Journal of Engineering and Thermal Sciences
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Numerical analysis of spiral curved tube of the solid liquid two phase abrasive flow polishing
Get PDFIn order to solve the problem that the inner surface of heterosexual surface parts is difficult to be machined, a solid-liquid two-phase abrasive flow machining method is proposed. The standard model and the pressure-coupled SIMPLEC algorithm are used. The dynamic characteristics of the dynamic pressure, turbulent kinetic energy and turbulence intensity of the polygonal spiral surface flow channel were obtained by numerical analysis of the solid-liquid two-phase abrasive grain polished polygonal spiral curved pipe under different outlet pressure conditions. The numerical simulation results show that the grinding effect is inversely proportional to the outlet pressure. We can achieve better polishing effect by appropriately reducing the outlet pressure
Test and analysis of three axis vibration of harmonic drives
Get PDFA new vibration testing method is introduced to measure three-axis vibration of harmonic drives used in industrial robots. To simulate the working state of industrial robots, a harmonic drive loading device was designed. In the case of loading, the vibration of a harmonic drive in three axes was measured. Experimental data was used to evaluate the vibration performance, analyze the vibration characteristics of the harmonic drive, and determine the cause of the vibration abnormality. The research results showed that the presented measuring method is helpful to monitor the vibration performance of harmonic drives, and control the quality of the product
Theoretical and experimental investigation of the tube-shaped waveguide wire
Get PDFCardiovascular diseases are the leading cause of death among people up to 65 years old. One of the most common cardiovascular disease is thrombosis. To remove the blood clot inside the artery, usage of advanced invasive mechanical devices is needed. There is a need for the new alternative less risky and hazardous way of arterial thrombosis treatment. This paper presents a new design of a less risky ultrasonic blood vessels cleaning system
Energy absorption characteristics of cement-soil under confining pressure based on SHPB test
Get PDFCement-soil has been widely used for engineering application. However, no attention has been paid to the energy absorption characteristics of cement-soil under impact loading. In this paper, a series of split Hopkinson pressure bar (SHPB) tests have been conducted to explore the energy absorption characteristics of cement-soil, and the effects of confining pressure (from 0 to 2.0 MPa) and strain rate (from 130 to 172 s-1) on the absorbed energy and the energy absorbency rate are investigated. The results show that the energy evolution of cement-soil under confining pressure is found to be similar at different strain rate. Both the absorbed energy and the energy absorbency rate are influenced by the confining pressure. Moreover, both the absorbed energy and the energy absorbency rate increase at first and then remain stable at a certain value with the increase of confining pressure. In addition, the absorbed energy linearly increases with the incident energy increasing, and a similar tendency is found between the absorbed energy and the strain rate, yet no obvious effect on the energy absorbency rate by the strain rate. Moreover, the energy mechanism of cement-soil is explained from the perspective of failure modes of cement-soil specimen
Vibration modal shapes and strain measurement of the main shaft assembly of a friction hoist
Get PDFIn order to evaluate the reliability of the main shaft unit of a friction hoisting system, strain measurement is a significant method. In this paper, a test rig of a friction hoisting system was built, which could applied periodically changing load on its main shaft unit; The mechanical analysis under the test load was conducted and the boundary limits were obtained; A three dimensional model of the main shaft unit was built in Pro-E and its finite element analysis was performed in ANSYS; With the analytical result, measuring points for strain rosettes were initially selected; Vibration modal shapes of the main shaft unit were analyzed, based on which Modal Assurance Criterion (MAC) was utilized in the Particle Swarm Optimization (PSO) algorithm to make the final decision of the number and positions of the measuring points; A wireless measurement system was developed to acquire strain signals from the optimized measuring positions; The test result verified the efficiency of the methods employed in this paper and revealed how strain of the main shaft unit changes during running process
A novel MPP-NSGA algorithm and its application in optimization for radiated noises in the aircraft cabin
Get PDFThe paper used the AML method to compute transmission loss of aircraft panels and verifies correctness of the numerical simulation model by experimental test. Finally, this paper used an improved genetic algorithm to conduct a multi-objective optimization for the cabin noise. When the analyzed frequency is less than 250 Hz, transmission loss decreased rapidly with the increased analysis frequency, and decreased from the maximum 63.2 dB to 18.5 dB. Within 250 Hz-4000 Hz, the transmission loss gradually increased with the increased analysis frequency. At 250 Hz, the transmission loss had an obvious valley value. Sound radiation power was then computed based on boundary element method, and panel contribution analysis was conducted to find those panels which had an obvious impact on the cabin noise. Therefore, a multi-objective optimization was conducted on these panels and reinforced ribs. In order to further verify effectiveness of the MPP-NSGA method, it was compared with the traditional GA model and NSGA model. Optimization accuracy using MPP-NSGA model is increased, and optimization time is reduced. Through optimization with traditional GA method, the maximum sound power level decreased by 15.4 %, and the total sound power level decreased by 21.9 %. Through optimization with the NSGA method, the maximum sound power level decreased by 21.7 %, and the total sound power level decreased by 29.0 %. Through optimization with the MPP-NSGA method, the maximum sound power level decreased by 46.3 %, and the total sound power level decreased by 36.0 %. Therefore, compared with