The Modeling Theory, Controlling Strategy And Optimal Designing Method For Ship Propulsion System

The propulsion shaft is one of the most important components of power device of the ship; its stability is the basic promise of the ship's life. Therefore, the modeling theory and vibration control of ship propulsion shaft become an important research content of ship propulsion shaft. However, for the modeling method and control theory of naval propulsion shaft, many of the issues still need to be resolved. Such as①the modeling of shaft by the dynamics of elastic body method with consideration of the effect of rotation velocity;②oil film model considering both flexibility of the oil film bearings and the bearing housing;③control theory under shock and stochastic sea waves;④the best control effects under the condition that the control parameter like the stiffness and damping of the support system remain the same, namely the optimal design problem and so on. In this paper, these issues are study and discussed in detail.Firstly, the latest achievements and the remaining problems on the modeling method, control theory and optimal design method of ship propulsion shaft are summarized and discussed in detail.Secondly, considering the limitations of the classical modeling methods of ship propulsion shaft, this paper proposes a new modeling method for ship propulsion shaft—the dynamics of elastic body method. The effect of rotation velocity on the response of the shaft under shock is studied. The comparison with the finite element method proves the reliability of the method.On this basis, the average eigenvalue method, which considers both stiffness of the oil film bearings and the bearing housing, is used to model the shaft. The vortex effect, the squeeze effect and the coupled effect of multi oil film bearings are considered; the effect of oil film forces and the effect of parameters and rotation velocity on the response of the shaft under shock are discussed; meanwhile, the correctness of the method is proved by the comparison with the approximate analytical method.Thirdly, the stochastic optimal control method is adopted in the shock control and the parameter design of the isolator of ship propulsion shaft. By means of Pierson-Moscowitz wave spectrum and the Fast-fitting algorithm of actual sea wave spectrum by fractional polynomials under the condition of smallest error, the transfer function is directly fitted by the frequency response characteristic data of the system which makes the simulation of the sea wave spectrum possible. On the basis of the dynamics of elastic body model proposed by this paper, the quasi optimal control method and the parameter design method of the propulsion shaft under shock and stochastic sea wave are discussed. Comparison is made between shock control effects under different control methods which clarifies the dynamic characteristics and the shock control mechanism of the propulsion shaft.Then in consideration of the perturbation in the control process, a variable structure control method with robustness is proposed by this paper. The switching function is designed by the quadratic optimal control theory; the terminal sliding mode controller is designed by using unit vector style. The variable structure control method of the propulsion shaft is preliminary studied.Fourthly, the genetic algorithm is adopted in this paper in the optimal placement of the support of the propulsion system. Comparison is made between the control effects before and after optimization which provides a theoretical basis for the design of the support position of the propulsion system.Finally, the conclusion of this paper is presented; the shortages in this paper and the further work direction are briefly discussed.