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What is the constraint violation?
In some cases, analysis of a dynamic model stops because a joint is disconnected due to a redundant constraint.
The figure on the right shows a revolute joint and the positions and postures of the related action markers and base markers at a certain time in the analysis. One thing to note is that the action and base markers are tangential to each other on the z-axis. A revolute joint supports the degree of freedom for only one axis. Therefore, if two markers are tangential to each other in the translational direction, as shown in the figure, then there is a problem with the model.
In MBD for ANSYS (or RecurDyn), this results in a constraint violation error and the analysis stops to indicate that there is a problem with the model.
A constraint violation error occurs if the deviation exceeds 0.001 mm.
If two markers are at least 0.001 mm apart, the analysis stops. The following model, which is more complex than the first, illustrates when a constraint violation occurs.
The following model simulates a part of the excavator. At first glance, the model seems perfectly valid.
However, even a small error in the parameters can dramatically affect the analysis results.
In this example, the parameters for the translational axis of the translational joint cause the constraint violation in the analysis.
The normal values of these parameters are 5.91937, 1, and 0.
These values correspond to the direction vector of the revolute joint that is present at both ends of the translational joint.
If you enter a value (0.00001) very close to 0 instead of 0, the analysis eventually generates a constraint violation.
When the analysis fails, click Solution Information to display the analysis results stored in the message file, as shown below.
This file indicates that a constraint violation occurred at Revolute Joint ID 148 in the direction of TRANSLATION ALONG Z.
If you look at the Model Information , you can see that a redundant constraint occurred at Revolute2.
At this joint, the action marker was disconnected from the base marker, so the analysis failed.
You can perform the analysis again and run RecurDyn Viewer for Multi-Body Dynamics to see the failure results as an animation or via a plot.
In RecurDyn Viewer, use the Camera functions at the top to the window to focus on a specific marker while the animation plays.
Use the Following Camera function for the marker that is present in the problematic Revolute2.
Then, use Animation Control to turn on the Display Markers during Animation option and zoom in on the marker to check if the action and base markers of the joint are tangential to each other, as shown in the figure on the right below.
When you draw the plot, you can see that a difference of 0.001 occurs at approx. 2.25 seconds.
