Learning Forum

[Manas123]

I am trying to analyze the shaft supported on spring connections as shown in figure. A force is applied at one end using remote force. As the shaft is supported on those springs, there is no more fixed supports in the set-up. I am getting the following warnings

1. '' Two or more remote boundary conditions are sharing a common face, edge, or vertex.   This behavior can cause solver overconstraint and is not recommended, please check results carefully.  You may select the offending object and/or geometry via RMB on this warning in the Messages window. "

2. " Not enough constraints appear to be applied to prevent rigid body motion.  This may lead to solution warnings or errors.  Check results carefully."

Kindly help.

[peteroznewman]

When a spring is scoped to some geometry, a face or an edge, under-the-hood, Mechanical is creating a Remote Point to attach one end of the spring.  

You probably have two springs and two remote points scoped to the same geometry and that is causing the warning message.

If you want a second spring scoped to the same geometry, first create the Remote Point and then attach each spring to the same Remote Point.

When you have just springs to ground, you need to have a sufficient number of them in a sufficient number of directions to control all 6 Degrees of Freedom. The solver can add "Weak Springs" if you allow it, which will prevent the matrix from being singular and it will solve. If there is no force in the direction where there is no spring, there will be no displacement, but without the weak spring, there would be no solution.

When you have just springs to ground, there will be some rigid body motion as well. You will see this in the results. If the solution looks reasonable, then you can ignore this warning, but make sure you have turned on Large Deflection in the Analysis Settings.

Regards,
Peter

[Manas123]

Thanks for the response. Actually my model consists of 6 springs at 6 different locations on the same face. I will first create the remote points and then attach the springs. Will update about the results soon.

[peteroznewman]

If you slice the one face so that there are six small faces at each of the six locations where you want each spring attached, then there will be no warning about a common face.

It looks like you want three radial springs at one point on the axis and three radial springs at another point on the axis. In that case, you could slice the face with two planes and make a remote point on each edge. Since there are only two points, there will be one rigid body motion unconstrained, the rotation of the axle. You can add one last Remote Displacement on the end of the axle and set only the rotation about the axis to zero and leave all other Degrees of Freedom set to Free.

Regards,
Peter

[Manas123]

The radial springs are attached on the surface of the shaft at specific locations. They are not connected to the axis.