Research On Ice Load Invese Method And Application Of Polar Navigation Ship

In recent years,people focus on the exploitation of resource and sea-routes near the arctic regions with global warming and ice-layer decreasing.And the interesting of safety and reliablity of polar navigation ship under ice load is increasing.To ensure the safety and reliablity of ship navigating in polar regions,the accurate and reliable ice load need to be obtained.However,the ice-induced load on ship structures is difficult to be measured directly due to the limitation of environmental and technical conditions,while the strain resopnse caused by ice-induced load could be measured easily and accurately.It's an important approach to determintation of the ice load on ship hulls using the inverse method based on the strain data of full-scale measurement.The aim of this paper is to establish the mathematical inverse models of ice-induced load on ship structures,and the following research has been done.In view of the mathematical characteristics of the inverse problem,the regularization methods of load inverse problems is studied,and three forward models of load inverse problems are established.Different regularization methods and principles are expounded from several aspects,such as iteration,projection and discretization,while the influence of regularization parameters and independence matrices on the solutions is discussed.To support the research of the mathematical models of inverse ice-induced load,the relationship between inverse load,structural system and response is established by model tests or finite element method.A mathematical model of inverse load of the frame system is established with the classical beam theory and characteristics of the frames on the stern shoulder of a ship hull.The relationship between inverse load and structural response is established by using the forward model of the kernel function and the projection method,and the amplitude and distribution of the load on the frame in the time domain are obtained.The results show that the mathematical inverse model could reduce the influence of ill-posed equation in the process of frame load identification,and the determined inverse load is completely closed to the real load.Three load discretization models with fixed boundary conditions are set up according to the natural features of ice load and the locations of instrumentions on the ship hull.The discretized matrices are determined by using the finite element model to construct the relationship between known load and structural response based on the forward model theories of known and multi-source loads.Tikhonov regularization is utilized to turn the load inverse equation into an unconstrained optimization problem to overcome the ill-posedness of traditional load inverse methods,while the Generalized Cross-Validation method is used to select the perfect regularization parameters of each discretization model.The Trust Region Algorithm is applied to solve the over dependence of the initial values and determine the ice load pressures of each diacretization regions for minimising the regularization equation.Whereafter,the amplitude and distribution of ice loads in the time domain are obtained.A mathematical model of inverse load with unfixed boundaries is established based on the thought of uncertain structural load identification.The longitudinal inverse region of the hull palte is separated into a few sub-regions containing the longitudinal boundary conditions of the inverse load.The linear equations containing the information of ice load heights(longitudinal boundaries)are set up by utilizing the projection method and the forward model.Whereafter,the equations are transformed into an optimization problem under contrains by using Tikhonov regularization.Finally,the ice-induced loads pressures and heights of each sub-region are determined by using Simulated Annealing Algorithm,which turn the contrain conditions into objective functions to optimize the regularization equation.The studied mathmatical models of inverse load are utiliezed to determine the ice-induced load on a ship hull based on the full-scale measurement data of Antarctic navigation.The amplitudes and distributions of ice-induced load on the frames and hull plates are identified accurately under different ice conditions and ship operations,and the transformation process of the ice loads is also determined.