Making simple chang...
 
Notifications
Clear all

Making simple changes in my model results in the simulation crashing.

5 Posts
2 Users
1 Likes
92 Views
Posts: 3
Topic starter
(@cptmarais)
Unpaid Intern
Joined: 3 weeks ago

Hello all,

I made a basic simulation on LS-Dyna of a generic aortic valve opening and closing due to a pressure profile being applied to it. I made the valve geometry in Inventor and meshed it in MSC Apex. I meshed it in Apex because I used MSC Marc originally but Marc could not run the simulation therefore I moved to LS-Dyna. 

Once in LS-Dyna I set up the model, I have attached the K word file, in the most basic way that I knew how to just to get something working. For this first iteration, I was planning on using this as a baseline and then improving on it.

Once the simulation had run I saw that there were various problems that were occurring. The most notable being hourglassing. Another problem was that in the region of contact, there were high 'vibrations'. 

So I started by making some changes to the model by adding global damping, the HOURGLASS keyword and changing the ELFORM of the elements. For the hourglass setting, I made use of an IHQ of 2 and 3 and I changed the ELFORM from 2 to 5, 9 and 16. However, every time I assigned a part with an HGID or changed the section ELFORM the simulation would crash.  Sometimes the error that would occur is:

*** Warning 40864 (SOL+864)
Segment based contact stiffness was reduced due to
an increasing solution time step. The new time step for
the stiffness calculation is 5.3086E-06
Contact Interface # 1

So what I want to know is, is it the way I set up the new options or contact that is the problem or does it go further back to the meshing? 

I know another way of getting rid of hourglassing is refining the mesh but I am still waiting for my university to get LS-Dyna on its HPC system.

PS I've only been using LS-Dyna for the past 5 months so I am relatively new to it. I have completed the training that is given by LS-dyna and I have been searching the internet as well as the theory and VOL I and II manuals LS-Dyna for answers. I have been fighting with this problem, mentioned above, for the past two weeks and I hope you guys can assist me. I found the Unpopular Mechanics which led me to this forum.

 I'm sorry ahead of time if my question is dumb or on the wrong forum but at the moment at my faculty, I'm the only person using LS-Dyna, the rest are making use of MSC Marc.

Topic Tags
4 Replies

icon
icon

icon
icon

Posts: 3
Topic starter
(@cptmarais)
Unpaid Intern
Joined: 3 weeks ago

I've done some more experimenting with different ELFORMS and HOURGLASS keywords and it seems to be that the warning mentioned above is a common problem that occurs.

** Warning 40864 (SOL+864)
Segment based contact stiffness was reduced due to
an increasing solution time step. The new time step for
the stiffness calculation is 5.3086E-06
Contact Interface # 1

I've searched Ansys Forums for this problem and couldn't find anything. what would be the cause of this problem and how would you fix it?

Reply

icon
icon

icon
icon

Negative Volume
Posts: 598
Admin
(@negativevolume)
CEO
Joined: 4 years ago

Hi @cptmarais

Sorry for the delay, it seems like you've got a problem with your contact. I removed it and it appears to be running. Anytime you see an error about "Contact Interface" it's generally either a contact with intersecting parts or something critically wrong with the contact. 

I'd try removing your additional options in the contact that includes the soft parameters etc. and change your "SSTYP" to 2, and reference a SSID that is a *Set_part with all the parts of your model. This is the preferred method to do what you were trying, not SSTYP=5. 

Reply

icon
icon

icon
icon

Negative Volume
Posts: 598
Admin
(@negativevolume)
CEO
Joined: 4 years ago

@cptmarais there is something else wrong with your model. It will run but it's blowing up. Can you double check that you've kept consistent units throughout your model? And make sure that your load values make sense. 

Reply
1 Reply
(@cptmarais)
Joined: 3 weeks ago

Unpaid Intern
Posts: 3

@negativevolume so there are extreme forces on a heart leaflet within a few milliseconds the pressure can change dramatically that is being applied to the surface but I will check that and get back to you. But thank you for your help so far

Reply

icon
icon

icon
icon




Share: