Modified Static Mooring Analysis of Oil and Gas Marine Jetties Compared with Dynamic Mooring Analysis

Marine jetties form an important link between land and sea areas for the transport of oil and gas products. Mooring forces are considered a key factor in marine jetties design, which can be calculated using static or dynamic mooring analysis. In general, the dynamic mooring analysis (DMA) is considered a more complex task compared to static mooring analysis (SMA), due to the dynamic behavior of mooring lines and body motion of moored vessels. So, DMA always provides the most accurate and reliable results. Although the DMA is the ideal choice for detailed engineering projects, in feasibility studies and the FEED phase it will be time-consuming and less added value. In this paper, a methodology for calculating mooring forces using a modified SMA was implemented through the so-called dynamic mooring analysis factor (FDMA), which will take into account the dynamic response of the wave forces. For this purpose, more than 190 sea state load combinations were carried out, including different return periods, water depths, and wide range of vessel sizes. To determine the mooring forces in vessels' mooring lines, SMA is performed using the OCIMF approach, while DMA is performed by the Finite Element Model (SESAM Marine Software). The nonlinear regression concept was used to correlate the results of the SMA and DMA in conjunction with the vessel’s dead weight tonnages (DWTs). Finally, the dynamic mooring results using the modified SMA were validated against the DMA results generated by SEASM Marine Software, which gave promising results. As a conclusion; using the modified SMA approach will be as an alternative solution to the DMA approach at earlier stages of any project. This will also facilitate selection of the appropriate mooring pattern on marine jetties and the determination of the size and material of the mooring lines, thus contributing effectively to the cost estimation phase.