Chinese Journal of Mechanical Engineering

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Mechanism of Spine Motion About Contact Time in Quadruped Running

Qi Liu, Yannian Bao, Wei Yu, Jianming Zhang, Chao Li, Xinru Xie

Chinese Journal of Mechanical Engineering. 2019, 32(2): 18-18. https://doi.org/10.1186/s10033-019-0333-y

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The current research of quadruped robot focuses on the quadruped robot with spine motion. Contact time is a very important part of system performance. However, the mechanism of spine motion about contact time has not been clearly elucidated. In this paper, the effect of spine motion on contact time is studied deeply from dynamic view. Firstly, a simplified model of the quadruped robot with spine joint is set up, its dynamic equations are derivated, and a method that can generate passive periodic locomotion is proposed. Secondly, according to the vertical spring oscillator model, the two-dimension planar locomotion of the simplified model is regarded as a special vibration in the vertical direction, and the approximate formula of calculating contact time is obtained. Finally, the approximate formula of calculating contact time is verified by the simulation results of passive periodic locomotion, and the effect of spine motion on contact time is deeply discussed based on the approximate formula of calculating contact time. The discussion proves that spine motion indeed has little effect on contact time, but spine motion can slightly reduce body pith movement and regulate the leg stiffness in leg contact phase. This research proposes an effective research method which can be used to study the motion mechanism of the quadruped robot with spine motion, and the mechanism of spine motion about contact time is clearly elucidated which is helpful to set the parameters of mechanical structure and study control algorithm about the quadruped robot with spine motion.

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Design and Simulation of Flow Field for Bone Tissue Engineering Scaffold Based on Triply Periodic Minimal Surface

Zhen Wang, Chuanzhen Huang, Jun Wang, Peng Wang, Shisheng Bi, Ch Asad Abbas

Chinese Journal of Mechanical Engineering. 2019, 32(2): 19-19. https://doi.org/10.1186/s10033-019-0329-7

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A novel method was proposed to design the structure of a bone tissue engineering scaffold based on triply periodic minimal surface. In this method, reverse engineering software was used to reconstruct the surface from point cloud data. This method overcomes the limitations of commercially available software packages that prevent them from generating models with complex surfaces used for bone tissue engineering scaffolds. Additionally, the fluid field of the scaffolds was simulated through a numerical method based on finite volume and the cell proliferation performance was evaluated via an in vitro experiment. The cell proliferation and the mass flow evaluated in a bioreactor further verified the flow field simulated using computational fluid dynamics. The result of this study illustrates that the pressure value drops rapidly from 0.103 Pa to 0.011 Pa in the y-axis direction and the mass flow is unevenly distributed in the outlets. The mass flow in the side outlets is observed to be approximately 24.3 times higher than that in the bottom outlets in the range 6.13×10^-8 kg/s to 1.49×10^-6 kg/s. Moreover, the mass flow in the bottom outlets decreases from the center to the edge, whereas the mass flow in the side outlets decreases from the top to the bottom. Importantly, although the mean value of wall shear stress is significantly more than 0.05 Pa, there is still a large area with a suitable shear stress below 0.05 Pa where most cells can proliferate well. The result shows that the inlet velocity 0.0075 m/s is suitable for cell proliferation in the scaffold. This study provides an insight into the design, analysis, and in vitro experiment of a bone tissue engineering scaffold.

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Hierarchical Optimization of Landing Performance for Lander with Adaptive Landing Gear

Zongmao Ding, Hongyu Wu, Chunjie Wang, Jianzhong Ding

Chinese Journal of Mechanical Engineering. 2019, 32(2): 20-20. https://doi.org/10.1186/s10033-019-0331-0

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A parameterized dynamics analysis model of legged lander with adaptive landing gear was established. Based on the analysis model, the landing performances under various landing conditions were analyzed by the optimized Latin hypercube experimental design method. In order to improve the landing performances, a hierarchical optimization method was proposed considering the uncertainty of landing conditions. The optimization problem was divided into a higher level (hereafter the "leader") and several lower levels (hereafter the "follower"). The followers took conditioning factors as design variables to fnd out the worst landing conditions, while the leader took bufer parameters as design variables to better the landing performance under worst conditions. First of all, sensitivity analysis of landing conditioning factors was carried out according to the results of experimental design. After the sensitive factors were screened out, the response surface models were established to refect the complicated relationships between sensitive conditioning factors, bufer parameters and landing performance indexes. Finally, the response surface model was used for hierarchical optimization iteration to improve the computational efciency. After selecting the optimum bufer parameters from the solution set, the dynamic model with the optimum parameters was simulated again under the same landing conditions as the simulation before. After optimization, nozzle performance against damage is improved by 5.24%, the acceleration overload is reduced by 5.74%, and the primary strut improves its performance by 21.10%.

