Study On The Roll Stabilization Control Method With Speed Loss Minimization

A ship sailing in a seaway typically experiences large motions and accelerations due to waves,and rolling is the most problematic of ship motions.At the same time,the total water resistance of a ship is increased by added resistance which the magnitude is about 20%-40%of the resistance in calm water,resulting in power consumption and speed reduction.There is an increasing awareness of the effects of global warming and also an economic crisis prompting the need for energy minimization and emission reduction.A ship speed loss and consequently the higher lever of fuel consumption in different sea states is currently one of the major areas for improving marine vehicles in the ship building and marine industry,since legislative action has been taken on global levels make sea transport more clean and efficient.Base on this international background,considering the energy efficiency problem in ship control engineering area,a ship motion control system with minimization speed drop(i.e.sailing resistance)is studied.A three degrees of freedom nonlinear coupled motion equition is presented according to the Newton's law,both time and frequency domain wave disturbance models are analyzed base on the stochastic wave theory,comparing the PM spectrum and ITTC double paremeters spectrum,then a simulation platform of horizontal motions in three degrees of freedom is established.Stating the principle of fin roll stabilization and rudder roll damping,finally the linear ship roll motion model for actual engineering application is presented.From the principle of integrated pressure method,a rolling-added-resistance model is set up according to the potential flow theory.A series 60 ship model is selected to compute roll motion and added resistance in different encounter sea states by ocean engineering software ANSYS-AQWA.The modeling feasibility is validated in comparison with the data from ANSYS-AQWA.Analyzing the relationship between roll motion and added resistance at every time point,then the roll angle which can minimize the value of added resistance(i.e.optimal roll angle)is described.A fin stabilizer control system with added resistance minimization is presented base on the generalized predictive control method which is combined with output constraint,the results show that this control system can reduce more added resistance compared with the traditional roll stabilization control system.A practical estimation method of calm water resistance is presented after analyzing the componants of calm water resistance.Base on the extended radiated energy method,key factors of added resistance caused by five degrees of freedom motions in oblique waves are analyzed.The computation method of the speed loss in waves is written,the influence of ocean environment(significant wave height,average encounter period,etc.)on speed loss are are emphatically analyzed.According to the nonlinear lift hydrodynamic performance of the foil,a double nonlinear generalized minimum varience fin stabilizers control system with constrained speed resuction is designed and a speed loss evaluating index is also performed.The simulations show that,considering the master voluntarily reduces the speed due to the rough weather,the controller can achieve a good performance with a simple structure which can be easlily performed,and the speed can be maintained very well.Studing the still water resistance increased by ship yawing and steering,then key factors of the whole speed loss induced 5-DOF motions are analyzed.A computation method of the whole speed reduction is presented base on the former studies.Accoring to the rudder angle separate control strategy,an autopilot system with constainted speed loss is proposed,two types of adapitive sliding mode control law are shown and their stability are proved by Lyapunov stability theory.Discussing the performance(i.e.roll stabilization?heading error?speed maintenance?rudder cost)of "Heading" and "Heading+Anti-roll" working mode.It is interesting to find that,the speed can be maintained effectively by this method,from an energy saving point of view,for vessels which are equipped with both fins and rudders,the rudder/fin roll stabilization control is not encouraged.