# Finite element method help

• Apr 28th 2011, 08:51 AM
Josh146
Finite element method help
I'm currently programming the finite element method to construct the stiffness matrix and RHS vector to solve poissons equation on a 2d mesh.

I've been given a vector "connectivity" which is the connectivity array and "xy_coords" which give the coordinates for each node. I've constructed the global stiffness matrix but I'm unsure how to construct the RHS vector. I'm given this:

http://img98.imageshack.us/img98/6618/feaok.jpg

I'm quite new to FEA and I have limited applied knowledge so I'm unfamiliar with centroids etc. Can someone help me with the construction / explain what the one-point quadrature formula means?
• Apr 28th 2011, 10:12 AM
Bwts
What is f(x)? Is that the force vector?.

One point quadrature refers to a numerical approximation of the integral.

Centroid means the geometrical centre of the element.
• Apr 28th 2011, 10:41 AM
Josh146
Thank you. I'm not sure what a force vector is. Here's the question:

http://img576.imageshack.us/img576/1322/fea2.jpg

To compute the LHS (global stiffness matrix), I computed the local stiffness matrix for each element then inputted these matrices into the global matrix. I'm not sure how to implement this numerical approximation to find the RHS vector (what do I do with the linear finite element function?).
• Apr 30th 2011, 06:40 AM
Bwts
I think we may be having a terminology mismatch. Whe you say "linear finite element function" do you mean the shape function?
• Apr 30th 2011, 07:16 AM
Josh146
I've never heard of the shape function but it might be the same thing. Here are some notes which outline the method which I've been using. They don't give an example of the construction of the RHS vector though which is why I have this problem:

FEMNotes - PDFCast.org

The 'v' function is given on the first page.