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A Modified Iterated Greedy Algorithm for Flexible Job Shop Scheduling Problem

Ghiath Al Aqel, Xinyu Li, Liang Gao

Chinese Journal of Mechanical Engineering. 2019, 32(2): 21-21. https://doi.org/10.1186/s10033-019-0337-7

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The flexible job shop scheduling problem (FJSP) is considered as an important problem in the modern manufacturing system. It is known to be an NP-hard problem. Most of the algorithms used in solving FJSP problem are categorized as metaheuristic methods. Some of these methods normally consume more CPU time and some other methods are more complicated which make them difficult to code and not easy to reproduce. This paper proposes a modified iterated greedy (IG) algorithm to deal with FJSP problem in order to provide a simpler metaheuristic, which is easier to code and to reproduce than some other much more complex methods. This is done by separating the classical IG into two phases. Each phase is used to solve a sub-problem of the FJSP: sequencing and routing sub-problems. A set of dispatching rules are employed in the proposed algorithm for the sequencing and machine selection in the construction phase of the solution. To evaluate the performance of proposed algorithm, some experiments including some famous FJSP benchmarks have been conducted. By compared with other algorithms, the experimental results show that the presented algorithm is competitive and able to find global optimum for most instances. The simplicity of the proposed IG provides an effective method that is also easy to apply and consumes less CPU time in solving the FJSP problem.

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Analysis of Electrical Characteristics of Inter-wire Arc in Cross-Coupling Arc

Zhenyang Lu, Shanwen Dong, Fan Jiang, Cheng Li

Chinese Journal of Mechanical Engineering. 2019, 32(2): 22-22. https://doi.org/10.1186/s10033-019-0340-z

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As a new composite welding heat source introduced in recent years, the cross-coupling arc uses a non-consumable electrode arc (plasma arc) and a consumable electrode arc (inter-wire arc) in cross-coupling, in which the plasma arc is the main arc and the inter-wire arc is the vice arc, to realize the separate control of the heat input to the workpiece, arc force, and droplet transfer. To reveal the electrical characteristics of the inter-wire arc under the action of the plasma arc, in this study, rotating probes are used to sweep across the plasma arc. When the probes rotate into the plasma arc, a circuit is formed, and the electrical characteristics of the inter-wire arc are indirectly analyzed according to the circuit: the probe centering current and input voltage are used as the physical quantities. The results show that at a certain wire feed rate, the inter-wire arc current increases with increasing input voltage. When the input voltage is low, the wire feed rate has no obvious effect on the inter-wire arc current. At a higher input voltage, where the wire feed rate is high, the inter-wire arc current decreases. With the increase in the plasma arc current, the inter-wire arc current first increases quickly and then increases slowly, and simultaneously, the striking arc time becomes longer. With the increase in the interval between the nozzle and the workpiece, the inter-wire arc current increases, but when the arc length increases to a certain limit, the slope of the welding current clearly declines.

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Lubrication Performance of Connecting-Rod and Main Bearing in Diferent Engine Operating Conditions

Jun Sun, Biao Li, Shaoyu Zhu, Enming Miao, Hu Wang, Xiaoyong Zhao, Qin Teng

Chinese Journal of Mechanical Engineering. 2019, 32(2): 23-23. https://doi.org/10.1186/s10033-019-0335-9

