西南交通大学学报

Review and Prospect of Structure Research of Underwater Shield Tunnel with Large Cross-Section

HE Chuan, FENG Kun

2011, 24(1): 1-11. doi: 10.3969/j.issn.0258-2724.2011.01.001

[Abstract](2129)

Abstract:

Comparison Research of Some Approximate Analytical Methods for Seismic Design of Circular Tunnel

YAN Qi-Xiang, MA Ting-Ting, WU Lin, HE Chuan

2011, 24(1): 12-17. doi: 10.3969/j.issn.0258-2724.2011.01.002

[Abstract](1899)

Abstract:
In order to cut down the complexity and workload of seismic analyses, three approximate analytical methods for seismic design of circular tunnels were discussed. The first one is based on the function of complex variable and improved by using shear stresses in strata gained by the vibration equation for stratification strata, the second one is founded on the Bessel function, and the third method is grounded on the theory of elasticity mechanics. Seismic analyses of a circular tunnel were carried out respectively using the three analytical methods and by numerical calculation based on the seismic deformation method. The results show that the first two analytical methods can obtain relatively close results, so it is feasible to carry out the seismic analysis by the worst combination of their calculation results, and the third analytical method can be only used at the preliminary stage of seismic design.

Pressure Distribution Model of Simultaneous Backfill Grouting of Shield Tunnel

YUAN Xiao-Hui, HAN Ru-Wang, ZHONG Xiao-Chun

2011, 24(1): 18-23. doi: 10.3969/j.issn.0258-2724.2011.01.003

[Abstract](1825)

Abstract:
In order to probe into the transfer process of grouting pressure in an annular tail void during the backfill grouting of a shield tunnel, rheological properties of cemented mortar were tested by rotary viscometer. The experimental result indicates that the cemented mortar is a Bingham fluid, and its plastic viscosity and shear stress vary respectively from 1 to 4 Pa·s and from 10 to 40 Pa. The Bingham fluid was used to describe the rheological properties of the cemented mortar, and expressions for grouting pressure in the annular tail void were derived. The validity of the expressions was certified by the monitoring results obtained from the Sophia rail tunnel.

Seismic Behavior of Low Masonry Structure with Core-Tie-Columns

ZHENG Ni-Na, LI Yang-Min, PAN Yi

2011, 24(1): 24-30. doi: 10.3969/j.issn.0258-2724.2011.01.004

[Abstract](1300)

Abstract:
In order to research the seismic behavior of core-tie-column, non-linear dynamic time-history responses of three types of two-story masonry structures with the same architectural layouts were analyzed. They are a masonry structure without restriction and two masonry structures with four core-tie-columns (CTC) or four cast-in-place tie-columns (CPTC). Their periods, vibration modes, acceleration responses, deformations and plastic strains in walls were contrasted and analyzed. The research results show that the period of a masonry structure with CTC or CPTC is shorter than that of a masonry structure without restriction, and the vibration modes of all these masonry structures are almost identical. Under a seismic intensity of 8 degrees, the maximum acceleration responses of the masonry structure with CTC or CPTC are much greater than that of the structure without restriction, and compared with the structure without restriction, the masonry structure with CTC or CPTC has significantly small story-drifts and plastic strains in the walls. The seismic behavior of the masonry structure with CTC is improved and close to that of the masonry structure with CPTC.

Seismic Evaluation Method of Multi-storey Masonry Buildings Based on Earthquake Damage

SU Qi-Wang, SUN Yu-Peng, ZHAO Shi-Chun

2011, 24(1): 30-35. doi: 10.3969/j.issn.0258-2724.2011.01.005

[Abstract](1609)

Abstract:
In order to evaluate the seismic performance of existing masonry buildings rapidly, a seismic evaluation method for masonry buildings was proposed based on the theory of seismic evaluation of existing buildings in Japan. By taking the lateral bearing strength of walls and tie columns of every floor of a masonry building as structural seismic capacity (SSC) index, the seismic performance was evaluated by comparing its SSC index and SSC requirement indexes. The SSC requirement indexes were obtained by analyzing the damaged multi-storey masonry buildings subjected to seismic intensities of 9 and 10 degrees in the Wenchuan earthquake. The results show that the proposed method can evaluate the seismic performance of multi-storey masonry buildings and assess the degree of earthquake damage.

