西南交通大学学报

Analysis of AT Power Supply Network in AC Electrified Railway

LI Qunzhan, GUO Kai, ZHOU Fulin

2012, 25(1): 1-6. doi: 10.3969/j.issn.0258-2724.2012.01.001

[Abstract](2273)

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Abstract:
The method of compound sequence analysis based on two-phase symmetrical components transform was used to further analyze AT (auto transformer) power supply network in AC electrified railway with clear concepts. Sequence models for AT power supply network components were described, such as traction power network, auto transformer, traction main transformer, traction load, power source, and so on. The way of building compound sequence network for AT power supply network was proposed. The definitions of power supply capacity and power supply capacity utilization ratio were determined, and the importance of matching between power supply capacity and load power demand was demonstrated by comparing 227.5 kV with 55 kV AT power supply modes. Simulation results show that the method of compound sequence network analysis based on two-phase symmetrical components transform is applicable in precision and clear in concept.

Transmittal Signal Frequency of Centre-Fed Ballastless Track Circuit

ZHANG Youpeng, , ZHAO Bin, TIAN Mingxing

2012, 25(1): 7-11. doi: 10.3969/j.issn.0258-2724.2012.021.01.002

[Abstract](1548)

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Abstract:
To determine the frequency range of centre-fed ballastless track circuit, based on the frequency character of the first parameters and the two-port network coefficient expressions of centre-fed ballastless track circuit in normal, shunt and broken-rail operation modes and the different initial values of minimum ballast resistance, surface-conductivity coefficient, input impedance and output impedance, the frequency characters of track circuit broken sensitivity and train shunt sensitivity was simulated by the graphical method. The result shows that the frequency of centre-fed ballastless track circuit is not larger than 700 Hz when the first parameters is the standard parameters of ballastless track circuit.

Method of Cross-Layer Performance Optimization in Wireless Multi-hop Networks

LI Zhijie, , FANG Xuming

2012, 25(1): 12-18,31. doi: 10.3969/j.issn.0258-2724.2012.021.01.003

[Abstract](1652)

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Abstract:
In order to meet the different performance requirements of traffics in wireless mesh network and Ad Hoc network, a cross-layer optimization algorithm was proposed. An adaptive modulation and coding method to keep constant average packet error rate was presented, and the performance of traffics was analyzed based on the channel, collision, buffer size and traffic characteristics. An optimization algorithm was given by tuning the packet error rate, optimizing throughputs and a weighted optimization to meet the different requirements of throughouts and delays. This algorithm integrates the parameters of physical layer, media access control layer and link layer and the requirement of traffics. In addition, a simulation was carried out to validate the correctness of the proposed algorithm. The research result shows that the proposed algorithm decreases packet drop rate about 35.3%, and drops delay about 65.6% relative to the fixed packet error rate under the given parameters.

PedestrianDetectionandTrackingBasedonAutomotiveVision

Guo Lie, GAO Long, ZHAO Zongyan

2012, 25(1): 19-25. doi: 10.3969/j.issn.0258-2724.2012.021.01.004

[Abstract](1616)

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Abstract:
To improve the automotive active safety and guarantee the safety of pedestrians under urban transportation conditions, a pedestrian protection method based on automotive vision was presented. The Adaboost algorithm was utilized to detect pedestrians rapidly, and the Kalman filter principle was adopted to track these pedestrians and obtain their trajectories. With this method, the samples' Haar-like features are calculated and trained by the discrete Adaboost algorithm to obtain the cascaded pedestrian recognition classifiers. These classifiers are exploited to search for pedestrians by scanning those images captured by automotive vision. The Kalman filtering principle is applied to track these pedestrians and build the dynamic region of interest for pedestrian detection. The tracking results are used to analyze their behaviors. The experimental results show that the proposed method can detect pedestrians in about 80 ms per frame with an accuracy of 88%. The time cost can reduce to 55 ms per frame after using the Kalman-based pedestrian tracking method.

