Marine growth and the hydrodynamic loading of offshore structures
This thesis presents the results of a study on the effects of marine growth on the hydrodynamic loading of offshore structures and proposes an approach that can be adopted by designers and operators to quantify these effects. The approach is based upon the realistic characterisation of marine growth and its temporal variations during the life span of template structures. Past research work and current design, inspection and maintenance practices are critically reviewed and their limitations with respect to marine growth are highlighted. The ecology of marine growth for a sample of North Sea platforms was examined to establish the variety and physical attributes of the fouling colonies. The traditional single-parameter characterisation of marine roughness was found to be inadequate. Appropriate parameters, verified by fluid loading experiments, are established. Details of the laboratory experiments undertaken with both real marine growth and artificial macro-roughness on circular cylinders are given. These tests were carried out at large scale (cylinders up to 521mm diameter) in a novel "buoyant cylinder" test rig (steady flow) and in a large wave flume (regular waves). A wide range of parametric variations were undertaken for the various types of marine growth in an attempt to establish a comprehensive database from which the loading effect of any likely, practically occuring, marine growth pattern can be estimated. The extent to which this is achieved and the requirements for further research are discussed in detail. It is concluded that the effects of marine growth are both substantial and diverse. Drag forces vary with type of fouling, overall thickness, surface cover, and distribution. Finally, detailed procedures are recommended for the design of new structures and the improved loading assessment of existing ones.