Journal of Northeastern University(Natural Science)

Mobile Robot Path Planning Based on Improved Bidirectional RRT^*

WANG Hai-fang， ZHANG Yao， ZHU Ya-kun， CHEN Xiao-bo

2021, 42 (8): 1065-1071. DOI: 10.12068/j.issn.1005-3026.2021.08.001

Abstract ( 1159 )

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Aiming at local optimal path planning of mobile robots in complex environments， a bidirectional rapidly exploring random tree star(Bi-RRT^*)path planning algorithm based on target offset expansion and Cantmull-Rom spline interpolation is proposed. In the Bi-RRT^* algorithm， two search trees are created at the same time， and opposite searches are alternately performed with the target bias of random points selected at a certain probability， in order to improve the overall convergence efficiency of the algorithm. By reselecting the parent node of the current node and rewiring the nodes， the sensitivity to the environment of path planning is enhanced. To ensure the path safe and feasible， the obstacles in environment are expanded and collision detection is performed on the initial path. Redundant nodes are trimmed so that the feasible path length is shortened. Then， the path is smoothed by the Cantmull-Rom spline interpolation. The 2D and 3D comparative experiments were conducted for the improved Bi-RRT^* algorithm based on Matlab and ROS robot simulation platform， respectively， and the experiment results verified the effectiveness and superiority of the improved Bi-RRT^* algorithm.

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Multi-focus Image Fusion with Multi-scale Based on Fractional Order Differentiation

ZHANG Xue-feng， HE Hao

2021, 42 (8): 1071-1078. DOI: 10.12068/j.issn.1005-3026.2021.08.002

Abstract ( 567 )

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Aiming at multi-focus image fusion， the complementary information at each scale is fused in a targeted manner using a multi-scale fusion method. First， the source image is decomposed into a background layer and a detail layer using the L_○0 gradient minimization smoothing method， and then a fractional-order edge detection mask is used to preserve the edge information in the background layer， and a fractional-order gradient energy operator is introduced in the detail layer for weight assignment. The experimental results show that the proposed fractional-order gradient energy operator is more sensitive than the integer-order gradient energy clarity operator， which is consistent with the human visual perception. The fusion method proposed effectively avoids artifacts and block effects in the fused images， and retains the source image information more fully.

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Encrypted Image Search Scheme with Forward Security

GE Yue， LI Yu-xi， ZHOU Fu-cai， ZHANG Xin-yue

2021, 42 (8): 1079-1085. DOI: 10.12068/j.issn.1005-3026.2021.08.003

Abstract ( 541 )

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In most encrypted image search schemes， the information leaked during the update is easily used by attackers. In order to solve this problem， an encrypted image search scheme with forward security is proposed. A Tensorflow machine learning model implements image recognition and an efficient image keyword extraction method is designed， and based on dynamic searchable encryption， a GGM range-constrained pseudorandom function constructs search tokens and a secure encrypted image index that supports dynamic update. In the search phase， the search token and Hash function are used to calculate the matching results， and the privacy of the query is not disclosed. Security analysis and experimental results show that this scheme achieves forward security and guarantees good update performance.

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A Novel Approach to Simulate Particle-Particle Interaction and Dielectrophoretic Dynamics

HU Sheng， WU Huai-jing， LYU Xiao-yong

2021, 42 (8): 1086-1091. DOI: 10.12068/j.issn.1005-3026.2021.08.004

Abstract ( 672 )

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Electrical polarization strength of a particle is calculated by finite element method to obtain the dielectrophoretic and the secondary dielectrophoretic forces. Relying on the commercial software COMSOL Multiphysics 5.3a， the electrical polarization strength can be obtained in the AC/DC module from COMSOL， and then the module of particle tracing for fluid flow(PTF)is used to realize the dynamic simulation of particles on which the dielectrophoretic force， secondary dielectrophoretic force， fluid force and repulsive force are exerted. This novel method in which AC/DC module coupled PTF module in multi-physical fields provides an insight into the particle trajectories with positive or negative dielectrophoresis， which has a good agreement in other particle simulation methods. Whatever positive or negative dielectrophoresis is， these results imply that it is essential to consider secondary dielectrophoretic effect on metal electrodes to improve the prediction of experimental observation.

