion formulas of natural frequency and vibrational acoustic radiation of onshore cabin and underwater cabin are derived.Numerical examples from simple cylindrical shell to complex cabin structure show that the method meets the requirements of engineering precision.Finally,the influence of structural truncation on the vibration performance of the cabin and the correction method are studied.According to the characteristics of intermodal coupling of each sub-compartment,it is necessary to adopt the mode synthesis method to modify the truncated sub-compartment.The free interface mode synthesis method is adopted to obtain the dynamic parameters of the whole model by synthesizing the modal results of each substructure.By changing the degree of freedom of boundary forces,the influence of interface forces on the modal synthesis is studied.The results show that at least X,Y and Z forces need to be considered in order to ensure the accuracy of the modal synthesis results.By constructing residual stiffness and residual mass,the modal synthesis of test and theoretical compartments can be realized.