Introduction

Self-elevating mobile drilling or accommodation platforms, generally referred to as "jack-ups" have been on the offshore scene in some form or other for many years.

In recent years the range and capability of such structures has extended to enable them to operate in water depths of greater than 400 feet, and in areas with very severe meteorological conditions.

At the some time designers have made great efforts to avoid concomitant increases in costs by paying great attention to the structural design of legs, jack frame, jacking system, and hull. Whereas the duplication of static design methods have been successful in water depths up to above 300 feet, increasing the allowable water depth above this necessitates the detailed consideration of dynamic effects and foundation behaviour.

The object of this paper is to evaluate the structural considerations which influence the viability of a platform to operate in a particular environment.

At the time of writing the detailed dynamic behaviour of such platforms is not entirely known and this paper will address this platforms is not entirely known and this paper will address this problem, indicate the known areas and also the areas which require problem, indicate the known areas and also the areas which require further research and study.

ENVIRONMENTAL CONDITIONS

The evaluation of environmental conditions for specific areas of the worlds' waters is on extremely complex task; likewise the evaluation of seabed conditions.

Meteorological conditions impose severe loads on the platform and when considering the viability of operating a given platform at a particular location it is of fundamental importance to ensure that particular location it is of fundamental importance to ensure that the assessment of wind, wave, current and water depth is made with the latest and best researched data. If one examines a typical set of mapped data for any area of the earth's surface, one can easily see that the correct assessment of the environmental condition is not an easy task to perform, requiring the analysis of a very large amount of data.

Seabed conditions provide the external reaction system for the platform and three fundamental answers are sought from an platform and three fundamental answers are sought from an evaluation of seabed conditions, namely (i) likely leg penetration, (2) likely rotational restraint, (3) factor of safety against further penetration.

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