Node Performance Analysis Of Composite Shell Under Ocean Internal Waves

Internal waves is a kind of gravity waves which is happened to ocean layered structure (such as the density is stable stratified).And its maximum amplitude occurs in the inside of the ocean. With the same dynamics as surface waves, internal waves play an important role in the ocean.This paper firstly reference other peoples'results on constructing a math model for internal waves based on theory of the boundary element method and numerical simulation about the force exerted by internal waves on an underwater composite shell in the stratified ocean. Based on this conclusion, I find that practical internal waves loading is uneven distributing on the surface of composite shell and its magnitude is also changing with the distance between structure and density-spring layer changing. In this paper, internal waves model select frequency , which is spring layer has a 50 meter distance to the surface of ocean, then divides structure surface into 480 pieces. After simplifying it just analysis eighth, which means giving different pressure on the areas of 60 pieces, so that we can get the data for analyzing node stress of practical internal waves loading with ANSYS.Spherical-drum shell is a representative structure as a kind of underwater body, which will change the junction stress with different central angle of spherical shell. Based on other peoples'result on junction stress of the no weld defect spherical-drum shell, and take it as criterion to analysis the junction stress of this spherical-drum shell which has weld defect。This paper illustrates four models which half-central angle is gradually changing from 90 degree to 50 degree and gets the result of the maximum stress on the join section and calculate the factor of stress concentration.Based on the above, this paper adopt Fracture Mechanics method to analysis and calculate the spherical-drum shell's structure fatigue and damage life. Because of the maximum stress is on the weld join section of the underwater body which suffered the internal waves load, so this paper take the weld section for research subject. By reference other peoples'research, select a suitable method to calculate and modify the stress intensity factor of the surface crake of the composite shell. Then estimate the life of the composite shell. Analysis results show that the effect of composite shell junction stress and the factor of stress concentration of the composite shell which under internal waves has three reasons, First, internal waves loading is different depending on different depths; Second, junction stress is different depending on different central angle. Third, stress intensity is different by the effect of different crake quality grade and different crake defect.The fatigue and damage life of the composite shell is not just in relation those reasons, but also depending on the materials of the structure, the shape and size of the crake, the frequency of the internal wave and so on. At last, I make a result of the connection between the factor of stress concentration and the stress intensity factor .moreover discuss the effect of the stress concentration to the life of the structure.