交通运输工程学报

Aging behaviors of nanoscale mechanical properties of asphalt phases

WANG Ming, LIU Li-ping

Abstract: The original, short-term aging and long-term aging base asphalts and SBS modified asphalts were selected as the research objects, the atomic force microscopy with quantitative nano mechanical(QNM) property function mode was used to measure the mechanical properties of the asphalts in nanoscale phases. The software Nano Scope Analysis was applied to quantitatively analyze the mechanical images of asphalt phases. Two indicators such as the phase modulus and adhesion were mostly analyzed. The Halpin-Tsai model in the field of mesoscale mechanics was used to study the composite behaviors of mechanical properties of the asphalts in multiple phases, and the aging behaviors of mechanical properties of the asphalt phases in nanoscale were investigated. Analysis result shows that the nanoscale moduli of bee phase and base phase in the base asphalt are concentrated at 600.0 and 18.3 MPa, respectively, and the corresponding nanoscale adhesion are concentrated at 10.3 and 18.6 nN, respectively. The nanoscale moduli of bee phase and base phase in the SBS modified asphalt are concentrated at 899 and 35 MPa, respectively, and the corresponding nanoscale adhesion are concentrated at 30.2 and 38.4 nN, respectively. For the base asphalt, the composite moduli of original, short-term aging and long-term aging asphalts are 111, 138, and 187 MPa, respectively, and the composite adhesion are 16.7, 14.3, and 4.2 nN, respectively. For the SBS modified asphalt, the composite moduli of original, short-term aging and long-term aging asphalts are 158, 313, and 547 MPa, respectively, and the composite adhesion are 32.2, 35.0, and 15.8 nN, respectively. In the nanoscale phase structure of asphalt, the bee phase has a high modulus and a low adhesion, while the base phase has a low modulus and a high adhesion. The phase modulus and adhesion of SBS modified asphalt are significantly higher than that of base asphalt. As the aging degree increases, the mechanical properties of asphalt phases change, and the aging behaviors of different phases vary significantly. Therefore, the QNM technology can effectively identify the nanoscale mechanical properties of asphalt phases, and the Halpin-Tsai model can be used to quantify the composite behaviors of mechanical properties of asphalt phases.More>

2019, 19(6): 1-13. doi: 10.19818/j.cnki.1671-1637.2019.06.001

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Rheological property of polyphosphoric acid modified asphalt

WEI Jian-guo, SHI Song, ZHOU Yu-ming, LI Ping, CHEN Zhi-yuan, GUAN Yang

Abstract: To study the effect and action mechanism of polyphosphoric acid(PPA) on the asphalt performance, the effects of PPA on the chemical compositions of different matrix asphalts were studied by performing the four-component analysis test and three major indices test of asphalt. Based on the dynamic shear rheometer(DSR), the temperature scanning test and frequency scanning test of asphalt were carried out. The changing trends of rheological properties of PPA modified asphalt, PPA/SBS modified asphalt and PPA/rubber powder modified asphalt with different ratios under different temperatures and different dynamic frequency loading conditions were analyzed. Analysis result shows that as the PPA content(mass fraction, same later) increases, the asphaltene content increases gradually, and the oil content(saturation and aromatic) decreases. The asphalt changes gradually from the sol structure to the solution-gel structure, and the high temperature performance of asphalt enhances gradually. The high temperature performance of PPA modified asphalt is related to the asphaltene content of matrix asphalt. After being modified by PPA, the asphaltene content of matrix asphalt with high asphaltene content increases the most, its penetration reduces the most, and it has better high temperature performance. The rutting resistance factors of matrix asphalt, SBS modified asphalt and rubber powder modified asphalt increase by 1.0-8.2, 0.8-13.9 and 2.9-19.7 kPa, respectively, indicating that the PPA can effectively improve the high temperature performances, temperature sensitivities, and rheological properties of matrix asphalt, SBS modified asphalt and rubber powder modified asphalt, enhance the elastic characteristics of the asphalts, and improve their resistances to shear deformation. Compared with the single modified asphalt, the rheological property of PPA composite modified asphalt improves more obviously. There exists a good compatibility between the PPA and the polymer modified asphalt. As the PPA content increases, the ductility of asphalt at 10 ℃ decreases gradually. When the PPA content is 1.5%, the ductilities of matrix asphalt, SBS modified asphalt and rubber powder modified asphalt at 10 ℃ decrease by 77%, 64% and 39%, respectively, indicating that the PPA has a certain negative effect on the low temperature performance of asphalt. It is recommended that the PPA content should not exceed 1.0%. The optimal compound ratio of PPA/SBS modified asphalt is 1.0% PPA compounding 3%. The optimal compound ratio of PPA/rubber powder modified asphalt is 0.75% PPA compounding 15% rubber powder.More>

