FENET Copenhagen Feb2002 MPA Ellis

7/31/2019 FENET Copenhagen Feb2002 MPA Ellis

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FENET THEMATIC NETWORKCOMPETITIVE AND SUSTAINABLE GROWTH(GROWTH) PROGRAMME

Industry Sector RTD Thematic Area Date Deliverable NrMulti Physics and Analysis 27th February 2002

Challenges of Multi-Physics Coupling in a Commercial FE Code

David EllisIdac Ltd, London, United Kingdom

SummaryThis presentation will illustrate the capabilities of the ANSYS program for solvingMultiphysics Coupled Field solutions and describe the challenges faced in solving theseproblems as well as offering some advice in tackling these challenging physics simulations.


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Introduction

Idac We are a London based Engineering Analysis Consultancy company performingthe following activities:

Consultancy Analysis Customisation & Implementation Software Sales

ANSYS DesignSpace LS-DYNA DynaForm PowerFLOW

Training Courses Technical Support


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What Type of Coupling Can be Solved?

The Physics involved are the following:

Structural Thermal Acoustics Electrostatics Electro-magnetics Computational Fluid Dynamics (CFD)

The physics above can be coupled together and solved in one of two ways:

Sequential Analysis Direct Coupled Analysis


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History of Multi-Physics within the ANSYS program

Early 1970s - Thermal and stress analysis linked via temperatures. Simple load vector coupling of thermal strain.First commercial code to introduce thermal-stress analysis. Geared toward power industry (GE, Westinghouse,etc.)

Late 1970s - Add thermal-electric capability to compute Joule heating effects coupled through load vector fromcurrent solution to compute I**2R heating. Applications: Bus bars, switchgear, etc.

Mid 1980's - Introduced first general-purpose coupled-field elements SOLID5, SOLID98, PLANE13. MultipleDOF options. Load vector coupling:

Allowed for thermal-electric, magneto-structural, electro-magnetic coupling. Also, first fully-coupled formulation (matrix coupling) for Piezoelectric analysis.

Late 1980's, early 1990's - Addition of matrix coupling for acoustic-structural analysis. Time-transient currentconduction-electromagnetic coupling (for eddy current/skin-effect analysis). This was also coupled to thermal andstructural analysis.

Late 1990s through 2002 - Introduced Physics file concept for general coupling of field solutions using the samemesh.

Introduced electrostatic-structural coupling for MEMS devices, both load-vector coupled and matrixcoupled.

Introduced induction heating. Now releasing fully coupled transient FSI.


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History of Multi-Physics within the ANSYS program

Some examples of coupled solutions through from the first ones that were implementedthrough to the coupling that we can perform today:

Early: Static thermal-stress analysis

Today: Dynamic fluid-structure interaction with dissimilar mesh interfaces betweenfluid and solid. Coupled-field dynamic FSI simulation: Ink-jet printer simulation withelectrostatic-actuated MEMS device ejecting a fluid droplet simulated using anALE/VOF method CFD formulation.


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Challenges Faced in Introducing Coupled Solutions in the ANSYS Program

Convergence - Some physics do not lend themselves to loose coupling (eddycurrents, piezoelectrics)

Time-accurate transient solutions - Most early coupling was static or time-harmonic,current needs are dynamic. This required time-transient solutions with "staggers"between physics and equilibrium iterations to converge each physics at each timepoint. Compatible time-stepping algorithms for each physics is an issue.

Convergence of non-linearities is an issue.

Efficient equation solvers for coupled problems - Resulting matrices of coupledsystems can be ill-conditioned, dense, etc., leading to inefficiencies in standarditerative solvers, and direct solvers.

Finite-element methods with structural coupling to a field solution (magnetics,electrostatics, fluids) involving mesh "morphing". This has limitations and robustnessissues.