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Only the lubrication performance at rated engine operating condition was generally analyzed in current design and research of engine connecting-rod and main bearing. However, the actual engine (especially vehicle engine) does not always operate in rated operating condition and its operating condition changes constantly. In this paper, a four-stroke four-cylinder engine is taken as the studying object, the load and lubrication of connecting-rod and main bearing in different operating conditions are analyzed. The load of connecting-rod bearing is calculated by the dynamic calculation method, the loads of all main bearings are calculated by the whole crankshaft beam-element finite element method, and the lubrication performance of connecting-rod and main bearings are analyzed by the dynamic method. The results show that there are major differences in the changes and numerical value at corresponding moment of the loads and lubrication performance of connecting-rod and main bearings in an engine operating cycle in different engine operating conditions; the most unfavorable case of the lubrication performance of connecting-rod and main bearings may not take place in the rated engine operating condition. There are also major differences between the lubrication performance of connecting-rod bearing and that of main bearing and between the lubrication performances of main bearings one another. Therefore, it will not be reasonable that the lubrication performance of a certain connecting-rod bearing or main bearing is analyzed in the design of the engine bearing. It is necessary to analyze simultaneously the lubrication performances of all bearings in different engine operating conditions.

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On-Machine Measurement of the Straightness and Tilt Errors of a Linear Slideway Using a New Four-Sensor Method

Lei Zhao, Kai Cheng, Hui Ding, Liang Zhao

Chinese Journal of Mechanical Engineering. 2019, 32(2): 24-24. https://doi.org/10.1186/s10033-019-0338-6

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Although there are some multi-sensor methods for measuring the straightness and tilt errors of a linear slideway, they need to be further improved in some aspects, such as suppressing measurement noise and reducing precondition. In this paper, a new four-sensor method with an improved measurement system is proposed to on-machine separate the straightness and tilt errors of a linear slideway from the sensor outputs, considering the influences of the reference surface profile and the zero-adjustment values. The improved system is achieved by adjusting a single sensor to different positions. Based on the system, a system of linear equations is built by fusing the sensor outputs to cancel out the effects of the straightness and tilt errors. Three constraints are then derived and supplemented into the linear system to make the coefficient matrix full rank. To restrain the sensitivity of the solution of the linear system to the measurement noise in the sensor outputs, the Tikhonov regularization method is utilized. After the surface profile is obtained from the solution, the straightness and tilt errors are identified from the sensor outputs. To analyze the effects of the measurement noise and the positioning errors of the sensor and the linear slideway, a series of computer simulations are carried out. An experiment is conducted for validation, showing good consistency. The new four-sensor method with the improved measurement system provides a new way to measure the straightness and tilt errors of a linear slideway, which can guarantee favorable propagations of the residuals induced by the noise and the positioning errors.

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Mathematical Model of Drag Torque with Surface Tension in Single-Plate Wet Clutch

Zengxiong Peng, Shihua Yuan

Chinese Journal of Mechanical Engineering. 2019, 32(2): 25-25. https://doi.org/10.1186/s10033-019-0343-9

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Reduction of drag torque in disengaged wet clutches is essential for transmission research because it is one of the potentials of efficiency improvement. Aeration of oil film between two closely rotating plates promotes the decrease of drag torque at high speed region. The effects of surface tension and static contact angles during aeration are non-negligible showed by test results. The traditional lubrication model does not adequately predict the experimental results with different surface tension and contact angles during aeration. Hence, in this present paper, contact angles between Aluminum and Teflon materials were firstly measured, and the drag torques under two different contact angles were examined experimentally. An improved lubrication model of drag torque based on Navier-Stokes equations at the gas-liquid interface was built. The lubrication boundary condition was modified to introduce the effects of surface tension and contact angle. The model shows that the effects at the beginning of aeration of oil film are significant. These effects almost occur at stationary plate due to low Reynolds number and Weber number. The model shows that an increase in the surface tension promotes aeration, but does not affect the peak drag torque. Increasing contact angle also promotes the aeration, and accelerates the decrease of drag torque. The larger contact angle is, the smaller the peak drag torque will be. A computational fluid dynamics (CFD) model based on volume of fluid (VOF) method was presented to validate the interface shape when aeration occurs. The model prediction has a good agreement with experimental observations for Aluminum plates and Teflon plates. The modified lubrication model of drag torque gives a convenient description of the effects of surface tension and contact angel, and lays down a frame to understand the beginning of aeration.

