Study On Ship Hull Vibration Model Building

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.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.Therefore, it is necessary to research the ship hull vibration model building for getting a simple, accuracy calculation model to calculate the ship hull vibration characteristic. It is built a thin-walled box beam base on ship hull in this thesis, and the frequency of box beam is calculated with some different model building method. Some useful conclusion is put forward from the analysis of the calculation result, which could be used in the ship hull vibration calculation.In the high order frequency calculation, using one dimension beam model for the ship hull vibration is not exact. The main reason is ignoring the shear lag effect; so that the analysis of the shear lag effect is necessary. The box beam vibration is calculated with one dimension and three dimension Timoshenko beam model in this thesis. From the comparison and analysis of the result, the shear lag effect of one dimension beam model vibration is researched. And a modified frequency coefficient considering shear lag is put forward. It is demonstrated that this method which is applied in one dimension beam vibration characteristic calculation of ship hull vibration calculation and proved by 11000t tanker is feasible.