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ICNAMEModel Tests and Numerical Wave Tank

Prof. Allan R. Magee

29-June-2015

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Agenda

Why Do Model Tests?Examples• Spar Tests for Riser Performance/ Airgap• Wheatstone SGS• TLP in South China Sea• Vortex Induced MotionsUpdate of TCOMS Ocean Basin StatusNumerical Wave Tank (Dr. Bai Wei)

2

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Modernization has its drawbacks. But it’s a lot more comfortable to cry in a Buick than on a bicycle!

Traffic jam in China in 1975

Traffic jam in China in 2010

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5

Water Depth Records

>50,000 tons of structural steel

• Petronius Compliant Tower• Water Depth = 534m• Chevron 1998

<20,000 tons of structural steel

• Perdido Floating Spar Platform• Water Depth = 2315m• Shell, 2008

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Risers

Hull Mooring

Waves, Wind & Current

Stiffness

Motions, OffsetSet DownHull VIM Stationkeeping

Stiffness Tensioning

Hull And Mooring And Riser Interactions

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Hull, Mooring and Riser Interactions

Increasing effects in deeper water

When & Why do we need a Model Test?

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Before you do this,… You must do this

Or risk this

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Why Do Physical Model Tests?Reality Check – for frontier applicationsPrototype platform configurations

Cell Spar, Wind-Float, HVS SEMINovel wave-current energy devices

Non-linear phenomenaVIV, VIM, Run-up, air-gap, green water loads, ringing,

under deck slamming, Fluid-Structure Interactions (FSI)Low-motion floaters with top-tension risers

Spars, TLP, Dry-tree Semisub motions and loadsNew environment considerations

Unusual wind, wave, current conditionsCross waves/current, short-crested seas, sheared currents

Multi-body InteractionsFLNG side-by side, TLP plus TAD vessel, Catamaran Floatover

Others

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TP Semi

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Hurricane Environment

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Vertical Top Tensioned Riser Modeling

Load Cell

Load Cell

Load Cell

Riser Sleeve

Heave Plates

Normal Force Measurements

Pin

Brake

Forc

e(ki

ps)

Stroke (ft))

Z0=15 ft, F0=1.6*685 kips

In series linear springs

Courtesy of Technip

Hydro-pneumatic tensionersNon-linear Force vs Displacement

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Modeling And Measuring Green Water

Green Water on Spar Deck Video Recording

Run-up Probe

Vertical Green Water Probes

Horizontal Green Water Probes

Courtesy of Technip

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Steel Gravity Base Structure Technip designed structure and topsides

with floatover topside installation

Chevron had concern with resonance of platform-soil system due to nonlinear higher-harmonic wave load in extreme wave environment

Inconclusive results from conventional analysis (FNV Theory, SACS, MOSES, etc):

0% - 200% dynamic amplification

Model tests and advanced CFD analyses used to meet design requirements on hull structure and soil integrity with manageable design modifications

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MeasurementsLoads (Forces/ Moments)

Global structureOverall topsidesDeck legsWave deflectorsCellar deck beam

Pressure impact sensorsIncident waves, run-up, airgapTwo data acquisition systems

Normal 250 HzHigh speed 10kHz

High speed video

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Ringing Analysis Methodology1.

CFD analysis calculates dynamic

pressure on structure

2. Modal analysis

simulates dynamic structural response

of structure

3. Approximation

method calculates ringing response from model test

4. Calibration of short-

duration CFD-modal analysis

results

5. Structural analysis using ringing loads

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Metocean Comparison

Liuhua 16-2

Malikai

Browse

12.8

Deepwater Offshore Basin, Shanghai Jiao Tong University

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Ringing Response of TLP Tendons With CFD

Tension Leg Platform (TLP) in severe environment

Key issue is the high-frequency tendon tensions, known as ringing

Model test data compared to Computational fluid dynamics (CFD)

Excellent agreementLeeside tendon tension

Weather-side tendon tension

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Loop/ Eddy Currents Speeds can exceed 4 knots (2m/s)

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Vortex Induced Motion (VIM)

Vortices shed from the column legs• Function of viscous effects in flow• Sway motion affects risersUse CFD to create Numerical Wave Tank • Experiments provide benchmark data• CFD predicts model results … 95% correlation• Simulation for 40 sway cycles (~ 80 minutes):

240 minutes with 320 cores • OMAE 2013 Paper

Sway

Yaw

Plan view of vortex shedding

Sway motion

Yaw Rotation

Current

direction

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Ocean Basin

L 60m

W=48m

50m Deep pit for modeling risers

Movable floor (Max WD=12m)

Wavemakers on 2 adjacent sidesPassive beaches opposite

Current generation systemWorkshops, offices, numerical facilities

Volume ~25 Olympic Pools

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Technology Center for Offshore and Marine Singapore - TCOMS

Strategic Thrusts:• Create a vibrant ecosystem for offshore & marine R&D around the national ocean

basin and numerical simulation facility involving private and public sector participation

• Position NUS and Singapore as a world-class hub for offshore & marine R&D

Parcel A: Ocean Basin and Numerical Simulation Facility

Parcel B: Research Office Building

Parcel C: Research Infrastructure Building

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Ocean Basin Status UpdateOngoing Tender ProcessSeparate contracts for • Specialized equipment (EPC)

• Overseas specialists• State of the Art wave and current generation systems,

movable floor, instrument cum towing carriage,…• Status: Tender closed April, 2015• Co-Innovation phase to follow award

• Infrastructure (tank, building, utilities,..)• Local construction contractors • Basic design developed and being refined• Status: Preliminary contract for land clearing ongoing• Requires EPC contractor inputs to finalize main tender offer

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Numerical Wave TankDr. Bai Wei