Transform stiffness matrix from local to global 1

[hosein990]

Hi
I want to compute transformation matrix for a flat shell element which has 6-dof per node to convert stiffness matrix from local to global coordinate. does anyone know about this?

 

[rb1957]

CID transformation ... your element is in a local CID (defined by the nodes) and you want a global CID ... 1st year math, no?

another day in paradise, or is paradise one day closer ?

 

[hosein990]

yes

 

[rb1957]

so you're looking for a simple transformation from one co-ord system to another ... it'll be in any vector math book (or wiki). Your local co-ord system is defined by three nodes.

The complexity for you is warped elements (when the four points do not fall on a plane). The "best" way to solve this is ...
1) don't allow warped elements, or
2) use a best fit solution (you'll have four equations defining the plane, ie redundant equations, and the solution is well known).

another day in paradise, or is paradise one day closer ?