Vibration Characteristic Analysis Of Unsymmetrical Catamarans

Sometimes ship hull resonates by the action of main engine,propeller or wave excitement and so on. To avoid the deleterious vibration, ship hull vibration and mode is necessary to calculate for choosing main engine and propeller in the design period.At present, there are three calculation methods for calculating the nature frequency of ship hull vibration including experience formula, one dimension ship hull beam transfer matrix method, one dimension fem method and three dimension space fem model method.Experience formula is used in the initial stage of design, it is simple and convenient, but not exactly enough. The one dimension beam model is a simple model, it is nicely for calculating ship hull vibration in low order, but the precision drops greatly up in high order. The reason is that the hull shear deformation and shear lag effected greatly at high orders. Three dimension fem model is good at describing the structure of ship hull, and the results of three dimensions space FEM model calculation has been proved to be more accurate, but it consumes too much time and energy, and it is difficulty to find hull model in the post process.In this paper take an unsymmetrical catamaran as an object, used 3-D finite element method and empirical formula for the vibration characteristics of the hull. Finite element method is based on the actual ship models, a true reflection of the real ship distribution of the specific structure. This paper also uses empirical formula to calculate the inherent frequency of the catamaran; contrast them in the process of modeling the structural stiffness, and quality of the different treatments, as well as natural frequency calculated from the results of differences analyze the different and the reason between the finite method and the empirical formula method which used to calculate the inherent frequency of catamarans in the vibration analysis. Empirical formula generally applicable to the design of the initial estimates, the method is simple and convenient, but the accuracy is not precision, finite element method is based on the actual ship models, the real manifestation of the structure of the specific characteristics, which enabled them to more realistically simulate the actual structure vibration.Finally, analyse the calculated results of this ship with another catamarans. From this result obtained unsymmetrical catamaran hull of this particular special vibration mode and analyse the vibration mode in order. The calculation is fairly reasonable, for the future of the asymmetric catamarans to calculate the vibration analysis of a number of reference.