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Image-Based Feature Extraction Technique for Inclined Crack Quantifcation Using Pulsed Eddy Current

Faris Nafah, Ali Sophian, Md Raisuddin Khan, Syamsul Bahrin Abdul Hamid, Ilham Mukriz Zainal Abidin

Chinese Journal of Mechanical Engineering. 2019, 32(2): 26-26. https://doi.org/10.1186/s10033-019-0341-y

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Existing eddy current non-destructive testing (NDT) techniques generally do not consider the inclination angle of inclined cracks, which potentially harms a larger region of a tested structure.This work proposes the use of 2D scan images generated by using pulsed eddy current (PEC) non-destructive testing (NDT) technique in the quantifcation of the inclination and depth of inclined cracks.The image-based feature extraction technique efectively identifes the crack axis, which consequently enables extraction of features from the extracted linear scans.The technique extracts linear scans from the images to allow the extraction of three novel image-based features, namely the length of extracted linear scans (LLS), the linear scan skewness (LSS), and the highest value on linear scan (LS_max).The correlation of the three features to surface crack inclination angles and depths were analysed and found to be highly dependent on the crack depths, while only LLS and LSS are correlated to the crack inclination angles

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Characterization of Passive Films Formed on As-received and Sensitized AISI 304 Stainless Steel

Yubo Zhang, Hongyun Luo, Qunpeng Zhong, Honghui Yu, Jinlong Lv

Chinese Journal of Mechanical Engineering. 2019, 32(2): 27-27. https://doi.org/10.1186/s10033-019-0336-8

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The current research of corrosion resistance of stainless steels mainly focuses on characterization of the passive films by point defect mode and mixed-conduction model. The corrosion resistance of the passive films formed on as-received and sensitized AISI304 stainless steel in borate buffer solution were evaluated in this paper. The degree of sensitization and corrosion resistance of AISI304 stainless steels was evaluated by double loop electrochemical potentiodynamic reactivation and electrochemical impedance spectroscopy. The passive films formed on the stainless steels were studied by XPS technique. It was found that as-received specimen had higher pitting corrosion potential and corrosion resistance than sensitized one. The Mott-Schottky results showed that sensitized stainless steel had more defects in the passive film than as-received one. The compositions of the passive films were mainly Cr and Fe oxides according to XPS results.

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An Iterative Compensation Algorithm for Springback Control in Plane Deformation and Its Application

Rui Ma, Chunge Wang, Ruixue Zhai, Jun Zhao

Chinese Journal of Mechanical Engineering. 2019, 32(2): 28-28. https://doi.org/10.1186/s10033-019-0339-5

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In order to solve the springback problem in sheet metal forming, the trial and error method is a widely used method in the factory, which is time-consuming and costly for its non-direction and non-quantitative. Finite element simulation is an effective method to predict the springback of complex shape parts, but its precision is sensitive to the simulation model, particularly material model and boundary conditions. In this paper, the simple iterative method is introduced to establish the iterative compensation algorithm, and the convergence criterion of iterative parameters is put forward. In addition, the new algorithm is applied to the V-free bending and stretch-bending processes, and the convergence of curvature and bending angle is proved theoretically and verified experimentally. At the same time, the iterative compensation experiments for plane bending show that, the new method can predict the next compensation value based on the springback of each test, so that the target bending angle with the error of less than ±0.1% and the target curvature with the error of less than 0.5% are obtained after 2?3 iterations. This research proposes a new iterative compensation algorithm to predict springback in sheet metal forming process, where each compensation value depends only on the iteration parameter difference before and after springback for the same forming process of same material.

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Investigation on LCF Behavior of Welded Joint at Diferent Temperatures for Bainite Steel

Ke Xu, Xiongfei Wang, Haichao Cui, Fenggui Lu

Chinese Journal of Mechanical Engineering. 2019, 32(2): 29-29. https://doi.org/10.1186/s10033-019-0346-6

