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An efficient approach to acoustic emission source identification based on harmonic wavelet packet and hierarchy support vector machine
Get PDFA new approach for acoustic emission (AE) source type identification based on harmonic wavelet packet (HWPT) feature extraction and hierarchy support vector machine (H-SVM) classifier is proposed for solving the fatigue damage identification problem of helicopter moving component. In this approach, HWPT is employed to extract the energy feature of AE signals on different frequency bands, as well as to reduce the dimensionality of original data features. We trained the H-SVM classifier on a subset of the experimental data for known AE source type, and then tested on the remaining set of data. Also, the pressure off experiment on specimen of carbon fiber materials is investigated. The experimental results indicate that the proposed approach can implement AE source type identification effectively, and achieves better performance on computational efficiency and identification accuracy than wavelet packet (WPT) feature extraction and RBF neural network classification
Methods for testing and optimizing composite ceramics-compound joints by solving inverse problems of mechanics
Get PDFThe paper demonstrates methods for testing and selecting composite ceramics-compounds by solving inverse problems of mechanics. A method for the identification of physical and mechanical characteristics of the compound is proposed. The idea of the method is that the studied material is connected with other materials, the characteristics of which are well known and differ from the characteristics of the material. Desired physical and mechanical properties should be considered unknown in the proposed calculation model. Values of the parameters can be measured accurately with experimental methods in the process of product operation. Characteristics of test materials and geometric dimensions of proposed structures are suggested. The solution of the problem of optimizing the tolerances of physical and mechanical characteristics of materials is proposed. In order to ensure the strength of the structure, the geometric dimensions of the composite construction ceramic resistor-compound are suggested
Seismic response of beam-column joints rehabilitated with FRP sheets and buckling restrained braces
Get PDFAn experimental test was performed to evaluate the seismic resistance of reinforced concrete beam-column joints rehabilitated with FRP sheets and Buckling Restrained Braces (BRBs). Six beam-column joints were rehabilitated and tested. The test results were compared in terms of hysteresis loops, stiffness degradation, energy dissipation and ductility. The comparison result showed that wrapping FRP sheets can contribute to increase the effect of confinement and to delay crack development in the joints. Also retrofitting buckling restrained braces (BRBs) can improve the stiffness and energy dissipation capacity. Both FRP sheets and BRBs can effectively improve the strength, stiffness and ductility
Influence of seismic effect of bridge piles on a subway station
Get PDFAs separated platform subway station structures are close to bridge piles, their analysis under static and seismic loading is required. An artificial earthquake record, generated by using Kanai-Tajimi model and trigonometric series superposition method, is used to analyze the seismic performance of the subway station structure. Different construction sequences of bridge piles and subway stations are considered in the analysis of structural seismic performance. Irrespective of the type of analysis, most of the horizontal and the vertical stresses of the subway station with existing bridge piles show a decreasing trend as compared to those without bridge piles. The stresses associated with post-constructed bridge piles increase significantly as compared to those without piles, especially in areas of stress concentrations. A parametric analysis of the distance between the subway station and the bridge pile is also conducted. The percentage increase in horizontal and vertical stress of the subway station, with post-construction pile, gradually decreases with increasing distance. However, in case of existing piles the percentage increase in stress, as a function of distance, has an inflection point
Quantification and minimization of sensor effects on modal parameters of lightweight structures
Get PDFThis paper aims to quantify the adverse effects of contact type sensors on modal parameters of lightweight structures and to present a practical way for identification of modal parameters of structures with minimal sensor effects. The adverse effects of a contact type sensor on natural frequencies, damping levels and mode shapes are explored using the theoretical model of a typical beam-like sample carrying a sensor and a controlled experimental study based on measurement of frequency response functions using non-contact excitation and response sensors. The half-power and circle fit modal identification methods are used to extract modal parameter from measured data. The experimental and theoretical modal analysis results are evaluated, and a practical methodology based on classical acoustic and vibration frequency response functions is suggested to identify modal loss factors and natural frequencies of lightweight structures with minimal sensor effects
Measurement of stresses in a vibrating polymeric film
