No abstract

In response to Florida's growing energy needs and drive to develop renewable power, Florida Atlantic University's Center for Ocean Energy Technology (COET) plans to deploy a mooring near the core of the Gulf Stream off southeast Florida's coast. This mooring system testing platform will be used to evaluate the performance of prototype ocean current turbines including COET's 20 kW turbine that is currently under development. No mooring systems for deepwater hydrokinetic turbines have been constructed, tested and installed; therefore little is known about the performance of these moorings. To investigate this, a numeric model is used to predict the static and dynamic behavior of the mooring system and attachments, quantifying sensitivity of the system's response to parametric variations. This numeric model of COET's proposed mooring system has been created in OrcaFlex to model static and dynamic effects of the system. It includes numerical models of its two surface buoys, a rotating ocean current turbine, and the lines associated with the system. Wind, wave, and current profiles represent the environmental conditions the system is expected to experience.

Marine renewables have made great strides in recent years. The IEC, ABS, and DNV GL continue to generate standards and recommended practices in an effort to formulate approved processes as the renewable products make their way offshore and into the market. There are many similarities in some of the processes and designs when compared to oil and gas structures, especially when it comes to moorings. However, many design areas are uniquely related to renewables, even within the same field of energy conversion (e.g. multiple types of wave energy converters). As more renewable systems are installed, the standards will continue to transition from philosophical to more prescriptive recommendations. One area in which the lines are blurred between oil and gas and renewable industries is mooring systems. The interdependency between the mooring and power generation systems plays a crucial role early in the design phase. Modeling marine energy converters and the mooring system can be complex due the variability of moving parts, and without proper attention, it may be easy to underestimate the loads and fatigue cycles to which moorings will be exposed. Moorings for these structures should incorporate existing standards and recommended practices to ensure safety and reliability. Inspection, maintenance, repair, and replacement should also be considered. As the renewable industry continues to move forward from scaled prototypes to farms of devices, the oil and gas supply chain will contemplate when to become involved from a financial and resource perspective. However, there are still hurdles within the US authorization bodies like BSEE, BOEM, FERC, NOAA, USCG, etc. to overcome. This paper addresses the existing mooring related standards and delineates areas that need further refinement or conservatism as the renewable industry moves forward with the installation of offshore energy converters.

Movement of moored floating production vessels, such as Spars, Semi-submersibles, Deep Draft Floaters and Floating Production Units, due to environmental loading is often considered a design challenge to be addressed during the design phase of a structure. Proactive vessel relocation through mooring line adjustment can be integrated as part of an operational method to improve and extend component lives. This method may be implemented during the initially planned life of the structure to overcome riser fatigue life challenges, or as one of the methods to extend service life. The benefits are particularly noteworthy for steel catenary risers and mooring systems and have been discussed in previous works. However, vessels often deviate from the original relocation plan in practice. This paper assesses the benefits of a vessel relocation program with conscientious focus on the associated operational challenges. Risks associated with vessel relocation are also investigated. Suggestions are made to optimize such a program and to minimize interruption to production.