User Forum of Software BASEMENT

Dominik

User

From: Bern

Registered: 2018-09-26

Posts: 19

Basement Error: Neg. Area of triangles

Hello everyone,

I'm trying to run a simulation and keep getting the following error:

"Simulation stopped due to error(s):
Negative value for area of element #58583!
Check the element node definition sequence.

Basement must be terminated now.
Check 'AareV8_DV_restart.err' for details"

And when I open the specified file:
ERROR -> Negative value for area of element # 58583 !
   Check the elment node definition sequence.

However, when looking at the element in a GIS Software the element has an area of 0 (which is certainly small but not negative).

Therefore, I got two questions:
1. I got multiple triangles with an area of 0m2. Is that a problem and if so, how could I avoid such small triangles? By trying the option "minimum triangle angle" I could not prevent such small features so far.

2. How do I have to handle the error described above? Is there a workaround?

Cheers and have a nice day
Dominik

Last edited by Dominik (2019-04-10 07:36:44)

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Dominik Vogt
MSc Student Institute of Geography University of Berne

Matthias Bürgler

Developer

From: Zürich

Registered: 2019-04-04

Posts: 150

Re: Basement Error: Neg. Area of triangles

Hi Dominik

This error message is produced if cell areas are smaller or equal than 0.0. The only way you can handle the described error is by improving your mesh.

The quality of the mesh is a major factor influencing the accuracy of the simulated results, therefore sufficient time should be spent on mesh generation. Further, the computation time is directly related to the element size via the CFL number. Having very small elements can significantly slow down your simulation.

Since i don't know how your mesh looks like, makes it difficult to determine where the problem lies in your case.

Some general advice: Try increasing the minmum triangle angle (i recommend >=32°) and using only as few breaklines as necessary.

Best regards
Matthias

Dominik

User

From: Bern

Registered: 2018-09-26

Posts: 19

Re: Basement Error: Neg. Area of triangles

Hi Matthias,
thank you very much for the reply. I could solve this specific issue by creating a new feature class in ArcGIS and add the data to the newly created feature class. I must have messed up the shapefile as there were other errors as well.
The suggest to use large triangle angles might not be good fore me. As far as I know this will increase the number of triangles in the mesh and will therefore produce much smaller triangles which lead to greater computation times. I guess this will not work for my case as I need to perform up to 50 simulations of an area of 57'208'366m2. Indeed my breaklines are rather detailed, I might have to delete some.

Might it be an idea to include a feature for minimum triangle areas in future basement versions?

Cheers and happy Easter time!
Dominik

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Dominik Vogt
MSc Student Institute of Geography University of Berne