China Mechanical Engineering

Reliability Evaluation of Accumulator in Single Failure Data

GUO Rui1，2;ZHANG Rongbing1，3;ZHAO Jingyi1，2，4;WANG Jinfeng1，3

2018, 29(16): 1891-1899.

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The single failure data were obtained by means of no replacement time truncation test method，the reliability curves of the reliability model under the xponential distribution and the reliability function，the failure probability density function and the failure rate function under the Weibull distribution were obtained respectively.Through the analyses of the reliability life of the accumulators，Weibull distribution took into account the influences of experimental data before failure，failure time and failure on reliability evaluation，in terms of experimental data integrity，it was superior to the exponential distribution，which failed to take into account the failure data.The reliability data are closer to reality，and have more theoretical and engineering significances to evaluate the reliability of small data and small sample.

Study on Influence Factors of Chip Deformation and Breaking for Staggered Teeth BTA Deep Hole Drilling

LI Xubo;ZHENG Jianming;KONG Lingfei;XIAO Shiying;LIU Chi;GUO Bian

2018, 29(16): 1900-1906.

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The influence factors on chip breaking were analyzed by using the chip bending deformation rules of staggered teeth BTA deep hole drilling. The varation rules of deformations and breaking along with drilling radius， drilling process parameters and chip breaker dimension parameters were studied. The results show that the drilling radius has a great influence on the chip thickness. With the drilling radius increasing, the chip thickness increases.The maximum chip thickness is located on the teeth periphery， and the external tooth chip thickness is the smallest. Compared with drilling speed， drilling feed has a greater impact on the chip deformation and breaking. With the increases of the feed， chip thickness increases， chip strain increases. As the chip-breaker width decreases and the height increases， the chip strain increases and the chip breaking conditions improve.

Fault Diagnosis Method of Resonance Demodulation under Compressive Sensing Frameworks

WANG Ke1，2;LYU Yong1，2;YI Cancan1，2

2018, 29(16): 1907-1911.

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In the early fault diagnosis of wind turbine rolling bearings,the compressive sensing algorithm might denoise the noisy signals utilizing the signal sparsity，but the selection of sparseness had a great influence on the denoising effectiveness.Since the sparseness of signal fault components was known in the Fourier domain，the envelope feature of wind turbine signals might be reconstructed by Fourier transform basis and compressive sensing subspace pursuit（CS＿SP）algorithm.As a result，the effects of noises and other irrelevant informations would be reduced，and the fault characteristic frequency might be extracted from the signal components directly reflecting fault characteristics.The results demonstrate that the resonance demodulation technique under compressive
sensing frameworks may effectively acquire the fault characteristic informations of wind turbine rolling bearings.The effectiveness of the proposed method was verified.

A Merged Binding Modeling Method for Contact Fields of Bolted Joints

CUI Fangyuan;HUA Dengxin;LI Yan;KONG Lingfei;LI Pengyang

2018, 29(16): 1912-1920.

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A merged binding modeling method for contact areas of bolted joints was presented in order to improve the accuracy of on-line dynamic monitoring and real-time updating of large-scale complex structures' models.During the modeling processes，the contact field elements were constructed by separating a part of elements from the two mating substructures at each side of the interfaces.The elements in the contact regions would meet the isotropic conditions after a equivalent treatment，and a merged binding contact relationship was established among the elements.The greatest advantage of this modeling method is timesaving because it may effectively avoid increasing the numbers of degrees of freedom in the joint model.Moreover，this method is more universal with advantages of convenience in parameter identification.In the interest of the consistent accuracy between the calculation model and the physical model，the effects of additional masses of bolts，nuts and sensors on modeling accuracy were taken into account together with an optimization and identification of physical characterization parameters of bolted joints based on multi-objective genetic algorithm.The results show that the first six order theoretical mode shapes are in excellent coherence with their experimental counterparts，and the absolute values of the relative errors of corresponding natural frequency are less than 10%， which shows the proposed modeling method may effectively solve the dynamic modeling problems of joints in engineering practices.

