Boundary conditions > Simulation objects > Simcenter 3D Thermal/Flow, Electronic Systems Cooling, and Space Systems Thermal simulation objects > Thermal Coupling — Advanced

User function thermal coupling

The User Function type of the Thermal Coupling — Advanced simulation object creates a linear conductance proportional to the overlap area of the primary region elements and the secondary region elements. If you select a non-geometric element as the secondary region, the User Function type creates a linear conductance from each primary region element to a non-geometric element proportional to the primary region element areas.

The proportionality factor is specified by the user defined subroutine USERF.

The USERF subroutine provides a programmable extension for table interpolation. It allows you to alter parameters taking into account more complex behavior than simple table interpolation.

You specify the Correlation Number which represents the value of the variable ITAB in USERF subroutine.

You can write any complex correlation in your USERF subroutine for the proportionality factor VDEP. VDEP represents the heat transfer coefficient. For example, your VDEP variable can be function of time or temperature of other elements.

A single USERF subroutine may contain several correlations. The model refers to these correlations by creating separate User Function couplings, each with a different Correlation Number.

You can use groups that contain elements or nodes in user subroutines, but you cannot use groups that contain only model geometry as the thermal solver does not write these kinds of groups to the scratch file.

Note:

You specify the path to the include file containing the USERF subroutine on the Thermal page in the Solution dialog box.

Sample user defined subroutine

The following example of the USERF subroutine contains two correlations:

The first correlation is associated with table 7 and sets the heat transfer coefficient to 2. In the Thermal Coupling — Advanced dialog box with the Type set to User Function, enter 7 in the Correlation Number box.
The second correlation is associated with table 4 and sets the heat transfer coefficient as a function of time. In the Thermal Coupling — Advanced dialog box with the Type set to User Function, enter 4 in the Correlation Number box.

SUBROUTINE USERF(ITAB,IDEP,VDEP,CHARA,+GG,T,C,Q,QD,R,TIME,DT,IT,NOCON,MAXNO,ICONV,DTP,TF)CC This subroutine provides an alternative to table interpolationC functions. If the independent variable code on TABTYPE CardC ITAB is “USERF”, then instead of performing table interpolationC the Analyzer enters the subroutine USERF. This way,C table-dependent functions may be replaced by user-written logic.C  DIMENSION GG(*),QD(*),T(*),C(*),Q(*),R(*),ICONV(*)C  IF(ITAB.EQ.7)THENCC For conductance number IDEP which is associated with table 7C the heat transfer coefficient is set to 2.C   VDEP = 2  ELSE IF(ITAB.EQ.4)THENCC Different correlation — in this case associated with table 4C	 VDEP = 3.14+TIME*10  END IFC  RETURN  END

Note:

For more information, see Thermal Solver API Manual .

How do I

Create a 1 Way Thermal Coupling

Create a user function thermal coupling

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Inputs to expressions

Specifying a Coupling Resolution

Using the Only Connect Overlapping Elements option

Using the Overlap Projection Direction option

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1 Way options

User Function options

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Thermal Coupling — Advanced dialog box

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Simcenter 3D Thermal/Flow, Electronic Systems Cooling, and Space Systems Thermal boundary conditions

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