Study On Dynamic Impact Response Of Ship Propulsion Shafting System Under Non-contact Explosion

With the promulgation of the “strengthening the armed forces through science and technology” policy and the deepening of “the national Marine” strategy,the requirement of Chinese navy for ships’ anti-strike capability is increasing day by day.The impact resistance of shipborne equipment is an important index to reflect the vitality of ships.Propulsion shaft is the ship’s power actuator,of which impact resistance is particularly important.According to the standard of the navy,shock resistance test should be carried out before the equipment installation.However,the scale of Marine diesel engine shaft system is always too large to conduct physical test.Meanwhile,in physical test,the dynamic load generated by underwater explosion is difficult to implement.Therefore,numerical simulation is often used to estimate the dynamic shock response in engineering.In this paper,the numerical method for calculating the impact resistance of ship propulsion shafts was studied.The dynamic response of the shafts was analyzed by simulation.First of all,numerical calculation method of the impact resistance of shafting was introduced in this paper.A theoretical derivation of the direct integration method was given.Based on the beam model,the equivalent dynamic model of a large shafting was established.According to the empirical formula of underwater explosion load in the Standard bv043/85,shock wave(scattered wave)load model and bubble pulsation load model were used as input excitation respectively.Newmark method was applied to calculate the shock dynamic response of shafts.The shock dynamic response characteristics of key nodes were analyzed.The difference and correlation between the two load models were compared.Then,the theory of non-contact explosion load was derived.The fluid-solid coupling theory of underwater explosion and the acoustic solid coupling method of numerical calculation of far-field explosion were theoretically deduced.The finite element model of the installation base of propulsion shafts was established.According to the often-used simulation condition of underwater explosion in engineering,the response of the shafting’s installation base was calculated based on the acoustic solid coupling method.The stress response of typical elements and the acceleration response of typical nodes were calculated.The acceleration and stress response of bearing nodes were extracted.The propagation law of loadin the installation infrastructure was analyzed.The impact response of shafting base was obtained.By comparing the response characteristics under different working conditions,the influence of underwater explosion parameters on the response was summarized.Then,by referring to the experimental model of the scaled shafting in the reference,the3 D finite element model of a small naval vessel’ shafting was established.Then,the model was coupled with the installation base.Two coupling forms,rigid connection and considering the equivalent dynamic stiffness of bearing,were used to calculate the equipment response and base response of coupling model.The stress cloud diagram of the coupled system and the load propagation law were obtained by simulation.Under various working conditions,the time-history curve and response peak of bearing support nodes and shafting connection nodes’ dynamic stress were obtained.The difference in response characteristics between the two coupling forms was compared.The calculation deviation of the dynamic response of propulsion shafting was obtained only when the foundation was considered and when the ship-equipment was rigidly connected.Finally,based on the theory of dynamic substructure,a semi-decoupling equation to calculate the response of ship-equipment coupling system was obtained using the “virtual constrained interface modal method”.In this method,the effect of the ship substructure on the equipment substructure was obtained by the constrained modes on the interface between equipment and ship.This method only needs to solve the equations of which degrees freedom equal to each substructure’s.This reduces the size of the dynamic equations.The effectiveness of the proposed method was verified by numerical examples.Simulation results using finite element method and dynamic substructure method were compared.The dynamic response of shipborne equipment and ship local structures were calculated.