Learning Forum

[peteroznewman]

The material is BRASS from the Explicit Dynamics category of Engineering Data.

A solid tube has an initial condition of an Angular Velocity of -36.65 rad/sec

[Chris Quan]

If you suppress Remote Displacement BC and just use the Initial Angular Velocity, will the tube erode? nInitial Angular Velocity already defines the rotational motion, there is no need to use Remote Displacement to define the rotation. nIf Remote Displacement BC must be used, I would suggest you to relax the BC, for example, set X/Y/Z component = Free.n

[peteroznewman]

nThank you for your reply. I set the rotation to be Free on the Z axis of the Remote Displacement instead of suppressing the entire BC. I will let that run overnight and reply tomorrow what happened with erosion, but from the first couple of hours, the elements are starting to skew. Why would they do that?nThe Remote Displacement is intended to be the machine rotating the tube-shaped workpiece for a single point cutting simulation. The cutting tool was suppressed to see if the tube would rotate on its own. When it did not, I made this Question. After I have found out how to successfully turn a workpiece, the tool will be unsuppressed and the cutting simulation can begin. A constraint that keeps the workpiece turning at a constant angular velocity is required because the cutting tool will create a large torque that would tend to immediately stop the rotation of the workpiece if all it had was an initial angular velocity.nLook at the link on the last line in my original post to see what the full model is supposed to do.n

[peteroznewman]

nThe model with the rotation to be Free on the Z axis of the Remote Displacement and the same Initial Angular Velocity as described above resulted in erosion.nHere are the erosion controls:nWhat do you suggest?n

[Chris Quan]

The erosion strain is too small. Try the default: 1.5.nThe alternative way to rotate a body is creating a Revolute Joint connection and then using Joint Load to rotate the geometry.n

[Chris Quan]

I built your model in 2020R2. Here are model setup & results:nnnnn

[peteroznewman]

nThank you so much for taking the time to build this model in 2020 R2. I have been working in 2020 R1, and don't expect any difference between these two versions.nI just setup my model to exactly replicate your conditions, where all DOF on the Remote Displacement are Free except for the 1800 deg of rotation about Z. I will let that run overnight and report back tomorrow. I also set the erosion control to the default value of 1.5. However, this model is a subset of a model in order to do troubleshooting on this part. Your test, even if it does behave, is not useful in the full model. The full model needs support (and rotation input) on the central hole so that large forces from a tool tip can be applied to the outer edge to simulate cutting.nIf you run your model with all DOF set to 0 (instead of Free) on the Remote Displacement, except for the 1800 deg rotation about Z, does it still solve? That would be useful to know as it would replicate the model I showed above.nYes, I could replace the remote displacement (behavior=Rigid) with a Revolute Joint and Joint Load. I haven't tried that yet, I may try that tomorrow. I wonder if the underlying APDL elements would be different than those generated by the Remote Displacement.n

[peteroznewman]

nI ran my geometry using the same configuration on the Remote Displacement where five DOF are set to Free, with Rotation Z set to 1800 degrees and there is only an Initial Angular Velocity. The mesh is getting wound up. nPlotting the Energy Probe, the Hourglass energy is growing to a large value, pulling down the Kinetic energy, which should remain constant. What is going on here?n=============================================================================nI have another model with a Revolute Joint to Ground scoped rigidly to the ID of the hole, with a Joint Load of Rotational Velocity of 36.7 rad/s and an Initial Condition of Angular Velocity on the body of 36.7 rad/s. I expect to see an almost strain-free rotation of the mesh, instead I see the same problem that happened with the Remote Displacement.nPlease see if you can replicate this result using 2020 R1.n

[peteroznewman]

For anyone following this thread, I found a way to rotate a tube and not have the mesh skew the way it does for both Remote Displacement and Revolute Joint.nI opened the model in this thread: https://forum.ansys.com/discussion/22403/can-anyone-help-me-to-do-explicit-dynamics-for-turning-operation and found a third way to constrain a tube on its axis while also providing a rotation input. That was to use a Cylindrical Coordinate System. That provides a path for anyone needing to rotate a workpiece and use a tool to simulate turning.nIt does not answer the question posed by the original post, why does a Remote Displacement (or the Revolute Joint as suggested by ) skew the mesh?n

[javat33489]

Hello sir.

I have a similar problem but in Ls-Dyna Workbench.

I have a rigid body - a drill, on it there are deformable bodies of bits. This is a test model.

I need to set a rotation speed of 27 rad/s and a feed of 40 mm/s. The drill is only rotated by the remote displacement when setting degrees. Velocity tool doesn't work, Rotation Velocity tool doesn't work.

Rigid angular velocity works, but then the feed does not work.

I'll try the Rigid Constraints tool and free up the bit for movement there, maybe that will help.

In Ls-Dyna Workbench, you cannot set a cylindrical coordinate system, perhaps this is the problem.

What do you say? I will attach the archive of the model.

ARCHIVE

[javat33489]

Looking forward to your tips and advice! Thank you.

[peteroznewman]

Best to keep the drill rotating about a fixed axis and feed the workpiece toward the drill. That nicely separates the two motions. You can use a Translational Joint or a combination of displacements to move the workpiece.

Rotational Velocity is a load that applies an acceleration that has a radius squared field about an axis, it does not rotate bodies.

I don't have much experience with LS-Dyna so I can't give you more specific advice on that.