Volume 47,Issue 5,2024 Table of Contents

1 SEA performance analysis based on parameter estimation-sliding mode impedance control

CAO Xuepeng , ZHANG Zheng , LI Caihong , LU Hang

2024, 47(5):1-12. DOI: 10.11835/j.issn.1000-582X.2023.226

[Abstract](263) [HTML](46) [PDF 1.59 M](405)

Abstract:
Heavy quadruped robots are subjected to uncertain impact loads during foot-to-ground contact and gait transition, which can easily lead to excessive load on the foot mechanism and structural impact damage. Therefore, a sliding mode impedance control method based on environmental parameter estimation (EPESM) was proposed to solve the problem of poor dynamic performance when using hydraulic series elastic actuators (SEA) as foot ends in unstructured environments. Based on the piston displacement transfer function of the valve controlled hydraulic cylinder, an SEA impedance control model based on the position inner loop is established, with PID serving as the basic controller. To improve the dynamic performance of SEA impedance control, a stable adaptive environment parameter estimation method based on Lyapunov’s second method is constructed to compensate for the expected SEA position using feed forward compensation. To improve the dynamic performance and adaptability of adaptive environmental parameter estimation methods at different stages of SEA work, fuzzy control methods are used to optimize the adaptive parameters in these methods. Based on the SEA state equation, a sliding mode controller and a PID controller are constructed for dynamic performance comparison and analysis. Simulation results show that under variable SEA spring stiffness and variable ambient stiffness conditions, the response speed of EPESM impedance control is significantly faster. The adjustment time can be significantly reduced from an average of 5 s to within 1 s, achieving faster expected displacement and expected contact force, while keeping the steady-state error slightly reduced and the contact force error within ±6 N. Under dynamic tracking conditions, EPESM impedance control exhibits better dynamic performance, maintaining a phase delay within 0.2 s and an amplitude error of 5.2 % for an extended period after quickly entering the tracking state.

2 Simulation of energy-saving control strategy for independent metering electro-hydraulic system based on hydranlic-resistance full-bridge network

LIU Guoping , XIONG Jianfeng , LU Zhenyu , ZONG Huaizhi , ZHANG Junhui , CAO Tangmao , WU Jianpeng

2024, 47(5):13-23. DOI: 10.11835/j.issn.1000-582X.2023.225

[Abstract](279) [HTML](43) [PDF 3.98 M](356)

Abstract:
To address issues such as high throttle loss, high energy consumption, and low efficiency in traditional electro-hydraulic control systems, a novel electro-hydraulic control system characterized by independent metering is introduced in this study. This system incorporates a full-bridge hydraulic resistance network, and its energy-saving control strategy is extensively investigated under typical four-quadrant load. Comprising five two-position two-way proportional valves, the hydraulic-resistance full-bridge electro-hydraulic system is categorized into three control modes: a traditional three-position four-way control mode, an independent metering control mode, and a load sensitive control mode. In the traditional mode, the opening control of the two load ports mimics three-position and four-way inlet and outlet coupling. In the independent metering mode, one cavity regulates the flow, while the other cavity controls the full opening of the valve port. The load-sensitive mode ensures a fixed pump outlet pressure higher than the intake cavity pressure, achieving load-sensitive functionality. Additionally, a flow regeneration circuit is used for energy-saving control across all three modes. Results of combined simulation using AMESim+MAT2 show that compared with the traditional three-position four-way valve mode, the three-position four-way flow regeneration mode, the independent metering flow regeneration mode, and the load sensitive mode can achieve energy savings of 43.38%, 65.27%, 77.91% and 83.58%, respectively.

3 Numerical simulation of heat transfer characteristics and heat dissipation optimization for electromagnets

LI Yingjie , CHEN Chuan , ZHANG Yu , LI Qiang , SI Guolei , SONG Peng

2024, 47(5):24-36. DOI: 10.11835/j.issn.1000.582X.2024.05.005

[Abstract](256) [HTML](83) [PDF 3.35 M](671)

Abstract:
Electromagnets, serving as core hydraulic components in electro-hydraulic control systems, are widely applied in aerospace and petroleum industries. The operational generation of Joule heat and electromagnetic loss results in rapid temperature increase, local thermal stress and uneven expansion deformation, significantly affecting stability and service life. The evolution of temperature, stress and deformation in the electromagnet was studied using finite element software, and the influence of heat dissipation, with considering both heat conduction sleeve and forced convection, on its thermal performance was analyzed. The results show that the maximum temperature, thermal stress and deformation of the electromagnet exhibit a linear increase with the increase of the coil power. Additionally, the steady-state maximum temperature, deformation and thermal conductivity demonstrate a linear decrease with an increase in sleeve thickness, with the temperature drop recorded at 12.5 ℃/mm. Moreover, as the flow rate rises, there is a notable decrease in maximum temperature, thermal stress and deformation, within a temperature drop range of 45.5 ℃/(m·s^-1). This indicates that both enhanced heat conduction and convection contribute to improving the thermal performance of electromagnet, with convection exhibiting a more significant effect.

