Offshore Mechanics and Arctic Engineering

During the 2018 International Conference on Offshore Mechanics and Arctic Engineering, a project was presented containing a review of the industry standards on both experimental and Computational Fluid Dynamic (CFD) approaches, which used the Qualisys motion capture system to track the vessel model and measure its performance when certain conditions were replicated.

The study involved the analysis of Vortex-Induced Vibrations (VIV) on spool and jumper geometries, which are known to present several drawbacks when approached with conventional engineering. The complex, 3D form of the spools and jumpers makes the fluid three-dimensional and the vibratory response can exhibit a complex, non-linear, multi-modal response due to the structural form.

The current industry guidelines and VIV engineering tools are not well-adapted to these structures. CFD-based fluid-structure interaction (FSI) is a promising alternative to currently used tools.

To prove the success of the FSI method, experiments were carried out in Océanide’s BGO FIRST wave, current and wind basin. The tank is 16m wide and 40m long, and a movable floor creates a water depth that varies between 5m down to a few centimeters.

Researchers collected measurements at both anchorage points to determine displacement using a 4 camera Qualisys underwater system. The system tracked the position of six markers affixed to the model, and the mean current velocity checked downstream of the model and out of its wake.

The tests were conducted with several current velocities, and several spool headings. The measurement of the six marker positions allowed the group to quantify the VIV’s amplitudes and frequencies, leading to a great experimental database of numerical tools for reliability assessment.

The group concluded that the experimental studies complement numerical approaches and when executed carefully and with precision, they can serve as a valuable resource for the validation of CFD based FSI approaches.