Journal of Engineering and Thermal Sciences
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Study on determination of borehole drainage radius by gas content method
Get PDFIn order to determine the radius of borehole gas drainage, using five kinds of gas content under different conditions corresponding to the extraction rate were compared according to different drainage objectives, determine the need for gas drainage amount, according to a certain period of time the average single hole gas drainage quantity, calculate the number of drilling in the region need to be arranged, and then get the borehole gas drainage radius. Based on the actual investigation and comparison analysis, the effective radius of borehole gas drainage in certain extraction time is obtained. The results show that the method of gas content determination of drilling drainage radius is feasible
The fabrication of electrochemical geophone based on FPCB process technology
Get PDFThe subject of the studies presented in this paper is the fabrication of electrochemical geophone, especially the electrochemical transducer with symmetrical four-electrode cell by FPCB process technology. The geophone assembled by transducer, dumbbell-shaped tube, highly-flexible membranes, electrolyte solution and signal-amplification circuit, is calibrated using a standard vibration platform, and the results show a good consistency of each geophone parameters. Coupled with low cost, the electrochemical geophone by FPCB shows a good potential application prospect
Modeling and simulations on automated vehicles to alleviate traffic congestion
Get PDFAutomated vehicle technologies have the potential to improve traffic efficiency, stability and safety. Some models of mixed traffic are presented, which consist of automated vehicles and regular vehicles. First, a differential equation model based on automated vehicles is developed by regarding the traffic flow as a whole and using three continuous variables (traffic density, driving speed and traffic volume) to reflect the basic characteristics of traffic from the macroscopic perspective. Second, by taking into account (1) Actual Expected Speed Ratio (AESR), (2) Change Lane Count (CL), (3) Backward Distance (BD), and (4) Over Take (OT), the traffic flow evaluation model is established. Furthermore, by selecting locations randomly, we take the average value of the five cellular automata to the simulating results and validate the reliability of the model in the tolerance. Finally, optimal solutions to accommodate automated vehicles are given
A parametric study on the dynamic response of reciprocating compressor with a revolute clearance joints
Get PDFDue to the friction and manufacturing and assembly errors, the clearance of revolution joints is unavoidable. When the clearance value increases to a certain value, the influence of clearance on the performance of the equipment could not be ignored. In this paper, the contact collision model is used to describe the effect of clearance. The model of reciprocating compressor is simplified properly, and the influence of revolution joint clearance on the system is studied by contact impact function. The influence of parameters on the acceleration of piston is studied by changing the size, position of clearance and velocity of crankshaft. The Lyapunov exponent of crosshead acceleration under the condition of load and no load are compared, which lays the foundation for studying the vibration of reciprocating compressor caused by clearance
Reliability analysis of an engine under uncertainty based on D-S evidence theory and Bayesian network
Get PDFThere are many methods applied including Bayesian network and D-S evidence theory to cope with uncertainty involving aleatory uncertainty and epistemic uncertainty in reliability analysis of complex systems. This paper introduces theories of these two methods briefly, and then conversion rules that convert fault tree into Bayesian network under uncertainty are put forward, including AND node, OR node, XOR node, NOT node and Two-out-of-three vote node. Comparing to probability importance, structural importance and criticality importance, epistemic importance is given to measure the influence of root event to top event. At last, a type of engine is taken for example. Bayesian network model is established by referring to the fault tree of the engine, and D-S evidence theory is used to determine the belief functions and plausibility functions of uncertain nodes by data fusion. Weak nodes in reliability design and distribution are pointed out after reliability assessment, importance analysis, and backward reasoning. And corresponding measures can be taken to improve the reliability of the whole system
Modal analysis of HPGe detector assembly in gamma-ray spectrometers
Get PDFThe HPGe detector assembly of gamma-ray spectrometer cooled by Stirling cycle cryocooler is under consideration. Modal analysis based on the compiled dynamic model was carried out. The natural frequencies and modes shapes for HPGe detector with relative efficiency 15 % mounted by supports made from composite G-Etronax and CESTILENE HD 1000 were calculated by Solidworks simulation. The frequencies of the axial mode are in range of 200-600 Hz where electrical interferences caused by mechanical vibrations (so-called microphone noise) has a large impact on the resolution of spectrometer. It is shown that for cryostat cap the lowest natural frequencies determined by the thickness of input window lay in higher frequency range. The validity of the adopted model was confirmed by the experiments. The calculated natural frequencies of the detector assembly are compared to the harmonics of cryocooler’s vibration. The results obtained are useful to identify the interferences source in electrical circuits of spectrometer at its adjusting
