again I'm dealing with the basics of the Finite Element Method. I found a very nice PDF on tetrahedral elements: . I'm intersted in the "general" / "arbitrary" Iso-P Tetrahedron. But I have a little problem figuring out the derivatives of the shape functions for global coordinates.
At the top of page "17?12" they give the partial derivatives for a function F. dF/dx = F_k * dN_k/dZeta_i * a_i/J
where "F_k" is the value of the function "F" at node "k". "N_k" is the shape function of node "k" and "Zeta_i" is the i-th local coordinate. "a_i" and "J" are also given.
My problem: I need the derivative of N_k with respect to the global coordinates. I like to assemble the strain-displacement matrix '[B]' of this values. Can I get this from the function above? My guess is for a given node: