Study On Method Of Added Mass And Analysis Of Vibration Characteristics Of Double Bottom Structure In Ship'S Engine Room

It is necessary to calculate the natural frequencies and response characteristics of the double bottom structure accurately and quickly since the double bottom structure can resonate under the excitation like the main engine.Based on the classical singularity distribution method,a modified formula of linear free surface is proposed.The first three-order lateral vibration frequencies of submerged cantilever plate are calculated and compared with the experimental results.The results show that the correction formula can improve the accuracy of the calculation,especially for the condition that the draft is not deep and low frequency vibration.The results also show that the added mass of the first-order vibration can be regarded as the added mass of the structure.The first three natural frequencies of the double bottom model of an engine room were calculated by the above method,and the results were compared with the results of the virtual mass method to verify the accuracy of the calculation method.In order to obtain a fast and accurate method for calculating the quality of the added mass in the double bottom structure of the engine room,the added mass of the plate is firstly analyzed by the above method,considering the immersion depth ratio,plate thickness,size ratio,scale ratio and boundary condition,The influence of various parameters on the added mass of the plate is analyzed and the approximate calculation method of the added mass of the plate under different boundary conditions,depth of immersion and size ratio is summarized and the approximate method is compared with the empirical formula.The results show that the experimental results are in good agreement with the results of this method in the infinite water depth,which verifies the correctness of the approximate method and gives a detailed analysis of the relationship between the submerged depth and added mass.Finally,the added mass of the double bottom structure of the engine room was estimated based on the above-mentioned approximate added mass calculation method and applied to the bottom plate for analysis of vibration characteristics.Compared this calculated results with the virtual mass method and experience results,which shows this method is more accurate than the empirical formula.The dynamic response characteristics of two kinds of bottom structures are calculated by using the added mass obtained from this method.