VIVANA drilling riser

This example models a top-tensioned drilling riser in a water depth of 600 m. The riser extends from a fixed bottom node at the seabed — representing the connection to the blowout preventer (BOP) — to a top node above the water surface at z = +12 m, representing the connection to the drilling vessel. The riser is held in tension by an applied top tension force and carries drilling mud as internal fluid with a density of 1400 kg/m³.

The riser consists of three segments: bare slick joints at the lower and upper ends, and buoyancy joints in the mid-section. The buoyancy joints have a thick external coating that increases the outer diameter to 0.800 m, providing net buoyancy to reduce the required top tension. The slick joints have no coating and a smaller hydrodynamic diameter of 0.500 m.

The primary purpose of this model is vortex-induced vibration (VIV) fatigue analysis using VIVANA. The sheared current profile, with a surface velocity of 0.6 m/s reducing to 0.1 m/s at the seabed, drives multi-mode VIV response across the riser length. VIVANA computes the VIV response in the frequency domain using the riser’s natural frequencies and mode shapes, and accumulates fatigue damage using Rainflow counting against an S-N curve.

The static analysis establishes the equilibrium configuration of the riser under gravity, top tension, vessel offset and current before the VIV fatigue calculation is performed. A parameter variation applies a 12 m horizontal offset to the top node to represent vessel offset, which changes the riser’s static curvature and affects the VIV response.

The critical areas for fatigue assessment are the regions of high modal stress. For a sheared current profile, the highest VIV response generally occurs in the upper part of the riser where the current velocity is greatest, but multiple modes may be excited simultaneously across the full water column.