High-Accuracy Continuous Function-Based Modification of Slope Mass Rating

ZHANG Ju-Lian, CHEN Meng-Rong

2011, 24(1): 36-41. doi: 10.3969/j.issn.0258-2724.2011.01.006

[Abstract](1198)

Abstract:
In order to raise fitting accuracy of the existing modified continuous functions for slope mass rating (SMR), based on the least-squares-fit algorithm, the table-form-rating SMR was modified by using new continuous functions. Continuous fitting functions of ratings for point-load strength, uniaxial compressive strength, rock quality designation, discontinuity spacing, persistence, separation width, filling thickness and geometric correction factor for discontinuity and slope surface were proposed. These proposed functions were used for the fitting analyses of 57 slopes from hydropower stations, mines and highway projects. The fitting result shows that the residual standard deviation is 2.180 and the correlation coefficient is 0.996 7, and compared with other modified SMR systems, rating result of the SMR system modified by using the above continuous functions is closest to result of the table-form-rating SMR system.

Measurement of Water Content of Multiple Geomaterials by Time-Domain Reflectometry Technique

CHEN Yun, CHEN Yun-Min, ZHOU Qun-Jian

2011, 24(1): 42-48. doi: 10.3969/j.issn.0258-2724.2011.01.007

[Abstract](1276)

Abstract:
In order to find a suitable method for measuring the water content of multiple geomaterials, an interaction model between electromagnetic wave and mixed media was built based upon polarization mechanism. The relationships between dielectric constant and each of material, porosity, and water content of multiple geomaterials including silt, sand, clay, paper, plastic, organics, and municipal solid waste were studied by time-domain reflectometry (TDR) technique. The results show that the dielectric constant of different geomaterials is mainly determined by its water content and porosity, and slightly influenced by its material type. The theoretical model proposed is suitable for geomaterials with different material type and porosity. In addition, the square root of dielectric constant is in good linear relationship with volumetric water content. The dielectric constant of geomaterial has a negative correlation with its porosity under the same volumetric water content. Furthermore, the water content of organics can be measured by TDR technique nondestructively, which provides an experimental basis for the use of TDR in landfills.

Braking Forces and Displacements of Longitudinally Counpled Ballastless Welded Turnout on Bridges

REN Juan-Juan, WANG Peng, LIU Xue-Yi, LIU Jia

2011, 24(1): 49-55. doi: 10.3969/j.issn.0258-2724.2011.01.008

[Abstract](1579)

Abstract:
A finite element model of turnout-track slab-bridge beam-pier was established to analyze the forces exerted on ballastless track and welded turnout on bridge and their displacements under braking forces, in which a single crossover (composed of 2 sets of No.18 welded turnouts）, the longitudinally coupled ballastless track, the bridge beam and the pier are regarded as one system.The welded turnout of longitudinally coupled ballastless track on Leida bridge on Wuhan-Guangzhou high speed passenger line was taken as an example. Calculation results show that braking forces on and displacement of the stock rail increase with a decrease in the slab stiffness, and the displacement between the slab and the rail is less than 1 mm. The structure of the ballastless track has a little effect on the longitudinal forces exerted on the position-limited devices and spacers, and the displacements of nose rail and switch rail. Braking forces do not result in contact between the two blocks of the position-limited device, and the forces exerted on them are less than 13 kN. A decrease in slab stiffness reduces the forces exerted on it, with a maximum value of 3 832.9 kN, and increases its displacement, with a maximum value of 17.4 mm. Decreasing slab stiffness and friction coefficient of slip layers increases the forces exerted on the piers, and when the friction coefficient is less than 0.2, the longitudinal forces exerted on the piers decreases by about 500 kN.

