Journal of Engineering and Thermal Sciences
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Experimental study of a viscous damped portal frame
Get PDFThe prototype analysed is based on the structure of a gantry made to scale for didactic purposes, relating its dimensions to large structures used in buildings. The present work contributes substantially in the vibrational analysis of structures, simulating in a practical way the behaviour of the portal against the action of external loads. Additionally, the contribution provided by the incorporation of a viscous damper in the structure is observed. The structure includes a mechanism that generates dynamic loads inducing horizontal movement in the system exactly as it happens during a telluric movement. The graphs that characterize the movement of the system are obtained, showing the notable reduction of the acceleration when including a viscous shock absorber. The behavior of a building that incorporates a viscous dampening system in its gantry presents ideal characteristics during a seismic movement reducing the damage generated to the structure during the event
Life prediction method of rolling bearing based on CNN-LSTM-AM
Get PDFBearing is the key component to determine the health of machinery, and it is of great significance to monitor its working status in real time and predict its remaining useful life. In recent years, the RUL prediction method based on deep learning has been widely used and achieved good prediction results. Here, a bearing life prediction method based on convolution neural network (CNN), long short term memory (LSTM) and attention mechanism (AM) is proposed. First of all, the time domain and frequency domain features of the original vibration signals of rolling bearings are extracted, and the extracted feature set is normalized as the input of CNN. The main function of CNN is to extract spatial features and reduce the dimension of the data. Then, using LSTM to extract the information that may be ignored by CNN, the feature information extracted by CNN-LSTM is input to the attention mechanism for weighting, and the key information is screened. And then more accurately represent the degradation characteristics of the equipment, and finally get the bearing remaining life. The performance of the model is verified by two sets of public data sets, and the experimental results show that it is compared with the CNN-LSTM method. The root mean square error (RMSE) index based on CNN-LSTM-AM method is reduced by 14.6 % and 13.8 % respectively, and the score index is increased by 2.0 % and 2.4 % respectively. The results show that the proposed method has higher accuracy in bearing RUL prediction
Analytical determination of critical velocity and frequencies of beam with moving mass under different supporting conditions
Get PDFFor a moving mass-beam system, the critical velocity of the moving mass is a key parameter that relates to the vibration stability of the system. In fact, the critical velocity obtained by the commonly used assumed mode method (AMM) differs from the actual situation. In this study, an analytical procedure is introduced to determine the critical velocity and frequency of the moving mass-beam system. The influence of moving mass is considered in the modal functions of the beam, and the frequency equations of the system were obtained through the modal analysis method and Laplace transform. And beams with four types of boundary condition were analyzed, which are hinged-hinged (HH) beam, clamped-hinged (CH) beam, clamped-clamped (CC) beam, and cantilever (CF) beam. By solving the frequency equations, the vibration frequencies of the system can be obtained, and the critical velocity can be determined. The results of the proposed method were validated by the finite element method (FEM). Through some examples, it was found that the natural frequency and critical velocity obtained by AMM is relatively high. And the critical velocities of the same moving mass-beam system under different supporting conditions ranked in ascending order are as follows: vcrHH<vcrCH<vcrCF<vcrCC. It is also found that when the moving mass undergoes variable motion on a beam, the vibration frequency obtained with acceleration considered is higher than that obtained with acceleration neglected. The results of this article will be helpful for structural design and its dynamic analysis
Design methodology of permanent magnet eddy current brake and optimization based on the Stackelberg game theory
Get PDFThe permanent magnet eddy current brake (ECB) discussed in this paper are expected to brake a strong impact load for a large-scale machinery, and its design requirement is to brake smoothly within a given displacement limit. A design method is proposed to be able to design and calculate the based on the design requirements. According to the requirements of the brake displacement, an expected brake force can be calculated. Then, through the analysis of the permanent magnet operating point and the analysis and calculation of the design parameters, a reasonable design scheme that matches the prime design requirements can be obtained. When facing strong shock loads, in addition to satisfying braking requirements, different shock conditions can lead to different practical braking process. Making the corresponding braking process smoother can be regarded as an additional design objective, thus the design scheme obtained can be optimized in a certain range accordingly. A multi-objective optimization design of the ECB is carried out in combination with the Stackelberg game theory. After verifying the optimization results, it can be obtained that the given design and optimization methods are applicable and can satisfy the design and optimization objectives
Two-stroke engine with constant crank angular velocity