Output Control of CLC Type Contactless Power Transfer Systems

WANG Zhihui, SUN Yue, DAI Xin, SU Yugang, TANG Chunsen

2012, 25(1): 26-31. doi: 10.3969/j.issn.0258-2724.2012.021.01.005

[Abstract](1660)

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Abstract:
To achieve the output control of CLC type contactless power transfer (CPT) systems, a system model was built using the discrete time mapping method, and an analytic expression of periodic fixed points was given. On this basis, a soft-switching frequency computing method and an output power calculation method at different frequencies were developed. An output power control method based on average power balance was proposed, and then verified experimentally. The results show that the combined control at different frequency operating points can switch the output voltage between 20 and 50 V in maximum 41 ms to satisfy different load requirements, and the switching devices operate in the soft-switching state.

Backdoors of Message Propagation Algorithm Convergence

WANG Xiaofeng, XU Daoyun, QIN Yongbin

2012, 25(1): 32-38,62. doi: 10.3969/j.issn.0258-2724.2012.021.01.006

[Abstract](1285)

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Abstract:
In order to investigate the convergence of the WP (warning propagation) algorithm, backdoors of the WP algorithm were given. By assigning values to variables in the backdoors, the Boolean formula can be simplified to sub-formula having factor graph with tree structures, and the convergence of the WP algorithm can be guaranteed in the sub-formula. Finally, a randomized algorithm for solving the backdoors was designed and its feasibility was analyzed. The result show that the randomized algorithm is feasible.

Adaptive Evolution Technology for Collaborative SaaS Platform of Industrial Chains

WANG Shuying

2012, 25(1): 39-45. doi: 10.3969/j.issn.0258-2724.2012.021.01.007

[Abstract](1353)

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Abstract:
An adaptive evolution method for a collaborative SaaS (software as a service) platform of industrial chains was proposed based on dynamic binding, implicit authority, and autonomous model for enterprises, to adapt itself to frequent changes in users and their businesses. An adaptive evolution model for business functions and data, and a synchronous evolution algorithm for online update of the business functions and database were presented, which represent the adaptive evolution mechanism of a SaaS platform. The proposed method was applied to the an research and development project of a collaborative SaaS platform for an automobile part industrial chain, showing that it meets the needs of online update of user businesses without disturbance to continuous service.

Design of Zero Correlation Zone Sequences via Interleaving Perfect Sequence

WANG Longye, WANG Xian

2012, 25(1): 46-49. doi: 10.3969/j.issn.0258-2724.2012.021.01.008

[Abstract](1245)

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Abstract:
Abstract: To reduce the limit on the relevant parameters during constructing zero correlation zone (ZCZ) sequences, a novel construction method was proposed to design the near-optimal sequence set with ZCZ. Using the interleaving technique and recursive algorithm, a new ZCZ sequence set can be generated from an arbitrary perfect sequence with a period longer than 4. With the size (i.e. the number of sequences) of the new sequence set kept unchanged, the length and ZCZ width of the new sequence can be doubled by each recursive operation. The constructed near-optimal ZCZ sequence set can approach the mathematical bound, and can successfully provide quasi-synchronous CDMA communication without co-channel interference.

Aerodynamic Characteristics of Vehicle-Bridge System under Cross Wind: Wind Tunnel Test System with Moving Vehicle Model

LI Yongle, HU Peng, ZHANG Mingjin, LIAO Haili

2012, 25(1): 50-56. doi: 10.3969/j.issn.0258-2724.2012.021.01.009

[Abstract](1678)

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Abstract:
In order to consider the effects of vehicle motion on the aerodynamic characteristics of a vehicle-bridge system, a new test system with a moving vehicle model was developed regarding to the aerodynamic characteristics of ambient flow around the vehicle-bridge system to realize the synchronous measurement of the aerodynamic forces on bridge deck and vehicles in a large wind tunnel when a train is running through the bridge deck under cross wind. In the wind tunnel test system, wind velocity, vehicle velocity, test objects and relative position of vehicle and bridge are easy to change. Based on the characteristics of time-history of testing signals, a data processing method was presented, and changes in the dynamic aerodynamic force signals of bridge and moving vehicle were analyzed. The wind tunnel test results indicate that the aerodynamic force signals of both bridge deck and vehicle are relatively stable, and the test results are relatively reliable.

