Learning Forum

[perryn]

Hi there,

I'll preface this question by saying I am relatively inexperienced in finite element analysis, with only a bit of prior experience in using Ansys for running static structural models.

For my current research I am trying to model the insertion of a needle into a cube of flesh. After a few days of trying to model this, I have some questions.

Firstly, what Ansys module do you think would be best to achieve this? From a quick review of models already out there it seems most people use explicit dynamics, however, since this is a low velocity insertion and I have limited computational power I was wondering whether this choice was appropriate.

Secondly, it seems that unless the elements are very large, my model seems to take too long to solve (the largest estimated solve time being ~3000 hours). Apart from increasing element size and reducing the problem to 2D, are there any other ways that one can reduce computation time?

Lastly, is anyone aware of any available problems that are similar to this? I know there are existing posts on this forum, however, most of these fail to mention the specifics of their model. I would love to see how someone with more experience in Ansys would tackle a similar problem.

For your reference, this is what I have been able to achieve thus far:

[Chris Quan]

For a typical needle penetration problem, the needle material is much harder than the flesh. So most likely the time step is controlled by the elements in the needle.
If your simulation goal is on the behavior of the flesh, not on the needle, you can change the needle behavior from Deformable to Rigid. This will increase the time step and thus reduce the running time, since the flesh is soft and its material sound speed is low.
You can use either LS-DYNA system or Explicit Dynamics system in Workbench to run this simulation.

[perryn]

Awesome thank you very much!
Perry

[vikaskaul]

Firstly, those are good questions. It is rare to find good questions so that is a good sign :)
Secondly, I am not sure if I would recommend such an abrupt jump; it takes careful thought in making appropriate choices for these challenging simulations to be insightful. Otherwise, at the very least, they can easily be massive time/compute sinks or they could easily be spitting out garbage without you recognizing the signs. So, unless you get yourself professionally trained in the method of choice, I would recommend against using these methods.

[Calum Bowmaker]

Hi Perry, did you ever manange to create the simulation for needle insertion, I am in a similar posistion to what you were in and struggling to proceed. Any help would be appreciated.