Modeling and Natural Characteristic of Non-sinusoidal Oscillator of Continuous Casting Molds

ZHOU Chao1，2;ZHANG Xingzhong1;LIU Pingfei1;GUAN Jie3

2018, 29(16): 1921-1926.

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To realize modification ratio of non-sinusoidal oscillation adjusted on line for mold driven by mechanisms，a non-sinusoidal oscillator driven by double servomotors was proposed.Firstly，working principles of the oscillator were described.3D model of the system was established，which was analyzed by simulation software.Secondly，the torsional-translational coupling dynamics model was created，and the dynamics equations of which were deduced.The results show that mass matrix of non-sinusoidal oscillation is constant，stiffness matrix and damping matrix change with time.At last，based on instantaneous mechanism-solidified method，natural frequency of the system was analyzed ，which was influenced by rotational angles of eccentric shaft，amplitudes,inertia parameters and stiffness.

Flow Filed Analysis and Performance Evaluation on Axis-in Dual-Stage Tandem Hydrocyclones

XING Lei1，2;ZHANG Yong1，2;JIANG Minghu1，2;GAO Yang3

2018, 29(16): 1927-1935.

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To solve the problems of oil/water separation in narrow spaces might not keep high precision，axis-in dual-stage tandem hydrocyclone was designed according to theory of cyclone separation.Flow field characteristics and separation efficiency of the hydrocyclones were analyzed.The distribution rules of velocity field，pressure field， concentration field and separation efficiency influenced by inlet flow rates and split ratios were obtained.Results show that as the increasing of inlet flow rates，maximum pressure drop grows exponentially，tangential velocity increases as well；tangential velocity of ring runner and second hydrocyclone are gradually decreased with the split ratio of first hydrocyclone increases.The effects of split ratio of second hydrocyclone
in separation efficiency of first hydrocyclone are very little.First hydrocyclone plays main role in separating oil and water，second hydrocyclone plays main role in removing oil from water.Research results identify that the best split ratio of first hydrocyclone is as 20%，to the second hydrocyclone is as 15%.The best inlet flow rate is as 4.8 m3/h，and the best total flow rate of hydrocyclone is as 32%.The axis-in dual-stage tandem hydrocyclone accommodating to variable processing and split ratio completely meets the requirements of practical applications，the maximum separation efficiency reaches 99.6%.

Simulation and Verification of Hydraulic Control Systems for Continuous Lifting

ZHOU Yuwei;ZHANG Qing;SHI Yunfei

2018, 29(16): 1936-1942.

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By the large scale structure continuous synchronous lifting technology，the supporting structure with four jack-up points and each point with four jack-up hydraulic cylinders was used for the system.The volume synchronization control mode was applied in the single jack-up point based on synchronous split-flow hydraulic pump.The multi-point master-slave control mode was used between the jack-up points based on displacement fuzzy control.The system based on synchronous split-flow hydraulic pump and displacement fuzzy control was modeled and simulated.The system prototype tests and the data analysis were
completed.The results show that due to the various factors in the actual conditions，the actual errors are bigger than the simulated one but still meet the requirements of synchronization.The results validate the application feasibility of the hydraulic control systems.

Analysis and Extraction Technology in Frequency Domain for Phase Angles of Shafting Vibration Dampers

ZHANG Xin1;SONG Xuan1;JIANG Li2

2018, 29(16): 1943-1946.

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In order to prevent the harms caused by too large ship shafting vibrations when the performances of vibration dampers declined during the ship moving，an algorithm of analysis and extraction of the phase angles of ship shafting vibration dampers in frequency domain was proposed herein,a twist vibration meter was used to constantly measure and compute the inner and outer angular velocities of vibration dampers，the phase angles and damping coefficients of the vibration damper were obtained and error reasons were analyzed，large error data were excluded ，then the fitted curves were compared with standard curves to estimate the performances of vibration dampers.The prototype test results show that the algorithm may accurately calculate the phase angles of the vibration dampers，and the fitted curves are of high accuracy，which satisfy the design requirements on ship shafting performances of vibration dampers.

