Journal of Vibroengineering
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Energy weighting method and its application to fault diagnosis of rolling bearing
Get PDFFeature extraction of vibration signal is the key factor of machine fault diagnosis. This paper proposes a novel method of capturing shock energy based on multi-scale weight evaluation of high definition time-frequency map. Specifically, the proposed method is conducted by the following steps. First, ensemble empirical mode decomposition (EEMD) preprocessor-based Hilbert-Huang Transform (HHT) is applied to the raw signal for high definition time-frequency map acquisition. Second, an original algorithm named multi-scale binary spectrum was applied to extract impulsive energy features with different frequency characteristics. Then weights of energy can be calculated by dimensionality reduction of each binary spectrum and merged by summation after blank processing. Finally, power spectrum of compound weight of energy can reveal characteristic frequency corresponding to specific fault. In this method, the key point is enhancement of frequency spectrum using higher dimension details. The process of multi-scale binarization and weight summation were aligned and the effectiveness is verified by simulated signal processing and actual case of train bearing experiment
Using optical code-division multiple-access techniques in Michelson interferometer vibration sensor networks
Get PDFThis study proposes a spectral-amplitude-coding optical code-division multiple-access (SAC-OCDMA) framework for accessing the vibration frequency of a test object by using a Michelson interferometer vibration sensor (MIVS). Each sensor node possesses an individual signature codeword, and liquid crystal spatial light modulator (LC-SLM) encoders/decoders (codecs) are adopted to provide excellent orthogonal properties in the frequency domain. The proposed LC-SLM-based OCDMA system mitigates multiple access interference among all sensor nodes. When optical beams strike and are reflected by the object, the sensing interferometer becomes sensitive to external physical parameters such as temperature, strain, and vibration. The MIVS includes a Michelson interferometer placed at a specific distance from the test object on a designed vibration platform. A balanced photodetector (BPD) was used to convert the light output of the LC-SLM decoders into electrical signals, and a digitizing oscilloscope was used to Fourier transform the BPD electrical signal output, thereby yielding the vibration frequency of the test object. The results showed that the proposed sensor network with an interferometer can be used as a distributed highly sensitive sensor to obtain mechanical values. This study provides a new optical sensor network for current vibration frequency measurements
A novel method to analysis strong dispersive overlapping lamb-wave signatures
Get PDFDispersive propagation and overlapping wave modes are two main obstacles for guided Lamb wave SHM applications. In an effort to overcome such obstacles, a new signal-processing technique taking advantage order tracking based on dispersion relation, is developed. In this approach, by referencing the wave number-frequency function of specified mode, the operations of resampling and interpolating are performed on the frequency-spectral series of raw signal. The orders referenced to wave number-frequency are calculated, according to which the individual wave-packet is identified and its corresponding propagating distance is estimated. In the order domain, the overlapping modes are readily separated by Gabor expansion on the frequency-spectral series of raw signal. Numerical and FEM simulations on strongly dispersive and multimode overlapping guided waves were carried out to evaluate the performance of the proposed approach. The results demonstrated that the proposed approach is effective in dispersion analysis, mode differentiation and overlapped wave-packets separation
Study on the nonlinear transient response for the non-contact mechanical face seal
Get PDFConsidering the tilt of the seal ring, the transient vibration response analysis model of the non-contact mechanical seal is presented. The model is consisted of the transient Reynolds equation, the equation of motion and the equation for solving the high order nonlinear dynamic coefficients of seal. The relative error of the high order nonlinear film force to the linear film force is also obtained. With Euler method, the characteristic parameters of the transient vibration response are obtained, which include the axial vibration displacements and the angle-swing of the static ring. The 14 nonlinear force and 14 nonlinear overturning moment dynamic coefficients for the non-contact mechanical seal are calculated. The results show that the influence of the damping effects of the sealed fluid between the seal gap on the axial vibration displacements and the angle-swing is linear. The film thickness distribution changes with the axial vibration of seal, which will lead to static ring swing, and the swing also can cause the axial vibration of the seal. With the increase of the nonlinear order, the relative error of the nonlinear film force decreases. All of the nonlinear film forces, the non-linear stiffness coefficient and damping coefficient decrease with the seal film thickness increases
Improved Craig-Bampton method for transient analysis of structures with large-scale plastic deformation
Get PDFThis paper reports on the improvement of Craig-Bampton (CB) method for transient analysis of structures with large-scale plastic deformation. As is known, the CB method is effective and accurate in reduced order modeling for linear system. In contrast to this, an improved CB method using tangent modes for nonlinear dynamic analysis has been developed. To do this, the incremental governing equations of nonlinear system are linearized in each time step by using tangent stiffness matrix, and the corresponding tangent modes are proved to be orthogonal with respect to mass matrix as well as with respect to tangent stiffness matrix by incorporating the elastic-plastic material behavior. Thus, the tangent modes can be used to assemble the transformation matrix of CB method in nonlinear dynamic analysis. Using the proposed method, two elastic-plastic beams loaded impulsively are examined. Simulation results show that the improved CB method is valid and accurate for transient analysis of structures with large-scale plastic deformation and has lower computational cost compared with full order model
