Internal ＆ external duct acoustic fields are calculated in this thesis by using a finite element method. The far field's nonreflecting boundary condition is enforced by using a wave enveloped element, which is a kind of finite element method. The geometry is assumed an axisymmetric duct. This thesis is divided into three categories; internal duct acoustic field, external acoustic field, and a combind internal ＆ external acoustic fields.
To consider the internal problem, the sound pressure are calculated when a fan is located at the exit part of the duct. Effects of uniformly moving medium are also calculated inside duct. and the sound reductions of the primary source are observed when both the primary and secondary source is located inside the duct. A pulsating sphere and an oscillating sphere problem are calculated to verify the external problems, and compared with exact solutions. When the wave envelope element method is applied at the far boundary, the calculated finite element solutions show good agreements with the exact solutions.
As the last problems, the combind internal ＆ external duct acoustic fields are calculated and visualized when monopole sources are distributed inside the duct. The more realistic propeller sources are solved when are distributed inside the duct with a shroud. Effects of propeller's blade number, slope of the shroud, and mean flow are also calculated at far field under the constant thrust condition. It is observed that the directivity of sound intensity outside the duct is beaming toward the axis for high frequency of sources.
