Experimental investigation on the interference mechanical behavior of standing deepsea riser group coupling transient collision

Abstract

Interference effect coupling transient collision between adjacent marine risers has become an important issue as the oil and gas industry moves to deepsea. The vortex-induced vibration experiment on a near-spaced, standing two-riser group was conducted to analyze the evolution from interference to collision and the mechanical behavior coupling transient collision. In this paper, the risers with the spacing of 2.0 D were arranged in two forms: tandem and side-by-side. Each riser had an effective length of 2.0 m and 40% of the riser length was submerged in the uniform flow. The result shows that the collision behavior of the risers was significantly constrained by flow velocity. The interference region, collision region, and destruction region in tandem and side-by-side arrangements were different. The cross-flow displacement amplitudes in side-by-side arrangement were larger than the isolated riser, and the wake and clearance flow caused that the displacement amplitude deviated to the interference side, so that the potential collision risk in the side-by-side arrangement was intensified. During the collision, the frequency components were abruptly changed, and the vibration dominated frequency was unstable. Simultaneously, the riser vibration trajectory deviated from the standard “8”, and the vibration state appeared unstable fluctuations. The response amplitude increased or decreased drastically in a short time, which increased the fatigue damage of the structure to a certain extent.