Hull Dimensions of a Semi-Submersible Rig: A Parametric Optimization Approach

Semi-submersible rigs are utilized to perform drilling, production and intervention operations in the oil and gas industry. The design of the rigs is a complex task which today is highly dependent on manual iteration and experience. In this thesis, the prospect of using optimization methods to establish the main dimensions of the hull was investigated. A nonlinear optimization model which minimizes the hull weight was developed taking the most important properties of the semi-submersible rig such as stability, motion characteristics and air gap into account. The model was solved in Microsoft Excel to enhance the availability and make it easier to implement for engineers with solid experience using the software. The add-in algorithms solved the model in matter of minutes and the output was compared to other rigs operating in the North Sea. The results were verified by experienced engineers in Aker Solutions and were found feasible and interesting. Based on the results from the computational study and the sensitivity analysis performed, it is concluded that the model can be used as a decision support tool to establish the main dimensions of the hull structure