Current Issue : April - June Volume : 2019 Issue Number : 2 Articles : 5 Articles
Abstract: It has been demonstrated that a single shunted loudspeaker can be used as an effective low\nfrequency sound absorber in a duct, but many shunted loudspeakers have to be used in practice for\nnoise reduction or reverberation control in rooms, thus it is necessary to understand the performance\nof an array of shunted loudspeakers. In this paper, a model for the parallel shunted loudspeaker\narray for multi-tone sound absorption is proposed based on a modal solution, and then the acoustic\nproperties of a shunted loudspeaker array under normal incidence are investigated using both the\nmodal solution and the finite element method. It was found that each shunted loudspeaker can\nwork almost independently where each unit resonates. Based on the interaction analysis, multi-tone\nabsorbers in low frequency can be achieved by designing multiple shunted loudspeakers with\ndifferent shunt circuits respectively. The simulation and experimental results show that the normal\nincidence sound absorption coefficient of the designed absorber has four absorption peaks with\nvalues of 0.42, 0.58, 0.80, and 0.84 around 100 Hz, 200 Hz, 300 Hz, and 400 Hz respectively....
Abstract: A model for acoustic transmission through a 2D square crystal of R-radius bubbles with\na lattice constant L was previously proposed. Assuming a purely monopole response of the bubbles,\nthis model offers a simple analytical expression of the transmission. However, it is not applicable\nwhen the bubbles are too close to each other (L/R < 5). This article proposes an extension of the model\nby including the dipole response of the bubbles. Comparisons with numerical and experimental\nresults show that the new expression gives a good estimate of the concentration at which the monopole\nmodel is no longer valid, but fails at properly predicting the transmission....
Abstract: The ubiquity of sensor-rich smartphones provides opportunities for a low-cost method\nto track indoor pedestrians. In this situation, pedestrian dead reckoning (PDR) is a widely used\ntechnology; however, its cumulative error seriously affects its accuracy. This paper presents a method\nof combining infrastructure-free indoor acoustic self-positioning with PDR self-positioning, which\nverifies the rationality of PDR results through the acoustic constraint between a sound source and its\nimage sources. We further determine the first-order echo delay measurements, thus obtaining the\nmobile user position. We verify that the proposed method can achieve a continuous self-positioning\nmedian error of 0.19 m, and the error probability below 0.12 m is 54.46%, which indicates its ability to\neliminate PDR error, as well as its adaptability to environmental disturbances....
Abstract: Acoustic streaming is the steady flow of a fluid that is caused by the propagation of sound\nthrough that fluid. The fluid flow in acoustic streaming is generated by a nonlinear, time-averaged\neffect that results from the spatial and temporal variations in a pressure field. When there is\nan oscillating body submerged in the fluid, such as a cavitation bubble, vorticity is generated\non the boundary layer on its surface, resulting in microstreaming. Although the effects are\ngenerated at the microscale, microstreaming can have a profound influence on the fluid mechanics of\nultrasound/acoustic processing systems, which are of high interest to sonochemistry, sonoprocessing,\nand acoustophoretic applications. The effects of microstreaming have been evaluated over the years\nusing carefully controlled experiments that identify and quantify the fluid motion at a small scale.\nThis mini-review article overviews the historical development of acoustic streaming, shows how\nmicrostreaming behaves, and provides an update on new numerical and experimental studies that\nseek to explore and improve our understanding of microstreaming....
Abstract: Reliable fault diagnosis of rolling bearings is an important issue for the normal operation\nof many rotating machines. Information about the structure dynamics is always hidden in the\nvibration response of the bearings, and it is often very difficult to extract them correctly due to the\nnonlinear/chaotic nature of the vibration signal. This paper proposes a new feature extraction model\nof vibration signals for bearing fault diagnosis by employing a recently-developed concept in graph\ntheory, the visibility graph (VG). The VG approach is used to convert the vibration signals into\na binary matrix. We extract 15 VG features from the binary matrix by using the network analysis\nand image processing methods. The three global VG features are proposed based on the complex\nnetwork theory to describe the global characteristics of the binary matrix. The 12 local VG features\nare proposed based on the texture analysis method of images, Gaussian Markov random fields,\nto describe the local characteristics of the binary matrix. The feature selection algorithm is applied\nto select the VG feature subsets with the best performance. Experimental results are shown for\nthe Case Western Reserve University Bearing Data. The efficiency of the visibility graph feature\nmodel is verified by the higher diagnosis accuracy compared to the statistical and wavelet package\nfeature model. The VG features can be used to recognize the fault of rolling bearings under variable\nworking conditions....
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