Journal of Engineering and Thermal Sciences
Not a member yet
1200 research outputs found
Sort by
The influence of the smoothing component on the quality of algebraic forecasts
Get PDFShort term time series forecasting model with different internal smoothing techniques is presented in this paper. Computational experiments with real world time series are used to demonstrate the influence of different smoothing techniques in fitness. Algebraic forecasting results with any internal smoothing model outperformed results of the algebraic forecasting without smoothing
Simulation analysis on inner flow field and optimization design of air knife
Get PDFThis paper conducted a parametric modeling for air knife structure in a printing factory, used HYPERMESH software to divide the meshes of air model and combined with actual conditions to define various boundary conditions in the inner flow field of air knife. Meanwhile, this paper adopted fluid dynamics software Fluent to conduct numerical simulation for the internal airflow of air knife, obtained the distribution regulation of flow field, conducted a parametric modeling for air knife structure under many internal structural proposals through ANSYS design module based on the simulation computational result, conducted optimization design for the position of guide plates, the number of outlets and the size of return air tank in the detailed structure in the air knife in order to determine specific dimension parameters and optimal proposals. Based on the computational results of simulation, this paper found that the original air knife structure had a non-uniform flow field and low velocity at the inlet and outlets. With the increase of length of air knife, the velocity of the middle outlet reduced to zero and did not have obvious effects any more. Guide plates in the air knife had a great influence on the inner flow field of air knife. Through optimization design, the inner flow field of air knife became uniform when there was only one guide plate. When the guide plate was close to the front end of the air knife, the inner flow field of air knife was relatively uniform and velocity at the inlet and outlets was relatively high. This paper conducted a model design for air knives with different structural types and determined proposal 4 as the optimal design through repeated analysis. The design method in this paper could provide guidance for studying and designing air knife structures in the aspect of technological approach and theory
Hybrid residual fatigue life prediction approach for gear based on Paris law and particle filter with prior crack growth information
Get PDFGear has been widely used in the modern industry, and the gear reliability is important to the driving system, which makes the residual fatigue life prediction for a gear crucial. In order to realize the residual fatigue life of the gear accurately, a hybrid approach based on the Paris law and particle filter is proposed in this paper. The Paris law is usually applied to predict the residual fatigue life, and accurate model parameters allow a more realistic prediction. Therefore, a particle filtering model is utilized to assess both model parameters and gear crack size simultaneously. As a data-driven method, particle filter describes the dynamical behavior of model parameters updating and gear crack growth, whereas the Paris law, as a model-based method, characterizes the gear’s crack growth according to the physical properties. The integration of the Paris law and particle filter is proposed as a hybrid approach, which is suitable for nonlinear and non-Gaussian systems, and can update the parameters online and make full use of the prior information. Finally, case studies performed on gear tests indicate that the proposed approach is effective in tracking the degradation of gear and accurately predicts the residual gear fatigue life
Numerical computation for the impact of pantograph angles on the near-field and far-field aerodynamic noises of pantographs
Get PDFPantographs are an important part of power supply systems of high-speed trains, whose good working performance is a guarantee for the steady power supply and safety operation of high-speed trains. The aerodynamic drag of pantographs will have negative impacts on the running of high-speed trains. In the meanwhile, the disturbance effect of pantographs on airflow will cause large aerodynamic noises when a high-speed train runs at a high speed. Therefore, this paper conducted a numerical simulation for the flow field and aerodynamic noises of pantographs on the symmetrical plane, compared simulation results with experimental one, verified the correctness of the numerical simulation model, and further studied the impact of pantograph angles on radiation noises. When pantographs were working, cylindrical rods which were vertical to the direction of airflows had a more obvious disturbance effect on airflows and caused a larger range of vortex shedding. Shedding vortexes were mainly distributed at the pantograph head, hinge joints between upper and lower arms, and rear bases. Near-field aerodynamic noises on the longitudinal symmetrical plane of pantographs were distributed at the lower arm, middle hinge joints and bases. The maximum appeared at the middle hinge joints. The intensity of vortexes at the middle hinge joints, lower arms and bases when the pantograph angle was 60° was more than that at other pantograph angles. In this case, the near-field aerodynamic noise of pantographs was more than that of other pantograph angles. In addition, radiation noises of observation points of pantographs in all directions presented an obvious linear relationship. The far-field radiation noise of pantographs was gradually decreased with the increased distance from pantographs. In addition, the far-field radiation noises of pantographs on the same vertical plane had the intensity with the same level
Dynamic analysis and control of strip mill vibration under the coupling effect of roll and rolled piece
Get PDFAccording to the “Hill rolling force formula”, taking particular account of the influence from horizontal vibration of rolled piece in roll gap, a dynamic rolling force model is analyzed. Considering the interaction between vibration of strip and roll, the dynamic vibration model of rolling mill is established. On this basis, the time delayed feedback is introduced to control the vibration of the roll system. The amplitude frequency response of the coupled vibration control equation is obtained by using the multiple scales method. Different time delay parameters are selected to test the control effect. Research results show that the unstable vibration of the roll system can be suppressed with appropriate time delay feedback parameters. Because it is simpler and has good control effect in solving nonlinear mechanical vibration, so these results will make a difference for the research of strip mill vibration, and provide theoretical basis for strip steel production
