Journal of Engineering and Thermal Sciences
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Fault diagnosis of rotor using EMD thresholding-based de-noising combined with probabilistic neural network
Get PDFDe-noising of signal processing is crucial for fault diagnosis in order to successfully conduct feature extraction and is an efficient method for accurate determination of cause. In this paper, the empirical mode decomposition (EMD) thresholding-based de-noising method and probabilistic neural network (PNN) are respectively used in the de-noising of the vibration signal and rotor fault diagnosis and compared with wavelet thresholding-based de-noising technology and back propagation neural network (BPNN). The results show that the clear iterative EMD interval thresholding performs better than wavelet thresholding in the de-noising of the vibration signal, and avoids the determination of wavelet basis and decomposition level. In addition, the PNN created by feature samples does not require training and has a higher accuracy than BPNN
Adopting method of key block and energy distribution to predict the slope stability under blasting
Get PDFAt present, an important slope stability analysis method consists in the evaluation of the bearing capacity of key block, which is located between the joints and fissures in rock mass, and plays the decisive role on the slope stability. Because of the defective equivalent accuracy and elusory mechanical path, the traditional analysis methods have some inevitable errors. However, the energy theory can avoid the above defects easily, in this paper, the analytical input energies are potential energy and blasting vibration energy, and the consumed energies are fractured dissipative energy, friction dissipative energy and kinetic energy of instability. In order to eliminate the size effect problem, it is necessary to emphasize each part of energy expression as the energy density form. And the first four items would be confirmed by different theories and tests, so that the instability kinetic energy could be evaluated by the energy conservation law, and then the instability velocity could be calculated to predict the instability grade of slope
Study on aerodynamic characteristics and running safety of two high-speed trains passing each other under crosswinds based on computer simulation technologies
Get PDFWith the continuously increased running speed of high-speed trains, aerodynamic problems become more and more obvious. Running safety of trains under crosswinds is a serious problem among numerous aerodynamic problems. Aiming at this problem, this paper combines computational fluid dynamics with multi-body dynamics to study aerodynamic characteristics and safety problems when the high-speed train is running under crosswinds. Based on fluid software FLUENT, this paper computes the flow field of two high-speed trains passing each other under crosswinds. Meanwhile, with combining the multi-body dynamic software SIMPACK with theories, the paper establishes a multi-body dynamic model of the high-speed train, and applies random aerodynamic loads which act on the high-speed train to this model. Impacts of aerodynamic forces (force moments) on aerodynamic characteristics and running safety of each train compartment in the open air are analyzed. Analyzed results show that: when two high-speed trains are passing each other at the same speed of 350 km/h and the crosswind speed is 15 m/s, maximum pressure fluctuations are at observation points near the lateral windows of the head train; aerodynamic forces and force moments of the head train are more than those of the mid-train and tail-train; the high-speed train still has a high safety performance under crosswinds, where the maximum derailment coefficient is 1.9, the reduction rate of the wheel load is 1.1 and the overturning coefficient is 0.98, all of which are smaller than the limit value. More comprehensive factors are considered by the computational model in this paper. It can be used as an effective method to study and evaluate the performance of two high-speed trains passing each other under crosswinds
Generalized gap function in the dynamic interaction problems of elements of vibrational technological machines with “not holding” ties
Get PDFIssues of formation of rational modes of dynamic interaction of contacting elements of vibrating machines in problems of increase in quality of technological vibrohardening processes are considered. Mathematical models and criteria of an estimation of forms of movement with “not holding” ties are developed. For analytical research of “not holding” ties the concept of the generalized gap function is entered. The model of dynamic interaction of a solid with a vibrating surface is developed at introduction of additional external forces and elastic interactions. On the basis of a method of gap function criteria of a separation are formulated and forms of movement of a material particle in dynamic interaction with a vibrating surface are proved. The generalized approach for problems of dynamic synthesis of the vibrating technologies realized in modes continuous tossing is offered. Conditions of realization of multiple modes continuous tossing when the period of free flight of a material particle makes an integer of the periods of a basic vibrating surface are formulated. Generalization of considered models on a compound solid, interaction between which elements has “not holding” character is offered. The problem of definition of gapless conditions of movements at vibrating influence on a compound solid by a surface is posed. Conditions of formation of reaction in the oscillatory system formed by several solid elements with “not holding” ties, connected among themselves by means of elastic interaction and power factors are defined. In respect of practical appendices, the problem of development and experimental approbation of the measuring devices fixing modes of continuous tossing is posed
Finite element simulation of the airbag deployment in frontal impacts
Get PDFVirtual modeling and simulation are increasingly used to help develop restraint systems, and airbag simulation is the necessary steps during airbag research and design progress. In this work, the squeezed airbag has been simulated by a uniform pressure method in which the pressure of the airbag is considered as constant. The main aim of this study is evaluate the performance of deploying of passenger side airbag using finite element methods (FEM) to handle different collision scenarios