2019, 19(6): 14-26. doi: 10.19818/j.cnki.1671-1637.2019.06.002

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Real-time monitoring of asphalt mixture mixing process

CHEN Yan, GE Ling-bo, SONG Huan-sheng

Abstract: To control the mixing quality and mixing state of asphalt mixture during the road construction process, a method based on the template matching recognition algorithm in a non-intrusive manner was proposed to extract the asphalt mixture principal component data, such as aggregate, powder, asphalt quality data, mixing time, and temperature in real-time. Based on the identified asphalt mixture data information, the time sequence logic relationship between data acquisition and transmission was established. The WEB monitoring center visually displayed the key information such as the asphalt mixture ratio error, gradation error, mixing time, and temperature. The multimodal information fusion strategy was used to evaluate the asphalt mixture's mixing quality. Based on the prior knowledge of asphalt mixture type during the construction process, the dynamic change of mixture data was analyzed, and the type of asphalt mixture produced in real-time was automatically identified without the manual intervention. The running and screening statuses of mixing equipment were determined by the established model distribution of aggregate data and the mixing time. The historical data were queried across time and the construction cost was assessed according to the stored real-time received data. Research result shows that the time for collecting the character data of asphalt mixture is 4.9 ms by using the template matching recognition algorithm, and the recognition accuracy rate is up to 100%. It meets the time interval requirement that the mixing data collection of asphalt mixture during the construction is less than 0.02 s. The continuous detection, automatic identification, real-time tracking and visual monitoring on asphalt mixture data during the construction process are realized. The real-time warning is realized when the quality of asphalt mixture is unqualified or the mixing equipment fails. It provides a basis for the comprehensive evaluation of mixing process and the real-time control of mixing quality for asphalt mixture.More>

2019, 19(6): 27-36. doi: 10.19818/j.cnki.1671-1637.2019.06.003

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Fiber monitoring of cold-casting anchor's performance

WU Jun, ZHOU Shi-liang, SHU Yue-jie, CAO Shi-bao, ZHOU Yuan-hang

Abstract: To monitor the performance of cold-casting anchor, the structural stress characteristics were analyzed, and the micro unit static balancing model of steel wire in the anchor and modified epoxy filler was established. The impact of bond stress between steel wire and epoxy filler on the steel wire stress distribution characteristics was analyzed, and the failure of anchor was characterized as a singular change of bond stress. A non-destructive monitoring method of anchor's performance status by measuring the axial multi-point stress distributions of steel wires was proposed. For the LMLPES-7-211 anchor, the axial stress distribution characteristics of steel wires in the anchor were analyzed by using the finite element method. According to the non-uniform strain characteristics and harsh environment requirements, a strain-equalized DTG measurement scheme using the capillary encapsulation was proposed, and a special implantable distributed strain sensor for cold-casting anchor was developed. The simulation tests of cable anchor's performance state monitoring were carried out, two DTG distributed strain sensors were implanted into anchor 1 with normal performance and anchor 2 with abnormal performance, respectively, and then the distributed strains of steel wires under the standard stress state of anchor were monitored. Analysis result shows that the distributed strains of steel wire in the anchors 1 and 2 present a big difference. The strain attenuation trend in the anchor 1 is smoother, and the error is less than 5% compared with the finite element simulation result. The smoothness of strain attenuation trend in anchor 2 is insufficient, and the maximum error is more than 40% compared with the finite element simulation result. The performance degradation causes the bond stress of near the anchoring section to drop sharply, reaching a maximum of-2.55 MPa, and the bond stress near the anchoring section of tapping base plate increases greatly, and the increment reaches 3.25 times. Therefore, by setting the reasonable threshold of bond stress, the online monitoring and early warning of anchor's performance state can be realized.More>

2019, 19(6): 37-44. doi: 10.19818/j.cnki.1671-1637.2019.06.004

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Temporal-spatial features of probability distribution of vertical irregularity in ballasted track

