Current Issue : July-September Volume : 2022 Issue Number : 3 Articles : 5 Articles
This paper proposes a reliable technique for pipeline leak detection using acoustic emission signals. The acoustic emission signal of a pipeline contains leak-related information. However, the noise in the signal often obscures the leak-related information, making traditional acoustic emission features, such as count and peaks, less effective. To obtain leak-related features, first, acoustic images were obtained from the time series acoustic emission signals using continuous wavelet transform. The acoustic images (AE images) were the wavelet scalograms that represent the time–frequency scales of the acoustic emission signal in the form of an image. The acoustic images carried enough information about the leak, as the leak-related information had a high-energy representation in the scalogram compared to the noise. To extract leak-related discriminant features from the acoustic images, they were provided as input into the convolutional autoencoder and convolutional neural network. The convolutional autoencoder extracts global features, while the convolutional neural network extracts local features. The local features represent changes in the energy at a finer level, whereas the global features are the overall characteristics of the acoustic signal in the acoustic image. The global and local features were merged into a single feature vector. To identify the pipeline leak state, the feature vector was fed into a shallow artificial neural network. The proposed method was validated by utilizing a data set obtained from the industrial pipeline testbed. The proposed algorithm yielded a high classification accuracy in detecting leaks under different leak sizes and fluid pressures....
Membrane-type acoustic metamaterials (MAMs) have recently received widespread attention due to their good low-frequency sound-transmission-loss (STL) performance. A fast prediction method for the STL of rectangular membranes loaded with masses of arbitrary shapes and surface density values is proposed as a semi-analytical model for calculating the STL of membrane-type acoustic metamaterials. Through conformal mapping theory, the mass blocks of arbitrary shapes were transformed into regular shapes, which simplified the calculation model of acoustic propagation loss prediction, and the prediction results were verified by finite element simulations. The results show that the change in mass surface density was closely related to the size and frequency distribution of STL. The influence of the mass center on the STL and characteristic frequency of the film metamaterial is discussed....
Although voiced speech signals are physical signals which are approximately harmonic and electric power signals are true harmonic, the algorithms used for harmonic analysis in electric power systems can be successfully used in speech processing, including in speech enhancement, noise reduction, speaker recognition, and hearing aids. The discrete Fourier transform (DFT), which has been widely used as a phasor estimator due to its simplicity, has led to the development of new DFT-based algorithms because of its poor performance under dynamic conditions. The multipleresonator (MR) filter structure proposed in previous papers has proven to be a suitable approach to dynamic harmonic analysis. In this article, optimized postprocessing compensation filters are applied to obtain frequency responses of the transfer functions convenient for fast measurements in dynamic conditions. An optimization design method based on the constrained linear least-squares (CLLS) is applied. This way, both the flatness in the passband and the equiripple attenuation in the stopband are satisfied simultaneously, and the latency is reduced....
Bamboo musical instruments, such as bamboo flute and Ching-hu (Beijing opera fiddle), can generate a crisp and melodious sound closely related to the delicate multiscale pore structure of bamboo. Bamboo is a natural hydrophilic material, and its acoustic vibration characteristics are highly sensitive to changeable environmental humidity levels. Herein, we investigated the acoustic vibration characteristics of bamboo under three conditions: constant relative humidity (status I), changeable relative humidity (status II), and subjected to water extraction (status III). Three typical parameters were selected as evaluation indicators of bamboo acoustic vibration characteristics, namely, specific dynamic elastic modulus (E/ρ), loss tangent (tanδ), and acoustical converting efficiency (ACE). The outer bamboos (OB) had higher E/ρ and ACE but lower equilibrium moisture content (EMC) and tanδ than the inner bamboos (IB). Under status I, bamboo showed the maximum E/ρ and ACE and the minimum tanδ at 35% RH (relative humidity) and about 6% MC. Compared with the bamboo under status II, the bamboo under status I retained higher E/ρ and ACE and lower tanδ. However, the bamboo under status (III) reached the maximum E/ρ and ACE and the minimum tanδ. The bamboo musical instrument is made of bamboo with proper removal of water-soluble extractives and high fiber volume fraction and stored in a stable relative humidity environment of 35%, which has suitable acoustic vibration characteristics....
We propose a method of defining absorbing boundary conditions for use in finite element modeling of mechanoacoustic systems. The finite element model of an elastic body is expanded by a water domain, bounded by an axisymmetric surface, to which boundary conditions are applied. The boundary conditions are formed using the method of equivalent sources, so the integral relations for the pressure and its gradient are derived. The method retains its validity for the modeling of radiation in the lowfrequency range, as it provides not only the absorption of outgoing waves but also the modeling of the added mass of vibrating elastic bodies....
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