I would like to calculate the local force vector using a stress field of the size of (0, Vh). Assuming that the stress field is already projected on to the x, y and z components (so I have three stress components) how do I obtain F(0, Vh) ?

Thank you for your reply. In my case the stress vector is already calculated, i need to calculate the local force on each node using this stress vector. So i thought that i need to take the average stress on each cell then multiply by this cell area to get the force then project onto the nodes. I was wondering how can i implement it, or is there a better way to do it?