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Author Topic: Duplicated obstructions in FDS export  (Read 6696 times)

Andreas

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Duplicated obstructions in FDS export
« on: September 24, 2012, 03:14:59 am »

Hello,

I started building a large geometry and experienced some strange misbehaviour. A large number of obstructions which do exist once in the model are written twice in the output. The additional obstructions are dedicated to the first object that is listed in the model-category. I added a screenshot for clarification. I beneficial I could provide the Pyrosim file to the support team.

Thanks a lot for any suggestion!
Andreas

edit:
the community software's upload folder seems to be full. Here's the screenshot:
http://dl.dropbox.com/u/70693234/pyrosimscreenshot.JPG
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Charlie Thornton

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Re: Duplicated obstructions in FDS export
« Reply #1 on: September 24, 2012, 08:42:35 am »

I suspect that, instead of a bug, you are seeing sub-blocks of your obstruction needed to describe the object to FDS. I notice that none of the records are duplicate lines because they differ in the XB field. This is the expected behavior if you have a block has been rotated in PyroSim and must be decomposed into axis-aligned boxes for FDS. I've attached a couple images to illustrate.
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Andreas

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Re: Duplicated obstructions in FDS export
« Reply #2 on: September 24, 2012, 09:56:39 am »

Hi Charlie,
thanks for your quick reply! I'm afraid your suggestion doesn't apply. The obstruction is just an outside wall which fits to the mesh (please see screenshot)
« Last Edit: September 24, 2012, 11:48:54 am by Andreas »
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Andreas

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Re: Duplicated obstructions in FDS export
« Reply #3 on: September 24, 2012, 09:59:52 am »

When I export the geometry as fds file and try to reimport it, most of the chairs (that's what "Stuhl" means) and tables will show up twice at the same position. I'm afraid this might be bug.
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Charlie Thornton

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Re: Duplicated obstructions in FDS export
« Reply #4 on: September 24, 2012, 12:24:48 pm »

Can you post the PSM file or send it to support@thunderheadeng.com?
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Andreas

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Re: Duplicated obstructions in FDS export
« Reply #5 on: September 25, 2012, 09:08:23 am »

I've just sent it. Thank's for having a look at it!
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Charlie Thornton

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Re: Duplicated obstructions in FDS export
« Reply #6 on: September 25, 2012, 01:27:00 pm »

(I added additional space for attachments.)

I think I understand at least a portion of what is going on. There still may be a problem with duplicate obstructions, but first I need to understand your Angled Geometry conversion settings.

I've attached a screenshot that highlights the two non-default options active in this model. The Conversion Filtering option controls what objects will be chopped up into blocks and then reassembled into FDS-safe axis-aligned blocks. By default, PyroSim will not modify axis-aligned objects because they can be used directly by FDS. Selecting Rasterize all objects forces PyroSim to decompose axis-aligned blocks. The benefit of this option is that it gives you explicit knowledge of object dimensions in the simulation as opposed to trusting FDS to snap objects to the correct grid line, but the cost is that you can potentially get lots of extra obstructions.

When PyroSim converts an object to blocks, the object is decomposed against any grids it is touching, then (if the Block Size setting permits) joined up into the largest combinations possible. During this process, objects will invariably overlap, leaving multiple single-cell blocks in the same location.

To decide how to resolve overlapping objects, PyroSim uses the merging options. By default, if multiple blocks have identical properties (e.g. all six surfaces), the duplicates will be discarded and only one will be retained. By default, the Ignore names while merging option is disabled. This means that two objects will not be considered "identical" if they have different names. When that option is enabled, name information is not considered as part of the comparison.

With that said, there appears to be a problem with the merging portion of PyroSim. It is giving you a lot of single cell objects where it could easily merge them into larger blocks. On the other hand, I could not find an OBST record (from "Auusenwand Links") that was repeated/duplicated in the input file. They all appeared to be the individual blocks that made up that wall.
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Andreas

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Re: Duplicated obstructions in FDS export
« Reply #7 on: September 25, 2012, 03:11:06 pm »

I've attached a screenshot that highlights the two non-default options active in this model. The Conversion Filtering option controls what objects will be chopped up into blocks and then reassembled into FDS-safe axis-aligned blocks. By default, PyroSim will not modify axis-aligned objects because they can be used directly by FDS. Selecting Rasterize all objects forces PyroSim to decompose axis-aligned blocks. The benefit of this option is that it gives you explicit knowledge of object dimensions in the simulation as opposed to trusting FDS to snap objects to the correct grid line, but the cost is that you can potentially get lots of extra obstructions.
Yes, I noticed that many obstructions didn't fit to the mesh with some 0,0001m difference. I try to do a sensitivity study if there is any additional ram requierement at the cluster for converting this during the fds simulation. I haven't come that far, so I disable it for now.

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[...] During this process, objects will invariably overlap, leaving multiple single-cell blocks in the same location.
Sorry, I dont' fully understand this part.

Quote
To decide how to resolve overlapping objects, PyroSim uses the merging options. By default, if multiple blocks have identical properties (e.g. all six surfaces), the duplicates will be discarded and only one will be retained. By default, the Ignore names while merging option is disabled. This means that two objects will not be considered "identical" if they have different names. When that option is enabled, name information is not considered as part of the comparison.
I tried this option because I had problems with the output, see below
Quote
With that said, there appears to be a problem with the merging portion of PyroSim. It is giving you a lot of single cell objects where it could easily merge them into larger blocks. On the other hand, I could not find an OBST record (from "Auusenwand Links") that was repeated/duplicated in the input file. They all appeared to be the individual blocks that made up that wall.

Ok, let's take the geometrie and use standard settings (uncheck the two mentioned options). The output fds has 189648 lines (which is a lot).
Example: My geometry has 72 glass elements at the outside walls ("Glaselement"). Now I close the psm file and import my just created fds file to pyrosim. There I have a look at the group "Glaselement" (please see attachement) and see that each elements shows up several times (in total there are more than 3000 instead of 72 (+ some steelframe elements)). I don't know if I did anything wrong to this point!?

So I check "rasterize all objects" and uncheck "ignore names". The fds file contains 11045 lines (!). I import that fds file again and it looks perfect. Great!!
___

So while writing this post I figured out a way which works for me now. Thank you for pointing that conversion settings out! I just didn't realize that these parameters have any impact except of exporting the fds file.

Still I wonder why standard settings don't work for me?
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Charlie Thornton

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Re: Duplicated obstructions in FDS export
« Reply #8 on: September 28, 2012, 10:57:41 am »

Out of curiosity, does your normal work flow have you importing the PyroSim-generated FDS file back into PyroSim?

My assumption was that you wanted to visually inspect the generated model because you were already suspicious that something was wrong. Talking to my colleagues, I've come to learn that sometimes users routinely "cycle" their models because we've omitted some feature that they need. For example, I'm told that some users find it easier to bulk-edit certain obstruction properties in a text editor.
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Andreas

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Re: Duplicated obstructions in FDS export
« Reply #9 on: October 01, 2012, 02:03:53 am »

My assumption was that you wanted to visually inspect the generated model because you were already suspicious that something was wrong.
Yes, that's right. I just tried to figure out why the fds file were that large.
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