The Calculation Of Hydrodynamic Performance And Optimization Design For Towed Vehicle

The towed vehicle is a kind of marine equipment,which is mostly used for underwater detection and mapping of submarine topography.It is very practical due to its flexible design according to detailed requirements.The research object in this paper is a large scale composite towed vehicle used for underwater exploration and experiment,which is composed of two different units and a buoyancy tank.Because the buoyancy tank and a unit are above the water surface during the towage,it is necessary to consider the influence of the free surface and the interactions between the units when using numerical calculation to analyse the hydrodynamic performance of the towed body.So this study carries out the model towing experiment,and according to the theory of computational fluid Dynamics(CFD),the STAR CCM commercial code combined with the discrete form of the Cartesian grid is used to calculate the resistance of towed body under water surface.By comparing with experiment data,the accuracy of the numerical algorithm has been proved.Also,based on the calculation results along with design constraints,the towed body shape has been optimized: under the same conditions of buoyancy and draft position,increasing the aspect ratio of the horizontal section of the buoyancy tank,and changing the front end from a semicircle to a double arc transition.According to the acquired analysis method,it is found that the wave height decreases sharply after being optimized and the total resistance decreases by 25%.The results of this study can be used as a reference to calculate and optimize the drag resistance of the composite towed body with water surface structure.Based on the shape optimization,the stability of towed system is analyzed by AQWA software,which is based on potential flow theory.According to the towed system and real sea conditions,the paper first builds the simulation model,controls the current and wave parameters,and then studys the relationship between towed point positon and six degrees of freedom of towed body through changing the X and Z coordinate of Intersection,the Z coordinate of Upper tow point.The result shows that when the X and Z coordinate of Intersection is in [8m,8.5m] and [-2m,-1.5m],the Z coordinate of Upper tow point is in [-1m,-0.5m],the stability of the towed system is the best.This study provides a reference for the design of towed cable in towing system.