1. EXPRO-CFD
An Overview of European Research in CFD-Based Fluid Loading and Fluid Structure Interaction

2. Contents Background. The Main Objectives The Partnership
Main Technical Features
The Workplan
The Deliverables
Progress to date
Systems development
Experimental programme
Early validation results
Current Work and Case Studies
Further Work

3. Background
EXPRO-CFD was instigated through consultation with oil companies and contractors who need:
improvements in the prediction of wave loads on floating systems
more account to be taken of non-linearities in design
better validation
better models for dealing with deep water behavior
improved integration with other design tools
application guidelines specific to CFD for offshore engineering applications.

4. The Main Objectives
To develop new methodologies in offshore hydrodynamic analysis based on:
Coupling or co-processing systems,
Using readily available, commercial CFD codes,
Existing hydrodynamic diffraction tools,
Existing vessel response and riser/mooring system models.
To ensure that we have the right working methodologies for these systems.
To validate, by carrying out detailed flow visualization experiments.
To critically review via case studies.

5. The Partnership Atkins Process* - Coordinators
Det Norske Veritas* MARIN* Statoil*
BP Single Buoy Moorings*
Aker Kvaerner LMG Marin
Imperial College* Sirehna* CIMNE
Ecole Centrale de Nantes University College London

6. Key Technical Aspects
The main technical features of the project fall into three areas:
The coupling, or integration, of existing software tools and methodologies,
The validation and tuning of the models within the coupled system through experiments and some detailed studies,
Concept design case studies to provide benchmarks, demonstrate practicalities and establish application guidelines.

7. Typical Offshore Problems of Concern
Slow drift damping and viscous drag effects
Extreme or steep wave loads - viscous effects in trough to crest region,
Vortex shedding at all scales - riser interactions
Wave impact, run-up and air-gap.
Tether ringing and springing.
Local, non-linear free surface problems.

8. The Work-plan 6 Work-packages
Integration and Testing of CFD/diffraction and platform dynamics programs.
Key technical studies (Cylinder LES and FPSO modeling)
Validation experiments
Tuning and validation of the hydrodynamic systems
Design evaluation case studies
Benchmark tests.

9. The Deliverables
Systems for coupling unsteady RANSE, diffraction and systems response models, built from readily available tools.
New experimental data for flow and loading on floating offshore systems.
Guidelines for the application of these systems aimed at specific design and safety related problems.
A software environment for set-up and control.
Demonstration case studies.

10. Work Packages (1) Stage 1 – First 18 months
Integration and testing of CFD/diffraction and platform dynamics programs (Atkins, DNV, CIMNE).
Key technical studies (ECN, Imperial College, University College)
Validation experiments (SIREHNA, ECN, MARIN)

11. Systems Integration

12. The Scope of the Developed System
Provide engineers with a single point of entry to the modelling system (i.e. using CAD)
Should provide a common grid generation capability and common interfaces to commercial CFD tools
Allow traditional hydrodynamic tools to be used independently
Rigid body motions only for floater, but with mooring, riser, tether models included.
Should allow set up and control of the simulation parameters through a single interface.
Common post-processing, but again – interfaces to other systems.

13. Example coupled system (Atkins solution)
At present based on AQWA/CFX4 with GiD front end
“Control box” determines which module runs when
Data to files in a common directory
Use of files is the most flexible way of reading / writing data
Indirect interaction between individual modules
Individual modules can easily be replaced

14. Experimental Work

15. Measurements - FPSO Measurements by MARIN
Freely floating 1:80 scale FPSO model
5 wave periods/2 wave heights
wave directions at 90,135 degrees
Measurements of global loads and moments, wave profiles, PIV velocity measurements

16. Measurements – vertical cylinder
Fixed vertical cylinder
Tests by ECN and Sirenha
Regular waves
Monochromatic: 9 combinations of L and H
Bichromatic: 2 combinations of 2 wave periods
PIV measurements of velocities on radial slices
Pressure measurements at vertical and horizontal sets of pressure tappings
Overall forces and moments

17. Example Simulation ECN Cylinder
Example case
Vertical cylinder in regular waves:
Period = 1.26 seconds
Amplitude = 0.127m

18. Early Validation Results

19. Vertical cylinder tests
Fixed vertical cylinder as per WP3 experiments
‘Beach’ downstream
Extent of domain limited at present – testing to determine optimum extents will be undertaken.
Grid movement to follow potential flow free surface to aid propagation of wave through the domain

20. Vertical cylinder – preliminary results
Comparisons with experimental data
Noticeable effects of VOF, and grid dependency
Wave kinematics at inlet, and propagation – test of consistency
pressures - experiments
pressures – coupled system

21. Coupled model Floating cylinder depth 1m, mass 205kg
1D motion with simple AQWA-NAUT model
Extinction tests in surge and heave
Surge added mass from CFD 95% (AQWA-LINE 92%)
Heave added mass from CFD 17% (AQWA-LINE 16%)
increased damping over radiation/diffraction only AQWA-LINE – comparable to additional viscous effects

22. Surge in waves Two cases: k = 4000, 1000N/m
Comparison with AQWA-NAUT with no added viscous effects – radiation / diffraction only.
After initial transients both calculations reach a motion of constant amplitude
Coupled system with effects of viscosity included shows expected reduced amplitudes

23. Current Work Completing the process of validation and tuning
Work Package 6 – Design evaluation case studies
Focus has shifted from development to prototype application.
Tools to be applied to case studies within a design environment.
Independent physical testing of 2 cases at MARIN and ECN.
Guidelines for application to be developed.
Completion in January 2004

24. Case Studies (1) AKER KVAERNER TLP KEY ISSUES Wave run-up and air gap
Extreme wave loads
Tether ringing
Overlap study involving both Atkins and DNV systems to allow benchmarking

25. Case Studies (2) LMG MARIN FPSO KEY ISSUES
Wave Drift Damping
Fishtailing
Green water (if time allows)
The DNV system only to be applied to this case

26. Case Studies (3) SBM – Export Buoy KEY ISSUES Skirt damping
Extreme loads
Mooring/floater interaction
The Atkins system only to be applied in this case

27. Further Information Publications
Forthcoming OTC – Overview including more technical details
ISOPE – Session of 6 papers dedicated to the project
Additional publications by ECN, Imperial College and UCL
EXPRO-CFD web site.
Further Developments
EXPRO-CFD Brochure – available on request
EXPRO-CFD Participation Programme – aimed at exploiting deliverables
EXPRO-CFD II