Table of Content

25 May 2019, Volume 30 Issue 10

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Multi physics Coupling Simulation of ECM Based on Gas Liquid Two phase Flow Model

ZHOU Xiaochao1,2;CHEN Yuanlong1;HOU Tingbo1;WANG Zhuangzhuang1

2019, 30(10):  1135-1141. 

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Considering the effects of bubbles on processing precisions, a gas liquid two phase flow field in ECM processes was described according to the Euler Euler two fluid model. Coupling with the electric field and the temperature field, the distributional regularities of the cathode and anode surface bubble rate, temperature, electrical conductivity and current density were analyzed. The simulation optimizations of the anode surface bubble rate and current density were researched by adjusting voltages, inlet pressures and outlet pressures. The simulation results show that reducing machining voltages and increasing the outlet pressures may improve the electrical conductivity distributions and make the current density distribution on the anode surfaces more uniform, under the same flow rate. The experimental results show that the distributions of the current density on the anode surfaces are consistent with the height error distributions of the workpieces. The precisions of the workpieces are improved by optimizing the parameters.

Non-random Vibration Analysis of Mechanical Arm Systems

ZENG Guang1,2，3;DUAN Minfeng1，2;NI Bingyu1，2;JIANG Chao1，2

2019, 30(10):  1142-1149. 

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The vibrations of mechanical arm systems under uncertain dynamic excitation were studied. Aiming at the difficulties in getting specific probability and statistics informations due to the limited numbers of sample functions of uncertain dynamic excitations，the dynamic uncertainty of the excitation was described by interval process. Based on the structural unit pulse response, the convolution integral and the correlation properties of interval process, the upper and lower boundaries of dynamic uncertain excitations were obtained. Finally, as a typical engineering equipment component, the dynamic responses of mechanical arm systems of concrete pump truck in operation processes were studied and analyzed by the above methods.

Static Characteristic Analysis of Bolt Joints under Preloads

HUI Ye1;HUANG Yumei2，3;LI Pengyang2，3;LI Yan2，3

2019, 30(10):  1149-1155. 

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The contact deformations of the joint surfaces and the member deformations of bolt joints were in coupling relation. To improve the accuracy of the result in analyzing the whole machines, a virtual material layer was added between the elements to reflect the non-linear property of bolt joints in building analysis model. Based on interface basic characteristic parameters, the physical parameters of virtual material layer were obtained and the analysis model of the bolt joint features were built. A series of static load tests were carried out on the bolt joints under pre-tightening forces of various materials, different pre-tightening forces and element different thicknesses. Based on the analyses and test results, the deformations of joint surfaces were separated from the whole deformations. A comparison of joint deformations with theoretical ones verifies the accuracy and effectiveness of the modeling theory and test approach proposed herein.

Research on Mechanism of Combined Rotor's Fatigue-Creep Joint Damages

WANG Ailun 1，2;DENG Guilong 1，2;LIU Qiang1，2;LI Shijie1，2

2019, 30(10):  1156-1162. 

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A study of the combined rotor of a heavy gas turbine was conducted, and the whole damage model of the combined rotor was established. Based on the damage research of pure fatigue and pure creep, the damage variables under joint actions were expressed as the nonlinear superposition of two kinds of damages according to the damage mechanics accumulation model, therefore the damage mechanism of the combined rotor under the actions of fatigue-creep joints was revealed, and the damage rules of the combined rotor were verified experimentally.The results show that the whole damage model is correct and effective, and it may provide a reference for component damage prediction of the overall damages of the combined rotor.

An Incremental Bayesian Algorithm on Fault Diagnosis of Grate Coolers

LIU Zhaolun1,2;ZHANG Chunlan2;WU You2;WANG Haiyu2;LIU Bin1,2

2019, 30(10):  1163-1171. 

