A displacement related force load

General Questions
1

I need to make a foece which is displacement realted, like a spring.
Calculix is support *SPRING, and i notice there is POINT SPRING, SURFACE SPING in the PrePoMax constraint tab. Is there any tutriol or notes to use these ?

Is there anyone have the experiace about this ?

2

Springs currently available in PrePoMax are spring to ground elements so they can be used only to connect a point or surface to “ground”. To apply force via spring (if that’s what you want to do), you would need two node spring elements. For now, they have to be added via Keyword Editor: Spring between two nodes

Otherwise, to make force vary with the solution (displacement), you would need CalculiX Fortran subroutines and this is really complicated.

3

Thank you for reply the quesiton.

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I am making a simulation to estimate a rubber material hardness, a spring to “ground“ is easy for me. Then how to make a “ground“ element ?

4

This is how the two types of springs work:

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  1. Spring to ground (top) - available as Point Spring or Surface Spring in PrePoMax. One end is attached to the selected vertex/surface of the model, while the other end is always grounded (not available for boundary conditions, loads, or attachment to another part of the model).
  2. Two-node spring (bottom) - currently available only in the form of a manual definition using CalculiX keywords in the Keyword Editor. Both ends are available for definitions so one can be attached to the model while the other has force or boundary condition applied (or is connected to another part of the model).

In your case, it seems that you need number 2, right ?

5

For my use ,it is grounded. The force is only generated from that compressed spring, it push the prob in to material. And the displacement can shows the hardness of the material.
So do you mean when i add a “spring “, then this spring is fixed at model locaiton at one end, and another end connector to the face / point I select?
Let me try another.

6

Yes, it’s basically just a compliant boundary condition - instead of rigidly fixing a vertex/face in a given direction, it holds it with a finite (spring) stiffness.

Two-node spring would just give you more ways to use both nodes.

PrePoMax also has compression-only constraint that uses GAPUNI elements. It’s just a compression-only spring - provides resistance in compression but not in tension. It can be used to imitate contact.

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7

I make a new model and make displacement on the bottom block and you are right a Two-node spring is what meet the requirement.
And I check forum seems I could not make the right model for Two-node spring , is there a sample .pmx file I can refer ?
or is there anyway to make 2 reference_point “rigid body“, then 1 point can push another point with spring.

8

Here’s a simple example:

SPRINGA.pmx (2.8 MB)

The last keyword is optional but gives you results from the spring.

2 Likes
9

Excellent reference sample,thank you for your patience

My model is also working, I add a temperary refference point 2 rigid body to get the node number. Then, make a displacement on reference point 2. Spring is working,great.

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