Full scale VIV response measurements of a drill pipe in Gulf of - - PowerPoint PPT Presentation

Full scale VIV response measurements

• f a drill pipe in Gulf of Mexico loop

currents (OMAE2008-57610)

Beynet, Shilling, Campbell, Tellier, Howells Estoril Portugal - June 2008

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

6040 ft Keel 6000 ft Drill floor 6133 ft 1080 ft Vessel mounted motion logger 5 motion loggers 6040 ft Keel 6000 ft Drill floor 6133 ft 1080 ft Vessel mounted motion logger 5 motion loggers

Did it VIV?

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

Test set-up

• 1080 ft length
• 6-5/8 inch OD
• 0.492 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

6040 ft Keel 6000 ft Drill floor 6133 ft 1080 ft Vessel mounted motion logger 5 motion loggers 6040 ft Keel 6000 ft Drill floor 6133 ft 1080 ft Vessel mounted motion logger 5 motion loggers

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 Logger ID Depth Below MWL (ft) x/L 17 Vessel Vessel 22 52.0 0.866 21 443.2 0.503 13 713.2 0.253 29 848.3 0.128 14 983.3 0.003

0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1

• 1
• 0.5

0.5 1 Normalized Displacement x/L 1 2 4 6 8 10

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)

0.0 100.0 200.0 300.0 Current Direction (degrees) 100 200 300 400 500 600 700 800 900 1000 0.0 0.5 1.0 1.5 2.0 Current Speed (knots) Depth Below MWL (ft)

# 2 # 5 # 13 # 19

KEEL

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

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

Vessel stationary Current ~1.8 knots Vessel stationary Current ~1.8 knots Vessel drift – vertical pipe Current Vessel drift – vertical pipe Current Vessel drift = surface current Current ~1.8 knots Vessel drift = surface current Current ~1.8 knots

Drill pipe response at base – 0 to 30 minutes

• X and Y waterfall plots side by side

Varying vessel drift with current – Objective: maintain vertical pipe Approx max cross flow frequency (St=0.20) Water fall Plots X and Y (Lateral) Accelerations

100 200 300 400 500 600 700 800 900 1000

• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 1.5 Current Speed (knots) Depth Below MWL (ft)

KEEL

Drill pipe response at base – 30 to 60 minutes

• X and Y waterfall plots side by side

Varying vessel drift with current – Objective: maintain vertical pipe Increase vessel drift to ~equal surface current

Drill pipe response at base – 60 to 90 minutes

• X and Y waterfall plots side by side

Multi-mode cross flow VIV 6th Higher harmonic

100 200 300 400 500 600 700 800 900 1000

• 2.0
• 1.5
• 1.0
• 0.5

0.0 0.5 1.0 Current Speed (knots) Depth Below MWL (ft)

KEEL

Reduce drift to zero knots, return to loop current profile

FEA vs. Actual Modal Response

10 20 30 40 1 2 3 4 5 Frequency (Hz) Mode Number

Waterfall Δf = 0.0195 Hz

Drill pipe response at base – 90 to 120 minutes

• X and Y waterfall plots side by side

Single mode cross flow VIV Strong 6th harmonic Return to varying vessel drift with current Objective: maintain vertical pipe

100 200 300 400 500 600 700 800 900 1000

• 0.5

0.0 0.5 1.0 1.5 2.0 Current Speed (knots) Depth Below MWL (ft)

KEEL

Severity of higher harmonics – 90 to 95 minutes

• 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

0.2 0.4 0.6 0.8 1 1.2 0.55 1.1 1.65 3.3

Frequency (Hz) Normalized to Maximum

Displacement Fatigue Damage

Cross flow In-line 3rd Harmonic 6th Harmonic

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

• If 100% travelling wave

measured motion envelopes and fatigue along length will be similar

Standing Wave Travelling Wave

Spectral response along pipe - 90 to 95 minutes

Crossflow VIV 3rd Harmonic 6th Harmonic?

Theoretical standing wave vs. measurements

0.2 0.4 0.6 0.8 1 1.2 1.4 1.6 0.2 0.4 0.6 0.8 1

x/ L Acc (m/ s^ 2)

Measured Theoretical at Measurement Locations Theoretical

• Measured Accelerations at 0.552Hz with Mode 10 Superposed
• Measured response fits standing wave

Are the higher harmonics standing wave?

3.3 Hz response is theoretically mode 32 Varying amplitude: standing wave?

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

Questions?

Spatial aliasing example

Spacial A liasing

• 1.5
• 1
• 0.5

0.5 1 1.5 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Length (units) Amplitude (units)

N um ber of loggers 5 N um ber of nodes/antinodes 3

M

• de

Shape N

• .of

Loggers Logger Start Locn

S pacial A liasing

• 1.5
• 1
• 0.5

0.5 1 1.5 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 Length (units) Amplitude (units)

N um ber of loggers 5 N um ber of nodes/antinodes 7

M

• de

S hape N

• .of

Loggers Logger S tart Locn

FEA vs. Actual Modal Response

10 20 30 40 1 2 3 4 5 Frequency (Hz) Mode Number

Waterfall Δf = 0.0195 Hz