Dynamic Responses of High-Speed Train-Track-Bridge System under Seismic Excitations

WANG Shao-Lin, ZHAI Wan-Meng

2011, 24(1): 56-63. doi: 10.3969/j.issn.0258-2724.2011.01.009

[Abstract](1878)

Abstract:
In order to analyze the effects of seismic excitations on the running safety of a high-speed train passing a bridge, a train-track-bridge dynamic model considering seismic loads was set up based on the train-track-bridge dynamic interaction theory. As an example, a simply supported beam with a span of 32 m and bi-block track was modeled, and the dynamic responses of a high-speed train-track-bridge system under seismic excitations were analyzed. The results show that the effects of an earthquake on the dynamic responses of a high-speed train-track-bridge system is significant, and compared with the vertical response, the lateral response of a bridge is influenced greatly. The running safety and running stability of a train passing a bridge are affected due to seismic loads. When El Centro seismic waves with a normalized horizontal component of 1.0 m/s2 and a normalized vertical component of 0.5 m/s2 are subjected to, the reduction radio of wheel-load exceeds the safety limit if its running speed is greater than 250 km/h, and the derailment coefficient exceeds the safety limit if its running speed reaches to 300 km/h. Therefore, the influences of train speed should be taken into account in evaluating the running safety of a train passing a bridge under seismic excitations.

Automatic Incident Detection Technology Based on SVM

CHEN Wei-Rong, GUAN Pei, ZOU Yuexian

2011, 24(1): 63-67. doi: 10.3969/j.issn.0258-2724.2011.01.010

[Abstract](1357)

Abstract:
In order to reduce traffic delays caused by traffic incidents, an new AID (automatic incident detection) algorithm, SVM-AID algorithm, was proposed based on support vector machines (SVM). Using actual traffic data of the I-880 database, the classification performance of the SVM-AID algorithm was tested, and the effects of the parameters in SVM on the classification were analyzed. The experimental results show that the parameters should be chosen carefully because they have great effects on the classification. The correct classification rate of the proposed algorithm is more than 98% and its mean time to detect is less than 5 s to indicate a better performance over other AID algorithms based on artificial neural networks.

Design and Realization of Security Monitoring System for Speed-up Railway Crossing

XU Zhi-Gen, CHEN Ji-Lan, YANG Xi-Ke, MENG Xin-Zhi

2011, 24(1): 68-75. doi: 10.3969/j.issn.0258-2724.2011.01.011

[Abstract](1359)

Abstract:
In order to improve the status of security monitoring when a speed-up train is passing through a railway crossing, a system for security monitoring and information management of railway crossings was designed and realized. This system adopts a wireless communication mode with a frequency of 150 MHz and is supplied with solar energy power. By the real-time acquisition, transmission, analysis, storage and display of data and the monitoring and security alarm of running status, the functions of security monitoring and information management are realized. The system has been used at a railway crossing on the Chengdu-Chongqing railway for 2 years so far to successfully monitor over 24 thousands trains running through the railway crossing.

Synthesis Optimization for Construction Project Based on Modified Particle Swarm Optimization Algorithm

WANG Weibo, FENG Quanyuan

2011, 24(1): 76-83. doi: 10.3969/j.issn.0258-2724.2011.01.012

[Abstract](1514)

Abstract:
A modified PSO (particle swarm optimization) algorithm—hierarchical subpopulation PSO（HSPSO) was proposed to avoid the premature phenomenon of the PSO algorithm during evolution. By using the strategy of subpopulation hierarchy, the algorithm can improve the convergence speed and accuracy. For the synthesis optimization of a construction project, mathematical optimization models and a multi-objective optimization model of construction time, cost and quality were established. In a case study, the standard PSO (SPSO) and differential evolution (DE) algorithms were compared, and the HSPSO algorithm was utilized to its synthesis optimization. In addition, the exhaustive enumeration was used to verify the effectiveness of these models and the feasibility of the HSPSO algorithm. The result shows that the HSPSO algorithm can quickly obtain satisfied results with average iterative times of less than 20 under the condition of a swarm size of 20 particles.

Fault Diagnosis Method for Jointless Track Circuit Based on AOK-TFR

ZHAO Lin-Hai, MU Jian-Cheng

2011, 24(1): 84-91. doi: 10.3969/j.issn.0258-2724.2011.01.013

[Abstract](1435)

