Meeting the Challenges of Fluid-Structure Interaction

Alan Mueller, Chief Technology Officer

Air Interaction with a Flexible Structure

What is FSI?

Water/Air Interaction with a Structure

What is FSI?

Vortex Induced Vibration and Galloping

What is FSI?

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Aeroelastic Flutter

What is FSI?

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Hydroplaning

What is FSI?

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Gulping

What is FSI?

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Ask 20 engineers “What is FSI?” and you will likely get 20 different answers There is not simply one approach valid for all FSI problems The analyst must be presented with a range of options and chose the most suitable

What is FSI?

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Mapping data techniques – Finding neighbors and interpolating

Protocols and formats for exchanging data – Getting data from Code A to Code B

Coupling methods – Algorithms for accuracy, stability

Dynamic fluid mesh evolution – Topology changes in the fluid domain

Validation of FSI results

The Challenges of FSI

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The Challenges of FSI

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MAPPING

Searching for opposing neighbors Interpolating source stencil data on a target point – Source and targets may be face or vertex

Often requires integration (quadratures) – intensive extensive variables

• pressure force • heat flux heat

– FEA nodal loads: integration of intensive variables against the shape function.

The 3 steps of “Mapping”

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Search requires little user intervention The search excludes potential neighbors based on proximity and orientation Critically important for sheet metal parts – resolve ambiguities of poor geometry – thin solid parts may be on the wrong side of the fluid surface

Parallel Mapping is a must! – Takes advantage of distributed memory

Source Neighbor Search Imperative

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Co-Simulation Vehicle Thermal Management

Mapping Displacement in Low Y+ Prism Meshes

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C0 continuous mapping very important for low y+ meshes

Otherwise very easy for morpher to invert high aspect ratio cells in prism layer

The Challenges of FSI

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DATA EXCHANGE

File Based Transfer: Import/Map/Export – Data exchange via files on a hard-disk – CAE codes need not be resident in memory – Often called “Loose Coupling” – User responsible for exchange synch

Socket Based Transfer: Co-Simulation API – CAE code and STAR-CCM+ in memory – Data exchanged via sockets – API controls exchange synchronization

Methods for Exchanging Data

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Coupling via Abaqus Co-Simulation API of SIMULIA – Manages Coupling Synchronization/Exchange/Mapping – Abaqus v6.12/STAR-CCM+ v7.04 (implicit coupling)

STAR-CCM+ Abaqus (explicit or standard) – Initial geometry – Pressure(relative or absolute pressure) – Shear traction – Surface heat flux

Abaqus STAR-CCM+ – Displacement, velocity – Temperature

Abaqus/STAR-CCM+ Co-Simulation

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Abaqus/STAR-CCM+ Co-Simulation Interface

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Hit the Step or Run button to commence the co-simulation

The Challenges of FSI

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Coupling Technique

Two-way coupling for aeroelastic or hydroelastic equilibrium

One way static coupling for thermal stresses – structural temperature computed by CFD CHT

One way dynamic coupling – Loads only go from fluid to structure – Loads only go from structure to fluid

Two way dynamic coupling – explicit (exchange once per time step) – or implicit (multiple exchange per time step)

Degrees of Coupling

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Dynamic Mesh Evolution

The Challenges of FSI

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Completely define a good quality fluid mesh – Using as little user intervention as possible

Options within STAR-CCM+ – Rigid body motion, sliding interfaces – Morphing – User Defined Motion

Overset Mesh

Dynamic Mesh Evolution

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Overset Mesh Motion and Fluid Flow : Stop Valve

The Challenges of FSI

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Validations

AeroElastic Prediction Workshop: HIRENASD

2.3M cells

53K nodes

Static Structure, Steady airflow at deformed shape Ma=0.8, Re=23.5x106, q/E=0.48x10-6

Aerodynamic Equilibrium at different AOA

Wing Tip Displacement Lift Coefficient

Cp: AOA 2°

FUN3D

STAR-CCM+/Abaqus

Cp: AOA 2°, Station 7

x/c

STAR-CCM+/Abaqus NASA FUN3D

Wind-off Vibration Modes : Abaqus vs Experiment

f=25.55 Hz (26.25)

f=80.25 Hz (78.20)

f=106.20 Hz

f=160.35 Hz (165.25)

AeroElastic Prediction Workshop: Forced Vibration of 2nd Flap Bending Mode

Magnitude

Wing Tip Response of Cp

Phase

Fluid-Elastic Instabilities in a Tube Bundle

Weaver & Abd-Rabbo, “A Flow Visualization Study of a Square Array of Tubes in Water Crossflow”

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HydroDynamic Damping: Simulation vs Measured Vibration RMS vs Inlet Velocity: Simulation vs Measured Tube Bundle Vorticity

Co-Simulation DOT Tank Impact

32 Experimental Test Impact

DOT Tank Impact Simulations

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Von Mises Stress (Abaqus Explicit)

STAR-CCM+ Pressure

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DOT Tank Impact Comparisons

Mapping Data Techniques Procedures for Exchanging Data Coupling Methods Dynamic Fluid Mesh Evolution Validations

The Challenges of FSI

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Thank You For Your Attention & Enjoy

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