Spring damper marker issue in Hypermesh

Simon Križnik

Hi,

 

there appears to be an issue with markers when spring damper (CMSPDP) is defined in Hypermesh.

I am using the following procedure to create a torsion spring damper:

https://altairuniversity.com/wp-content/uploads/2017/09/how_do_I_ver1.pdf

The spring has some stiffness and damping with non-zero free length (3.14 or 180 degrees). But it does spring back to free-length angular position.

In the xml motionsolve solver deck, the automatically created markers lack orientation (they only have x,y,z position, same as fix joint markers). The issue can be resolved by manually modifying the xml solver deck by either:

-appending orientations a00, a10, a20, a02, a12, a22 to offending markers

-using markers of revolute joints

This workaround works for this simple model, but it is not practical to modify multiple spring dampers in more complex models.

Can someone provide solution?

AnanthK

Simon - As you maybe aware, we have a dedicated pre-processor for MS, which is called MotionView. Creating and manipulating torsional spring damper is a cinch there, much more so for large, complex models. I'm curious to hear your reason for using Hypermesh to create a MotionSolve (MS) model? I realize this doesnt immediately help with the issue, but perhaps we can suggest an alternative, maybe even a more expedient path to solving your problem. 

Simon Križnik

Hi Ananth,
thanks for your reply. I am well aware of MotionView, however, there are some limitations with regards to flexible body implementation. I personally find it easier and faster to set up flexible models in HM, especially for quick flexible body geometry changes. While align interface nodes is a nice functionality in MotionView when swapping flexible bodies it does involve back and forth between HM and MV. More importantly, MV does not support shape optimization of a flexible body (hardpoints are on flexible body boundaries, influencing kinematics).

AnanthK

Fair enough, thank you for the explanation. There are customers using HM and MS together, but I have to say they're few and far between. For that reason, and in order to ensure that you get timely support, I would advise creating a support case in Altair One. That would be the best path forward for this particular issue.  

Simon Križnik

Thanks for the suggestion. Hopefully Altair will fully integrate its solvers into HM and I believe shape optimization of flexible MBD mechanisms is the way forward.

AnanthK

Simon - Have you looked at using CMSPDPM - a recent addition to our HM+MS capabilities? It is similar to CMSPDP, but with the addition of the ability to orient the spring-damper using explicitly-defined markers. Would this work for you? 

 

https://2021.help.altair.com/2021/hwsolvers/os/topics/solvers/os/cmspdpm_bulk_r.htm

In addition there are other ways to define SPDPs as well: 

 

https://2021.help.altair.com/2021/hwsolvers/os/topics/solvers/os/cmspdpt_bulk_r.htm

https://2021.help.altair.com/2021/hwsolvers/os/topics/solvers/os/cmspdp_bulk_r.htm

 

Hope this is useful! 

Simon Križnik

Thanks for the tip, but CMSPDPM is not supported in HM or HW 2020.0

It may be inserted through unsupported bulk card, though defeating the purpose of rapid setup and manipulation.

AnanthK

Yes, it is brand new. Cross-posting or submitting a ticket/Case for HM might help expedite its addition though.