Active noise control in a duct with flow

In this thesis, active noise control in a duct with flow is investigated. A one dimensional acoustic duct model, in which fluid medium inside the duct has a mean flow velocity, is presented. The acoustic duct model is solved in Laplace domain and infinite dimensional system transfer functions are obtained. For controller designs, appropriate microphone and noise canceling source locations inside the duct are determined. In numerical studies, ideal boundary condition case (open end) and general boundary condition case (frequency dependent impedance end) are investigated. For these boundary conditions, low order finite dimensional transfer function approximations of actual system transfer functions are obtained. It is found that, in a selected frequency range, approximations represent actual system in a satisfactory way. By using approximated system transfer functions, low order optimal H2 and H? controllers are synthesized via linear matrix inequalities method found in linear time invariant finite dimensional control theory. Closed loop frequency response and time domain simulations show that the controllers successfully suppress unwanted sound which propagates along the duct.