Longitudinal Motion Prediction of Planning Craft in Water-Air Dual Porous Media

In order to probe motion response of high-speed planning craft in water-air dual porous media,this paper established a mathematical model for the non-linear longitudinal motion according to high-speed sliding theory of water-jet propelled planning crafts.Firstly,the forces on sliding planning craft hull in water-air dual porous media were analyzed,and gravitation,buoyancy,hydrodynamic lift and pressure resistance were presented.Se condly,the calculation method of windward area and wing pressure level were improved,and the calculation formula of the wetted length was proposed.Finally,the paper worked on a longitudinal motion prediction program for planning craft,and finished the result analysis of planning crafts motion prediction in different conditions.The results show that,when the output power of main engine is constant,considering air versus not consideri ng air makes the ship speed decrease 5.1%,the heave decrease 0.006 m,the pitch angle increase 0.2°,resistance increase 1 893 N,the hydrodynamic lift decrease 404 N.Meanwhile,considering wind resistance has a great inffluence on motion of the planning craft： the ship speed decreases 15.3%,the heave decreases 0.021 m,the pitch angle increases 0.6°,resistance increases 5 472 N.