SHEN Jian-feng

Abstract: To study the optimum probability distribution function and the temporal-spatial features of vertical irregularity standard deviations on different sections of ballasted track, the three-parameter probability distribution function was used to fit the features of peak value and the tail of vertical irregularity standard deviations of ballasted track. Five three-parameter theoretical distribution functions were selected, and the selection principle of the optimum probability distribution function was determined. Taking the existing Shanghai-Kunming Line as an example, the optimum probability distribution functions of vertical irregularity standard deviations on six different linear sections of ballasted track were fitted. The temporal feature of vertical irregularity standard deviation was analyzed. The variations of distribution function parameters with time were fitted by non-linear functions. The spatial feature of vertical irregularity standard deviation was analyzed. The differences of track quality statuses in spatial dimension were compared. Analysis result shows that in the large value region of vertical irregularity standard deviations, the relative error between the theoretical value obtained from the three-parameter Lognormal distribution and the actual value is less than 5%, while the relative error between the theoretical value obtained from the normal distribution and the actual value is more than 50%. Therefore, the three-parameter probability distribution function can effectively solve the deviated problem between the theoretical value of two-parameter probability distribution function and the actual value in this region. When describing the statistical distribution features of linear sections, different distribution functions should be selected on different linear sections, and the same distribution function should be selected on the same linear section. On the bridge and tunnel sections of existing Shanghai-Kunming Line, the Burr distribution obtains the optimum probability distribution for five times, and the mean and standard deviation of difference of P values are 0.09 and 0.12, respectively. When using the non-linear function to fit the parameters of the distribution obeyed by the vertical irregularity standard deviation on each section, the fitting goodnesses of three parameters are all greater than 0.6. Therefore, the non-linear function can be used to fit the variations of three parameters with time. Both the over-range percentages of vertical irregularity standard deviations on bridge and tunnel sections before and after the repair and maintenance operations are less than 3%. The over-range percentages of vertical irregularity standard deviations on circular, transition and straight line sections are 3.5%-12.8%, while the values on the speed-limit and switch sections are greater than 25%. Therefore, the determined selection principle of the optimum probability distribution function can be used to study the probability distribution feature of track irregularity.More>

2019, 19(6): 45-53. doi: 10.19818/j.cnki.1671-1637.2019.06.005

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Mechanism and influencing factors of mud pumping in railway subgrade

WANG Wei, WU Yu-jian, YANG Cheng-zhong, FENG Qing-song

Abstract: In order to study the mechanism of mud pumping in railway subgrade, many investigations were conducted and two subgrade models that prone to mud pumping in current railways were summarized. A governing differential equation for the description of the increase and dissipation rule of vibration pore-water pressure in subsoil under cyclic train load was established. The growth law of pore-water pressure ratio in subsoil was calculated, which accordingly decided whether the subsoil was liquefied to cause the mud pumping. The effects of different parameters, such as train operation speeds, axle weighings of train, consolidation coefficients of subsoil, consolidation stress ratios and confining pressures on mud pumping, were analyzed for the general-speed and high-speed railways. Analysis result indicates that when the subgrade is under the continuous combined action of train load and water, the pore-water pressure ratio in subsoil grows quickly with the increase of vibration number of train load, but its growth rate continuously decreases and its value stabilize in final. With the increase of the depth, the change pattern of the pore-water pressure ratio in subsoil grows first and then falls. Its value is normally largest at 0.6 m under the surface of subsoil. The faster the train speed is, the quicker the pore-water pressure ratio grows, and the simpler the mud pumping takes place. When the train speed is 200 km·h^-1, the vibration numbers for mud pumping to appear in subsoil under general-speed railway are 19% of that under high-speed railway. The pore-water pressure ratio grows quicker as the axle weighing of train increases. When the axle weighing is 18 t, the vibration number for mud pumping to appear in subsoil under general-speed railway is 24% of that under high-speed railway. Increasing the consolidation coefficient of subsoil can reduce the growth rate of the pore-water pressure ratio, and the subsoil will need more vibration number to liquefy, which makes it more difficult for mud pumping to appear. The subsoil is easier to liquefy under isotropic consolidation than that under anisotropic consolidation, which leads to mud pumping. Increasing the confining pressure can reduce the growth rate of pore-water pressure ratio, which makes it more difficult for subsoil to liquefy and less likely for mud pumping to appear. It is more likely for mud pumping to appear in general-speed railway than in high-speed railway.More>

