Study On The Hydrodynamic Prediction Method In Various Wave Directions Of Trimaran And The Navigation Performance

As one of the high-performance ships,trimaran is considered as an advanced hull form both domestically and internationally,and is highly focused on by many countries all over the world.The trimaran has been applied in both military and civil ships,such as liner,cruise,ferry and so on.Based on the theretical research and navigation of full-scale ship,there is complex interaction between the hull forms of trimaran,which will lead to some characteristics different from momohulls,and the theory of the interaction is complicated.Many trimaran forms have been built,but the trimaran is still on the stage of building and investigation simultaneously.Most of the investigation about trimaran is fixed on resistance in calm water,seakeeping performance in heading wave and layout optimization by potential flow theory and model test.The study shows that,the simulation by potential flow method is fast,which could be used for the hull form design and optimization to choose and study different cases.The potential flow method could be accurate enough when predicting the wave-making resistance and interaction between hull froms,et al.However,the accuracy of hull attitude prediction by potential flow method is not accurate enough now,and the application of potential flow method to seakeeping performance in different wave directions and maneuver of trimaran is still limited,which means that the potential flow method is not enough for the study of comprehensive hydrodynamic characteristics of trimaran.Therefore,on one hand,it is necessary to take the advantage of rapidity of potential flow method,and improve the accuracy of numerical simulation by potential flow method.On the other hand,the force and motion of trimaran is nonlinear when it is moving in waves of different directions or doing turn and zigzag maneuvers in calmwater and waves,and the effect of viscosity and nonlinear motion is not negligible.So,it is necessary to discuss a viscous-flow-based numerical method to predict the complicated motion and force of trimaran.By which,more investigation about the comprehensive hydrodynamic characteristics of trimaran could be carried out.Based on the shortage and demand of trimaran hydrodynamic study method,the work of this paper is as follws:Based on potential flow theory,the nonlinear terms of free surface condition are studied,and the numerical method is improved.The influence of normal derivatives ?zz associated terms in free surface condition on the wave-making and hull attitude of trimaran.Based on monohull,twinhull and trimaran respectively,the numerical method is validated and analyzed.The study shows that modified method could improve the accuracy of the wave-making resistance and hull attitude prediction of the hull forms mentioned before.The wave-making resistance and hull attitude of trimaran with various layouts and hull form parameters are predicted.By detailed study of many cases,the modified method in this paper could be universally applied to monohull,twinhull and trimaran.The validation of numerical method shows that,the modified method could improve the prediction accuracy of the wave-making resistance and hull attitude.Aim to the motion and added resistance of trimaran in high sea condition and various wave directions,and take the nonlinear phenomenon into account,such as large motion,interminent emergence and green water,based on the open source tool OpenFOAM,the external potential flow wave tank QALE-FEM is combined with the internal viscous flow domain by the developed solver QaleFOAM,and the wave propagation and transition is realized by the interface and transition zone.Instead of the relative motion which convert the ship advance speed to the speed of incident flow,the absolute motion of trimaran in wave tank is applied in this paper,by which the simulation of trimaran nonlinear motion in various wave directions is realized.An acutal trimaran form is taken as example to validate the theoretical method,mesh scheme and accuracy.The result shows that,the hybrid method by QaleFOAM is accurate for wave simulation and propagation between external wave tank and internal NS domain.By analysis and comparison,the method in this paper could be better applied to predict trimaran motion in high sea condition.Through current method,the added resistanc and motion of the acutal trimaran in various wave directions and wave parameters at different speeds are predicted.The computed result shows that,the nonlinear phenomenon is impacted by the wave parameters in wave directions ranging from head wave to oblique head wave.The functions of 6DOF maneuver is adopted,and the maneuver preditction method of trimaran in calmwater and waves are presented.The control module of maneuver motion is combined with the external full nonlinear potential flow wave tank,by which the numerical simulation of 6DOF trimaran turn and zigzag maneuvers in both calmwater and waves is realized.The convergecy and accuracy of current method are validated by an acutal trimaran.The maneuver characteristics of trimaran is studied by current method.By comparison with the simulation result with hull attitude fixed,it shows that the 6DOF self-navigation maneuver simulation is more accurate to show the maneuver characteristics of trimaran.The influence of hull attitude on the maneuverability of trimaran is discussed.With combination of maneuver simulation and FNPT wave tank,the trimaran maneuver in wave is predicted by self-navigation method,and the effect of wave parameters on the trimaran maneuver is discussed and analyzed.With studied theoretical method,the investigation of trimaran comprehensive hydrodynamic characteristics is carried out.With the instance of an actual trimaran,trimaran models with different layouts are obtained by chaning the hull separation and longitudinal position of side hulls.The resistance and hull attitude in calm water,the motion and added resistance in whole wave directions and sea conditions,and the maneuver in calm water and wave are predicted.By the computed result,the comprehensive effect of layout on the resistance in calmwater,resistance and motion in whole wave directions and the conresponding hydrodynamic characteristics is discussed,and the trimaran comprehensive hydrodynamic characteristics is analyzed.The study shows that,the key factors about the prediction accuracy of the wave-making resistance and hull attitude is found by current study on the potential flow method,and the prediction accuracy of wave-making resistance and hull attitude is improved.The study presents the hybrid method based on fully nonlinear potential flow method and viscous flow method.which could be used to simulate the motion response in whole wave directions and 6DOF maneuver in clamwater and waves.Based on OpenFOAM,the numerical simulation module is developed,and the code is compiled.The prediction of trimaran nonlinear motion response and maneuver is realized,which surrport the study about trimaran hydrodynamics in high sea condition and complicated flow.