The Application of Vector Form Intrinsic Finite Element Method to Template Offshore Structures

Abstract

A vector form intrinsic finite element method (plane frame element) is adapted and applied to study the dynamic responses of offshore template platform under wave forces. The vector form intrinsic finite element method (VFIFE) was firstly developed by Ting, Wang and Shi in 2002 by adopting the traditional co-rotational explicit finite element method to improve the solution procedure for the mechanic problems. As we know, the development of traditional co-rotational explicit finite element method is well over three decades. In 1973 Belytschko and Hsieh first established the theoretical foundation for the co-rotational explicit finite element method. In 1993 Rice and Ting revised the traditional co-rotational explicit finite element method to adopt an updated geometry during the calculation for the structural members, which allows a large deformation problem to be observed. The method adopted in this study is a similar scheme to updating the geometry of the structural system during the calculation of each time step, which is also called the coordinate moving frame approach. The offshore template structure has been widely applied for the petroleum exploitation and is subjected to dynamic forces all the time in the ocean. Therefore, in this study in order to take the advantage of the VFIFE that is a time-saving scheme for the dynamic analysis, the solution procedure is developed in cooperating to the effect of the wave motions interacting with the offshore structure. A typical offshore template structure is analyzed for both the static and dynamic behavior by utilizing the developed solution scheme. The motions in the horizontal and vertical direction and the rotation at each node are calculated and presented into figures. It is found from this study that the new developed VFIFE could be a promised method in analyzing the offshore template structures in lieu of its dynamic characteristic, large displacement motion and structural type.