Mesh sizing help

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Ntamoafo

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Oct 5, 2022, 2:58:44 PMOct 5
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Hello,

I am simulating an object that has its thickness larger than that of a unit cell mesh. I am not able to make my mesh smaller due to the computational time. Is there a way to allow FDS to predict the mesh size needed for a simulation to be effective? This is a solid phase. Will FDS still simulate it accurately if the mesh is thicker than the object thickness?

dr_jfloyd

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Oct 5, 2022, 3:53:36 PMOct 5
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The XB on &OBST defines how many grid cells or grid cell faces are defined as being solid for the fluid calculation. The THICKNESS on &SURF is used for the solid phase heat transfer calculation. So your THICKNESS does not have to be the same as the gird size defined by &MESH. They are independent. 

Ntamoafo

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Oct 6, 2022, 3:13:30 PMOct 6
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Hi dr_jfloyd thanks for your response. To be sure I understand an example is my object thickness in &SURF is 15mm and a unit cell of my mesh has a z (thickness) of 20mm, meaning the unit cell is larger than the thickness of that object in the computational domain. My goal was to ensure the object has a number of unit cells going through it for accurate calculations. Does this not happening still ensure accurate calculations? Hope its clearer now?

dr_jfloyd

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Oct 6, 2022, 6:12:54 PMOct 6
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The 1D wall noding is completely independent of the MESH size. The THICKNESS on SURF is independent of the OBST XB. If you have a 10 cm mesh and define a OBST that is 50 cm thick based on XB but assign a SURF with a THICKNESS of 30 cm, the 1D wall noding will be based on the 30 cm THICKNESS and not the 10 cm MESH size or the 50 cm OBST size.

Ntamoafo

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Oct 7, 2022, 9:50:35 AMOct 7
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Alright. Thank you. How do I see the meshing that FDS uses to solve the solid phase? I saw in a previous discussion with someone else that its in the manual and the .out file but not seeing that information.

dr_jfloyd

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Oct 7, 2022, 10:43:37 AMOct 7
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Look for the section of the .out file that echoes the MATL and SURF information. For each SURF with a MATL it will give the noding.
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