This paper reports on extensive wavetank investigations of the hydrodynamic loading on a large scale model of an offshore jacket in waves and current. Two independent series of tests were conducted. In the first series the structure was mounted on the bottom of the tank and tested in regular and irregular waves. In the second series of tests, the model structure was towed by a carriage to simulate a current, first in still water and secondly against regular and irregular waves. This experiment was repeated for different riser con.figurations, in order to determine wave/current blockage effects. The data collected in the experiment has been systematically analysed to obtain the wave profile, speed of towing, overall loading, water-particle velocities and near field velocities. Maximum wave loads were determined over a period corresponding to seven hours at full scale. Also, base-shear force and overturning moment have equally been assessed in prototype conditions by means of a probabilistic approach.
Recent research on the flow around complex structures has been stimulated to a large extent by challenges of designing and constructing offshore structures. Particular problems have arisen in connection with the development of the oil and gas fields in the North Sea where the extremely severe environmental conditions have demanded major advances in understanding of the wave loading. Pressure for further progress is generated by the need for periodic re-certification of existing structures, where the reserves have been found to outlive the original design, and by the formulation of new concepts to meet the challenge of new fields, in deeper water and still more hostile conditions. The validity of current design practice has, therefore, been assessed by means of model tests and by field measurements.
