Working with a geometry database

Some installations, especially old ones, do not have any existing geometric (CAD) model in digital format. To be able to conduct CFD modelling for such installations you need to generate a representative geometric model. The most common way to create a new geometry is to build it manually based on all the information available, such as general layouts, drawings and photographs of the facility. In this article we will discuss the structure of a geometry database in FLACS and the procedure to work with it.

Launching the geometry database window

How to launch the database window is explained in the article What is a geometry database?

The database dialogue window

Geometric models are created and organized into projects, geometries and objects in the order described in the figure below. You can have up to 99 projects each containing up to 99 geometries in a database.

In the Geometry tab, you can create a new database or connect to an existing one. The same tab allows you to create, modify, or delete a project or geometry.

The geometry database window with an opened project and geometry

In the Objects tab, you create, modify, and delete objects before inserting instances of them in geometry. You can also use the Filter text field to search for object names.

The objects tab in the geometry database window lists all objects defined in the database

In the Materials tab you can create, modify and delete materials.

The materials tab shows all material definitions of the current database, and the associated colours

Building objects

You have to create all the objects you need in your geometry and then insert these objects in the desired positions in your geometry.

When you click on New Object in the Objects tab you will get a field to enter the object name.

Before creating a new object, you have to specify the object’s name

After confirming the new object’s name, the object window will open. You may also open an existing object for modification by double-clicking the object, or by marking the object with a single left-click and then hitting the Open button. Either way you will get the object window where you can build and modify the objects.

The object window before adding any primitives

For information on all the functionality in the object window please refer to the FLACS User’s Manual. In this article, we will discuss the most commonly used steps to build objects.

From the Add menu, you can add the primitives defined in CASD, such as box, cylinder, ellipsoid, CP8, and GTC.

The Add menu gives access to the primitive types that can be used to build objects

Next, you can perform various operations on the created primitives. Some of these operations can be accessed from the Add menu (union, left difference, copy), others from the Edit menu, see below.

The operations accessible through the Edit menu

Two commands that deserve explanation are Union and Left difference. The Union command binds the primitives of an object together so that transformations can be applied to them as a whole. Left difference is used to subtract a primitive from the one created just before it. This operation is quite useful to create openings and holes.

An example of a left difference operation: The yellow cylinder is deducted from the red one created just before it, to obtain a hollow pipe that the flow can go through (if the grid is fine enough to resolve the opening)

In addition, there are a number of other commands to move, rotate, scale and change the material of the built primitives.

Using the objects

Having built and object from primitives, you save it and exit the object window. The new object will appear with the given object name in the selected group (normally Default). To use the object in your geometry, you select the object (by clicking on it) and click on the Instance button. A window will open where you can specify the position of the object instance in the geometry.

Specify the position of an object in the overall geometry
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