Study on Influence Factors of Connection Stiffness of Rocket Structure

LI Cao;SHANG Xianyang;ZHOU Xin;LENG Yue

2018, 29(16): 1947-1951.

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The rocket cabin docking connection stiffness was one of the important factors that affected the flight safety.At the same time，due to capacity constraints，the rocket structure was strict with the weight.The finite element simulation analysis method was adopted herein.The influence factors of the connection stiffness were analyzed and researched.The influence factors included connecting bolt preload，the thickness and distribution of bolts.The regular patterns of the influence factors on connection stiffness were obtained.The rocket structure design may be guided by these researches.

Contact Performance Degradation Mechanism of Electrical Connectors under Vibration Conditions

LUO Yanyan1,2;ZHANG Le3;MENG Fanbin4;HAO Jie5

2018, 29(16): 1952-1957.

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In view of the problems of stress relaxation and fretting wear caused by metal contacts of electrical connectors under alternating vibration stresses, the contact reliability of electrical connectors might be reduced.Firstly, the mathematical model of electrical connector contacts was established.Secondly, vibration test scheme of electrical connectors and testing circuit were designed,and the tests were carried out subsequently.During the tests, the contact resistances of the test specimen increased slowly with the increases of the vibration frequency, and the fluctuation of the contact resistances was related to the vibration amplitude and frequency.After the tests, the pore sizes of jacks increasess and the values of insertion and withdrawal forces increased or decreased.It is concluded that the stress relaxation phenomenon in the jacks and fretting wear phenomenon between the contacts of the electrical connectors are two main factors leading to the contact performance degradation of the electrical connectors.In addition, the decreases of the crystal sizes and the increases of the slip line density are the fundamental reasons for the stress relaxation phenomenon in the jacks of the electrical connectors.

Trajectory Tracking Control of Wheeled Mobile Robots under Longitudinal Slipping Conditions

BEI Xuying1，2;PING Xueliang1，2;GAO Wenyan1，2

2018, 29(16): 1958-1964.

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An trajectory tracking control of mobile robots was presented based on wheeled mobile robots with unknown longitudinal slip parameters.Firstly，the kinematic model of the mobile robots under longitudinal slips was established，and the sliding parameters were used to express the slip degrees of the left and right wheels.Then，a suitable sliding mode observer was designed to estimate unknown slip parameters，and the influences of chatters on estimation of slip
parameters were reduced by using the low-pass filters.Finally，a trajectory tracking control law was designed based on Lyapunov direct method，and a method of determine the control parameters was proposed according to the pole distributions of the control systems.Numerical simulation results show that the proposed trajectory tracking control method is accurate and effective.

Recommendation Method and Applications for Personalized Product Service Plans

YANG Zhen;GENG Xiuli

2018, 29(16): 1965-1974,1983.

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Traditional LFM didn't consider the database dynamic update which would affect the program recommendation results，so a weighted LFM was proposed based on the dynamic update mechanism to recommend the personalized product service plans. Firstly，aiming at the problems of cosine similarity neglecting individual differences，a comprehensive similarity weighted by cosine similarity between cloud drop distance measure and cloud was proposed to predict and fill vacancy data and reduce data sparsity.Then，the difference of interests of new users could be restrained and the recommendation accuracy could be improved by using the weighted LFM recommendation service scheme. Finally，the proposed method was updated with the method of difference averaging，and the efficiency of different recommended algorithms was compared with mean absolute error （MAE）. The practicality and validity of the proposed algorithm were verified by examples.

Multi-objective Optimization Design of Small-centrifugal Compressor under Variable Flow Conditions

TANG Xinzi;XIAO Peng;CAI Peng;PENG Ruitao

2018, 29(16): 1975-1983.