Electromechanical coupling characteristics and synchronization control of two-hammer synchronous vibration system
Get PDFTwo-hammer synchronous vibration system which consists of two hammers is a complex electromechanical system with complex electromechanical coupling. In this paper, electromechanical coupling characteristics of this system are studied in detail using the methods of theoretical derivation, numerical simulation and experiment. The kinetic models of this system are established, and approximate expressions of electromechanical coupling strength are solved using periodic averaging method (PAM). Basic coupling rules and reasons are obtained. Subsequently, numerical simulation is carried out, and simulation results demonstrate the correctness of model and approach. After that, based on electromechanical coupling characteristics, compound synchronization error feedback and composite control based on inching control (CSEB-CCBIC) strategy and algorithm are proposed, and simulation results validated the effectiveness of the proposed strategy. Finally, experiments are carried out, and the results show that, speed and phase achieve synchronization quickly under the action of synchronization controller, which are agree well with theoretical and numerical results. The research conclusions and methods also provide theoretical foundations for multi-hammer synchronous vibration system and its synchronization control
A stochastic averaging method on the strongly nonlinear Duffing-Rayleigh oscillator under Gaussian colored noise excitation
Get PDFA modified stochastic averaging method on a Duffing-Rayleigh oscillator with strongly nonlinearity subject to Gaussian colored noise excitation was proposed. The so-called He’s energy balance method was applied to obtain the averaged frequency of the conservative system. Subsequently, the stochastic averaging method of strong nonlinearity was used. The modified method can offer more concise approximate expressions of the drift and diffusion coefficients without weakening the accuracy of predicting the responses of the systems too much. The stationary responses of probability density of amplitudes, together with joint probability density of displacement and velocity are studied to verify the presented approach. The reliability of the systems was also investigated to offer further support. Digital simulations were carried out and the output of that are coincide with the theoretical approximations well
Numerical investigation on noise reduction for an in-line fan equipped with Helmholtz resonator
Get PDFThis research intends to analyze and improve the flow-induced noise of an in-line fan with Helmholtz resonator by the numerical simulation. At first, the flow and acoustic fields associated with the fan are simulated and analyzed via the CFD simulation. Subsequently, a thorough understanding on the aerodynamic and acoustic features of this mixed-flow fan is achieved. Later, to reduce the fan noise, a set of Helmholtz resonators for this inline-fan is designed and installed onto the critical regions inside the fan. Also, the flow-induced-noise reduction due to the resonator is examined and discussed in details. As a result, the maximum noise reductions on the 1st and the 2nd characteristic frequencies are obtained at 6.9 dBA and 9.8 dBA, respectively. Moreover, there is a minor noise-elimination effect found on the other harmonic frequency while the significant result appears on the designed characteristic frequency. However, all resonators used yield a significant noise reduction at the second BFF. In conclusions, a comprehensive parametric study on Helmholtz resonator is carried out and summarized for attaining a design guideline for its application on the in-line fan. The accomplishment of this study provides a systematic scheme of noise reduction for an inline-fan with the addition of Helmholtz resonator design
Relative ride vibration of off-road vehicles with front-, rear- and both axles torsio-elastic suspension
Get PDFWheeled off-road vehicles are known to transmit higher magnitudes of low frequency whole-body vibration (WBV), which have been associated with an array of health disorders among human drivers apart from fatigue and reduced work rate. In this study, the ride performance potentials of a torsio-elastic suspension employed in the front-, rear-, and both axles of an off-road vehicle are investigated. A three-dimensional ride dynamic model of the vehicle is formulated and analyzed under excitations arising from correlated random elevations of two terrain tracks. The model validity is demonstrated on the basis of reported field measured data of a rear-suspended frame-steered articulated forestry vehicle. The ride responses are evaluated in terms of unweighted and weighted root mean square (rms) accelerations along the translational and rotational axes near the driver seat. The results show that fully-suspended vehicle can yield substantial reductions in vibration along all the axes, and suspension in the axle in the proximity of driver cabin is relatively more effective in limited the WBV exposure. It is further shown that the linkage suspension helps preserve roll stability while providing adequate ride performance
Vehicle steering wheel angle identification research based on dynamic program method
Get PDFIn order to improve the safety of vehicle manipulation as well as to provide a theoretical basis for the study of vehicle steering system and intelligent parking systems, a new method of vehicle steering wheel angle identification is presented – the dynamic program method. First, three freedom degrees of vehicle model is established. Then Bellman’s principle of optimality is used for minimizing the objective function. The dynamic optimization model of the load identification that the yawing angular velocity, lateral acceleration and vehicle body roll angle identified the steering wheel angle and angle velocity. The result shows that the dynamic program method for the steering wheel angle identification problem containing the measurement noise has strong adaptability, high accuracy and good anti-jamming capability