Any alternative to SAWTOOTH option in FDS6.6

[Ravi Kumar Siddana]

Hi,

Recently I have moved from FDS5.3 to FDS 6.6.  I noticed that "SAWTOOTH" feature which helps in smoothing CURVED/INCLINED obstructions in FDSV5.3 has been eliminated in FDS6.6.

Is there any other option to smooth such obstructions in FDS6.6. Any suggestions are most welcomed.

Thanks & Regards,
Ravi Siddana

[Salah Benkorichi]

Well, you can refine your mesh to get more smoother objects. You don't have to do it for entire domain, you might have one local mesh for the object of interest and coarser one for the domain. 

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[Kevin]

This feature was removed because it did not work as intended. There is work currently underway to implement an immersed boundary method that will account for obstructions that are not stair-stepped.

[Ravi Kumar Siddana]

OK. Thank you for your suggestion. Just to confirm that when i am splitting zones for local mesh, they should be aligned with sizing. isn't it?

that's going to be more hectic. 

[Ravi Kumar Siddana]

Thank you for reply. when can we expect that feature?

[Salah Benkorichi]

Check a section in user guide called mesh alignment. That should explain it. If there is not clear let us know.

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[Ravi Kumar Siddana]

Thank you for sharing. my doubt is giving fine mesh will change shape of an obstruction defined by its coordinates?

[Salah Benkorichi]

I give a simple example, suppose you want to create a sphere, in FDS, currently, we use cube cells, so you would ended up by having large cube instead of a sphere. To get around this, is to refine your mesh, which will allow you to avoid having OBST at the edges of your big cube, smoothing it to a sphere (not perfectly sphere though). Also, either you need to use packages as Pyrosim or Blender, to get it done, or write your own script to create the OBST lines that meets the needs for your shape if it's complex. 

On 7 December 2017 at 18:13, Ravi Kumar Siddana <sravi...@cadfem.in> wrote:

Thank you for sharing. my doubt is giving fine mesh will change shape of an obstruction defined by its coordinates?

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[Ravi Kumar Siddana]

Thank you so much Salah for your suggestions. Actually we are importing blocks from AUTOCAD to fds using 3DtoFDS option. Earlier we used to typical blocks and appied SAWTOOTH which helped in getting good represent of obstructions. Now seems we have left with an option of taking very fine blocks in AutoCAD to represent the shape of obstructions.

Thanks & Regards,
Ravi

[Salah Benkorichi]

Yes, true, if you need to reduce the resolution. This issue will be tackled in the near future as Kevin already stated. There is already an ongoing work on this.

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[dr_jfloyd]

While reducing the grid size will let you have a surface that looks better in Smokeview, it will also increase the computational time (more grid cells and smaller time steps). You should evaluate if there is any significant benefit to your specific problem in the added computational expense.

On Friday, December 8, 2017 at 7:09:32 AM UTC-5, Salah Benkorichi wrote:

Yes, true, if you need to reduce the resolution. This issue will be tackled in the near future as Kevin already stated. There is already an ongoing work on this.

On 8 December 2017 at 01:39, Ravi Kumar Siddana <sravi...@cadfem.in> wrote:

Thank you so much Salah for your suggestions. Actually we are importing blocks from AUTOCAD to fds using 3DtoFDS option. Earlier we used to typical blocks and appied SAWTOOTH which helped in getting good represent of obstructions. Now seems we have left with an option of taking very fine blocks in AutoCAD to represent the shape of obstructions.

Thanks & Regards,
Ravi

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[image: ANSYS_DiscoveryLive_600x74_DesignWorld_Download.png]
<https://goo.gl/Fj9fPF>

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[Ravi Kumar Siddana]

Hi,

We are importing fine blocks from auto cad to FDS however we are not getting the proper shape as expected. FDS is considering only coarse blocks. Files are attached for reference. Is it because of the mesh size we are using?

 

Regards,

Ravi

[dr_jfloyd]

OBSTs will snap to size of the local grid.  This is what looks to be happening in FDS.png.