Research On Complicated Multi-mode Vibration And Optimization Of A Ship Stern Structure

The propeller and the propulsion shafting are important components of the ship’s propulsion device.The vibration responses caused by the excitation force of the propeller are superimposed on each other,and it is easy to form the torsional,longitudinal,lateral and even multi-modal coupled vibration of the stern structure.Since the formation mechanism of multimodal coupled vibration of the stern structure is not clear,it poses a potential threat to the safety of the ship structure near the water surface.Therefore,based on engineering practice,this paper studies the multi-modal vibration characteristics of the ship’s stern structure,aiming to clarify the vibration law of the ship’s stern structure,reduce the vibration level of the ship’s stern structure by combining the optimization algorithm,and provide a new method for solving practical problems.First of all,this paper carries out the research on the complex multi-modal coupled vibration of the stern structure of the ship.This paper firstly conducts the modal analysis based on the stern structure model of the ship,and the coupled structure of the stern of the ship.Find out the potential causes of the line spectrum vibration of the stern structure of the ship,provide a basis for the complex multi-modal coupling study of the stern structure of the ship,carry out the analysis of the impact of the coupling vibration characteristics of the stern structure,and further determine the local structure to the ship stern structure.The effect of modal coupling vibration.Secondly,the vibration response analysis of the stern structure under the propeller excitation is carried out.Using the finite element(FEM)/boundary element method(BEM)method,based on the basic theory of sound-structure coupling and the basic theory of finite element,the vibration response simulation calculation of the coupled vibration simulation model of the ship stern structure under the excitation load of the propeller is carried out.According to ISO 6954-2000 vibration evaluation standard,the vibration response is evaluated to determine whether there is an area where the vibration response exceeds the standard of the ship’s stern structure.The effects of structural parameters such as plate thickness and profile size on the vibration response of the stern structure were studied by finite element method.Thirdly,carry out the research on the optimal design of the stern structure coupled vibration,and realize the structural optimization design based on the embedded optimization theory algorithm with the help of the Isight optimization platform.Firstly,the realization process of the global optimization method based on the Isight platform is explained in detail based on the optimization theoretical calculation method.The effect of the optimization method is verified by the structural parameter optimization design of the simple plate frame structure based on the global optimization algorithm of the Isight platform,and the simplified model of the stern structure of the ship is established.Variable structural parameter optimization design,and proposed a stern structural vibration optimization scheme based on global optimization.Finally,this article carried out the ship stern structural vibration test,and verified the effectiveness of the simulation calculation method by comparing the simulation results with the test results.First,a comparative test of vibration response of a simplified model of ship stern structure is designed.The test model includes two kinds of benchmark test model and optimized optimization model.The test models include the benchmark test model and the optimized optimized model.The test is divided into two parts: using a hammer and a vibration exciter to excite the structure vibration transfer function in the air.When the exciter excitation vibration test is performed,the exciter excitation is used to simulate the actual propeller excitation.The acceleration sensor is used to measure the vibration transfer function curve at the same measurement point in the typical assessment area of the two test models.By comparing the test models before and after optimization The vibration transfer function verifies the optimization effect of the previous stern structure vibration optimization scheme based on global optimization.At the same time,the effectiveness of the simulation calculation method is verified by comparing the simulation results with the test results.