expro-cfd an overview of european research in cfd-based fluid loading and fluid structure...
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EXPRO-CFD
An Overview of European Research in CFD-Based Fluid Loading and
Fluid Structure Interaction
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
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.
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.
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
SIREHNA
Key Technical Aspects
The main technical features of the project fall into three
areas:
1. The coupling, or integration, of existing software tools and
methodologies,
2. The validation and tuning of the models within the coupled
system through experiments and some detailed studies,
3. Concept design case studies to provide benchmarks,
demonstrate practicalities and establish application
guidelines.
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.
The Work-plan
6 Work-packages
1 Integration and Testing of CFD/diffraction and platform dynamics programs.
2 Key technical studies (Cylinder LES and FPSO modeling)
3 Validation experiments4 Tuning and validation of the hydrodynamic systems5 Design evaluation case studies 6 Benchmark tests.
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.
Work Packages (1)
Stage 1 – First 18 months
1. Integration and testing of CFD/diffraction and platform dynamics programs (Atkins, DNV, CIMNE).
2. Key technical studies (ECN, Imperial College, University College)
3. Validation experiments (SIREHNA, ECN, MARIN)
Systems Integration
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.
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
GiD launcher
Control box
Potential flow solver
RANS solver Motions solver Moorings Risers
Experimental Work
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
Incoming waves
PIV FoV
y
x
FPSO at 90°
FPSO at 135°
Camera housing
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
Example Simulation ECN Cylinder
Example case
Vertical cylinder in regular waves:
Period = 1.26 seconds
Amplitude = 0.127m
Early Validation Results
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
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
ECN data - pressures - l2a20ld10
-1000
0
1000
2000
3000
4000
5000
6000
10 12 14 16 18 20
Time (s)
Pre
ss
ure
(P
a)
p1
p3
p4
p5
p6
p7
p8
p9
p10
p11
p12
p14
p15
p16
p17
CFD data - pressures - l2a20ld10
-1000
0
1000
2000
3000
4000
5000
6000
0 2 4 6 8 10
Time (s)
Pre
ss
ure
(P
a)
p1
p3
p4
p5
p6
p7
p8
p9
p10
p11
p12
p13
p14
p15
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
1DoF surge extinction
-0.12
-0.10
-0.08
-0.06
-0.04
-0.02
0.00
0.02
0.04
0.06
0.08
0.10
0 1 2 3 4
Time (s)
Dis
pla
ce
me
nt
(m)
radiationonly
CoupledSystem
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
Displacement - surge only - k = 4000n/m
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
0.20
0 5 10 15 20 25 30
Time (s)
Dis
pla
ce
me
nt
(m)
Coupledsystem
diffraction /radiation
Displacements - surge only - k = 1000n/m
-0.15
-0.10
-0.05
0.00
0.05
0.10
0.15
0 5 10 15 20 25 30
Time (s)
Dis
pla
cem
en
t (m
)Coupledsystem
diffraction /radiation
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
Case Studies (1)
AKER KVAERNER TLP
KEY ISSUES
1. Wave run-up and air gap
2. Extreme wave loads
3. Tether ringing
Overlap study involving both Atkins and DNV systems to allow benchmarking
49.0
9.5
31.0
1000
951
Z
XCoG
10
Case Studies (2)
LMG MARIN FPSO
KEY ISSUES1. Wave Drift Damping
2. Fishtailing
3. Green water (if time allows)
The DNV system only to be applied to this case
Case Studies (3)
SBM – Export Buoy
KEY ISSUES
1. Skirt damping
2. Extreme loads
3. Mooring/floater interaction
The Atkins system only to be applied in this case
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