Identification And Location Of The Sound Source Based On The Phase Conjugation Method

Currently, the ship noise has become an important factor of threat to the safety and the influence to its battle effectiveness of the vessel. The main tool of the control of the ship noise is the identification and location of the sound source. Therefore, to study the identification technique of the sound source has important theoretical and practical value for the noise reduction to improve and accelerate the modernization of naval equipment.This dissertation addresses a detailed study of numerical analysis and experiment research of the identification and location of the sound source based on the phase conjugation method. The major contribution and conclusion of this dissertation are as follows:The basic theory of phase conjugation is stated at first. The parameters such as element spacing, array area, source frequency, array forms of phase conjugation arrays consisting of discrete elements are studied numerically for point sound source localization. The effect of the reflecting surfaces on focusing properties of phase conjugation was also discussed. The amplitude of the acoustic sink which is based on the concept of the sink by introducing in time reversal method is calculated by two different kinds of methods and the effect of the spherical radius on focusing properties was also discussed. The numerical results show that: The element spacing should be less than 0.5?, to break the diffraction limit with the phase conjugation array only made of dipole transceivers in the near field and the optimal element spacing is 0.15?. Regarding to the number of array elements and the performance the optimal array form is the cross array which leads to subwavelength focusing with fewer elements. If the array and the sound source are the conformal surfaces, the field amplitude is proportional to the sound radiation power. The surface increases the field magnitude produced by the phase conjugation array when the reflection coefficient increases. The reflecting surface does not increase the spatial resolution. The diffraction limit could be broken at certain distance by introducing the acoustic sink for the two methods. The radius of the spherical measurement face must be less than one wavelength according to the properties of the evanescent waves.The identification and reconstruction of the acoustical steady propagation field radiated from a single frequency in room are studied numerically using discrete elements based on the phase conjugation method by FEM. Two different kinds of array forms of phase conjugation arrays are studied for sound source localization such as the planar array and the linear array. In addition, the influences of the existence of sound absorbing material on the wall on the focusing properties are also discussed. The numerical results show that:The phase conjugation method can completely achieve the identification and location of the acoustical source in room no matter using the planar array form or the linear array according to FEM. The linear array form can obtain the subwavelength focusing with fewer elements. The optimal distance between the array and the sound source is 0.5??2?to get the best reconstruction results. The smaller the absorption coefficient, the more to meet the multi-path phase compensation principle, the better reconstruction of the sound source.The phase conjugation method has been used for the identification and reconstruction of the complex sources. Three kinds of sound source such as a plate, a pulsating cube and the vibro-acoustic underwater cylinder shell are involved to verify the effectiveness of the method. The surface pressure, the surface normal velocity, the radiation power, and the intensity are reconstructed with different phase conjugation arrays. The influence of the reflecting surface such as sea surface or sea bed on the identification is investigated for the underwater cylinder shell. Then the normal velocity distribution of the plate and the cylinder shell is reconstructed by two different methods after the surface pressure distribution is obtained by the phase conjugation method. The numerical results show that:The best identification results could be achieved by the array made of dipole transceivers based on pressure gradient measurement in the near field for these three kinds of sound sources. Phase conjugation arrays achieve very high resolution to identify the surface pressure and normal velocity and reconstruct the radiation power and the intensity very well. The reflecting surface improves the identification accuracy of phase conjugation arrays. The method based on the pressure gradient method can get the approximate distribution of the surface normal velocity and is simple to implement if the surface impendence relationship is unknown. The method based on the surface impendence relationship achieves better identification results of the surface normal velocity.A method combining phase conjugation with interior boundary element method is developed for the identification of the pressure and normal velocity distribution of a vibrating plate. An interior problem is formed by enclosing the phase conjugation array plane and the plate surface. The pressures at the array elements are phase-conjugated as the specified pressure boundary condition. The impedance relationship between the surface pressure and the surface normal velocity of the plate is utilized as a specified impedance boundary condition. The interior boundary element method is applied to solve the interior problem. The identification of the surface pressure and normal velocity distribution is studied numerically. The numerical results show that with the array located in the near field the proposed method achieves subwavelength focusing to identify the surface pressure and normal velocity distribution and clearly shows the response shapes. The reconstruction precision increased when the measurement array is closer to the plate, and the distance should be less than 5 A. When the force located at the different point and the excitation frequency is low, the results are also accurate.The experiment of the cylinder shell is performed in the semi-anechoic room to confirm the validity of the phase conjugation method applying to the identification of the sound source. The radiated complex pressure of the cylinder shell is measured through the scanning array and the radiated pressure and the normal velocity is reconstructed by phase conjugation method. The test results show that:The phase conjugation arrays achieve very high resolution to reconstruct the radiated pressure and normal velocity amplitude distribution. This experiment verified the feasibility of the phase conjugation method utilized in identification and location of the sound source and has the huge utility value in engineering.