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Influence of Data Interval Optimization on SSVEP Algorithm Performance

DUAN Zhi-hao， LIU Chong， CHEN Jie， LU Zhi-guo

2021, 42 (8): 1092-1097. DOI: 10.12068/j.issn.1005-3026.2021.08.005

Abstract ( 497 )

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Steady-state visual evoked potential(SSVEP)responses vary greatly among individuals， which results in the quality difference of EEG signals from subjects in different environments. So， the effect of EEG data interval on CCA(canonical correlation analysis) and ECCA(extended canonical correlation analysis) classification results is investigated. The optimal data interval of EEG signals is determined through grid search， then， the EEG features in the optimal data interval are identified by CCA and ECCA， with the recognition results improved. The results show that the information transfer rate(ITR)can be effectively improved by optimizing the starting and ending points of the data interval. The average ITRs of CCA and ECCA classification after interval optimization are (61.18±27.20)bit/min and(71.37±32.24)bit/min， which are 29.89% and 8.3% higher than that of the traditional method which only optimizes the ending point of data interval. The results proved that the performance of SSVEP algorithm can be improved by optimizing data interval.

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Analysis and Optimization of Damping Performance of Suspension System of Hybrid Connected Vehicle

LI Fan-jie ， LI Xiao-peng ， WO Xu， WEN Bang-chun

2021, 42 (8): 1098-1104. DOI: 10.12068/j.issn.1005-3026.2021.08.006

Abstract ( 558 )

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To further improve the damping performance of automobile suspension， the structure and parameters of automobile suspension are optimized. Based on the electromechanical similarity theory， a suspension structure of hybrid connected vehicle with spring， damper and inerter is proposed， and the multi-objective genetic algorithm is used to optimize the parameters of vehicle suspension damping system. By solving the dynamic equation， the vibration response of vehicle suspension damping system under road pulse excitation is analyzed in time domain， and the influence of parameter optimization on suspension damping performance is analyzed in frequency domain. The results show that， compared with the traditional vehicle suspension， the proposed hybrid connected vehicle suspension structure can effectively reduce the resonance peak of the vehicle damping system and improve the damping performance of the vehicle suspension. Compared with the initial design parameters， the parameters obtained by using the multi-objective genetic algorithm can further improve the damping performance of the vehicle suspension.

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Fault Diagnosis Method of Rolling Bearing Based on VMD-DBN

REN Zhao-hui， YU Tian-zhuang， DING Dong， ZHOU Shi-hua

2021, 42 (8): 1105-1110. DOI: 10.12068/j.issn.1005-3026.2021.08.007

Abstract ( 671 )

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In order to identify the vibration signal features of faulty bearing， a feature extraction method of bearing vibration signals based on the variational mode decomposition (VMD) and deep belief network (DBN) is proposed. First， the signal is decomposed based on VMD and the parameters of each modal component are determined by the modal component spectrogram， thus several modal components being obtained. Then an unsupervised feature extraction method based on DBN， which has powerful feature extraction ability， is used to map the modal components obtained to one dimension， and the DBN features of each component are merged to form feature vectors and input into particle swarm optimization support vector machine (PSO-SVM) for fault diagnosis. Experimental verification and comparative analysis show the feasibility and superiority of the VMD-DBN method proposed.