4 Influences of the components of magnetorheological grease on its dynamic magnetorheological performances

HU Zhide , ZHANG Hansong , ZHANG Shihao , ZHAO Hujun , XU Chunxia , JIANG Haoyang

2024, 47(5):37-46. DOI: 10.11835/j.issn.1000-582X.2022.122

[Abstract](217) [HTML](38) [PDF 2.54 M](375)

Abstract:
Magnetorheological grease (MRG) consisting of different types of carriers and magnetic particles was prepared with the in-situ saponification method, and the influences of different carriers and magnetic particles on the magnetorheological performances of MRG were tested with a rheometer. The suspension stability of MRG was tested by direct observation. The experimental results indicate that the skeleton microstructures inside MRGs can be controlled by changing the type of base oil and its viscosity, so as to effectively improve the magnetorheological performance and suspension stability of MRG; and larger magnetic particles are likely to improve the mobility of MRGs, contribute to stronger microstructures, and thus enhance the magnetorheological response of MRGs.

5 AEB system control strategy considering vehicle motion prediction

WEI Minxiang , ZHENG Ling , YANG Wei

2024, 47(5):47-56. DOI: 10.11835/j.issn.1000-582X.2022.113

[Abstract](127) [HTML](82) [PDF 1.46 M](456)

Abstract:
To address the issues of poor corner adaptability and discomfort in the autonomous emergency braking (AEB) system during cornering, a control strategy for the AEB system is proposed. This strategy is based on Gaussian process motion prediction, with variable curvature corners and braking comfort taken into account. A road model is established by using cubic spline curves to locate the obstacle and calculate the relative distance. Taking into account the nonlinear characteristics of vehicle motion and the effect of time, a vehicle motion prediction model based on Gaussian process theory is developed. A hierarchical early warning and braking control strategy based on predicted collision time is designed. The results of the co-simulation show that the proposed control strategy can effectively achieve collision avoidance, solving the AEB system’s curve adaptability and braking comfort problems under complex dynamic conditions.

6 Starting control of wet DCT vehicle considering clutch friction performance attenuation

RAO Kun , HU Minghui , QIN Datong

2024, 47(5):57-66. DOI: 10.11835/j.issn.1000-582X.2022.118

[Abstract](99) [HTML](91) [PDF 2.96 M](491)

Abstract:
A dynamic model of the starting process for a wet dual clutch transmission (DCT) vehicle, reflecting changes in clutch friction coefficient and the attenuation of clutch performance, is established. Taking minimum jerk intensity, friction work and starting sliding time as optimization objectives, the optimal transmission torque of the clutch during the vehicle starting process is determined by using the linear quadratic regulator (LQR). To address the impact of clutch performance attenuation and the variation of clutch friction coefficient with the sliding velocity on clutch pressure control, a nonlinear robust control strategy for clutch pressure is proposed. This strategy is designed to track the optimal transmission torque obtained by LQR. Results show that the proposed strategy can effectively track the optimal transmission torque even under changes in clutch friction coefficient, with an average tracking error of about 0.02 N·m. In comparison with the PID control strategy, it exhibits a more accurate control effect and greater robustness.

7 Architecture design of flight control system for electric vertical takeoff and landing aircraft based on safety analysis

LIU Jujiang , TAN Yusong

2024, 47(5):67-75. DOI: 10.11835/j.issn.1000-582X.2023.215

[Abstract](244) [HTML](99) [PDF 2.89 M](662)

Abstract:
The flight control system serves as the key airborne system for electric vertical takeoff and landing (eVTOL) aircraft, necessitating safety standards akin to those applied to civil aircraft. This study introduces redundancy design technology for the flight control computer, sensor and actuator in eVTOL aircraft flight control systems. It proceeds to design an architecture adhering to safety requirements in accordance with airworthiness regulations. The rotor configuration of eVTOL aircraft is considered, and typical functional hazards are analyzed. Safety analysis is carried out using fault tree analysis technology. The results show that the flight control system architecture designed in this study can effectively address the typical functional hazards, meeting the stipulated failure probability requirements.

