Learning Forum

[Harshil_Gohel]

Respected all,

I am doing drop test simulation of a 3D printed structure in ansys. Due to structure complexity i tried it in explicit dynamics but with CFL conditions it is taking forever to solve.

So I thougt of shifting to implicit schemes, in transient dynamics simulation is running well, but after contact structure supposed to collapse under given loading conditions but instead of that simulation is stopping with error showing high distortion of element.

Here I am attaching my simulation settings with this discussion. Any help would be greatful.

Initial condition for the impactor is 1m/s and the bottom of the solid geometry is fixed.

[Harshil_Gohel]

Also I saw posts on ekill command to eliminate failed element but It is not working for me. Any suggestion to that also would be appreciated.

[peteroznewman]

If you expect elements to fail, you will be better off in Explicit Dynamics. Spend time optimizing the mesh. Look at the Mesh Metric called Characteristic Length. It may be possible that there are a few elements that cause the time step to be 4 times smaller than it needs to be with a better mesh. Next try Mass Scaling and increase the density of the few elements that cause the smallest time step. Allow those elements to increase in density by a factor of 4. With those two treatments, you might find the solution will finish in 1/8 of the time it would have without them.

[Harshil_Gohel]

Thank you for the suggestion.
As per your instruction I tried to do, but I cannot change meshing too much as it is .stl import and having facet edges on it. I was able to reduce time little from Mass scaling.
But is it not possible to do failure analysis through implicit methods like transient or statics dynamics in ansys?
Which will remove time constraint on time stepping and we can get a rough(Not too much accurate results) for the simulation?

[peteroznewman]

Spend time in SpaceClaim to put a skin over the facets of the STL file. I have made several videos to show how to do this.
Once you have a solid geometry with much larger faces, you can mesh with much larger elements. The Minimum Characteristic Length might increase by a factor of 10 or more!
https://youtu.be/Gj3bTd0aN8I
https://www.youtube.com/watch?v=d4ZXSFjIAII&t=240s
https://www.youtube.com/watch?v=ARy7EvA3LTg&t=23s

[Harshil_Gohel]

Thank you for your suggestion it helps. One more thing I want to know is like in ANSYS explicit I want to meassure force reaction but not at the boundary condition. I want to meassure force reaction at the surface of impactor body. Like in attached image I am not able to select any other option than fixed boundary condition. Is there anything in output control i have to turn on to get that option.

[peteroznewman]

I'm not expert at Explicit Dynamics but it may be possible to request contact force.
An output to request that has smooth (not noisy) data are the various Energy outputs. Look at all the various types of energy available such as Kinetic Energy and Internal Work.