Current velocity, profile, direction, and duration may affect hydrodynamic loads and VIM of offshore structure. It is often recommended that physical experiments are carried out in sheared current, in multiple directions and for sufficiently long period of time to investigate the hydrodynamic characteristics of deep draft offshore structures to obtain better correlation to the field measurements. This necessitates generating sheared current with acceptable turbulence level. This paper presents a recent advancement in generating sheared current in a flume tank facility. In this process, the test specimen remains moored and the water flows past with its velocity varied with depth as long as necessary.
A combination of synthetic and wire meshes are used to provide the required amount of blockage onto the circulating channel flow of the flume tank to obtain specified current distribution across the cross-section and at the longitudinal center of the tank. The final set-up of the current screen provided a sheared flow distribution within 10% of the targets. Also, the measured turbulence level was below 10% in all the locations measured.
VIM studies of a model spar were successfully carried out in the generated sheared current in the flume tank facility. The ability to accurately model the sheared flow essentially improves the accuracy of the measured VIM type response measurements. The generated sheared current can also be applied for other hydrodynamic experiments where sheared current is relevant.