Find Closest Vector

I am working on an optimization definition where I use Karamba output.

Each mesh face is assigned a value for bending moment stress, and match the value with the mesh face normal to make a vector. 

What I would like to do next is draw beams across the surface and adjust their depth using the stress-driven vectors.

Is there a way to search for the closest vector? Similar to searching for closest point?

I'd appreciate anything you think would help!

M