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The current research of low cycle fatigue (LCF) is mainly focused on the components with uniform microstructure. Compared with these typical components, LCF behavior of welded components are more complex due to their great gradient microstructure, especially for different temperature. In this paper, LCF properties were conducted on the welded joint at different temperatures for bainite steel, and the failure mechanism was systematically discussed. Fatigue parameters derived from fitting curves indicated that welded joint had worse plastic deformation resistance and experienced more significantly strain hardening effect at 300 ℃. The joint failed in the weld metal at room temperature, which attributed to the softening in weld metal combined with cyclic strain hardening effect in heat-affected zone, which meant the joint was more sensitive with the hardness at this condition. When it came to 300 ℃, more cracks appeared near to HAZ and the heterogeneous distributed surface inclusion was responsible for the fracture transition to HAZ adjacent to bainite steel rather than the softest zone in HAZ, reflecting the joint was more sensitive with the surface inclusion at 300 ℃. This research could support the design on loading of welded component at different temperature, and further ensure the safe operation.

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Reliability and Availability Models of Belt Drive Systems Considering Failure Dependence

Peng Gao, Liyang Xie, Jun Pan

Chinese Journal of Mechanical Engineering. 2019, 32(2): 30-30. https://doi.org/10.1186/s10033-019-0342-x

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Conventional reliability models of belt drive systems in the failure mode of fatigue are mainly based on the static stress strength interference model and its extended models, which cannot consider dynamic factors in the operational duration and be used for further availability analysis. In this paper, time-dependent reliability models, failure rate models and availability models of belt drive systems are developed based on the system dynamic equations with the dynamic stress and the material property degradation taken into account. In the proposed models, dynamic failure dependence and imperfect maintenance are taken into consideration. Furthermore, the issue of time scale inconsistency between system failure rate and system availability is proposed and addressed in the proposed system availability models. Besides, Monte Carlo simulations are carried out to validate the established models. The results from the proposed models and those from the Monte Carlo simulations show a consistency. Furthermore, the case studies show that the failure dependence, imperfect maintenance and the time scale inconsistency have significant influences on system availability. The independence assumption about the belt drive systems results in underestimations of both reliability and availability. Moreover, the neglect of the time scale inconsistency causes the underestimate of the system availability. Meanwhile, these influences show obvious time-dependent characteristics.

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Analysis of the Internal Characteristics of a Deflector Jet Servo Valve

Hao Yan, Yukai Ren, Lei Yao, Lijing Dong

Chinese Journal of Mechanical Engineering. 2019, 32(2): 31-31. https://doi.org/10.1186/s10033-019-0345-7

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In current research on deflector jet servo valves, the receiver pressure estimated using traditional two-dimensional simulation and theoretical calculation is always lower than the experimental data; therefore, credible information about the flow field in the prestage part of the valve can hardly be obtained. To investigate this issue and understand the internal characteristics of the deflector jet valve, a realistic numerical model is constructed and a three-dimensional simulation carried out that displays a complex flow pattern in the deflector jet structure. Then six phases of the flow pattern are presented, and the defects of the two-dimensional simulation are revealed. Based on the simulation results, it is found that the jet in the deflector has a longer core area and the fluid near the shunt wedge cannot resist the impact of the high-speed fluid. Therefore, two assumptions about the flow distribution are presented by which to construct a more complete theoretical model. The receiver pressure and prestage pressure gain are significantly enhanced in the calculations. Finally, special experiments on the prestage of the servo valve are performed, and the pressure performance of the numerical simulation and the theoretical calculation agree well with the experimental data. Finally, the internal mechanism described by the theoretical and numerical models is verified. From this research, more accurate numerical and theoretical models are proposed by which to figure out the internal characteristics of the deflector jet valve.

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Force Analysis and Curve Design for Laying Pipe in Loop Laying Head of Wire Rod Mills

Shuangji Yao, Marco Ceccarelli, Giuseppe Carbone, Bin Ma

Chinese Journal of Mechanical Engineering. 2019, 32(2): 32-32. https://doi.org/10.1186/s10033-019-0344-8

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Laying head is a high-precision engineering device in hot-rolled high speed wire rod production line. Previously research works are focused on the laying pipe wear-resisting. Laying pipe curve design method based on wire rod kinematics and dynamics analyses are not reported before. In order to design and manufacture the laying pipe, the motion and force process of the wire rod in the laying pipe should be studied. In this paper, a novel approach is proposed to investigate the force modeling for hot-rolled wire rod in laying pipe. An idea of limited element method is used to analysis and calculates the forces between laying pipe inner surface and wire rod. The design requirements of laying pipe curve for manufacturing are discussed. The kinematics and dynamics modeling for numerical calculation are built. A laying pipe curve equation is proposed by discussing design boundary conditions. Numerical results with different laying pipe curves design parameters are plotted and compared. The proposed approach performs good result which can be applied for laying pipe curve design and analysis for engineering application.

