Abstract
This study involved using typical Joint North Sea Wave Project (JONSWAP) based Umbilical design of lengths 3044m, 3215m, 4481m and 2873m clamped to Floating Production Storage and Offloading (FPSO) unit in Deep Offshore Nigeria at water depth of 2000m. Relevant metOcean data was used to simulate the environmental conditions. The process was simulated using different wave spectra on OrcaFlex software. JONSWAP spectra results for Umbilical-1 to Umbilical-4 at near-surface current (End A: 850m) showed a Transverse Vortex Force (TVF) range of 0.0115 – 0.018kN/m; 0.009 – 0.0149kN/m; 0.006-0.014kN/m; 0.0048 -0.009kN/m, respectively. For Ochi-Hubble spectra, the corresponding TVF range obtained include: 0.004 - 0.0305kN/m; 0.004 - 0.028kN/m; 0.003 - 0.027kN/m; 0.003 - 0.0232kN/m, respectively. JONSWAP spectra showed maxima (t, TVF) values of (0.013, 0.018); (0.012, 0.0149); (0.008, 0.014); (0.0074, 0.009) from Umbilical-1 to Umbilical-4, respectively. With the Ochi-Hubble spectra, maxima (t, TVF) values were (0.018, 0.0305); (0.016, 0.028); (0.013, 0.027); (0.0141, 0.0232) for Umbilical-1 to Umbilical-4, respectively. Hence, maxima (t, TVF) values were greater for Ochi-Hubble than JONSWAP. Simulation plots indicate that adjusting the peakedness parameter (γ) of the JONSWAP spectra does not give the required accuracy for this region. Therefore, using a JONSWAP based Umbilical design in Ochi-Hubble environment like Offshore Nigeria shows higher vortex induced vibration (VIV) at near surfaces leading to higher TVF, and higher fatigue damage tendency.
Highlights
The marine umbilical may be defined as a coupling of fluid conduits, electrical and fiber optic cables, which are on their own or in combinations of each other, joined together for flexible purpose
It can be seen as a bundled assembly of tubing, piping and electrical conductors in armoured sheath which is installed in internal facility of the subsea production system equipment
Results were obtained for the Transverse Vortex Force (TVF) at different sections for both Ochi-Hubble and JONSWAP wave spectra
Summary
The marine umbilical may be defined as a coupling of fluid conduits, electrical and fiber optic cables, which are on their own or in combinations of each other, joined together for flexible purpose It can be seen as a bundled assembly of tubing, piping and electrical conductors in armoured sheath which is installed in internal facility of the subsea production system equipment. Global analysis involves simulation of the field conditions in terms of sea state and vessel motion and doing the calculation of the umbilical dynamic responses to the typical environmental conditions. This global analysis will generate time series of cross section curvatures and tensions for each specified longitudinal position along the Umbilical. The increasing occurrence of fatigue damage on the umbilical motivates us to better understand the effects of Umbilical global configuration and friction stresses
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