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Aiming at the shortcomings of incremental maintenance performance of batch algorithm, an incremental learning algorithm(ILA) of Bayesian network was proposed. When the new data sets were detected, the WTUN function was constructed to determine whether to update the structure. If the structure was updated, the Affect function was constructed to obtain the set of nodes that needed to be modified in the structure. The candidate structure was obtained by hill climbing operator correction in the Markov range of these nodes. The improved scoring function was used to select the largest structure as the optimal structure. Whether the structure was updated or not, the original parameters were used as the prior parameters, and the parameters were updated with the expectation maximization(EM) algorithm.The algorithm may incrementally maintain the network and save space and time to a certain extent compared with hill climbing(HC),incremental hill climbing(IHC) and incremental genetic algorithm(IGA). The fault diagnosis model of the technological parameters of grate coolers was established by ILA algorithm, which may be used to realize the accurate fault diagnosis of the secondary air temperature.

Study on Surface Quality Improvement by Abrasive Water Jet Secondary-reverse Cutting

SONG Lei1,2;WU Meiping1,2;MIAO Xiaojin1,2;REN Zhonghe1

2019, 30(10):  1172-1177,1187. 

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According to the quality problems like trailing stripe, kerf taper and cutting tail in the abrasive water jet cutting(AWJC) processes, three experimental groups were designed under different combinations of cutting process parameters, including single-positive cutting, single half-speed-positive cutting and secondary-reverse cutting experiments based on the theory of AWJC. The mechanism of the section morphology under three different cutting modes was fully discussed, and the experimental results were deeply compared and analyzed. The results show that secondary-reverse cutting may reduce the surface roughness about 52%~85% and the kerf taper about 66%~72%, with efficient elimination of the cutting tail. Therefore, the operation, adopting the method of secondary reverse cutting may significantly improve the section surface quality of the target workpiece in AWJC.

Identification and Optimization Verification of Key Parameters for Pressure Fluctuations in Hydraulic Reduction Circuit of CVT

LUO Wei1;ZHOU Yunshan1，2;QU Daohai1;ZHANG Feitie1;HU Xiaolan1

2019, 30(10):  1178-1187. 

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For the pressure reduction circuits of independent hydraulic systems of CVT, a hydraulic model was established. By introducing Sobol' sensitivity analysis algorithm, the key parameters of pressure fluctuation attenuation in pressure reduction circuits were analyzed on the platform of MATLAB/AMESim software. The results of first-order sensitivity and first-order total sensitivity analysis show that the pilot orifice, throttle groove of reduction valve and load flow (equivalent load orifice) have the greatest influences on pressure stability, and the second-order sensitivity index shows that the coupling effects between throttle groove and load flow are the strongest one. Finally, according to the analysis results, the response surface optimization of key parameters for pressure fluctuation during vehicle tests was carried out, and the validity of the analysis method was proved by the test results.

Experimental Study of Vibrations, Noises and Pressure Fluctuations of Centrifugal Fan

CAI Jiancheng;E Shiju;JIANG Yonghua;JIAO Weidong;WANG Dongyun

2019, 30(10):  1188-1194,1206. 

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Microphones, accelerometers, and pressure transducers were used to measure the centrifugal fan noises, pipe vibrations and pressure fluctuations respectively. The results show that in the spectra of the fan noises, pipe vibrations and pressure fluctuations, the discrete frequency components related to the impellor rotations are notable,and the rotational frequency(RF) components are the maximum in general.The coherence of the noises and vibrations with the pressure fluctuations is higher than 0.5 at discrete frequencies, but lower at broadband frequencies. The most intensive pressure fluctuations are within 5D from the fan outlet, where D is the pipe hydraulic diameter, with the strength almost equaling to the reference dynamic pressure ρv2b/2 (ρ as fluid density, vb as bulk velocity). After 10D where the flow became quite uniform, the amplitude of pressure fluctuations is approximately 20% of the reference dynamic pressure. The RF components are the most conspicuous in the pressure fluctuation spectra, and the maximum valute is around 25% of the reference dynamic pressure occurring within 2D~4D from the fan outlets.

