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# RBE elements with conductivity in THERMAL SOLUTION 153

Phenom

Hello Experts,

can RBE2 elements in thermal solution 153 (steady state) transfer temperature information?

I have a model with solids and screws as beams with rigid spiders (RBE2) and thermal definitions on solid surfaces (heat flux and convection). Although I did not define any heat transfer value onto beams they provide varying nodal temperatures. Where do they come from?

Any suggestion will help.

Best regards, Michael

5 REPLIES

# Re: RBE elements with conductivity in THERMAL SOLUTION 153

Solution Partner Phenom

Dear Michael,

Yes, in fact, a Coefficient of Thermal Expansion CTE for any Rigid element using Lagrange multiplier method can be entered to use with NX NASTRAN.

Thermal expansion on the RBE2 elements is calculated when:
• ALPHA is defined on the rigid element definition.
• The case control RIGID = LAGRAN is defined.
• The grid point initial and load temperatures are defined using the TEMPERATURE case control command on the grids defining the rigid element connectivity.

The change in temperature is the difference between the grid point temperatures selected with the TEMPERATURE(LOAD) and TEMPERATURE(INIT) case control commands.

On RBE1, RBE2 and RBE3 elements, an average load and initial temperature value is calculated for each leg of the element using the values on the independent/dependent grid pairs such that each leg can have a different thermal strain if the temperatures vary at the grids.

Best regards,
Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/

# Re: RBE elements with conductivity in THERMAL SOLUTION 153

Siemens Phenom

CTE is for thermal expansion in a structural analysis.

I believe that the original question was about thermal conductivity (alpha) in a thermal analysis. In a thermal analysis, the unknown dof is a termperature at each grid. The RBE2 is a constraint that couples the temperature at the independent grid to the temperature at dependent grid(s). In that sense, it is a perfect conductor.

# Re: RBE elements with conductivity in THERMAL SOLUTION 153

Phenom

Dear Blas, dear JimB,

I will answer both thread lines at once.

JimB was right and the answer is exactly what I was looking for. Thank you.

Is it the same with glueings connections?

Blas_Molero, the information about giving a RBE element a linaer expansion coefficient of was really very interesting. Thank you, too.

With besat regard,

Michael

# Re: RBE elements with conductivity in THERMAL SOLUTION 153

Solution Partner Phenom

Dear Michael,

To learn more about GLUE Surface-to-Surface Thermal Coupling please visit the IBERISA Support page where a HEAT TRANSFER Coefficient = 40E3 W/m2ºC between PCB and Chip is defined used the GLUE condition, here you are in the following address:

http://www.iberisa.com/soporte/femap/termico/Heat_Transfer_from_Chip_to_PCB.htm

GLUE Surface-to-Surface Thermal Coupling

Best regards,
Blas.

Blas Molero Hidalgo, Ingeniero Industrial, Director
IBERISA • 48004 BILBAO (SPAIN)
WEB: http://www.iberisa.com
Blog Femap-NX Nastran: http://iberisa.wordpress.com/

# Re: RBE elements with conductivity in THERMAL SOLUTION 153

Phenom
Hello Blas, thank you for the documentation. It is very helpful. Michael