Get PDFOne dimensional model for the investigation of longitudinal vibrations of polymeric film is investigated. Comparison of stroboscopic and time averaged intensities in the photo-elastic images is performed. Results about the required number of images for performing time averaging are provided. Recommendations for simultaneous application of both stroboscopic and time averaged photo-elasticity for measurement of stresses are given. One dimensional model for the investigation of vibrations of polymeric film having two nodal degrees of freedom (longitudinal displacement and displacement of the upper surface, assuming that displacement of the lower surface is of the same value but in the opposite direction) is investigated. This model is applied for the interpretation of results of thermo-elastic analysis. Recommendations for the interpretation of the stress field by using photo-elastic and thermo-elastic methods are provided
Human activity recognition: classifier performance evaluation on multiple datasets
Get PDFHuman activity recognition is an active research area with new datasets and new methods of solving the problem emerging every year. In this paper, we focus on evaluating the performance of both classic and less commonly known classifiers with application to three distinct human activity recognition datasets freely available in the UCI Machine Learning Repository. During the research, we placed considerable limitations on how to approach the problem. We decided to test the classifiers on raw, unprocessed data received directly from the sensors and attempt to classify it in every single time-point, thus ignoring potentially beneficial properties of the provided time-series. This approach is beneficial as it alleviates the problem of classifiers having to be fast enough to process data coming from the sensors in real-time. The results show that even under these heavy restrictions, it is possible to achieve classification accuracy of up to 98.16 %. Implicitly, the results also suggest which of the three sensor configurations is the most suitable for this particular setting of the human activity recognition problem
Combination resonances of parametric vibration system of the field modulated magnetic gear
Get PDFConsidering the time-varying magnetic coupling stiffness caused by the component eccentricity, the parametric vibration model of the field modulated magnetic gear (FMMG) system is founded and the corresponding dynamic differential equations are deduced. The expressions of the combination resonances are worked out when the excited frequency is close to the combination frequency between the meshing frequency and the natural frequencies, and the resonance responses are discussed. The results show that the resonance amplitudes are much bigger when the excited frequency is close to the combination frequency between the meshing frequency and the natural frequency of the inner rotor torsional mode than when the frequency is close to other combination frequencies. Meanwhile, because the magnetic coupling stiffnesses are much smaller than the supporting stiffness, the resonance displacement of only one degree of freedom is always much bigger than the displacements of other degrees of freedom. The combination resonances make the stability regions of the FMMG system decrease and worsen the dynamic characteristics. All these can lay the foundation for the parameter optimization of the FMMG system
Computational considerations of 3-D finite element method models of railway vibration prediction in ballasted tracks
Get PDFThe study of vibrations induced by a passing train is of utmost importance to understand better this phenomenon and to design efficient mitigation measures. Within all the techniques used to model vibrations, finite element methods allow introducing in the model detailed characteristics of the real vehicle-train-soil system. However, the accuracy of the results is linked to how detailed the real elements implemented in the model are and consequently, with the computing time. In this paper a three-dimensional finite element method to predict vibrations is developed and validated with real field-measured data. Then, different scenarios are represented to assess the efficiency of the model linking the quality of the results obtained with the calculation time required in each case. Finally, a reflection regarding the constitutive model of the materials when working with finite element models is done
Numerical calculation and finite element calculation on impeller of stainless steel multistage centrifugal pump
Get PDFIn order to save energy and materials, some mechanical structures are very thin. Aiming to study the influence of impeller blade thickness on the performance of stainless steel multistage centrifugal pump, the whole flow field of stainless steel multistage centrifugal pump with different blade thickness were calculated based on ANSYS Fluent. The relationship between the impeller blade thickness and the overall performance of the pump was analyzed. To further study the reliability of the impeller structure for stainless steel multistage centrifugal pump, based on the ANSYS Workbench, the final stage impeller of the pump with different blade thickness were calculated by using the finite element method. Results indicate that with the increase of blade thickness, the maximum stress and deformation of the impeller gradually decreased, while the stability of the impeller structure increased