Study on the experiment and dynamical characteristics of vibrating icebreaking system
Get PDFIn view of the design problem of the working amplitude and working frequency of vibrating icebreaking machine, the stiffness and damping value of the ice-snow was identified with the mechanical vibration theory and finite element method. The two-degree-of-freedom mathematical model was established in this paper. And numerical simulation was performed. Then the related icebreaking experiment was carried out. A lot of test and experiment results had proved that experimental data was consistent with the theoretical analysis of mathematical model of vibrating icebreaking system. It was confirmed that the correctness of vibrating icebreaking system’s mathematical model and the rationality of its design could be proved
Design and implementation of DC source fed improved dual-output buck-boost converter for agricultural and industrial applications
Get PDFThe proposed research involves, a design and implementation of DC source fed improved Dual output Buck-Boost converter for agricultural and industrial applications. It consists of step up and step-down converter, DC-link module. Compared with conventional two converters, the designed system results in reduction of voltage tension across the switches, compact power switches, DC source reckoning and reduced inrush current. DC-link switching is achieved by reduced ripple voltage which results in improved quality of obtained output power. Reduction in switch count makes the system more cost effective. In addition, the motor speed is regulated by PI controller. Brushless DC Motor produce torque ripple and cause mechanical vibration, acoustic noise due to structural imperfectness and control system, to overcome this suppression control method of vibration for brushless DC motor utilizing feedforward compensation with Fourier transform utilizing a vibration signal acquired by an acceleration sensor attached to the motor frame is proposed. A simulation and prototype model of Dual output Buck-Boost converter is developed, and its performance is analysed for various operating conditions
Ultimate shear performance and friction sliding response of laminated elastomeric bridge bearings
Get PDFIn major earthquakes, friction sliding of common laminated elastomeric bearings limits the force transmitted from the superstructure to the substructure. Experiments were carried out to investigate the ultimate shear performance and the friction sliding response of laminated elastomeric bridge bearings. First, the hysteresis curve of the common laminated elastomeric bearings present narrow ribbon which meant the energy dissipation capacity induced by the shear deformation was weak. The ultimate shear deformation of the bearings could reach 300 % to 400 % of the elastomeric thickness. The damage of bearings was mainly focused on the rubber layer fracture. Second, the energy dissipation capacity of elastomeric bearings induced by the friction sliding was larger than the shear deformation, and was similar with the lead rubber bearing. Since the total displacement include both elastomer shear deformation and sliding components, the dissipated energy continuously increased with the increasing of the sliding distance. When the tests finished, the bearings were basic intact, only the rubber surface was worn down. Last, the bilinear elastic-plastic model is proposed to take as the theoretical model of the elastomeric bearing with friction sliding for the research and design of bridge in earthquake
Feature extraction method based on VMD and MFDFA for fault diagnosis of reciprocating compressor valve
Get PDFAiming at the nonlinearity, nonstationarity and multi-component coupling characteristics of reciprocating compressor vibration signals, an integrated feature extraction method based on the variational mode decomposition (VMD) and multi-fractal detrended fluctuation analysis (MFDFA) is proposed for a fault diagnosis for a reciprocating compressor valve. Firstly, to eliminate the noise interference, a novel VMD method with superior anti-interference performance was utilized to obtain several components of the quasi-orthogonal band-limited intrinsic mode function (BLIMF) from a strong non-stationarity vibration signal, and a consistent number K of BLIMFs was selected based on a novel criterion for all fault states. Secondly, the MFDFA method, which can describe the multi-fractal structure feature of non-stationary time series, was applied to analyze each BLIMF component, and the parameters of MFDFA were employed as the eigenvectors to reflect the structure characteristics and local scale behavior of the vibration signal. Then, the principal component analysis (PCA) was introduced to refine the eigenvectors for a higher recognition efficiency and accuracy. Finally, the vibration signals of four types of reciprocating compressor valve faults were analyzed by this method, and the faults were identified correctly by pattern classifiers of BTSVM and CNN. Further results comparison with other feature extraction methods verifies the superiority of the proposed method
A parameter optimization method for stress simulation of double horse head pumping unit dynamics model with cable
Get PDFSome components in Double horse head (DHH) pumping unit may occur cracking failure due to high cycle alternating stress, and this makes the research on dynamic stress simulation for them more interesting topic in its maintenance operation. This paper aims to improve the accuracy of dynamic stress simulation model through a parameter optimization method for the cable joints in DHH pumping unit. A series of cylinders was employed to model the steel cable, and the back horse head was also transformed to flexible body, then a rigid-flexible multibody dynamics model with cable was constructed to simulate the dynamic stress of components in DHH pumping unit. Stiffness and damping coefficient in cable joints have a significant effect on the model performance, and an unreasonable value may cause a strong vibrational and undesirable model response, therefore, a Memetic Algorithms based method was proposed to optimize them for improving the simulation accuracy using tested stress as objective function. Results show that the dynamic stress simulated from improved model is much closer to the experimental test compared with the original model, and these optimized parameters are also valid for the model in other working condition