FAQ and Important Tips
8. In fire simulation, I have multiple fire sources and I want to let the secondary fire source and other fire sources start when the radiation at these fire source locations reaches a certail level, can I do that and how? This can apply to a situation like a parking garage where other cars can be ignited by the first car fire.
A: To start a new Simtec simulation project:
1. Click Simtec GUI (Grahpical User Interface) function button 'Create a New Project' and then follow the instruction to create a new Simtec project.
2. Use Simtec GUI preprocessing functions to make necessary changes. The necessary changes may cover the basic physical description such as ambient condition, the geometry, the boundary conditions, the gas phase mesh and solid phase mesh, etc. In many cases, the major change is with the geometry. Simtec as its own rather convenient preprocessor for creating complex geometry. To facilitate and reduce the work with setting-up geometry model, as an extra facility, Simtec provides a powerful GUI function to directly import 3D CAD (Computer Aided Design) geometry. If you already have the 3D CAD geometry file, you can make a direct import. The importing itself will normally only takes a few minues. If you do not have the 3D CAD geometry file, you can make the CAD geometry using many powerful free or commercial CAD softwares and then import it to Simtec.
A: Simply click Simtec GUI (Grahpical User Interface) function button 'Import Geometry' and then follow the instruction to import the geometry. This will normally only take a few minutes. Simtec accepts the very popular 3D CAD geometry file in STL format.
A: In CAD community, there are a number of different CAD file formats which are supported by different CAD software. The good thing is that these different file formats can be converted into each other. To import 3D CAD geometry which is not in STL format, you just need to first convert your 3D CAD geometry file into STL format.
Below description will be given on converting the popular DWG format to STL format. There can be different ways for this converting. Below is just one method using free software.
1. First convert DWG file into SKETCHUP file (SKP file).
To do this, you can download free Google SKETCHUP 7 and the Plugin for converting 3D DWG file to SKETCHUP file (SKP file). This plugin only works for SKETCHUP 7. The free version of SKETCHUP 8 does not support this plugin. But the non-free version of SKETCHUP 8 can have its own DGW to SKP convertor. The download link is http://www.blender3darchitect.com/2011/02/how-to-import-dwg-files-to-sketchup-8-free/
2. Secondly convert SKP file to STL file
To do this, you can download Plugin for converting CAD SKETCHUP file (SKP file) to CAD STL file. This Plugin works for SKETCHUP 7 and SKETCHUP 8. The download link is http://www.guitar-list.com/download-software/convert-sketchup-skp-files-dxf-or-stl
A: In Simtec, you can setup arbitratry transient boundary condition for all the relevant boundary variables. To setup a transient boundary condition, in Simtec boundary condition preprocessing, for the boundary you want to apply transient boundary condition, you select a specifc variable such as U_VELOCITY for which you want to define transient boundary condition, you specify the variable value as a profile instead a constant value by typing a profile name such as PROFILE_01. Later, you create a text file PROFILE_01 using an text editor (Simtec GUI itself can also be used as a text editor). In this text file, you deifne how the boundary variable value will change with time. For example, if you have specified a profile name PROFILE_01 for TEMPERATURE, then you create a text file PROFILE_01 with a content like this:
With this profile, the temperature at the boundary will be 300 K at 0.0 seconds, become 310 K at 10.0 seconds and then 320 after 20.0 seconds.
Please note that all the boundary value is in SI unit.
A: Simtec allows a boundary to be removed at certain time or temperature condition, using two boundary variables: REMOVE_TIME and REMOVE_TEMP(K). With this two boundary variables, during computation, the boundaries can be automatically removed at the specified time (in seconds) or temperature (in K).
If the original boundary is wall boundary, when it is removed, the boundary place will become a free space.
If the original boundary is a non-wall boundary, when it is removed, the boundary place will become an ordinary wall boundary.
A: You can setup a VIRTUAL_BOUNDARY at the place where you want to have a wall boundary at your specified condition using either REMOVE_TIME and REMOVE_TEMP(K). When the VIRTUAL_BOUNDARY is removed at specified condition during computation, a wall boundary will automatically be placed there. In fire simulation, this can represent the close of a door or a window during fire.
A: The INLET boundary is for flow-in and the EXTRACT boundaries is for flow-out. To specify flow conditions, you can specify either VOLUME_FLOW rate (in m3/s) or the velocity vector (in m/s) which includes three components U_VELOCITY, V_VELOCITY and W_VELOCITY for three dimensional case.
With the VOLUME_FLOW input, the gas flow velocity is assumed to be normal to the boundary surface and the flow direction will automatically be determined to ensure the gas will flow in for INLET boundary and flow out for EXTRACT boundary.
If you specify velocity vector for INLET and EXTRACT boundaries, Simtec will check the velocity vector direction to see if the flow direction is consistent with INLET and EXTRACT boundary type. If the flow direction given by the specified velocity vector is not consistent with INLET and EXTRACT boundary type, the velocity direction will be reversed in the computation to ensure the gas will flow in for INLET boundary and flow out for EXTRACT boundary.
