Ocean Current Monitoring from 500 - 1,000 meters
Authors: Ozturk Burak , Sharma Kartik , Eltaher Ayman , Nair Aravind , Jukes Paul 
Published: April 2012

The Ocean Current Monitoring from 500 – 1,000 meters study is part of theTechnology Assessment & Research (TA&R) program of the Bureau of OceanEnergy Management, Regulation and Enforcement (BOEMRE) of the U.S. Departmentof the Interior. The objectives of the study were:To assess the characteristics of Gulf of Mexico current, forcing in the 500to 1,000 meter water depth range and occurrence of elevated events; andTo use those data to assess the importance of such currents on the fatigueand design of risers, moorings and TLP tendons.

The study was conducted as collaboration between MCS Kenny, Fugro GEOS, andPrinceton where the first objective of the study was addressed by Fugro GEOSand Princeton. The first objective is a topic for another paper and it will notbe discussed in detail in this paper. This paper addresses the second objectiveonly and was undertaken by MCS Kenny.

Fugro GEOS study describes how BOEMRE's NTL ADCP data, historical mooringcurrent data and Princeton University's PROFS model data were used to derivethe current profiles to be used in the riser/Tension Leg Platform (TLP) tendonVortex Induced Vibration (VIV) fatigue study described in this paper.

In particular, based on the analysis of current characteristics, ocean currentkinetic energy distribution and observational data availability; fourrepresentative zones (1-4) for Gulf of Mexico were indentified. Zone 1 and zone3 represented the area dominated by Loop Current/Loop Current Eddies andhurricane generated currents. Zone 2 represented an area with relatively strongcurrents found near the continental rise and slope in the northern Gulfespecially where isobaths converge are narrow. Zone 4 represented the new frontarea corresponding to the high kinetic energy at 500 m water depth. For each ofthe zones, both long term and short term full water column current profilecharacterizations (represent current profiles and associated probabilities)were derived and provided for the use in the riser VIV fatigue study, by FugroGEOS.

These current profiles were then used as a part of the study performed by MCSKenny, to address the second objective. In particular, the current profilesprovided by Fugro GEOS were used in determining whether monitoring oceancurrent between 500 m and 1,000 m water depth range should be required and usedin assessing VIV fatigue damage of risers (Drilling, SCR, TTR, and Hybrid) andTLP tendons in the GoM.

As a part of the methodology to achieve this objective was to compare the VIVfatigue damage calculated based on the following current characteristicsbetween 500 m and 1,000 m:Existing Current Profile: Current profile typically assumed by designers, with the lack of actual recorded profiles, which is generally an extension ofthe current velocity at 500, dubbed as linear current profile;New Current Profile: Current profiles, as monitored and provided by FugroGEOS.

Depending on the relative values of the VIV damage resulting from eithercurrent profile, a conclusion can be drawn as to the importance of monitoringand using current data between 500 m and 1,000 m in assessing VIV damage ofrisers and tendons in the GoM.