Full scale VIV response measurements of a drill pipe in Gulf of Mexico loop currents (OMAE )

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Baldric Christian Melton
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1 Full scale VIV response measurements of a drill pipe in Gulf of Mexico loop currents (OMAE ) Beynet, Shilling, Campbell, Tellier, Howells Estoril Portugal - June 2008

2 The Test September 2004 Test of opportunity Waiting on weather to run conductor (~2 knot surface currents) VIV monitoring system already on the rig 6-5/8 inch drill pipe was instrumented and deployed to 1,000ft water depth On-board acoustic doppler current profiler (ADCP) measured current Vessel mounted motion logger Keel 6000 ft 5 motion loggers Drill floor 6133 ft 6040 ft 1080 ft

3 Did it VIV?

4 Agenda Background Test set up Monitoring system Test timeline Observed response VIV occurrence and effect of changing current Single mode, multi-mode or time sharing? Higher harmonics Standing or travelling wave Conclusions

5 Test set-up Vessel mounted motion logger Keel 6000 ft 5 motion loggers Drill floor 6133 ft 6040 ft 1080 ft 1080 ft length 6-5/8 inch OD inch wall thickness 32.2 lb/ft (47.9 kg/m) in air 80ksi strength, carbon steel Drill pipe was free flooding water filled up to mean water line

VIV monitoring system 6 standalone motion sensors, 5 on drill pipe, 1 on vessel INTEGRIpod: Field proven, high reliability Acceleration in 3 DOFs and 2 DOF angular rates Continuous logging at 10 Hz

6 VIV monitoring system 6 standalone motion sensors, 5 on drill pipe, 1 on vessel INTEGRIpod: Field proven, high reliability Acceleration in 3 DOFs and 2 DOF angular rates Continuous logging at 10 Hz sampling frequency Test specific limitations: Low sampling frequency for measured response Number of instruments Drill pipe base is location of max displacement for all modes x/l Logger Depth Below ID MWL (ft) x/l 17 Vessel Vessel Normalized Displacement

7 Current measurement 38 KHz Acoustic Doppler Current Profiler (ADCP) Designed for measurement of ocean currents Provides 10 minute average speed and direction Measures 95ft to 3,600ft below surface every 100ft Max measured current = 1.8 knot Strouhal (0.20) frequency = 1.1 Hz 50ft missing between drill ship keel and first data point Vessel mounted system measures effective current on drill pipe whilst drifting (which we want) Depth Below MWL (ft) Current Speed (knots) KEEL #2 #5 #13 #19 Current Direction (degrees)

8 Test timeline 2 hour test with 16:03 (4:03pm) start time Vessel drift relative to the current was varied Objective: Determine effect of maintaining vertical pipe Vessel Vessel Vessel drift drift stationary vertical = surface pipe current Time Vessel Drift Information 16:00 Varying vessel drift, speed unknown 17:08 Vessel drift at 1.8 knots in current direction 17:17 Reduce drift speed to 0 knot 17:28 Vessel at 0 knot 17:38 Increase vessel drift to 1 knot in current direction Current ~1.8 knots

Drill pipe response at base 0 to 30 minutes Varying vessel Water drift fall with Plots current X and Y (Lateral) Objective: Accelerations maintain vertical pipe X and Y waterfall

9 Drill pipe response at base 0 to 30 minutes Varying vessel Water drift fall with Plots current X and Y (Lateral) Objective: Accelerations maintain vertical pipe X and Y waterfall plots side by side Current Speed (knots) KEEL Depth Below MWL (ft) Approx max cross flow frequency (St=0.20)

10 Drill pipe response at base 30 to 60 minutes Varying vessel drift with current Objective: maintain vertical pipe X and Y waterfall plots side by side Increase vessel drift to ~equal surface current

11 Drill pipe response at base 60 to 90 minutes X and Y waterfall plots side by side Current Speed (knots) KEEL Reduce drift to zero knots, return to loop current profile Depth Below MWL (ft) Multi-mode cross flow VIV 6 th Higher harmonic

12 FEA vs. Actual Modal Response Waterfall Δf = Hz Mode Number Frequency (Hz)

13 Drill pipe response at base 90 to 120 minutes X and Y waterfall plots side by side Current Speed (knots) KEEL Depth Below MWL (ft) Return to varying vessel drift with current Objective: maintain vertical pipe Single mode cross flow VIV Strong 6 th harmonic

14 Severity of higher harmonics 90 to 95 minutes Normalized to Maximum Cross flow In-line 3 rd Harmonic 6 th Harmonic Frequency (Hz) Displacement Fatigue Damage Higher harmonic fatigue damage is negligible compared to cross flow Conflicts with test findings fatigue from higher harmonics > factor of 10 Fatigue damage calculation assumes standing wave

15 Standing or travelling wave? Standing wave typically assumed in design High fatigue damage along the entire length if travelling wave If 100% standing wave there will be locations of zero measured motion and fatigue along length Standing Wave Travelling Wave If 100% travelling wave measured motion envelopes and fatigue along length will be similar

16 Spectral response along pipe - 90 to 95 minutes Crossflow VIV 3 rd Harmonic 6 th Harmonic?

17 Theoretical standing wave vs. measurements Acc (m/s^2) x/l Measured Theoretical at Measurement Locations Theoretical Measured Accelerations at 0.552Hz with Mode 10 Superposed Measured response fits standing wave

18 Are the higher harmonics standing wave? Varying amplitude: standing wave? 3.3 Hz response is theoretically mode 32

19 Conclusions Strong BP on-shore and offshore teamwork allowed test of opportunity Valuable data set that complements and extends existing tests Observed single mode, multi-mode and time sharing VIV Time sharing typically coincides with changes in vessel drift speed Higher harmonics up to 6 times cross flow VIV observed Cross flow VIV fatigue damage dominates Contribution of dynamic positioning prop wash excitation is uncertain VIV response is standing wave, up to mode 14, possibly mode 32 Greatest VIV risk: short term temporary operations in high currents Drifting to maintain verticality recommended to minimize VIV

20 Questions?

21 Spatial aliasing example Spacial Aliasing Spacial Aliasing 1.5 Mode Shape No.of Loggers 1.5 Mode Shape No.of Loggers 1 1 Amplitude (units) Amplitude (units) Length (units) Logger Start Locn Length (units) Logger Start Locn Number of loggers 5 Number of nodes/antinodes 3 Number of loggers 5 Number of nodes/antinodes 7

22 FEA vs. Actual Modal Response Waterfall Δf = Hz Mode Number Frequency (Hz)

Learn more at

Learn more at STRIDE JIP Phase III SUT Talk 15th November 2 Offshore VIV monitoring (vortex induced vibration) Catenary riser interaction with deepwater seabeds 3 Full Scale Riser Monitoring To get real measurements