Q: In fire simulation, I have multiple fire sources and I want to let the secondary fire source and other fire sources start when the radiation at these fire source locations reaches a certail level, can I do that and how? This can apply to a situation like a parking garage where other cars can be ignited by the first car fire.
A: Yes, you can do that. In the burner power input in the boundary condition input file, you can just add like: 2 5 TRIGGER_RAD_FLUX 10000. In this case, burner 2 to 5 will be switched on when the radiation flux reaches 10000 W/m2. After being switched on, the fire power will output according the specified transient behaviour. If TRIGGER_RAD_FLUX not specified, it is assumed to be switched on from beginning.
A: Simtec is a fully parallelized software. To do a parallel computation, you just need to specify how many processors you want to use for your computation as shown here, using the parallelization setting function of Simtec GUI. You do not need to make any changes with your input file, no matter how many processors you use for your parallel computation.
A: Simtec does not have any particular requirement on mesh number. The number of mesh on X, Y and Z directions can be any number. Simtec does not have any requirement on cell size either. Simtec allows very flexible and non-uniform cell size. In Simtec, you can have fine cells in high gradient region and coarse cells in low gradient region. Thus, the computation cost can be minimized while having an optimum resolution.
With advanced numerical method, Simtec can easily simulate for example a fire in long tunnels while providing an optimum resolution. For example, Simtec was used to simulate a 12 km tunnel using a notebook computer, with a good resolution around fire in all three spacial directions.
A: Yes. Simtec provides fully coupled three dimensional calculation of heat transfer inside solid walls. The heat transfer calculation is fully conupled and interacting with the gas flow, gas combustion and thermal radiation. To have the necessary very fine resolution of the wall transfer, Simtec uses a separate solid mesh for calculation of wall heat transfer. The solid mesh is typically on the order of 1 mm or even smaller.
If the solid wall is combustible, when the ignition condition is reached, the pyrolysis and consequent combustion of solid wall is also automatically calculated together with the 3D wall heat transfer.
A: Yes. In Simtec, you can view your computation result anytime during the computation, without going out of the computation. On the Simtec GUI, you just go to the 'Computation-Control' menu and then you will find 'Pause for Simple Visualization' sub-menu and 'Pause for Visualization' sub-menu. You can view your computation results at run time using these two sub-menu functtions.
As in post-processing visualization, afte creating plot, giving focus to the graphical window, you can use PgUp and PgDn keys to sweep over different slices.
To go back to the computation, you just close the graphical display window and then the computation continues.
A: 'Volume 3D' visualization requires information of temperature and at least one of combustion products including CO2, H2O and SOOT. This menu function will be enabled if the temperature andat least one such chemical species are selected when reading results for post-processing.
A: At post-processing, after time sweep, user can not only use F1 and F2 to view different time plot images one by one. If you have many time plot images and want to quickly jump to certain time plot image, you can use SHIFT-F1, CTRL-F1, SHIFT-F2 and CTRL-F2 to have a fast view of different time plot images.
A: It is a scientific mathematical notation used by most computer programs to render numbers. 1.00E+01 means 1.00 times ten to the power of 01 (which is 1). More examples:
2.00e+00 = 2.00x1000 = 2.00x100 = 2.00
1.00e+01 = 1.00x1001 = 1.00x101 = 10.0
3.00e-02 = 3.00x10-02 = 3.00x10-2 = 0.03
And so on.
A: There are several important methods for use to speedup Simtec computation.
In the input set file, increase the "Residual tolerance for flow". For high accuracy demand computations where accuracy is on priority, this residual tolerance can be given a small value such as 0.0001 or even much smaller. Simtec can reach machine accuracy computation if this residual tolerance is given a very small value. However, for many other computations such as practical engineering computations, error of 1% is of no major importance. In this case, this residual tolerance can be given a value of 0.01 (or 1.0E-02 in scientifc data format). This will speedup Simtec computation by a factor of 2 or even more.
Use parallel computation. Simtec supports parallel computing on both local machine or on cluster. If you have multi-core single machine, you can do parallel computing on local machine to make use of the multi-core processor. To setup the parallel computing, follow the illustration below:
Parallel Computing Setting on local machine:
Parallel Computing Setting on cluster:
First, please make sure your cluster has been set-up correctly. You can follow the MPI manual and test the MPI example program cpi.exe in a command prompt. Everytime your compuer is restarted, it is recommended to test cpi.exe to make sure the cluster works properly.
Afterward, you can use the cluster for Simtec parallel computing, as illustated below:
- Another important method to make Simtec computation fast is to optimize grid system. The basic principle to optimizing grid system is to use fine grid for high gradient region and coarse grid for low graident region. With a good grid system, the number of cells can be drastically reduced while the proper resolution is still maintained.
Q: How to increase computer system virtual memory?
A:When running large computations, during the initialization stage, Simtec may need to use some swapping virtual memory space to compensate the limit of the accessible physical memory. User can adjust the swapping virtual memory space as following:
A: At present, Simtec does not support blank space in the case directory and input file name. If you have a blank space in the case directory and input file name, replace the blank space with a non-blank space character. Otherwise, Simtec may have difficulty yo find the right directory and input file. For example, if you want to do a computation in a directory d:\case 1, rename the directory 'case 1' to 'case_1' instead.