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Thermo-Structural Coupling Sequential Analysis

Power Station Expansion Joint Analysis


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Sequential Analysis: Data Flow for a Sequential Coupled-Field Analysis


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Sequential Analysis: Data Flow for a Sequentially Coupled Analysis (Using Physics Environments)


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Thermal Analysis

Solid Elements, Temp DOF, (1 DOF per node)

Shell Elements, Temp DOF, (1 DOF per node)

Structural Analysis

Solid Elements, UX, UY, UZ DOFs, (3 DOFs per node)

Shell Elements, UX, UY, UZ, ROTX, ROTY, ROTZ, (6 DOFs per node)


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Thermo-Structural Coupling Direct Coupling Analysis

Bi-metallic Strip Thermo-structural Analysis


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Direct Coupled Analysis:

The direct method usually involves just one analysis that uses a coupled-field element type containing all necessary degrees of freedom. Coupling is handled by calculatingelement matrices or element load vectors that contain all necessary terms.


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Coupling Methods Used in Direct Coupled-Field Analyses

Type of Analysis Coupling Method

Thermal-structural Load vector (and matrix, if contact elements are used)Magneto-structural Load vectorElectro-magnetic MatrixElectro-magnetic-thermal-structural Load vector

Electro-magnetic-thermal Load vectorPiezoelectric MatrixThermal-pressure Matrix and load vectorVelocity-thermal-pressure MatrixPressure-structural (acoustic) Matrix

Thermal-electric Load vectorMagnetic-thermal Load vectorElectrostatic-structural Load vectorElectromagnetic-circuit MatrixElectro-structural-circuit Matrix


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Direct Coupling

The finite element formulation which treats a single phenomenon uses matrix algebrarepresented by:

[ K ] { X } = { F }

where [ K ] is the coefficient matrix

{ X } is the vector of nodal unknowns

{ F } is the known load vector


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Direct Matrix Coupling

[ K

11 ] [ K

12][ K 21] [ K 22]] } [ F

1][ F 2]{ }[ X

1][ X 2]=[ {

Coupled effects are accounted for by off-diagonal coefficient terms K 12 and K 21Provides for coupled response in solution after one iteration.


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Matrix Coupling Examples

Category Applications

Electromagnetics Induction motors

Piezoelectrics Microphones, sensors

Thermal-pressure Piping networks

Pressure-structural Acoustics

Circuit-magnetic Motors with circuitry

Fluid-structural High speed machinery


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Direct Load Vector CouplingDirect Load Vector Coupling

[ K 11

] [ 0 ][ 0 ] [ K 22][ {] } [

F1][ F 2]{ }[

X 1][ X 2]

=

Coupled effects are accounted for by load terms F 1 and F 2

At least two iterations, one for each physics, in sequence are needed to achieve a coupledresponse.


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Thermo-Structural Analysis

Solid Elements, Temp, UX, UY, UZ DOF, (4 DOFS per node)

Shell Elements, Temp, UX, UY, UZ, ROTX, ROTY, ROTZ (7 DOFs per node)


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Electrostatic-Thermo-Structural Coupling Sequential Analysis

MEMS Thermo-Electric Actuator


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Electrostatic-Thermo-Structural Coupling Sequential Analysis

Electrostatic Analysis Solid Elements, Volt, Curr (2 DOFS per node)

Thermal Analysis Solid Elements, Temp (1 DOF per node)

Structural Analysis Solid Elements, UX, UY, UZ (3 DOFS per node)


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Electromagnetic-Structural Coupling

Rotational Solenoid Analysis


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Fluid-Thermo-Structural Coupling

Automotive Radiator Analysis


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Fluid-Thermo-Structural Coupling

Fluid-Thermo-Structural Analysis

Solid Elements, VX, VY, VZ, Pres, Temp, UX, UY, UZ (8 DOFs per node) Shell Elements, VX, VY, VZ, Pres, Temp, UX, UY, UZ, ROTX, ROTY, ROTZ

(11 DOFs per node)


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Why Perform Coupled Analysis Solutions?

