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Dec 6, 2013 - for Computational Solid Mechanics ! ! ! School of Mechanical & Materials Engineering. University College Dublin. Joint Symposium of.
5th & 6th December 2013

Joint Symposium of Irish Mechanics Society Irish Society for Scientific & Engineering Computation

An Open Source Finite Volume Method for Computational Solid Mechanics Philip Cardiff A Karac, A Ivankovic, Z Tukovic

School of Mechanical & Materials Engineering University College Dublin ! ! ! !

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Historical Background & Motivation

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Finite volume developed for CFD highly nonlinear strong conservation required Multi-physics e.g. Fluid Structure Interaction (FSI)

I. Demirdzic, D. Martinovic, A. Ivankovic, Numerical simulation of thermal deformation in welded workpiece (in croatian), Zavarivanje 31 (1988) 209– 219. 3

2

I

n·Dd

@ u ⇢ 2 =r· @t

Z

Q d⌦ = 0 ⌦

@T 2 ⇢C = kr T @t

Mathematical Model

4

Governing Equations Strong Form of Governing Equation

@ @t

Z

@u ⇢ d⌦ = ⌦ @t

Z





Momentum

d⌦ +

Z



⇢f b d⌦

5

Weak Form of Governing Equation

@ @t

Z ✓ ⌦

@u ⇢ @t



· w d⌦ =

Z



Momentum

· rw d⌦ +

Z

⇢f b · w d⌦ ⌦ Z + t·w d t

6

Weak Form of Governing Equation

@ @t

Z ✓ ⌦

@u ⇢ @t



· w d⌦ =

Z



Momentum

· rw d⌦ +

weighting function

Z

⇢f b · w d⌦ ⌦ Z + t·w d t

7

2

Strong form is a function of

Weak form is a function of

@ u 2 @x

@u @x

Numerically nicer smaller computational molecule

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Constitutive Relation Use constitutive law of choice e.g. hypo/hyper elastic, incompressible, etc.

= 2µ✏ + tr(✏)I

1 T ✏= ru + ru 2

Isotropic Hooke’s law

for small strains

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Development of the Mathematical Model Insert constitutive relation into governing equation

@u ⇢ d⌦ = ⌦ @t

Z







r · µru + µruT + tr(ru)I d⌦ +

Z



⇢f b d⌦

{

@ @t

Z

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@ @t

Z

@u ⇢ d⌦ = ⌦ @t

Z

µr2 u d⌦ + ⌦

Z







r · µruT + tr(ru)I d⌦ +

Z



⇢f b d⌦

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laplacian term implicitly approximated using compact molecule @ @t

Z

@u ⇢ d⌦ = ⌦ @t

Z

µr2 u d⌦ + ⌦

Z







r · µruT + tr(ru)I d⌦ +

Z



⇢f b d⌦

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Nonlinear stress analysis Choice of total/updated/deformed Lagrangian approaches Choice of stress tensor (or stress rate) may be used P. Cardiff et al. / Comput. Methods Appl. Mech. Engrg. 268 (2014) 318–335

@ @t

Z

@ðu þ duÞ q dXu ¼ @t Xu

I

nu % ðC u : dEu Þ dCu þ Cu Z þ q ðb þ dbÞ dXu

I

Cu

nu % ½ðS u þ dS u Þ % rdu' dCu þ

I

Cu

nu % S u dCu

Xu

where dF u ¼ rdu, and the increment of Green strain (Eq. (3)) reduces to:

dEu ¼

1!

T

rdu þ rdu þ rdu % rdu

T

"

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Discrete System outer iterations are performed until

Au = b

b

has converged linear system is sparse

diagonally dominant iteratively solved

14

FEM & FVM Comparison

for solids FVM

Pros

Cons

attractively simple strongly conservative memory efficient straight-forward nonlinearity suitable for FSI/cracks general polyhedral cells

segregated solution not always efficient higher order elements are more difficult less development 15

FEM Pros

Cons

efficient for linear problems

weakly conservative

higher order elements

memory hungry

plethora of development

different shape functions for every shape

inclusion of discontinuities

FSI

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fvVectorMatrix UEqn ( rho*fvm::d2dt2(U) == fvVectorMatrix UEqn ( fvm::laplacian(K, U) + rho*fvm::d2dt2(U) fvc::div(C && epsilon) - fvc::div(K & gradU) == );

fvm::laplacian(K, U) + fvc::div(C && epsilon) - fvc::div(K & gradU)

Implementation in OpenFOAM );

UEqn.solve();

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C++

object oriented

open source code resembles PDEs fvVectorMatrix @2u ⇢ 2 = K r2 u + r · (C : @t

) + r · (K · ru)

UEqn

(fvVectorMatrix UEqn ( rho*fvm::d2dt2(U) rho*fvm::d2dt2(U) == == fvm::laplacian(K, U) U) +fvm::laplacian(K, fvc::div(C && epsilon) + fvc::div(C && epsilon) - fvc::div(K & gradU) - fvc::div(K & gradU) ); );

UEqn.solve(); 18

Numerical Examples

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20

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23

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distinguishing feature of OpenFOAM is that the partial differential equation and tensor operations syntax closely resemthe equations being solved. An extract of the code from the developed elasticOrthoNonLinULSolidFoam solver, ementing the developed orthotropic updated Lagrangian approach, is given in Appendix (A), and shows remarkable simy to the previously described mathematical model.

Accuracy...

Orthotropic plate with a hole

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T

2

2

4

sin h þ

!k cos h þ ð1 þ nÞ sin h ðn2

2

! 2kÞ sin

h cos2

2

h þ k cos4 h

polyhedral mesh

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second order accuracy

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Parallelisation

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Summary & Conclusions

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Finite volume may not optimal for all problems but it is a viable alternative to FE in many applications

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Open source may not optimal for all problems but it is a viable alternative in many applications

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5th & 6th December 2013

Joint Symposium of Irish Mechanics Society Irish Society for Scientific & Engineering Computation

An Open Source Finite Volume Method for Computational Solid Mechanics Philip Cardiff A Karac, A Ivankovic, Z Tukovic

School of Mechanical & Materials Engineering University College Dublin ! ! ! !

33

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