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THE CHALLENGES OF FLUID STRUCTURE INTERACTION

Alan Mueller CD-adapco Seattle

19th Annual HP CAE Symposium

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Take the FSI challenge

ACM1

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Slide 2

ACM1 Ask an engineer what he thinks FSI is and you will get a 100 different answers - all of them right.

The truth of the matter - FSI is actually a very broad subject with a range of challaenges from the relatively simple to the extremlydifficult.

Often an engineer looking from outside may not appreciate what goes on "under the hood" and it may be difficult to asses the level ofdifficulty of a problem

The movie depicts a VOF simulartion of wave loading on a relatively realistic off-shore platform. It gives a glimmer of what is to comein the area of FSI.

So join me in this FSI challenge, it may not be quiite as simple as the "Pepsi Challenge" but I hope that it will be ever bit a satisfying.Alan Mueller, 4/1/2008

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Outline

FSI Instances and Classification

Mapping and Data Exchange Mesh Motion Demands

Robustness and Stability

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Instances of Fluid-Structure Interaction (FSI)

Pressure-actuated valves, pumps

Flow induced vibration of structures

cables, risers, towers, etc. flutter

Free surface applications

sloshing in fuel tanks, wave

loading, etc. Solid/Fluid thermal interaction

Tire hydroplaning

Biomedical applications

An understanding of both solid andfluid domains is essential for anaccurate simulation.

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Fluid-Structure Interaction Classifications

1 way or weakly 2 way coupling Deformation has little effect on fluid motion

Mechanical, thermal loads: fluid structure Surface temperatures: structure fluid

Thermal or hydrodynamic induced loads

Steady state

Transient (multiple transfers)

2 way coupling Deformation or rigid body motions significantly impact

the fluid motion

Mechanical, thermal loads: fluid structure

Displacement & temperatures: structure fluid

Motions require CFD moving mesh capability

2 Way coupled FSI places anextreme burden on the CFD solver to

produce good, body conforming grids

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Avenues for FSI Coupling in STAR-CD/STAR-CCM+

1-way or weakly 2-way coupling Prep/Post: STAR FEA

MpCCI, DCI: STAR FEA

STAR fluid STAR solid

2-way coupling MpCCI, DCI: STAR FEA

STAR fluid STAR solid

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Outline

FSI Instances and Classification

Mapping and Data Exchange Mesh Motion Demands

Robustness and Stability

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STAR Integration Pre/Post FEA support

Import FEA Mesh (ABAQUS, ANSYS)

Non-conformal mapping STAR-CCM+ FEA

Surface to Surface

Volume to Volume

Conserved & 1st order

Export FEA Loads

Pressure, Nodal Forces

Heat flux, Nodal Heat

Heat Transfer Coefficient, Ambient Temperatures Import FEA Results

Displacement

Temperature

import from/export to the native FEA format

Java scripting for dynamic exchange

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Steady-State Bidirectional Heat Transfer Analysis

Solid Temperature(ABAQUS)

Fluid Temperature

Heat Transfer CoefficientFluid Polyhedral Grid

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ABAQUS and STAR Direct Coupling Interface (DCI)

process 1process 0

ABAQUS

...

All face matching and interpolation onSTAR faces local to each processor

e

nprocess 2

process nSTAR

k

n

i

m

MPI socket

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Aquaplanning Simulations

STAR-CD Moving Deforming Mesh

Arbitrary Sliding Interface

VOF for fluid/air interface

Cavitation

ABAQUS Steel Belted Tires

Lateral Treads Vehicle weight, Fluid loads

Static or Dynamic

DCI Pass fluid loads

Pass surface deformation

Important Considerations

Tread surface contacts pavement

Hydrodynamic loads significantly deform tire

No circumferential symmetry Periodic frequency as tread patterns move in/out of contact

Tire is able to slip (motion defined by contact friction)

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Stucture Motion defined as Rigid Body (6DOF) Fluid Forces and Moments Structure

Body Surface position Fluid

Fluid mesh translates/rotates with rigid Structure Implicit Coupling between Fluids/Structure

Canister Example CFD of both air and water VOF (Volume of Fluid) free surface capability