other two kinds of genetic algorithms, the MPP-NSGA method is obviously superior in noise optimization in the cabin. In the whole analysis frequency band, noise of the optimized cabin panel at each frequency point was smaller than that of the original structure, fully verifying feasibility of the optimization algorithm proposed in the paper. In addition, in the optimized structure, no panel made obvious contributions to the cabin noise, and each panel showed an equivalent contribution level. Transmission loss of the optimized cabin panel was obviously improved. However, the sound insulation valley still appeared at 250 Hz, but it was not so obvious like the original structure. After optimization, the sound insulation valley was 31.6 dB. The sound insulation valley of the original structure was 18.5 dB. Obviously, the sound insulation valley value of the optimized structure was increased by double compared with the original structure. This paper provided a valuable reference for noise reduction in the aircraft cabin
Fault diagnosis of rolling element bearing based on wavelet kernel principle component analysis-coupled hidden Markov model
Get PDFDifferent description results will be obtained when apply hidden Markov model (HMM) to the two different channel signals from the same data collection point respectively. Besides, wrong fault diagnosis result might be obtained because fault feature information would not be described comprehensively by using only one single channel signal. In theory, two channel signals collected form the same data collection point will contain much more fault information than the single channel signal contain, but the coupled phenomenon might occur between the two channel signals. Coupled hidden Markov model (CHMM) is the improved method of HMM and it can fuse the information of two channel signals from the same data collection point efficiently, so much more reliable diagnosis result could be obtained by using CHMM than by using HMM. Stated thus, the fault diagnosis method of rolling element bearing based on wavelet kernel component analysis (WKPCA)-CHMM is proposed: Firstly, use WKPCA as fault feature vectors extraction method to increase the efficiency of the proposed method. Then apply CHMM to the extracted fault feature vectors and satisfactory fault diagnosis result is obtained at last. The feasibility and advantages of the proposed method are verified through experiment
Influence of support stiffness on aero-engine coupling vibration quantitative analysis
Get PDFThis paper investigates the whole aero-engine coupling vibration, as a rotor tester to be the research object. The rotor tester system is composed of two mountings, stator system, support structures and the rotor system. The modal experiment of the whole tester under the condition of mounting in the test room is carried out. The finite element (FE) model of the rotor tester is built, and the model was modified and validated according to the modal test results. A rotor-stator coupling factor and a section rotor-stator rubbing risk coefficient are proposed, the influence of the support stiffness values on the engine vibration characteristics, such as natural frequencies, modal shapes, rotor-stator coupling degree, and stator-rotor rubbing risk degree at compressor and turbine section is quantitative studied. Results show that the support stiffness contributes to the rigid body modal shapes greatly and to the rotor bending ones slightly. The factor and coefficient defined in this study are both reasonable, and they can reflect the corresponding characteristics exactly. Moreover, the effect of the supports stiffness values on the rotor-stator coupling degree and the rotor-stator rubbing risk degree is nonlinear. The rotor-stator coupling factor and the section stator-rotor rubbing risk coefficient proposed in this study provide a new way to quantitatively research the whole engine coupling vibration
Load spectrum generation of machining center based on rainflow counting method
Get PDFReliability bench tests and probability design method are two important means to improve the reliability of machine tools, while the load spectrum of machine tools is the foundation of reliability bench tests and probability design. According to the load spectrum, the actual working conditions can be simulated in laboratories. A dynamic load spectrum generation method is proposed to establish a representative load spectrum. Firstly, the cutting load measuring system is established based on the characteristics of the cutting loads, and then the actual cutting experiments designed by the orthogonal experimental method are conducted on the basis of the typical cutting conditions in laboratories. Secondly, the counting method of the cutting loads cycles is presented based on the dynamic load characteristics of a machining center. And loads cycles are counted by the proposed counting method, and then a rainflow matrix is formed. Thirdly, in order to improve the precision of the load spectrum the extrapolation of the loads is carried out using the parametric extrapolation method. Then the probability distribution functions of the mean and amplitude of the cutting loads are provided by the K-S goodness-of-fit test method. The case study indicates that the radial force, axial force, and cutting torque of the tested machining center follow gamma, normal, and Weibull distributions with different parameters, respectively. Finally, the joint distribution function of the mean and amplitude of the radial force, axial force, and cutting torque is obtained by using a combination of statistical analysis method, and the two-dimensional load spectrum of the MC is compiled
Industrial level analysis of air quality and sound limits monitoring in Bangladesh using real time control system
Get PDFThis paper presents an important study of environmental Atmospheric analysis at industrial factories in Bangladesh. An Arduino based real time control system with gas and noise sensors has been developed to collect the data in various industries. The system then has been made operational at few cement factories to measure the noise (db) and dust (μg/m3) and compared with international standard requirements to understand whether the factories are providing healthier environment. Result shows both the noise and air quality to be within the borderline except few cases in which the solution has been proposed to improve the factors