Modal Analysis Of HAP Fuel Tank Structure Based On Time-Varying Mass

HAP tri-propellant fuel tank is an important part of the power and energy section of the high power gas turbine of the torpedo.Due to the significant difference in the density of aqueous solution of HAP and seawater,the pressure chamber extrusion process is a typical time-varying system.In this paper,according to the HAP fuel tank,the modal analysis in the time-varying process of mass is studied.It can lay a good foundation for the analysis of the vibration characteristics of the fuel tank and the analysis of the whole mine vibration and noise,which has important theoretical significance and engineering application value.In this paper,based on the Rayleigh-Ritz energy method,the dry state structural dynamic equations for the unfilled HAP fuel tank are established.On the basis of the dry state equations,the dynamic equations of the wet-mode structure under the condition of liquid filling are established by the acoustic-structure coupling method,the additive mass method and the virtual mass method.According to the mass change of the aqueous solution HAP and the extruding water,and the change of the piston position during the work process,combining the difficulty and accuracy of finite element modeling of the three calculation methods,the virtual mass method is used to establish the time-varying wet modal dynamics equation of the HAP fuel tank.The HAP fuel tank’s finite element analysis models of dry mode and wet mode are established in Patran-Nastran software.Using the combination of finite element simulation and modal testing,we obtain both the parameters of dry modal and the wet modal of HAP aqueous solution and seawater under different mass conditions of the test fuel tank.By adjusting the virtual mass coefficient,the modelling method of the finite element model of the test fuel tank is corrected with the experimental results.Finally,the HAP fuel tank’s finite element model of the wet mode is corrected and improved.The first four-order non-rigid modal parameters in the free-free state of the HAP fuel tank are calculated and analyzed.According to the time-varying dynamic equations of the wet-mode structure,the secondary development of the finite-element software is performed through the Matlab program and the PCL language of Patran-Nastran software to calculate the modal parameters during the mass-time-varying process of the HAP fuel tank.The changes of the natural frequency and mode shape for HAP fuel tank over time are analyzed.The results of this paper provide a reference for vibration fault diagnosis,structural design and performance optimization of the HAP fuel tank and other similar structures.