Simulation of Thermal Expansion. [Please help...I am so frustrated]

[lawrence528]

Hi everyone,


I am trying to simulate the thermal expansion of a cubic model under Global temperature load.


My question is how to constraint the model so that expansion can be seen on EVERY surfaces? For some reasons Wildfire 4.0 requires not a point, not an edge but at least one surface to be fixed in order to run the analysis.


I tried placing another model underneath and defined the interface between two models as "contact" with infinite friction enabled. However the result was totally incorrect even though expansion did appear on all surfaces.


Any advices would be greatly appreciated!!



Lawrence

 

[brep]

This is a common issue (actually a fact of life) with any FEA you choose to use. You need to make sure that the body is constrained correctly to eliminate rigid body motion (unconstrained translation or rotation) but allow it to expand freely in the required directions.

For your cube (or indeed any model!) you do this with 3 separate point constraints. Example in a 100mm cube: constrain the origin (0,0,0) of the cube in X,Y and Z TRANSLATIONS. Constrain the point (100,0,0) in Y, Z TRANSLATIONS. Constrain point (0,0,100) in Y TRANSLATION. That's all you need, there are 6 degrees of freedom constrained. The cube will expand as required/expected with a global T load.

 

[corus]

..or simply use symmetry conditions on 3 faces of a quarter cube model.

 

[brep]

Of course Corus is absolutely correct in this case, the use of symmetry makes the most sense! In other cases where you cannot exploit symmetry it is worthwhile to understand how to use the 3 point constraint technique (as I described.)