Jameel, Mohammed (Department of Civil Engineering, University of Malaya) | Khaleel, M. (Department of Civil Engineering, University of Malaya) | Saiful Islam, A.B.M. (Department of Civil Engineering, University of Malaya) | Ahmad, Suhail (Department of Applied Mechanics, Indian Institute of Technology Delhi)
A reliable mooring system is a critical aspect where survivability is considered. Total loss of a structure can occur during mooring system failures. With the advancements of the next generation circular hull shape FPSOs; Satellite Service Platform SSP320 Plus has the ability to utilize a spread mooring design that can be arranged to achieve the most cost effective and reliable design compared to a traditional ship shape FPSO. An additional factor with these increasingly large floaters that have a rectangular hull design is the gyration distance from the tipping point, which generates a significant larger moment than on a circular hull form. Thus, on a ship shape vessel, the mooring spread has limited structural real estate to sea fasten its winches and chain devices.
SSP320 Plus platform's new circular hull design provides better stability with the capability to accommodate a dry tree riser system with minimal yaw excitation whereas traditional ship-shape FPSOs motion varies considerably from head to beam seas.
Torpedo, suction pile and suction embedded plate anchor (SEPLA) have been considered for the permanent mooring system that will be installed in regions off the coast of Brazil. Torpedo pile anchor tends to be favored for these locations however the three anchors mentioned provide different advantages and cost values.
The study also focused on a pure technical evaluation of the influence to "peak shave?? high loading forces when the sea state reaches an extreme event by introducing thruster assist positioning, which can be favorable for an omni-directional hull shape. This results in installation of fewer mooring lines and introduces a higher safety contingency thus giving the mooring system a more cost effective design and the ability to survive extreme events with minimal offsets.
Model tests were conducted in LabOceano, Brazil, with MARIN (Maritime Research Institute) and Oceanica Offshore. Tests were executed for three different loading conditions, ballast, fully loaded and 50% loaded cargo. These tests confirm that the circular shaped hull FPSO response with a larger natural period and hydrodynamic responses similar to a SPAR platform. To further design and analyze a mooring system to meet the design standards, a parametric model was created and analyzed within AQWA. AQWA provided the ability to carry out a frequency domain as well as time domain dynamic analysis of several different mooring line configurations considering a variety of global environmental conditions.
Mooring design results from this extensive study confirm that the mooring materials are well within acceptable market parameters and the mooring systems can be adapted/flexible to allow a variety of services and applications for deep and ultra deep waters.
Jameel, Mohammed (Department of Civil Engineering, University of Malaya) | Saiful Islam, A.B.M. (Department of Civil Engineering, University of Malaya) | Jumaat, Mohd Zamin (Department of Civil Engineering, University of Malaya) | Ahmad, Suhail (Department of Applied Mechanics, Indian Institute of Technology Delhi (IIT Delhi))
A floating platform for arctic regions is required to break ice and withstand high ice loads, be disconnected and towed away in the event of approaching icebergs, leaving the mooring lines and risers in-place, support large topsides and provide large quantities of utility storage. Additionally the platform should provide low motion response to storm and ice loads to maximize the operational uptime and enable the use of current state-of-the-art riser systems.
This paper presents the details of a Spar platform that has been configured to satisfy all requirements for Arctic operation. The paper describes a number of key features that are specifically designed to reduce ice loads on the hull and to allow ice floes to break around the hull without damaging the hull, topsides, mooring or risers, while maintaining the characteristic low motion response to storm environments. The paper also describes the system for disconnecting and reconnecting the moorings and risers in response to approaching large icebergs.
This article, written by Senior Technology Editor Dennis Denney, contains highlights of paper OTC 20885, "Perdido Development Project - Spar and Moorings," by Curtis Lohr and Keith Smith, Shell International Exploration and Production, prepared for the 2010 Offshore Technology Conference, Houston, 3-6 May. The paper has not been peer reviewed.
The Arctic is the next frontier for oil and gas production, and it will offer new challenges for engineers who must design safe and efficient systems to operate under new environments. Some designs will be based on existing ones modified for these new conditions. In this paper, two floater designs, a Spar and Single Column Floater (SCF), are evaluated for deployment in an arctic environment. The floaters are assumed to support identical topsides and riser payloads and to be subjected to the same environments composed of level ice sheets and ice ridges, wind, waves and currents. Hull steel weights and mooring systems are similar for both designs. The comparison is based on general arrangements and global performance comparing motions responses and moorings loads. Results show that the motion global performance of the SCF is marginally better than the Spar. The ice breaking cone, used on both designs, shows unacceptable heave response on the hulls, requiring them to change drafts depending on whether the environments present ice cover or open-water conditions.
Kim, M.H. (Department of Civil Engineering, Texas A&M University, College Station, Texas, USA) | Ran, Z. (Department of Civil Engineering, Texas A&M University, College Station, Texas, USA) | Zheng, W. (Department of Civil Engineering, Texas A&M University, College Station, Texas, USA)
Nonlinear hull/mooring coupled dynamic analysis of a truss spar in waves with collinear steady winds and currents is numerically carried out in the time domain and the results are compared with 1:61-scale experiments as well as uncoupled analyses. The first- and second-order wave forces, added mass and radiation damping, and wave drift damping are calculated from a second-order diffraction/radiation hydrodynamics program. The total wave force time series is generated based on a 2-term Volterra series model. The hull/mooring coupled dynamics are then solved using a time-domain 3D mooring dynamics program based on a generalized-coordinate-based finite element method. The mooring lines are coupled to the platform through generalized springs and dampers. A case study was conducted for the Marlin truss spar with 9 taut mooring lines in 3240-ft (988-m) water depth. The numerical results show that dynamic effects are very important for the present mooring design. The motion and tension spectra of uncoupled analyses with a linear massless spring or nonlinear massless spring are also compared with those obtained from fully coupled analysis to assess the importance of hull/mooring coupling and mooring-line damping.
The deep-draft cylindrical spar has been shown to be an efficient platform for deepwater production, drilling, and storage (Glanville et al., 1991). Its deep draft gives it excellent motion characteristics even in the most severe sea states, which has been proved through numerical simulations, model tests and field observation. The relevant theory and comparison with experiments for this kind of spar are reported in Ran et al. (1996), Mekha et al. (1995), Cao and Zhang (1996), Kim et al. (1997) and Ran and Kim (1997). Recently, an alternative shallower-draft truss spar received considerable attention as a more economical design (Halkyard, 1996), especially in a loop-current environment.