Abstract
The mooring and riser system is the most critical part of an offshore oil terminal. Traditionally, these two parts are designed separately without considering the nonlinear interaction between them. Thus, the present paper aims to develop an integrated design process for riser systems with a lazy-S configuration and mooring systems in the offshore catenary anchor leg mooring (CALM) oil terminal. One of the important criteria considered in this integrated design is the offset diagram and safe operation zone (SAFOP) related to the mooring system and the riser, respectively. These two diagrams are obtained separately by different analyses; therefore, codes or standards are available separately for two components. In this methodology, the diagrams of both risers and mooring lines are incorporated into a single spiral, thus identifying the safe and failure zones of risers and the mooring lines of the oil terminal. This, in turn, leads to substantial benefits in terms of overall system response, cost reduction, and safety to the offshore oil terminal. To implement this process, three different riser lengths with the lazy-S configuration are considered at three different sea depths at the terminal installation site. For each condition, the integrated design of the mooring system and riser is executed according to the derived procedure. Then, coupled dynamic models, wherein both buoys and hoses are included, are developed using OrcaFlex. Results show that the criteria of the relevant regulations are not satisfied by reducing the length of the riser relative to the designed size. Further, as water depth increases, this type of riser configuration shows good coupled performance while interacting with the mooring system. In the cross offset mode, the maximum margin is created between the offset diagram and the SAFOP diagram, while the most critical dynamic response of the tanker and terminal system occurs in the near and far modes. Therefore, with this method, the best position for the riser direction with the tanker direction is 90° in the best case.
Highlights
The transport of petroleum products to export destinations is done either through pipeline transport or in oil terminals
Offset diagrams show the maximum displacement of the terminal buoy under the influence of all load cases in different directions
The offset diagrams show a good view in terms of maximum floating displacement in each direction based on the maximum environmental conditions of that direction
Summary
The transport of petroleum products to export destinations is done either through pipeline transport or in oil terminals. Onshore and offshore terminals are the common types of oil terminals. Due to the high cost of construction and maintenance, complexity in berthing, dredging issues, and low safety, offshore terminals have received growing interest. The most common type of offshore terminal is the catenary anchored leg mooring (CALM) type. A CALM terminal consists of a moored main buoy permanently connected to the seabed via three to six mooring lines. The buoy contains a bearing turntable system that allows the turntable to freely weathervane around the lower part
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