
Hello,
I am new to modeling and simulation in general and am trying to find the modes of an acoustic resonator including dissipative effects and thermal conductivity. I am using the Poisson equation as given in FEATool by
dts_poi*p'  d_poi*(px_x + py_y + pz_z) = f_poi
with dts_poi as the time scaling coefficient, d_poi as the diffusion term, and f_poi the source term, set to 0. I have tried at length to figure out how this equation is obtained, or even the Helmholtz equation as provided in the "Resonance Frequencies of a Room" tutorial, given by
u'  (ux_x + uy_y + uz_z) = 1.
Neither one seems like a standard variational construction of the equation. I get the modes predicted but don't understand why. So how can one obtain these equations from the standard (nabla)^2 * f = x?