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Dynamic Modeling Method of Bolted Joint Interfaces Based on Nonlinear Transversely Isotropic Virtual Material

MA Hui， YU Ming-yue， GAO Ang， ZHAO Chen-guang

2021, 42 (8): 1111-1119. DOI: 10.12068/j.issn.1005-3026.2021.08.008

Abstract ( 471 )

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To simulate the nonlinear dynamic characteristics of bolted joint， a dynamic modeling method of bolted joint based on nonlinear transversely isotropic virtual material is proposed. Based on the finite element method， 8-node solid elements are used to construct the connected parts and the bolted joint that is simulated by the transversely isotropic virtual material， and the virtual material is fixed to the connected parts. The nonlinear virtual material is used to simulate the nonlinear stiffness characteristics of the bolted joint under different external harmonic excitation forces. In order to make the calculation of the nonlinear model more accurate， the nonlinear transversely isotropic virtual material is partitioned， and the virtual material parameters of each region are determined by the deformation of the virtual material in the region. Finally， the dimension of the model is reduced partly and the amplitude frequency response of the model is solved in time domain. The feasibility and effectiveness of the as-proposed modeling method are verified by comparing the theoretical calculation results with that of the experiments.

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Dynamic Recrystallization Behavior of Grinding Surface Based on 40Cr High Temperature Dynamic Mechanical Properties

YAO Yun-long， XIU Shi-chao， SUN Cong， HONG Yuan

2021, 42 (8): 1120-1126. DOI: 10.12068/j.issn.1005-3026.2021.08.009

Abstract ( 566 )

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Through the split Hopkinson pressure bar experiment， the true stress-true strain curves of 40Cr alloy steel at high temperature and high strain rate are obtained. Then， the critical conditions for dynamic recrystallization of 40Cr are determined. An analytical method and experimental method are used to solve the temperature field and plastic strain field distribution of the grinding strengthening layer(GSL). The results show that the GSL has a large temperature and plastic strain gradient in the direction of grinding depth. The austenite transformation occurs within 150μm of the GSL. The maximum temperature of the ground surface can reach 1060℃. The severe plastic deformation can occur within 60μm of the ground subsurface， which reaches the critical condition of the dynamic recrystallization(DRX). With the larger grinding depth， the plastic strain of GSL increases， the DRX behavior is more sufficient， and the degree of microstructure refinement is higher.

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Numerical Modeling for the Material Interface of Heterogeneous Rock at Mesoscale and Hydraulic Fracturing Based on the PHF-LSM-MT

LI Ming， ZHAO Qi， ZHANG Yan-kun， LIANG Li

2021, 42 (8): 1127-1135. DOI: 10.12068/j.issn.1005-3026.2021.08.010

Abstract ( 484 )

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The permeability-based hydraulic fracture(PHF) method is integrated with the level set method(LSM) and Mori-Tanaka(MT) model to study the hydraulic fracture propagation in heterogeneous rock(HR)with the mesoscale material interface being considered. In the proposed method， the PHF method is for simulating the hydraulic fracture propagation， and the LSM is for capturing the material interface with the mesoscale material properties of integration points being homogenized by MT model. To verify the mesoscale homogenization modeling procedure for HR， numerical simulations were carried out to estimate the effective elastic properties of HR with the volume fraction and inclusions’ dimension being taken into account， and the results indicate that the proposed method is capable of homogenizing the material properties at mesoscale. Numerical simulations of hydraulic fracture propagation in HR with the mesoscale material interface show the characteristics of hydraulic fracture development， the features of pore pressures and stress paths of the equivalent fracture zone.

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Influence of Contact Behavior on Stress Wave Velocity and Energy in Granular Materials

PAN Yu， WANG Jiao， CHU Xi-hua

2021, 42 (8): 1136-1142. DOI: 10.12068/j.issn.1005-3026.2021.08.011

Abstract ( 565 )

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The discrete element method is used to study the energy attenuation and wave velocity change of granular system in the process of wave propagation with linear-elastic contact model， Hertz contact model and linear parallel bond contact model. Meanwhile， the influences of elastic modulus on wave propagation in granular materials are also studied. Finally， the Hertz contact model is used to study the wave velocity and the energy attenuation of granular materials under different confining pressures. The results show that the wave velocity and energy attenuation rate of wave propagation are different with different contact models; when the sample is arranged from regular to random， the wave velocity is smaller and the energy attenuation rate is larger; with the increase of elastic modulus of particles， the wave velocity increases logarithmically; in the process of wave propagation， the energy dissipates rapidly， and with the increase of confining pressure， the wave velocity and energy attenuation rate both increase.

