Study On Robust H_∞ Estimation And Prediction For Ship Motion

Sailing in the ocean, ship inevitably produces 6-DOF swinging motion under wave disturbing force and disturbance torque. If the ship motion attitude can be estimated and predicted, it will bring great benefit to the take-off and landing of carrier aircraft, ship anti-rolling, ship mating and so on. Therefore, ship motion estimation and prediction have been attracting much attention. Supported by the National Defence Foundation "Extreme Short-time Prediction of Aircraft Carrier and Attitude Prediction System of Guiding Carrier Aircraft Landing" and "Research of Warship Attitude Prediction Control and Simulation", Problem of ship motion estimation and prediction is researched based on robust H∞method in this dissertation. The main contents of this dissertation are as follows:In this dissertation, the hydrodynamic force coefficients of the ship motion model is analyzed using the hydrodynamics knowledge based on the strip theory. The coefficients are weighted average by wave spectrum, and ship motion model based on weighted average by wave spectrum is established, which provides nominal model for the research of ship motion estimation and prediction. Under the circumstance with pertubing hydrodynamic force coefficients, estimation errors of Kalman filtering is analyzed, and the necessity of applying robust H∞method to research ship motion estimation and prediction is demonstrated.The methods of robust H∞estimation and prediction are proposed in the dissertation, that is, considering synthetically two aspects of perturbation in ship motion model and unknown uncertainty of disturbance input statistic characteristics, stable filter and predictor is designed to make the attenuation level of wave disturbance to estimation and prediction error (H∞norm) lower than setting value. The main contributions of this dissertation contain the following three aspects:Firstly, for the ship motion estimation, the ship motion robust H∞filter based on the quadratic stability and parameter-dependent Lyapunov function is designed via linear matrix inequality (LMI) method, and the filter stability condition and the solution method of the parameter matrices are obtained. The filter design based on the quadratic stability does not need to consider material characteristics of parameter perturbations and exogenous disturbance, such that the design method is easily implemented. However, the method requires that there is a unified Lyapunov function for all the permitted uncertain parameters, which leads to more conservativeness. The parameter-dependent robust H∞filter is abtained by designing Lyapunov function correlated with systmen uncertainty, which reduces the design conservativeness and enhances the precision of ship motion estimation.Secondly, there is singular perturbation phenomenon in ship motion system, thus the robust H∞estimator based on singular system theory and is developed. Existential condition of the estimator that the error system is regular, impulse-free and stabile is given, and its parameter matrices can be derived by resovling linear matrix inequalities. This estimator design method is simulated and applid to the ship motion estimation, simulation result verifies the validity of this method.Thirdly, ship motion robust H∞predictor is proposed to resolve the problem of ship mition prediction, and stability condition of the predictor and the solution method of parameter matriecs are given. It transforms the problem of robust H∞prediction into the problem of time-delay system robust H∞filtering. The distance-independent and distance-dependent robust H∞predictors are designed according to the delay-independent and delay-dependent ideas, and the solution of H∞, predictor is derived by minimizing linear object functions of LMI. The ship prediction problem with model perturbation and unknown disturbance statistic characteristics can be solved by the proposed method.