Journal of Engineering and Thermal Sciences
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Modeling the coupled flexural and torsional vibrations in rotating machines in transient states
Get PDFThe paper presents an example of modelling of coupled flexural, torsional and longitudinal vibrations occurring during the startup of machine consisting of rotors and elastic shaft. The authors’ Simulink block library was used, by which one can model the serial rotating mechanical power transfer systems in any configuration. The main element of the library being development is the rigid rotor model with six degrees of freedom elaborated by the authors. The authors proposed a method for the decoupling equations of motion of the rotor, which allowed their use in Simulink. The general concept of the library assumes division of the rotating system of rigid components (inertial) and elastic components. In this sense, the methodology used is similar to the transfer matrix method developed by Myklestadt and Prohl. The library is open, it can be expanded by new blocks with a particular functionality (bearings, couplings, dampers, drive elements), while maintaining the established structure of signals and method of joining inertial blocks with elastic blocks. In comparison with existing systems of vibration analysis of rotating machinery based on FEM, the major advantages of the Simulink library being developed are: definitely smaller number of degrees of freedom needed to describe the motion, which shortens the simulation times; and the possibility to combine with ready libraries available in Matlab
Theoretical study on self-synchronization of two homodromy rotors coupled with a pendulum rod in a far-resonant vibrating system
Get PDFThe objective of this paper is to investigate the self-synchronization of two homodromy rotors coupled with a pendulum rod in a far-resonant vibrating system. Using the average method and revisionary small parameters, we derive the dimensionless equation of the self-synchronization criterion and synchronous stability of the vibrating system. Meanwhile, to prove the correctness of the theoretical analysis, the diversity feature of the vibrating system is simulated numerically. Both results of theoretical analysis and numerical simulation show that increasing the length of the pendulum rod or decreasing the mass of the rotor connected with pendulum rod can ensure the self-synchronization and synchronous stability of two homodromy rotors in the vibrating system
Contact characteristics of orthogonal face gear with spur involute pinion
Get PDFThe proposed mechanism of face gear shaping is applied to develop the mathematical model of face gears. Based on the developed mathematical model of the face gear, computer graph of the face gear set is created. Then, the transmission errors of the face gear pairs under various assembly errors are investigated based on the constraints theory of six-degree-of-freedom rigid body motion. The assembly errors are finally obtained by applying the TCA (tooth contact analysis) method. Also, the developed computer simulation programs quantitatively evaluate the influence of assembly errors including offset and angular position errors on the position of contact path and TE (transmission error) in a complete mesh cycle. Besides, the loaded tooth contact characteristics are investigated by using the FEM (finite element method) to study the stick-slip trajectories of the surfaces. The results are illustrated with numerical examples
Piezoelectric actuator for micro robot used in nanosatellite
Get PDFThe nanosatellites of the CubeSat standard (10×10×10 cm and with mass 1-10 kg) was designed to reduce cost and development time and to maximize science return. However, the small size of the spacecraft imposes substantial mass, volume, and power constraints. The challenge remains to be the miniaturization of the various robots for the manipulation of functional objects, such as cameras, laser sources, mirrors and other used in nanosatellites. Therefore in particular, precision positioning of the manipulated object is important task for robots used in nanosatellites as well. In this paper authors present the design of robot driven by the piezoelectric actuators. Investigations of the robot are presented and they prove ability to improve the accuracy of the movement for the robot arm using two bending bimorph type piezoelectric actuators and 3DOF rotary piezoelectric motor
Influence of imbalance force angular position to vertical and horizontal rotors rolling bearings defects diagnostics
Get PDFInstead of using the traditional periodical diagnostics, modern technological machinery has increasingly been using monitoring systems based on acceleration transducers of mechanical vibrations. Although, oftentimes it is difficult to identify rolling bearing faults, even if constantly monitoring and analyzing the machinery vibration acceleration or vibration velocity FFT spectra or their cascades. We usually run into such problems when analyzing gravity based technological processes (separators, diffusion machinery) in vertical machinery observations. This is because the angular position of imbalance mass varies often in this type of machinery, which causes the inner ring race fault in the bearing. This article describes the comparative experimental research data between the vertical and horizontal axis rotors. The test rig consists of the disk fixed onto the end of the shaft; the deep groove rolling bearing 6004-2Z/C3 with inner ring race defect is mounted behind the support. Throughout the experiment tests, the angular position of imbalance mass and inner ring race local defect is switched from 00 to 3600, each 450 angular step value. The study is carried out both with rotor axis oriented vertically and horizontally. In order to simplify the data being analyzed and to quantifiably assess the diagnostic experiments of vertical and horizontal rotor defects, statistical processing parameter called “Defect Visibility Ratio” (DVR) is being designed. Through the use of this statistical parameter, the defect-detection capabilities of rotor with bearing inner ring race fault can be determined quantifiably
A revised averaging method and general forms of approximate solution for nonlinear oscillator with only polynomial-type displacement nonlinearity