Limit Bearing Capacity of Longitudinal Clapboard of Long-Span Single Pylon Cable-Stayed Bridge

WEI Xing, QIANG Shizhong

2012, 25(1): 57-62. doi: 10.3969/j.issn.0258-2724.2012.021.01.010

[Abstract](1871)

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In order to investigate the limit bearing capacity of longitudinal clapboard, nonlinear buckling analysis and model test on the longitudinal clapboard used in streamlined steel-box girder of Pearl River Huangpu bridge in Guangzhou were performed. Based on the ANSYS software, a refined finite element model for one section of the steel-box girder was founded. Stress distribution and elastic buckling coefficient of the longitudinal clapboard under a designed load were obtained by FEM (finite element method) analysis. By considering initial disfigurement, geometrical and material non-linearities, limit bearing capacity of the longitudinal clapboard was get. A static test on a specimen for a part of the steel-box girder with a scale of 1 to 2.5 was carried out to obtain stress and deformation of the longitudinal clapboard under the designed load. Nonlinear buckling coefficient of the longitudinal clapboard under the designed load was achieved through a test on the ultimate bearing capability of the specimen. The research results show that the stability of the longitudinal clapboard used in the Pearl River Huangpu bridge in the whole construction meets the need of design. Nonlinear FEM considering initial disfigurement can be used to investigate the local stability of the longitudinal clapboard of steel-box girder.

Multi-scale Monitoring System Construction of River-Bed Scouring around Sutong Bridge

CHEN Zhijian, TANG Yong, CHEN Song

2012, 25(1): 63-67,77. doi: 10.3969/j.issn.0258-2724.2012.021.01.011

[Abstract](1285)

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In order to monitor the river-bed scouring depth around Sutong bridge, a small-scale monitoring system was established with water piezometers to realize the real-time monitoring of the scouring depth in the middle area of pile-group foundation, and the sites of the water piezometers were optimized based on the network coverage model. A large-scale monitoring system of protected river-bed area was constructed using a multi-beam sounding system, and parts of monitoring data were analyzed. The result shows that the multi-scale monitoring system can monitored the scouring depth with high precision, and its monitoring precision can reach decimeter level.

Optimization of Complex Cross-Section Metro Tunnel Excavation and Its Influence on Building

QI Taiyue, BAI Yongxue, LI Bin

2012, 25(1): 68-77. doi: 10.3969/j.issn.0258-2724.2012.021.01.012

[Abstract](1833)

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Abstract:
A 3D numerical model for complex cross-section tunnel and building was set up based on the FLAC3D, and five construction methods were optimized by numerical simulations to determine the optimal construction method by taking subsidences of ground surface and the building and stress in the structure as the optimal object. The optimal construction method was adopted to excavate the tunnel, plastic areas induced by excavation using the optimal construction method were predicted, and corresponding pre-reinforcement measures were given. The subsidence characteristics and maximum subsidences of ground surface and building foundation in different excavation periods under the condition of pre-reinforcement plastic areas were forecasted. The differences between the subsidence curved surfaces of ground surface and building foundation were comparatively analyzed. The safety of the building and key structures of the tunnel in the whole excavation process was evaluated. The simulations results and in-site measured data have the same regularities to provide an important technical support for environment control of metro tunnel excavation with complex cross-sections.

Microstructure Fractal Feature of Dredger Fill during Seepage Flow Consolidation

NIU Cencen, WANG Qing, TAN Chun, CHEN Huie, ZHOU Fujun

2012, 25(1): 78-83. doi: 10.3969/j.issn.0258-2724.2012.021.01.013

[Abstract](1217)

