×
INTELLIGENT WORK FORUMS
FOR ENGINEERING PROFESSIONALS

Log In

Come Join Us!

Are you an
Engineering professional?
Join Eng-Tips Forums!
  • Talk With Other Members
  • Be Notified Of Responses
    To Your Posts
  • Keyword Search
  • One-Click Access To Your
    Favorite Forums
  • Automated Signatures
    On Your Posts
  • Best Of All, It's Free!
  • Students Click Here

*Eng-Tips's functionality depends on members receiving e-mail. By joining you are opting in to receive e-mail.

Posting Guidelines

Promoting, selling, recruiting, coursework and thesis posting is forbidden.

Students Click Here

Jobs

contact problem

contact problem

contact problem

(OP)
I want to model a steel silo under earthquake excitation.
I used a umat subroutine for constitutive behavior of granular material (hypoplastic mateial with inergranular strain) I tried to model a steel silo with granular material under earthquake excitation with Abaqus standard. I modeled silo walls and bottom with 4 node shell elements and granular material with 8 node solid elements then I used surface to surface contact between silo walls, silo bottom and granular material, when I use default hard contact for normal behavior of contact in Abaqus standard I have overconstraint problem due to using contact pair and earthquake motion applied to the silo bottom as acceleration boundary condition together, and when I use penalty or augmented lagrange method for normal behavior of contact, I encounter two type of warnings

in first step that I apply gravity load the waring is

1)During back substitution 625 elements encounter a load applied to a degree of freedom that does not have any stiffness. The elements have been identified in element set WarnElemBackSubNoStiffStep1Inc1.

and in second srep the warning is

2)There are 2 unconnected regions in the model.

when I increase stiffness scale factor the first waring is ommied but in the second step I have warning that says

There are 2 unconnected regions in the model.

in fact solid elements penetrate into silo wall and my model becomes unstable. please help me I am completely confused.  

RE: contact problem

Try starting with a simple contact analysis with only 2 parts and without a umat.  2 steel blocks is where I would start.  I hope this helps.

Rob Stupplebeen

RE: contact problem

(OP)
now my model have only two parts. I have used drucker prager model instead of umat before for modeling of granular material and these warnings still exist.

RE: contact problem

Look in Viewer at your results to see where the elements with no stiffness are. It sounds like a numeric problem though if the warning disappears with a change in material.

If one body passes through another then you haven't made contact for whatever reason. As in all these cases, start with a dummy load case of fixed displacements to ensure some contact is made before applying your real loads.  

corus

Red Flag This Post

Please let us know here why this post is inappropriate. Reasons such as off-topic, duplicates, flames, illegal, vulgar, or students posting their homework.

Red Flag Submitted

Thank you for helping keep Eng-Tips Forums free from inappropriate posts.
The Eng-Tips staff will check this out and take appropriate action.

Reply To This Thread

Posting in the Eng-Tips forums is a member-only feature.

Click Here to join Eng-Tips and talk with other members!


Resources