2019, 19(6): 54-64. doi: 10.19818/j.cnki.1671-1637.2019.06.006

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Effects of harmonic torque on vibration characteristics of gear box housing and traction motor of high-speed train

ZHU Hai-yan, YIN Bi-chao, HU Hua-tao, XIAO Qian

Abstract: In order to research the vibration amplitudes and frequency spectrum distributions of gear box housing and traction motor under the coupling action of electromechanics and their changing trends with the speed of high-speed train, the harmonic frequency distribution of three-phase inverter output voltage and the harmonic torque of traction motor were analyzed, and the torsional vibration model of drive system was established. Based on the theories of direct torque control and vehicle system dynamics, the traction motor control model and multi-body dynamics model of high-speed train were constructed. By means of Simulink-SIMPACK joint simulation platform, the constant torque input model was compared with the torque input model with harmonic torque, and the effects of traction motor harmonic torque on the vibration characteristics of high-speed train gear box housing and traction motor were analyzed at different speeds. Analysis result shows that when the high-speed train runs at a uniform speed of 250 km·h^-1, the longitudinal vibration above the large gear, the longitudinal and vertical vibrations above the small gear of gear box housing are seriously affected by the traction motor harmonic torque. The vibration acceleration amplitude increases significantly at the main frequency of 700 Hz that is exactly up to the 6 times of fundamental frequency of traction motor output torque. Under the influence of harmonic torque, the transverse vibration acceleration amplitude of traction motor at the main frequency of 52 Hz increases by 52.78%, and the vertical vibration acceleration amplitude at the main frequency of 49 Hz increases by 18.95%. As the speed of high-speed train increases, the longitudinal vibration of gear box housing and each direction vibration acceleration of traction motor increase gradually, and the influence of traction motor harmonic torque on the root mean square(RMS) of longitudinal vibration acceleration of gear box housing decreases gradually. The longitudinal and vertical vibration accelerations above the small gear of gear box housing and traction motor increase first and then decrease at the 6 times of fundamental frequency, and reach the maximum at the speed of 250 km·h^-1. The influences of 6 times fundamental frequency of harmonic torque on the vertical vibrations of gear box housing and traction motor are more obvious than those on their longitudinal vibrations, and the harmonic torque has slight influence on their lateral vibration characteristics.More>

2019, 19(6): 65-76. doi: 10.19818/j.cnki.1671-1637.2019.06.007

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Structural modal parameter identification method based on variational mode decomposition and singular value decomposition

SHEN Jian, ZHAO Wen-tao, DING Jian-ming

Abstract: To obtain the structural natural frequency, damping ratio and vibration mode, a new modal parameter identification method was proposed by combining the variational mode decomposition with the singular value decomposition. Based on the existing time-frequency parameter identification method, the system frequency response function was estimated according to the measured impulse excitations and accelerations. The inverse Fourier transform was applied to the system frequency response function to obtain the impulse response function. The intrinsic mode components corresponding to the structural natural frequencies were obtained by executing the variational mode decomposition on the impulse response function for each measuring point. The natural frequencies of intrinsic mode components were extracted, and the intrinsic mode components close to the natural frequency were used as the row vectors to construct the singular value decomposition matrix, and the singular value decomposition was performed on the constructed matrix. The left and right singular value vectors reconstructed by the maximum singular values were used to identify the vibration mode, natural frequency and damping ratio of the structure. The effectiveness of the proposed modal parameter identification method was verified through a four-degree-of-freedom mass-spring-damping theoretical model and a hammering modal test on the vehicle body crossbeam. Research result indicates that in the parameter identification of four-degree-of-freedom theoretical model, the maximum relative errors of system natural frequencies and damping ratios between the identified and theoretical values are no more than 0.025% and 1.490%, respectively. The modal assurance criterions of 1 to 4-order vibration modes between the theoretical and identified values are 0.999, 1.000, 0.999 and 0.999, respectively. In the hammering modal test on the vehicle body crossbeam, the maximum relative errors of natural frequency and damping ratio between the results identified by the proposed method and the theoretical results are not more than 1.57% and 1.47%, respectively, and the theoretical and identified vibration modes have the same trend. Therefore, the proposed method can effectively identify the structural modal parameters.More>

