The Effect Of Earthquake And Soil On The Dynamic Response Of Offshore Jack-up Platform

Jack-up platform is one kind of the chief engineering structure, which serve for the ocean engineering. While the environment where the platform stands has a significant effect on the ocean platform. The research of the platform subjected to the soil and the earthquake is still less. Some researches of the jack-up platform subjected to the soil and earthquake are carried out according to the existing platform parameters and the research results, and some conclusions which can be applied in engineering practice are provided in this paper. The major work and the research results are as follows:Firstly, the three-dimensional finite element model of the platform is established based on the actual jack-up platform parameters by the ANSYS finite element software. The static and dynamic responses of the platform under the extreme wave conditions are analyzed. It can be found from the modal analysis that the flexibility of the jack-up platform itself is large, a clear nonlinear characteristic of the platform occurred under the waves and ocean current load. The dynamic response is significantly larger than the static response, which that the static strength analysis of the platform is inadequate, the dynamic factor and the non-linear factor must be considered. The method and the theory of nonlinear calculation in the ANSYS are discussed.Secondly, the influence on the response of the platform by its soil layer is considered. Two different numerical modeling methods based on two different theories are discussed and the calculation results are analyzed. One modeling is based on API regulations, using nonlinear spring element to simulate the constraints to platform legs by soil layer, and the other is based on D-P material, the complete modeling of the soil body is established. The soil body's constrain to leg bottom by the definition of interface between them is analyzed.Thirdly, the influence on jack-up platform by earthquake is discussed based on the related regulations and combine the designed soil types.