Journal of Vibroengineering
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Tacholess order tracking method for gearbox based on time-varying filter and energy centrobaric correction method
Get PDFUnder the premise that the instantaneous speed can be accurately measured or precise estimated, order tracking is considered to be a classical and effective technique for non-stationary vibration analysis of rotating machinery. The meshing frequency components of the vibration signal measured from complex gearbox system interfere with each other mutually. The energy centrobaric correction method exhibits exact instantaneous frequency estimation (IFE) ability under the interference, but is susceptible to strong noise. Combining with time-varying filter and energy centrobaric correction method, a tacholess order tracking technique for gear fault diagnosis under the rotating frequency multi-linear fluctuation is proposed. The time-varying filter is designed to filter the strong noise signal, and then IFE could be accurately calculated from the filtered signal by energy centrobaric correction method. The instantaneous phase of reference shaft based on the Vold-Kalman filter (VKF) is used for angular resampling of the original vibration signal. The results show that the shaft rotating speed could be accurately identified from extracted gear meshing components. The order spectrum obtained by the proposed method with tacholess is substantially the same as the order spectrum obtained by a tachometer. Simulation analysis and experimental results verify the advantages of proposed tacholess order tracking technology for monitoring and fault diagnosis of gearbox vibration under the condition of strong noise and large speed variation
Combustion monitoring in engines using accelerometer signals
Get PDFRecent regulations for emission control from combustion engines have led to focus on various methods to monitor control and the combustion process. The presented work explores the potential relationship between various combustion events monitored using in-cylinder pressure transducer and the resulting block vibration measured using accelerometers. Various features of combustion development process were derived from the vibration data acquired. The methodology was analyzed using a single cylinder diesel engine. The heat release data was able to detect and extracted various indicators of the combustion process like start of combustion and half of injected fuel positions. Higher correlation was observed for the data computed using heat release curve obtained from the in-cylinder pressure measurements and those obtained using the accelerometer signals. The proposed methodology can be used to optimize the fuel injection timing in order to reduce emissions from engines to comply with various regulations. The practical importance of presented work demonstrates use of monitoring of block vibration signals as a mean of non-intrusive methods of diagnosis of engine for its effective condition monitoring
Natural frequency sensitivity and influence analysis of TBM cutterhead system
Get PDFTBM cutterhead works in complex working conditions, which endures the reverse impact forces of rock breakage, resulting in parts abnormal failure. Hence, the study of the system inherent characteristics is the basis for cutterhead dynamic design. Based on the established vibration model of a TBM split-cutterhead system, the modal method is used in the dynamic model and the natural frequency sensitivity expressions to system parameters are deduced. Then a cutterhead system of a water conservancy project in China is taking as an example, the natural frequency sensitivity with respect to the cutterhead support stiffness and mass parameters is obtained, and the influence of the two parameters on natural characteristics is analyzed. The results show that, the 10th-20th order natural frequencies are mainly affected by the cutterhead support stiffness and mass parameters, and the 9th-11th order frequencies are mainly influenced by cutterhead moment of inertia. Besides, with the change of stiffness and mass parameters, the cutterhead system natural frequency curves cut across each other and there are also many inflection points in the sensitivity curves, then the modal jumping occurs near these points. The parameter sensitive points were obtained from the results, which can provide reference for TBM cutterhead system parameters matching
Multi-body dynamic simulation and vibration transmission characteristics of dual-rotor system for aeroengine with rubbing coupling faults
Get PDFIn this paper, a dual-rotor system multi-body dynamic model with rubbing coupling faults is established for practical aero-engine. In the model, the rubbing fault simulation method is introduced, the coupling effect between the internal and external rotor is considered. The numerical simulations of rotor vibration are accomplished by the utilization of multi-body dynamic platform, where the simulation model consists of discs unbalances and local rub-impact between discs and casing shells. The time-domain responses, the frequency spectra and the shaft-center trajectories of dual-rotor with different unbalance and different rubbing positions are obtained. The vibration and its transmission characteristics of the inner and outer rotors are calculated. Finally, the simulation results are compared with the measured vibration of a dual rotor tester with rubbing fault. The simulation results are consistent with the measured results, which confirms the feasibility of the established model and the multi-body dynamics simulation method in this paper. The application of multi-body dynamics simulation method in aero-engine can deepen the understanding of the internal operation nature and laws of aero-engine, reduce the repetition of physical tests, greatly improve the efficiency and quality of development, accelerate the research and manufacture process
A modified damage index probability imaging algorithm based on delay-and-sum imaging for synthesizing time-reversed Lamb waves
Get PDFImaging for damage in plate structure by Lamb waves is one of the most effective methods in the field of structural health monitoring. In order to improve the accuracy of damage localization, a novel method is proposed to modify damage exponent probability imaging algorithm based on delay-and-sum imaging by using time reversal Lamb waves. A new probability distribution function is introduced to improve the damage index probability method and is combined with delay-and-sum method for damage localization. Experimental results on aluminum plate show that the hybrid algorithm achieves better accuracy of damage location and imaging quality than the conventional delay-and-sum method
A study on the behavior of structures based on the rocking motion of rigid cores involving pre-compressed springs and viscous dampers
