Simcenter Testing Solutions Tips and Tricks for Torsional Orders

Simcenter Testlab



Taking torsional data with Simcenter Testlab (formerly called LMS Test.Lab)? Here are three tips that will save you time!

TIP 1: Acquisition: Change the channel group from Tacho to Vibration

  1. In Channel Setup, turn on a tachometer channel.
  2. Change the ChannelGroupId from Tacho to Vibration (Figure 1).

With this trick, there is no need to split the tacho channel and route it into both a dynamic channel and a tacho channel. Both a tachometer and vibration channel are calculated.

Figure 1: Change the ChannelGroupId from Tacho to Vibration in the drop-down menu.

When the tacho channel is set to vibration, it is possible to create order cuts and FFTs from the throughput data.

Figure 2: Change the ChannelGroupId to vibration and it will be possible to make colormaps and order cuts of the torsional vibration.

TIP 2: Display vibration in angle, RMS, peak, or peak-to-peak

An example of a torsional order is below. The x-axis represents the overall RPM level and the y-axis represents the fluctuation in RPM (torsional vibration).

Figure 3: 2nd Torsional order from an engine run-up.

To view the torsional vibration in rotational displacement rather than rotational speed:

  1. Right click on the y-axis
  2. Click “Processing”
  3. Click “Integrate (Single)”

Figure 4: The above menus will open when following the steps to convert the Y-axis to angle.

The graph will then appear as below in Figure 5.

Figure 5: The Y-axis is now represented in terms of angle.

Want to display the maximum angular displacement?

To change whether the axis is represented in Peak, RMS, or Peak-to-Peak values:

  1. Right click on the y-axis
  2. Click “Processing”
  3. Select “RMS”, “Peak”, or “Peak-to-Peak” from the “Section Scaling” menu

Figure 6: The above menus will open when following the steps to change the axis scaling.

The graph will then appear as shown below in Figure 7.

Figure 7: The y-axis is now represented in peak-to-peak format.

TIP 3: Torsional Vibration Animation

Create an operational deflection shape of your torsional vibration:

  1. Create / Import a geometry into Simcenter Testlab using the Geometry worksheet.
  2. Go to the “Torsional node” sub-worksheet of the Geometry worksheet (Figure 8).

Figure 8: In the Geometry worksheet, open the Torsional node sub-worksheet (red circle near the top).

3. Click on “Add Disc…”. The “Add disc” window will appear (Figure 9).

4. Type in the node name, the radius of the rotating component, and the orientation in which you want to create the disc.

5. Click apply and then click close.

Figure 9: The “Add disc” window allows the user to enter the node name, shaft size, and orientation of the node.

The torsional node will appear in the Geometry Display as shown below (Figure 10).

Figure 10: The torsional node.

Once all the desired nodes and torsional nodes are created, it is possible to animate the nodes with spectrums, orders, and time histories of the nodes (Figure 11), just as you would animate any geometry.

User-added image

Figure 11: An animation of the torsional nodes shows the fluctuation in the shaft as it rotates.

Both translational and rotational vibration can be displayed simultaneously.

Enjoy these tips when working with torsional vibration.


Questions? Email or download the Torsional Vibration White Paper.


Rotating machinery dynamics:

Simcenter Testlab AcquisitionTips:

KB Article ID# KB000042560_EN_US



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