Review on Precision Machining Technology for Outer Diameters of Cylindrical Rollers

YAO Weifeng1;YUAN Julong2;ZHONG Meipeng3;WANG Chengwu4;ZHOU Fenfen5

2019, 30(10):  1195-1206. 

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Precision machining technology for outer diameters of cylindrical rollers was the final manufacturing process of cylindrical rollers, which made a great role on the geometric and dimensional accuracy, surface quality and their consistence. At present, according to the machining principles, the precision machining methods of cylindrical rollers were mainly divided into traditional methods which were applied widely in the industries, including centerless grinding and centerless superfinishing, and non-traditional methods developed recently, including center-fixed superfinishing with oscillation, electrochemical mechanical finishing, magnetic fluid lapping, both-sides cylindrical lapping and polishing. The basic principles and the research status of above processing methods were introduced herein, their advantages and disadvantages were both discussed on the aspects of machining accuracy, surface quality, production efficiency, etc. The future development trends of precision machining technology for outer diameters of cylindrical rollers would be toward to ultra-precised workpiece and device, high efficient automated production, high flexible production, small or micro parts, composite processes and intelligent equipment.

Effects of Shell Profile Modification of Engine Conrod Bearings on Lubrication Characteristics

RUAN Dengfang1,2;CHEN Li2;GAO Zhenchao2

2019, 30(10):  1207-1211,1218. 

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To solve the shell edge wear of engine conrod bearings and reduce the asperity contact power losses, a flexible multi-body dynamics analysis model of engine crankshafts was established and a dynamics simulation calculation was carried out. According to the simulation results of the deformations of inner diameters of conrod bearing shells, the contours of bearing surfaces were modified. The simulation results show that after the shell profiles of conrod bearings were modified, the lubrication performances change less and the lubrication performances including the maximum oil film pressures and minimum oil film thicknesses are basically the same as those of the original bearings with cylindrical shell profiles, but the shell edge wear problems in the work strokes are solved, either the maximum values or average values of the asperity friction power losses are reduced and the asperity contact pressures are distributed uniformly along the axial directions of the conrod bearing shells.

Finite-time Control and Vibration Suppression of Two-flexible-link Space Robots with Dead-zone

HUANG Xiaoqin1,2;CHEN Li1,2

2019, 30(10):  1212-1218. 

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The trajectory tracking and flexible vibration suppression of a two-flexible-link free-floating space robot system were discussed based on finite time with the joint torque output dead-zone. Using singular perturbation theory, the dynamics equations of the system were decomposed into a slow subsystem for rigid motions and a fast subsystem for flexible vibrations. For the slow subsystem with unknown model parameters and dead-zone parameters, a dead-zone pre-compensator and a finite-time controller were designed based on nominal model. An integral sliding mode surface with finite time convergence property was introduced, which had faster convergence speed, better robustness and anti-interference performance than the traditional asymptotic convergence control method. For the fast subsystem, the linear quadratic optimal control method was adopted to suppress the vibrations actively to ensure good stability of the system. Combined with the finite-time stability lemma, the Lyapunov theory was used to prove that the proposed control algorithm may make the tracking errors converge to the origin within a finite time. The simulation examples confirm the effectiveness of the proposed method.

Dynamics Optimization and Simulation of 3-RSR Parallel Vehicle-borne Antenna Mechanisms

YANG Yandong1;ZHOU Zhiyu1;DENG Yunjiao1;DUAN Yanbin2;DOU Yuchao2;ZENG Daxing1，3;HOU Yulei1，3

2019, 30(10):  1219-1225,1232. 

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Dynamic characteristics are the key to realize the high-speed and high-precision antenna functions. Using 3-RSR (R as a rotating pair, S as a spherical pair) type parallel mechanism as the configuration of the vehicle antenna, the dynamics model of the mechanisms was established by using Lagrange equation. With the natural frequency as the goal, the parameters of 3-RSR antenna were optimized by genetic algorithm, and the performance comparisons verified the effectiveness of the optimization results. Considering the wind-snow loads and the random excitation conditions of the vehicle bodies, a simulation model of the vehicle-mounted antenna mechanisms was established, the change curves of driving torques were obtained under the corresponding working conditions. The research work has a reference meaning to the dynamics design of vehicle antenna mechanisms and prototype development.

