Coupled DEM–FEM Analysis of Ice-Induced Vibrations of a Conical Jacket Platform Based on the Domain Decomposition Method

Wang, Shuailin (Dalian University of Technology) | Ji, Shunying (Dalian University of Technology)

OnePetro 

The discrete-finite element coupling method is an effective approach to simulate the complex interactions between sea ice and offshore structures and ice-induced vibrations (IIVs) of structures. However, the small time step in the discrete element method, as the time step of the coupled method, is time-consuming. Adoption of a time multiscale strategy can solve this problem. This paper proposes a coupled discrete-finite element method based on a domain decomposition method to analyze the interactions between sea ice and a conical jacket platform. Moreover, IIVs of the platform were analyzed. The computational domain is split into several subdomains based on whether sea ice interacts with the platform. The subdomains directly impacted by sea ice use small time steps of the discrete element method. The numerical results show that the proposed time-efficient method is reliable and stable for the simulations of ice-platform interactions.

INTRODUCTION

In cold regions, the vibrations of offshore platforms induced by sea ice can be harmful for not only the routine production but also the serviceability and safety of platforms. Conical jacket platforms have been used considerably in the Bohai Sea of China. The forces induced by sea ice are the dominant environment loads acting on the platforms. Ice-induced vibrations (IIVs) of platforms have also been reported by Yue et al. (2009).

To overcome IIVs of platforms, some beneficial work including field measurements, model tests, and numerical simulations has been conducted on the interactions between sea ice and offshore platforms (Huang et al., 2013; Nord et al., 2015). Because field and scale tests are difficult and expensive, numerical simulations are usually adopted for investigating the dynamic behaviors of offshore platforms under ice loads (Hopkins, 1997; Paavilainen and Tuhkuri, 2013). Kärnä and Turunen (1989) calculated the IIVs of a narrow structure by assuming ice load to be a function of the relative displacement and relative velocity between ice and the structure. The finite element method (FEM) has also been utilized in ice load analyses in which the sea ice is approximated using the material’s nonlinear model (Sand and Fransson, 2006). However, the continuum-based FEM is limited by the inherently discrete nature of sea ice, especially in the case of floe ice.