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Realization of face feature point recognition based on cascaded convolutional neural network ZHANG Yun, LI Lan Journal of Lanzhou University of Technology    2020, 46 (3): 105-109.   Abstract （664）      PDF（pc） （862KB）（2071）       Knowledge map    Save If a face image is interfered by redundant information, the accuracy of the extracted effective feature points from the image is not high enough. To solve this problem, a face feature point detection algorithm based on a cascade convolutional neural network is proposed in this paper. The algorithm reads in information of an original image via the input-function first, then extracts local features of the image through neurons in a receptive domain, and inputs all local features into a pooling domain. After doing that, the algorithm is able to average all captured local features stored in the pooling domain, and further do down-sampling to the pooling domain, and reduce the dimension of the convolution results, and finally output detection results of those feature points by virtual of iterative training. In this study, Python language is used to program the algorithm, and simulation experiments are carried out with the help of face data set. Simulation results show that the algorithm has a high recognition rate for face feature points. Reference | Related Articles | Metrics

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Cleaning and modeling of abnormal data of wind farm power curve CAO Li-xin, LIU Wei-min, GUO Hu-quan Journal of Lanzhou University of Technology    2022, 48 (4): 64-70.   Abstract （647）      PDF（pc） （3178KB）（1726）       Knowledge map    Save The wind speed and power data of wind farms usually contain a large number of abnormal data, which is difficult to reflect the real working conditions of wind turbines, affect the accuracy of wind power prediction, and then cause certain economic losses. To solve this problem, the characteristics of abnormal data are analyzed, a slip-quartile abnormal data elimination method is proposed, and the wind speed power curve of the eliminated data is modeled by using high-order polynomial and Logistic function. Finally, the applicability and effectiveness of this method are verified by variance, root means square error and determination coefficient. The analysis in the example shows that the method is simple, efficient and versatile, and can significantly improve the accuracy of wind turbine power characteristic analysis. Reference | Related Articles | Metrics

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Hydraulic optimization of spatial guide vane on submersible well pump based on the orthogonal design CHENG Xiao-rui, ZHANG Xue-lian Journal of Lanzhou University of Technology    2020, 46 (5): 61-67.   Abstract （362）      PDF（pc） （1454KB）（1650）       Knowledge map    Save The orthogonal design method is used to optimize design of a submersible well pump spatial guide vane. Three main geometric parameters of the submersible well pump spatial guide vane are selected, which are the inlet width, the axial length of the guide vane blade and the axial distance between the outlet edge of the guide vane blade and the field exit of the guide vane respectively. Nine groups of schemes are designed on the basis of the orthogonal method. All results from our numerical calculations and range analyses show that the axial length of the guide vane blade has a significant effect on the head and shaft power of the submersible well pump, and the inlet width of the guide vane is more sensitive to variation of the submersible well pump efficiency. The performance of the submersible well pump can be improved by fixing a certain outlet distance between the outlet edge of the guide vane blade and the field exit of the guide vane. Based on multi-objective optimization design methodology, the optimal scheme of this investigation is determined as follows: the inlet width is 25 mm, the axial length of the guide vane blade is 101 mm and the axial distance between the outlet edge of the guide vane blade and the field exit of the guide vane may take 20 mm.By further analyzing efficiency of the first three stages of the impeller and the static pressure and streamline distribution at the exit of the guide vane, it is found that current excellent design of the spatial guide vane makes the internal fluid state of the guide vane better and ensures the impeller efficiency to maintain a higher level. At the same time, the flow stability in the submersible well pump becomes better. Reference | Related Articles | Metrics

