CFD FOR OFFSHORE APPLICATIONS USING REFRESCO. Arjen Koop - Senior Project Manager Offshore MARIN

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1 CFD FOR OFFSHORE APPLICATIONS USING REFRESCO Arjen Koop - Senior Project Manager Offshore MARIN

2 COMPUTATIONAL FLUID DYNAMICS (CFD) Advantages: Quantitative predictions Detailed insight in physical processes using flow visualizations Determine design trends by comparing alternative configurations Determine Reynolds scale effects Quantify limitations in experimental set-ups Disadvantages: User dependency/experience CFD: Color Full Diagrams, Colors For Directors -> be aware of accuracy! Numerics must be controlled for accurate answer: appropriate grid/time resolution, iterative convergence Turbulence makes things difficult Trend nowadays: more CFD, due to existence of user-friendly commercial codes and powerful cheap hardware Optimum approach: combination of CFD and dedicated experiments

3 CFD AT MARIN Complex Ships Submarines Manoeuvring Propellers Cavitation Turbines Current Loads Wind Loads VIV & VIM Thrusters Propulsion FreeSurface&Waves Roll-Damping

4 CFD AT MARIN 14 researchers (R&D) + 10 Applied CFD-ers (Ships + Offshore): Development of CFD codes Cooperation with universities Modeling of physics Turbulence models Free surface Moving bodies and fluid-structure interaction Grid generation techniques Verification and validation Large validation data base available at MARIN (Commercial) Applications Large clusters of 4000 and 1500 cores 4

5 CFD CODES AT MARIN FOR OFFSHORE APPLICATIONS ReFRESCO MARIN code -> Unlimited number of licenses available Unsteady Reynolds averaged Navier-Stokes (RANS) solver Aimed at viscous hydrodynamic applications with complex geometries, blunt bodies with massive flow separation Structured and unstructured grids Refresco-operation with industry Comflow (non-viscous) free-surface code developed within Comflow JIP at University of Groningen Mainly aimed for free-surface problems such as wave impacts and slamming 5

6 CFD FOR OFFSHORE APPLICATIONS AT MARIN 2006: Start with 2D cylinder : Participation in Comflow JIP s : Current Affairs JIP - Current loads on semi-submersible - Current loads LNG carrier from Hawaii JIP 2009-today: extend experience with: - Current loads: semi s, TLP s, FPSO s, LNG carriers, shallow water effects, side-by-side offloading, basin effects, scale effects - Wind loads: LNGC, FPSO, Shuttle tanker - Wind Shielding on offshore vessels - Thruster-interaction effects (TRUST JIP) - Disconnectible buoys (DISCO JIP) - Vortex Induced Motions (VIM JIP) - Roll motions of FPSO s (Roll JIP) - Moonpools (MoonPool JIP) 6

7 CFD FOR OFFSHORE APPLICATIONS BLUNT BODIES Bare Smooth Cylinder Flow Very difficult due to: Turbulence transition Flow separation

8 CURRENT LOADS FOR OFFSHORE CONSTRUCTIONS Current Affairs JIP Semi-submersible LNG carrier CFD: 5-10% from experiments 8

9 CURRENT LOADS SEMI-SUBMERSIBLE Current Very good agreement between measurements and CFD! For total force as well as for force on pontoons separately Measurement for lowest velocity inaccurate?

10 SHALLOW WATER EFFECTS LNGC WD/T = 1.36 WD/T = 2.73 WD/T = 4.82 Large increase in current loads on shallow water CFD 2-8% from experiments for all water depths

11 SIDE-BY-SIDE CURRENT LOADS LNGC Shuttle

12 WIND LOADS ON OFFSHORE VESSELS

13 WIND SHIELDING Good agreement in velocity field between CFD and windtunnel

14 THRUSTER UNDER BARGE CFD versus PIV (solid line) thruster wake for straight thruster Base case Larger bilge radius Shorter distance With bilge keel 14

15 THRUSTER-HULL RESULTS DRILL SHIP Actuator disk 15

16 CFD FOR IMPACT LOADS Wave impact on fixed semi-submersible: Wave run-up Wave impact (horizontal and vertical) 16

17 MOONPOOL S MoonPool JIP Model tests with different moonpools In transit condition Comparison with CFD work in progress MoonPool 2 JIP Being started Focus on flow behavior in moonpool for ship in waves

18 CFD FOR DISCONNECTIBLE BUOYS DISCO JIP - calculate loads on re-/dis-connectible buoys and predict drop path Runs until 2016 Forced oscillation of buoy in turret Drop of buoy 18

19 CFD FOR VISCOUS ROLL-DAMPING Non-Linear Roll JIP Runs until 2016 Hull with bilge keels and sharp bilges: good comparison with experiments

20 CFD FOR VORTEX-INDUCED MOTIONS Good comparison between CFD and model tests CFD seems to slightly underpredict VIM response Differences observed for high UR (UR 12)

21 CFD FOR SCALE EFFECTS ON OFFSHORE STRUCTURES Scale-effects for blunt bodies are different than for ship flows, due to unsteady and separation effects General scaling laws do not exist High-quality validation material at full-scale very difficult to obtain MARIN is investigating possible scaling procedures using CFD Flow patterns Resistance, propulsion Force coefficients Hydrodynamic damping Roll damping VIM

22 WORK IN PROGRESS Turbulence modeling for laminar-turbulence transition Full-scale effects Current/Wind shielding effects Free-surface problems Waves + slamming moonpools Forced-motions 3D Roll-damping with free-surface Forced oscillating cylinders Fluid-structure interaction (e.g. VIV) Thruster-thruster interaction Offshore renewable energies

23 REFRESCO-OPERATION Joint Maritime CFD development, validation, and application MARIN wants to share Its dedicated maritime CFD code ReFRESCO with the industry Its knowledge on accurate CFD simulations MARIN wants to open its computer facilities to customers Marin seeks for cooperation on further development and validation of ReFRESCO for maritime applications.so that we can jointly work on the reliable and robust application of CFD in our maritime field. 23

24 REFRESCO-OPERATION BENEFITS Dedicated, validated code for maritime applications Use of ReFRESCO on any number of computers, or with any number of users, within your own company Training on the job, best-practice guidelines by MARIN specialists Quick-start for new users Perform large computations on MARIN s clusters Exchange of experiences with other ReFRESCO-operation members Fast access to new capabilities from many developers and researchers Access to source code, participation in developments 24

25 REFRESCO-OPERATION IN PRACTICE Yearly fee euro (SME euro) 2-3 day training for a specific application This is a paid and dedicated study and training Use of ReFRESCO on your own computers with an unlimited number of users and on an unlimited number of computing cores -> cluster installation on project basis Use your own geometry and grid tools for the calculations as well as your own post-processing software Support (limited to a certain amount of hours) Joint QA check and first runs possible Scale up your calculation by running on MARIN s cluster (1600 cores) against a reasonable fee per CPU hour that includes the use of the cluster and the code. 25

26 THANKS FOR YOUR ATTENTION! Questions? Contacts: Arjen Koop (MARIN) Wei Xu (MARIN USA)