Journal of Vibroengineering
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The effect of cooling the foil bearing on dynamics of the rotor-bearings system
Get PDFIn order to protect rotors and foil bearings operating at high temperatures from being overheated and damaged, these components are often cooled by air. In addition, such a cooling method is accompanied by an axial temperature gradient that changes the shape of the lubrication gap in a way likely to affect the operation of a foil bearing. This article presents the research on various methods for cooling a foil bearing and discusses the impact of these methods on dynamic parameters of the rotor-bearings system. To be able to assess the temperature inside such a bearing, there is a need for a reliable measurement method. The authors of the article measured the temperature of the top foil using thermocouples and showed that their measurement method does not exert any significant impact on the operation of the rotor-bearings system. The article also describes a novel method for compensating the axial temperature gradient occurring in the bearing bush using Peltier modules
A more accurate dynamic model for dual-side excitation large vibrating screens
Get PDFCompared with a traditional unilateral-driven large vibrating screen, the proposed dual-side excitation large vibrating screen (DELVS) has a simpler screen structure and less vibration mass, which might improve its reliability. A DELVS with metal cylindrical coiled springs is theoretically and experimentally studied in this paper. With the rotation considered, a fundamental three-degree-of-freedom (3-DOF) dynamic model for DELVS is established firstly. Then an elastic compression bar model method (ECBM) is proposed for transverse stiffness determination of a metal cylindrical coiled spring and applied into the numerical simulation of DELVS. Finally, an experimental test on a DELVS of 4.25 m×6.00 m is conducted. It is seen that numerical simulation with the proposed ECBM is more closely related to the experimental data, hence the accuracy of the proposed dynamic model of DELVS is enhanced. The conclusions may provide guidance on a design of a high-performance large vibrating screen
Erratum: Structural health monitoring of 3D frame structures using finite element modal analysis and genetic algorithm
Get PDFAn analytical investigation on the dynamic stability of a rotor filled with liquid
Get PDFThis paper deals with the dynamic stability of a rigid rotor arbitrarily filled with liquid. On the basis of the established coupled-field equations of the rotor system, the general whirling eigenequation, which is a quartic complex coefficients equation, is derived. In order to obtain the solutions of the general whirling eigenequation, a mathematical method is proposed. To illustrate the precision of calculating results, a comparison is carried out between the present analysis and the numerical results. The results show that two calculation results are in good agreement. Then the stability of the rotor system is analyzed. It is shown that the dynamic instability occurs at a particular bound of the spinning speed. Moreover, the effects of system parameters, such as fluid-fill ratio and mass ratio, on the unstable regions are discussed
Near-optimal pitch of a moiré grating in dynamic visual cryptography
Get PDFDynamic visual cryptography (DVC) is a technique for the encryption and decryption of visual secret information. The confidential visual information in DVC is concealed embedding the secret image into the regular moiré grating. The secret can be perceived from the cover image if only the cover image is oscillated according to a predefined law of motion and time-averaging techniques are used. The security of the encryption procedure and the quality of the decrypted image depend on the proper preselection of the pitches of a moiré grating used in the encryption stage. This paper presents the main principles of the determination of near-optimal pair of the pitches of moiré grating as well as graphical schemes and analytical equations in case of harmonic and chaotic oscillations
Acoustic horn design for joining metallic wire with flat metallic sheet by ultrasonic vibrations
Get PDFUltrasonic Metal Welding is a green manufacturing technique and one of the most advanced solid state welding processes in which similar or dissimilar metallic components are joined by the application of high frequency vibrations (> 20 kHz) and pressure. Ultrasonic metal welding is accompanied by slip and plastic deformation so that the base metals being welded will not melt and in turn forms a homogenous coalescence of two metals at the joining area so that the joint retains the parent metal properties. The major problem faced by the industries using ultrasonic metal welding process is the poor weld quality and weld strength. The design of acoustic horn or sonotrode plays a dominant role in producing quality welds. The primary function of sonotrode is to vibrate at a level required for welding and also to transmit the vibration energy to the point where welding of metals takes place. For producing quality welds, the vibration energy is to be transmitted to the weld interface without much loss. Therefore, there is a need for accurate design of sonotrodes in ultrasonic metal welding process. This work focuses on designing a stepped sonotrode used for joining metallic wire with metallic sheet based on significant design parameters such as amplitude gain and von Mises stress factor using modal and harmonic analysis. Experimental trials are conducted using the stepped sonotrodes and the effectiveness of the designed sonotrodes is evaluated based on improvement of strength of the joint in tension