Get PDFTo create a partial rocking mode in a building structure during an earthquake, two or more rigid cores with joint connection to the foundation, and capable of moving in the two main directions of the building’s plan, can be used. A rigid core with a hinge connection to the foundation is essentially unstable. However, two rigid cores can be connected together by springs and dampers in certain floors to create a stable structure. At the same time, the structure shows a rocking behavior in which the building moves almost as a rigid body. In fact, the effects of all modes other than the fundamental one is almost eliminated. The use of yielding or friction dampers leads to permanent displacements in the structure in an earthquake. Therefore, in this study pre-compressed springs were employed, which do not create any permanent displacement. The pre-compressed springs were used to provide the structure with initial stiffness and prevent any displacement by small forces. Since an elastic spring does not have any damping, it was decided to control the structural displacements by viscous dampers in certain floors. Finally, the proposed structure underwent static and time-history analyses in plastic range, and the results suggested the desirable behavior of the proposed structure. In particular, there were no permanent displacements left in the structure after the earthquake
Effect of heat transfer optimization on brake noise characteristics of automotive disc brake
Get PDFHeat effect is one of the most important factors affecting the brake noise level. The finite element model for transient heat transfer analysis of disc brake is established based on heat transfer control equation and heat dissipation boundary conditions of dynamic convection. According to the NVH test and modal calculation, the brake noise characteristics are tested and analyzed. Meanwhile, the heat transfer simulation is verified and shows high accuracy. The discrete data for the response surface function are obtained by the Central Composite Design method with the peak temperature and mass as the target variables. The error of regression function is judged by fitting decision coefficient, correcting decision coefficient and root mean square error. By the optimizing mathematical model, the brake disc temperature peak can be greatly reduced and the heat transfer ability is obviously optimized without mass increasing, the time with temperature above 120 °C can be reduced by 46 %. Through the comparison of brake noise level before and after optimization, it can be known that the noise level can be significantly decreased after structural optimization, except the first order resonance frequency. The optimization result has good social and economic value
Damping effects of different shock absorbing materials for tunnel under seismic loadings
Get PDFCircular tunnels are widely used in infrastructure. Under the action of earthquakes, the destruction of circular tunnels will result in a large number of economic losses and casualties. Therefore, the study on shock absorption of tunnels is important. However, the research has not been sufficient on the effect of the damping layer on seismic response of a circular tunnel in sand. In this paper, the influence of the damping layer on the seismic response characteristics of circular tunnels in sand is studied by large-scale shaking table test. The actual El-centro wave is loaded to the model system in three directions during the tests. The input peak seismic acceleration values are 0.05 g, 0.1 g and 0.2 g. Then the effects of two different damping materials on the dynamic response characteristics of circular tunnels are analysed quantitatively. The test results show that the damping layer reduces the seismic response of the circular tunnel. The response accelerations of the tunnel bottom and crown without damping layer are greater than that with the damping layer, which indicates that damping layer absorbs the energy caused by the seismic motion. When the sponge rubber is used, the circular tunnel dynamic response is more attenuated than that with foam board. In conclusion, the shock absorbing layer can effectively reduce the seismic response of tunnel. As a result, the damage of the tunnel decreases under the earthquake. This study has clarified the isolation mechanism of the shock absorbing materials. It is recommended to use sponge rubber material as the shock absorbing layer
Research on static load sharing characteristics of power split two-stage five-branching star gearing drive system
Get PDFPower split two-stage five-branching star gearing drive system has been widely used in the aviation engine reducer and the helicopter’s main reducer. For the problem of load sharing characteristics of this system, a static load-sharing calculation model is established. According to the power flow closed loop characteristics of the whole system, the torque equilibrium condition and deformation compatibility condition of the system are established. The load sharing coefficient of the star gears and the system is calculated by using the principle of the integrated equivalent mesh error and the static equilibrium condition of the floating element. Further, the influence of manufacturing error, installation error and floating on load sharing coefficient is analyzed. When the load sharing characteristic is independently influenced by the error, the load sharing coefficient of each star gear changes periodically with time. Basic component floating can significantly improve the load sharing performance. The correctness of the theoretical algorithm is verified by experiments. A new algorithm is proposed for engineering application
On-line prediction remaining useful life for ball bearings via grey NARX
Get PDFThe Huge vibration data are generated continuously by many sensors in daily high-speed rotating machinery operations. Accurate online prediction based on big vibration data streaming can reduce the risks related to failures and avoid service disruptions. This paper presents a hybrid nonlinear autoregressive network with exogenous inputs (NARX) model to forecast the remaining useful life of ball bearings through health index based on big vibration data streaming. This approach is validated by a real data from PRONOSTIA experimentation platform and industrial test rig compared with backpropagation neural network (BP), Elman and general regression neural network (GRNN) prediction model. Root mean square error, mean absolute error and correlation coefficient were used as performance indexes to evaluate the prediction accuracy of these models. The mean absolute error, the root mean square error and the correlation coefficient of hybrid NARX model evaluation index are 2.04, 2.85 and 0.98 respectively. It shows that the model presented in this paper has higher prediction accuracy. It can meet the needs of actual ball bearing remaining useful life prediction and also provide reference in other fields