# Coupling constraints: capabilities and local coordinate systems not compatible

**URL:** <https://calculix.discourse.group/t/coupling-constraints-capabilities-and-local-coordinate-systems-not-compatible/4111>\
**Category:** Uncategorized\
**Created:** [September 15, 2026, 1:05pm UTC](https://calculix.discourse.group/t/coupling-constraints-capabilities-and-local-coordinate-systems-not-compatible/4111 "2026-09-15T13:05:55Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![roy.roffler](https://avatars.discourse-cdn.com/v4/letter/r/71c47a/32.png) [@roy.roffler](https://calculix.discourse.group/u/roy.roffler)\
**Post date:** [September 15, 2026, 1:05pm UTC](https://calculix.discourse.group/t/coupling-constraints-capabilities-and-local-coordinate-systems-not-compatible/4111/1 "2026-09-15T13:05:55Z")

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I’m very new to CalculiX and so far, are only using it via PrePoMax. However, I do have experience with Ansys and NX Nastran. In both of these programs, you can apply loads or BCs on external points/nodes, which are coupled to regions of meshed bodies with coupling constraints. These can be rigid or allow the coupled regions to deform.

In NX Nastran, as an example, these two options are:  
RBE2: Rigid Multi-Point-Constraint  
RBE3: Deformable Multi-Point-Constraint  
(I’m aware that these elements also have limitations.)

To my understanding, CalculiX has 3 options for such coupling constraints (taken from here: [Different coupling constraints and their limitations](https://calculix.discourse.group/t/different-coupling-constraints-and-their-limitations/2586) ). The first in the table below is rigid, while the other two are deformable.

 ![image](https://global.discourse-cdn.com/free1/uploads/calculix/original/2X/e/e2a9a13a292a5275c2d90902fc5489692ac297d8.png)

Now, when defining loads or BCs, local coordinate systems are often very helpful and sometimes even necessary. However, defining loads or BCs on coupled nodes **using local coordinate systems** is not supported by CalculiX.

Therefore, my questions related to local coordinate systems:

- Could that functionality be added to CalculiX in the future?  
(Or is this just not possible due to numerical reasons?)
- Is there an established workaround for that issue?

Then, while at it, I do have some additional questions concerning coupling constraints and their capability:

- **\*Coupling & \*Distributing:**  
Is it possible to include BCs (Ux & URx) in future versions of CalculiX?
- **\*Distributing Coupling:**  
Is it possible to include URx & Mx in future versions of CalculiX?
- Again: Are there established workarounds for these issues?

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**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:** [September 15, 2026, 1:14pm UTC](https://calculix.discourse.group/t/coupling-constraints-capabilities-and-local-coordinate-systems-not-compatible/4111/2 "2026-09-15T13:14:40Z")

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It seems that `*DISTRIBUTING COUPLING` can work with `*TRANSFORM` applied to its ref node (tested using a modified `distcoup.inp` file from the documentation). However, `*COUPLING` + `*DISTRIBUTING` fails with an error:

> \*ERROR in cloaddistributing: a transformation  
> is not allowed in the reference node  
> of a \*distributing definition;  
> reference node: 67757

As an alternative, one may consider coupling orientations.