Journal of Engineering and Thermal Sciences
Not a member yet
1200 research outputs found
Sort by
Wavelet transform and current signature analysis for welding machine measurement
Get PDFThis study aims to extract the stationary features from a non-stationary data using continuous wavelet transform. For this purpose a Hall effect sensor is used to obtain current measurements during the welding operation. A welding process includes several stages referred to as the initial case, transient case and operation case. In this manner, some frequency components can be determined for these cases thereby defining behavior of a particular welding machine. Regarding to the wavelet analysis results, fundamental frequency at 50 Hz is determined to be a dominant characteristic for the considered application. Moreover, side band effects are observed around the fundamental frequency. A sinusoidal waveform of 50 Hz is localized with huge amplitude values in very short time of the time-scale plane and this duration is required during the welding operation in terms of contact between the electrode and material surface
Vibration condition monitoring of planetary gears based on decision level data fusion using Dempster-Shafer theory of evidence
Get PDFIn recent years, due to increasing requirement for reliability of industrial machines, fault diagnosis using data fusion methods has become widely applied. To recognize crucial faults of mechanical systems with high confidence, indubitably decision level fusion techniques are the foremost procedure among other data fusion methods. Therefore, in this paper in order to improve the fault diagnosis accuracy of planetary gearbox, we proposed a representative data fusion approach which exploits Support Vector Machine (SVM) and Artificial Neural Network (ANN) classifiers and Dempster-Shafer (D-S) evidence theory for classifier fusion. We assumed the SVM and ANN classifiers as fault diagnosis subsystems as well. Then output values of the subsystems were regarded as input values of decision fusion level module. First, vibration signals of a planetary gearbox were captured for four different conditions of gear. Obtained signals were transmitted from time domain to time-frequency domain using wavelet transform. In next step, some statistical features of time-frequency domain signals were extracted which were used as classifiers input. The gained results of every fault diagnosis subsystem were considered as basic probability assignment (BPA) of D-S evidence theory. Classification accuracy for the SVM and ANN subsystems was determined as 80.5 % and 74.6 % respectively. Then, by using the D-S theory rules for classifier fusion, ultimate fault diagnosis accuracy was gained as 94.8 %. Results show that proposed method for vibration condition monitoring of planetary gearbox based on D-S theory provided a much better accuracy. Furthermore, an increase of more than 14 % accuracy demonstrates the strength of D-S theory method in decision fusion level fault diagnosis
Coherence analysis and transfer function model for ceramic plate vibrations
Get PDFCorrelations on the state of ceramic plates, that are either intact or cracked, are performed through the data obtained. In the analysis the frequency range of coherence has been identified in the form of the two regions. Low-frequency region is spectral amplitude that is below the threshold defined by the level of coherence about 0.2, which is on the level of little correlation. This region is in the frequency range of approximately 0-28 kHz. In this frequency range a weak correlation between the spectra of solid ceramic plates and cracked ones is observed
Active synthesis of machine drive systems using a comparative method
Get PDFIn this work the method of active synthesis of mechanical systems in accordance with the desired frequency spectrum has been formulated and formalised. Active synthesis of a proportional regulation system has been performed in accordance with the method formulated and a verification of the correctness of the results has been carried out
Biomedical signal identification and analysis
Get PDFIn the article there have been presented methods of measuring and analysis biological signals, which may be used as signals control mechanical system. Among others, ther have been decribed the usage of EEG (electroencephalographic signal). Like in the case of other signals, the analysis of bio-medical signals most often resolves itself to the frequency analysis of their content with the help of Fourier transformation, and their processing the most often has a form of frequency filtering; in other words, removing from a signal its components with defined frequencies, for example, interferences. The researches have two parts. In the first part date was generated in Lab View program, and next the analysis was done (it was an example of EEG signal). In the next part the EEG signal was measured using 32 channels apertures and next real signal was analyzed using Lab View
Analysis of the vertical vibration effects on ride comfort of vehicle driver
Get PDFVehicle vibrations affect the health and comfort of the driver and passengers considerably. The aim of this study is to analyze the effects of vertical vehicle vibrations on the driver. To achieve this goal, a human biodynamic model with 11 degrees of freedom was incorporated into a full vehicle model and this combined human-vehicle model was subjected to the road disturbance. After dynamic analysis of the proposed model, root mean square (RMS) acceleration responses of the human body parts over a certain frequency range were obtained. Physiological effects of the vibrations on the human body were analyzed using the criteria specified in International Organization for Standardization (ISO) 2631. Then, in order to observe the effectiveness of a controller on the vibration isolation of human body, sliding mode controller was applied to the model. Comparison of the vibration effects for the uncontrolled and controlled cases of the human-vehicle model was presented. It can be concluded from the results that sliding mode controller considerably reduces whole body vibrations compared with the uncontrolled case and thereby improves the ride comfort satisfactorily
