When performing a modal analysis, it is common to create a simple wireframe geometry that represents the product under test (see Figure 1, left). This wireframe simply consists of the test nodes with lines linking the nodes together.
The wireframe geometry is adequate to display mode shapes, but often it is desired to animate CAD geometry with the test data to make the mode shape easier to understand.
With Simcenter Testlab Mode Shape Expansion it is possible to link together a wireframe and CAD geometry so that the modes can be animated on the full CAD geometry. Simcenter Testlab was previously called LMS Test.Lab.
Look at Figure 1 below to see how animating the CAD geometry gives a more complete picture of the mode shape than just the wireframe.
To animate the CAD, links between the wireframe and the CAD must be established. These links will allow the CAD to move with the wireframe as the mode shape is animated. To link the wireframe and the CAD, follow the steps below:
1. Import the CAD file of the object under test.
In this example, a fixture was tested. The .stl file is imported into the Geometry workbook.
2. Import the wireframe geometry.
Now, the wire frame created in Simcenter Testlab Geometry must be superimposed onto the CAD geometry.
To add the wireframe, highlight the component(s) in the browser tree on the left of the screen and click “Duplicate/Import Component”.
The wireframe and the CAD file are now both in the Geometry workbook. See Figure 4 below: the wireframe is superimposed over the CAD.
NOTE: Take care to ensure the CAD file and the wireframe were created with the same coordinate system. Otherwise one of the two will need to be translated / rotated.
3. Link the CAD and wireframe together.
An association needs to be made between the wireframe nodes and the CAD nodes. This will give the software the appropriate information about which wireframe node corresponds to which CAD node. This is required to animate the CAD geometry properly.
The association between the two geometries is done by drawing lines between the wireframe nodes and the CAD nodes.
Go to the “Lines” sub-worksheet of the Geometry tab. Add lines between nodes on the wire frame and nodes on the geometry that are at the same location.
NOTE: Not every node needs to be mapped, just enough to give definition to the model.
4. Display mode shapes.
Now that the wireframe and the CAD are linked together, go to the Navigator to display some mode shapes.
In the navigator, add the entire geometry to a geometry display. This will bring in the wireframe and the CAD.
Drag and drop a mode shape onto the geometry. Initially, only the wireframe will animate. To animate the CAD as well, right click in the display, go to “Animation Settings” and turn on “Automatic Topological”.
This will slave together any nodes between the wireframe and the CAD that are connected by lines. The geometries will become linked and both will animate at the same time.
To remove the wireframe from the animation and just have the CAD animate, right click in the display and select Component Visualization.
The Component Visualization window will open. Turn off the visibility for all components except for the CAD.
Now, only the CAD will remain for the visualization.
The CAD and wireframe animations are now linked. This is a great way to obtain good-looking mode shape representations for presentations and reports.