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In order to improve the performances of centrifugal compressor under variable flow conditions，the influences of geometric parameters on aerodynamic performances of the centrifugal compressor were investigated by three-dimensional computational flow analysis.The optimal design variable space was established based on correlation analysis.By employing the method of Latin hypercube test design，Kriging model and NSGA-Ⅱ algorithm，the multi-objective optimization of a micro-centrifugal compressor impeller was carried out under variable flow conditions.The pressure ratio and the efficiency of the optimal impeller at the design flow conditions increase by 6.43% and 3.99% respectively；the pressure ratio and the efficiency at the lower-flow conditions increase by 5.62% and 3.52% respectively.The internal flow loss is reduced，the stall flow reduces by 2.7%，the blocking flow increases by 6.85% and the stable working ranges are widened.

Path Planning for Dual-robot Coordinate Welding Based on Multi-objective Genetic Algorithm

HOU Yangqiang;WANG Tianqi;YUE Jianfeng;JIA Zhenwei

2018, 29(16): 1984-1989.

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A welding path planning method was proposed by studying the path planning problems of dual-robot coordinated welding of complex spatial welds based on multi-objective genetic algorithm .Parameters of affecting the weld's quality and the stability of robot's movement were analyzed， and the objective function of the evaluation of welding paths such as welding quality function，collide with dual-robot and robot motion stability function were established.A multi-objective genetic algorithm was used to solve the coordinated welding paths，and the optimal welding path planning of the dual-robot was realized.Taking the "saddle shaped" space seam as an example，the welding paths of 2 robots were tested and verified.The results show that the proposed scheme may realize the
planning of dual-robot coordinated welding paths.

Hybrid Gray Wolf Optimization for Energy-efficient Type-II Robotic U-shaped Assembly Line

ZHANG Zikai1，2;TANG Qiuhua1，2;ZHANG Liping1，2;LI Zixiang1，2

2018, 29(16): 1990-1995.

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Considering task assignment and robot assignment，gray wolf algorithm was proposed based on random key code to minimize energy consumption.Considering precedence relations and cycle time constraint， the algorithm allocated the tasks and robots into workstations in decoding
phase.Based on social hierarchy in the population of gray wolf，3 optimal wolves were selected to guide other wolves to update the population.Simultaneously，based on the task assignment and robot allocation，2 crossover operators were designed to enhance the
communication among low-grade wolves.The proposed algorithm was proved to have great performance under benchmarks of U-shaped assembly lines.

Formability of HSS in Cold Stamping Based on Variable Friction Coefficient and Thermal-mechanics Coupling

NIE Xin;TAN Guang;QIAO Xiaoyong

2018, 29(16): 1996-2002.

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Measured friction coefficient of DP780 dual phase HSS under different temperatures，a novel variable friction coefficient model was
established，and the formability during room temperature cold stamping was researched based on thermal-mechanics coupling and variable friction
coefficients.The results show that temperature is increased obviously in some areas of sheet metal in heat variable（HV） groups，and comparing the
same places with compared groups，the thinning ratio is smaller，not easy to crack，better ductility are showed.From spring-back displacement
contour，values in HV groups are smaller than the measured values in stamping experiments.However values in compared groups are bigger，and
compared with the experimental measured values，the errors of HV groups are only 27.8% of compared groups，and are agreed with stamping
experiments better.

Magnetic Property Simulation of Defects in Ferromagnetic Pipes under Magnetization

ZHANG Lipan1;MA Bingyang1;SONG Kai1;WANG Zhen2

2018, 29(16): 2003-2009.

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A 3D model of DC magnetization pipes was built with finite element method.Meanwhile the ferromagnetic material magnetic properties
and the distribution of magnetic permeability around defect areas were analyzed.The effects of magnetization intensity，the thicknesses of the
pipes and the depths of the flaws on magnetic permeability distribution were studied.The results show that the magnetic permeability of the defect
areas is uneven distributed while saturation magnetized，and the internal defects may even cause the magnetic permeability of exterior surface
changing under magnetization.The mechanism of internal defects on the ferromagnetic pipes is revealed，and the applications of the eddy current
testing method are expanded.

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