Solving Linearized Euler Equation in frequency space using Weak Form PDE module

Hi,

I am trying to solve the Linearized Euler Equation (LEE) in frequency space using 'Weak form PDE' module. For 1-D, uniform mean quantity assumptions, the LEE is given by:

Momentum: rho_mean(iomegau+u_meanux)+px = 0 Energy: iomegap+u_meanpx+gammap_mean*ux = 0

If the BCs are rigid at both ends, the first theoretical eigen-frequency is given by:

f1 = c/(2L(1-M^2))

However, when I solve this problem with weak form PDE module, I got a different answer from the theoretical one, and could not find where I am wrong.

The attached files contain the ppt that summarized the procedure I took as well as the COMSOL file.

Thanks,