Internal solitary waves (ISWs) can impose significant loads on offshore structures. During the past several decades, ISWs have led to a series of incidents. With large draughts, spar platforms can be affected by ISWs; therefore, the ISW effect should not be neglected during the design, installation and operation in areas where ISWs can occur. However, there is a gap in research into this area with only a few preliminary studies published so far.
In this paper, a series of experiments are carried out with a spar platform model in a large-scale stratified tank at Shanghai Jiao Tong University to investigate interaction characteristics of ISWs. Based on a two-layer ISW theory, a simplified theoretical model is established for predicting the ISW loads on a spar platform. It is shown that the horizontal ISW loads consist of drag and inertia components, which can be calculated using the Morison's equation, while the vertical loads are mainly the vertical Froude-Krylov force, which can be obtained by integrating the ISW-induced dynamic pressure over the spar bottom.
By fitting theoretical results with experiments, specific formulas are established to determine two empirical coefficients in Morison's equation under ISW conditions, which are different from traditional methods. The numerical results from this method show good consistency with experimental results on both the amplitude of the loads and the time varying characteristics. This research provides a practical theoretical model for predicting ISW loads on spar platforms.
Although engineers often assume that waves and currents are collinear, they propagate in different (unparallel) directions, i.e. the incoming angle between waves and currents is not generally zero or 180° in reality. This paper makes a special effort to investigate how the different incoming directions affect motions of a Truss SPAR platform. In order to achieve this, the six degrees of freedom motion of the platform is considered with the wave and current loads evaluated by a slender body formulation. Various cases with different wave and current parameters are calculated and the effects of waves and currents on mean offset and oscillation motions of Truss SPAR are investigated.
Lu, Haining (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Xiao, Longfei (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Li, Xin (School of Naval Architecture, Ocean and Civil Engineering, Shanghai Jiao Tong University) | Xie, Wenhui (China National Offshore Oil Corp. Research Center)
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))
Li, Lu (School of Civil and Hydraulic Engineering, Dalian University of Technology) | Li, Binbin (School of Civil Engineering, Harbin Institute of Technology) | Ou, Jinping (School of Civil and Hydraulic Engineering, Dalian University of Technology, School of Civil Engineering, Harbin Institute of Technology)
One of the key features of the Spar platform is its low motion response characteristics. This results in a high degree of functional flexibility that has enabled the Spar to be employed in a variety of different applications such as wet tree host, dry tree wellhead, with or without platform drilling facilities and with or without production facilities. The Spar has also been employed as wellhead only platform, utilizing Tender Assisted Drilling in place of a Spar mounted drill set. While all but one of the Spars in service today operate in the US Gulf of Mexico (the one exception being the Kikeh Spar in Malaysia), new designs have been developed for the Spar platform to further extend its use, both in terms of function and geographic location, in order to meet the needs of other oil and gas producing regions as they extend their E&P activities into deeper waters and more harsh environments. These designs range from relatively simple modifications, such as the incorporation of crude oil storage in the hull to facilitate the use of dry tree completions and motion sensitive riser systems in infrastructure-remote locations, to more significant modifications, such as the reconfiguration of the Spar as a power and control buoy platform, or as a deep water Arctic platform, which requires the Spar to function as an ice-breaker in sheet ice conditions, while also allowing it to be disconnected to avoid larger icebergs.
The functional requirements, export infrastructure, operating environments and construction and installation capacity vary significantly across regions. Each of these variations has the potential to drive alterations to the Spar hull configuration. This paper discusses the most significant requirements of a number of key regions where Spar technology can provide significant value, and addresses these requirements in terms of the resulting Spar configuration and how the Spar design has been, or can be, adjusted to meet the local challenges and requirements. The specific regions covered are the ultra deep waters of the Gulf of Mexico, S.E. Asia, West Africa, North Sea, Brazil and the Arctic regions of East Canada and the Barents Sea. A variety of Spar configurations are presented to address nominal solutions for each of the regions, each based on either the Classic, Truss or Cell Spar technology.