Remaining life assessment for boiler tubes affected by combined effect of wall thinning and overheating
Get PDFBoilers, the most troublesome components of electric power, chemical and processing plants generate high costs in unscheduled shutdowns, repairs and power replacement. Every occurrence of ruptured tubes leads to emergency shutdown of the entire plant. This paper describes the joint international effort to develop faster and more efficient methods for condition assessment and remaining life prediction for boiler tubes made of low-carbon steel. Authors have undertaken a systematic research with the major objective to correlate the results of combined nondestructive testing (NDT) with condition assessment of boiler tubes. The evaluation included non-contact wall thickness measurement with EMAT technology plus internal oxide layer measurement with specialized ultrasonics. While the first method shows the remaining tube wall thickness, thus allowing calculating total stress, the latter one has the potential to characterize microstructure degradation, which up to now could only be determined by destructive analysis. The special attention was directed towards identification and analysis of creep damage due to overheating. In recent years, techniques were developed to identify heat damage by measuring the thickness of internal oxide scale because even a thin scale can seriously impede heat transfer causing elevation of temperature in tube wall. A combined effect of wall thinning and the “degree of overheating” on tube remaining life was investigated. The uniqueness of this work lies in one of the first attempts to develop and validate a tool for methodology for condition assessment and remaining life prediction, for Steel20 tube material, while most of previous authors had concentrated on Cr-Mo steels. Another contribution is the combined treatment of two different damage mechanisms and practical utilization of two various NDT techniques. To-date, both results are treated separately, and consequently separate reject criteria exist for overheating and separate for wall thinning. As a result of work presented in this paper, a procedure was recommended to calculate the tube remaining life based on the results of two ultrasonic tests
An experimental study on the shear property dependency of high-damping rubber bearings
Get PDFThis paper investigates the characteristics of high-damping rubber bearings (HDRBs) through various prototype tests. The characteristics were dependent on the displacements, number of load cycles, frequencies, vertical pressure, temperature, shear deformation capability, and vertical stiffness. The prototype tests showed that the displacement was the most influential factor on the characteristics of the HDRB. The effective stiffness and equivalent damping of the HDRB decreased with the displacement and increased with the frequency. The effective stiffness decreased at higher vertical pressure, while the equivalent damping increased. The equivalent damping was more dependent on the vertical pressure than the effective stiffness. The results show that careful examination is required to design the effective stiffness and equivalent damping ratio while considering the dependencies of the design displacement and excitation velocity
Dynamics analysis of the pitch control reducer for MW wind turbine
Get PDFAn analytic dynamics model was presented for the three-stage planetary transmission in the pitch control reducer for MW wind turbine based on the lumped-parameter method. The mechanical characteristic of the contact components was analyzed using the stiffness factor method. All the stiffness sub-matrices were combined to form the overall stiffness matrix of the three-stage transmission. According to the analytic model and the parameters of the pitch control gearbox, the movement differential equations were solved to investigate the natural frequencies and the vibration modes. Then, the undamped and damping forced vibration response were studied. A test rig was set up to measure the vibration displacement of the ring at the second stage and the output shaft under the nominal load condition, the comparison of the analytic forced vibration response with the experimental results validates the effectiveness of the lumped-parameter dynamics model for the pitch control reducer. This paper provides a reference for the dynamics optimization of multistage planetary transmission
Influence of semi-trailer truck operating conditions on road surface friendliness
Get PDFIn order to analyze the influence of semi-trailer truck operating conditions on road surface, a three-dimensional vehicle-pavement coupled model with 14 degrees of freedom is established for simulation and calculation. The influence of the different vehicle operating conditions on the dynamic tire loads, dynamic load coefficient (DLC) and road-friendliness which include road surfaces, vehicle speeds, vehicle loads are analyzed in this study. The results shown that the influence of the road surface roughness and vehicle loads on the tire dynamic load coefficient as well as road-friendliness is very obvious. Especially, the DLC values of the 3rd axle increase from 23.97 %, and 34.88 % when vehicle moves on three different road conditions with a velocity of 20 m/s and fully loaded. Finally, this study result gives the road-friendly limit of driving speed for 5-axle semi-trailer truck when vehicle operates under the different conditions