Coupling Analysis

This solution sequence performs a coupling analysis between a nonlinear implicit analysis, a transient heat analysis and a multi-steady electrical conduction analysis.

The implicit analysis can be either static or transient. Both small and large displacement analysis are supported.

This allows a real-time update on heat transfer path and electric current transfer path due to contact status change. On the other hand, heat generated from inelastic strain can also be considered during the analysis.

Coupling Sources

Some examples of coupling sources are depicted in Figure 1, among which the quantities in red dashed circle can be captured by coupling analysis.

Heat/Current Path Based on Contact Status

Heat transfer path can change with contact status change. For instance, when a contact closes due to thermal expansion on both sides, a new heat transfer path is formed. It is hard to capture this phenomenon by using only One Step Transient Thermal Stress Analysis (OSTTS). A similar complication arises when electric conduction is included in simulation. Furthermore, the heat/electric conduction coefficient of a thermal/electric contact can be pressure dependent.

Heat from Mechanical Dissipation

In some special cases, heat generated by inelastic strain is important to be considered in a simulation. For instance, heat generated during rubber deformation, results in an increase in the temperature of the rubber. Since the properties of rubber are temperature dependent, the interaction between deformation and temperature needs to be considered simultaneously.
Figure 1. Coupling sources in coupling analysis


Solution Method

In a coupling analysis, the mechanical part of the solution can be either small or large displacement nonlinear static or transient analysis. Material, geometrical and contact nonlinearity can be considered together. When the material is temperature dependent, the thermal part of the solution is also nonlinear. The convergence criteria can be defined by NLCTRL via different tolerance types.

The mechanical part of the solution can be either a nonlinear static or nonlinear transient analysis. When a static mechanical solution is chosen, the TTERM in NLCTRL card governs the whole duration of the coupling analysis.

The thermal simulation must be linear or nonlinear transient heat transfer analysis. The electrical conduction simulation must be multi-steady, meaning no electric capacitance or magnetic effects are considered.

Problem Setup

The setup for the coupling analysis is outlined here.

In the first step, three subcases need to be defined:
  • An implicit nonlinear static/transient structural analysis subcase,
  • a nonlinear or linear transient heat transfer analysis subcase, and
  • multi-steady electrical analysis subcase.

In the second step, define COUPLE(HEAT) and COUPLE(ELEC) in the implicit nonlinear structural subcase to link the thermal and electrical parts of the solution. The initial temperature can be defined by TEMPERATURE(INIT) and the time integration can be controlled by NLCTRL/TSTEP defined in the implicit nonlinear structural subcase.

Example

TEMPERATURE(INIT) = 100
SUBCASE 10
   LABEL = mechanical part
   ANALYSIS = NLSTAT
   COUPLE(HEAT) = 20
   COUPLE(ELEC) = 30
   SPC = 1
   LOAD = 2
   NLCTRL(LGDISP) = 99

SUBCASE 20
  LABEL = thermal part
  ANALYSIS = HEAT
  IC = 100
  SPC = 11
  DLOAD = 12
  TSTEP = 13
SUBCASE 30
   LABEL = electric part
   ANALYSIS = MSEC
   SPC = 21
   DLOAD = 22

BEGIN BULK 
…
ENDDATA

Output

The supported output requests (example: DISPLACEMENT, STRESS, STRAIN, THERMAL, and so on) for the mechanical, thermal and electrical parts of the solution can be used to request the corresponding output for Coupling Analysis.

The NLOUT Subcase and Bulk Data Entries can be used to request intermediate results. On-the-fly .h3d output is also available in coupling analysis.

Guidelines

Here are some tips for coupling analysis modelling which can be useful to obtain meaningful results from a coupling analysis:
  1. Unit system must be consistent for all physical quantities in a model.
  2. When material density defined in the thermal material card is different from the mechanical material card, the density defined in mechanical material card takes precedence and will be used in thermal heat capacity calculation.
  3. TABLEM1 uses a different algorithm when referenced on a thermal material as opposed to a mechanical material.
    • The TABLEM1 entry when referenced on a thermal material, specifies corresponding multipliers for the base values defined in MAT4/5 entries to generate the final material properties.
    • The TABLEM1 entry when referenced on a mechanical material. The curve values replace the base values defined in MAT1.
  4. Ensure that the value of TTERM defined in NLCTRL makes the analysis duration realistic. TSTEP definition in the transient thermal subcase is not taken into consideration.
  5. Ensure that the time increment size defined by DT or NINC in NLCTRL is not too small in transient heat transfer analysis. A good DT or NINC value satisfies the criteria.
    Δ t > Δ L 2 ρ c / ( 6 k ) MathType@MTEF@5@5@+= feaahGart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaaeaaaaaaaaa8 qacqqHuoarcaWG0bGaeyOpa4JaeuiLdqKaamita8aadaahaaWcbeqa a8qacaaIYaaaaOWdaiabeg8aY9qacaWGJbGaai4laiaacIcacaaI2a Gaam4AaiaacMcaaaa@434A@
    Where,
    Δt MathType@MTEF@5@5@+= feaahGart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaaeaaaaaaaaa8 qacqqHuoarcaWG0baaaa@3876@
    Time increment size
    ΔL MathType@MTEF@5@5@+= feaahGart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaaeaaaaaaaaa8 qacqqHuoarcaWGmbaaaa@384E@
    Typical element dimension
    ρ
    Mass density
    c MathType@MTEF@5@5@+= feaahGart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaaeaaaaaaaaa8 qacaWGJbaaaa@36FF@
    Specific heat
    k MathType@MTEF@5@5@+= feaahGart1ev3aaatCvAUfeBSjuyZL2yd9gzLbvyNv2CaerbuLwBLn hiov2DGi1BTfMBaeXatLxBI9gBaerbd9wDYLwzYbItLDharqqtubsr 4rNCHbGeaGqiVu0Je9sqqrpepC0xbbL8F4rqqrFfpeea0xe9Lq=Jc9 vqaqpepm0xbba9pwe9Q8fs0=yqaqpepae9pg0FirpepeKkFr0xfr=x fr=xb9adbaqaaeGaciGaaiaabeqaamaabaabaaGcbaaeaaaaaaaaa8 qacaWGJbaaaa@36FF@
    Thermal conductivity
  6. Define TEMPERATURE(INITIAL) in a deck file. IC Subcase Information Entry defined in transient thermal subcase is not considered.
  7. It is always considered a good practice to define curves covering all possible time/temperature range and set 'FLAT'=FLAT for a good convergence.
  8. Ensure that 'EXTN' in TLOAD1/2, does not cause an unexpected shift in the curves when using subcase continuation (especially when there is a PRETENSION subcase).
  9. When electric field is present with electric contact, Joule heating in electric contact is also considered as a heat source automatically.
  10. When the thermal conductivity of the two sides of a thermal contact are very different in value, the time step increment size should be small enough to ensure that the analysis gets converged.
  11. In order to activate frictional heating, PCONTHT must be defined.
  12. On-the-fly .h3d results are recommended to be on.