A Study on the Reduction of the Aerodynamic Drag and Noise Generated By the Roof Air Conditioner of High-Speed Trains

In order to investigate how the aerodynamic drag and noise produced by the roof air conditioner of a high-speed train can be reduced,the related unsteady flow in the near-field was computed using the method of large eddy simulation.In this way,the aerodynamic source for noise generation has initially been determined.Then,the far-field aerodynamic noise has been computed in the framework of the Lighthill’s acoustics analogy theory.The propulsion height and flow-guide angle of the roof air conditioner were set as the design variables.According to the computational results,a lower propulsion height or flow-guide angle is beneficial in terms of aerodynamic drag and noise mitigation.However,compared to the design scheme with propulsion height of 0mm,the aerodynamic drag coefficient of the configuration with propulsion height of 190mm and flow-guide angle of 30°is slightly larger,while the aerodynamic noise is obviously reduced.Thus,from the viewpoint of the aerodynamic drag and noise,the design scheme with propulsion height of 190 mm and flow-guide angle of 30°is the optimal configuration in the range of conditions examined in the present work.

Distinguishing Oil and Water Layers in a Porous Cracked Medium by Interpreting Acoustic Logging Data on the Basis of Hudson Theory

During surveys, water layers may interfere with the detection of oil layers. In order to distinguish between oil and water layers in a porous cracked medium, research on the properties of cracks and oil and water layers and their relation to acoustic logging rules is essential. On the basis of Hudson＇s crack theory, we simulated oil and water layers in crack-porous medium with different crack parameters corresponding to the well-field response. We found that in a cracked medium with high crack angle or low number density of cracks, compressional and shear wave velocities are sensitive to crack characteristics; further, these velocities are more sensitive to crack characteristics when the waves propagate through the water layer than when they propagate through the oil layer. Compressional and shear wave velocities increase with an increase in crack angle： in the water layer, the increase is approximately linear. On comparing the full waveforms observed in the oil and water layers, we find that the amplitudes of most waves are higher in the water layer. Among the considered waves, the Stoneley wave suffers maximum amplitude attenuation in the oil layer. The maximum excitation intensity for oil layer is greater than that for the water layer. These results can guide further cracked media logging field exploration work.

Theory of passive localization for underwater sources based on acoustic ray modeling

The theory of passive localization for underwater sources based on acoustic ray channel modeling is discussed. The principles of channel modeling in Ray-theory, determination of eigenrays which connect source and receiver, analysis of DOA arriving structure and time delay spectrum arriving structure, their relationship to source location are given in the paper. Source location is estimated by matching measured DOA and TDS to their calculated counterparts. The method of Ray-theory based passive localization features its simplicity, less calculation, short array aperture and robust performance to environment parameters, as compared with those methods based on Normal Mode theory.

Feynman diagram theory for multifrequency nonlinear acoustics

The Feynman diagram theory with the state-space formalism is adopted to study the multifrequency nonlinear acoustics effects. By establishing the relation between the strain magnitude corresponding to any final state S(m1,…,mn; x) and the number of paths from the initial state of the interactingphonons to the final state, not only the complete perturbation solutions but also the corresponding analytical expressions of the acoustic harmonics and intermodulation products have been obtained. For a few special cases, results of our theory is consistent with those obtained by conventional methods. While the general solution for any number of frequencies can easily be obtained by our theory, this is impossible by using conventional methods.