Learning Forum

[marasionis]

Hello all, I am having a very peculiar problem attempting to do a simple ball impact on plate simulation on Workbench LS Dyna. I create the model in Spaceclaim, mesh it, select an initial velocity for the ball of 6000m/s, generate a fixed support for the plate and try to do the simulation. However the result is very strange- the ball moves towards the target plate at a very small velocity (maybe 5-10m/s), usually gently turning the other way before it comes near it. This happens if the velocity is 6, 60, 600, 6000, or 600000 m/s. I have tried several times changing different parameters, but still get the exact same result. The thing is this exact same simulation runs perfectly in Workbench Explicit Dynamics with virtually no changes. Below I have posted a video of the problem happening and the .k file of my LS Dyna setup. Any help would be appreciated, cheers.

https://youtu.be/3yIUbvH8_00

https://drive.google.com/file/d/1D-xqba6vQ8mapPSnN7IKga4mhqrZSGok/view?usp=sharing

[Nanda]

Hello User,

Ansys employees are not authorized to access any files posted in the forum. Is the ball close to the plate? Ideally, the ball should be placed just above the plate, such that it impacts the plate within less than 5-10% of your solution end time. We have the exact problem setup and documented by our Expert, please use this as reference.

LSDYNA Sphere — Welcome to LS-DYNA Examples

Let us know how this goes.

Regards,

Nanda.

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[marasionis]

Hi, thank you for the answer. Unfortunately coming from Explicit Dynamics Workbench I am not very familiar with the LS Pre UI and layout, and I am only capable of setting up the simulation at the Workbench interface. I will post some photos below to help illustrate my problem better. This is a snapshot of the simulation beginning:

After moving to the left for a very brief moment ( initial velocity is correctly set to the left) the ball changes direction going to the right without seemingly touching the plate:

The balls velocity goes from 6000m/s to 0, then more than 6000m/s in the opposite direction without touching/interacting with the plate. On a simulation where I placed it extremely close to the plate, the ball seemingly clipped through it at a low velocity without interacting with the plate at all. Could this be a body interaction problem? Or perhaps a unit mismatch? Thanks for any advice

[Nanda]

Not sure what's going on here. Maybe turn off body interactions and assign a manual frictionless contact and see if it helps. And are you interested in studying the ball or the plate? If the ball is of interest, then the plate can be rigid, and vice-versa. If the plate can be rigid, you can suppress this plate completely and utilize the rigid wall available under LS-DYNA Pre >> Rigid body tools.

Best,

Nanda

[Nanda]

Also, you might find this learning series useful. It uses LS-PrePost and discusses the same problem you're trying to simulate.

Ball Impact on a Plate Using Ansys LS-Dyna - Part-1

[marasionis]

Hi, I am more interested in studying the plate, and plan to do composite plates in the future, hence my decision to use LS DYNA. I deleted body contacts which resulted in the ball clipping through the plate, while a manual contact region or automatic frictional contact recreated the initial problem I have. I think the problem is probably with the units, as the ball mass is listed at 3.67kg, which is impossible for a steel ball of 4mm radius. Maybe a unit mistranslation from spaceclaim is possible, I will try designing the parts in a different CAD and importing them seperately.

[Nanda]

Sounds good, let us know how it goes!

[marasionis]

It did not work, units were correct after all. I  am still having the same issue and I am out of ideas. Any suggestions would be welcome.