Speed Ratio Follow-up Control of HMCVT Based on Variable Universe Fuzzy PID

YU Jin1,2;CHEN Hua1,2;LIU Junhao1,2

2019, 30(10):  1226-1232. 

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In order to optimize speed ratio follow-up control effects of HMCVT, a variable universe fuzzy PID controller was designed based on the expansions of quantizing factors and decision-making factors. The speed ratio characteristics and the mathematical model of HMCVT   were analyzed. A simulation model of HMCVT was established based on AMESim and MATLAB, and the simulation model was verified by the experimental platform. Simulation control effectivenesses between the variable universe fuzzy PID controller and fuzzy PID controller were compared. Simulation results show that the variable universe fuzzy PID controller has smaller exceeding value, shorter adjusting time in step single inputs, and the speed ratio follow-up tracking errors are reduced about 50% in ramp signal inputs and sine signal inputs. The variable universe fuzzy PID controller has more superior speed ratio follow-up control effectiveness and smaller speed ratio follow-up tracking errors, which presents better control effectiveness and dynamic quality. The research provides a theoretical reference for the control strategy of optimal fuel economy and optimal power performance of vehicles.

Multiple Module Neural Network Solving for Inverse Kinematics of Space 3R Manipulators

XIAO Fan;LI Guang;YOU Yulong

2019, 30(10):  1233-1238. 

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A multiple module neural network method was proposed to solve the inverse kinematics multiple solutions of space 3R manipulators.The joint spaces were divided into several joint subspaces with unique inverse kinematics solution through geometric analysis. Each subspace was trained and solved by 3 single output BP neural networks. After the simulation and comparison with other methods, results show that the method herein may accurately divide the value ranges of inverse kinematics solutions, and quickly obtain high precision inverse kinematics multiple solutions.

Applications of Separability Index of High-dimensional Space in Rotor Diagnosis System Optimization

XU Bochao

2019, 30(10):  1239-1243. 

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The selection of positive and negative samples in the related vector machine multi-fault classification system based on binary tree was often measured by the Euclidean distance. Traditional Euclidean distance couldn't reflect the separability of sample points properly because of the measurement concentration of data points in high-dimensional spaces. As the differences of high-dimensional space distance calculated by fractional norm were greater, an index of high-dimensional space sample point distances was proposed based on fractional norm. Optimizing sample selection of classifiers at different levels based on this index, the results of experiment 1 prove that the optimized system based on high-dimensional space separability index has a significant improvement in classification accuracy than the optimized system based on Euclidean distance. The results of experiment 2 show that compared with intelligent diagnosis algorithm, the normal binary tree structure has advantages in classification efficiency and time consuming.

Applications of P-V Diagram and Valve Motion Diagram in Performance Evaluation of Refrigerator Compressors

GAN Hongwei1;JIN Huaqiang1;GU Jiangping1;HUANG Yuejin1;WANG Xinlei2;SHEN Xi1

2019, 30(10):  1244-1249. 

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By establishing a new experimental platform, the gas pressures in each chamber of the compressors and the movements of the suction and exhaust valves were measured, and the true P-V diagram and valve motion diagram were obtained. By studying and analyzing P-V diagram and valve motion diagram of  the compressors synchronously, the coupling relationship between valve actions and internal working processes of compressors was obtained, which provided a method for compressor optimization. The experimental data show that under the working conditions of ASHRAE, the compressor cycle power consumption is as 66.825 W, the percentage of the loss of exhaust pressure consumption is  4.254%, the percentage of the loss of suction pressure consumption is 1.2%, the displacement of suction valve plate is as 2.148 mm, and the displacement of the exhaust valve plate is as 0.825 mm. The phenomena of the delay of suction and exhaust valves of compressor were analyzed.