Question: Variable change in PDE

Hello All,

I am doing research for my master's thesis and I am trying to type a PDE into maple and have been struggling for about 2 weeks now. I am new to Maple but have had a lot of Matlab experience. I've seen a couple of ways to do variable changes and things but I'm still.

These are the substitutions I'm trying to do.

into this equation, but and some of these terms are 0 (x*d/dt are 0, P, and M_e, and q_ye).

 So it is basically a Euler-Bernoulli beam with a free vibration.

I tried to use dchange to do the substitutions but I am having trouble defining ...

 or doing both

 I see why there is an error but I don't know how to fix it.

I've also tried

Which is close but still doesn't look quite right. because d/dt(omega*t/2) -> omega/2

Any thoughts?

Thanks in advance