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An approach for tool health assessment using the Mahalanobis-Taguchi system based on WPT-AR
Get PDFA real-time tool health assessment has a significant implication on reliable machining operations. This paper proposes a health assessment method for tools in milling machine using the Mahalanobis-Taguchi system (MTS) based on wavelet packet transformation and autoregression. In this method, the nonlinear and non-stationary vibration signal from the milling process is first decomposed using wavelet packet transforms. Then, an autoregression (AR) model is constructed for each coefficient of the reconstructed signal, and the parameters as well as variance of the remnants of each AR model are employed to form the initial feature matrix. Singular values of this feature matrix are obtained through singular value decomposition, at which point MTS is employed. In this study, MTS provides (1) a computational scheme based on the Mahalanobis distance for obtaining the health index of a tool, and (2) Taguchi methods to extract the key features and reduce the redundant ones. Finally, the performance and effectiveness of the proposed method are validated by vibration signals acquired from the milling machining process
Influence of hole-drilling diameter on aluminum alloy residual stress measurement
Get PDFA hole-drilling method and finite element (FEM) numerical simulation are used to estimate the residual stress of aluminum alloy welding joints. In order to study the influence of hole diameter on measurement accuracy, a group of experiments are conducted. Experiment results show that the measuring error can be the minimal when the drilling hole diameter is 4 mm. Residual stress of 2219-T87 aluminum alloy welding joints under this optimal hole diameter are obtained. The distribution of the residual stress from the welding seam to the outward is first tensile stress and then compressive stress. And the maximum residual stress is 123.2 MPa
Analysis of camera orientation variation in airborne photogrammetry: images under tilt (roll-pitch-yaw) angles
Get PDFTaking images for airborne photogrammetry, tilt angles (drifts) variations of camera are resulting to objects positions on the images therefore influence to correctness and accuracy of produced geodata. Several experiments have been done for investigation of camera’s roll-pitch-yaw angles determination regarding to technical flying means orientation in the space. Using aerial triangulation technique, exterior orientation parameters of each image from entire flight strip – projection center coordinates and image tilt angles with estimated accuracy are presented. Results show coincidences or discrepancies to requirements specified in aerial photography regulations. In order to investigate deflections of camera’s tilts, stereo pair of images has been processed using airborne photogrammetric approach and different software. Two digital photogrammetric software (DDPS and LISA PHOTO) used in experimental image orientation operates on particular algorithms. Determined values of exterior orientation parameters differ not significantly. Exterior orientation of images gained by Unmanned Aerial Vehicle (UAV) with mounted CCD camera has been done. As shows analysis, images from UAV Photogrammetry are under marketable tilts. Using a certain number of Ground Control Points (GCP) measured by GPS, exterior orientation was not possible; the results not meet the accuracy requirements
MED and WPT based technique for bearings fault detection
Get PDFA new technique is proposed in this work for fault detection in rolling element bearings, which is based on minimum entropy deconvolution (MED), wavelet packet decomposition (WPT) and envelop analysis. Firstly, the collected vibration signal is preprocessed to highlight defect-related impulses, and a new indicator named envelope spectra sparsity (ESS) is proposed to automatically select the filter length of MED. Then the preprocessed signal is decomposed into WPT nodes, and the most sensitive node containing fault-related information are selected from all the nodes to improve the accuracy of the fault detection. Sparsity of wavelet packet nodes signal (SWPN) is proposed in this step as a measure indicator. Lastly the power spectrum is used to highlight the bearing fault characteristic frequencies. The effectiveness of the proposed AMED-WPT technique in feature extraction and analysis is verified by a series of experimental tests corresponding to different bearing conditions
Fuzzy semi-active control for seismic response reduction with magnetorheological dampers
Get PDFBased on the dynamic characteristics obtained with a three-dimension finite element method, a reduced mechanical model and parameters for the ship lift can be modified and obtained. Simulated analysis shows that the reduced mechanical model can adequately represent the dynamic characteristics and earthquake responses. The reduced mechanical model can be used to control the seismic whiplash effect of the top workshop of the ship lift with intelligent control methods. A modified Bingham model was proposed to simulate the machinery property of a magnetorheological smart damper. A roof intelligent isolation system was also proposed. Seismic simulation analysis of the ship lift was conducted using a fuzzy control strategy. Simulation analysis results show that the fuzzy semi-active control with a magnetorheological smart damper is beneficial in suppressing the seismic whiplash effect on the top workshop and confirm that the fuzzy semi-active control strategy is valid in this scenario
Numerical and experimental verification of finite element mesh convergence under explosion loading