Get PDFThe work is devoted to the dynamics of a two-stroke engine. The engine used in sea vessels is considered. A new scheme of the crank mechanism of a two-stroke engine is proposed. An elastic hinge with a given angular characteristic (dependence of the restoring moment on the angle of rotation of the crank) is supposed to be installed between the strut and the crank. The work shows that with certain parameters of the hinge it is possible to obtain a constant angular velocity of the crank for any angle of rotation of the crank. Currently, flywheel inertia can account for up to 80 percent of all moving parts in an engine. Since the mass of engines is large, eliminating the flywheel from the engine design or reducing its mass may be a promising direction in the production of two-stroke engines. The proposed hinge is a structure in which an elastic element (spring or air spring) moves between circular guides of a calculated shape, resulting in a given hinge characteristic. In this work, an air spring was chosen as the elastic element of the hinge, since in this case it becomes possible to change the characteristics of the hinge by changing the pressure in the air spring. The shape of the guides is such that when adding the characteristic of an elastic hinge to the existing characteristic of the engine, an “ideal” characteristic of the considered engine with an elastic hinge is obtained, at which the angular velocity of the crank will be constant. When the angular velocity of the crank changes, a different characteristic of the hinge is required. In progress it is supposed to change the characteristics of the elastic hinge by changing the pressure in the air spring, which is the elastic element of the hinge. It turned out that by changing the initial excess pressure in the air spring it is possible to compensate for the change in the characteristics of the hinge required for the angular velocity of the crank to remain constant at any angle of rotation when its value changes. The results of these studies can be used both in the production of two-stroke engines and for any two-stroke engines
Gas parameter characteristics in Reflux Flotation Cell
Get PDFFlotation is a primary method for separating fine particles, and the growing demand for processing these particles has driven recent research efforts towards developing and designing more efficient flotation devices. Among these, the Reflux Flotation Cell (RFC) stands out as an innovative solution specifically tailored for fine particle flotation. Gas parameters are crucial factors influencing flotation and are essential indicators for evaluating flotation equipment. This study primarily investigates the gas characteristics within the RFC, including bubble size, gas holdup, and bubble surface area flux. The experimental results indicate that bubble diameters range from 0.4 to 0.8 mm, gas holdup ranges from 30 % to 50 %, and bubble surface area flux ranges from 120 to 400 s-1. These findings demonstrate that the RFC provides an optimal gas environment, conducive to effective mineral flotation
Numerical analysis of the influence of air flow channel on ear pressure during door closure
Get PDFIn this paper, Numerical simulation analysis was conducted on the ear pressure of a certain vehicle model during door closing process. Firstly, relevant airflow channel parameters are formulated based on the benchmark vehicle data, and transient closing ear pressure simulation calculation is carried out using overset grid technology. Then, the impact of key structural parameters on the interior ear pressure of the car was analyzed. Finally, based on the requirements of actual engineering design, the design scheme for the peak pressure of the car was determined, and the results will be a reference for the development and design of later vehicle
Modeling of unsteady-state creep of asphalt concrete
Get PDFThe article experimentally investigated unsteady-state creep of a hot fine-grained dense asphalt concrete under uniaxial tension at temperatures of 22-24 °C. 61 samples of the asphalt concrete in the form of a rectangular beam with dimensions of 50×50×150 mm were tested to complete failure at seven different stresses (from 0.084 MPa to 0.3053 MPa) in a special installation with a heat chamber. Based on the test results, unsteady-state creep curves were constructed, which were normalized and approximated with high accuracy by a power function. Reliable dependences of the limiting time of hardening, the limiting strain of hardening, and the hardening rate on stress have been established
Research on dynamic characteristics of wind turbine’s transmission system considering gear tooth lubrication
Get PDFTo improve wind turbines’ reliability and lifespan, taking the two-stage fixed shaft gearbox of wind turbines as study object. The oil stiffness and meshing stiffness of the transmission system are calculated, and the composite stiffness is obtained with the consideration of lubricating film. Then analyzed the dynamic characteristics of wind turbines’ transmission system before and after consider the oil stiffness in different operating conditions. The findings indicate that after considering the gear lubrication effect, the composite stiffness gradually decreases as rotational speed increase; within a certain rotational speed range, the tooth-surface load can be reduced, making the system run more smoothly. Therefore, the presence of oil film and its impact on its stiffness cannot be ignored. This study has certain guiding significance in improving the transmission efficiency and reducing noise of wind turbines
Research and design of a small self-heating high-temperature lithium plugging meter system
Get PDFIn the research of new reactors, lithium has become a research direction as a new coolant after sodium. Lithium working fluids introduce various metallic and non-metallic impurities such as oxygen, calcium, carbon, nitrogen, etc. to a greater or lesser extent during production, filling, and even operation. In addition, the processing, welding, and cleaning steps of the pipeline and equipment in the circuit during manufacturing inevitably result in residual dirt, grease, surface oxides, and moisture. These will have a certain impact on the performance of heat transfer and circuit safety through accelerated corrosion or plugging. Therefore, in high-temperature lithium circuits, the impurity concentration of lithium working fluid must be strictly controlled and purified before use. At present, the detection methods for impurity content in lithium working fluids can be divided into two categories: sampling analysis method and online measurement method. Sampling analysis is the most direct detection and analysis method, which can directly obtain the content of various impurities in lithium working fluids, and the results are relatively accurate; The online detection method can generally only detect non-metallic impurities, but it is relatively fast and simple, and is currently a commonly used measurement method on lithium working fluid devices. The plugging meter method has been studied and used as a rather convenient online detection method. This article introduces a small, self-heating, and mobile high-temperature lithium plugging meter system to meet the online detection of different points in the lithium circuit of system engineering