Vibration control of a hydrostatic bearing using magnetorheological elastomer shell bearing
Get PDFIn rotating machines, random movements or sliding movements of the rotor in its housing can produce undesirable phenomena for some parts. To solve this problem, a new hydrostatic bearing with an intelligent magnetorheological elastomer sell bearing has been designed to control the undesirable vibrations of rigid rotors. The different effects of the influence parameters on the vibratory behavior of the sell bearing are calculated numerically using Abaqus software, and the results found are encouraging
Development and analysis of a new technology of freight cars modernization
Get PDFPaper contains a report of the part of works conducted in the research and development project concerned with a modernization of freight wagons during their periodic repair. The aim of this research was to obtain better exploitation conditions of freight cars. Two elements of those works are presented: a computer aided analysis of the freight car’s CAD model and results and analysis of the real object elements’ vibrations during exploitation. The aim of numerical analysis was to determine the maximal permitted speed at which the car does not go off the rails. These tests were performed using the “Motion Simulation” module of the software of the CAD/CAE/CAM class Siemens PLM NX. The real freight car’s elements vibration were measured and analysed in order to verify if it is possible to create a mechatronic approach for technical condition analysis of modernized freight cars during their exploitation based on their dynamic response as well as to validate the CAD model of the considered freight car
Nonlinear dynamic response analysis of two-stage spur gear space driving mechanism with large inertia load
Get PDFLarge inertia load has been widely used in space driving mechanisms, but the research concerning theory is still an unexplored scientific field. Towards the problem of nonlinear disturbance in space driving mechanism with large inertia load, a 14-DOF (Degree of Freedom) nonlinear, time-varying, dynamic model of two-stage spur gear system was established, taking into consideration time-varying stiffness, backlash and transmission error. The dynamic response of the load, under large or small inertia was investigated, basing on the dynamic model. The results indicate that at starting, normal operation and braking, large inertia load system has obvious hysteresis, compared to small inertia. The factors that improve dynamic response speed under large inertia load were studied. The results indicate that improving the stiffness and damping of the output shaft and changing the material of second gear pair to titanium alloy are helpful in improving the dynamic response speed of the system. Some results enrich the research of two-stage spur gear nonlinear model and large inertia load, since they provide important reference for the actual design of the gear system
Dispersed operating time control of a mechanical switch actuated by an ultrasonic motor
Get PDFThe ultrasonic motor is an uncertain time-varying nonlinear system because of the nonlinearity of the piezoelectric material, the friction and the temperature. For example, the operating time of the mechanical switch actuated by the ultrasonic motor in regular stroke is highly dispersed. Unfortunately, it is difficult to establish accurate mathematical model. In this paper, an analytical autoregressive process model (AR) is employed to identify and control the ultrasonic motor. First of all, dispersed operating time of the mechanical switch actuated by the ultrasonic motor is investigated. Then, the AR model is established to predict the operating time of the ultrasonic motor on the basis of the statistical data to reduce the nonlinear behavior of the ultrasonic motor, and to improve the accuracy and obtain a good time response of the switch. The simulation results are agreed with experimental results, confirming the effectiveness of proposed model. Furthermore, we adopt the predicted result of the AR model to control the mechanical switch actuated by the ultrasonic motor. The analytical investigation is fulfilled with two target operating time ranges, namely 12 ms and 24 ms. Comparison of the results obtained from the AR model and the experimentation reveal that the standard deviations are less than 95.3 μs and 102.7 μs with maximum errors equal to 0.41 % and 0.44 % respectively. Thereby, the proposed dispersed operating time control is performed. Findings indicate that the maximum errors for the operating time of the mechanical switch are less than 140 μs and 110 μs with ±0.85 % and ±0.42 % respectively