Online Estimation Of Ship Resonant Frequency And Research Of Fin Stabilizing Multiple Controllers Switch Strategy

The undesirable multiple degree of freedom motions of a ship in a seaway is inevitably induced by the action of external marine environmental disturbances: waves,wind and current.Among the undesirable multiple degree of freedom motions,due to the small damping characteristics of ship rolling motion,so ship tends to produce rolling motion,and this kind of extent of undesirable rolling motion is more intense,the adverse effects of it on ship is fairly large.Therefore,reduce the rolling motion of ship is particularly important.When the encounter angle(that is,the angle between the sailing direction of ship and the waves' main direction)is changing,the stabilizing efficiency of fin stabilizer's PID controller which is designed in advance in a certain encounter angle is reduced under the encounter angle which is suffered by the ship in the current moment.Consequently,encounter angle is a principal factor that affects the stabilizing efficiency of fin stabilizer.Knowing the encounter angle which is under the ship's sailing direction is very necessary to select a set of optimal control parameters for anti-rolling fin control system.However,because of the difficulty of acquiring the encounter angle,and ship has a encounter frequency which is corresponding to the biggest rolling resonance energy at every encounter angle,hence based on ship's rolling motion,the encounter frequency of rolling resonance is estimated online,and the estimated encounter frequency is taken as the switch law of multiple controllers of fin stabilizer,thus anti-rolling fin will have a better stabilizing efficiency under different encounter angles.Based on above reasons,the following contents are studied:(1)The online estimation of the encounter frequency of ship's rolling resonance is researched.Firstly,based on the established model of the effective wave slope angle of long-crested random waves which act on the sailing ship and the established model of the linear model of ship's rolling motion,the spectrum of rolling angle of the rolling motion's time response of the ship is established by using the WELCH spectrum estimation method.And then encounter frequencies which are corresponding to the biggest rolling resonance energy are figured up by using MAX function.(2)The research of parameters set of fin stabilizer's PID controller based on quantum particle swarm optimization algorithm.Firstly,the mathematical models of kinds of links of fin stabilizer's control system are introduced.Secondly,in view of time-consuming,difficulty of the conventional PID controller parameter setting of anti-rolling fin control system and the standard particale swarm optimization algorithm is easy to fall into the defect of the localoptimum and so on.Parameters of fin stabilizer's PID controller are set by using quantum particle swarm optimization algorithm.And anti-rolling effect of fin stabilizer control system is emulated and verified based on the optimal control parameters of well-tuned PID controller.The statistic and analysis of damping efficiency are done.(3)The switch of multiple Controllers of fin roll stabilizing is studied.Firstly,the estimated encounter frequency is taken as the switch law of controllers of fin stabilizer control system under different encounter angles to realize variable parameter control of fin stabilizer control system.And then minimum average dwell time of guaranteeing stabilization of two controllers' switching of fin stabilizer control system is solved by using the theory of slow switching and the undisturbed switching technology which decomposes controller into fast attenuation parts and slow attenuation parts is also used to decrease the switching disturbance of anti-rolling fin controller in the switching moment.At last,the stability and smoothness of the switch of multiple controllers of fin stabilizer in the switching moment are emulated and verified by means of SIMULINK.