Re: [sparta-users] ERROR: Collision cell volume is zero

[Poovathingal, S. <sav...@uk...>]

Pierre,

It happens sometimes with axis-symmetric simulations especially with when the ratio of grids (high density) to surface elements is small (small grids and large elements). It's a general floating-point issue where the surface cannot be infinitely watertight. Essentially, occasionally, a particle tunnels through inside the body. Our solution has been to tag the molecule for deletion but we also count/keep track of it. If we are deleting 1 particle in many timesteps, it's okay.  If we delete too much, we know it's a bad simulation. We reset our surface-element resolution.

If you go into collide.cpp, you can hack it a little bit for your need. Alternatively, make surface elements of different resolutions for different densities, which could fix the problem.

Savio
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Subject: [sparta-users] ERROR: Collision cell volume is zero

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Dear SPARTA users/developers,

I am having the following error with many of my simulations:

ERROR on proc 18: Collision cell volume is zero ~/workspace/sparta/src/collide.cpp:481)


The cases model an Earth reentry from 110 km to 72 km for a 1-meter diameter sphere using a 2D axisymmetric computation. All my simulations use the same geometry file, but the free-stream conditions change. I experience no issues from 110 km down to 86 km - the less challenging cases. However, the problem starts at 82 km and below.

The error occurs randomly after a few hundred thousand iterations (at 82 km, 78 km), and sooner - after just a few tens of thousands of iterations - at 72 km, during the "run" command. Occasionally, adjusting a single parameter, like FNUM by a small factor, resolves the issue or causes it to appear sooner or later.

I have noticed that the problem is more likely to occur with a large number of particles (approximately 1e8) and, on average, arises sooner with more particles. This suggests to me that the error might be caused by a rare, unhandled event in the code. However, I hope I am wrong and that there is another way to resolve the issue.

Has anyone else encountered this problem, and if so, how did you fix it?

Thank you in advance and best regards,

Pierre