| As a kind of fast and convenient waterborne vehicle,the planing craft is designed to be high speed and more effective in carring capacity,that has been an important direction in planing hull development.However,the large resistance and stability loss have always been obstacles for the conventional planing hull to break the speed limit.In this paper,this problem is solved by means of investigations on aerodynamically alleviated effect of planing trimaran hull,which is a novel planing hull form and has unique hydrodynamic and aerodynamic structure.Therefore,focused on the resistance performance and longitudinal motion stability,hull form design of planing trimaran was carried out.Depending on the advantage of FVM based CFD technology in simulating the flow flied of high-speed planing hull,the hybrid hydroaerodynamic characteristics of tunnel and step and the influence from hull configuration were researched.A series of planing tramaran hulls with excellent navigation performance were developed.Accordingly,the uncertainty evolution of numerical method become the first critical problem to be solved.Considering the dynamic behavior of planing hull at high speed,numerical simulation of hull body forward motion with two degrees of freedom were implemented by coupling the flow field solver with motion solver.Then,a mesh convergence study was carried out based on the experiment data from Taunton C model,after which the numerical credibility was improved significantly.To analyze the variation of hull behavior caused by aerodynamically alleviated effect,the demihull and tunnel are treated as appendages mounted on a slender main hull.This strategy comes from Collu,who has used it to calculate dynamic charactetristics of Aerodynamically Alleviated Marine Vehicles(AAMV).Following this basic idea,hull form design and hydrodynamic characteristics investigations were firstly performed for the slender stepped planing hull,the correlationship between drag-reducing effect of step and air cavity development were analyzed,and the influence of step arrangement on hydrodynamic performance were discussed.Model tests were also carried out to further validate the step design,the critical flow feature of air cavity was observed during towing test.Considering the interference caused by the inconformity of hydrodynamic and aerodynamic scale laws,the hydrodynamic research in model scale are expanded to the real scale and numerical simulations on full scale hull body are presented.The flow similarity of stepped planing hull in different scale and the influence of scale effect on resistance and longitudinal motion stability were analyzed.Then,in real scale,slender planing monohulls with different configuration were developed based on the experimental model(series 40,deadrise angle is 20°),which including series 30 and 50(the deadrise angle is 15° and 25°,respectively)and series 41 and 42(the chine width is decreased by 10% and 20%,respectively).Numerical simulation were carried out for these hulls to investigate the difference in resistance and motion stability.The planing trimaran of series 40 is designed out by mounting tunnel and demihull on the same series monohull.To analyze the drag-reducing characteristics and dynamic coupling effect of tunnel and step,the calculated results of planing trimaran were compared with those of equalwidth monohull and main hull.It is found that the demihull plays an important role in the aerodynamically alleviated system.Therefore,the influence of demihull configuration on the hybrid hydro-aerodynamic performance of planing trimaran was investigated,and its action laws on resistance and longitudinal motion stability were sum up.In accordance with the design principles of tunnel and demihull in series 40,planing trimaran with different configuration were developed based on the aforementioned four hull series.To estimate the benefit in resistance and motion stability brought by the aerodynamically alleviated effect,simulation results of these planing trimarans were compared with the corresponding main hull data.A novel multi-chine planing trimaran hull,developed from the most slender hull,was utilized to improve the motion stability of large deadrise angle planing trimaran.According to the demihull action laws,demihull modifications were implemented to reduce the resistance of planing trimaran of series 30 and multi-chine planing trimaran of series 42;moreover,for the sake of improving motion stability,the demihull of multi-chine planing trimaran of series 50 were also modified. |
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