thermal analysis - code_asterthis time, use « thermo-mechanical analysis » assistant enter...

Thermal analysis

code_aster, salome_meca course materialGNU FDL licence (http://www.gnu.org/copyleft/fdl.html)

Outline

1. Overview of the main features

2. A simple example of thermo-mechanical computation

3 - Code_Aster and Salome-Meca course material GNU FDL Licence

A simple example : pipe in thermal equilibrium

We want to know the temperature field in the thickness of the pipe

40°C

15°C

Infinite pipe

Load : a temperature field on each side

3


Code_Aster : main features for thermics

Pipe in thermal equilibrium : isothermal values

Frequently used as a prerequisite to a mechanical calculation

Example : pipe with prescribed temperature on each side

Thermic calculation

Mechanical calculation

Final displacement and circumferential pipe stresses

4

Outline




What is the problem to be solved?

The problem can be :

AFFE_MODELE ( ...PHENOMENE = ‘THERMIQUE’... )

6

stationnary transient

linear

non-linear

0=sλΔTTρC 0=sλΔT

0)()( =TsΔTTλ 0)()()( =TsΔTTλTTρC

equation in the bulk


linear

non-linear

supported Neumann boundary conditions

xtf=dn

dTλ ,

Tf=dn

dTTλ )(


What is the problem to be solved?

The problem can be :

AFFE_MODELE ( ...PHENOMENE = ‘THERMIQUE’... )

7


linear THER_LINEAIRE

ETAT_INIT ETAT_INIT

non-linear THER_NON_LINE

ETAT_INIT ETAT_INIT


Available finite elements

AFFE_MODELE ( … PHENOMENE = ‘THERMIQUE’

… MODELISATION = ‘XXXX’ ...) )

3D / AXIS / PLAN

3D_DIAG / AXIS_DIAG / PLAN_DIAG

regularization during heat shock

splitting of quadratic elements in 2D

splitting not avalaible in 3D

COQUE / COQUE_PLAN / COQUE_AXIS (linear)

thermal shell "thin" structural elements

temperature field in the thickness : 3 degrees of freedom (Tsup, Tinf and Tmiddle)

Example of a sudden cooling :

289°C

20°C

T

temps

8


Precautions for use in thermics

nnnn TTTTt

C

)1()(

.11

Time discretization with the -méthode.

Ability to change with PARM_THETA

In case of unstable results, in spite of lumped elements :Minimal time step proven to yield stable results, good start to increase from :

λΔxρC

Δt

mesh

16 3

2

9


Material behavior

DEFI_MATERIAU

At least these two characteristics:

3 main materials :

+ other specific materials For concrete : drying, hydratation ... etc

For metals : metallurgical transformations, hardness ... etc

Thermal conductivity

Heat capacity

PρC

)(T )(T

THER Linear isotropic

THER_ORTH Linear orthotropic (definition of in 3 directions)

THER_NL Non-linear behaviour : one has to define or and

!! THER_NON_LINE has to be used

)(TρCP

10


Boundary conditions and loadings (1)

AFFE_CHAR_THER (...)

AFFE_CHAR_THER_F (...)

Full list : https://www.code-aster.org/V2/doc/v14/fr/man_r/r5/r5.02.02.pdf

Boundary conditions (Dirichlet)

Imposed temperatures function of time and space TEMP_IMPO

Linear relationships between the nodal temperatures

LIAISON_DDL

LIAISON_GROUP

LIAISON_MAIL

11

https://www.code-aster.org/V2/doc/v14/fr/man_r/r5/r5.02.02.pdf


Boundary conditions and loadings (2)

Loadings (Neumann)

Natural convection (Fourier law) ECHANGE

Heat exchange between walls ECHANGE_PAROI

Normal imposed flux : constant or

function of time and space FLUX_REP

Non linear normal flux : function of

the temperature

FLUX_NL

RAYONNEMENT

Heat source SOURCE

TTextth=dn

dTTλ

)Th(T=dn

dTλ

1

1121

x)f(t,=dn

dTλ(T)

f(T)=dn

dTλ(T)

t)s(x,

Non-linear only

12


Is the problem well defined?

Résults of a stationnary calculation STATIONNAIRE ='OUI'

A constant temperature VALE = T0

A known temperature field CHAM_NO = …

for example, created with CREA_CHAMP

The result of another thermal calculation A result concept (EVOL_THER = resu)

+ chosen time (NUME_ORDRE or INST )

For a stationnary calculation : YES

For a transient calculation : NOA condition is missing : the temperature at the initial time

Defined in THER_LINEAIRE or THER_NON_LINE with ETAT_INIT4 possibilities :

13


Post-processing options

What's the result of THER_LINEAIRE / THER_NON_LINE ?

By default : only the nodal temperatures

How to get the thermal fluxes ?

With CALC_CHAMPFLUX_ELGA

FLUX_ELNO

FLUX_NOEU

14


And mechanics?

How to take into account the temperature field in the mechanical calculation?

The mesh to be used in mechanics must be different from that used for thermics. For two main reasons:

A linear mesh is better in thermics, while rather quadratic in mechanics

Areas of interest are different => the refined areas are different

One must project the temperature field on the mesh used for mechanics

PROJ_CHAMP ( … )

In AFFE_MATERIAU (...AFFE_VARC=_F( NOM_VARC = 'TEMP',

EVOL = EVOTH,

VALE_REF = 20. )

...)

15

Outline



17 - Code_Aster and Salome-Meca course material GNU FDL Licence17


Add a stage from computation assistant → allows to quickly start a computation

Pick mesh Select FEM modelling Enter material properties

Define loading and

boundary conditions

Specify path for output result



Datasettings panel :

lists created commands

Edit command panel :

adjust command data

19


Results tab : select field

Get live field visualization

Results tab : select component


And mechanics ?This time, use « thermo-mechanical analysis »

assistant

Enter mechanical material

properties, including expansion coefficient

Enter initial temperature, even for stationnary computation

(useful for thermal induced strains)

Enter time or pseudo-time

discretization

Goes through same steps as before, plus…

Enter FEM modelling for

mechanical computation

Enter mechanical loading and

boundary conditions


And mechanics ?

Uncheck ETAT_INIT

in THER_LINERAIRE

Tip : the presence of ETAT_INIT keyword indicates a transient computation.

Otherwise, it is stationnary.

22

And mechanics ?

Results tab : select field

Get live field visualization

on the deformed shape

Results tab : select component


To go further…

Start a computation taking your inspiration from an existing testcase

For instance :

SSLP117 Provide an analytical temperature field as input to mechanical computation

TPLP107 Prescribed fluxes, temperature or source variable in space

TTNL04 Prescribed fluxes variable in time

FORMA30,

FORMA21Transient thermal computation

SSNV301 Elasto-plastic mechanical computation

And much more at https://www.code-aster.org/V2/doc/v14/fr/index.php?man=cas-test

https://www.code-aster.org/V2/doc/v14/fr/index.php?man=cas-test

End of presentation

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dedicated thread.

GNU FDL licence | code_aster, salome_meca course material
http://www.code-aster.org/forum2/viewtopic.php?id=17343

thermal analysis - code_asterthis time, use « thermo-mechanical analysis » assistant enter...

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