8 Optimization design for TPMS lattice structures combining density gradient with hybridization

ZENG Yuanhui , ZHAO Miao , ZHANG Zhengwen , ZHOU Hailun

2024, 47(5):76-86. DOI: 10.11835/j.issn.1000-582X.2022.120

[Abstract](167) [HTML](29) [PDF 4.59 M](774)

Abstract:
The triply periodic minimal surface (TPMS) lattice structures have attracted extensive attention from scholars worldwide. In practical applications, these lattice structures are typically designed optimally to meet the requirements of both lightweight and load-bearing capacity. However, current optimal designs for TPMS lattice structures are limited to density gradients, and the influence of loading directions on their mechanical properties has not been comprehensively considered. To address this gap, the anisotropic characteristics of TPMS lattice structures were investigated. Their equivalent elastic matrixes were calculated by using the homogenization method, and three-dimensional Young’s modulus diagrams were generated with Matlab. The results showed distinct anisotropy characteristics for different types of TPMS lattice structures. For instance, the W structure exhibited higher strength in the axial direction [100] and weaker strength in the diagonal direction [111]; whereas the P structure showed the opposite trend. Subsequently, an optimization design method was proposed, combining density gradient with hybridization, considering both density distribution and principal stress directions. The optimization process involved topology optimization of a cantilever beam structure, and mapping the obtained density cloud to the relative density distribution of the lattice structure. Based on the anisotropic characteristics of TPMS lattice structures, W and P lattice cells were selected to fill the cantilever beam, aligning the principal stress directions with the strong mechanical properties of the lattice cells. After reasonable distribution of TPMS lattice cells of different types, they were smoothly connected by an activation function. Finally, the relative density and lattice cell type distributions were combined to obtain a density-graded hybrid lattice structure. The load-bearing performances of lattice structures before and after optimization designs were compared through finite element analysis. The results showed that the stiffness of density gradient W and P lattice structures was significantly improved compared with uniform structures. Moreover, the stiffness of the graded hybrid lattice structure was the highest, surpassing the density gradient W and P lattice structures by 4.63% and 33.63%, respectively. This demonstrates that hybridization design, achieved through a reasonable distribution of different lattice cells according to principal stress directions, can further improve overall stiffness. The established optimization method, combining density gradient with hybridization for TPMS lattice structures, provides a guidance for their application in lightweight designs.

9 A new path planning strategy for unmanned surface vehicle based on improved crow searching algorithm

LIN Weiqing , LIN Xiufang , CHEN Guotong , HUANG Hui

2024, 47(5):87-97. DOI: 10.11835/j.issn.1000-582X.2023.216

[Abstract](116) [HTML](33) [PDF 2.13 M](350)

Abstract:
Becaused of the actual navigation requirements of unmanned surface vehicles, the planned path should meet the criteria of smoothness and economy. Therefore, a novel path planning strategy based on an improved crow search algorithm combining straight lines and circular arc turns is proposed. A new path fitting method is introduced to optimize the number of turning points and address the issue of arc transition at turning points. This method overcomes the problem of frequent direction adjustments caused by B-spline curve paths for unmanned surface vehicles, while ensuring that they can achieve steering while maintaining a stable speed, thereby improving navigation stability and economy. Based on this, an improved crow search algorithm is introduced to optimize the location of path turning points. The improvement of the algorithm is mainly reflected in three aspects: the use of a reverse learning strategy to optimize the quality and the diversity of the initial population, the proposal of a dynamically changing awareness probability to improve the global search ability of the initial segment and the local search ability of the final segment of the algorithm, and the utilization of the Levy flight strategy to improve the directionality and the effectiveness of the search. The simulation results show that the proposed new path fitting method is superior to the B-spline curve fitting method and the straight line segment fitting method. Building on this fitting method, the improved crow search algorithm, the standard crow search algorithm, the differential evolution algorithm, and the genetic algorithm are used to optimize the location of the path turning point. Iterative calculation and variance analysis results demonstrate that the proposed improved crow search algorithm exhibits higher convergence accuracy and robustness compared to the other three algorithms, effectively addressing practical problems in unmanned surface vehicle path planning.

