Modal Analysis Of Water Lubrication Stern Tube Rubber Bearing Based On Finite Element Method And Experiment

Water lubrication stern tube bearing is one of the most critical components of ship whose liner is generally made by rubber materials. Rubber materials qualifications are as follows:alleviating the vibration of the tail shaft, reducing the noise sent out by bearing, improving the working conditions of tail shaft, reducing the distance that ship could be discovered by sonar, enhancing survival ability of ship. But when the lubricating condition is bad, such as start or stop, low speed, heavy load, high temperature, the rubber bearing will generate abnormal vibration and squeal which would seriously affect the elusive of ship.In order to investigate the mechanism of the vibration of water lubrication stern tube rubber bearing in some special conditions, it is needed to make a deep study in the dynamic characteristic of water lubrication stern tube rubber bearing. Modal analysis is the main method of studying the dynamic characteristic. In this paper, modal analysis is used to research the law of different structure and properties of material influence on the dynamic characteristic of water lubrication stern tube rubber bearing.In this paper, Finite Element Modal Analysis and Test Modal Analysis is introduced into modal analysis of water lubrication stern tube rubber bearing, bearing liner, and bearing bush separately. The results are as following.(1) The lower-order mode of water lubrication stern tube rubber bearing is mainly affected by the structure and material property of bearing liner, and its higher-order mode is mainly affected by the structure and material property of bearing bush.(2) The lower-order mode of water lubrication stern tube rubber bearing is slightly affected by constraints conditions, and finite element analysis result shows that there is correspondence between free modal analysis and constraints modal analysis.(3) The finite element analysis result shows that the hardness and thickness of bearing liner, and depth of flume have considerable influence on the lower-order natural frequency of water lubrication stern tube rubber bearing. With the increasing of liner's hardness, and decreasing of liner's thickness or flume's depth, the lower-order natural frequency increase markedly. L/D (Length/Diameter) of bearing, number and surface shape of lath have slightly influence on lower-order natural frequency. L/D, thickness of liner, and depth of flume have great influence on lower-order modal shape of bearing. Liner material, number and surface shape of lath and hardness of liner have slightly influence on lower-order modal shape of bearing.(4) Test modal analysis is introduced into verification of finite element modal analysis. The result shows that the natural frequency of finite element modal analysis has the same range with the natural frequency of test modal analysis. As the increasing of hardness of liner or decreasing of depth of liner, the low-order natural frequency increase markedly. In addition, the liner which is made by rubber has low pass characteristic because it produces partial collapse in test modal analysis using hammer impact. However, the bearing bush has high pass characteristic to the impact operated on it.