Practical approach to macro-element modeling of soil-structure interaction for floating offshore structuresTitle of the project

This research work deals with the development of a practical macro-element model for floating offshore structural foundations. Offshore studies have increased significantly over the last few decades. This is primarily due to the continued interest in offshore oil and gas exploration, but also due to the growing production of clean wind energy and the recent creation of floating infrastructure for wave and tidal energy. Floating structures are anchored to the seabed by various types of anchors, such as gravity foundations, caissons, drag anchors, vertically loaded anchors, suction-embedded plate anchors, gravity anchors, etc. With the discovery of more oil and gas deposits and the advancement of wind power generation towards deep water, a tool for practical and reliable design and analysis of foundations for floating structures that can model the coupled nonlinearities of the behavior of anchorage, anchor and soil (soil-structure interaction - SSI) in the dynamic analysis of the floating structure is very important.

Currently, SSI is not directly considered in the dynamic analysis of structures with foundations. The usual procedure, which involves an iterative analysis between a structural model with simplified assumptions on soil support and a separate geotechnical model with load assumptions from the structural model as a comprehensive finite element model of the structure and the supporting soil, may be oversimplified if the soil support model is too simple or the load assumptions are not correct, and the finite element analysis of the entire structure-foundation-soil model is too complex and expensive. Finite element analysis is computationally intensive and ineffective in terms of time and cost. Due to these limitations, macro-element models are increasingly used for the investigation of nonlinear SSI.

From a computational point of view, macroelement models are particularly interesting as they can capture the core of SSI with all six (6) degrees of freedom and have already been successfully used to predict the mechanical response of onshore and offshore foundations. The main advantages of such models are their simplicity and their ability to represent the overall behavior of load-bearing foundations (e.g. foundation capacity under combined loads, nonlinear behavior of structures, evaluation of seismic behavior of structures, etc.). On the other hand, their use in real applications is limited by the fact that the macroelement parameters have to be calibrated numerically or by experiments for each individual case, thus limiting them to specific applications and questioning their ability to solve a wide range of problems. Therefore, their use at this stage would require time-consuming finite element modeling or physical testing beforehand.

This research aims to investigate the concept of macro-element model for offshore mooring foundations supporting floating structures and to develop a practical macro-element framework in which macro-element parameters can be related to soil parameters commonly determined during ground investigation.

The new macro-element model will be implemented in Matlab and validated against available experimental or numerical results from the literature. The created macro element framework will serve as a tool for the practical design and analysis of offshore foundations for floating structures.