Journal of Engineering and Thermal Sciences
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Analysis of vibrations in a modeled ballasted track using measured rail defects
Get PDFVibrations generated by trains and transmitted to the ground and nearby structures are a known source of problems associated with railway transport. Therefore this phenomenon should be studied in detail to avoid a negative impact on the environment. Within this framework, the article develops an improved version of a previously published analytical model capable of predicting ground vibrations caused by the passing railway vehicles. The new features include a new formulation of the models with five layers of material and an enhanced load input process that takes into account actual rail defects data as well as the Hertz theory for the rail-wheel contact. The model is adapted to a conventional ballasted track in Solares (Spain) as well as calibrated and validated with data collected on site. Hence the model is proved to be able to properly reproduce vibrations for the case of varying track typologies, constituting a useful research and design tool
Fault diagnosis of main engine journal bearing based on vibration analysis using Fisher linear discriminant, K-nearest neighbor and support vector machine
Get PDFVibration technique in a machine condition monitoring provides useful reliable information, bringing significant cost benefits to industry. By comparing the signals of a machine running in normal and faulty conditions, detection of defected journal bearings is possible. This paper presents fault diagnosis of a journal bearing based on vibration analysis using three classifiers: Fisher Linear Discriminant (FLD), K-Nearest Neighbor (KNN) and Support Vector Machine (SVM). The frequency-domain vibration signals of an internal combustion engine with intact and defective main journal bearings were obtained. 30 features were extracted by using statistical and vibration parameters. These features were used as inputs to the classifiers. Two different solution methods - variable K value and RBF kernel width (σ) were applied for FLD, KNN and SVM, respectively, in order to achieve the best accuracy. Finally, performance of the three classifiers was calculated in journal bearing fault diagnosis. The results demonstrated that the performance of SVM was significantly better in comparison to FLD and KNN. Also the results confirmed the potential of this procedure in fault diagnosis of journal bearings
Bearings coefficients effects on chaotic and bifurcation behavior of flexible rotor systems subjected to rub-impact
Get PDFThis study investigates the influence of end-support conditions on the chaotic and bifurcation behavior of a rotating flexible shaft-disk system. The system is modeled as a continuous shaft with a rigid disk in its mid span whilst supported by multi-coefficients bearings. Both Coriolis and centrifugal effects due to shaft flexibility are included. The partial differential equations of motion are extracted using the Rayleigh beam theory and the assumed mode method is used to discretize them in order to be solved numerically. The analytical tools used in this work include time series, phase plane portrait, power spectrum, Poincaré map, bifurcation diagrams, and Lyapunov exponents. The main objective of the present study is to investigate the effects of end-supports stiffness and damping coefficients on the chaotic vibration behavior of a rotating system. Periodic, sub-harmonic, quasi-periodic, and chaotic states have been observed for each case. As demonstrated, inclusion of the bearing effects can primarily change the speed ratios at which rub-impact occurs. The principal and cross-coupling stiffness and damping coefficients have quite different effects in the chaotic behavior of the system
Oscillations of cylinder piston rod – comparison of amplitudes and frequencies for the transient phenomena in tap water- and oil-based PCHS
Get PDFPower-control hydraulic system (PCHS), as a part of a machine or production line, provides it with all or most of the necessary movements. Most of the movements in PCHS are carried out by means of hydraulic cylinders. In this case movements are mostly generated by cylinder piston rods. More or less obvious transient phenomena occur during these movements under conditions of acceleration and deceleration. As a consequence, oscillations are induced in the system. In our work we investigate the phenomena and parameters of such PCHS for two hydraulic fluids. Most of the PCHSs still use mineral oil as hydraulic fluid but it is environmentally very harmful. Ecological awareness during natural disasters and man-made pollution is the subject of much discussion. It is everybody’s responsibility to take care of the natural environment and reduce the threats to our future existence. The preservation of drinking water and the prevention of its contamination by pollution are particularly important. Powercontrol hydraulics is one important area in which a positive step could be made to protect the resources of drinking water. The use of tap water instead of the conventional hydraulic fluids in power-control hydraulics is one of the most environmentally friendly changes that could be implemented. Therefore in this paper we show, based on dynamic-transient parameters, both the functionality and the usability of water hydraulics in comparison to the more familiar oil hydraulics. A comparison of the dynamic behavior between the conventional oil and the relatively new water hydraulics under the same conditions is described. Mineral hydraulic oil was used in the oil hydraulic test rig and distilled water was used in the water hydraulic test rig. The tests were conducted at different flow rates (11, 22 and 33 lpm) and system pressures (70, 110 and 160 bar) as well as applying different loading conditions (first, with a mass of 163 kg in the horizontal and vertical positions and, second, without the mass). The registered amplitudes of the cylinder piston rod oscillations were 20-30 % smaller in the water hydraulics with respect to the case of oil hydraulics, while the frequencies of the piston rod oscillations were 7-20 % higher
Frequency domain identification of the active 3D mechanical structure for the vibration control system