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Impact on the Stability of Surface Construction by Filling Method of Deep Complex Gold Ore Body

ZHANG Chao， SONG Wei-dong， FU Jian-xin， LIU Jian-bo

2021, 42 (8): 1143-1152. DOI: 10.12068/j.issn.1005-3026.2021.08.012

Abstract ( 477 )

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In order to study the effect of deep complex orebody mining on the stability of surface buildings， the probability integral method was used to calculate the safe mining depth. The 3D Mine-Rhinoceros-FLAC^3D coupling method was used to construct a refined 3D model of mining area to study the surface safety and deformation characteristics. The results are as follows: when deep ore body mining is carried out by filling method， uniform settlement deformation occurs on the surface; the maximum principal stress increases polynomially with the increase of mining steps， the minimum principal stress increases linearly， and the disturbance height presents a normal distribution trend along the ore body; the mining of ore body causes ‘basin deformation’ over the ore body， and disturbance boundary is delineated according to surface safety parameters; when the subsidence deformation value is less than 10mm and the change rate is greater than 0.5， or when the subsidence deformation value is greater than 10mm but less than 20mm and the change rate is greater than 1.5， the whole surface subsidence is negligible.

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Coupling Evaluation Method of the Construction Risk for Subway Deep Foundation Pit

WANG Qian-kun， KANG Xian-wei， ZHU Ke

2021, 42 (8): 1152-1158. DOI: 10.12068/j.issn.1005-3026.2021.08.013

Abstract ( 549 )

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A set of index system and method suitable for risk assessment of subway deep foundation pit construction was developed to analyze and judge the risk level of a project， and to guide and improve the risk management of site construction. Firstly， the risk evaluation system with 29 indexes of subway deep foundation pit construction was established according to FTA， 4M1E system safety theory and literature analysis. Secondly， the interaction between risk factors was analyzed with the risk coupling theory， and the construction risk evaluation model is established based on C-OWA operator and interaction matrix method. As a case， the construction risk level of a subway deep foundation pit construction project was calculated by the evaluation index system and method proposed， and the results show that the risk level was medium， which accords with the actual situation of construction project， thus verifying the feasibility of the method above mentioned.

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Calculation Model of Flexural Stiffness of STS Structure and Parameters Optimization

JIA Peng-jiao， SHI Pei-xin， GUAN Yong-ping， ZHAO Wen

2021, 42 (8): 1159-1165. DOI: 10.12068/j.issn.1005-3026.2021.08.014

Abstract ( 481 )

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As a new buried excavation support system， the application and popularization of steel tube slab (STS) method are limited due to the unclear deformation mechanism of STS structure and lack of further optimization of the connection parameters between the tubes. So， a series of three-dimensional finite element models (FEMs) is established and verified by laboratory tests to investigate the influence of the flange thickness and diameter of bolts on flexural stiffness of STS structure. By means of SPSS software and normalization method， it is indicated that when the ratio of the diameter of bolts to the flange thickness ranges from 2.0 to 2.5， the deformation state of the STS structure is the most appropriate. Subsequently， a calculation model of flexural stiffness of STS structure is proposed according to experimental and numerical results. Reasonability of the presented model is evaluated， and the error is less than 20%.

