This research study focused on wave-current interaction with a single, flexible cylinder representative of a riser in 500 m (1640 ft) of water. Realistic environmental conditions were obtained by combining wave and current conditions which were based upon advise from the offshore industry. These tests provided unique data at large model scales. The experiments were conducted in the deepwater wave basin at the Offshore Technology Research Center (OTRC) at Texas A&M University. As part of the experimental study, a new underwater video tracking technique was developed to directly measure the inline and transverse displacement fields of the riser. Other standard instrumentation was also used to determine the cylinder tension and reaction forces.
The validity of the underwater tracking methodology was assessed and this established an alternative to strain gage measurement which will prove valuable for future riser experiments. The wave and current environments selected were characterized separately before combined testing. The wave spectra with and without the presence of current compared consistently with previous mathematical models. The inline riser displacements were compared to predicted response envelopes, using a standard two-dimensional finite element model. The program is based on linear theory to obtain the wave kinematics and uses Morison’s equation to model external forces due to waves. Additional terms were included into Morison’s equation to account for current as well as mean drift due to mass transport. The results obtained using this simulation model were discussed and choices for added mass and crag coefficients were motivated. The riser simulations reproduced response envelope trends quite accurately when current was superimposed onto the various waves conditions.