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Improved calculation formula of fundamental frequency for the fabricated concrete simple supported skew girder bridges YU Zhen-gang, LI Yan, YANG Ting-ting, LU Kai-yuan Journal of Lanzhou University of Technology    2020, 46 (5): 144-148.   Abstract （584）      PDF（pc） （1526KB）（1574）       Knowledge map    Save Taking a prestressed concrete prefabricated simply supported girder bridge asengineering background, the influence of oblique angle, span, bridge width and transverse torsional stiffness on the fundamental frequency of the bridge is analyzed by numerical method. The results show that as the skew angle becomes larger, the first three orders of the vertical natural vibration frequencies increase. With the increase of the span, the whole vertical stiffness becomes lower, the fundamental frequency reduce obviously, but the rate to deduction decreased gradually. The fundamental frequency affected by the mechanical characteristic of coupling of bending and torsion increases with the increase of torsional stiffness. Based on the influence of key factors above on the base frequency of the skew beam bridge, an improved formula, taking the torsional stiffness and the skew angle into account, for estimating the base frequency of the concrete simply supported skew beam bridge is therefore proposed. The precision and the applicability of the formula are verified by all measured data of several real bridges. Reference | Related Articles | Metrics

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Analysis of thrust and velocity variation of permanent magnet synchronous linear motor under variable load SHEN Hao, ZHANG Wang, TAN Wei-rong, DANG Sheng-hui Journal of Lanzhou University of Technology    2021, 47 (2): 54-59.   Abstract （844）      PDF（pc） （1152KB）（1444）       Knowledge map    Save Taking the permanent magnetic synchronous linear motor as the research object, its force was analyzed; mathematical model was established, and the simulation model of the linear motor by using Matlab/Simulink in order to study the thrust and speed change of the linear motor when different loads are applied. The results show that with the increase of the workpiece’s mass, the state response time and maximum deviation of the linear motor increased; the response time curve of the speed is flat; the response time curve of thrust changed obviously; the overshoot curve of thrust increase flatly; the overshoot curve of velocity increased stably, the overshoot curve of speed is obvious.When the quality of the workpiece is 240 kg, the over-adjusting amount of motor speed exceeds 30%, which seriously affects the operation of the motor. In order to reduce the effect of load change on linear motor stability, the maximum load quality and maximum motor thrust are calculated. Reference | Related Articles | Metrics

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General model for kinematic analysis of swash plate axial piston pump WANG Jian-sen, CAO Wei-dong, HE Xin-long, WANG Zheng-rong, ZHANG Zhi-wei Journal of Lanzhou University of Technology    2021, 47 (5): 59-64.   Abstract （763）      PDF（pc） （3701KB）（1236）       Knowledge map    Save Based on the comprehensive consideration of swash plate angle, cross angle and piston inclination angle of the swash plate axial piston pump, the general piston kinematics model is established by coordinate transformation method. The analysis results show that the cross angle of swash plate and the inclination angle of piston will increase the maximum amplitudes of displacement, velocity and acceleration of piston, and then increase the displacement of pump, the maximum transient flow velocity in the piston chamber and the inertia force of piston; the cross angle of swash plate will change the phase of piston movement and make the internal and external dead points deflect, which will change the pre-compression and pre-expansion angle of valve plate; the inclination angle of piston will affect the movement of the piston, the smaller the inclination angle of the plunger, the closer the movement of the plunger is to the simple harmonic motion, on the contrary, the larger the deviation is, the maximum deflection angle of internal and external dead center is 90°, the smaller the absolute value of the cross angle is, the smaller the deflection angle of internal and external dead center changes in the range of big swash plate angle, and the greater the gradient of change when swash plate angle is close to zero displacement. Reference | Related Articles | Metrics

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Effect of impeller exit width on performance and pressure fluctuation of centrifugal pump ZHAO Wei-guo, ZHAI Li-jing, XIAN Li-xia, MA Liang-liang Journal of Lanzhou University of Technology    2020, 46 (2): 62-68.   Abstract （970）      PDF（pc） （6499KB）（1230）       Knowledge map    Save Taking a single-stage end-suction centrifugal pump as study object and assuring the inlet and outlet setting angle and diameter and as well as other parameters unchanged, five sets of pump models with different outlet width of impeller were designed respectively, their numerical simulation was carried out one after another and the influence of impeller outlet width on the performance and pressure fluctuation was analyzed. It was shown by the study result that with the increase of impeller outlet width, the lift and shaft power would increase to different extent, the efficiency curve would be hump shaped, indicating that there would be an optimum impeller outlet width to make the flow loss minimum; increasing the width of the impeller outlet, flow separation phenomenon in flow channel would be enhanced, blocking phenomenon there would decrease hydraulic loss would decrease thereby, indicating that an appropriate width of impeller outlet would be effective for reducing the energy loss of centrifugal pump. With progressive decrease of impeller outlet width, the shaft frequency peak would change obviously, assuming progressive increase trend, indicating that an excessive narrow impeller outlet width would easily lead to flow blocking in flow passage and hinder the development of the flow mode, At the same time, the impeller outlet width would also have a greater effect on pressure pulsation in centrifugal pump. Reference | Related Articles | Metrics

