Active Control on Duct Noise and Isolation Platform

Base on the principle of the superposition of waves, active noise control (ANC) and active vibration control (AVC) is achieved by adaptively tuning a secondary source which produces an anti-noise of equal amplitude and opposite phase with primary source.
This thesis includes two parts of study which are shown as below.
The first part of this thesis presents the study on the acoustic attenuation in a duct by using the combination of fuzzy neural network (FNN) with error back propagation algorithm to control secondary source. The most important advantage of fuzzy inference system is that the structured knowledge is represented in the form of fuzzy IF-THEN rules. But it lacks the ability to accommodate the change of external environments. Combining neural network with fuzzy system can help in this tuning process by adapting fuzzy sets and creating fuzzy rules. The performance of attenuation and control error can be measured by the microphone placed in the downstream of duct. The results of this study show that the acoustic attenuation by 40dB for pure-tone noise and nearly 30dB for dual-tones noise are obtained.
In the second part of this thesis, it presents the study on the vibration attenuation in an isolated platform by combining multi-layer perception (MLP) neural network, radial basis function (RBF) neural network, cerebella model articulation controller (CMAC) neural network and fuzzy neural networks (FNN) with error back propagation algorithm to control voice coil actuator. Besides, for 3-points and 4-points control for this isolated platform, a simple control method, the adaptive finite impulse response (FIR) control method is applied to attenuate vibration of external disturbance.
Usually, the methods in past time to control vibration were mainly designed by using mathematical models, which must be nearly close to the actual plant models. As regards to these utilized control methods, the most important advantage of them are that they have capability of self tuning the parameters of controllers and could adapt the changes of the environments. The performance of attenuation and control effectiveness can be evaluated by placing the accelerator to measure the amplitude at the center of the isolated platform. The experimental results in this study show that the control methods as adopted could greatly attenuate the vibration of resonance and external disturbance in an isolation platform.