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Development and Analysis of the Magnetic Circuit on Double-Radial Permanent Magnet and Salient-Pole Electromagnetic Hybrid Excitation Generator for Vehicles

Xueyi Zhang, Qinjun Du, Jinbin Xu, Yuzhen Zhao, Shilun Ma

Chinese Journal of Mechanical Engineering. 2019, 32(2): 33-33. https://doi.org/10.1186/s10033-019-0334-x

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With the improvement of vehicles electrical equipment, the existing silicon rectification generator and permanent magnet generator cannot meet the requirement of the electric power consumption of the modern vehicles electrical equipment. It is difficult to adjust the air gap magnetic field of the permanent magnet generator. Consequently, the output voltage is not stable. The silicon rectifying generator has the problems of low efficiency and high failure rate. In order to solve these problems, a new type of hybrid excitation generator is developed in this paper. The developed hybrid excitation generator has a double-radial permanent magnet, a salient-pole electromagnetic combined rotor, and a fractional slot winding stator, where each rotor pole corresponds to 4.5 stator teeth. The equivalent magnetic circuit diagram of permanent magnet rotor and magnetic rotor is established. Magnetic field finite element analysis (FEA) software is used to conduct the modeling and simulation analysis on double-radial permanent magnet magnetic field, salient-pole electro-magnetic magnetic field and hybrid magnetic field. The magnetic flux density mold value diagram and vector diagram are obtained. The diagrams are used to verify the feasibility of this design. The designed electromagnetic coupling regulator controller can ensure the stable voltage export by changing the magnitude and direction of the excitation current to adjust the size of the air gap magnetic field. Therefore, the problem of output voltage instability in the wide speed range and wide load range of the hybrid excitation generator is solved.

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Indirect Adaptive Robust Trajectory Tracking Control of Hard Rock TBM with Load Variation of Tunneling Face

Chengjun Shao, Jianfeng Liao, Zhitao Liu, Hongye Su

Chinese Journal of Mechanical Engineering. 2019, 32(2): 34-34. https://doi.org/10.1186/s10033-019-0347-5

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Posture adjustment of open-type hard rock tunnel boring machine (TBM) can be achieved by properly adjusting the hydraulic pressure of gripper cylinder and torque cylinders. However, the time-varying inhomogeneous load acting on tunneling face of TBM and complex stratum working condition can cause the trajectory deviation. In this paper, the position and posture rectification kinematics and dynamics models of TBM have been established in order to track the trajectory. Moreover, there are uncertain parameters and uncertain loads from complex working conditions in the dynamic model. An indirect adaptive robust control strategy is applied to achieve precise position and posture trajectory tracking control. Simulation results show when the position deviation only occurs in Y-axis and the current orientation is parallel with the designed axis, the deviation can be corrected by controlling the pressure of gripper cylinder and the actual trajectory meets the designed axis when TBM is pushed forward 0.14 m in X-axis. If the deviation only occurs in Z-axis, then the deviation can be corrected by controlling torque cylinders. If the position deviation occurs both in Y-axis and Z-axis at the same time, the pressure of gripper cylinder and torque cylinders should be controlled at the same time to rectify the deviation. Simulation results are shown to illustrate the effectiveness and robustness of the proposed controller. This research proposes an indirect adaptive robust controller that can track the planned tracking trajectory smoothly and rapidly.