Abstract:
In order to make up for the shortcoming of the existing methods for compensation capacitor fault detection in both timeliness and cost aspects, a simulation model for induced voltage envelope of cab signal was proposed based on the transmission-line theory. On this basis, the influence law of compensation capacitor failure on the induced voltage envelope was analyzed, and a frequency-based equivalent regression model for the induced voltage envelope was built and verified. Based on this regression model, a compensation capacitor fault detection method was proposed based on the AOK-TFR (adaptive optimal kernel time-frequency representation) and the fact that the frequency of the induced voltage envelope changes ahead and behind the location of the defected capacitor. In this method, the signal to be processed, directly from a cab signal recorder, is denoised by using the B-spline discrete binary wavelet transform (DBWT). Then its time-frequency distribution information is extracted by the AOK-TFR, and the fault compensation capacitor is lastly located in light of the change of the frequency extracted. The experimental result of actual data from 100 segments selected randomly shows that the accuracy rate is about 92.58% to indicate that the proposed method can accurately detect the location of a defected compensation capacitor under the condition that other capacitors are in good condition.

Detecting High-Speed Maglev Line Irregularity Based on Intrinsic Mode Function Analysis

SU Yan-Chen, WU Chuan-Hui

2011, 24(1): 92-97. doi: 10.3969/j.issn.0258-2724.2011.01.014

[Abstract](1162)

Abstract:
In order to assess the track irregularity of maglev lines, an analysis was made of the practical data of track-inspection acceleration signals of a high-speed maglev train, which indicates that the longitudinal vibration acceleration signal of the train guidance system is most sensitive to the long-wave irregularity of the maglev line. Hilbert-Huang transform is used to extract the intrinsic mode functions (IMFs) of the long-wave frequencies of the acceleration signals to obtain the instantaneous amplitude (envelope) and instantaneous frequency and then extract the long-wave irregularity signals. The proposed method was applied to analyze the practical data of a maglev train moving at a speed of 430 km/h, and the obtained long-wave irregularity signals of the maglev line agree with the ground survey results well.

Handoff Algorithm for Hierarchical Cell Networks Based on Received Signal Strength and Power Loss

徐鹏, 方旭明, 杨俊

2011, 24(1): 98-102,108. doi: 10.3969/j.issn.0258-2724.2011.01.015

[Abstract](1877)

Abstract:
In order to settle the handoff problem resulted from deploying femtocell base stations in a macrocell, a new handoff algorithm for hierarchical cell networks was proposed. This algorithm makes a handoff judgment in light of signal strength received by users and signal power loss during transmission. When the received signal strength (RSS) can not work efficiently, the power loss serves as the auxiliary condition to improve the usage of femtocells and cut down the complexity of the new handoff algorithm. The simulation results show that the proposed algorithm doubles the number of handoffs compared with the conventional algorithm but reduces half the number of unnecessary handoffs compared with a handoff algorithm based on the combining RSSs from macrocell and femtocell base stations.

Grounding Effect of Integrated Grounding Wire for High-Speed Railway

GAO Guoqiang, DONG Anping, ZHANG Xueyuan, LEI Dong, WANG Bo, WU Guangning

2011, 24(1): 103-108. doi: 10.3969/j.issn.0258-2724.2011.01.016

[Abstract](1188)

Abstract:
In order to improve the utilization of integrated grounding wire (IGW), the inflences of its radius, buried depth, interval of transversal connections and soil resistivity on grounding effect were analyzed by taking IGW grounding impedance and shunting coefficient for rail current as the assessment indices of the grounding effect. The research result shows that the grounding impedance and the shunting coefficient are sensitive to the changes of IGW radius, interval of transversal connections and soil resistivity, but insensitive to buried depth. A comparison between the theoretical results and the test ones on Suining-Chongqing ballastless railway indicates that differences in the grounding impedance and the shunting coefficient are respectively 17.3% and 11.4%.

Numerical Analyses of Air Ionization and Breakdown of Short-Pulse High-Power Microwave

ZHAO Pengcheng, LIAO Cheng, LIN Wenbin, TANG Tao

2011, 24(1): 109-114. doi: 10.3969/j.issn.0258-2724.2011.01.017

[Abstract](1228)

Abstract:
In order to investigate air breakdown caused by short-pulse HPM (high-power microwave), the effective electric field, an important parameter for the calculation of ionization parameters, was obtained by solving the electron momentum equation for air. The effect of altitude on the air breakdown thresholds of narrowband and ultra-wideband HPM pulses and the relationship between escaping time or energy and pulse amplitude were given by substituting the effective ionization parameters into and solving the continuity equation of electron density. In addition, the energy transmission of an ultra-wideband HPM pulse under the condition of air breakdown was analyzed. The research results show that altitude, pulse width, spectrum distribution and amplitude have a significant impact on the air breakdown.

