Learning Forum

[Peter Nomura]

Hello,

I am trying to simulate a drop test whereby a cylinder falls onto a curved model as shown below.

I am using a transient structural system, with a standard earth gravity applied. 

Using velocity equations, I have calculated the time of impact to be 0.142 seconds after the cylinder is dropped. 

Is transient structural the best way to solve this?

Currently, my results have not shown any impact between the falling body and body taking the load. How can I fix this?

Thanks.

[Sampat Kumar]

Hi 
You can perform this on LS-DYANA, Explicit Dynamics, and Transient structure as well. It depends upon your requirements. We generally suggest the user to Use explicit solver for short time duration analysis. LS-DYNA tool is specifically designed to simulate the effects of dropping a product, or dropping something onto a product, and can account for complex contact and material nonlinearities that may result during drop tests. you can avoid this if you are using long-time duration simulation. 

My suggestion is to reduce the height of the cylinder and adjust the velocity accordingly. More height will unnecessarily increase your computational time. Check your drop orientations as well. You can define this by using the substeps instead of the program control. 
For more information, You can search on youtube with the keyword" Drop test analysis in ansys Workbench" 

Best Regards,
Sampat

[peteroznewman]

Hello Peter,

I agree with what Sampat said and will just add that I adjust the distance between the objects to zero for the start of the simulation and assign an Initial Velocity to the cylinder that you can calculate from the velocity equations for the drop height selected.  That way you don't waste 142 ms of compute time where nothing happens except the cylinder moves closer to a zero distance.  You may only need to simulate 50 ms or less to see the specimen get squashed by the cylinder.

In a drop test I performed, I only needed to obtain the peak stress in a plastic part to decide if it would survive or fail to know if I needed to change the design so Transient Structural was fine for my needs.

If your specimen undergoes large plastic deformation, Transient Structural may have issues with highly distorted elements that you may need to address with a remesh method, but I have no experience with that.

Good luck!
Peter