What does the $n$ do in $1/(j \omega)^n$
What do you mean with Beam in this context.... Particle Beams in LINACs? Structural Beams in Buildings?. 

$j\omega$ is a phasor term from frequency analysis. 

$\frac{1}{j\omega}$ is the integration as @msm showed. 

If you want to integrate two times, just use cumtrapz two times.

But as you said, this is only a "term" complementing a frequency model, which it would be really good to have here in order to help you more... You never simulate that term alone.