Get PDFIn this paper a revised averaging method is presented, that does not need the detuning factor in the solving procedure. Comparison with the traditional averaging method shows that it has the similar solving procedure and the same result as the primary resonance of the traditional averaging method. Then the nonlinear oscillator with only polynomial-type displacement nonlinearity is studied, and the general forms of the first-order approximate solution by this revised averaging method, and by the traditional averaging method for the super-harmonic resonance and sub-harmonic resonance are established. At last, the Duffing oscillator is investigated as an example, and the comparison of the analytical and numerical results proves the validity and simplicity of the presented method
Establishment of ground vibration prediction model for high-speed trains on embankments
Get PDFA series of field measurement data is used to establish the prediction model of ground vibration induced by Taiwan high-speed trains on embankments. These measurements consist of various possible influence factors, such as train speed, ground shear wave velocity, and structure volume. The characteristics of near-field ground vibration, far-field vibration propagation, and vibration influence distance are then evaluated from these measurement data. The analyses reveal that the near-field ground vibration level mainly depends on train speed and ground shear wave velocity. The influence of structure volume on the vibration level is minor. The far-field vibration propagation is affected by ground shear wave velocity. The analysis results also show that the attenuation coefficient is different for each frequency range. In general, the measured ground vibration in the high frequency range has the highest attenuation coefficient and that in the low frequency range has the lowest. For the vibration influence distance, the rock can propagate the vibration to the farthest distance among all soil types while the sand/silt/clay soils show the shortest. Finally, a specific ground vibration prediction model is established using these characteristics
An approach to performance assessment and fault diagnosis for hydraulic pumps
Get PDFThe hydraulic pump is the heart of the hydraulic system. Therefore, monitoring the condition of such a pump in real time is crucial to the reliability of the entire system. In this study, a method that assesses the performance of and diagnoses faults in hydraulic pumps is proposed. This method is based on wavelet packet transform (WPT) and a self-organizing mapping (SOM) neural network. First, WPT is used to decomposes the vibration signal into components. The energy of each component is then extracted and normalized to form feature vectors. Second, the SOM neural network, which is trained by normal data only, maps feature vectors into minimum quantization errors, which are then normalized into confidence values (CVs). Performance is assessed by tracking CV trends. Finally, SOM, which is trained by both normal and faulty samples, classifies faults into different groups when they occur. These groups represent the various fault modes of the hydraulic pump. In addition, Taguchi method is employed to reduce the number of redundant features and extract the principal components, thereby ensuring the effectiveness of the approach. A case study based on the vibration dataset of the rig of a test plunger pump is conducted to demonstrate the ability of the proposed method to assess the performance of a hydraulic pump and suitably diagnose faults
Health assessment and fault diagnosis for centrifugal pumps using Softmax regression
Get PDFReal-time health monitoring of industrial components and systems that can detect, classify, and predict impending faults is critical to reduce operating and maintenance costs. This paper presents a softmax regression-based prognostic method for on-line health assessment and fault diagnosis. System conditions are evaluated by processing the information gathered from access controllers or sensors mounted at different points in the system, and maintenance is performed only when the failure or malfunction prognosis is indicated. Wavelet packet decomposition and fast Fourier transform techniques are used to extract features from non-stationary vibration signals. Wavelet packet energies and fundamental frequency amplitude are used as features, and principal component analysis is used for feature reduction. Reduced features are input into softmax regression models to assess machine health and identify possible failure modes. The gradient descent method is used to determine the parameters of softmax regression models. The effectiveness and feasibility of the proposed method are illustrated by applying to a real application
Application of Butterworth filter for fault diagnosis on journal bearing
Get PDFJournal bearings are widely used to support the shaft of industrial machinery with heavy loads, such as compressors, turbines and centrifugal pumps. The major problem in journal bearing is catastrophic failure due to corrosion and erosion, results in economic loss and creates high safety risks. So, it is necessary to provide condition monitoring technique to detect and diagnose failures, to achieve cost benefits to industry. The method of vibration signal processing using filter analysis for condition monitoring and fault diagnosis has been evolving at a very rapid rate in recent years. The use of filter technique has proven to be a very powerful and reliable tool for fault detection and its most important attribute is its ability to efficiently detect non-stationary, non-periodic, transient features of the vibration signal. In this paper the application of Butterworth filter for processing vibration signal to detect faults in journal bearing is presented. A bearing testing apparatus is used for experimental studies to obtain vibration signal from a healthy bearing and a fault bearing. The signal processing methods using Fast Fourier Transform, enveloped filtered power spectrum based on Butterworth filter method and their implementation are presented. Further applications of Artificial Neural Network (ANN) are investigated as a model for automated fault diagnosis