Any tips for debugging MCNP geometry errors?

In summary, quarkle said to change all cells to have a void material, surround the geometry with a void sphere, and create a generic point source. He then ran MCNP for a very high number of histories and found the geometry errors.
  • #1
Kirk Truax
9
2
Hey all,

I was wondering if anyone had any good tips on debugging mcnp geometry? I'm an intermediate user working on better understanding the program. Does anyone have any tips or tricks that go beyond simply reading the manual?
 
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  • #2
Hi
I think there are no easy answers or ready-made solutions. For my part I use a X-server (X-ming for me) and look at the geometry in XY, XZ AND YZ. But it is true that for complex geometry you can not see everything. With x-ming you can also see the cookie-cutter.
PSR
 
  • #3
or you can try using MCNPX Visual Editor
 
  • #4
If you have a tiny or non-obvious geometry error (caused by rounding off errors, overlaps, skewed lattice etc) that you can't find with the MCNP plotter or Visual Editor, the following technique can help you pinpoint the error:
- Change all cells to having a void material, but a non-zero neutron/photon importance.
- Surround the entire geometry with a void sphere, again non-zero particle importance
- Surround the sphere with a zero importance void as usual.
- Create a generic point source somewhere within the geometry.
Run MCNP for a very high number of histories. If there are any geometry errors, the run will terminate because of lost particles. You can find the coordinates of the lost particles in the output and file and use those to pinpoint the error.
 
  • #5
I did what quarkle said and strangely without material the error disappeared, Is that mean losing particles are not caused by geometry error ?
 
  • #6
Show us the input file, or a simplified input file that still shows the issue. The trick is to make things fast for large numbers of particles. If it's fixed the issue, you may have an obvious undefined area around your problem. Or you didn't set the importance correctly.
 
  • #7
No sorry, I found the geometrical error , maybe number of particles were not large enough in the previous run (without material) to reach the erroneous parts of geometry.
 
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Likes Alex A

Related to Any tips for debugging MCNP geometry errors?

What is MCNP Geometry Error Tips?

MCNP Geometry Error Tips is a set of guidelines and suggestions for avoiding common errors when creating geometric models in MCNP, a computer code used for simulating and analyzing radiation transport.

Why is it important to be aware of MCNP geometry errors?

If not addressed, geometry errors can significantly impact the accuracy and reliability of MCNP simulations, leading to incorrect results and potentially misleading conclusions. Therefore, it is crucial to be aware of these errors and how to avoid them.

What are some common geometry errors in MCNP?

Some common geometry errors in MCNP include improper use of universes, incorrect use of cell cards, and non-overlapping volumes. These errors can arise due to incorrect input of parameters or misunderstandings of the code's syntax and logic.

What are some tips for avoiding geometry errors in MCNP?

Some tips for avoiding geometry errors in MCNP include always double-checking input parameters and syntax, using the appropriate plotting tools to visualize the geometry, and breaking large geometries into smaller, more manageable parts. It is also essential to refer to the MCNP manual and seek help from experienced users if needed.

How can I ensure the accuracy of my MCNP geometry?

To ensure the accuracy of your MCNP geometry, it is recommended to perform various tests, such as checking for overlapping volumes, verifying the results with other codes or hand calculations, and comparing the results with physical measurements. It is also essential to document and track any changes made to the geometry to avoid confusion and potential errors.

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