The workpresented here starts with discussion of shallow water mooring philosophy andthe motivation for the development of such a system.
The tests are conductedrecently at the ocean engineering basin of the State Key Laboratory of OceanEngineering in Shanghai Jiao Tong University.ĭevelopment of a shallow water FPSO mooring concept called Turret Mooring withSelf Adjusting Stiffness system is introduced in this paper. Satisfactory results are obtained from model tests of a TUMSASsystem designed for the China Bohai BZ3-2 field. TUMSAS system has been developed and ready for FPSO shallow water mooringapplications. As a keycomponent of the TUMSAS design, the weight module combined with catenaryprovides self adjusting restoring stiffness required for shallow water mooringwhich has been designed by one of the authors and successfully used for thepermanent mooring of a retired aircraft carrier for more than ten years. It consists of a turret, a hanging weight module andcatenary moorings connecting to the lower edge of the weight module. TUMSAS has advantages taken from both conventional catenary turret mooring andsubmerged yoke systems. TUMSAS is developed with helpfrom various offshore engineering companies and research institutions toprovide an effective and economical solution for FPSO shallow watermooring. Over stress and even total damage has been reportedfrom applications in the China production field.
Submerged soft yoke turret mooring systems are economicaldesigns for shallow water marginal field applications, but they cannot providelong enough FPSO offset. A conventional catenary turretmooring system is suitable for mid to deep water applications due to itscatenary configuration only can be maintained at a small vessel offset forshallow water. The work presented here includes thedevelopment of TUMSAS and supporting model tests results.įPSOs at 20m to 30m water depth range require nonlinear mooring systems whichcan only provide a soft initial restoring stiffness at small vessel offsets andlarge stiffness at relatively large offsets. I have two questions about this:ġ) the WAMIT*.out file used for Orcaflex is the same as the WAMIT*.out file used for HydroDyn? I mean there is no difference between the input files of WAMIT.Shallow water mooring for an FPSO system is a challenge for offshore engineers.TUMSAS - Turret Mooring with Self Adjusting Stiffness system is invented toprovide a new and effective solution. When I use Orcaflex with FASTv8, the WAMIT*.out file is imported to the Orcaflex model. You can find this slight customization of the FAST executable, as well as the FAST model of the NREL 5-MW wind turbine atop the OC3-Hywind spar buoy here. Instead, we modeled the "additional linear damping" with a slight customization to the HydroDyn module and a recompiled version of FAST. So, when I use WAMIT as a preprocess for FAST, I always set the center of mass, and radii of gyration to zero in WAMIT.įor the OC3-Hywind spar buoy, the "additional linear damping" cannot currently be specified within the FAST/HydroDyn input files or WAMIT. This can be achieved by setting VCG to zero in WAMIT. To avoid double booking these terms, it is important to neglect the terms in WAMIT. However, FAST intrinsically accounts for the platform weight's influence on the pitch and roll restoring if the platform weight and center-of-mass location (PtfmCM) are defined appropriately.
In WAMIT, the vertical center of gravity (VCG) is also used to determine the pitch and roll restoring associated with platform weight and WAMIT will include these effects in the restoring matrix that it outputs (the *.hst file). One important thing to keep in mind is that the pitch and roll restoring of a floating body depends on the vertical distance between the center of buoyancy and center of mass of the body. All other terms are included in FAST, including the platform weight and inertias, so, it is not important to specify the mass, center of mass, and radii of gyration properly in the WAMIT model when using it as a preprocess for FAST. However, when WAMIT is used as a preprocess to FAST's HydroDyn module, WAMIT is only needed to compute the hydrostatic restoring matrix (*.hst), the frequency-domain added-mass and damping matrices (*.1) and the frequency-domain wave-excitation force vector (*.3) (not the ROAs). If you want to use WAMIT to compute the proper RAOs, it would be important to specify the mass, center of mass, and radii of gyration of the complete system (platform + tower + nacelle + rotor) properly in the WAMIT model. In WAMIT, the mass, center of mass, and radii of gyration are used to form the 6圆 body-mass matrix needed to compute the response amplitude operators (RAOs).