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Regarding the damping settings in Inspire/Motionview

Jin1

I currently have an object consisting of three bodies that form a rigid group on top, with a plate below connected to the ground. The three upper bodies slide on this plate that is connected to the ground. I will apply a horizontal leftward force to the upper rigid group. I have now set a damping for the sliding joint in the global coordinate system's Y‑axis (the direction of motion). What I want to know is how to set this damping such that it is related to the velocity itself. Suppose that when the leftward velocity is less than 0, the damping is 500; when it is equal to 0, it is 500; and when it is greater than 0, it is 1000. I tried expressing this damping value using a function and used the IF function, but it seems that the nesting caused the software to report an error and the simulation cannot continue. Are there any alternative measures? Below is my model.

Model.stmod

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Inspire

MotionView/MotionSolve

Accepted answers

Orestis_YB

Of course you can still control it like you are describing. I am just highlighting that expression uses force and not damping ratio (like in constant option). So, in the IF you'll have to multiply by the velocity. The damping part can be of course a value that comes from a Twin Activate model. Also to use the expression I would suggest migrating to MotionView as we've found an issue in expression option in Inspire Motion Analyst. I am attaching a MotionView model with an updated expression.

model_MMKS_3_archive.zip

Hope this helps!

Best regards,
Orestes

All comments

Orestis_YB

Hello @Jin1,

just keep in mind that when you are using expression option you actually define the force and not the damping itself. So here you'll have to multiply by the velocity. You can find more info in Edit Compliant Joints or Bushings. I have noticed that there might some issues with bushing expression. When I exported in MotionView the model worked just fine.

Hope this helps!

Best regards,
Orestes

Jin1

If damping force is applied, would that cause incorrect forces on the sliding hinge of the object? My idea is to treat it as a solver variable and use TWIN to control it—output the object's velocity, then determine the velocity magnitude in TWIN and input the corresponding damping value accordingly. I'm not sure if this approach is feasible. Since my TWIN encountered a path issue with C, I haven't had a chance to try it yet.

Orestis_YB

model_MMKS_3_archive.zip

Hope this helps!

Best regards,
Orestes

Jin1

I saw the model you sent. I'm quite curious – does this formula essentially equate to C*V, applying a damping force in the place where damping needs to be filled? I'm a bit confused because you can actually fill in a force in the field that is supposed to be for damping. How should I understand this?