Presentation on theme: "EXPRO-CFD An Overview of European Research in CFD-Based Fluid Loading and Fluid Structure Interaction."— Presentation transcript:
1EXPRO-CFDAn Overview of European Research in CFD-Based Fluid Loading and Fluid Structure Interaction
2Contents Background. The Main Objectives The Partnership Main Technical FeaturesThe WorkplanThe DeliverablesProgress to dateSystems developmentExperimental programmeEarly validation resultsCurrent Work and Case StudiesFurther Work
3BackgroundEXPRO-CFD was instigated through consultation with oil companies and contractors who need:improvements in the prediction of wave loads on floating systemsmore account to be taken of non-linearities in designbetter validationbetter models for dealing with deep water behaviorimproved integration with other design toolsapplication guidelines specific to CFD for offshore engineering applications.
4The Main ObjectivesTo 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.
5The Partnership Atkins Process* - Coordinators Det Norske Veritas* MARIN* Statoil*BP Single Buoy Moorings*Aker Kvaerner LMG MarinImperial College* Sirehna* CIMNEEcole Centrale de Nantes University College London
6Key Technical AspectsThe 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.
7Typical Offshore Problems of Concern Slow drift damping and viscous drag effectsExtreme or steep wave loads - viscous effects in trough to crest region,Vortex shedding at all scales - riser interactionsWave impact, run-up and air-gap.Tether ringing and springing.Local, non-linear free surface problems.
8The Work-plan 6 Work-packages Integration and Testing of CFD/diffraction and platform dynamics programs.Key technical studies (Cylinder LES and FPSO modeling)Validation experimentsTuning and validation of the hydrodynamic systemsDesign evaluation case studiesBenchmark tests.
9The DeliverablesSystems 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.
10Work 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)
12The 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 toolsAllow traditional hydrodynamic tools to be used independentlyRigid 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.
13Example coupled system (Atkins solution) At present based on AQWA/CFX4 with GiD front end“Control box” determines which module runs whenData to files in a common directoryUse of files is the most flexible way of reading / writing dataIndirect interaction between individual modulesIndividual modules can easily be replaced
15Measurements - FPSO Measurements by MARIN Freely floating 1:80 scale FPSO model5 wave periods/2 wave heightswave directions at 90,135 degreesMeasurements of global loads and moments, wave profiles, PIV velocity measurements
16Measurements – vertical cylinder Fixed vertical cylinderTests by ECN and SirenhaRegular wavesMonochromatic: 9 combinations of L and HBichromatic: 2 combinations of 2 wave periodsPIV measurements of velocities on radial slicesPressure measurements at vertical and horizontal sets of pressure tappingsOverall forces and moments
17Example Simulation ECN Cylinder Example caseVertical cylinder in regular waves:Period = 1.26 secondsAmplitude = 0.127m
19Vertical cylinder tests Fixed vertical cylinder as per WP3 experiments‘Beach’ downstreamExtent 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
20Vertical cylinder – preliminary results Comparisons with experimental dataNoticeable effects of VOF, and grid dependencyWave kinematics at inlet, and propagation – test of consistencypressures - experimentspressures – coupled system
21Coupled model Floating cylinder depth 1m, mass 205kg 1D motion with simple AQWA-NAUT modelExtinction tests in surge and heaveSurge 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
22Surge 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 amplitudeCoupled system with effects of viscosity included shows expected reduced amplitudes
23Current Work Completing the process of validation and tuning Work Package 6 – Design evaluation case studiesFocus 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
24Case Studies (1) AKER KVAERNER TLP KEY ISSUES Wave run-up and air gap Extreme wave loadsTether ringingOverlap study involving both Atkins and DNV systems to allow benchmarking
25Case Studies (2) LMG MARIN FPSO KEY ISSUES Wave Drift DampingFishtailingGreen water (if time allows)The DNV system only to be applied to this case
26Case Studies (3) SBM – Export Buoy KEY ISSUES Skirt damping Extreme loadsMooring/floater interactionThe Atkins system only to be applied in this case
27Further Information Publications Forthcoming OTC – Overview including more technical detailsISOPE – Session of 6 papers dedicated to the projectAdditional publications by ECN, Imperial College and UCLEXPRO-CFD web site.Further DevelopmentsEXPRO-CFD Brochure – available on requestEXPRO-CFD Participation Programme – aimed at exploiting deliverablesEXPRO-CFD II