This paper presents the results of aerodynamic and hydrodynamic model tests of the ENSERCH Garden Banks, a semisubmersible Floating Production Facility (FPF) moored in 2, 190-ft waters. During the wind tunnel tests, the steady component of wind and current forces/moments at various skew and heel axes were measured. The results were compared and calibrated against analytical calculations using techniques recommended by ABS and API. During the wave basin test the mooring line tensions and vessel motions including the effects of dynamic wind and current were measured. An analytical calculation of the airgap, vessel motions, and mooring line loads were compared with wave basin model test results. This paper discusses the test objectives, test setups and agendas for wind and wave basin testing of a deepwater permanently moored floating production system. The experience from these tests and the comparison of measured tests results with analytical calculations will be of value to designers and operators contemplating the use of a semisubmersible based floating production system. The analysis procedures are aimed at estimating 1)vessel motions, 2)airgap, and 3)mooring line tensions with reasonable accuracy. Finally, this paper demonstrates how the model test results were interpolated and adapted in the design loop. INTRODUCTION ENSERCH Production Operating Limited Partnership (EPO) has selected the Glomar Biscay I, an Ocean Victory-class semisubmersible MODU for conversion to the FPF and renamed it the ENSERCH Garden Banks. The FPF will be located in Garden Banks Block 388 in the Gulf of Mexico in 2,190 feet of water. The FPF will be permanently moored using a 12 point combination chain and wire rope system. The mooring system is designed for the 10o-year hurricane condition at the site. In this paper results of 1) wind tunnel testing, 2) global performance analysis, 3) mooring system design and analysis, 4)wave basin model testing, are presented. DESIGN PREMISE The mooring system has been designed according to practices and procedures recommended by ABS [1] and API [2]. Mooring design criteria are summarized in Table 1. The worst one-line damage condition was determined by analyzing cases with either the most loaded line or the second most loaded line broken. Mooring Line Scope The mooring line scope was designed to ensure no uplift of the mooring line at the seafloor in the 10o-year storm condition with all lines intact. Also, no mooring line was allowed to contact an environmentally sensitive seafloor area within the mooring pattern. Platform Offset Requirements The vessel offset requirements used in the mooring system design for the ENSERCH Garden Banks are shown in Table 2. Metocean Criteria The following three conditions are used to design the permanent mooring system:1ao-year hurricane survival condition,1a-year winter operating condition and5-year winter storm combined with loop current operating condition. Metocean criteria for a similar region (27º N and 86º W) of the Gulf of Mexico, studied by API and presented in [3], suggested that a set of reduction factors may be applied to the omni-directional wave height to account for the directionality of the severest hurricanes in this region.
This paper presents design considerations of a SWATH (Small Waterplane Area Twin Hull) Diving Support Vessel (DSV) presently under construction for delivery in 1995. It is designed to transit on twin pontoons at 12 knots and operate semi-submerged with dynamic positioning or a spread mooring. It will provide multi-purpose support for sheik w or deep water operations that include saturation diving support, pipe laying, trenching, well intervention, and offshore fire fighting services for worldwide use. This vessel greatly increases the capability of the offshore industry to perform deep water diving and other support functions in sea conditions that significantly exceed tha operating limits of mono hulls. This paper summarizes the design basis for the SWATH DSV encompassing the evolution from concept to the final design approved by the American Bureau of Shipping. Validation of analytical predictions of motion and station keeping with model tests are also presented. The vessel represents an important advance toward cost effective deep water operations. INTRODUCTION The acronym SWATH DSV stands for small waterplane Area Twin Hull, giving support vessel. Thesemisubmerged SWATH DSV hull form (Figure 1) developed by BSM is a novel design that blends the technologies of semisubmersible drilling vessels and constant draft SWATH 2. This multi-draft SWATH vessel will be the first of its kind to support a variety of functions including saturation diving support, pipeline laying and jetting, well work over, wireline servicing, ROV intervention, and fire fighting support for worldwide service including Gulf of Mexico and North Sea. The vessel will transit at 12 knots in sea state 4, and operate in sea states 5 and 6. Monohulls performing similarunctions rarely can operate beyond sea state 4. The vessel has a diesel electric dynamic position system with three 930 KW diesel engine generators in the upper hull and four 800 HP azimuthing thrusters in the pontoons. It is equipped with two heavy lift cranes, a large stern A frame, two moonpools and accommodations for 57 persons. Table 1 summarizes the principal particulars and Figure 2 shows the outboard profile and end views. The design project was performed on a fast track schedule. Conceptual design was completed in the month of September 1993. Preliminary design was completed in two months ending in March 1994. Model testing was performed in April and the final design was substantially complete by June 1994. A construction yard was selected in June and a contract awarded in September. Regulatory submittals overlapped initiation of construction, Vessel delivery is expected in the fall of 1995. FUNCTIONAL REQUIREMENTS The primary function of the vessel is diving and ROV operations in open ocean environments worldwide. The overriding requirement is for a ship which can perform diving and/or ROV operations, while under thruster assisted dynamic positioning or in a four (4) point mooring, in higher sea states than can be tolerated by equivalent monohulls. The vessel is required to support a minimum of 100 long tons of variable deck load in addition to the mission equipment. The basic necessity is to provide flexibility in the design.
I%WWI 1996, OFFSHORE TECHNOLOGY CONFERENCE Thh w was wOpar.d for IWOSO!WIW3!I q tfM OffsiWO Tscfwdogy Confefenw hdd m Housfon Texas, S-9 Msy 199S Tfns papa was wbcted fof presenlatc+ by the OTC Pqram Commmee Iolloiwng revmw of Infwmelmn conlatmd n an abstract submmed by the aulhOV[$] Content% of the papa as fwesonted, have nci been fovmwed by the Offshore Techno@Jy Confere.nca and we suolec! to crmecfum by tfm author(s) The malerm as pre$enled 608s not necessarily reflect any POSII!OI'Iof the Offstwra Technology Conference or Its OHIWSPennkswon to mpy IS restrcfed to an abstract of not more than 300 words 111.slra!masmay not be coped The abstraci sfwuld cmlam con$ptcuou$ acknowledgment of wtmre W% by whom tlw paper was presel-lted ABSTRACT Semisubmersibie based Floating Production $ystems (FPS) have been extensively used in oflshore field developments worldwide. Most have been converted~om existing drilling semisubmersibies. Faced with a rapidly dwindling inventoty of existing platforms to convert, the industry neea?r cost competitive newbuild units. Zhis paper presents the principles and development of just such a plaflonn.It will be demonstrated that this newbuild pla~orm is cost and schedule competitive with a
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