# Bend-twist coupling

**URL:** <https://forums.nlr.gov/t/bend-twist-coupling/2180>\
**Category:** Structural Analysis\
**Created:** [December 12, 2019, 9:24am UTC](https://forums.nlr.gov/t/bend-twist-coupling/2180 "2019-12-12T09:24:24Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Dhivya.Sundar](https://avatars.discourse-cdn.com/v4/letter/d/e36b37/32.png) [@Dhivya.Sundar](https://forums.nlr.gov/u/Dhivya.Sundar)\
**Post date:** [December 12, 2019, 9:24am UTC](https://forums.nlr.gov/t/bend-twist-coupling/2180/1 "2019-12-12T09:24:24Z")

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Hello

I am trying to study the effect of bend-twist coupling on the structural mechanics of a wind turbine blade using FAST. In order to incorporate the coupling using the anisotropic property of composite laminates can I possibly change the stiffness matrices in the blade input file with the laminate stiffnesses? Is that enough?

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**Author:** ![Jason.Jonkman](https://dub1.discourse-cdn.com/nrel/user_avatar/forums.nlr.gov/jason.jonkman/32/3086_2.png) [@Jason.Jonkman](https://forums.nlr.gov/u/Jason.Jonkman)\
**Post date:** [December 12, 2019, 1:48pm UTC](https://forums.nlr.gov/t/bend-twist-coupling/2180/2 "2019-12-12T13:48:41Z")

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Dear Dhivya,

There are two ways to induce bend-twist coupling in a blade…through the geometry of the blade and through an anisotropic composite laminate layup. Both of these effects can be simulated in the BeamDyn module of FAST / OpenFAST. For the latter, BeamDyn allows the user to specify the full 6x6 stiffness matrix at each beam cross section, which allows for analyzing any anisotropic composite laminate layup.

Best regards,