Application Of Vector Form Intrinsic Finite Element Method In Study On Performances Of ACV Skirt

Due to the speedability and amphibious performances,ACV(air-cushion vehicle)is the best choice for amphibious landing boat.The development of ACV has drawn much attention of many countries.The skirt system is very important to the overall performances of ACV.Design parameters such as bag cushion pressure ratio,speed,draught and geometric parameters,have great effect on ACV performance parameters including stress level,response ability and ability to resist indentation.The design of skirt is a process of continuous optimization and needs to be calculated repeatedly.The traditional simplified analysis method is not precise and applicable enough.The design efficiency of general finite element software that have limitations is very low.A finite element program based on the improved and simplified Vector Form Intrinsic Finite Element theory is written to design the performances of ACV.Influential factors of performances of ACV are studied.The main contents are listed as follows:(1)The common methods of calculating skirt shape including analytical method,general finite element method,and Vector Form Intrinsic Finite Element method are introduced.The advantages and disadvantages of each method are also analyzed.By improving and simplifying the Vector Form Intrinsic Finite Element plane element theory,the plane membrane element theory is obtained.(2)Bar element program based on Vector Form Intrinsic Finite Element is written with Matlab sofeware to calculate the two-dimension skirt shape and tension of ACV.The influences on skirt shape and tension of elastic modulus,connection between finger and bag,tension calculation formula are researched.The result shows that the traditional simplified analysis method has large deviation.(3)The influence of water on skirt is added to the bar element program.Then the response ability and ability to resist indentation are calculated with this updated bar element program.The influences on skirt performance parameters of bag cushion pressure ratio,speed,draught and geometric parameters are also studied.Based on the air cushion system characteristic equation,the dynamic response characteristics of skirt tension and skirt height are analyzed.(4)Based on the improved and simplified Vector Form Intrinsic Finite Element plane membrane element theory,program of plane triangular membrane element and quadrilateral membrane element are written.The shape,tension and response ability of three-dimensional skirt are calculated with this program.The calculation results are compared with calculation results from bar element program,so the deviation brought by simplifications of bar element can be amended.The collision detection and collision response mechanism is added to the program of plane triangular membrane element.So the unreasonable mutual penetration between skirt and ground can be avoid.Based on the anisotropic constitutive relation matrix,the performances of skirt with anisotropic elastic modulus are calculated,the influence on skirt shape and tension of anisotropic material is also discussed.By combining the bar element and the plane membrane element program,not only the calculation error is reduced but also the design efficiency is improved.