Non-linear finite element modelling of dynamic loads on offshore structures

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Structures utilized for the exploration and development of hydrocarbon resources in ice-covered water are by nature expensive and complex. Molikpaq, Gulfs Mobile Arctic Caisson, is one of such structures which was used successfully to drill in the Canadian Beaufort Sea. During one deployment of the caisson, it was subjected to ice interaction events resulting in critically large dynamic loads. Various models have recently been developed to describe the interaction between moving ice sheets and structures. While these models show considerable promise to adequately describe the problem, they do not provide a full description of the process nor have they yet met the challenge of modelling actual interactions. The main objective of this study is to develop a detailed non-linear finite element model which is capable of predicting the dynamic loading on offshore structures due to the movement of ice against them, and to study the behaviour of such structures under these dynamic effects. Molikpaq is taken as a study case in this work. The complete model consists of three major components: The structural model for the steel caisson and the sand core, the moving intact ice sheet, and the interaction between them. The structural model is developed using the sub-structuring technique to model the complicated steel caisson, while the sand core is modelled using simple three dimensional isoparametric elements. Continuum damage mechanics is employed to model the behaviour of the moving intact ice. A new finite element is developed to model the interface between the structure and the ice sheet. The element has two components: one to model the deformation and damage accumulation in the intact ice nearest to the structure, and one to model the extrusion of the pulverized ice between the intact ice and the structure. Details of the model components, and the parameters which affect them most, are explained in detail. The complete model is used to simulate some actual recorded events. It accurately predicts the loading and the structural response. The behaviour of the structural elements under these loadings is analyzed.
Bibliography: p. 243-252
Morsy, U. A. (1995). Non-linear finite element modelling of dynamic loads on offshore structures (Doctoral thesis, University of Calgary, Calgary, Canada). Retrieved from doi:10.11575/PRISM/15646