Fluid Forces and Structure-Induced Damping of Obliquely-Oscillating Offshore Structures

We use high-order CFD methods and statistical analysis techniques to study the flow over a cylinder, approximating circular cross-section offshore structures, oscillating in a direction inclined to the horizontal direction. We vary the orientation angle from 0 to 180 degrees, where the 90-degree case corresponds to oscillation perpendicular to the incoming stream. We study (in the time-domain and through the angle-response curves) variations of the induced force properties, their symmetry or skew symmetry about the case of a 90-degree orientation angle, and the structure-induced damping of the flow. We identify the range of orientation angles where the entrainment phenomenon takes place and study the influence of the motion amplitude on this phenomenon. We propose a technique to derive reference (scaling) quantities for the oblique fluid force. Unlike the lift and drag, such reference quantities cannot be obtained from the stationary-structure case because such an oblique force is not defined then.