Analysis On Hydrodynamic Performance Of Double-stepped Planing Craft And Its Appendages

The stepped planing craft is a common type of planing hull form,which has been applicated widely due to its excellent speediness performance at high speed.The present paper deals with the numerical simulation of the flow field on series of double-stepped planing craft models with the incremental researching methods of CFD method,and takes research on the hydrodynamic performance of double-stepped planing craft and its appendages.In this paper,numerical simulation calculation for models is carried out by using mixture mesh of the structured and unstructured to discrete the entire computing domain,using RANSE method,using SST turbulence model,solving Navier-Stokes equation and using VOF method to capture free surface.To avoid calculation errors caused by the estimating sailing stance of planing craft,the paper uses a dynamic mesh,and brings to the six degrees of freedom equations of motion for the ship in order to achieve simulations of the hydrostatic direct unconstrained model,and computations have been perform to check the a feasibility of the present method versus the empirical data available.The researched objects considerd in the paper mainly include step,stern flap and spray rails,the increment parameters involved the study mainly contains the longitudinal location and the height of step,the centre of gravity position,the length and mounting angle and horizontal mounting position of stern flap,mounting position and mounting number and mounting angle of spray rails etc.As step is the major factor in determining the shape of the sliding surface,its impact on resistance performance of planing craft is the most obvious.The computational results show that the vary in location and height of step leads to obvious changes of resistance simultaneously,and the prediction resistance shows a strong regularity corresponding to different center of gravity position.In the study on drag reduction appendages,the stern flap mainly adjusts sailing stance of planing craft slightly,and spray rail is mainly used to reduce the waves and splashes generated by the boat bottom.The computational results show that,the stern flaps with different mounting angles play a role in drag reduction,and the spray rails on the bow should be designed to the form of a certain mounting angle,and the spray rails after the step reduce resistance obviously.In the final paper,the numerical simulation calculation for double-stepped planing craft models with entire appendages have been performed to check the joint drag reduction efficiency with step,stem flap and spray rails.