Numerical And Eexperimental Stability Analysis Of Planing Craft Sailing At High Forward Speed

Planing craft as a kind of simple structure high performance littoral ship benefiting its good rapidity and flexibility attracts widespread attention and application in cruising,searching,rescuing,detecting,observations,entertainment,military uses and so on.Since the planing craft is uplifted by hydrodynamic lifts and the displacement decreases at high forward speeds,the planing craft has good resistance performance.As the decreasing displacement the planing craft has lower dynamic stability and difficultly adapts the complex and adverse sea conditions.In order to estimate the factors of the high-speed stability of the planing craft,based on the Computational Fluid Dynamics(CFD)method and model test method this paper has researches on transverse stability loss of planing craft at high forward speed,effects of starting acceleration on hydrodynamic performance of the planing craft,performance of planing craft in the regular head waves and so on.Firstly,the calculating method and accuracy of the Volume of Fluid(VOF)Reynold Average Navier Stokes(RANS)solver applied in hydrodynamic problems of high speed planing crafts are studied.The accuracy of water entry problem of a 2-dimensional wedge body is tested and verified,and the 3-dimensional planing craft hydrodynamic lifts are solved based on water entry calculation of a deforming 2-dimensional section.The hydrodynamic performance of 3-dimensional planing surfaces is studied in steady simulations,and the multi-freedom motions are solved in unsteady simulations.Both steady and unsteady numerical values are compared with experimental results.The numerical method is certificated to solve the multi-freedom motions and hydrodynamic performance of the high-speed planing craft accurately and efficiently.Secondly,both model test method and numerical simulation method are presented to study on the stability loss problem of the planing craft.The fixed heel angles model test is designed and simulated by numerical method.The planing craft model is fixed with different heel angles and sails at different forward speeds,while the restoring moments are measured.The numerical and experimental results are compared.The transverse stability of the planing craft loses at high speeds especially in half-planing condition by comparing with static stability at zero speed except for very high speed conditions with large heel angles.The free heel angle simulation of the planing craft is promoted by numerical method.The heeling moments are added on the planing craft model and the rolling motion is set free.The heel angles are measured as the judgment of transverses stability when the motions of the planing craft are converged.The results of free heel angle solutions support the conclusions of the fixed heel angle solutions.Therefore the solving accuracy of the transverse stability loss is verified again.The transverse stability loss of the planing craft discovered in the research has relationships with the trim angle,and the effects of longitudinal gravity centre positions on transverse stability loss are discussed.Thirdly,the starting process of the planing craft which is assumed as uniformly accelerated process is numerical simulated and the effects of acceleration on running posture and hydrodynamic performance are discussed.The results show that with the increasing of the acceleration the resistance performance keeps unchanged but the trim angle decreases obviously which is beneficial to sailing stability of the planing craft.When the acceleration is very small in the uniformly accelerated process,the planing craft is considered as forced balance and assumed as steady condition.Therefore,with only one starting process simulation of very small acceleration the sailing postures and hydrodynamic parameters at all speeds are obtained.The computational efficiency is significantly improved by this means.Fourthly,the laws of the planing craft sailing in regular head waves are studied based on the numerical wave generation technology.The high speed seakeeping model tests of planing craft are simulated to verify the accuracy.There are three kinds of planing craft motions in regular head waves-no jump,regular jump and irregular jump whose occurrence have relationships with the wave parameters and forward speeds.According to numerous simulations,the criteria of motions and the effects of jump occurence on the amplitudes of longitudinal motions are studied.Finally,the hydrodynamic performance of an independent design channel type planing trimaran is studied by both model tests and numerical simulations.The resistance performance and factors are analyzed combing the ship type characters.The two phase distribution in the channel and the pressure distribution of the planing trimaran are discussed in numerical simulation.The effects of the longitudinal gravity center positions and displacements on the resistance performance are discussed according to the design requests.