The propagation and radiation of sound from ducts is of practical concern in many area of engineering among which is engine exhausts, gas-turbin and turbo-jet intakes and exhausts.
In ducts of small cross-sectional area, such as car exhaust pipes, sound propagates in the form of plane waves over most of the frequency range of practical interest, and it is easy to impose the boundary condition. However in ducts of larger cross-sectional area higher order modes can also exist, it is very hard to impose the boundary condition on the outlet end witch is open. Both propagation and radiation from the duct is calculated to treat the boundary condition on the outlet. Boundary condition on the outlet is naturally satisfied. Radiation requires to handle the wave equation in an unbounded(infinite) domain. Finite elements are selected in the near field and the far field's nonreflecting boundary condition is enforced by using a wave envelope element.
The geometry is an axisymmetric duct. A pulsating sphere and an vibrating baffle are calculated to verify the radiation problem. Basic mufflers are calculated and compared the measured value. As the last problems, propagation and radiation from the very large cross-sectional muffler is analyzed.