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Functional Experiment and Simulation Study of Explosion Isolation Flap Valves

LI Gang， KANG Jin， CUI Zhen， HU Peng

2021, 42 (8): 1166-1173. DOI: 10.12068/j.issn.1005-3026.2021.08.015

Abstract ( 508 )

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In order to study the influencing factors and mechanism of the function of dust explosion isolation flap valves， the corn starch isolation experiments were conducted based on the 1m³ standard explosion test system and the DN600 flap valve. In addition， the Fluent software was applied to simulate the isolation process of the flap valve at different installation distances. The two-dimensional corn starch dust explosion model was built and the dynamic process of flap closing was solved by the 6 DOF dynamic mesh model. The results show that the pressure development， flame propagation behaviors and flap closing process are consistent with the experiment. Furthermore， the flow velocity distribution in the flow field during the flap closing process is revealed， and the speed of the flap movement is affected significantly by the rising rate of dust explosion pressure. The increasing rate of explosion pressure rise often leads to the increasing closing speed. The backflow behind the valve forms due to the negative pressure， and the minimum installation distance of the DN600 flap valve should be 6 to 7 times of its pipe diameter.

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Propagation of Laminar Premixed Flames of CH₄/H₂/Air Mixtures at Elevated Temperatures

SHANG Rong-xue， YANG Yue， LI Gang

2021, 42 (8): 1173-1179. DOI: 10.12068/j.issn.1005-3026.2021.08.016

Abstract ( 561 )

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The laminar flame speeds of CH₄/H₂/air mixtures were experimentally studied at elevated initial temperatures using the Bunsen burner method combined with the Schlieren technique， and the corresponding cases were computed using CHEMKIN-PRO. The effect of initial temperatures on the propagation characteristics of laminar premixed flames was discussed from the perspectives of thermodynamics and chemical kinetics. The results show that the laminar flame speeds of the mixtures at 293-500K can be predicted well by GRI-3.0 mechanism. The greater increments of laminar flame speeds of mixtures are presented at higher H₂ fractions under all tested initial temperatures. The laminar flame speeds and adiabatic flame temperatures of mixtures almost linearly increase with a growth of initial temperatures with the same equivalence ratios. With the rise of initial temperatures， the dominant promotion of H+O₂=O+OH on the mass burning rates of mixtures can be enhanced by the great growth of the mole fractions of H radicals. Therefore， the laminar flame speed of CH₄/H₂/air mixtures significantly increases at elevated temperatures.

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Time-Varying Mechanical Properties of Laminated Scrap Tire Rubber Pads Subjected to Aging and Loading

ZHANG Guang-tai， WU Rui， LI Xue-fan， SAIMAITI Adili

2021, 42 (8): 1180-1186. DOI: 10.12068/j.issn.1005-3026.2021.08.017

Abstract ( 449 )

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To investigate the time-varying vertical mechanical properties of laminated scrap tire rubber pads (STRPs) within the design reference period of building structure (50 years)， the tests of aging coupled with loading were carried out on the 61 groups of 7-layer STRP bearings that were subjected to aging for 31， 62， 93， 124， and 154h and loading of 5MPa， separately， and the traditional aging tests without loading were also carried out under the same conditions. And then， the results of two groups were compared. The STRP failure feature， vertical bearing capacity， and vertical stiffness/deflection in different aging time were studied through vertical mechanical experiment and scanning electron microscopic. It is concluded that， as the aging time increases， the cracks of STRP surface propagate， the carbon black particles inside the tire move toward the surface of STRP， the vertical stiffness of STRP increases but vertical deformation performance of STRP declines， while the ultimate bearing capacity of STRP changes little.