A coupled-field analysis is an analysis that takes into account the interaction (coupling)between two or more disciplines (fields) of engineering. A piezoelectric analysis, for example,handles the interaction between the structural and electric fields: it solves for the voltagedistribution due to applied displacements, or vice versa. Other examples of coupled-fieldanalysis are thermal-stress analysis, thermal-electric analysis, and fluid-structure analysis.

Some of the applications in which coupled-field analysis may be required are pressurevessels (thermal-stress analysis), fluid flow constrictions (fluid-structure analysis), inductionheating (magnetic-thermal analysis), ultrasonic transducers (piezoelectric analysis), magnetic

forming (magneto-structural analysis), and micro-electro mechanical systems (MEMS).

By definition coupled solutions are problems where these physics interact with each otherand are dependent upon each other.


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Electronic Packaging

Electronics package cooling using CFDanalysis

Two-dimensional simulation

Heat sources from boards

Fan cooled

Need to predict

Velocity pattern Temperature profile


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Electronics System Cooling

Cooling simulation of a television set.

Conjugate heat-transfer simulation using FLOTRAN


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Electronic Package Cooling

Simultaneous solution of air flow and package temperature

Applicable to free-convection and forced convection problems


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Electronic Package Cooling

Air temperature profile

Chip Surface Temperature

Experimental: 78 deg C.

FLOTRAN: 77 deg C.


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Acoustics

Acoustics Capabilities

Two and three dimensional analysis

Modal, Harmonic, and Transient simulation to determine pressures, particle velocity, and decibel level

Fluid-structure interaction

Impedance boundary condition

Displacement, force, pressure loads

Absorbing boundary condition


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Speaker System

Acoustic simulation of a speaker system

Flexible tweeter dome

Axisymmetric model

Voice coil driven by applied force

Frequency domain solution


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Tweeter pressure and deflection

Pressure distribution and tweeter deflection @ 11.8 KHz.


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Tweeter sound pressure level


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Induction Stirring

Simulation of Induction stirring

Induction furnace modeled at 2500 F

Molten steel stirred by electromagnetic forces from coils

Forces coupled to CFD analysis to determine flow pattern


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Induction Stirring

Electromagnetic solution:

AC (Harmonic) electromagnetic field simulationperformed to predict magnetic field in conducting bath.(Flux lines shown)

Lorentz forces induced in bath are automatically

calculated for use in CFD run.


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Induction Stirring

Lorentz forces in bath

Electromagnetic forces provide driving force for fluidmotion


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Fluid motion computed from Lorentz ForceLoad

Computation fluid dynamics simulation performed to

determine stirring pattern

Turbulent flow reveals two eddy regions (Velocity profileshown)


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What Does the Future Hold?

New element architecture for fully-coupled multiphysics simulation Uses "core" single physics elements "Builds" a coupled-field element from "core" elements based on user

specification

Enhance material constitutive relations to handle advanced multiphysics

phenomena.

New Product - AI*EMAX for the Solution of High Frequency Phenomena (Antennas,Stealth Technology, EMC). It is also possible to couple AI*EMAX toANYS/Multiphysics to do RF heating!


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Recommendations

Build up to the full solution slowly, may be start with 2D solution Start with the physics that is driving the problem

Add subsequent physics one at a time

Try sequential solutions first of all Then run analysis as a directly coupled solution

In ANSYS use Run Time Statistics prior to solution gives memory & file size estimates Memory is crucial rather than disc space as there are physical limits on various hardware

platforms (64Mb = 50k DOFs)

Be careful in defining the FE mesh for coupled solutions The mesh for the solution of one physics problem is not necessarily a good mesh for other

physics ANSYS can perform mesh morphing and result mapping automatically


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THE END!!!Thank you for listening

Any Questions!!

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FENET Copenhagen Feb2002 MPA Ellis