Prediction of Outdoor Noise Propagation Induced By Single-Phase Power Transformers

Outdoor power transformers are one of the most pervasive noise sources in power transmission and distribution systems.Accurate prediction of outdoor noise propagation plays a dominant role for the evaluation and control of noise relevant to the transformer stations.In this paper surface vibration tests are carried out on a scale model of a single-phase transformer tank wall at different excitation frequencies.The phase and amplitude of test data are found to be randomly distributed when the excitation frequency exceeds the seventh mode frequency,which allows the single-phase power transformer to be simplified as incoherent point sources.An outdoor-coherent model is subsequently developed and incorporated with the image source method to investigate noise propagation from single-phase power transformers,due to the occurrence of multiple reflections and diffractions in the propagation path of each point source.The proposed model is used to calculate the sound field of the power transformer group by exploiting the additional phase information.In comparison with the ISO9613 model and the boundary element method,it is found that the proposed coherent image source method leads to more accurate prediction results,and hence better performance for the prediction of the outdoor noise induced by single-phase power transformers.

Efficient Computational Approach for Predicting the 3D Acoustic Radiation of the Elastic Structure in Pekeris Waveguides

Ocean boundaries present a significant effect on the vibroacoustic characteristics and sound propagation of an elastic structure in practice.In this study,an efficient finite element/wave superposition method(FE/WSM)for predicting the three-dimen-sional acoustic radiation from an arbitrary-shaped radiator in Pekeris waveguides with a lossy seabed is proposed.The method is based on the FE method(FEM),WSM,and sound propagation models.First,a near-field vibroacoustic model is established by the FEM to obtain vibration information on a radiator surface.Then,the WSM based on the Helmholtz boundary integral is used to pre-dict the far-field acoustic radiation and propagation.Furthermore,the rigorous image source method and complex normal mode are employed to obtain the near-and far-field Green’s function(GF),respectively.The former,which is based on the spherical wave decomposition,is adopted to accurately solve the near-field source strength,and the far-field acoustic radiation is calculated by the latter and perturbation theory.The simulations of both models are compared to theoretical wavenumber integration solutions.Finally,numerical experiments on elastic spherical and cylindrical shells in Pekeris waveguides are presented to validate the accuracy and efficiency of the proposed method.The results show that the FE/WSM is adaptable to complex radiators and ocean-acoustic envi-ronments,and are easy to implement and computationally efficient in calculating the structural vibration,acoustic radiation,and sound propagation of arbitrarily shaped radiators in practical ocean environments.

Response of saturated porous media subjected to local thermal loading on the surface of semi-infinite space

Heat source function method is adopted in the present paper to derive elementary solutions of coupled thermo-hydro-mechanical consolidation for saturated porous media under conjunct actions of instantaneous point heat source, instantaneous point fluid source and constant volume force. By using the so-called fictitious heat source method and images method, the solutions of a semi-infinite saturated porous medium subjected to a local heat source with time-varied intensity on its free surface are developed from elementary solutions. The numerical integral methods for calculating the unsteady temperature, pore pressure and displacement fields are given. The thermomechanical response are analyzed for the case of a circular planar heat source. Besides, the thermal consolidation characteristics of a saturated porous medium subjected to a harmonic thermal loading are also given, and the fluctuation processes of the field variables located below the center of heat source are analyzed.