some problems with Pyrosim

[ncepuzxt]

HI,
   I am new with the program, and would be glad to discuss with you. Here I have a few questions with the soft, and I will be very appreciated with your discussions or your instructions.
   a) I am puzzled about the ''Open Mesh Boundaries''. Does it mean the external walls of the buildings?
   b) I just would like to know whether all of the commands in FDS applied in Pyrosim. For example, the PRES Namelist Group in improving the Pressure Solver, i.e. how I can set the parameters MAX_PRESSURE_ITERATIONS and VELOCITY_TOLERANCE in Pysosim? Obviously, there are many other commands in FDS which I canNOT find in Pyrosim.
   c) How can deal with the floors in multiple-floor buildings? The examples in Pyrosim are one-floor building.
   Thanks a lot.

Best Regards

[Charlie Thornton]

A: When you right-click a MESH, then click Open Mesh Boundaries, PyroSim will add 6 OPEN vents at the boundaries of that mesh. These vents appear in the tree, but are "hidden" (i.e. they don''''t show up in Smokeview).

B: No. We have implemented support for the subset of FDS we believe to be most useful for PyroSim users. If there are specific features that you feel should be included in PyroSim, let us know. Alternately, you can use the Additional Records section to add arbitrary entries to the FDS input file. This approach works particularly well for "free floating" records that set global variables in FDS, but don''''t tie in to other input file entries (e.g. the PRES namelist).

C. In the PyroSim Users Manual, there is a brief section in Chapter 7 called "Organizing a Building Model by Floors" that you may find helpful. If that leads to additional questions, let us know.

[ncepuzxt]

I am very appreciated for you ready reply. For question A, maybe I did not make me clear. I just want to know what is the role of the Mest Boundaries? Of course, they can be ''hiden'' or not. Does it make difference whether created or not? In the samples provieded in Pyrosim, sometimes they are created (hidden), sometimes they are not created, and sometimes ''Vents for Xmin'' are left only (i.e. Xmax, Ymin, Ymax, Zmin, Zmax are deleted).
So I just want to know, what are the BOUNDARIES roles?( the building envelop?)

Thanks a lot.

[ncepuzxt]

Dear sir,
   I just confused about the difference between the Internal Wall (by drawing Obstraction) and the Mesh Boundaries. And, can the floors be created by drawing an obstracion(regarded as internal walls?), or let it be the default settings, i.e. the boundaries of the corresponding room?

[Charlie Thornton]

You might want to check out section the FDS Users Guide, Section 7.4.2: Special VENTs. It talks about the different options for boundaries.  Here''s an excerpt:

The first special VENT is invoked by the parameter SURF_ID=’OPEN’. This is used only if the VENT is
applied to the exterior boundary of the computational domain, where it denotes a passive opening to the
outside. By default, FDS assumes that the exterior boundary of the computational domain (the XBs on the
MESH line) is a solid wall. To change this, use an OPEN vent as if it were an open door or window. To create
a totally or partially open domain, use OPEN vents on the exterior mesh boundaries (MBs).

[ncepuzxt]

Thanks a lot for your reply. According to the FDS guidance, the mesh boundaries are not created by default. And the exterior boundary of the computational domain is a solid wall (the thickness is unnecessary?). 
If I want partially the domain open to the outside,  then creat the correspongding mesh boundary. Am I right?

Thanks.

[Charlie Thornton]

I think you''ve got it.

[ncepuzxt]

Hi, I am back for the problem of Mesh Boundaries again. In the FDS+EVAC samples, I have found that the ''Vent Ymin for mesh'' and ''Vent Ymax for mesh'' are created, and the surface type is OPEN. Thus, according to the FDS User guides, they are open to the outside. In my opinion, the people can evacuate directly, and it is unnecessay to creat the doors. Am I right?

Thanks.

[Charlie Thornton]

No. Your error is substituting an intuitive model of the actual world for the nuts and bolts of how the simulator works. FDS+Evac requires a very specific setup to generate the correct flow fields for people movement. If I remember correctly, you need an evac-specific MESH, an evac outflow VENT, and an EXIT record to get people out of the model. The PyroSim Examples Manual contains a simple, one-room case.

I''m told that the latest version of FDS+Evac is a bit easier to work with. It may have changed some of these details. Unfortunately, I''m not familiar with that version.

[ncepuzxt]

I have finished the sample in Pyrosim. I am confused, however, that the ''Vents'' are created in some samples and it does not seem to be special used in Eavc.

Here is another question I would like to know. In the Fire Simulation (without EVAC), the surface type of the Mesh Boundaries are selected as ''OPEN'', viz. they are open to the outside, the smoke will flow through the corresponding boundary. Am I right?

Thanks a lot.

[Charlie Thornton]

I don''t think I understand your question. When you use the OPEN surface type on a boundary vent, that indicates a passive opening and smoke can drift out.

If vents for FDS and FDS+EVAC still seem confusing, you should read the corresponding sections of the FDS and FDS+EVAC users guides:

FDS Users Guide, Section 7.4: Applying Surface Properties: The VENT Namelist Group In particular, check out 7.4.2: Special VENTs.

FDS+EVAC 5 Users Guide, Section 8.5: The VENT Namelist Group Also, have a look at Section 8: Setting up the Input File for FDS+EVAC.