Numerical Calculation And Model Test Study On A Quay Mooring Deep Water Semi-submersible Drilling Platform

With the fast development of economy, the energy resource imbalance between needs and supplies in China is getting larger. Design and manufacture heavy equipments for deep water oil and gas exploration has become one strategic choice of the Chinese government. As a result, the first deep water semi-submersible drilling platform of China is presently under construction in Shanghai Waigaoqiao Shipbuilding Co.Ltd (SWS).The out-fitting cycle of the SEMI when it is moored at the quayside is very long, which indicates that it may have to experience and survive a typhoon. It is necessary to acquire a reasonable quay mooring layout of the SEMI by numerical calculation and model test study.Compared with the quay mooring system of conventional huge ships,the one of a SEMI has its own specialty. Due to its huger wind areas in both transverse and longitudinal directions,a moored SEMI will experience larger wind loads than conventional ships.Besides,the draft of a SEMI in out-fitting condition is near the depth of its pontoons, which will lead to its very low freeboard. On the other hand, the anchor bolsters installed on the columns of a moored SEMI need to be well protected from the quayside.Considering such factors,a barge is usually applied between the SEMI and the quayside in a SEMI quay mooring system, acting as a force transmission and a anchor bolters protector. However, it has crucial effect upon the layout of the mooring lines and will complicate the dynamic response of the whole mooring system.Using the quay mooring guidelines of conventional vessels for reference and taking the practical condition of the SWS quayside into consideration, this paper firstly investigates the quay mooring layout based on static wind and current loads. According to the study on the preliminary layouts, together with the sensitivity analysis of the mooring line's pretension and stiffness,rules of the SEMI quay mooring system are obtained. Based on these rules, the quay mooring layouts in normal condition are compared and optimized. As for the typhoon condition, a layout applying four anchors is designed. The above investigations have laid a very good foundation for the model test study.Afterwards, model test with the scale of 1:50 is conducted for both normal and typhoon conditions in the basin of Shanghai Jiao Tong University. The wind-current-static model tests are performed to verify the reliability of the previous static calculation results.Wind-current-wave-dynamic model tests are also performed, in order to acquire the dynamic response of the SEMI quay mooring system. At last, a dynamic analysis of the quay mooring system in typhoon condition is carried out.Several principles for quay mooring layout of a semi-submersible drilling platform have been concluded. These conclusions can be used to support the design of similar systems in the future.