Intro2 06 Coupled

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Module 6

Coupled Field Analysis


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6. Coupled Field Analysis

Overview INTR

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INTR In this chapter, we will briefly describe how to do a thermal-stress

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The purpose is two-fold: To show you how to apply thermal loads in a stress analysis.

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Overview INTR

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INTRThermally Induced Stress

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en a s ruc ure s ea e or coo e ,

deforms by expanding or contracting.

If the deformation is somehow restricted

Thermal stresses

due to constraintsNT

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by displacement constraints or an opposing

pressure, for example thermal stresses

are induced in the structure.SYS

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Another cause of thermal stresses is non-

uniform deformation, due to different

materials (i.e, different coefficients ofThermal stresses

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thermal expansion).

materials


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Overview INTR

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INTR There are two methods of solving thermal-stress problems using

ANSYS. Both methods have their advantages.DUCTI

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Sequential coupled field

- Older method, uses two element types mapping thermal results asstructural temperature loads

+ Efficient when running many thermal transient time points but few structural NT

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time points

+ Can easily be automated with input files

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+ Newer method uses one element type to solve both physics problems

+ Allows true coupling between thermal and structural phenomena

- May carry unnecessary overhead for some analyses

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A. Sequential Method


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C. Workshop


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A. Sequential Method INTR

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INTR The Sequential methodinvolves two analyses:

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1. First do a steady-state (or transient) thermal

analysis. Model with thermal elements.

A l thermal loadin .

ThermalAnalysis

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Solve and review results.

2. Then do a static structural analysis.

Switch element types to structural.

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Tem eraturesSYS

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Define structural material properties, including

thermal expansion coefficient.

Apply structural loading, including

temperatures from thermal analysis.

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Solve and review results.jobname.rst


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Sequential Method INTR

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INTR1. Thermal Analysis

The procedure for this is described in Intro Part 1.DUCTI

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2. Structural Analysisa) Move to PREP7 and switch element types from thermal to structural.

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OrETCHG command

Caution: Switching element types will reset all element options backto their default settings. For example, if you used 2-D axisymmetricSYS

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elements in the thermal analysis, you may need to re-specify the

axisymmetric option after the switch. Therefore, be sure to verify and

set the proper element options:

Main Menu > Pre rocessor > Element T e > Add/Edit/Delete > art2

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[Options]

Or use ETLIST and KEYOPT commands


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INTR

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INTRb) Define structural material properties (EX, etc.), including the

coefficient of thermal expansion (ALPX). (If you use the ANSYS-DUCTI

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defined, so this step may not be needed.)Note: If ALPX is not defined or set to zero, no thermal strains will be

calculated. You can use this technique to turn off temperatureNTOA

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c) Specify static analysis type. This step is needed only if the thermal

analysis was a transient.

Main Menu > Solution > Anal sis T e > New Anal sisSYS

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OrANTYPE command

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INTR

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INTRd) Apply structural loads and include temperatures as part of the

loading.DUCTI

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a n enu > o u on > e ne oa s > pp y > ruc ura >

Temperature > From Therm Analy Or use the LDREAD command.

e Solve. NTOA

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f) Review stress results.

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B. Direct Method INTR

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INTR The Direct Methodusually involves just one analysis that uses a

coupled-field element type containing all necessary degrees ofD

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1. First prepare the model and mesh using one of thefollowing coupled field element types.

Thermal

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SOLID5 (hexahedron).

SOLID98 (tetrahedron).

2. Apply both the structural and thermal loads and

Combined

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3. Solve and review both thermal and structural

results.

Analysis

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Sequential vs. Direct Method INTR

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INTR Sequential

For coupling situations which do

Direct

Direct coupling is advantageous

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nonlinear interaction, the

sequential method is moreefficient and flexible because you

can perform the two analyses

is highly nonlinear and is best

solved in a single solution using acoupled formulation.

Examples of direct coupling NTOA

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independently of each other.

In a sequential thermal-stress

analysis, for example, you can

perform a nonlinear transient

include piezoelectric analysis,

conjugate heat transfer with fluid

flow, and circuit-electromagnetic

analysis.

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linear static stress analysis. You

can then use nodal temperatures

from ANY load step or time-point

in the thermal analysis as loads

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for the stress analysis.

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C. Workshop INTR

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INTR Refer to yourWorkshop Supplementfor instructions on:

W6A. Axisymmetric Pipe with Fins (Sequential Coupled Field)D

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W6B. Axisymmetric Pipe with Fins (Direct Coupled Field)

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Intro2 06 Coupled