Experimental investigation of hydrodynamic loads on subsea structures

Flexible riser systems are a commonly used and important component of floating production facilities. Mid Water Arches (MWA) are prominent features in such systems and understanding their response to prevailing environmental conditions is essential in effective design. This paper discusses experimental techniques developed to better understand the behaviour of these complex structures, achieved through model scale testing at the Australian Maritime College’s (AMC) Circulating Water Channel (CWC) facility. The experimentation was carried out using two arrangements; the first being captured testing to investigate drag forces on the structure to calculate drag coefficients. The second involved the model in a tethered condition, where the offsets of the structure in varying flow conditions were measured and the tension in the tethers was determined. The drag force on the MWA model varied with the orientation of the model. This was expected due to the complex geometry of the structure, although the largest axial forces were not observed for flow parallel to their respective directions. The variations in tether tensions coincided with the offsets observed, where correlation could be made between the incident force and model orientation. This work demonstrates the importance of model testing when studying MWAs and other complex structures.