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Tail Risk Spillover Effect Between Oil Market and Stock Market:Based on Variational Mode Decomposition and Dynamic Copula Function

HUANG Wei-qiang， ZHAO Yang， YAO Shuang

2021, 42 (8): 1186-1193. DOI: 10.12068/j.issn.1005-3026.2021.08.018

Abstract ( 599 )

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The variational mode decomposition method is used to decompose the raw return series into sub-sequences with different investment horizons.Based on the dynamic Copula function， the conditional value at risk index(VaR and CoVaR) are quantified to analyze the short- and long-term tail risk spillovers between oil market and stock market in the bear and bull markets. The empirical research results show that there is a two-way tail risk spillover effect between the oil market and the stock market. Firstly， in terms of the intensity of risk spillover， the tail risk spillover effect of the oil market on the stock market is significantly stronger than that of the stock market on the oil market. Secondly， in terms of the direction of risk spillover， the tail risk spillovers from the stock market to the oil market are all positive， the upside risk spillovers from the oil market to the stock markets of most countries are positive， and the downside risk spillovers from the oil market to the stock markets of all countries are positive. Finally， the long-term tail risk spillover effect between the oil market and the stock markets of most countries is stronger than the short-term tail risk spillover effect.The research results are beneficial to the formulation of relevant market investment strategies and the prevention of extreme risk contagion.

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Social Trust， Separation of Two Rights and Capital Structure Deviation: Based on an Empirical Test of China’s Small and Medium-Sized Listed Companies

LIU Ying， ZHONG Tian-li

2021, 42 (8): 1194-1202. DOI: 10.12068/j.issn.1005-3026.2021.08.019

Abstract ( 447 )

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The regulatory role social trust plays in the separation of ultimate controlling shareholders’ control right and cash flow right and capital structure deviation is explored using the data of SMEs. The empirical results show that the greater the separation degree of the two rights， the greater the degree of capital structure deviation， and the comprehensive level of social trust can alleviate the adverse effect of the separation of the two rights on capital structure deviation. According to the state-owned and non-state-owned nature of ultimate controlling shareholders and the strong control mode and weak control mode， a further empirical test shows that the different ownership nature and different control modes of ultimate controlling shareholders have different effects on capital structure deviation due to the separation of the two rights， and there are certain differences in the regulatory role of social trust between the two.

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Manufacturers’ Financing Strategy: Bank Credit， Retailer Credit or Blockchain-Driven SCF

TANG Dan， ZHUANG Xin-tian

2021, 42 (8): 1202-1209. DOI: 10.12068/j.issn.1005-3026.2021.08.020

Abstract ( 490 )

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Under the revenue-sharing contract， bank credit financing， retailer credit financing and blockchain-driven SCF (supply chain finance) are compared， the optimal strategies of supply chain actors are analyzed under different financing models， and the supply chain performances are studied as parameters vary. Research shows that if the capital cost of retailers is less than that of manufacturers， retailer credit financing is a better financing strategy; there are two threshold points of platform usage fee， and when the platform usage fee is lower than that of the low threshold point， blockchain-driven SCF is superior to the other two financing strategies. Moreover， as the revenue sharing rate and the profits of manufacturers increase， the profits of retailers decrease.

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Vehicle Scheduling Model and Optimization of Crowdsourcing Logistics Distribution

DU Zi-chao， LU Fu-qiang， WANG Su-xin， WANG Lei-zhen

2021, 42 (8): 1210-1216. DOI: 10.12068/j.issn.1005-3026.2021.08.021

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Considering the distribution characteristics of crowdsourcing order grabbing/dispatching modes， a crowdsourcing distribution vehicle scheduling model is established， in which two distribution modes are combined， complementing each other. According to the characteristics of the model， a hybrid algorithm of ant colony coupled with quantum particle swarm optimization is proposed to solve the model. Taking Qinghu cold chain distribution in Shenzhen as an example， the crowdsourcing distribution model is compared with the traditional model and order grabbing/dispatching models from the perspective of distribution distance and cost. The experiment fully proves the effectiveness of the crowdsourcing distribution model. The optimization results of hybrid algorithm proposed is compared with that of the ant colony algorithm and particle swarm optimization algorithm， thus verifying the effectiveness of the proposed algorithm.

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