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Frequency Loss and Recovery in Rolling Bearing Fault Detection

Aijun Hu, Ling Xiang, Sha Xu, Jianfeng Lin

Chinese Journal of Mechanical Engineering. 2019, 32(2): 35-35. https://doi.org/10.1186/s10033-019-0349-3

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Rolling element bearings are key components of mechanical equipment. The bearing fault characteristics are afected by the interaction in the vibration signals. The low harmonics of the bearing characteristic frequencies cannot be usually observed in the Fourier spectrum. The frequency loss in the bearing vibration signal is presented through two independent experiments in this paper. The existence of frequency loss phenomenon in the low frequencies, side band frequencies and resonant frequencies and revealed. It is demonstrated that the lost frequencies are actually suppressed by the internal action in the bearing fault signal rather than the external interference. The amplitude and distribution of the spectrum are changed due to the interaction of the bearing fault signal. The interaction mechanism of bearing fault signal is revealed through theoretical and practical analysis. Based on mathematical morphology, a new method is provided to recover the lost frequencies. The multi-resonant response signal of the defective bearing are decomposed into low frequency and high frequency response, and the lost frequencies are recovered by the combination morphological flter (CMF). The efectiveness of the proposed method is validated on simulated and experimental data.

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Effects of Flexibility and Suspension Configuration of Main Shaft on Dynamic Characteristics of Wind Turbine Drivetrain

Jianjun Tan, Caichao Zhu, Chaosheng Song, Huali Han, Yao Li

Chinese Journal of Mechanical Engineering. 2019, 32(2): 36-36. https://doi.org/10.1186/s10033-019-0348-4

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The current research of wind turbine drivetrain is mainly concentrated in dynamic characteristics of gearbox with a specific suspension of main shaft, such as one-point and two-point suspension. However, little attention is paid to the effects of these suspension configurations on the dynamic responses of wind turbine gearbox. This paper investigates the influences of suspension configurations of main shaft on the dynamic characteristics of drivetrain. For evaluating the dynamic behaviors of drivetrain with multi-stage transmission system more realistically, a dynamic modeling approach of drivetrain is proposed based on Timoshenko beam theory and Lagrange's equation. Considering the flexibility and different suspension configurations of main shaft, time-varying mesh stiffness excitation, time-varying transmission error excitation and gravity excitation, etc., a three-dimensional dynamic model of drivetrain is developed, and the dynamic responses of drivetrain are investigated. Results show that with the one-point suspension of main shaft, the resonance frequencies in gearbox, especially at the low-speed stage, obviously shift to the higher frequency range compared to the gearbox without main shaft, but this trend could be inversed by increasing main shaft length. Meanwhile, the loads in main shaft, main shaft bearing and carrier bearing are greatly sensitive to the main shaft length. Hence, the load sharing is further disrupted by main shaft, but this effect could be alleviated by larger load torque. Comparing to the one-point suspension of main shaft, there occurs the obvious load reduction at the low-speed stage with two-point suspension of main shaft. However, those advantages greatly depend on the distance between two main bearings, and come at the expense of increased load in upwind main shaft unit and the corresponding main bearing. Finally, a wind field test is conducted to verify the proposed drivetrain model. This study develops a numerical model of drivetrain which is able to evaluate the effects of different suspension configurations of main shaft on gearbox.

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Type Synthesis of Lower Mobility Parallel Mechanisms: A Review

Wei Ye, Qinchuan Li

Chinese Journal of Mechanical Engineering. 2019, 32(2): 38-38. https://doi.org/10.1186/s10033-019-0350-x

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Type synthesis of mechanisms aims to systematically determine all possible structures for a specific mobility requirement. Numerous methods based on different theories were proposed for type synthesis of lower mobility parallel mechanisms in past decades. However, there does not exist a comprehensive review on these approaches. Therefore, the goal of this paper is to give such a review, classifying the approaches proposed in the literature into three groups, namely, motion-based methods, constraint-based methods, and other methods. The motion-based methods include the Lie group based method, the G_F set method, the linear transformation method, the POC set method, and the finite screw method. The constraint-based methods involve the screw theory-based method, the virtual chain method, the method based on Grassmann line geometry and line graphs, and the motion constraint generator method. Other methods contain the enumeration approach based on the general CGK mobility formula and the graph theory method. Upon thoroughly analyzing the characteristics and/or limitations of each method, this review provides a well reference to help researchers find an effective synthesis method for innovative design and further scientific investigations for mechanisms.

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2019年, 第32卷, 第2期　
刊出日期：2019-04-16

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2019年, 第32卷, 第2期 刊出日期：2019-04-16

2019年, 第32卷, 第2期　
刊出日期：2019-04-16