×
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

How do I model rotational spring or give rotational stiffness at a node in Abaqus/standard?

How do I model rotational spring or give rotational stiffness at a node in Abaqus/standard?

How do I model rotational spring or give rotational stiffness at a node in Abaqus/standard?

(OP)
I am trying to model a normal spring and a rotational spring to find Pcr of the system. I have attached a figure for a better understanding of my problem. (The actual problem is different than this one. This problem is just to know how to model a rotational spring in Abaqus). I am able to model a normal spring because the measurement of delta(deformation) is pretty simple in this case which is the change in the distance between two nodes. I am having trouble modeling a rotational spring at a node because I am not able to understand the proper measure of rotation. Please let me know if somebody knows anything in this regard.

RE: How do I model rotational spring or give rotational stiffness at a node in Abaqus/standard?

Spring elements SPRING1 and SPRING2 (available only in Standard) can be used to model torsional springs. The first one acts between node and ground while second one acts between two nodes (in fixed direction). To associate the spring with rotational degree of freedom you have to specify the number of this DOF as the first entry in the first data line of *SPRING keyword. Rotational DOFs in Abaqus are measured with radians. If you have some difficulties with modeling this using springs keep in mind that you can use connector elements instead.

RE: How do I model rotational spring or give rotational stiffness at a node in Abaqus/standard?

(OP)
Hello,

Thanks for replying.

I used both of those options, one being torsional spring between two nodes (DOF 6 at both nodes) (SPRING1) and the second one being the spring between a node (DOF 6) and the ground (SPRING2). But in both these cases, when I increase the stiffness, it does not change the end result. If I increase the stiffness of the torsional spring there must be some change in the value of the Pcr but there is not. I also tried using the connector element. The story is the same. If I increase the stiffness, it does not change Pcr of the system. That is why I am curious to know as to how Abaqus is finding the amount of rotation. I understand that the measure is radians. But what is its value? How to see the amount of rotation in torsional spring.

And just to make sure, with SPRING1 and SPRING2 spring elements I should be able to model torsional spring correct?

RE: How do I model rotational spring or give rotational stiffness at a node in Abaqus/standard?

Can you attach your model (.inp or .cae file) ? I would take a look to see how you modeled this system in Abaqus and if BCs, connections and spring definitions are correct. Is that based on some example from literature ? Do you have analytical solution for that ?

RE: How do I model rotational spring or give rotational stiffness at a node in Abaqus/standard?

(OP)
I have attached the CAE file. In the model, I have introduced a normal spring, and a rotational spring in between two nodes. Here I am doing buckling analysis to find Pcr of the system. (Please refer to the jpg image.)

Yes, I do have an analytical solution for this system.

I am working with this system to find out how I can use rotational spring in Abaqus. My original problem is different than this one.

Boundary conditions: pinned at the bottom and a vertical load of value -1 is applied to the top.

In addition to this, I have attached one more CAE file where I have used normal spring and transverse spring. This works fine.

RE: How do I model rotational spring or give rotational stiffness at a node in Abaqus/standard?

Dear njain094,

Before starting further studies in buckle analysis, you should know that buckle analysis is very different from general static analysis. End restraints, imperfect members a and member with combined loading can be solved in buckle analysis, but the eigenvalues you get finally will be unaltered, meaning that Pcr is not correct. If you are seeking to find Pcr using Buckling analysis you should consider ideal case such as fixed-fixed, fixed-free and so on. If you wish to know the effect of rotational restraint I suggest you go by static general or Riks method (Post buckling analysis). I am looking forward to your reply, and I might as well wish to know more about the solution you got..

RE: How do I model rotational spring or give rotational stiffness at a node in Abaqus/standard?

(OP)
Hello Rakz.mech,

I was planning to do static general but in Abaqus if I directly use static general the spring will just compress because there is no imperfection in it. Imperfection is introduced in the model by updating the nodes by incorporating modeshapes. Am I right? Please let me know what you think.

RE: How do I model rotational spring or give rotational stiffness at a node in Abaqus/standard?

(OP)
Hello Rakz.mech,

I added an artificial imperfection in the location of the reference point (top). But the rotational spring still does not take any load. I have attached a CAE file here. Please let me know if you find anything. (The coordinate of top reference point is 0.001, 10.0)

RE: How do I model rotational spring or give rotational stiffness at a node in Abaqus/standard?

Imperfection can be also introduced in form of small lateral load applied in the step prior to buckling analysis. But you will need additional transverse spring to handle such load.

RE: How do I model rotational spring or give rotational stiffness at a node in Abaqus/standard?

(OP)
Yes FEA way, I understand that. Thank you for the suggestion.

Were you able to find anything regarding rotational stiffness? Please let me know.

RE: How do I model rotational spring or give rotational stiffness at a node in Abaqus/standard?

The model you have sent is in CAE format and it is of a higher version of abaqus. It would help if you copy the input file to notepad and send it using txt format. And again providing rotational spring and imperfection will not alter buckling load if you use Linear Perturbation (Buckle analysis), however, you can use static general or static risk. Let me know further.....

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! Already a Member? Login


Resources

White Paper - The Evolving Landscape of Commercial Battery-Powered Trucks
What’s driving the evolving landscape of truck electrification? What are the barriers, motivators and strategies for accelerating the electric transition? What insights and resources are available for today’s design engineers working to achieve industry disruption and evolution? For answers to these and other pertinent questions, read this white paper. Download Now
eBook - Rethink Your PLM
A lot has changed since the 90s. You don't surf the Web using dial-up anymore, so why are you still using a legacy PLM solution that's blocking your ability to innovate? To develop and launch products today, you need a flexible, cloud-based PLM, not a solution that's stuck in the past. Download Now

Close Box

Join Eng-Tips® Today!

Join your peers on the Internet's largest technical engineering professional community.
It's easy to join and it's free.

Here's Why Members Love Eng-Tips Forums:

Register now while it's still free!

Already a member? Close this window and log in.

Join Us             Close