Journal of Vibroengineering
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Method for the extraction of shock signal features based on the upper limit of density integral
Get PDFShock signal features must be extracted for use in pattern recognition or fault diagnosis. In this work, we proposed a method for the feature extraction of shock signals, which are vibration signals that change faster and have larger amplitude ranges than general signals. First, we proposed the concepts of amplitude density for monotonic functions and piecewise monotonic functions. On the basis of these concepts, we then proposed the concept of the upper limit of density integral (ULDI), which was adopted to obtain signal features. Then, we introduced two types of serious fault cracks to the latch sheet of an automatic gun mechanism that is used on warships. Next, we applied the proposed method to extract the features of shock signals from data acquired when the automatic gun mechanism fired with normal and two fault patterns. Finally, we verified the effectiveness of our proposed method by applying the features that it extracted to a support vector machine (SVM). Our proposed method provided good results and was superior to the traditional statistics-based feature extraction method when applied to a SVM for classification. In addition, the former method demonstrated better generalisation than the latter. Thus, our method is an efficient approach for extracting shock signal features in pattern recognition and fault diagnosis
Comparative vibration analysis on IC engine with biodiesel and multi-walled carbon nanotube
Get PDFSound and vibration caused in the engine due to combustion process may affect the users. One of the vital qualities of diesel fuel is high sound and vibration. The vibration of the engine is one of the primary factors in engine structure and maintenance. Vibration estimation on the engine block, cylinder head is a non-intrusive strategy and has been utilized effectively for fault prediction of diesel engines. The vibration signals along with signal processing techniques are utilized to highlights the features that are sensitive to faults. In this work, experimental tests have been carried out to assess the vibration of a diesel engine with diesel, 20 % biodiesel (Ethyl Ester of ground nut acid oil EEGOA) and 30 ppm Multi-walled Carbon Nano tubes with 20 % biodiesel (MWCNT30ppm B20EEGAO) at various load (20 %, 40 %, 60 %, 80 % and 100 %). Digital Vibration Meter Model: Equinox-VM 6360 is utilized to gauge the vibration in three unique positions, one is cylinder head of the engine, second one is crank of the engine, and third one is bottom of the engine. In this work, the vibration is measured in terms of acceleration. The MWCNT30ppm B20EEGAO blend demonstrates the lower vibration compared with different blends
Fault diagnosis using an improved fusion feature based on manifold learning for wind turbine transmission system
Get PDFIn this paper, a novel fault diagnosis method based on vibration signal analysis is proposed for fault diagnosis of bearings and gears. Firstly, the ensemble empirical mode decomposition (EEMD) is used to decompose the vibration signal into several subsequences, and a multi-entropy (ME) is proposed to make up the fusion features of the vibration signal. Secondly, an improved manifold learning algorithm, local and global preserving embedding (LGPE), is applied to compress the high-dimensional fusion feature set into a two-dimension feature set. Finally, according to the clustering accuracy of different feature set, the fault classification and diagnosis can be performed in the reduced two-dimension space. The performance of the proposed technique is tested on the fault of wind turbine transmission system. The application results indicate that the proposed method can achieve high accuracy of fault diagnosis
Numerical simulation and experimental analysis of magneto-mechanical behavior of anti-seismic active sandwich structure
Get PDFThis work focuses on the quasi-static behavior study for simply supported sandwich beams with aluminum faces and magnetorheological elastomer core subjected to three points bending subjected to a magneto-mechanical loading by numerical and experimental investigations. The mechanical properties of the magnetorheological elastomer core are measured experimentally and the mechanical behavior of the MRE was identified by the generalized Maxwell rheological model. Depending upon the adjustable properties of the beam, energy dissipation is by core shear. A systematic series of experiments and finite elements simulations have been performed in order to assess the static behavior of the beam. The results obtained show a significant influence of the magnetic field intensity on the flexural displacement of the beam
Research on cold mechanical vibration of air-cooled disc brake
Get PDFCold mechanical vibration of air-cooled brake disc is mainly caused by the non-uniform geometry, including disk thickness variation (DTV) and side face run-out (SFR). A mathematical model consisting of the non-uniform geometry is constructed, which is imported into the dynamic brake model established by Lagrange equation as initial parameters. The braking moment fluctuation during braking process is obtained by MATLAB software. The experimental verification is realized based on Link3900 NVH test platform, where result shows that the calculated brake pressure is quite consistent with the test value. By single variable method, the key influence factor that affected braking moment fluctuation is analyzed, including DTV, SFR, friction coefficient, contact stiffness coefficient and damping coefficient. The conclusion shows that reducing these parameters within a certain range can significantly reduce the amplitude of cold vibration, except for the contact damping coefficient
DEM simulation and experimental study on the screening process of elliptical vibration mechanical systems
