SolidWorks Simulation Tech Tip: Initial Temperatures

A friend recently emailed me an article that CERN researchers had ‘discovered’ that materials could be brought down to temperatures BELOW zero Kelvin. And I thought, “That’s gotta be against the law”. But it also reminds me of a common pitfall one encounters when doing thermal simulations. So here’s a SolidWorks Simulation tech tip to help prevent your Thermal studies from running really, really cold.

When you are applying a temperature condition, there is a crucial difference in where you select on the screen. This is true when you are setting a temperature as a Load condition in a static stress/strain study, and it is also true when you are setting initial conditions in a time-dependent Thermal study. The difference is this: If you click in the graphics area on any face(es) of the model to apply a temperature, you are only enforcing that temp on the nodes that lie one the selected faces – you are NOT specifying the temperature on any of the nodes interior to the part. And if you don’t specify interior node temps, they default to zero, Kelvin.

The first image below is a laminated strip of nickel and aluminum, assembled at 22C reference temperature. A boundary condition of 50C is then applied, but to the FACES of the parts, (in fact, I used the handy menu option, “Select All Exposed Faces”, because I’m lazy). Since the Aluminum has a higher CTE than the Nickel, it should grow more, and the strip should bend down. But it actually bends UP.., because the cold, cold interior nodes are overpowering the temperature condition on the outer faces. (and, the stresses on the surface will be weird).

The second image below is a copy of the problem, but this time, in the dialog where you apply the temperature, I selected the ICON for the part files from within the Feature Manager. This works whether you select Parts in an assembly, or Bodies within a part – either way, picking the volume from the Feature Manager is the key to initializing all nodes of the mesh, inside and out, and so you see the strip bends downward, as we should expect.