Sliding Mode Control of Acrobot Robot with External Disturbance

WANG Zhong-Hua, YANG Ji, CHENG Jin, ZHANG Yong

2011, 24(1): 115-120. doi: 10.3969/j.issn.0258-2724.2011.01.018

[Abstract](1280)

Abstract:
To increase the anti-disturbance ability of Acrobot systems, a dynamic model for the underactuated Acrobot system was built, and a silding mode control strategy for the system was proposed. In the strategy, the model in cascade normal form is expanded to the common form with disturbance term, and the hyperolic tangent function is used to substitute the sign function to eliminate chattering. The Acobot system with the proposed control strategy was proved asymptotically stable and robust using Lyapunov theory and perturbation theory. This method can be applied to other underactuated systems. Simulation results show the effectiveness of the proposed control strategy to Acrobot balance control.

Dynamic Responses of Shaft System of Hydraulic Generator Set with Coupling Faults of Bearing Looseness and Rotor Rub-Impact

HUANG Zhi-Wei, ZHOU Jian-Zhong, ZHANG Xiao-Yuan, WANG Chang-Jing, ZHANG Yong-Chuan

2011, 24(1): 121-126. doi: 10.3969/j.issn.0258-2724.2011.01.019

[Abstract](1325)

Abstract:
For the fault problems of the bearing looseness and rotor local rubbing caused by some nonlinear factors, a six-degree-of-freedom dynamic model for the hydraulic generator set with coupling faults of bearing looseness and rub-impact between rotor and stator was established, with the rigidity and damping between the stator and foundation being considered. The nonlinear dynamic behaviors of the shaft system were analyzed by Poincaré maps, amplitude spectrum and bifurcation diagrams, as the ratio of rotor circular frequency to its bending natural frequency and the rotor mass eccentricity varied. The research results revealed that various non-linear phenomena including periodic, period-three and quasi-periodic motions occurs at different circular frequencies and there are some low-frequency harmonics with large amplitude at the 1/3X component. Moreover, the circular frequency range of rub impact enlarges constantly and the dynamic responses of the system become more complex with the increasing of the rotor mass eccentricity.

Preparation of Cu2-xS Nanotubes and Their Surface Photovoltaic Properties

LIAO Xin, YANG Feng, PU Minghua, ZHAO Yong

2011, 24(1): 127-131. doi: 10.3969/j.issn.0258-2724.2011.01.020

[Abstract](1070)

Abstract:
In order to explore the photoelectric applications of CuS materials, copper sulfide (Cu2-xS) nanotubes were prepared via hydrothermal method. The structure and morphology of the Cu2-xS were characterized with X-ray diffraction (XRD) and scanning electron microscopy (SEM). The surface optoelectronic properties of the products and their photovoltaic properties in varying electric field were investigated by UV-vis spectrophotometer, surface photovoltage spectrum (SPS), and field-induced surface photovoltage spectroscopy (FISPS). The results show that the outer diameter, thickness, and length of the nanotubes are 325—675 nm, 70—125 nm, and 10—20 μm, respectively. There are two absorption areas in the wavelength range of 300—800 nm according to the UV-vis spectrum. The FISPS shows that the copper sulfide (Cu2-xS) nanotubes are n-type semiconductor.

Simulation and Experimental Investigation of Tortional Wear Corrosion at Constant Temperature

LIN Xiu-Zhou, CAI Zhen-Bing, HE Li-Ping, YI Jing-Hua, XIE Xin-Yuan, SHU Min-Hao

2011, 24(1): 132-137. doi: 10.3969/j.issn.0258-2724.2011.01.021

[Abstract](1296)