Get PDFExplosions inflict severe damage to building structures and threaten national security as well as social stability; their scope of impact and damage level is subject to the energy contained in the shock waves. Explosion testing is limited by the test site and amount of explosive used; a large scale explosion test is not viable. Therefore, numeric analysis is adopted as the preferred research method instead of an actual field test. The application of finite element analysis requires consideration of the complexity of an analysis model and the mesh density. An explosive load violent enough to cause distortion to mesh cannot reveal the actual mechanical behavior and will compromise the convergence and accuracy of the results. The purpose of this study is to analyze the optimal mesh density of the finite elements under an explosive load, in order to explore the element mesh convergence and to compare the results with the experimental. The results of this study can reasonably simulate an explosion effect, achieve the convergence as indicated by calculation results, and provide a foundation upon which future dynamic mechanic studies may establish numerical models. To enhance the calculation accuracy, this study adopts a fluid dynamic analysis program, LS-DYNA, finite element analysis software, to conduct Fluid-Solid Interaction (FSI). A TNT free-field explosion simulation is analyzed for mesh density convergence under an explosive load. The analysis results reveal a pattern where the shock wave diminishes as it moves further away from the explosion point. The results may serve as reference for studies involving the numeric analysis of explosions
Estimation of mode shapes expanded from incomplete measurements
Get PDFAnalytically obtained mode shapes do not match with those of the experimental results due to external noise, including modeling and measurement errors. This inconsistency can pose significant difficulties for the subsequent analysis and design. It is impractical to collect the data for the full set of degrees of freedom (DOFs) of a dynamic system. The incomplete data set should be expanded to the full data set. This work provides a method to correct the analytical mode shapes to match the measured modes. We present the updated forms of the parameter matrices based on the estimated mode shape data. A numerical example illustrates the validity of the proposed method
Vibration suppression using fractional-order disturbance observer based adaptive grey predictive controller
Get PDFA novel control strategy is proposed for vibration suppression using an integration of a fractional-order disturbance observer (FDOB) and an adaptive grey predictive controller (AGPC). AGPC is utilized to realize outer loop control for better transient performance by predicting system outputs ahead with metabolic GM(1,1) model, and an adaptive step switching module is adopted for the grey predictor in AGPC. FDOB is used to obtain disturbance estimate and generate compensation signal, and as the order of Q-filter is expanded to real-number domain, FDOB has a wider range to select a suitable tradeoff between robustness and vibration suppression. For implementation of the fractional order Q-filter, broken-line approximation method is introduced. The proposed control strategy is simple in control-law derivation, and its effectiveness is validated by numerical simulations
Experimental research on the dynamic characteristics of gas-hybrid bearing-flexible rotor system
Get PDFHigh-speed gas bearings for turbomachinery can dramatically improve the isentropic efficiency of turbine plants. Vibrations, especially low-frequency vibrations caused by the gas-film self-excited vibrations, significantly affect the safety and economy of the turbomachinery, which is dangerous at high rotational speeds. This experimental study focuses on the dynamic characteristics of a flexible rotor supported by gas hybrid bearing and driven by a radial turbine with high-pressure air. Cylindrical whirling, conical whirling, and first-order bending natural frequencies that change with bearing supply pressures were obtained by experimental modal analysis. Nonlinear mechanic behaviors, including gas film half-speed whirling and gas-film whip, in the experiments were identified by nonlinear measurements and analyses. The occurrence mechanism of gas-film whirling and whip is also discussed in this paper. Experiments for eliminating and restraining whirling and whip were conducted to investigate the gas bearing-rotor system stability effect of bearing supply pressure and elastic foundation. Some simple and effective measures were given to improve the stable rotational speed
Numerical calculation and experiment investigation of sound field in the full model car
Get PDFCurrently, much interior sound field research in car is based on the car body that many parts are missed, which is not consistent with the actual condition. In addition, the research results have not been verified by experiment; few things have been done in air tightness of car. In this paper, the full car model has been used to analyze the interior sound field in car, in order to simulate the actual condition accurately. Through the comparison between the analysis results and the experiment, there was a good agreement in full frequency hand. However, there was also a clear peak in 130 Hz that may cause roar; the reason was assumed to be sealing defects. After all the sealing defects were fixed, the sound pressure in the driver’s ear was measured again and compared to the results before. It was found that seal could reduce the sound pressure, which also means the sealing performance of car must be maximized when manufacturing. The contribution coefficient of each panel towards the sound pressure in the driver’s ear in 130 Hz has been calculated by using ATV method in this paper; the result showed that the top panel of car was the main reason for the existence of the clear peak in 130 Hz. Through the replacement of original interior decoration with compound sound package structure and the change of each layer’s properties, the sound package structure with the minimum transmission sound power has been found. The results showed that the combination of (3-4-1) sound package structure is optimal (which means the damping layer thickness was 3 mm, the porous material layer thickness was 4 mm and the viscoelastic cover layer thickness was 1 mm). Besides, the combination of the damping layer with new material has shown a better acoustic performance. This scheme has been used in the top panel of car and has apparently improved the sound pressure condition in the driver’s ear