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Abstract:
In order to analyze the change law of the microstructure of dredger fill in the process of seepage flow consolidation, the fractal theory was applied to quantitatively describe the structural characteristics of the microstructure of dredger fill and analyze the curing mechanism of dredger fill. Laboratory tests, including granule analysis and soluble salt tests, were conducted to evaluate the engineering geological properties of dredger fill in the new coastal region of Tianjin. Based on the fractal theory, a quantitative analysis of the microstructure photos of samples was performed by the WD-5 picture processing system, and the changing regularity of the fractal dimension of dredger fill in the new coastal region in the process of seepage flow consolidation was investigated. The result shows that with the increase of seepage pressure, the morphology fractal dimension of structure elements of dredger fill in the new coastal region increases, while the box-counting fractal dimension decreases. Besides, the arrangement of structure elements tends to be dense and the morphology becomes complex. With the increase of consolidation load, the morphology fractal dimension of pores in the dredger fill increases, while the box-counting fractal dimension decreases. Meanwhile, small pores in the dredger fill increase, the volume of pores decreases, and the complexity enhances.

Semi-analytical Solutions for One-Dimensional Consolidation of Layered Soil Obeying Exponential Flow Law

LI Chuanxun, XIE Kanghe, HU Anfeng

2012, 25(1): 84-89. doi: 10.3969/j.issn.0258-2724.2012.021.01.014

[Abstract](1166)

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Abstract:
To calculate one-dimensional consolidation settlement of layered soil obeying an exponential flow law, an exponential flow law model was introduced into the classical consolidation theory for layered soil. The governing equation for one-dimensional consolidation of layered soil was established by considering the exponential flow law and time-dependent loading. A semi-analytical method combining the analytical method with numerical discretization was adopted to solve the governing equation. On condition that the exponential flow law is degenerated into the Darcy's flow law, the reliability of semi-analytical solutions was verified by comparing the results of the semi-analytical method with those of the analytical method. Finally, consolidation behaviors under different parameters were analyzed by combining with a case study of the consolidation of double-layered soil obeying an exponential flow law. The results show that it is simple and reliable to apply the semi-analytical method to the one-dimensional consolidation of layered soil obeying an exponential flow law; compared with the bottom soil layer, the flow exponent of upper soil layer has a great effect on the rate of consolidation; the consolidation rate increases with increasing the thickness of soil layer with low compressibility and high permeability; and the faster the loading rate, the faster the rate of consolidation.

Failure Prediction and Post-Failure Behavior of Typical Rock under Triaxial Compression

WANG Dong, LIU Changwu, WANG Ding, CAO Lei, DU Xinliang, 　　

2012, 25(1): 90-96. doi: 10.3969/j.issn.0258-2724.2012.021.01.015

[Abstract](1354)

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In order to research the failure prediction and post-failure constitutive model of rock under triaxial stress, the triaxial compression tests of limestone and sandstone were conducted under different confining pressures, the regularities of deformation and failure and the relationship between strength and deformation in the whole loading process were analyzed. Based on the test result, a constitutive model for rock was founded. The research results show that the failure mode of limestone is stability loss under a low confining pressure condition, and high confining pressure can restrain rock burst to some extent. The circumferential strain corresponding to the peak stress is nearly a constant under different confining pressures, as a result, it can be taken as an index of rock failure prediction. The shear dilatancy occurs in the post-failure to limestone and at the moment when the axial stress reaches 70% of the peak stress to sandstone. The stress of rock is equal to its strength in the post-failure state, controlled by the lateral deformation, and decreases to the residual strength as the lateral deformation increases. The calculational results based on the constitutive model are consistent with the experimental results under triaxial compression.

Tool Trajectory Optimization of Spray Painting Robot for Composite Conical Surfaces

ZENG Yong, GONG Jun, YANG Dongya, NING Huifeng

2012, 25(1): 97-103. doi: 10.3969/j.issn.0258-2724.2012.021.01.016

[Abstract](1746)

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Abstract:
In order to solve the problem of poor coating uniformity of composite conical surfaces in tool trajectory optimization, a spray tool trajectory generation method was proposed according to the geometrical characteristics of conical surfaces. Using the spray trajectory optimization method that is based on the 3D model of a spray tool for conical surfaces, the tool trajectory optimization at the junction of the combined conical surfaces was discussed. Then, optimal objective functions were established to optimize the spray parameters. