Research On Small Water-Plane Area Twin Hull Ship Motion Attitude Prediction And Control Strategy Design

In order to meet the increasing need of ocean marine operations and better development of ocean resources,higher request is put forward to the characteristics of ship seakeeping etc.High performance ships with good seakeeping character such as catamaran have been get great attention and development.Small Water-plane Area Twin Hull(SWATH)ship uses two submergence bodies to move the drainage volume away from the water plane surface,to increase the damping,and to reduce the water plane area.So it has a much better seakeeping performance than normal ships for the structural features.But it is precisely because of the small water-plane area,SWATH ship can provide not enough restoring forces and torques to balance wave disturbances while sailing in waves.It results in a bad performance of longitudinal(heave and pitch)motion of SWATH ship stability.Otherwise traditional control strategy of SWATH ship motion is difficult to get satisfied effect because of ship structure and ship motion characteristics.Therefore,it needs to make SWATH ship motion attitude prediction.Also proper control strategy design would make great significance to the SWATH ship motion attitude control.To get SWATH ship motion characteristics,SWATH ship motion model is built firstly.2.5D strip theory is used to solve the problem of SWATH ship hydrodynamic coefficients.And SWATH ship motion attitude prediction is made.Meanwhile ship motion response is get,stability character,ship motion period and damping are used to analyze SWATH ship motion characteristics.Simulation makes a built SWATH ship as an example.Hydrodynamic parameters are computed,and ship motion performances are studied.Example results show that the longitudinal motion of SWATH ship had poor stability.And it need to control SWATH ship motion attitude by means of stabilizing fins.To study SWATH seakeeping character,wave disturbance model acting on SWATH ship heave forces and pitch moments is built.And optimal control of SWATH ship motion is proposed based on ship model character.Combing wave disturbance and ship motion model,SWATH ship motion disturbance observer is designed.Then wave disturbances is observed and compensated.Disturbance compensation control performance of SWATH ship is studied.Simulation results show that it can effectively improve the control effect of SWATH ship motion attitude by combinationof disturbance compensation and feedback control.Because there are two pairs of stabilizer fin equipped on SWATH ship to control ship motion attitude.It certainly results in hydrodynamic problem between fore and after stabilizing fins,and control mode selection problems of fins.To study stabilizer fin characteristics,CFD software is used to simulated dynamic lift characteristic of the equipped stabilizing fins.Distance influence between fore fin and after fin is discussed,and after fin lift changes by fore fin is studied.Then lift character is transformed into damping character to study stabilizer fin effect on SWATH ship motion characteristics.On the basis,longitudinal motion responses of SWATH ship to stabilizing fins are learned.And respectively control of a pair of fore fin,after fin or two pair of stabilizer fins is analyzed.Control mode effect on SWATH ship motion attitude is studied.Otherwise,roll reduction control strategy is designed to solve a ship sailing problem on the guarantee of SWATH pitch motion.And simulation results show the method efficiency.Uncertainty is induced by ship load,ship motion attitude change,speed change and wave disturbance etc when SWATH ship is sailing in a seaway.Considering the uncertainties of SWATH ship motion control,the uncertainty control model is modeled.And fuzzy adaptive control is proposed to control the SWATH ship motion attitude.The uncertainty is compensated by means of fuzzy and adaptive control law.It can effectively restrain the uncertainty effect on SWATH ship motion attitude control.In the end,in order to prevent "buried" and other phenomena occur,and to realize SWATH ship motion prediction of a next few seconds,nonlinear predictive control of SWATH ship motion attitude in time domain is proposed.The predictive law is based on a period of former SWATH ship motion attitude state data and desire set of a after few seconds contrail.Through the Taylor series expansion of SWATH ship motion model,it can get offline optimal control gain,which can solve the large computational problem of predictive control online optimization.Then the nonlinear predictive control law is combined with nonlinear disturbance observer.Stability of the closed-loop system is guaranteed.This method can get good predictive control performance of SWATH ship motion attitude,and effectively improve the robustness of the control system.