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-   -   snappyHexMesh stops meshing (http://www.cfd-online.com/Forums/openfoam-meshing-snappyhexmesh/128932-snappyhexmesh-stops-meshing.html)

Tensian January 24, 2014 07:45

snappyHexMesh stops meshing
 
1 Attachment(s)
Hi Foamers,

I am trying to simulate flow across a channel with two inlets, an outlet and a wall. The model have to take in count heat transfer. I have four separated stl files (one for each boundary) and I am meshing it with OF native meshers.

I am having some problerms with snappyHexMesh. It looks a good choice for meshing but it's quite difficult to understand what this mesh generator is doing and how to set all parameters in order to obtain an optimal mesh.

When I use snappy, sometiemes I am getting errors that I cannot understand. Basically, I have three situations:

1. snappy stops meshing without no information in the log file. I attach some cases at the end of the post.
2. snappy gives an error message when creating layers in step three.
3. snappy shows a message about memorym usage.

I am running about three or four executions of snappy simoultaneously. Could this be the source of the errors?I think the CPU have enough power and memory for do that, but I am not really sure...

Also I am having problems with the use of surfaceFeatureExtract. The surface is better represented, but the mesh doesn't pass checkMesh test (skewness mainly). Have I to use this tool for all my stl files or for example is enough to use it for wall.stl?

And with layers creation, I have never achieved a good visualization of layers, because they are always collapsed in some sharp places andf sometimes they are simply not created. Does somebody have any hint about that issue?

Thanks in advance for all the help provided!If more files are needed I can provide it...

Ruli January 25, 2014 06:23

Hi Tensian,

Quote:

Originally Posted by Tensian (Post 471593)
1. snappy stops meshing without no information in the log file. I attach some cases at the end of the post.

I will test it when I have got time.

Quote:

Originally Posted by Tensian (Post 471593)
2. snappy gives an error message when creating layers in step three.

How does it look like?

Quote:

Originally Posted by Tensian (Post 471593)
I am running about three or four executions of snappy simoultaneously. Could this be the source of the errors?I think the CPU have enough power and memory for do that, but I am not really sure...

How many cells does the mesh contain? Snappy is very RAM-intensive, especially in the layer addition phase. I would say you need 2-3 times the number of cells in GB RAM.

Bye
Julian

Tensian January 26, 2014 10:54

Hi Ruli and thanks for your interest,

Quote:
Originally Posted by Tensian http://www.cfd-online.com/Forums/ima...s/viewpost.gif
2. snappy gives an error message when creating layers in step three.

How does it look like?

The layer mesh is not being created. You can see all the information in log_stopped_layercreation (attached in previous post).

Anyway, I attach a new case with problems in layer creation (snappyDict, log file and a image with layers collapse). This time the layers are created, but they collapse in an unknown way. Maybe somebody could give me any hint on this. I am using surfaceFeatureExtract for preserve the feature edges of my geometry.

Quote:
Originally Posted by Tensian http://www.cfd-online.com/Forums/ima...s/viewpost.gif
I am running about three or four executions of snappy simoultaneously. Could this be the source of the errors?I think the CPU have enough power and memory for do that, but I am not really sure...

How many cells does the mesh contain? Snappy is very RAM-intensive, especially in the layer addition phase. I would say you need 2-3 times the number of cells in GB RAM.

The number of elements of the final mesh is around 3-4 million cells. I will work carefully then due to memory requirements of snappy. By the way I have 32 Gb RAM and 8 procerssors, so it will be enough!

Thanks, I am impatient with finding the solution of the problem!


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