Model Test Of A Pile-Founded Guyed Tower

ABSTRACT The development of structural concepts for deployment in deep waters has been actively pursued in the last decade by a number of oil operators and design contractors. Among the many concepts investigated, the Guyed Tower was the object of intense study, which eventually led to the first commercial application in 1983, when the Lena Guyed Tower was installed in the Gulf of Mexico by Exxon Co. USA in a water depth of about 1,000 ft. As part of the development effort, model tests were conducted to assess the viability of the concept. One was performed by Exxon in the mid-70's, with a 1:5 scale model installed in 300 ft water depth in the Gulf of Mexico. A few years later, as consideration was given to exploiting this technology in the North Sea, for different combinations of payload and water depth, another test was conducted on a 1:50 scale model in a wave tank. This test, sponsored by thirteen major oil companies, was performed in 1982 using an 8.0 m (26 ft) model, one of the largest models of an offshore structure ever used in a wave tank. Over 200 sea states were run past the model and 64 data channels were continuously monitored. As the confidentiality restrictions have now expired, this paper describes the details of the model configuration, instrumentation, experimental set up, and test program. A summary of the experimental measurements and of the relative correlation study results is also presented. 1.0 INTRODUCTION Compliant structures have been considered particularly suited for deep water deployment as an alternative to the traditional structural solution represented by fixed jackets. Among these, the Guyed Tower Platform (GTP) has been the object of intense development studies, leading to the successful installation of 1983 of the first commercial GTP in the Lena Field (Gulf of Mexico) for Exxon Co. USA, in a water depth of 1,000 ft (300 m). In early 1980, Brown &Root completed a preliminary design of a pile founded GTP (See Figure 1) as part of a Joint Industry Project sponsored by a group of North Sea operators and contractors, usually referred to as The Deepwater Production Platform (DPP) Project. The design specifications were for a 350 m (1,150 ft) water depth in the North Sea and a payload of 19,500 mt. The preliminary design proved the feasibility of the GTP for this environment. It also evidenced, however, the need for additional engineering studies addressing technical aspects which could be best investigated by means of a series of model tests in a wave tank. In 1980 a Joint Industry Project was founded for a GTP model test program to be conducted in the new facilities of the Norwegian Hydrodynamic Laboratories (now MARINTEK), in Trondheim, Norway. This paper presents a description of the program's objectives, technical contents, and some of the most meaningful results.