Abstract:
In order to reveal the wear and corrosion characteristics of metal materials under torsional contact in liquid medium at constant temperature, a new device for torsional wear corrosion test was developed. Using the test system, torsional wear corrosion tests of Ti6Al4V were carried out in saline solution at 37℃ under a normal load of 50 N, a torsional angular displacement amplitude of ±3°, and a frequency of 0.5 Hz. The results showed that the friction torque curves of the Ti6Al4V alloy in saline solution could be divided four stages: the friction torque was very low at first; it increased gradually to a peak value; after the peak, it decreased slightly; and then increased gradually to a relatively stable value at last. Three types of torques vs angular displacement curves in shapes of line, elliptical, and quasi-parallelogram presented during the tests. At the beginning of torsion, the free corrosion potential of the Ti6Al4V alloy had a rapid negative shift, followed by a slow positive shift to a relatively stable value lower than before torsion. Simultaneously, the corrosion current increased rapidly and then decreased to a relatively stable value higher than before torsion. The damage of Ti6Al4V alloy was typically caused by coupled wear and corrosion.

Strength Calculation of Planar Double-Enveloping Hourglass Worm Gears

ZHANG Yan-Qin, ZHANG Guang-Hui

2011, 24(1): 138-142. doi: 10.3969/j.issn.0258-2724.2011.01.022

[Abstract](1636)

Abstract:
In order to simplify the calculation method for bearing capacity of planar double enveloping hourglass worm gears, a contact stress analytic formula for the worm drive was proposed through regression analysis and interpolation method based on the Hertz theory. The bending strength calculation formula was improved by taking into consideration the load distribution coefficient among the meshing teeth. According to the contact finite element model of the worm-gears, three-dimensional stress distribution of the gears was obtained. The results show that the contact stress (or bending strength) obtained by the analysis formula is 6%—16% larger than that by the finite element method, and the analysis formula can meet the requirements for engineering use. The contact stress distribution is in a declining L shape along the contact line. As the load of the worm gear increased from 1 N·m to the rated value, the maximal load distribution coefficient among 5 pairs of meshing gears decreased from 32.4% to 27.5%.

Train Line Planning Model with Stochastic Stability in Passenger Flow Assignment Scheme for Passenger-Dedicated Line

PENG Qi-Yuan, JIA Xiao-Qiu, GUAN Xiao-Yu

2011, 24(1): 143-147. doi: 10.3969/j.issn.0258-2724.2011.01.023

[Abstract](1341)

Abstract:
In order to meet the requirements of mixed operation of trains with high and middle speeds on a passenger-dedicated line in China and increase the stochastic robustness of the train line planning system, a multi-objective expected value model for stochastic programming subjected to the carrying capacity of the train line system was built based on the graph theory, the probability theory, and the basic programming idea of expected value modeling. Then, a multi-parameter genetic algorithm with random simulation was designed for solving the model. The result of a computational example shows that the algorithm can obtain the satisfactory solution after 600 evolution generations when the detour rates for both the trains and passengers are 1.4, the period is 60 min, the K-shortest path parameter for the trains are 3 and that for passengers are 8. Therefore, a robust solution for train line plan and passenger flow assignment scheme can be generated by the proposed algorithm under the constraints of the carrying capacity of the railway network, the transportation capacities of the trains operated with different speeds, and the travel demands of passengers, etc.

Optimal Model and Algorithm for Allocation of Arrival and Departure Trains in Railway Passenger Terminal

ZHAO Jun, LI Yu, REN Qiliang, PENG Qiyuan

2011, 24(1): 148-153. doi: 10.3969/j.issn.0258-2724.2011.01.024

[Abstract](1613)

Abstract:
To optimally allocate arrival and departure passenger trains among passenger stations in a railway terminal that connects high-speed and intercity passenger railway lines, a multiple-objective nonlinear mixed integer programming model was proposed. In the model, decision variables include distribution of arrival and departure passenger flows, and routes of arrival, departure and through passenger flows; constraints are the carrying capacity of stations and railway lines, and demand of passenger transportation; and objectives are the costs of all passengers in the terminal. An exact algorithm was designed by combining enumeration method, multiple shortest algorithm and linear programming in consideration of that a railway terminal connects a few routes. An example demonstrates that the proposed method could quantitatively solve the problem of optimally allocating arrival and departure passenger trains among 3 passenger stations in a railway terminal.

