Development of Active Exhaust Noise Cancellation System (Part 1) * - Optimization of AENC System by use of Acoustic Analysis -

In recent years, the demand for the reduction of noise emitted into the environment has strongly increased in order to prevent noise pollution. As the major contributor of emitted noise into the environment is exhaust noise in ships, it is necessary to reduce exhaust noise as much as possible. Conventionally, passive silencer techniques are used, but larger silencers are now needed in order to achieve larger noise reduction. However, because of the limitation of space, it was actually difficult to reduce the exhaust noise on a ship. In order to reduce the exhaust noise as well as minimizing the occupied space, the active noise cancellation technique was applied to the exhaust noise silencer for diesel engines. To reduce the exhaust noise efficiently, at first, the acoustic behavior in an exhaust pipe was calculated by the boundary element method. At first, by optimizing the length of pipes and the positions of microphones and speakers, the active exhaust noise cancellation system (AENC) was applied to the main engine for marine use. Also, by applying acoustic resonance aggressively, the AENC, with only one speaker system, was developed for auxiliary engines. Finally, by assembling a passive silencer for high frequency noise, the active exhaust noise silencer was developed.