Research On The Methods Of Global Vibration Simplified Analysis Of Air-cushion Craft

With the progress of technology,the demands of people for ships are more and more diversified.The air-cushion craft,as a kind of new type ship,that has the characteristics of amphibious property and high speed,is widely used in military,transportation,emergency rescue and other fields.The overall vibration of the ship is an issue that must be considered in the design process of the hull structure.At present,there are few studies on the global vibration of the air-cushion hovercraft,so the research in this area has important engineering practical value.The analysis method of ship’s overall vibration mainly includes ship comparison method,empirical formula method,a one-dimensional beam model method and three-dimensional finite element model analysis method.Three-dimensional finite element model analysis can accord to the actual ship to modeling,and also can simulate the real structure effectively.It has a high precision in the total vibration analysis,but the workload is too large.In order to meet the needs of ship design,empirical formula method and one-dimensional beam model method are usually used to estimate the global vibration natural frequency of ship hull.However,the main scale and hull structure of the hovercrafts are very different from the normal drainage ships.Hovercrafts are usually large in type size,and the length-width ratio are very small,so the traditional empirical formula method and one-dimensional beam method have great errors in the global vibration analysis.Therefore,according to the characteristics of the air-cushion craft,in this paper,we simplify it to a model of cross beam system,using the vibration theory of the beam and the torsion theory to establish the dynamic differential equation,considering the influence of additional water at the same time,using the transfer matrix method to calculate the natural frequency of the model.The three-dimensional finite element method is used to calculate the natural frequency of the fully cushioned hovercraft in the drainage state.The calculation results are in good agreement with the numerical solution of the migration matrix method,and the feasibility of the migration matrix method is initially determined.The global vibration of the air-cushion craft is relatively complex in the fully cushioned state.In this paper,a simple finite element model of a fully cushioned hovercraft will be established to analyze the global vibration of the hovercraft in the hovering state,taking into account the impact of the air cushion and the air bag.According to the stiffness of the air cushion and the air bag,the spring unit is used to simulate the vertical stiffness of the air cushion,and the stiffness of the airbag is simulated by the “Hui” straight beam and the spring unit.The three-dimensional finite element method is used to compare and analyze the effect of different conditions on the global vibration.