# How to apply this boundary condition

**URL:** <https://calculix.discourse.group/t/how-to-apply-this-boundary-condition/2550>\
**Category:** Uncategorized\
**Created:** [January 6, 2025, 7:48am UTC](https://calculix.discourse.group/t/how-to-apply-this-boundary-condition/2550 "2025-01-06T07:48:35Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Anoop\_ng](https://avatars.discourse-cdn.com/v4/letter/a/4491bb/32.png) [@Anoop\_ng](https://calculix.discourse.group/u/Anoop_ng)\
**Post date:** [January 6, 2025, 7:48am UTC](https://calculix.discourse.group/t/how-to-apply-this-boundary-condition/2550/1 "2025-01-06T07:48:36Z")

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Hey All,

I want to perform a modal analysis in Prepomax.  
I want to apply a boundary condition that I come across.  
This is how the problem definition is:

 ![image](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/7/7323e9428019f66500310d5f45867574a74822d7.png)  
I want to create a rigid body element that connects all the inner nodes of a hole.  
This rigid body element should be attached to one end of a spring with translational stiffness 1N/mm and rotational stiffness of 1N/mm, while the other end of the spring is fully constrained in all 6 DOF’s. Couldd you help me solve this problem.

Thanks  
Anoop

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<div class="post-metadata">

**Author:** ![Calc\_em](https://avatars.discourse-cdn.com/v4/letter/c/43a26b/32.png) [@Calc\_em](https://calculix.discourse.group/u/Calc_em)\
**Post date:** [January 6, 2025, 8:20am UTC](https://calculix.discourse.group/t/how-to-apply-this-boundary-condition/2550/2 "2025-01-06T08:20:03Z")

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PrePoMax has point spring constraint. Those are node to ground springs so you select one node (reference point of a rigid body constraint in this case) while the other end is assumed to be grounded (fixed).