Rigid canister of given mass, mass moments

STAR Fluid STAR Rigid Body

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STAR Fluid STAR Solid Stress

Build one mesh in one GUI environment

Polyhedral meshing advantage

Immediate picture of impact of fluid on solid stresses Finite Volume, implicit iterative solver requires

significantly less memory than FEA

Implicit fluid/solid coupling via memory using similar

data structures and iterative procedures

Tighter fluid/solid exchange at subiteration level

Targeted Applications:

Conjugate heat transfer and thermal stresses Fluid-Structure Interaction

Casting and Solidification (fluids cells become solid cells)

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Flow, Heat, and Thermal Stress - Manifold

Manifold Temperature

Gas Temperature

Manifold effective stress

Gas Velocity

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Turbine Blade Analysis

Fluid Flow and Conjugate Heat Transfer

Static load: Elastic solid with centrifugal andthermal loads

Creep : Viscoplastic solid with stress andtemperature dependent creep rates

effective stress

temperature

fluid flow

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Examples of Finite Volume Stress Analysis

Stresses (6M DOF) Solid (12.6M DOF), Fluid (1 M cells)

Temperature (2M cells)

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Scalability: Engine Block and Head (12.6 M DOF)

Thermoelastic stress solves on Cray in 14 CPU min (28 Processors)

Convergence rate independent of # processors

Good scalability to about 20K cells per processor

Machine : Cray node AMD opteron 250, 2.4Ghz,

4Gb RAM per node, 2 processors per node,

Rapid Array MPI

Problem : 4.2M cells, 12.6M DOF, 9.8Gb RAM

0

4

8

12

16

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28

32

0 4 8 12 16 20 24 28 32

CPU processors

speed-up

Scalability of Solid Stress Solver

Turbo wit h 700414 cells, on White clust er

0

1

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0 4 8 12 16 20 24 28 32 36

number of processors

speed

up

HP Proliant 16 node(AMD Opteron 2dual core/node,Infiniband,8Gb/node,1GHz

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Outline

FSI Instances and Classification

Mapping and Data Exchange Mesh Motion Demands

Robustness and Stability

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Defining the Mesh at all times

Fluid mesh must conform to boundaries and

maintain cell quality

Mesh motion is difficult not simply because a

structure moves

Mesh motion is difficult when a structure moves

close to other structures (rigid or not)

The goal : Define the mesh motion with as little userintervention as possibleThink Contact!

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Mesh Evolution Strategies in STAR-CD/STAR-CCM+

Mesh translation/rotation

Mesh morphing (constant topology)

Sliding Interfaces

Topology changes

Cell Insertion/Deletion Re-meshing/Interpolation

Parallel Meshing

Immersed Boundary Method (Low Re)

Overlapping MeshesMany preprocessing meshing features availableto STAR-CD/STAR-CCM+ during solve

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Mesh Translates/Rotates with Rigid Body

Mesh conforms to motion of the body

External fluid BC must be preserved during motion

Even rigid body motionadds to the mesh motioncomplexity

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Advanced Morphing Polyhedral Meshes

Small number of control points define motion on

moving boundary region

Morpher preserves quality of grid, boundary layer

User control on other boundary regions

Morphing in Parallel

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Outline

FSI Instances and Classification

Mapping and Data Exchange Mesh Motion Demands

Robustness and Stability

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Explicit vs Implicit Coupling

Explicit coupling is the most widely used coupling

between FEA and CFD codes, but ...

A tighterimplicit coupling requires a deeper and

more intimate integration of the solvers

The STAR fluids/solids are implicitly coupled

CD-adapco is working with our FEA partners to

develop fully implicit coupling.

increasingly stiff,

and massivestructure

increasingly incompressible,and massive fluid

Unstable

Stable

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Conclusions

Fluid/Structure Interaction is a broad field

with many distinct challenges and classes

STAR offers many strategies by which to

couple the fluid to the structure appropriate

for the particular physics Mesh motion places extraordinary demands

on the CFD to preserve grid quality

STAR offers several strategies by which toevolve the mesh at solver time

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Enjoy the Conference