Seasonal Effects of Weather on Probability Distribution of Airport Arrival Capacity

ZHANG Jing, XU Xiao-Hao, WANG Fei

2011, 24(1): 154-161. doi: 10.3969/j.issn.0258-2724.2011.01.025

[Abstract](1658)

Abstract:
In order to study the effects of weather seasonal changes on airport arrival capacity distribution, the capacity probabilistic distribution of historical weather was obtained through statistical analysis of the original weather data. A periodic time-series model based on the capacity probabilistic distribution was built on the basis of the 1-parameter arrival capacity distribution model. Then, according to the similarity of the monthly capacity probabilistic distribution in the periodic time series, months are classified by genetic algorithm into four seasons: (3,4)，(5,6,7,8,9)，(10,11) and (12,1,2), and the capacity distribution and probability of each season are obtained. The results indicate that during the stratus season from May to September, the probability of reduced arrival capacity for 8 hours is 25.76% while normal capacity for 8 hours is 9.64%. The weather effects of the seasons based on the capacity probabilistic distribution are in accordance with the actual situation.

Probabilistic Methods for Airspace Sector Flow and Congestion Prediction

WANG Chao, YANG Le

2011, 24(1): 162-166. doi: 10.3969/j.issn.0258-2724.2011.01.026

[Abstract](1457)

Abstract:
In order to improve the accuracy of sector flow forecasting and diminish false congestion alerts, probabilistic models for sector entry time, sector transit time and sector exit time were established through analysis of the uncertain factors influencing air traffic operations. Then, a probabilistic method for calculating the sector occupancy by an aircraft was built using the cumulative distribution functions of sector entry time and exit time. On this basis, a probabilistic method for sector congestion prediction based on Monte Carlo simulation was proposed. The simulation results show that, compared with the deterministic method, the proposed probabilistic method could decrease the ratio of congestion time intervals from 42% to 33%.

Trajectory Optimization Method of Aero-Gravity Assist Orbital Maneuver

ZHANG Wan-Li, WANG Chang-Hong, XIA Hong-Wei, XIE Wei-Nan

2011, 24(1): 167-174. doi: 10.3969/j.issn.0258-2724.2011.01.027

[Abstract](1466)

Abstract:
In order to achieve the orbit maneuver and save the fuel consumption in the space travel mission of spacecrafts, the dynamic equations and performance index functions of aero-gravity assist (AGA) maneuver were established under the terminal constraints and path constraints. The continuous two-point boundary value problem was converted to the equivalent nonlinear programming problem using the pseudospectral method, and the optimal trajectories corresponding to the maximum and minimum heliocentric velocities of the spacecraft were obtained with SNOPT software. Finally, a simulation was made for the trajectory optimization algorithm, and the variation of optimal trajectories under the peak constraint of heat flow rate was obtained. The results show that the maximum velocity deviation is 0.009 m/s when the number of nodes is 40, which satisfy the convergence precision demand. In the AGA maneuver, the maximum heliocentric velocity increases by 8.02%, the minimum heliocentric velocity reduces by 32.26%, and the corresponding deflection angles increase by 42.74° and 68.40°, respectively, when compared with those in the gravity-assist orbit maneuver. When the peak heat flow rate is 500 W/(cm2·s), the depth of spacecraft into the atmosphere, the heliocentric velocity, and the deflection angle reduce 6.35 km, 93 m/s, and 6°, respectively, compared with those without heat flow rate constraint.

Method for Congested Traffic Network State Analysis Based on Reasonable Routes

QI Hong-Sheng, WANG Dian-Hai, XU Cheng

2011, 24(1): 175-181. doi: 10.3969/j.issn.0258-2724.2011.01.028

[Abstract](1219)

Abstract:
In order to prevent the propagation of traffic jam throughout the road network, a traffic network analysis model is built, which is based on reasonable routes taking into account both the degree of saturation and the travel time. The uncongested zone out of the central congestion layer is classified into four layers from inside to outside: control layer, guidance-and-control layer, guidance layer, and unrelated layer. These layers help reflect the spatial distribution of network traffic states and the potential evolution trend. Finally, a case study is conducted by simulation to testify the performance of the proposed model under assigned network traffic volumes. The results show that the proportion of each layer varies with the increasing traffic volume, and the congestion in congested zone tends to propagates throughout the whole network. During peak hours, the proportion of the above four layers is 20%, 5%, 10%, 10%, respectively. Within each layer, the link bearing a higher degree of saturation has a more influence on the congested zone.

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2011 Vol. 24, No. 1