What is meant by the warning "Inconsistent Constraints / Physical Instabilities"?

An inconsistent constraint is the result of two or more constraints that prescribe the motion of bodies in such a way that it is physically impossible for all constraints to be satisfied. In most cases, one of the constraints involved is either a Revolute Motor (of type Orientation, Angular Velocity, or Angular Acceleration) or a Linear Actuator (of type Length, Velocity, or Acceleration).

For example, consider a body that is connected to the background by a Revolute Motor enforcing an Angular Velocity of 90 °/s. If that body is also connected to the background by non-concentric Revolute Joint, it is inconsistently constrained. Clearly, the Revolute Joint would have to be broken for the body to be driven at 90 °/s!

A more obscure example might be a body that is connected to the background by a Revolute Motor enforcing an Angular Velocity of 90 °/s, but that collides with another body that cannot move sufficiently (for one reason or another) to allow the driven body's prescribed motion.

Other reasons why an "Inconsistent Constraint / Physical Instabilities" warning may arise:

Redundant Constraints:

Over-constrained systems will sometimes be interpreted as being inconsistently constrained. If your system appears to behave correctly when you allow it to continue after an "Inconsistent Constraint / Physical Instabilities" warning, your problem may actually be that you have created redundant constraints. Although it may be safe to ignore the warning message in this case (see What is meant by the warning "Redundant Constraints"?), it is advisable to eliminate the Redundant Constraints to attain a warning free simulation.

Contact Anomalies:

Contact anomalies will sometimes be the cause of "Inconsistent Constraint / Physical Instabilities" warnings. See How should collision problems be confronted?

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Versioni pertinenti:

Working Model 2D, visualNastran 3D Motion, 4D, SimWise

Data ultimo aggiornamento: 2 gennaio 2011



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