Objetivo Installation technique of the topsides of offshore production platforms is by crane lifting of reasonably sized modules. Considerable cost and time savings particularly with earlier production would be achieved if the inshore proven mating technique of platform deck and substructure could be transferred to at sea application. The present project is a feasibility study of a specialized transport and lifting barge design for worldwide operation combining semisubmersible motion characteristics and simple dock type lifting capability. Integrated decks would be picked up by the barge at the fabyard, transported to the site, lifted by deballasting and lowered gently to the preinstalled jacket.Review of installation modes shows superiority of integrated type. A vessel for one piece installation of topsides will, however, envisage strong competition by established heavy lift crane barges. Therefore, the barge must be also available for platform removal. The vessel will have U-shape in plan view with legs similar to the floaters and columns of a semisubmersible. Open at one side, they are cross-connected by two box shaped bars at the other side, one below and one above water to achieve good torsional resistance. With the deck spanned across the legs, conventionally shaped jackets will be forked in for mating.Environmental forces acting on deck and U-barge will load the jacket after the first contact is established. Jacket has to be designed accordingly. Dimensions of U-barge were chosen to serve jackets of a 60 m width at upper end, carrying a topsides weight of 30,000 t. Length and beam of the U-barge are 140 m and 120 m, the depth is 28 m. Best method of fabrication isin a large drydock, but there is a slight though more expensive chance for conventional shipyards to fabricate the barge in parts and assemble these in floating condition. Assuming a three day period necessary for transit from shore to location, positioning of anchors, and mating, it was found from weather statistics (North Sea, 66 deg. N, 2 deg. E) that such periods with significant wave heights of up to 1.9 m occur with a frequency of as much as 1.6 in January/February and 5.9 in May/June. Motion characteristics of the barge as found from calculations and model tests in such that mating is possible in seaways of up to 2 m significant wave height provided the prevailing wave periods do not surpass 7 s, maximum 9 s.Model tests also showed that the barge safely survives the 100 year storm in the North Sea in unloaded condition. The square arrangement and size of the columns warrant sufficient intact stability about arbitrary horizontal axes. Damage stability is provided by suitability selected compartmentation and buoyancy boxes at the four corners of the deck structure of legs and upper crossbar.Quasistatic strength analysis showed that the clamping connections of the legs at the cross bars would be slightly overloaded with plate thickness of 20 to 30 mm, and plate thickness of 20 to 25 mm would be sufficient for the cross bars and all other members of the barge, larger values for the underwater portions. Comparison of equivalent stresses in the clamping connections determined by the quasistatic analysis and by model tests in loaded and unloaded condition show up to 70 % higher stresses measured in the model tests which correctly reflected sheer stress influences. Apart from a slight increase in above plate thickness the critical points of the barge should be coped with by local reinforcements and application of higher tensile strength steel.Though the tolerable sea state in transit, loaded with a platform deck, must be limited for safety reasons.In a comparative study the requirements and merits of modularized and integrated deck installations are summarized. Various proposals for offshore mating devices are analyzed especially with respect to application in North Sea environment. The chances of a new mating device are discussed competing in the market with well established operators of heavy lift crane vessels. The size of the barge and its form are determined by an analysis of form and size of existing jackets and the weight of the topsides they carry. Operational aspects of load-out, transit amd mating procedure are looked into. By weather statistic of a relevant North Sea area the probability of encountering sufficiently long good weather periods for transport and mating is evaluated. Among the studies of the technical feasibility of the barge is a discussion of its fabrication on a conventional shipyard. The most critical load cases are defined which determine the detail design of form and structure. Ballast handlingduring the different loading conditions are considered and the compartmentation designed appropriately. Hydrostatic stability is checked and damage stability investigated. Motion behaviour in the decisive loading conditions is calculated by using potential theory. Model tests are performed to doublecheck motion characteristics and study the limiting conditions of the sea state for initiation of the mating procedure. Structural design is controlled by longitudinal strength calculations and stress analysis using finite element method applied to a beam model of barge and platform deck structure in the design wave. Internal forces and moments are also measured in model tests in regular and irregular waves. Comparison is made with forces obtained from the quasi-steady loaded beam model. Programa(s) ENG-HYDROCARB 1C - Programme (EEC) of Community projects in the hydrocarbons sector, 1973-1985 Tema(s) 1.1 - AUXILIARY SHIPS AND SUBMERSIBLES Convocatoria de propuestas Data not available Régimen de financiación DEM - Demonstration contracts Coordinador BLOHM & VOSS AG Aportación de la UE Sin datos Dirección 2000 HAMBURG Alemania Ver en el mapa Coste total Sin datos
