Table of Contents
PyroSim provides tools to help the user rapidly create model geometry. The 2D View is the fastest way to create a building model. The user can organize the model by floors, import a background image for each floor, and then sketch the walls of the building on top of the background image. PyroSim includes support for diagonal walls.
More complex geometry, such as curved walls and domes, can be created using the Block Tool or Wall Tool, as described in the chapter on Creating Complex Geometry.
Obstructions are the fundamental geometric representation in FDS. Obstructions are rectangular solids defined by two points. Surface properties are assigned to each face of the obstruction. Activation events can be defined to create or remove an obstruction during a simulation.
The geometry of an obstruction does not need to match the geometry of the mesh used for the solution. At the start of the simulation, all faces of an obstruction are shifted to correspond to the nearest mesh cell boundary. Thus, some obstructions may become thicker; others may become thin and correspond to a single face which has the potential to introduce unwanted gaps into a model. These ambiguities can be avoided by making all geometry correspond to the mesh spacing. The easy way to accomplish this is to draw geometry while snapping to the model mesh, however it is possible to create geometry manually by entering specific coordinates. This can be accomplished using the New Obstruction command, similar commands exist for holes and vents.
To create a new obstruction: on the Model menu, click New Obstruction...
This tab of the obstruction panel presents all options other than those controling geometry and surface information. This includes activation events (conditions that can cause the obstruction to be added or removed from the simulation) and miscelaneous options such as color and smoothing.
| Parameter | Description |
|---|---|
| Description | A human-readable description for the object. This value will not affect the result of the simulation. |
| Group | Controls the position of the object in PyroSim's tree view. |
| Activation | Bind this object to new or existing activation control logic. Activation control logic is used to add or remove the object based on time or measurement conditions. To learn more about activation events, please refer to Chapter 14, Activation Events |
| Specify Color | Override the material colors for this object. |
| Texture Origin | |
| Relative to Object | When textures are attached to an object, they are tiled based on an origin point. By default, this point is the origin, relative to object makes the default anchor point the min point of the object. |
| x,y,z | These values offset the texture origin based on the default texture origin. If the origin is relative to the object, leave at zero to use the object's min point. |
| Obstruction Properties | |
| Smooth | Prevents vorticity from being generated at the corners. This option is used to prevent flow problems along angled walls due to the stair-stepped, rectilinear geometry used by FDS. |
| Thicken | When this option is selected, this object will not be reduced to 2D faces by FDS. |
| Record BNDF | When this option is selected, this object is included in boundary data output. |
| Permit Holes | When this option is selected, holes can modify the geometry of this object. |
| Allow Vents | Makes it possible for this object to be the backing object for a vent. |
| Removable | Makes it possible for the object to be removed from the simulation by activation events or the BURN_AWAY surface option. |
| Display as Outline | Changes the appearance of this option in Smokeview. |
| Bulk Density | Use this option to override the amount of fuel provided by this object. |
This tab allows you to enter the min and max coordinates of the object. For more elaborate geometry, such as polygons, this tab may contain a table of points and extrusion options. Extrusion is the mechanism PyroSim uses to extend 2-dimensional objects along a vector - creating a 3-dimensional object.
A key concept is the organization of the model into hierarchical groups of objects. The "Model" is the base group. Groups can be nested inside other groups, which allows the user to work with thousands of objects in an organized way. When an action is performed on a group, that action will be propagated to all objects in the group.
By default, a new model has one floor 3 m (9.84 feet) high. To define the floors in your model, go to the 2D or 3D View and select the Define Floor Locations tool (
). This will display the Manage Floors dialog. In this example, two floors have been created, with each being 10 feet tall.
Once the floors have been defined, the user can filter the display to show either a single floor or all floors.
Modeling Hint: If your model has floors, we recommend creating corresponding floor groups (Floor 1, Floor 2, etc.). Then, as the building is drawn, make sure that the objects are placed in the matching group. This will help organize your model.
Each floor can have an associated background image. To add a background image to a floor, go to the 2D or 3D View, select a specific floor, then select the Configure Background Image tool
(alternately select the Define Floor Locations tool,
, and then in the Background Image column, select the Edit button). This will display the Configure Background Image dialog. You will be guided through the following steps:
Choose a background image file. Valid image formats are bmp, dxf, gif, jpg, png, tga, and tif.
Specify the Anchor Point for the image by clicking on the image. The Anchor Point is a point on the image at which the coordinates are specified in the model coordinate system. The model coordinates of the anchor point are not required to be at the origin.
Set the model scale. Select the Choose Point A button, then select the first point that will be used to define a length. Select the Choose Point B button and select the second point to define a length. Input the Distance between points A and B.
Use the sliding scale to change the image brightness.
Select OK to close the Configure Background Image dialog.
Now, in the 2D View, when the user displays a specific floor, the background image will be displayed. In the 3D View all background images will be displayed. To turn off the background images, go to the 2D or 3D View, and toggle View->Show Background Images.