2019, 19(6): 77-90. doi: 10.19818/j.cnki.1671-1637.2019.06.008

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Dynamics modelling of positioning rubber joint of a bogie based on physical parameters

LIU Shi-hui, SHI Huai-long, WANG Wei, LIU Hong-tao, TAN Fu-xing

Abstract: Aiming at the elastic rubber components in the suspension system of a high-speed train bogie, the nonlinear dynamics modelling method for the rubber component was studied based on the physical parameters. In order to accurately simulate the correlations between the nonlinear stiffness and the damping hardness, structural dimensions, excitation frequency and excitation displacement amplitude, the Mooney-Rivlin rubber constitutive model in the software ABAQUS was used to characterize the correlation between the rubber component's stiffness and the structural dimensions and rubber hardness. A dynamics model, including a fractional derivative damping force element, a friction force element, and a spring force element, was used to characterize the frequency-dependency and amplitude-dependency of stiffness and damping of a rubber component. The least squares method was used to identify the model parameters based on the lab tests. The nonlinear characteristics of rubber bearing and positioning rubber joint were numerically simulated and tested in the lab to validate the proposed model. The vehicle dynamics performance analysis was performed by using an user-coded force element defined in the software SIMPACK, and the finite element model was used to provide the basic model parameters for the dynamics model. Analysis result shows that the stiffnesses of rubber bearing and positioning rubber joint are basically proportional to the Shore hardness of rubber material, and the stiffness corresponding to the hardness of 80 HA is about twice that at 60 HA. The less the rubber material in the direction of load action, the greater the stiffness in the corresponding direction. The axial and radial stiffnesses of rubber bearing are decoupled, which is affected by the height and the size of inner and outer diameters, respectively, and the decrease rate of the axial stiffness of rubber bearing with the increase of height is 0.2-0.6 MN·m^-1·mm^-1. Both the axial and radial stiffness of positioning rubber joint varies with the change of mandrel size, and the increase rate of radial stiffness with the increase of inner diameter is 3.1-5.2 MN·m^-1·mm^-1. The vehicle dynamics simulation results by using the nonlinear rubber component dynamics model are 20% different from the results by using a conventional equivalent force element model, which means the nonlinearities of dynamics parameters of the rubber bearing and positioning rubber joint have severe influence on the vehicle dynamics.More>

2019, 19(6): 91-100. doi: 10.19818/j.cnki.1671-1637.2019.06.009

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Adhesive structure life prediction of EMU information window considering influence of temperature and load

TAN Wei, NA Jing-xin, FAN Yi-sa, MU Wen-long, LU Shan-bin

Abstract: Aiming at the adhesive structure of EMU information window, considering the influence of environment and load on the life of adhesive structure, a life prediction method combining the accelerated aging and natural aging was proposed. The influence factors of adhesive structure were analyzed, and the temperature-dynamic load coupling cycle spectrum of accelerated aging was established. The aluminum alloy butt joints were made and the accelerated aging tests with 0, 10, 20 and 30 cycles were carried out, respectively. The residual strength and failure mode of joint were tested regularly, and the change rules of adhesive residual strength under the load cycles were obtained. The real vehicle adhesive strips with different driving mileages under natural aging were extracted, and the residual strength test was performed to obtain the change rule of adhesive residual strength with driving mileage. The polynomial function was used to fit the function relations of load cycles and driving mileage with the residual strength attenuation rate of adhesive. The functional relation between the load cycle and driving mileage was established. Analysis result shows that compared with the initial strength of adhesive joint, the residual strength of adhesive joint decreases by 11.6%, 15.9%, and 20.7% after 10, 20, and 30 temperature cycles, respectively, while the strength of adhesive joint decreases by 14.1%, 18.9% and 24.8% after the coupling cycle of temperature and dynamic load, respectively, which shows that the dynamic load intensifies the decline of joint strength, and presents the decline trend fast first and then slow. After the coupling test of temperature and dynamic load, the failure mode and mechanism of joint section change obviously. Initially, the joint adhesive layer suffers aging failure, and then with the increase of load cycles, the main failure mechanism of joint changes from aging failure to fatigue failure. It is found that the attenuation rate changing trends of adhesive failure strength under accelerated aging and natural aging are basically the same. The functional relationship between load cycle and driving mileage can accurately predict the life of adhesive structure, and the maximum safe mileage of high-speed train is 8.34×10⁶ km.More>

