In 1883, Reynolds in investigating internal flow in pipes discovered that the transition between laminar and turbulence was a function of the density, viscosity and velocity of the fluid and of the diameter of the pipe. Leonardo Da Vinci in 1497 was probably the first to pay attention to how flow separates from the surface of different objects and what types of pattern were formed in their wakes.
Orcaflex seabed friction coefficients skin#
When exposed to current, a stationary circular cylinder such as a rigid riser experiences flow around it and this flow is characterized by large zones of separation which causes the riser to build-up a surrounding boundary layer due to skin friction between the fluid and the body. Marine risers are exposed to several environmental conditions which include wave, current, tides, wind, etc. "Fatigue Damage of Vertical Rigid Risers due to In-Line Vortex Induced Vibration in Nigeria Shallow Waters." American Journal of Mechanical Engineering 5, no.
Ezeonwumelu, Tobechukwu C., Chinwuba V. American Journal of Mechanical Engineering, 5(2), 33-40. Fatigue Damage of Vertical Rigid Risers due to In-Line Vortex Induced Vibration in Nigeria Shallow Waters. "Fatigue Damage of Vertical Rigid Risers due to In-Line Vortex Induced Vibration in Nigeria Shallow Waters." American Journal of Mechanical Engineering 5.2 (2017): 33-40. American Journal of Mechanical Engineering. Hence, fatigue damage and VF due to in-line VIV is important from the TDP to most parts of the UR on the VRR irrespective of the wave spectra and requires proper analysis in riser designs. The results for both spectra showed zero in-line VF on the VRR at 23.69m, 26.21m and End B (31.031m). Whereas, for the Ochi-Hubble spectra, VF range, from TDP to the UR, of 0.16 - 0.302kN/m 0.018 - 0.56kN/m 0 - 1.42kN/m at End A (0m) 8.74m and 21.00m, respectively, were obtained. Also, the in-line vortex force (VF) analysis on the VRR for the JONSWAP spectra showed VF range, beginning from the touchdown point (TDP) to the unstraked region (UR), of 0.16 - 0.34kN/m 0.01 - 0.53kN/m and 0 - 0.85kN/m at End A (0m) 8.74m and 21.00m, respectively. The results from the Ochi-Hubble spectra indicate a fatigue damage value of 96.2 x 10 -5 due to in-line VIV which is greater than 7.03 x 10 -5 due to transverse VIV. The results from JONSWAP spectra showed a fatigue damage value of 102.5 x 10 -5 due to in-line VIV which is greater than 29.1 x 10 -5 due to transverse VIV. The process was statically and dynamically simulated using different wave spectra on Orcaflex platform. In this paper, a typical VRR of 31.031m length clamped to a fixed jacket platform in 18.29m water depth was used while relevant metOcean data were used to simulate the environmental conditions. 
In-line and Transverse Vortex Induced Vibrations (VIV) pose potential Fatigue damage threat to Vertical Rigid Risers (VRR) even in the less volatile Nigeria Shallow Waters.
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