Investigation On The Theory And Its Application Of Sound Radiation Prediction

Sound radiation of moving sound sources, due to the complexity of sound field, hasbeen become a theoretical difficulty of the acoustics research. In order to deal with theproblem, the theory and its application of sound radiation prediction have been investigatedon the basis of the project of noise control of gas compressed system. The model of soundradiation prediction and sound field characteristics of moving sound sources are studieddeeply by employing the theory of moving medium acoustics and the Kirchhoff’s integralmethod.The mainly specific works finished in this dissertation are as follows.1) On the research of theory of moving medium acoustics, the method of analyticalGreen function is presented to predict the sound radiation from compact sources.Theanalytical sound pressure expressions in frequency domain for the dipole of rectilinear androtary motion and the monopole of helical motion in free field are deduced. The soundradiation predictive model of the body of rotary motion is established by the Kirchhoff’sintegral equation with analytical Green function and the mathematic expression of Dopplereffect of rotative sound sources in time domain is educed. Characteristics of radiating soundfield analyzed by the numerical methods include spectrums comprising vibration frequenciesof sound source, rotating basic frequency and harmonics, basic frequency transmitting in therotary shaft direction and harmonics spreading along radial direction and frequency shiftphenomena appearing clearly in higher rotating speed of source. The accuracy of thesesimulative results is verified by the experimentation of fan blades noise. This indicates themethod of analytical green function and the model of sound radiation prediction of movingsound sources in free field are accurate.2) Condisered the influence of sound field from boundares and barriers, the scatteredsound field of moving sound source is discussed theoretically. The model of sound scatteredprediction of rotating sound sources is deduced by the integral equation of Kirchhoff andHelmholtz with the fixed distributional sources. Expressions calculating the exteriorscattering sound fields of the rigid and flexible scatterers are given, which employs scatteredwave of fixed cylindrical surface instead of the incident wave as iterative factor. Soundcharacteristics of scattering field are discussed by simulative methods. Scattering sound fieldhas close relations with sound radiation of sound source, the type of scatterer and theirradiated area on scatterer surface.3) Sound radiation of moving sound source in closed space is developed based on the methods deduced above. By combining the analytical Kirchhoff’s integral equation of withGreen function of structural sound radiation, sound pressure expressions in frequencydomain of cylindrical shell excitated by rotating force and rotating source and the model ofsound radiation prediction of closed space with helical airflow are developed. By numericalanalysis, some key parameters affecting the radiative sound field include the vibrating androtating frequencies of the source, nature frequencies of structure and Mach number of floware explored.The characteristics of radiative sound field are verified by the experimentationof duct aerodynamic noise.4) On the basis of characteristics of sound radiation of moving sound sourcemeasurement method of sound field is presented by combining Focalization withBeamforming. The testing principle and technique are investigated and the rotating linearmicrophone array is designed for testing sound filed. The capability of array microphone istested in lab and its technical parameters and main reasons of errors are discussed.5) By applying the theory of sound radiation prediction, the noise of gas compressedsystemis analysed, especially sound prediction of aerodynamic and structural noise inducedby moving excitation. The accuracy of methods of sound radiation prediction and thevalidity of predictive results are proved by the local noise testing. This investigation willprovide an important foundation for the advanced development of the low noise revolvingmachines.