Get PDFFor an elliptical vibration system, the vibration parameters seriously affect conveying speed and sieving efficiency of the materials. In addition, considering the lack of studies about the elliptical vibration machine, we applied the discrete element method to simulate and analyze the elliptical vibration screening process in this paper. A vibration screening model is particularly based on the purpose of our research to fundamentally demonstrate the novel relationships among the conveying speed, sieving efficiency and vibration parameters of the materials. And the sieving experiment of typical materials is additionally carried out on the same simulation system. This paper analyzes the influence rule of vibration parameters on conveying speed and sieving efficiency of the materials during the elliptical vibration screening process by virtue of comprehensively comparing the results of experimental study coupled with simulation research. Consequently, we can throw up the optimal vibration screening parameters to guarantee high sieving efficiency and large throughput of the screening machine at the same time. The screening test carried out in this paper lays the experimental foundation for the study of the mechanism of elliptical vibration screening machine and the study of materials screening characteristics by combining the conclusions of DEM simulation analysis of lots of materials. It provides not only a basis for selecting the vibration parameters of the actual working process of the screening machine, but also data support based on the experiment and simulation for the study of the sieving mechanism of elliptical vibration systems. For screening mechanism, this is a significant progress which will affect future design and manufacture of elliptical vibration machines. Furthermore, the conclusions drawn from this research can help us study and explain better the screening process of other vibration machinery
Research on vertical vibration of hot rolling mill under screw-down-strip combined excitation
Get PDFIn this paper, we find the violent vibration of the hot rolling mill is induced by the combination of the screw-down system and the strip, explain how the srew-down-strip combined excitation effects the rolling mill, and introduce an effective method to restrain the vibration. First, two experiments, stripless rolling and turning off the screw-down system, are conducted, the first experiment simulates the rolling process without strip and the second experiment simulates the rolling process without the screw-down system, the results indicate that the rolling mill vibration is induced by the srew-down-strip combined excitation. Then, to explain this phenomenon, the mathematical model of the rolling mill under screw-down-strip combined excitation is proposed, we find that few excitation frequency components can induce more response frequency components, therefore it’s more possible to approach the natural frequency of the rolling mill. Finally, a vibration suppression method is introduced by eliminating some specified frequency components of the screw-down system with a filter, and the result shows that the vibration decreased by 98.7 %
Damage identification of bridge structure based on frequency domain decomposition and strain mode
Get PDFBecause it is difficult to determine the degree and location of damage to bridge structures under environmental excitation, a new method combining frequency domain decomposition and strain mode identification for bridge structure damage assessment is proposed and the related identification principle is derived. General variations in the strain mode parameters of different reinforced concrete beam damage states are accordingly studied under ambient excitation. The results show that the proposed strain mode identification method based on frequency domain decomposition has good anti-noise performance and can identify the strain mode parameters of a structure relying solely on the strain response information of the structure, even under strong background noise. The mutation of the strain mode was effectively used to determine the damage condition of reinforced concrete beams, and the adaptability, feasibility, and reliability of the proposed method for modal parameter and damage identification of reinforced concrete beams under environmental excitation were verified
Damage detection in concrete gravity dams using signal processing algorithms based on earthquake vibrations
Get PDFIn structural engineering, damage detection in concrete gravity dams (CGDS) is a practical problem. Dam destruction can have severe financial consequences and may even lead to fatalities. Therefore, structural health monitoring in advance is crucial. In this regard, a well-known CGD, namely the Pine Flat Dam, has been chosen for the Finite Element Modeling. In this paper, damage is induced in the dam neck through elasticity modulus reduction by 40 % and 80 %. In addition, after applying Northridge earthquake, the acceleration in structure nodes for intact and damaged cases are recorded in vector formats. Using various methods, such as Discrete-time Fourier Transform (DTFT), Wavelet transform and Wiener transform, the differences between these two signals are investigated. The standard deviation (S.D.) of variations is chosen as the performance metric and is applied to the signal amplitude between intact and damage observations/signals. The reason why several signal processing algorithms are used is finding an approach which shows more clearly the differences caused by the destruction. This is evaluated via S.D. values for different algorithms. The results confirm the superiority of DTFT over other given algorithms. DTFT has a negligible outperformance (approximately zero dB) with respect to the Wavelet transform in both the crest and the lower nodes of the dam. This rate for DTFT and Wavelet is 10dB higher than that of Wiener and 35 dB in comparison with the simple amplitude difference. Moreover, the detection thresholds for the given methods are compared, and it is verified that the DTFT and Wavelet indicate the best performance
Source localization in reverberation environment based on improved equivalent sound source near-field acoustic holography algorithm
Get PDFThe compressive-equivalent source method near-field acoustic holography (C-ESM) is disturbed by reverberation in the enclosed space such as room and cabin, which leads to large reconstruction error and disturbs the judgment of sound source position. In order to solve this problem, an improved C-ESM algorithm based on room impulse response (RIR) is proposed to filter out reverberation interference in this paper. Different from the original equivalent source method, the improved algorithm constructs the transfer function through the room impulse response to establish the relationship between the equivalent source and the sound pressure on any plane in space, and the sparse signal reconstruction method of the compressive sensing technology is used to obtain the strength of the equivalent source. Then the transfer function to any plane of space is established according to the free field Green’s function, to eliminate the interference of reverberation and improve the effect of sound source location. The accuracy and effectiveness of the improved method are verified by preliminary numerical simulation. And the results show that compared with the original algorithm, this method has obvious advantages in sound source localization in a reverberant field