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Reaction forces at nodes under NODAL_RIGID_BODY

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(@harsha)
Unpaid Intern
Joined: 4 years ago

Hi,

 

I am simulating the bending of a tape spring (a cut out from a carpenter's measuring tape) by applying rotation boundary conditions at both the ends. I need to compute moments at the ends but I could not output reaction forces at the nodes.

 

I placed a massless node at each end on the neutral axis and constrained the nodes on the end (along with this massless node) using *CONSTRAINED_NODAL_RIGID_BODY. This is to make sure that the end is clamped. X-rotation is applied on the two massless nodes. Currently, in binout, all the forces are 0 despite using *DATABASE_NODAL_FORCE_GROUP.

 

How can I output the reaction forces (or moment at the massless nodes)? 

 

I can email you the relevant files in case you need them.

Thanks very much!

 

Cheers,

Harsha.

6 Replies




Negative Volume
Posts: 639
Admin
(@negativevolume)
CEO
Joined: 5 years ago

@harsha Did you include the node ids that you want forces from in *Database_History_Node? This basically tells LS-Dyna that you want data for those nodes. One you have that you should be able to get forces using *DATABASE_NODFOR if the nodes have applicable forces. The setup could also be an issue, but check this first. 

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5 Replies
(@harsha)
Joined: 4 years ago

Unpaid Intern
Posts: 8

Hi @negativevolume,

Thanks for your quick reply. I tried that; did not work 🙁

My model is working well. I can see the deformed shapes. I simulated using load control also. I applied moments at the two massless nodes and I could output resulting rotation at those nodes. In experiments, the structure snaps after a certain rotation and the moment falls to a steady state so, I can only go so far with the load control. Rotation control can go all the way.

Regards,

Harsha.

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Negative Volume
Admin
(@negativevolume)
Joined: 5 years ago

CEO
Posts: 639

@harsha

So I guess I'm confused as to why you are trying to get the force from massless nodes? Theoretically that should not be possible. What you may have to do is create a zero-length discrete beam between the massless nodes and coincident nodes and get the force and moment from that beam. You can always email me your setup and I can take a look. 

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(@harsha)
Joined: 4 years ago

Unpaid Intern
Posts: 8

@negativevolume

Hi,

I also tried to get the forces from other original nodes on the edge but couldn't. I have to plot Moment vs angle so, I needed the forces on all the nodes OR directly, moment itself.

I am attaching my .k file here in the form of a text file. I can also email you if needed.

Thanks once again for your time and help.

Cheers,

Harsha.

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(@harsha)
Joined: 4 years ago

Unpaid Intern
Posts: 8

I have found another way to get the forces at the end nodes.

Instead of applying rotation displacements at both the ends, I applied it at one end and clamped the other end. For my problem, the result will be the same. Now, I am able to output spc forces at the clamped end and using these, moment at the clamped end can be calculated. Due to static equilibrium, we can assume that the moment at the other end is the same (although I couldn't compute it).

I am attaching the resulting Moment vs angle plot if you are interested.

Thanks once again for your time!

Figure LS Dyna vs ABAQUS
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Negative Volume
Admin
(@negativevolume)
Joined: 5 years ago

CEO
Posts: 639

@harsha

Awesome, great to hear that you got it working! Great job 

 

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