Research On Noise Source Sensitivity Analysis And Low Noise Structural Design For The Small Generator

Internal combustion engine driven generator sets are widely used in many fields both in military and civilian,while they can cause serious noise problem,not only affecting the normal work and life of nearby personnel,but also damage the equipment itself.Low-noise generator sets development is an essential work.Physical sound source identification and sensitivity analysis are important for the noise control of generator sets.However,the mapping relationship between physical sound source and radiated noise is highly nonlinear due to the influence of composite factors such as transmission path,mechanical structure,engine working cycle,speed fluctuation,etc.Sensitivity index cannot be directly calculated due to the complexity of the system equation.Accordingly,it is valuable to identify the main noise source of generator sets,to develop its sensitivity and low-noise structure in noise control of generator sets.In this paper,physical surface noise identification and physical source identification were conducted.Based on the identification of physical source,support vector machine(SVM)regression theory was applied to noise prediction,and noise source sensitivity was analyzed.Then,the design of low-noise structure was studied: for the main sound source from valve mechanism noise,the influence of main structural parameters on the dynamic character was analyzed;for the transmission path-acoustic enclosure,the influence of inlet and outlet position,sound source position,temperature field and flow field of circulating air on the external sound field was analyzed.Finally,low-noise structure design of the generator set was developed.The main research results are as follows:Taking a small generator set as the research object,near field acoustic holographic test was conducted with photoacoustic tomography technology.And sound intensity distribution and noise imaging was obtained by reconstructing the sound source surface according to the test result.The position of the main sound source on the surface of the generator set was centralized in the inlet and outlet vents area in accordance with sound intensity distribution.At the same time,noise imaging analysis cannot accurately identify the surface radiated sound,due to the lack of spatial resolution of the test array,the complex shape of generator surface and the mutual reflection of the parts.The empirical mode decomposition(EMD)for blind source separation cannot ensure that the IMF components are completely orthogonal.And independent component analysis(ICA)cannot be realized by using single channel signal input.To solve these problems,the EMD and ICA cooperative analysis were used to blind source separation.Simulation results show that the EMD-ICA collaborative analysis method can separate multiple independent source signals with single channel input,which provided a prerequisite for independent noise source identification.Based on the theory of wavelet analysis,the independent component of blind source separation was decomposed by continuous wavelet transform(CWT).Comparing to the prior knowledge on internal combustion engine noise signal in time and frequency domain,wavelet time-frequency diagram was analyzed to identify the main physical noise source represented by independent component.Results show that the radiated noise of the small generator set is mainly composed of valve opening and seating impact noise,gear meshing noise and intake noise.The support vector machine(SVM),multiple linear regression and neural network were respectively used to study the mapping relationship between the physical sound source and the sound pressure level of the measuring field.Results show that SVM is superior to multiple linear regression and neural network in predicting accuracy and stability.Sensitivity model of the physical sound source was build based on SVM,and sensitivity value was calculated using this model.For the transmission path control,this thesis aims at the low-noise structure design of the sound proof hood,the influence of inlet and outlet position,sound source position,temperature field and flow field of circulating air on the external sound field was analyzed.Simulation model was simplified according to the analysis,and the location of the air vents and sound source were optimized.Simulation results show that the noise level of the generator set is less than 66 dB(A)at 7m,after optimizing the sound proofhood structure under the consideration onto the influence of sound,heating and flow fields.For the main physical sound source control,dynamical model of the valvetrain multibody system was established.Dynamic characters of the model were simulated and analyzed by the actual boundary conditions.The effects of the stiffness of the parts,the rigidity and preload of the valve spring,and the valve clearance on the dynamic characters were simulated.Simulation results can guide low-noise structure design of the valve train.