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Structural design and modeling simulation of standing-to-lying changing angle swing head of five-faced body machining center YAN Chang-feng, LI Hui-long, LI Qiang, GAO Gang-gang, GOU Wei-dong Journal of Lanzhou University of Technology    2020, 46 (2): 35-40.   Abstract （501）      PDF（pc） （4323KB）（1221）       Knowledge map    Save Aimed at the problem of five-face body machining center that the transmission chain was excessive long and unfavorable for improving the machining accuracy in the case of standing-to-lying change, a novel project of angle swing head for standing-to-lying change was proposed. In this project, the measure of transmission was dropped, where the angle swing head employed individual set of power supply for cutting power transmission and also for standing-to-lying change, and a simple set of power supply was used either for cutting power transmission or for standing-to-lying change, so that the transmission chain was contracted extremely. A three-dimensional mechanical structure model of the assembly of angle swing head, spindle and its key components was established with software SolidWorks. The software Romax was used to conduct the modelling of the driven system of the angle swing head, and the reliability of the driven system was analyzed under different working conditions. The result showed that under given operation conditions the design of the drive system would be reasonable and the operational reliability would meet the design requirements. To ensure rigidity and stability of the standing-to-lying change spindle of angle swing head, the modality analysis was carried out by using the ABAQUS. The result showed that the spindle would not resonate within the range of rated operating speed. Reference | Related Articles | Metrics

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Influence of high rate charge and discharge cycle on the electronic performance and thermal safety of lithium ion battery LI Dong-qi, ZHANG Qing-song, ZHENG Shao-shuai Journal of Lanzhou University of Technology    2023, 49 (3): 30-35.   Abstract （844）      PDF（pc） （2624KB）（1200）       Knowledge map    Save Lithium-ion batteries are widely used in electric vehicles and various energy storage devices. In this paper, cyclic aging and thermal runaway experiments under different charge-discharge rates were carried out, and the effects of large-rate charging and discharging on the performance and thermal safety of single lithium-ion batteries were studied. The results showed that the actual capacity of single lithium-ion battery is attenuated under the large-rate charge-discharge cycle, and the degree of attenuation is positively relevant to the charge-discharge rate. With the charge-discharge rate increasing, the constant current ratio is stepwise attenuation, but the coulombic efficiency still maintains in the range of 99%-100%, indicating that the reversible performance of lithium-ion batteries is normal. With the increase of the magnification, the thermal runaway trigger time, explosion pressure and jet flame temperature first increase and then decrease. The average surface temperature of the battery during explosion is 655.8 ℃, which is close to the melting point of aluminum. The explosion injection powder products are mainly metal aluminum, graphite and lithium cobalt oxide. Reference | Related Articles | Metrics

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Research on DR digital imaging automatic detection method of blade air film hole processing defects LIU Tao, SHI Yu, LI Chun-kai, SUN Zhong-chen, MAN Yue-e, LV Jian Journal of Lanzhou University of Technology    2021, 47 (5): 19-23.   Abstract （483）      PDF（pc） （3987KB）（1192）       Knowledge map    Save Air film holes are one of the important cooling structures in turbine blades, it has great significance to improve the cooling efficiency of aircraft engines, reduce the temperature of the combustion chamber and even increase the service life of the engine. However, in the actual course of working, it is easy to have internal defects such as unopened air film holes, deflection, and damage to the inner wall due to external factors. Traditional detection methods mainly use artificial film X-ray method to detect internal defects, but there are problems such as low detection efficiency, high cost and high dependence on the experience and skills of the inspectors. This paper proposes an automatic detection method for air film hole defects based on X-ray digital imaging technology. By studying the equivalence of DR digital images and film images, the law of the effect of the transillumination angle on defect recognition and the optimization of the detection process, key technologies based on deep learning neural network defect self-recognition, high-precision detection and intelligent recognition of blade air film hole processing defects are realized. Reference | Related Articles | Metrics

