Studies Of Parameter Identification And Damage Detection For Ocean Engineering Structures

This paper studies parameter identification and damage detection of structures in incomplete conditions, and discusses the development in parameter identification and damage detection of the structures, the basic theory, the advantages and the development of genetic algorithm. It focuses on parameter identification and damage detection of structures-specially, ocean offshore platforms.The method that combined REKF and least square method is used to detect the physical parameters of the structure. In the condition that detected information is partial, firstly system input which is used as the input of REKF method can be get by statistic average method that based on least square method, then REKF method is applied to identify physical parameters and diagnose the damage of shearing structures. The numerical example shows that, the method is of robustness, high precision and error tolerance.To solve the problem that it has a slow convergence when Genetic algorithm is used to diagnose the damage of large structures, CHC algorithm, an improved Genetic algorithm, is applied to the field of damage diagnosis in this paper, and an improved CHC algorithm (ICHC), which combines the advantages of simple genetic algorithm (SGA) and CHC algorithm, has been put forward. Both SGA algorithm and improved CHC algorithm are applied to diagnose the damage of a 10-unit fixed-end beam and an offshore platform, and different objective functions are discussed in details. This paper discusses the damage diagnosis of offshore platform with six different sensor placements, based on six different methods. Based on the numerical examples, it can be concluded that the calculating time in damage diagnosis of structures could be largely shortened by improved CHC method. Also it has the advantages of faster convergence and robustness.Step-frequency filter method is applied in the calculating of structural modal parameters. The application of this method optimizes the program of structural analysis, especially, it can shorten calculating time and has higher efficiency to the diagnosis of large structures. Comparing with the simple analysis program, it can save 90% time and solve the problem of the application of GA.