Comparison of the mechanical properties of flax and glass fiber composite materials
Get PDFIn this paper, the comparison of static and dynamic properties of flax and glass fiber composite materials is presented. For this comparison, dynamic and quasi-static experimental studies were carried out. As a dynamic test, vibration tests were fulfilled using the Oberst apparatus and the tensile test was fulfilled by a quasi-static test. The vibration tests were carried out under different temperatures by using temperature and climatic test cabinets. Flax and glass fibers were used as reinforcements, and polyester resin was used as a matrix to make up the composite specimens. According to the obtained results, the strength of flax fiber composite is lower than the glass fiber under tensile loading, but approximately the same under vibration excitation. On the other hand, damping characteristics of flax fiber composite is higher than glass fiber composite materials. These results demonstrated that natural fiber materials can be used instead of chemical materials for vibration absorption due to their high damping
FRF-based model updating using SMURF technique
Get PDFFinite element (FE) method is a well-known technique in structural dynamic analysis. However, FE models may be inaccurate or even incorrect due to erroneous modeling, geometrical over-simplification or uncertainties in the element and joint properties. In contrast, modal models are generally considered to be correct or at least closely matching the actual dynamic behavior of a structure. Therefore, a model updating procedure should be introduced for adjusting the analytical model in order to reconcile theoretical and experimental results. In this paper, a new FRF-based model updating method is proposed based on the Structural modification using experimental frequency response functions (SMURF) method. It is demonstrated that the proposed method updates the parameters accurately using just a few frequency response functions from the mis-modeled regions. A 12-DOF mass-spring system is considered as a test case in a simulated experiment. The convergence of the method and its capacity to improve the accuracy of the FE model are evaluated. Moreover, the paper considers the effect of the number of modes, the frequency range of interest used in the calculations as well as the coordinate incompleteness and noise on the quality of the updated model. The updated models are compared in terms of the predicted natural frequencies, mode shapes and frequency response functions
Numerical modelling and validation of light gauge steel top-seat flange-cleat connection
Get PDFThis paper presents the numerical investigation on the moment-rotation behaviour of cold-formed top-seat flange-cleat connection, a type of light gauge steel connection which structural connection has sparked a wide range of research interest. The cold-formed channel sections were assembled back-to-back to form I-shape beam and column members. Two components were used to connect the members, notably the 2 mm cold-formed bracket and the 6 mm hot-rolled angle. The results were collected from different beam depths, namely 150 mm, 200 mm and 250 mm. The rotational stiffness and strength obtained from the numerical modelling were then compared with design requirements from BS EN 1993-1-8 and experimental data. The comparison showed not more than 35 % difference in strength and about 50 % difference in rotational stiffness between numerical modelling and experimental data. However, there was a noticeable difference between finite element models and analytical calculation. The differences were from 18 % to 66 % for strength and between 1 % and 145 % for stiffness. Finite element models showed a better agreement with experimental data as compared to analytical study. Edge stiffener of numerical model and theoretical stiffness calculation had caused significant difference in comparison
Bridge scour evaluation based on ambient vibration
Get PDFThe vulnerability of bridges to hazards such as earthquakes, wind and floods necessitates special structural characteristics. To guarantee the stability of bridge structures, the precise evaluation of the scour depth of bridge foundation has recently become an important issue, as most of the unexpected damage to or collapse of bridges has been attributed to hydraulic issues. In this paper, a vibration-based bridge health monitoring system that utilizes only the response of superstructure to rapidly evaluate the embedded depth of a bridge column is proposed. To clarify the complex fluid-solid coupling phenomenon, the effects of embedded depth and water level were first verified through a series of static experiments. A confined finite element model simulated by soil spring effects was then established to illustrate the relationship between the fundamental frequency and the embedded depth. Using the proposed algorithm, the health of the bridge is able to be inferred by processing the ambient vibration response of the superstructure. To implement the proposed algorithm, a SHM prototype system monitoring environmental factors such as temperature, water level, and inclination was developed to support on-line processing. The performance of the proposed system was verified by a series of dynamic bridge scour experiments conducted in a laboratory flume and compared with readings from a water-proof camera. The results showed that using the proposed vibration-based bridge health monitoring system, the embedded depth of bridge column during complex scour processes is able to be reliably calculated