2019, 19(6): 101-110. doi: 10.19818/j.cnki.1671-1637.2019.06.010

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Vibration comfort of mining dump truck based on particle damping

XIAO Wang-qiang, LU Da-jun, SONG Li-ming, YANG Zhe, LI Ze-guang

Abstract: Particle damping technology was used to reduce the vibration of the cab seat and improve its vibration comfort. The plinth between the cab floor and the seat was selected as a particle damper, and the discrete element model of the plinth damper was established. By simulating the vibration environment of the complete truck at the highest engine rotate speed, for different damper schemes(particle material, damper layer number, particle size, and particle filling rate), the energy dissipation based on the discrete element model was analyzed, and the optimal solution was obtained. The physical model was tested, and the root mean square values of the plinth acceleration of the original structure and the structure installed particle damper were compared, and the vibration reduction effect was confirmed. The feasibility of the discrete element model was verified by comparing the simulation results with the test results. The optimal scheme was applied in the test of the sample truck, the responses of the seat under different engine rotate speeds were collected and analyzed. At the highest engine rotate speed, the comfort analysis of human body vibration exposure was performed. Research result shows that based on the peak value of the time domain chart, the maximum acceleration response of the seat occurs at 425 Hz, which is 0.643 4 m·s^-2 before vibration reduction. The maximum value is 0.087 5 m·s^-2 occurs at 25 Hz after particle damper was installed. Based on the time domain chart, when the engine rotate speed is 750, 1 110, 1 470, 1 830, and 2 200 r·min^-1, respectively, after particle damper was installed, the acceleration root mean square values reduce by 24.2%, 29.6%, 34.7%, 39.2%, and 46.0%, respectively. The higher the engine rotate speed, the better the vibration reduction effect of particle damper. After installing the particle damper, the comfort durations at each frequency significantly increase. At 3.1 and 4.0 Hz, the comfort limit durations increase by 1.50 times after the particle damper was used. At 20 Hz, the comfort limit duration increases by 1.57 times after the particle damper was used.More>

2019, 19(6): 111-124. doi: 10.19818/j.cnki.1671-1637.2019.06.011

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SMILO-VTAC model based multi-aircraft conflict resolution method in complex low-altitude airspace

ZHANG Qi-qian, WANG Zhong-ye, ZHANG Hong-hai, JIANG Cheng-peng, HU Ming-hua

Abstract: Aiming at the two uncontrolled cases of traditional sequential mixed integer linear optimization-velocity change, turn change and altitude change(SMILO-VTAC) model, a new multi-aircraft conflict resolution model in complex low-altitude airspace under uncontrolled cases was proposed. Considering the constraints of terrain obstacles in complex low-altitude airspace, a low-altitude multi-aircraft conflict detection and resolution model for the obstacle-oriented scenarios was proposed based on the traditional SMILO-VTAC model. Combined with the priority of general aviation tasks, the rules and procedures of multi-aircraft conflict detection and resolution were established based on the task priority. A multi-aircraft head-to-head convergence scenario was established. Simulation and verification were performed based on the proposed method. Analysis result shows that compared with the traditional SMILO-VTAC model, the proposed method can meet the actual needs of multi-aircraft conflict detection and resolution in uncontrolled cases, and resolve the schemes based on task priority. The resolution cost allocation is reasonable, and the method is more suitable for the characteristics of aircrafts in complex low-altitude airspace. The solution time of the proposed method is slightly longer when the number of aircrafts is no more than 4, but it is basically controlled within 1 s. When the number of aircrafts is more than 4, the solution time of the proposed method is generally less than that of the traditional SMILO-VTAC model. When the number of aircrafts is no less than 7, the solution time of the proposed method is much lower than that of the traditional SMILO-VTAC model. Considering the priority factors, the average resolution cost of new method is 10%-20% higher than that of the traditional SMILO-VTAC model. Along with the small increase in the average resolution cost, the resolution cost is allocated in order of priority. The resolution cost of high-priority aircraft is passed to low-priority aircraft. Obviously, the improved method has higher resolution efficiency in multi-aircraft operation and multi-priority scenario, and has a higher limit of resolution amount in the same calculation time.More>

