A Geometry Trap for SolidWorks FlowSimulation

by Fuyang

Geometry check results - Invalid contacts and invalid parts

Geometry check results – Invalid contacts and invalid parts

I have been using SolidWorks Flow Simulation for sometime, and usually, in most cases, it works just fine. However this week, I encountered this small geometry issue which seemingly brought me a big headache.

The first geometry trap (and yeah, there is a second trap blow, just keep reading), as the plot shows above, is making the Flow Simulation cannot find the correct flow domain geometries. By using the Check-Geometry tool provided by the Flow Simulation software, it gives errors called “Invalid contacts” and “Invalid part”.(One will see this is not a leakage issue, if he or she continues reading on.)

This is somehow a little bit strange because the issue is within a sub-assembly, which has been successful  through the air-tight-check on the simple tool FloXpress, done by my colleague. But when I include this sub-assembly in to the top-assembly, the above errors show up while doing geometry check and no flow domain can be obtained… Anyway, all the problems are located in the part connection shown as below:

Overview 1

Problem parts

 

Note the problem happens on this internal geometry, which also indicates that the previous issue is not a leakage issue, but a geometry error, or invalid geometry. If one make a cut plot and zoom in to the connection where the pipes meet the baffle, one will see some of the intersection parts look like things below (the two figures above):

WrongModel_2WrongModel_1
WrongModel_3_1WrongModel_3

The idea of drawing the baffle which should be perfectly contact with the pipe is: firstly draw a block with a perfect round top surface (A) which has a diameter exactly as pipe diameter plus shell thickness (above lower figures); secondly make a shell operation through surface (B) and (A).

The reason those parts afterwards don’t contact well have showing up miss-alignments is simply because, some part of the edge of round surface A is connected to some fillets.

Look at the upper pictures on the right side, since there is a fillet surface marked as blue color, when adding a shell performance, the thickness is probably calculated based on the norm direction on the fillet surface thus the shell body will be slightly bent as shown in the red line. This will give a miss-alignment in the model after adding the pipe in.

So in short, the first geometry trap can be concluded as: be special caution while doing a shell performance on a surface which is connected to some fillet or other tilted surfaces.

——————————————————————————————-

Initially, after we saw the above miss-alignment, we decided a quick fix by using the “cavity” tool, simply cut the intersecting parts out from the baffle by using the pipe body.

This solves the problem of “flow geometry not found”. But there is still error or warning messages on some invalid contacts. We didn’t pay attention to that and just went on with the simulation however the following picture is what we got after we started running the simulation:

Error2

 

Yes, you saw it, a software crash or dead…

 

So here is the second geometry trap – the real trapIf one does not solve ALL the “Invalid contact” or “Invalid parts”, found by the flow simulation geometry check tool, even though one can get the flow domain and proceed with simulation, one may later suffer simulation/software frozen issue…

Also one thing worth mentioning is that, while those invalid contacts exist, it is extremely lagging or time consuming while doing some normal simulation setup operations and geometry check operations. So if you suddenly feel a new model is slow than usual while setting up, there probably might exist those “invalid” stuff in your model. I suggest you fix them first before going any further.

CorrectModelI am not sure whether the second trap can happen in all circumstances but in our case, later on we simply changed the baffle part and make sure the fillet is ended before it touches the boundary of the round surface which is used for guide a shell operation, all problem solved.

So if you have read so far, here is a post written by Christopher Ma –  4 Things to Do Before Every Flow Simulation Analysis. I believe if one follows the process described within this article, make sure all the invalid things are fixed, the chance of software/simulation crash can be minimized.

Thank you for reading so far, hope this article can give you some hints and as always, do have fun with simulations 🙂