Gimbal Joint Riser – A Novel Concept: Experimental Hydrodynamic Coefficients

Abstract

Abstract Gimbal Joint (GJ) is a device designed to connect the upper and lower parts of a steel riser in a free-hanging system. The mechanism consists of a flexible conduit, inside a structure that is made of several hinged connection elements, making the whole system work as an articulation. Hydrodynamic properties of GJ are recognized as an uncertainty source due to its novelty and very specific geometry. Recently, an experimental campaign of a model scale size — 1:9 — has been performed as a part of technology qualification programme. The forced oscillation tests focused on obtaining drag and hydrodynamic inertia coefficients of the GJ, as a recommended practice to estimate hydrodynamic coefficients of complex bodies. As an oscillating porous body, the hydrodynamic coefficients shall be assessed in terms of the Keulegan Carpenter number, at different flow regimes corresponding to varying Reynolds number. The focus of this paper is to present and discuss the hydrodynamic coefficients obtained in the forced oscillation tests. A discussion about the correlated effect of the model porosity and KC (Keulegan-Carpenter number) compared to Sarpkaya’s experiment from the literature is also presented. Results indicate that porosity changes significantly the hydrodynamic coefficients, providing that standard industry coefficients, normally used in dynamic analysis, shall not be used when GJ is part of the system.