2019, 19(6): 125-136. doi: 10.19818/j.cnki.1671-1637.2019.06.012

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Aggregation characteristics of anchored vessels based on optimized FCM algorithm

ZHOU Shi-bo, TANG Ji-hong, XIONG Zhen-nan

Abstract: For the lack of sensitivity of clustering results to noise sample points due to the random selection of initial clustering centers by fuzzy C-means(FCM) algorithm, by using the method of local density weighting, the selection range of the initial clustering centers was limited to the region of sample points with high local density, and the selection method of the initial clustering centers was optimized. The local density of sample points was used to improve the objective function, and then improve the influence of sample points with higher local density in the iterative process of the objective function, so that the clustering performance of FCM algorithm was promoted. The clustering effect of improved local density FCM(LD-FCM) algorithm was verified by artificial dataset and iris real dataset. The anchoring preference was analyzed by calculating the local density of anchored vessel's position data. Experimental result shows that compared with the FCM algorithm, the clustering accuracy rate, recall rate, and F-measure of the optimized LD-FCM algorithm improve by 2.9%, 3.8%, and 3.9%, respectively, which shows that the performance of the optimized LD-FCM algorithm is better than that of the FCM algorithm. The clustering results on the anchored vessels location data correctly reflect the aggregation characteristics and anchoring preference in Tianjin Port, and are consistent with the general practice of the vessels, which shows that the optimized LD-FCM algorithm is an effective way to analyze the aggregation characteristics and anchoring preference.More>

2019, 19(6): 137-148. doi: 10.19818/j.cnki.1671-1637.2019.06.013

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Definition of autonomous ship and its autonomy level

ZHOU Xiang-yu, WU Zhao-lin, WANG Feng-wu, LIU Zheng-jiang

Abstract: The development history of autonomous ship was sorted out, its definition was clarified, and its Chinese and English expressions were normalized. The relationship among the ship's automation, intelligence and autonomy was discussed based on the evolution path of autonomy. The taxonomies of autonomy level of 6 authoritative institutions in the world were summarized, the essence and limitation of taxonomy basis were deeply analyzed. Taking the task scenarios as objects and referring to 7 functions of seafarers' standards of competency in the STCW Convention, a taxonomy method of autonomy levels based on navigation practice was proposed. The method identified the levels of task scenarios according to water condition, complexity of operation, and independence from human intervention, and the overall autonomy levels of the ship were determined by the calculation result of the calibration equation. Two test ships carrying autonomous navigation technology were taking as examples, the classification results of autonomy levels of different institutions were compared. Analysis result shows that the key to the taxonomy basis of autonomy level is whether the autonomous ship can independently complete the corresponding task or achieve the corresponding function from the human intervention, rather than depending on the ship automation level or decision-making location. The taxonomy method of autonomy levels based on the navigation practice can reflect the autonomy level of the ship more objectively, and effectively avoid the disadvantage of inaccurate identification of overall autonomy level of the ship due to the autonomous implement of a single function. Therefore, the proposed method is scientific and reasonable.More>

2019, 19(6): 149-162. doi: 10.19818/j.cnki.1671-1637.2019.06.014

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Partition model of road traffic accident influence area based on density entropy

LIU Wei, CHEN Ke-quan, TIAN Zong-zhong, PENG Bo

Abstract: The initial load of network was identified based on the dynamic effect of path impedance. The duration of accident was considered as parameter, and the network load re-distribution was introduced based on the prospect theory. The dissipative structure model was established by the entropy of traffic flow density, and the change rate of traffic flow density entropy of each road was determined by combined with the load distribution process. The partition model of traffic accident influence area was established based on cluster analysis. The influence of partition was analyzed by simulation experiment under different initial loads and accident durations. Simulation result shows that when the traffic base is 800 pcu·h^-1and the accident duration changes from 20 min to 30 min, the number of directed road sections in direct impact area increases from 3 to 6, and the number of directed road sections in indirect impact area increases from 5 to 18, indicating that the entropy of road section affected by accident is on an upward trend and the cascading failure of road network is not obvious. When the traffic base rises to 1 000 pcu·h^-1 and the accident duration changes from 20 min to 30 min, the number of directed road sections in direct impact area increases from 8 to 19, and the number of directed road sections in indirect impact area increases from 16 to 21, indicating that the effect is concentrated on the direct impact area. Therefore, the influence degree of each directed road section affected by accident is obviously different under different traffic situations. With the increases of accident duration and initial traffic flow, the influence degree of accident on directed road sections increases. Therefore, the partition of traffic accident influence area can precisely describe the dynamic evolution process of road traffic performance.More>