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Fatigue strength analysis of high-strength bolts for tower flange of wind turbine LIANG Yuan, WANG You-liang, WEI Tai, LIU Jian-hui Journal of Lanzhou University of Technology    2023, 49 (2): 65-69.   Abstract （384）      PDF（pc） （1391KB）（1168）       Knowledge map    Save An analysis method for high-strength bolts of wind turbine tower flange was established by considering the influence of external load on fatigue damage. Firstly, the maximum load section was determined with the aid of the tower equivalent model according to the damage parameters of the stress state on the connection section. Secondly, the external load on any sector of the tower was obtained by Schmidt-Neuper algorithm. Afterwards, the fatigue damage distribution model of high-strength bolts was established and the relationship between the external load and the internal stress of high-strength bolts was explored based on the finite element model. Finally, the optimal bolt pretightening force was determined with comparing the fatigue cumulative damage values with different bolt pretightening forces by considering the influence of pretightening forces. The results show that the positions of the maximum fatigue cumulative damage of flange bolts were －4.17° and 175.87°, and the bolt pretightening force was the most suitable value when the bolt pretightening force ratio was 70%. Reference | Related Articles | Metrics

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Characteristic analysis of flow-dead-zone in pressure building of variable speed pump control system QIANG Yan, WANG Ya-qiang, ZHAO Chun-li, LI Wei, LUO Xiao-mei, WEI Lie-jiang Journal of Lanzhou University of Technology    2021, 47 (1): 54-60.   Abstract （371）      PDF（pc） （1556KB）（1110）       Knowledge map    Save In order to reveal dominant mechanism of the flow-dead-zone of a hydraulic pump in pump control system, a mathematical model of the hydraulic pump, including the flow-dead-zone, is established in this paper. The model takes into account the leakage in the hydraulic pump caused by differential pressure flow and shear flow as well as the compressibility of oil. Through analyses of the mathematical model, it is concluded that the width of the flow-dead-zone of the hydraulic pump increases with increase of the outlet cavity, load pressure, oil temperature and start-up acceleration of the hydraulic pump, and decreases with increase of displacement of the hydraulic pump. For this reason, taking a gear pump as an example, a Simulink-Amesim joint simulation model is established to study further effects of different load pressure, oil temperature and start-up acceleration on the dead zone width, and verify the results from theoretical analyses. The results show that the dead zone width of hydraulic pump flow has a linear relationship with load pressure and start-up acceleration, and is close to an exponential relationship with oil temperature. Reference | Related Articles | Metrics

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Discussion on calculation method of active earth pressure for limited soils ZHU Yan-peng, WEI Peng-yun, MA Xiao-rui, LI Geng, LIU Xin Journal of Lanzhou University of Technology    2020, 46 (2): 133-137.   Abstract （547）      PDF（pc） （2711KB）（1101）       Knowledge map    Save Based on the sliding plane hypothesis of Coulomb’s earth pressure theory and the limit equilibrium theory, a modified formulation for active earth pressure is derived according to the relationship between limited soils’ width b 0 (a distance between a supporting structure and an existing building) and triangular sliding wedge’s width b. Assumptions of formulation are that the limited soil is in horizontal and the support structure is in vertical. In addition, the formulation takes into account not only the adhesion between the supporting structure and soils but also the cohesion between the static soils and sliding soils. It is then analyzed that the impact of the external friction angle as well as the adhesion between the supporting structure and soils on the sliding soil mass’ cracking angle (failure angle of sliding soils) and active earth pressure. A viewpointabout generalized active earth pressure coefficient is also put forward in this paper. All results gaining from our calculated examples show that the formulation becomes more effective in practices. Evidently, taking the impact of the external friction angle into account in the formulation will reduce cost indeed. Reference | Related Articles | Metrics

