Analysis Of Diesel Engine Radiated Noise And Subjective/Objective Evaluations On Sound Quality

The diesel engine radiated nosie was taken as the subject of this research. The radiated noise sources were identified using experimental methods and virtual techniques. Virtual techniques such as finite element method and multi-body dyamic method were applied to predict the surface vibration and radiated noise from the diesel engine, and optimize engine structure. The sound quality of the radiated nosie was evaluated subjectively based on a cochlear model built from anatomical data and physiological characteristics, and objectively based on paired comparison and marking studies.The spectrum of the diesel engine radiated noise was obtained from experiments as well as the analytic hierarchy process, AHP, which was used to calculate contributions of different engine speed and frequency range to the overall nosie level. Next, the contributions of different engine components to the overall radiated noise at different frequency ranges at a given engine speed were also calculated using the AHP. The influence factors of the radiated noise were given in terms of weight factors which can show the quantitative importance of each engine component, providing guidance to structural optimazation. The virtual prototype of the diesel engine was built using the finite element method and the multi-body dynamic method. Comparison of the results of modal analysis between the simulation and experiments shows that the computational model is accurate. The predicted surface vibration level of the engine has a good correlation with the radiated nosie distribution obtained from the experiments, indicating that this virtual prototype can be used to predict the radiated nosie level of the engine. In order to reduce vibration and noise of the diesel engine, structural optimizations were carried out for engine body, skirt and crankcase. The oilpan was also optimized due to its contribution to the overall radiated nosie is maximal at the rated speed, 2200 rpm. Several actions, such as adding strengthening ribs and changing thickness, were applied to stiffen the oilpan.The traveling wave model of the cochlea was built in contrast with those formed based on filter band. Comparison between predicted results and experimental data of the chinchilla cochlea qualitively shows that this traveling model of the cochlea is reasonable. The wave finite element method was used to calculate wave propergation in the cochlea and the response of the basilar membrane was calculating using the WKB approximation for a stimulus at a given frequency.Noise samples at different frequency ranges were chosen based on engine experiments for the subjective evaluation. People of different age, background and gender were invited for the jury test. Paired comparison and marking were used as the jury test to evaluate the noise samples subjectively and subjective satisfaction was obtained. The loudness value due to a 1 kHz, 40 dB tone was first calculated using the aformentioned cochlear model to show its accuracy. The phyco-acoustic parameters such as loudness and sharpness were calculated using the cochlear model and the correlation between those objective parameters and subjective satisfaction was calculated to show the contribution of each phyco-acoustic parameter to subjective satisfaction. Finally, a neural network model was built and trained to show the nonlinear realation between objective phyco-acoustic parameters and subjective satisfaction.