INTRODUCTION:

The underlying idea leading to the concept of a tension leg platform (TLP) is more than 100 years old, but it was picked up by the oil industry some 20 years ago. In the early 70s two large scale prototype platforms, the Triton and the DOT TLP, [1], [2], were placed in areas where sea conditions would simulate full scale behaviour. At present the Hutton (installed 1984), Jolliet (installed 1990) and the Snorre (installed 1992) TLPs have been successfully deployed. Currently the Heidrun TLP, the largest TLP so far and the first floating platform ever to be built in concrete, and the Auger steel platform are under construction. Since the early 70s, extensive analytical work, model testing and large scale testing has been undertaken by several oil and engineering companies. Research institutions and academia have also been involved in resolving the many technical challenges associated with TLPs. The main attractions of a tension leg production platform are the very low vertical motion, which permits inexpensive sea bottom equipment, and deck mounted riser motion compensators, which cannot be installed on a semisubmersible alternative. A TLP offers most of the attractions of a bottom fixed platform without the high increase in cost with water depth associated with any bottom fixed alternative. The attractive properties of TLPs for deep water oil and gas production are, at least to some extent, counteracted by a number of technical issues in the mechanical, structural, installation and operational areas. This review paper, which is written as a contribution to the work of the ISOPE Offshore Technology Committee, will only discuss the hydrodynamic aspects of the practical design of tension leg platforms. The TLP surge, sway and yaw resonance frequencies would be far below, and heave, roll and pitch resonance frequencies above, the wave frequency range.

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