2019, 19(6): 163-170. doi: 10.19818/j.cnki.1671-1637.2019.06.015

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Timetable optimization of tram considering energy saving goals

ZHANG Tong, MAO Bao-hua, XU Qi, FENG Jia, TANG Ji-meng

Abstract: The optimization problem of tram timetable in semi-exclusive right of way mode was studied, and the operation section was classified based on the speed limit and the composition of the head and end nodes. The complexity of tram section operation process was considered, and an energy saving optimization model of tram section speed guidance was constructed to reduce the total travel time and the total energy consumption. In order to make the two optimization objectives of total travel time and total energy consumption have the same degree of satisfaction, a fuzzy mathematical programming method was proposed to transform the double objective optimization problem into a single objective optimization problem. According to the nonlinear characteristics of the energy saving optimization model, a genetic algorithm based on simulation was proposed to solve the model. In order to test the validity of the model, based on the actual data of Qilin Tram Line 1 in Nanjing, the designed optimization method was used to optimize the existing timetable by selecting the 7:00-8:00 early peak period of a working day. Considering the influence of managers' operational service concepts on the optimization results, two schemes of minimum travel time objective and minimum energy consumption objective were designed and compared with the model. Optimization result shows that, compared with the existing operating timetable, the timetable adjusted by the energy saving optimization model saves 124.9 s in the upward direction, reducing by about 7.7%, and saves 394.9 s in the downward direction, reducing by about 24.3%. So, the optimization model can effectively improve the operation efficiency of the tram. Compared with the minimum travel time scheme, the total energy consumptions obtained by the optimization model in the upward and downward directions reduce by 56.7% and 53.5%, respectively. Compared with the minimum energy consumption scheme, the total train travel times obtained by the optimization model in the upward and downward directions reduce by 14.9% and 14.1%, respectively. So, the energy saving optimization model can effectively eliminate the conflict between travel time objective and energy consumption objective.More>

2019, 19(6): 171-181. doi: 10.19818/j.cnki.1671-1637.2019.06.016

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Dynamic traffic signal control strategies considering traffic incidents

YU Hao, LIU Pan, BAI Lu, LU Xiao-bo

Abstract: The numerical simulation approach was applied to evaluate the dynamic operation efficiency of road network under 3 typical traffic signal control strategies, including the fixed traffic signal control(FSC), the adaptive signal control minimizing vehicle delay(ASC-VD), and the adaptive signal control maximizing intersection capacity(ASC-IC). The dynamic traffic simulation platform was constructed by the double queue(DQ) model. An intersection traffic flow transfer optimization model was proposed, and the running state of traffic flow at the intersection in the DQ model was analysed. It was assumed that the users selected their routes according to the instantaneous user optimal(IUO) principle, and the IUO constraint was proposed considering the penalty term caused by the traffic signal control. The system total travel time and the travel time affected by traffic incidents or not were taken as evaluation indexes, the signal control effects under low, medium and high levels of traffic demands were studied. Analysis result shows that under the low and medium levels of traffic demand conditions, the system total travel time of ASC-VD is the lowest. Compared to the ASC-IC, the ASC-VD reduces the system total travel times by 0.45% and 0.18% without the influence of traffic incidents, respectively, and by 5.95% and 2.52% with the influence of traffic incidents, respectively. Under the high levels of traffic demand condition, the system total travel time of ASC-IC is the lowest. Compared to the ASC-IC, the ASC-VD reduces the system total travel time by 5.31% without the influence of traffic incidents, and by 5.46% with the influence of traffic incidents. Compared with the change range of system total travel time with or without the influence of traffic incidents, the FSC shows the highest stability under different traffic demands. Under the low and medium levels of traffic demand conditions, the ASC-VD performs more stable than the ASC-IC, while under the high level of traffic demand condition, the stabilities of the two strategies have no significant difference. Therefore, when the traffic demand is high, the intersection capacity should be improved, and when the traffic demand is low, the vehicle delay should be reduced.More>

2019, 19(6): 182-190. doi: 10.19818/j.cnki.1671-1637.2019.06.017

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