Research On The Wave Loads Calculation And Structural Strength Assessment Of The Stabilizing Fins Of SWATH

Because of its unique advantages, such as excellent sea keeping capacity, spacious deck area and so on, SWATH has been widely used in marine transportation and other fields.Nevertheless, studies show that the longitudinal motion attitude of SWATH is likely to be unstable when the speed is high. And it is a good way to improve the longitudinal motion stability of SWATH by installing two pairs of fixed-stabilizing fins on its two submerged bodies. Currently, there are lots of researches on the whole ship structure characteristic and hydrodynamic performance. However, there are few studies on the wave loads forecast and structural strength assessment of fins. What’s more, there are currently no rules for the finite element calculation and the structural strength assessment of fins. Therefore, it is necessary to research on wave loads prediction and local structural strength assessment of fins, which might provide guidance for the structural design of fixed-stabilizing fins of SWATH in the future. And the main contents of this thesis are as follows:Firstly,the solution of modified hydrodynamic coefficients of stabilizing fins. The dynamic lift correction factor of fins can be solved by relevant empirical formulas and the viscous correction coefficients can be obtained with the method of potential flow theory and CFD;Secondly, the motion prediction of SWATH with fins. After adding the above modified hydrodynamic coefficients of the fins to the original longitudinal motion equations of the hull,the modified motions of SWATH with fins can be obtained by solving the modified motion equations. And the speed and acceleration of fins can be obtained by solving the derivative of motion. Then, the impacts of the fins on the hull can be obtained by comparing the longitudinal motions of the bare hull with those of the hull with fins.Thirdly,the wave loads forecast of fins. The dynamic pressures of the fins under different environment conditions are studied. Then, lift, resistance and torque of the fins are predicted and comparisons between the forecast values and experimental values are made.Meanwhile, the influences of fins on the wave loads of SWATH are analyzed.Lastly, local structural strength assessment of fins. Considering the structure type and stress condition of fins and rudders are similar, the FEM analysis method and local structural strength assessment criteria of fins can be determined by referring to relevant provisions of the specifications of CCS. Finally,yielding and buckling strength of the fixed-stabilizing fins of SWATH under design-load condition have been analyzed to check the local structural strength of fins and the connecting structural of hull and fins.