Research On Hydrodynamic Performance Analysis And Motion Reduction Method Of High-speed Trimaran Based On Viscous Flow Theory

In recent years,trimaran has been gradually applied in military and civil fields such as high-speed passenger,ferry,and coastal combat ships because of its relatively wide cabin volume and deck area,better lateral stability,and overall layout.However,the trimaran shows large amplitude and strong nonlinearity under the influence of high sea conditions and some wave parameters at high speed,and there are still many deficiencies in understanding the nonlinear characteristics of its motion and force;The wave attack on the bow of the middle hull and the frequent entry and exit of the side hull led to poor seaworthiness and personnel discomfort.The research on the motion of the trimaran under the action of anti-rolling appendages is still very limited in full wave directions and large wave steepness,which affects the real ship application and development of the trimaran hull.Therefore,it is of great theoretical and practival significance to explore more effective hydrodynamic performance prediction and roll reduction methods for trimaran to improve its comprehensive navigation performance.Based on the viscous flow theory,this paper deeply analyzes the hydrodynamic performance of the high-speed trimaran in order to obtain a more effective hydrodynamic performance prediction and roll reduction method of high-speed trimaran under the action of full wave direction and large wave steepness.The main work of this paper is as follows:(1)Research on hydrodynamic coefficient and vertical motion prediction method of highspeed trimaran.Aiming at the prediction of vertical motion prediction of high-speed trimaran under the action of the T-foil anti-rolling appendage,a numerical prediction method of ship radiated hydrodynamic coefficient and first-order wave excitation force transfer function based on viscous flow theory is proposed.The vertical motion response of the ship is obtained by solving the two-degree-of-freedom vertical motion equation.Firstly,the effectiveness of the numerical prediction method is verified by predicting the hydrodynamic coefficients and motion of conventional monohull and high-speed trimaran;On this basis,the nonlinear effects of different forced oscillation amplitudes and incident wave amplitudes on the forces acting on the hull and motion of high-speed trimaran are further considered,and the motion changes of the high-speed trimaran under different forced oscillation and incident wave amplitudes are analyzed.Finally,the vertical motion of the high-speed trimaran equipped with the T-foil is predicted,and the hydrodynamic contribution and anti-rolling effect of the T-foil as well as the nonlinear influence of wave steepness on the motion and forces acting on the high-speed trimaran are analyzed.(2)Research on the prediction of added resistance and motion of the high-speed trimaran in waves.Aiming at the problems of periodic oscillation and lower numerical calculation accuracy in the calculation of large wave steepness problems by the damping wave elimination method,based on the numerical prediction method combining overset mesh and EOM(Euler Overlay Method),the computational domain and meshing method based on overset mesh are studied firstly,and the effectivess of numericall prediction of added resistance and motion of the highspeed trimaran in full wave direction based on the EOM and overlap grid method is verified.On this basis,the motion of the high-speed trimaran in full wave directions with different parameters is numerically simulated,and the effects of wave parameters such as wave steepness and wavelength on the added resistance and motion of the high-speed trimaran are analyzed;Finally,based on the Fouier transform method,the nonlunear characteristics of the motion and forced acting on the hull of the trimaran in oblique head waves are revealed.(3)Research on the prediction of added resistance and motion of the high-speed trimaran equipped with combined appendageAiming at the problem of large longitudinal motion responses of the high-speed trimaran,a combined attachment scheme of installing T-foil under the bow of the middle hull and flap at the stern is proposed.Firstly,the independence of mesh generation of the high-speed trimaran considering the anti-rolling appendages is studied;On this basis,numerical simulation and calculation of the added resistance and motion responses of the high-speed trimaran under different combinations of appendage schemes by changing the longitudinal and vertical installation position of the T-foil and attack angles of the T-foil and stern flap,and the effectiveness of the numerical method is verified by comparison with the model test results.The effects of wave parameters such as wavelength and steepness on added resistance and motion of the high-speed trimaran equipped with combined appendages in head and oblique waves are discussed and analyzed.Finally,the coupled motion of roll and pitch motion of the high-speed trimaran in head oblique wave is analyzed through the phase plane plot,and the motion as well as the forces acting on the middle and side hulls are calculated based on the Fourier fransform method,and the nonlinear characteristics of the motion and forces of the high-speed trimaran under large wave steepness and different wavelengths are analyzed.(4)Research on the influence of hull layout on the comprehensive hydrodynamic performance on the high-speed trimaran.The resistance and hull gesture of the trimaran with different outrigger layouts are numerically simulated and predicted according to the ship type characteristics of trimaran with variable side body position,and the wave making interference between main and side hulls as well as the resistance components are analyzed.In order to solve the problem that the calculation accuracy reduction of the motion of the trimaran in oblique head wave due to the coninous increase of yaw angle when the commercial software,the coupling between the numerical wave making package waves2Foam and the dynamic mesh interDyMFoam solver is proposed and designed based on the open-source OpenFOAM platform.Firstly,the grid independence and numerical accuracy verification of the waveDyMFoam solver are studied.On this basis,the motion of the high-speed trimaran equipped with combined appendages under different side hull layouts in oblique head waves is numerically simulated,and the influence mechanism of side hull layout on the coupling motion of roll and pitch as well as added resistance of the high-speed trimaran under different wave steepness and wavelength is revealed;Finally,the motion of high-speed trimaran with different outrigger layouts and the forces acting on the middle and side hulls are calculated based on the Fourier transform method,and the nonlinear characteristics of the motion and forces of the high-speed trimaran under large wave steepness and different wavelengths are analyzed.The research shows that the numerical prediction method of ship hydrodynamic coefficient and vertical motion proposed in this paper can consider the nonlinear influence of forced motion amplitude and incident wave amplitude on the forces acting on the high-speed trimaran,and consider the hydrodynamic contribution of T-foil,so as to realize the high-precision prediction of the motion responses of the high-speed trimaran and anti-rolling effect of the T-foil;The numerical prediction method of resistance in calm water and motion responses of the trimaran in full wave directions based on the combination of overset mesh and EOM method proposed in this paper can predict the resistance and hull gesture in calm water,wave making interference between middle and side hulls as well as added resistance and motion responses in waves with high accuracy,and the real-time simulation of the nonlinear motions of hull bodies entering and coming out of water,slamming as well as the coupled of roll and pitch in waves is realized.Taking the combined appendage of T-foil and stern flap as the anti-rolling method of the highspeed trimaran,the maximum anti-rolling effect is close to 42%,and the effects of roll and pitch reduction in oblique head waves are up to 10.5%and 36%respectively.The waveDyMFoam solver developed based on the open source OpenFOAM platform solves the problem that the yaw angle continues to increase when numerically simulating the motion of the high-speed trimaran in oblique head wave by commercial software,making it possible to simulate and predict the motion of the high-speed trimaran as well as forces acting on the hull bodies in oblique head waves with higher accuracy.It provides a theoretical basis for the in-depth study of the hydrodynamic performance of the trimaran in high sea conditions and complex flow fields and the application of the anti-rolling appendages of T-foil and stern flap in high-speed trimaran.