10 Dual-stage feature selection for short-term load forecasting based on mRMR-IPSO

JIAO Lingxiao , ZHOU Kai , ZHANG Zixi , HAN Fei , SHI Weijun , HONG Ye , LUO Chaofeng

2024, 47(5):98-109. DOI: 10.11835/j.issn.1000-582X.2023.218

[Abstract](96) [HTML](23) [PDF 2.89 M](565)

Abstract:
Power load exhibits characteristics of temporal and spatial variation and is affected by various factors. In short-term load forecasting, an excessive number of input features can cause dimensionality disasters and lead to poor model prediction performance. Therefore, selecting a reasonable input feature set is crucial. This article proposes a novel feature selection method for short-term load forecasting–the mRMR-IPSO two-stage method. The max-relevance and min-redundancy (mRMR) criterion is employed to rank the original features, considering both the correlation between input and output features and the redundancy among input features. This process filters out less impactful features ranked lower and initially selects these significantly influencing the prediction. Then, an improved particle swarm optimization (IPSO) algorithm-based search strategy is adopted. The prediction accuracy of the LightGBM model is used as the fitness function during the search, facilitating the selection of primary feature subsets and obtaining optimal feature subsets. Calculation examples show that the proposed method improves prediction accuracy while substantially reducing the original feature set.

11 Digital twin system for TEG dehydration of natural gas device

WU Shuai , YIN Aijun , ZHANG Bo

2024, 47(5):110-121. DOI: 10.11835/j.issn.1000-582X.2023.104

[Abstract](97) [HTML](39) [PDF 4.47 M](395)

Abstract:
The digital twin concept completes the mapping and interaction between physical space and digital space, showing great potential for development in the industrial field. With considering the low detection efficiency of natural gas dehydration performance parameters and the inability to optimize gas station process parameters online, this paper applies the digital twin concept in the chemical industry to establish an overall framework of the digital twin system for triethylene glycol(TEG) dehydration. On one hand, the geometric model of the twin system is constructed by integrating physical devices. On the other hand, the flow model dehydration system technology is established based on the real-time driving of physical data. Finally, the twin model of dehydration is established by designing virtual-real mapping model, completing the mapping of physical space and digital space, which enables the parallel operation of the physical device and the virtual device. Through the proposed digital twin system, real-time prediction of natural gas water dew point and other dehydration performance parameters can be achieved. To achieve the goal of low power consumption, the optimization of dehydration process parameters is realized by combining optimization algorithms with the twin model, thereby improving economic efficiency.

12 Geometric structures, stabilities and properties of V₂Si

n–/0

(n=8~17) clusters

LI Chenggang , SHEN Zigang , CUI Yingqi , TIAN Hao , DING Yanli , REN Baozeng

2024, 47(5):122-132. DOI: 10.11835/j.issn.1000-582X.2022.128

[Abstract](100) [HTML](48) [PDF 4.30 M](605)

Abstract:
The study of silicon clusters has led to significant interest in transition metal atoms doped silicon clusters. In order to provide robust guidelines for future experimental and theoretical investigations of vanadium doped silicon nanomatrials, the geometric structures, stabilities and properties of V2Sin-/0 (n=8~17) clusters were systemically studied using density functional theory. Firstly, the lowest and lower lying energy structures of V2Sin-/0(n=8~17) clusters were globally predicted using the CALYPSO (crystal structure analysis by particle swarm optimization) searching method via the particle swarm optimization algorithm. Geometry optimization at the B3LYP/6-311+G(d) level revealed that two vanadium atoms tend to form V₂ bonds encapsulated gradually into silicon cages with an increasing number of silicon atoms. Secondly, based on the lowest energy structures, calculations of the average binding energy, second order energy difference, and HOMO-LUMO gaps indicated that the V2Si12-/0 clusters exhibit higher stability, respectively. In addition, magnetic properties analyses revealed that the total magnetic moment is zero for the closed-shell structures of V₂Si_n (n=8~17) clusters; However, the open-shell structures of V₂Si_n (n=8~17) clusters have magnetic moments with values of 1 μB. Upon polarizability analysis, V2Si8-/0 clusters with the highest mean dipole polarizability possess stronger nonlinear optical properties. Furthermore, the simulated PES(photoelectron spectroscopy), IR (infrared), and Raman spectra can provide theoretical guidance for future experimental investigations. Finally, the lowest energy structures of V₂Si_n (n=8~17) clusters are stable thermodynamically. Moreover, the heat capacity at constant volume (C_v) increases with the increasing of temperature, and standard entropy (S) decreases with temperature increasing.

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