COMSOL Multiphysics™

femwave
Purpose
femwave
Extend FEM structure to a wave equation problem.
Syntax
Description
fem1 = femwave(fem)
xfem1 = femwave(xfem)
fem1 = femwave(fem) extends the coefficients of the PDE problem to a wave
equation problem. xfem can also be an extended FEM structure. In the latter case,
use geomnum to specify the geometry number for the wave extension.
Note: Since COMSOL Multiphysics 3.2, wave equations can be more easily and
efficiently formulated using the e a coefficient or the second time derivative
variable.
When fem is given in coefficient form, fem1 contains extended PDE and boundary
coefficients to solve the wave equation problem
2
∂ u
d a 2 – ∇ ⋅ ( c∇u + αu – γ)
+ β∇u+ au = f
∂ t
where the d a coefficient was stored in the fem.equ.da field of the FEM structure
fem. In the same way, when fem is given in general or weak form, fem1 contains
extended PDE and boundary coefficients to solve the wave equation problem
obtained by replacing the first time derivative term in the standard problem by a
second time derivative.
The function introduces a set of new variables, v, such that
v =
∂u
∂t
172 | CHAPTER 1: COMMAND REFERENCE