Search found 63 matches

by tibich72
28 Apr 2011, 22:12
Forum: ElmerSolver
Topic: Cooling problem
Replies: 27
Views: 14981

Re: Cooling problem

Hi Juha, well, that body (the heatsink), should not be part of the air domain, but maybe I don't understand how to set up the model. Basically, I have a body that models the air, and for that I solve the heat equation as well as Navier-Stokes; all the other bodies (including the heatsink) are not fl...
by tibich72
28 Apr 2011, 21:11
Forum: ElmerSolver
Topic: Cooling problem
Replies: 27
Views: 14981

Re: Cooling problem

Hi Juha, the heatsink is body #2, name "HS_1", with this def: Body 2 Name = "HS_1" Equation = 1 Material = 1 Target Bodies(1) = 2 End Thanks for the clarification regarding the +/- rule. I'll have to re-run the system with all the boundaries between fluids and solids having a wal...
by tibich72
28 Apr 2011, 19:29
Forum: ElmerSolver
Topic: Cooling problem
Replies: 27
Views: 14981

Re: Cooling problem

There still seems to be something strange (if not wrong) with my model. I've added boundary conditions to each face between air and solids in my model, and now everything is much hotter than before (by about 70C). Moreover, if you look at this slice through the middle of the model (and through the h...
by tibich72
28 Apr 2011, 17:34
Forum: ElmerSolver
Topic: Cooling problem
Replies: 27
Views: 14981

Re: Cooling problem

Juha, thanks for the clarification. I understood your previous post to imply outwards -> inwards for plus. Having '+' in the direction of outward pointing normal makes sense.

Cheers,
Tibi
by tibich72
28 Apr 2011, 16:57
Forum: ElmerSolver
Topic: Cooling problem
Replies: 27
Views: 14981

Re: Cooling problem

Hi Juha, thanks again for the information. However, I'm wondering whether it's always the case that a '+' is outwards->inwards. I'm attaching two images from Paraview showing the velocity vectors on a slice through the middle of the model. vel_vect_plus.jpg vel_vect_minus.jpg As you can see, in the ...
by tibich72
27 Apr 2011, 19:13
Forum: ElmerSolver
Topic: Cooling problem
Replies: 27
Views: 14981

Re: Cooling problem

Juha, thank you very much for your reply. I've updated the model with the correct speeds, but I still have some issues with air speed. Just as a clarification. When I set the air speed to a value (say 13.6 in my case), how does Elmer know whether the flow is from the outside towards the inside of th...
by tibich72
27 Apr 2011, 17:36
Forum: ElmerSolver
Topic: Cooling problem
Replies: 27
Views: 14981

Cooling problem

Hi, I've inherited a system that uses Elmer to simulate cooling electronic components. Basically, we model the components in 3D, then immerse them in a box of air and specify an air flow. I'm not an expert on FEM and/or thermal analysis and now I have to modify the system a bit for a new problem. He...
by tibich72
22 Mar 2011, 18:31
Forum: ElmerSolver
Topic: Mesh size and accuracy of results
Replies: 1
Views: 2523

Mesh size and accuracy of results

Hope I've posted in the correct forum -- if not, please move to appropriate place. I'm working on a simple problem which consists of a board, and component consuming power, all placed within an airbox. Elmer solves flow and heat equations. The ambient temperature (i.e. the temperature at the boundar...
by tibich72
01 Dec 2010, 19:26
Forum: ElmerSolver
Topic: Divergence (with NaN steps) for Navier-Stokes equation
Replies: 16
Views: 12984

Re: Divergence (with NaN steps) for Navier-Stokes equation

Here's a solution to defining physical volumes for Gmsh meshing when importing a .brep (or .step or .igs) file for meshing. It's not an Elmer thing per se, but it may be useful for other people since Gmsh+Elmer seems to be pretty popular. I'm attaching "demo.geo", and then comment it a bit...
by tibich72
01 Dec 2010, 16:58
Forum: ElmerSolver
Topic: Divergence (with NaN steps) for Navier-Stokes equation
Replies: 16
Views: 12984

Re: Divergence (with NaN steps) for Navier-Stokes equation

Hi, Thank you very much for all these suggestions. First, let me say that using -autoclean in elmergrid did the trick -- elmersolver now finishes and produces the same results as some other older test cases. However, what Peter said about physical entities makes me nervous. On a couple of small test...