Correction Method Of Ship Low-frequency Impact Environment And Its Application In Shafting Impact Resistance

Ships will inevitably be subjected to underwater explosion impact loads during the service,resulting in impact damage on the hull structure and shipborne equipment.Under the action of underwater explosion load,the total vibration response of the hull is mainly the first three-orders of low frequency response,so the accuracy of low-frequency impact environment is of great significance for the impact resistance research of shipbome equipment.Through the analysis of the impact response data of the actual ship test,it is found that the strain response has good accuracy for the low-frequency total vibration.Therefore,the method of correcting the low-frequency impact environment by strain response is proposed.In this paper,the modal superposition method is used to calculate and analyze the total vibration displacement response under underwater explosion load.According to the elastic mechanics analysis,there is a corresponding relationship between acceleration and strain to realize the correction of the measured low-frequency impact environment.The impact characteristics of low-frequency equipment-axial system under underwater explosion load are analyzed,and the influence of support stiffness,impact factor and low-frequency environment on impact response are analyzed in details below.Firstly,the dynamic analysis of the hull girder under the underwater explosion load is carried out.The vibration response of the beam is analyzed by the modal superposition method.According to the principle of elastic mechanics,the proportional relationship between the acceleration response and the strain response of the system is found,it is related to and the natural frequency of the system and the mode shape,and provides a theoretical basis for realizing the strain response to correct the low frequency impact environment.The calculation and analysis of the single-span beam model are carried out by numerical simulation method to verify the feasibility of the above method.The strain transfer function is analyzed based on the principle of strain modal analysis,and the modal parameter identification method is used to determine the natural frequency and mode shape of the complex structure.Secondly,the underwater explosion impact test of the actual ship is briefly introduced,and the overall layout and test conditions of the test points are analyzed.Introduce the preprocessing method of test data,and perform preprocessing such as data screening,trend elimination,smoothing processing and digital filtering processing on a large number of experimental data.Perform spectrum analysis on the test impact environment and strain data,and analyze the distribution characteristics of the strain peaks in the vertical and vertical directions respectively.The modal superposition method is used to predict and correct the low-frequency impact environment using strain signals,and the influence of strain response on the impact environment is analyzed.Thirdly,the influence of the low-frequency impact shafting impulse response is explored.Based on the correction of the actual ship impact environment based on the strain signal,and the influence of low-frequency impact environment on the equipment’s impact load input is analyzed.The impact of the measured impact environment and the strain-corrected impact environment on the impact response of the shafting system is analyzed,which provides a reference for the impact analysis of the ship’s slender body equipment.Finally,the establishment and simplification of the model in the ship’s propulsion shafting impact analysis based on the paddle-ship-axle integration model are explored.Simplified issues in terms of attached water quality attached to the shaft string,propeller and bearing base are considered,and the hull-flow field-shaft coupling model of the shaft system impact analysis is finally established,and calculate and analyze the shafting impulse response under typical conditions.Based on this method,the influence of impact factor and support stiffness variation on the shafting impulse response is analyzed.