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Multi-objective parameters optimization of low specific speed centrifugal pump based on NSGA-Ⅱ genetic algorithm ZHAO Wei-guo, XIA Tian, SHENG Yuan-zhi, LI Shang-sheng Journal of Lanzhou University of Technology    2020, 46 (4): 55-61.   Abstract （407）      PDF（pc） （2744KB）（1038）       Knowledge map    Save In order to improve hydraulic efficiency and head of a low specific-speed centrifugal pump, a low specific-speed centrifugal pump with 30 specific-speed was selected as a research object in this study. By taking the maximum head and hydraulic efficiency of centrifugal pump as two optimization objectives, the basic equation of centrifugal pump and the Plackeet-Burman test are combined for screening parameters to be optimized. By doing so. the vane outlet placement angle of centrifugal pump impeller was selected, and the wrap angle and outlet width of the blades were selected too as variables for optimization in our study. In the optimization process, 30 groups of experiments were arranged using the optimal Latin super-cubic design method, and then an approximate model between the optimization target and the variables was fitted numerically by using the RBF neural network model. The multi-objective optimization was finally carried out in terms of NSGA-Ⅱ genetic algorithm. The optimization results show that the head of the optimized impeller basically remains unchanged, the hydraulic efficiency of the impeller is 5.82% higher than that before optimization. The optimization eliminates the hump on the flow-head curve of the impeller and makes the operation of the centrifugal pump more stable. The pressure gradient in the impeller flow channel is reduced after optimization, and the area as well as size of eddies are reduced apparently to some extent. The turbulence area in the impeller flow channel becomes uniformly distributed, and blades to work are enhanced as a result. Thus the hydraulic efficiency has been improved. Reference | Related Articles | Metrics

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Design and implementation of transmitting and receiving circuits in wireless laser data communication system WANG Hui-qin, MA Yu-kun, CAI Hong-liang, ZHANG Yue, CAO Ming-hua Journal of Lanzhou University of Technology    2021, 47 (3): 91-96.   Abstract （461）      PDF（pc） （4255KB）（1038）       Knowledge map    Save Wireless laser communication has numerous advantages that include high transmission rate, strong anti-jamming ability, low power consumption, etc. In this paper, the red light with the wavelength of 650 nm is used as the signal carrier to design a transceiver circuit for wireless laser communication. And we elaborate the designed principles and methods of laser transmitting circuit and photoelectric receiving circuit. In proposed system, the transmitting circuit has the functions of automatic power control, fault indication and current monitoring, while the receiving circuit has the functions of signal amplification, photocurrent monitoring and automatic noise. Furthermore, the performance of proposed circuit is tested by using the experimental platform, and the correctness and rationality of designed circuit are verified. The exprimental results showed that the designed circuit can achieve reliable transmission when the transmission rate is 16 Mbit/s. Reference | Related Articles | Metrics

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Dynamic output feedback control of cyber-physical systems under false data injection attacks ZHU Chao-qun, ZHU Yi-rong Journal of Lanzhou University of Technology    2023, 49 (1): 74-82.   Abstract （423）      PDF（pc） （1259KB）（999）       Knowledge map    Save In this paper, an H-infinity dynamic output feedback control strategy with attack defense ability is investigated to deal with the problem of security control of cyber-physical system (CPS) under false data injection (FDI) attacks, which is taken as a special kind of external disturbance. Firstly, the effect of FDI attacks in the measurement channel and random time-delay on the communication network is considered, and a closed-loop system model with FDI attack, random time-delay, and external disturbance is established. Secondly, the sufficient conditions for the asymptotic stability of the closed-loop system under FDI attacks are derived based on the Lyapunov stability theory, and then the design scheme of H-infinity dynamic output feedback controller by utilizing linear matrix inequality technology is presented. Finally, a simulation example is given to demonstrate the feasibility and effectiveness of the proposed method. Reference | Related Articles | Metrics

