Analysis Of The Underwater Launch Dynamics And Optimized Design Of The Vibration Reduction

Launch of the underwater vehicle will generate a huge impact acting on the launch canister,causing strong vibration of the Underwater Launch System(ULS),which has great influences on the structural strength and safety of the ULS.When launching consecutively,vibration superposition will occur to affect the reliability and accuracy of the subsequent launching,severely weakening underwater strike capability.It is one of the important research contents in underwater launch dynamics to analyze and control the transient responses.The difficulties of the study are that the mass,model structure,stiffness and loads of the ULS are changing when launching successively,which is a complex non-linear time-varying problem.In the thesis,the dynamic problems and vibration reduction design of the underwater General Launch Platform(GLP)with continuous launch capability are studied.Firstly,the structural models and fluid-structure coupled models of the GLP are established with coupled finite element method(FEM)to investigate its natural vibration and dynamic characteristics of the GLP.Secondly,the load of the underwater vehicle out of tube is simulated and the impact responses are obtained by means of the ABAQUS/Explicit method.Then,a substructure method based on modal synthesis is proposed to build the dynamic model of the ULS considering successive launch effects.State-space method is employeed to obtain the time-history of the responses.The validity of the method is verified by comparing the results with those obtained by FEM.In the end,a method is proposed for the optimized design of vibration reduction about the GLP,which is conducted from two aspects: structural improvement and parameter optimization of the longitudinal isolator.It is found that the GLP is more sensitive to transverse excitation since the bending vibration modes is primary.The vibrations of the launch canister take a leading role under the submarine vibration environment.Under transient impact loads,the main stress and strain area of the GLP are concentrated in the loading region.With the longitudinal isolators locked in succession,the attenuation amplitude of the impact response decreases.By comparing the results of the proposed method with those obtained by FEM,excellent agreements demonstrate the present method is accurate.Besides,obvious vibration reducing effects are achieved by adjusting spacing distance between the two horizontal adapter or adding one.The parametric studies show the performance of vibration reduction about the longitudinal isolator is favorable when the stiffness is 0.64-3.7 times of the initial stiffness and the damping coefficient is 0.004-0.007 times of that.The proposed method is an important innovation in this thesis,which not only can be used for dynamic modeling of complex vertical launch system,but also can take the time-varying nonlinear effects into consideration.Meanwhile,the present method is of high flexibility and high computing efficiency in parametric study,which may provide useful information for the design and optimization of underwater launch system in engineering practices.