Cracked modeling and vibration analysis of pipe with a part-through crack
Get PDFPipeline is an important transportation facility in the oil and gas industries. But cracks inevitably appear in the pipe body due to various factors. Mechanical analysis of cracked pipe structures based on local flexibility has received increased attention in the last three decades. However, few reports exist on the local flexibility of pipes with an arbitrary angled crack. In this paper, the general solution of the local flexibility equations of a pipe with a part through-crack subjected to axial force, shearing force, and bending moment is deduced with respect to an arbitrary angled crack. The proposed equations consider the influence of the crack orientation on the local flexibility coefficient. An adaptive Simpson method is used to calculate the local flexibility coefficients of a cracked pipe. The results of testing by Naniwadekar’s and Authors’ are used to validate the proposed method. The results demonstrate that the proposed method is accurate for calculating local flexibility and can be applied for vibration analysis in a pipe-like structure
Adaptive estimation of VMD modes number based on cross correlation coefficient
Get PDFThe variational mode decomposition (VMD) proposed recently is a kind of time-frequency signal analysis method. VMD has some advantages on signal decomposition such as high precision and noise robustness, but its serious shortcoming is that the number of modes (K) should be given in advance. And if the number is chosen inappropriately, VMD will lead to larger decomposition error. In this paper, the VMD method is introduced and the over- and under-segment characters of VMD are discussed. The cross correlation coefficients can express the similarity between the two signals. Cross correlation coefficients among VMD components and the original signal are used to judge whether over-segment takes place. As a result, the estimation method of VMD parameter K is proposed. Based on the method, the tri-harmonic signal and the vibration signals of ball bearings are analyzed in detail. The results show that the proposed method is feasible and effective
Detection of debonding in steel-reinforced bridges using wavelet curvature features of laser-measured operating deflection shapes
Get PDFHidden damage severely threatens the safety of structures due to its invisibility and indistinguishability. Debonding is typical hidden damage in steel-reinforced bridges. Detection of multiple debondings in steel-reinforced bridges poses a challenge for traditional nondestructive methods that require damage location as prior knowledge, but this condition is usually not satisfied for debonding located within the bridge. Differing from existing studies, this study explores a vibrational method of detecting multiple debondings needing no prior knowledge, that uses a scanning laser vibrometer to acquire densely-sampled operating deflection shapes of bridges. The operating deflection shape carries richer information than mode shapes for damage characterization. Nevertheless, densely-sampled deformed quantities are commonly susceptible to noise when used to identify damage. To detect multiple debondings, a new feature is developed, the wavelet-transform curvature operating deflection shape. This feature is used to identify multiple debondings in a steel-reinforced concrete slab dismantled from a bridge, clearly demonstrating the strengths of suppressing noise, intensifying the signatures of debonding, and requiring no prior knowledge of damage location. The proposed method holds promise for detecting multiple hidden damage in various structures besides bridges
Influence evaluation of wake shedding on natural frequencies of marine propulsion shafts
Get PDFThe calculation of natural frequencies is very significant at the design phase of marine propulsion shafts. And added mass of propellers has high effect on natural frequencies. At present, the effect of wake shedding from the propeller’s trailing edge on added mass is unclear. Then their influence on propulsion shafts natural frequencies is also vague. So in this study, the influence of wake shedding on propellers added mass and propulsion shafts natural frequencies is evaluated. Our results show that first, for the first lateral natural frequency, the max relative error reaches up to 6.52 % if the wake shedding is ignored. So for the lateral vibration, the wake should be considered. Second for the first torsion natural frequency, the max relative error amounts to 5.10 % when the skew angle is 108 degrees. So for the torsion vibration, the wake should also be considered when the skew angle is large. Third, for the axial vibration, the influence of wake is little and may be ignored
Analysis on the aerodynamic behavior and noises of the cross section of the cable tower for long-span bridges
Get PDFCable towers are an important aerodynamic noise source of long-span bridges. The flow effect of various parts of the cable tower on airflow will cause large aerodynamic noises and thus influence environments. This paper conducted on research on the cross-sectional structure of the cable tower of long-span bridges, built a computational model of aerodynamic noises for cable towers of long-span bridges with original rectangular cross section and improved cross section. The computational fluid dynamics was adopted to analyze the non-steady flow of cable towers, and the numerical value of aerodynamic noises was predicted based on Lighthill’s acoustic analogy. Then, acoustic BEM was also adopted to study radiation noises of cable towers in the far-field. Results showed that improved cable tower could reduce the dispersion degree of airflow and weaken Karman Vortex Street. Aerodynamic noises induced by cable towers with improved cross section mainly radiated in a direction perpendicular to airflow, and the directivity of noises was obvious. Sound pressure level (SPL) of aerodynamic noises of cable towers with improved cross section was 4.2 dBA less than that of initial rectangular cross section in the far-field, which showed obvious effect on noise reduction. In the meanwhile, this paper studied the mechanism of main frequency at various parts of cable towers with improved cross section and discussed the reason of noise reduction, whose research achievements could provide design basis for generation mechanism and reduction of aerodynamic noises of cable towers of long-span bridges