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Study on magnetic properties of Fe-based amorphous composites ZHAO Yan-chun, WANG Bo, LI Ze-feng, SUN Hao, KOU Sheng-zhong Journal of Lanzhou University of Technology    2021, 47 (2): 1-6.   Abstract （1018）      PDF（pc） （3215KB）（986）       Knowledge map    Save The Fe-15Mn-5Si- xCr-0.2C(wt.%) amorphous composite material was prepared by using water-cooled copper crucible smelting and copper mold suction casting. XRD was used to characterize the phase composition of the sample. Vibrating Sample Magnetometercombined with M-H and B-H curves were used to analyze the effect of the change of the Cr element content on the magnetic properties for amorphous composite material. The results show that the Fe-15Mn-5Si- xCr-0.2C ( x=1, 2, 4, 6, 8, 10, 12, 13, 14) samples are composed of α-Fe phase, γ-Fe phase and the amorphous phase. As thecontent of Cr element increases, the mixing enthalpy decrease while the mixing entropy increase. The synergistic effect of α-Fe phase and the amorphous phase made the Fe-15Mn-5Si-14Cr-0.2C exhibit the best soft magnetic properties, which the coercive force and saturation magnetization are 16.12A/m and 5.1T, respectively. Reference | Related Articles | Metrics

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Sentiment analysis of Chinese text based on feature fusion ZHAO Hong, FU Zhao-yang, WANG Le Journal of Lanzhou University of Technology    2022, 48 (3): 94-102.   Abstract （442）      PDF（pc） （1771KB）（976）       Knowledge map    Save To address the problems that the existing methods cannot comprehensively consider the semantic information of text in terms of syntactic structure, contextual information and local semantic features, a feature fusion-based Chinese text sentiment analysis method is proposed. Firstly, Jieba word segmentation tool is used for word segmentation and part of speech tagging of the review text, and a word vector training tool GloVe is used to obtain pre-trained word vectors with part of speech. Then, the word vector is used as the input of BiGRU and TextCNN with self attention respectively. The global features are extracted from the syntactic structure and the contextual information of the text using BiGRU with Self-Attention, and the local semantic ones are extracted using TextCNN. Finally, the global features and local semantic features are integrated, and Softmax is used for text sentiment classification. The experiment result shows that the proposed method can effectively improve the accuracy of text sentiment analysis. Reference | Related Articles | Metrics

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A machine learning methods for identifying the properties of Chinese medicinal materials from infrared spectrum data TIAN Chun-ting, ZHAO Ning, QIN Jian-wei, MENG Xiao-feng Journal of Lanzhou University of Technology    2023, 49 (3): 55-59.   Abstract （439）      PDF（pc） （2953KB）（962）       Knowledge map    Save There are great differences in the characteristics of near-infrared and mid-infrared spectra of different kinds of traditional Chinese medicine. Due to the different chemical components such as inorganic elements and organic substances, even if the origin of the same traditional Chinese medicine is different, the labeling effect under near-infrared and mid-infrared spectral irradiation will have different spectral characteristics which can be used to classify Chinese herbal medicine and identify the origin of Chinese herbal medicine. With the help of MATLAB software tool and K-means clustering algorithm in SPSS classification tool, unsupervised machine learning is carried out on traditional Chinese medicine to classify traditional Chinese medicine; Using SPSS neural network multilayer perceptron and the random forest algorithm provided by Python language, 70% of the data set is used as the training set and 30% as the verification set to train the supervised machine learning model which is finally used to identify and predict the origin of traditional Chinese medicine. Reference | Related Articles | Metrics

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Analysis of the weak points in the movement of slipper retainer from axial piston pump based on the joint simulation of ADAMS and Pumplinx ZHANG Jing, LIAO Wen-bo, SUI Rui-yang, ZHOU Guo-yang Journal of Lanzhou University of Technology    2021, 47 (3): 58-63.   Abstract （518）      PDF（pc） （3453KB）（946）       Knowledge map    Save In order to study the accidental fracture of the slipper retainer in the axial piston pump, the forces on the slipper retainer are analyzed in detail. The distribution of forces in all aspects is integrated, which shows that the slipper retainer reflects a bending moment with the boundary of suction and discharge side as the reference line in its structure. After the slipper retainer and the whole pump are simulated by ADAMS rigid flexible coupling finite element and Pumplinx fluid finite element, the calculation results show that while each piston moves around the boundary line of suction and discharge side, the stress concentration of the outer edge of the corresponding slipper retainer hole is the largest, which makes this area become the weak points of the slipper retainer movement, under the action of bending moment, these weak points become the most likely fracture risk area. Reference | Related Articles | Metrics