Get PDFNowadays structures are light and compliance therefore such structures are opened to the influence of external and internal excitations which in results lead to the structure vibrations and cause a loss of the energy which is used in the process realized by the structure. For example: arms, antennas, satellite solar batteries or slender skyscrapers are such plants. To damp the vibrations and save loss energy we develop design the active vibration control systems. To design such control system we should realized very important stages beginning from analytical investigations through process identification of the dynamical system. The 3D bar structure with sticked parallel piezo-stacks into chosen bars is considered in the paper. Piezo-elements play a role of piezo-actuators, while two eddy-current sensors located in free plane the structure are used to measurement displacement in directions X and Y. Such control plane will be considered as a two input and two output (TITO) system. As a result of analytical and numerical investigations such system was divided to two single input single output (SISO) subsystems. Such the coupled system was used in the process of the full model identification. The chirp signal was applied in identification process. The structure was excited according to single input single output controlling force while outputs signals were measured in perpendicular direction X and Y. In such way we have confirmed that for control purposes the plant can be decupled
Bond graph-based analysis of energy conversion in vibration-piezoelectricity coupling and its application to a cantilever vibra tion energy harvester
Get PDFThe energy flow in a piezoelectric vibration energy harvester (VEH) involves both the mechanical domain and the electrical domain. To better understand the vibration-piezoelectricity coupling of this device, a unified description approach based on the bond graph is proposed to analyze the influence of the piezoelectric VEH parameters on the electricity harvesting performance in the energy conversion. Both the mechanical structure and the electric circuit are modeled using the bond graph. The present method is applied to analyze the parametric configuration of a piezoelectric VEH, which is further tested on an experimental platform. The results show that the unified model using the bond-graph is well-suited for analyzing the vibration-piezoelectricity coupling. The proposed method can advance the design optimization of piezoelectric VEHs
Nonlinear dynamic characteristics of SMA simply supported beam in axial stochastic excitation
Get PDFIn this paper, nonlinear dynamic characteristics of shape memory alloy (SMA) simply supported beam in axial stochastic excitation were studied. Von del Pol nonlinear difference item was introduced to interpret the hysteresis phenomenon of the strain-stress curve of SMA, and the hysteretic nonlinear dynamic model of SMA simply supported beam in axial stochastic excitation was developed. The local stochastic stability of the system was analyzed according to the largest Lyapunov exponent, and the global stochastic stability of the system was discussed in singular boundary theory. The steady-state probability density function and the joint probability density function of the system were obtained in quasi-nonintegrable Hamiltonian system theory. The result of simulation shows that the stability of the trivial solution varies with bifurcation parameter, and stochastic Hopf bifurcation appears in the process. The result is helpful to stochastic bifurcation control to SMA simply supported beam
Dynamics of hybrid PM/EM electromagnetic valve in SI engines
Get PDFSome previous studies demonstrated the advantages of electromagnetic valve train (EMV) for controlling variable valve timing (VVT) in SI engines. EMV allows valve timings and duration events are optimized in wide operating ranges. However, conventional EMV with solenoid actuator consumes a larger amount of energy in catching the valve at engine start and in keeping valve at open or closed position. A new EMV with hybrid permanent magnet and electromagnetic coil (PM/EM) has been proposed in this paper. An engine model with new EMV has been built to simulate the valve dynamics. Additionally, the effects of the flow gas resistance and damp coefficient have also been examined and analyzed. The results show that the new EMV can satisfy the valve dynamics in transition time, valve velocity, acceleration, energy consumption, etc. in controlling valve timing for SI engines
Identification of modal parameters from structural ambient responses using wavelet analysis
Get PDFRunyang suspension bridge is the longest suspension bridge in China with a main span of 1490 meters. During the construction of the bridge, a structural health monitoring system was installed, which was designed by the Southeast University. Since the bridge was open to traffic, quantities of structural ambient vibration responses have been recorded by the monitoring system. It is important to extract dynamic characteristics from these responses for structural assessment and maintenance. This paper presents the study on extraction of modal parameters from the Runyang suspension bridge structural health monitoring system records using wavelet analysis. Time-frequency domain modal identification using wavelet analysis is studied with an emphasis on the efficient approach for determination of the dilatation parameter. Then the wavelet analysis based method was adopted to identify dynamic properties including modal frequencies, mode shapes and damping ratios from the ambient vibration responses recorded by the monitoring system. Identified results were compared with those from Enhanced Frequency Domain Decomposition method and Stochastic Subspace Identification method. The differences between results are analyzed. Suggestions on future study are also given
A quantitative study of the blade passing frequency noise of a centrifugal fan
Get PDFTonal noise constitutes the major part of the overall fan noise, particularly the blade passing frequency (BPF) noise, which is generally the most annoying component. This paper quantitatively studies the BPF tonal noise of a centrifugal fan, including casing aerodynamic noise, blade aerodynamic noise and casing structural noise. Firstly, fan noise generation and propagation is discussed and the measured spectra of fan noise and casing vibration are presented. Secondly, a fully 3-D transient simulation of the internal flow field of the fan is performed. Flow interactions between the impeller and the volute casing result in the periodic pressure fluctuations on solid walls of the impeller and casing. This pressure fluctuation, in the aeroacoustic study, is modeled as aeroacoustic dipole source according to the Lighthill’s acoustic analogy theory. With the inhomogeneous wave equations solved by the boundary element method, the BPF casing and blade aerodynamic noise radiation is obtained. Finally, in the casing structural noise study, the casing structural vibration under the excitation of BPF pressure fluctuation is calculated by the finite element method and sound radiation is solved by the boundary element method subsequently. Results demonstrate that the casing aerodynamic noise is the main contribution to the centrifugal fan noise with the sound power level of 103 dB followed by the blade noise (91 dB), and the casing structural noise is 79 dB