Current Issue : January - March Volume : 2021 Issue Number : 1 Articles : 5 Articles
In order to avoid the dependence of mesh method on grids, a 3D global weak-form mesh-free method (MFM) is applied to study\nthe three-dimensional acoustic characteristics of silencers. For the expansion chamber silencers, the 3D acoustic modes are\nextracted and the transmission loss results are computed by using the 3D global weak-form (MFM), which is based on the radial\nbasis function point interpolation method (RPIM) for calculating the shape functions and Galerkin method for discretizing the\nsystem equation. The first 15 order 3D acoustic modes and TL results of a special expansion chamber silencer are presented to\nvalidate the computational accuracy of the proposed technique, and the relative errors are controlled within 0.5% by comparing\nwith the 3D finite element method (FEF) calculations. Additionally, the effects of axial modes on the acoustic characteristics are\ninvestigated, and the pass through frequencies can be eliminated to enhance the acoustic attenuation performance by locating the\nside branch outlet on the nodal lines of axial modes....
This paper presents the comparison of three methodologies to detect if some fans in a matrix are not working properly. These\nmethodologies are based on detecting fan failures by analysing acoustic images of the fan matrix, obtained using a planar array of\nMEMS microphones. Geometrical parameters of these acoustic images for different frequencies are then used to train a support\nvector machine (SVM) classifier, in order to detect the fan failures. One of the methodologies is based on the detection of the faulty\nfan in the matrix, under the hypothesis that only one fan can fail. Other methodology is based on the detection of the specific\nworking situation of the matrix. And finally, the third methodology that is compared is based on determining individually if each\nof the fans of the matrix is working properly or not. The comparison shows that this third methodology is the most reliable....
In order to study the acoustic emission characteristics and Felicity effect in the process of coal fatigue failure and reveal the internal\nrelationship between the fatigue damage evolution law and the acoustic emission activity, with the help of MTS815.02 electrohydraulic\nservo rock mechanics test system and PCI-2 acoustic emission detection and analysis system, a triaxial cycling\nloading acoustic emission test was carried out on the coal samples. The results show that the higher the upper limit stress is, the\nmore obvious the degree of fatigue damage will be caused by coal samples. At the same time, the more active acoustic emission\nsignal will appear. The coal samples under linear loading are on the initial damage state, and slight fatigue, moderate fatigue, deep\nfatigue, and ultimate fatigue failure under cyclic loading. The acoustic emission shows the â??L-â? type development evolution law in\nany previous stress level range, while at the last stress level, it shows the obvious â??U-â? type development evolution law. The higher\nthe frequency of the cyclic loading is, the higher the rate of initiation and expansion of the microcrack will be, while the more\nobvious acoustic emission phenomenon will appear. Furthermore, the ringing counting rate is basically the same as that of the\nenergy counting rate. Under triaxial cyclic loading, a shear failure mode that extends along different directions of fracture surface\nwill be presented. The acoustic emission in the range of different stress levels shows a different degree of Felicity effect. In contrast,\nit is more reasonable to use the principal stress difference as a parameter to study the Felicity effect of coal under cyclic loading....
This paper examines the effects of borehole arrangement on the failure process of coal-like materials based on its energy\nconversion and acoustic characteristics from the perspectives of energy, AE energy, AE spectrum, and frequency band. Findings\nfrom the study revealed that the presence of borehole can significantly reduce the conversion ratio and growth rate of elastic\nenergy during the loading of coal-like material sample and delay the release of internal energy of the sample. Also, it can reduce the\nfrequency band energy of the main frequency of acoustic emission signal but has little effect on the size and richness of the peak\nfrequency of acoustic emission signal. The practice that makes drilling diameter and depth increase stepwise can minimize the\nelastic energy conversion ratio, the growth rate, and the main frequency band energy of acoustic emission signal of coal-like\nmaterial sample and postpone the internal energy release of the sample to the greatest extent, so as to enrich the richness of the\nsecondary frequency of acoustic emission signal. The results of this study have certain guiding significance for the layout of\npressure relief boreholes in the production process of coal mines....
A theoretical and experimental study on the separation method of the incident sound field based on a small-scale vector sensor is\nproposed in this study, with the aim of resolving the problem of separation and acquisition of an incident sound field under the\ninterference of near-field sound scattering from a cylindrical shell in water. The method of identifying and separating sound waves\nobtained under plane wave conditions is extended to complex sound-field conditions. Simulation and experimental results show that the\nvector separation method can greatly reduce the sound pressure amplitude and the phase deviation of the incident sound field, which is\naffected by near-field scattering from the cylindrical surface. The separation accuracy is related to the deviation angle and the distance\nfrom the target surface. The maximum deviation of the pressure amplitude is less than 1 dB, and the phase deviation is less than 3°. This\nmethod can effectively suppress the near-field scattering of the cylindrical shell and improve the separation accuracy of the incident\nsound field. The research results have reference value for a range of practical engineering applications....
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