SimScale CAE Forum

Error in Simulation

I was trying do do a simulation of the aerodynamics of a car, when I got this error. I have no idea how to fix it so I would appreciate any help.

Project Link: SimScale Workbench

Hi there, have a look here:

My guess is that you will have to re-set the region refinements and the local element refinement, as the rest of the settings look good. (The region refinements are not even visible on the final mesh, make sure to decrease the maximum length input)

Best regards,

The point where the problem occurs is the center (I think) of the Rear Wheel, what could that be caused by?

Indeed, this means that you should refine the mesh especially there

So the problem is, that there is that weird green part which causes the error and I have to remove it in, say, solid edge?

These green cells are considered “bad”, as they have really high values, the way to solve this issue is to refine these areas, with region refinements for example. As I mentioned before, you have a couple of region refinements in you run, but with a large maximum length limit, so they are negligible right now.

Wait so you are saying I have to make a small region refinement for just that point or I have to make the existing ones smaller?

I recommend to decrease the maximum length size of your existing refinements as a start, otherwise it does not make sense to have them, they have no impact. If the issue insist there, you can try to add a dedicated region for your wheels too, with an even smaller maximum length size. Does this make sense?

That makes sense, do I have to decrease it as much, so that it “touches” the car, or leave space between?

I am afraid I do not understand what you mean, you will decrease the maximum edge length, that determines the size of the cells inside this region, it is this option:
Screenshot from 2021-02-18 12-32-33

Ohhh I thought of the completely wrong thing, my bad, do I have to decrease it only for the large one or also for the small one?

Neither of them has an impact, so I would definitely say both :slight_smile:

How much do you think I should decrease it? Like to 0.01 or even less for example? Also, after doing that, can I just run the simulation again or do I have to delete the mesh and make a new one first?

After you change the settings, you will have to re-generate the mesh.
I would go for a 0.006 for the big box and 0.004 for a start, and see how this goes. If it takes a long time to be generated, you can cancel the mesh and increase the length sizes.

That worked :smiley: One question, in which unit is the drag coefficient measured? Is it newtons? Don’t wanna mess that up :slight_smile: Btw I really appreciate you answering/helping so quickly, so thanks a lot for that

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Sure thing, the forces are in N, the coefficients are dimensionless though

What does dimensionless mean?

Actually another question :smiley: The new car looks like it has less drag (it should obviously because we tried to improve it, but the drag graph says 0.00075 for the old one and 0.001 for the old one, does that mean, that the new one has more air resistance/drag?

Edit: And is the Drag Coefficient a good way to measure the aerodynamic improvements from the old to the new car?

This page describes this parameter: Drag coefficient - Wikipedia

The answer is yes, it is a good way to measure aerodynamic performance. The smaller the value of the coefficient, the less the aerodynamic resistance (drag).
Check this blog too, you might find this interesting :slight_smile: Aerodynamics of Road Vehicles in the Computational Domain

Oh so the new one has more drag than the old one? Where does that come from? In the images it looks like the new one is better off.


Keep in mind that these are not using the same scale, so the maximum pressure of the old one is different than the maximum pressure of the new one. What I mean is that you can only compare these colored images if they are using the same pressure range for their scales.