The Active Noise Control In Innlet And Exhaust Ducts Of Reciprocating Machines

In recent decades, active noise control (ANC) has become a hot research subject in noise control field. With the advantages of small volume, light mass and effectiveness in low frequency, it attracts much attention. But the researchers have less focused on ANC for inlet and exhaust pipe of reciprocating machines. The critical factors influencing noise attenuation and improving measurements have been studied through the noise property in inlet and exhaust ducts of reciprocating machines.On the basis of the principles of acoustic field in a duct and ANC algorithms, simulated and experimental programmes were carried out aimed at the main frequencies of the noise from the inlet and exhaust pipe of reciprocating machines. The programmes for simulation and experimental study were developed by LabView.The simulation algorithms come from the classic control algorithms , which are the least mean square (LMS) and the recursive least mean square (RLS). A great deal of simulation study was accomplished with both algorithms and some factors such as sampling rate were analyzed on the level of noise attenuation. Then some useful conclusions were presented for the applications in engineering. Considering that the fundamental frequency and multiple frequencies make up the main frequencies in the noise of reciprocating machines, the signals mixed with the fundamental frequency and multiple frequecies were calculated by two algorithms.An experimental system for ANC in a duct was designed and the reasons for deciding major parameters of the system were analyzed. Installation and debugging of the system was completed. The experimental study is based on LMS and the experimental data showed that major phase difference existing between the two acoustic sources would affect noise reduction seriously. A new delayed LMS was brought forward to further improve the noise attenuation. The amount of noise attenuation was obviously increased.During the process of experiments, it found that different positions of error sensor and secondary acourstic source were compared in terms of noise attenuation result. The paper concluded that the best positon for the system is thatthe error sensor lay in the center of the duct and secondary acourstic source was opposite to primary acoustic source.The above simulation and experimental researches analyzed the influencing factors and changing tendency of noise reduction, and an improved algorithm was put forward. The research work has some referential value to the industrial application.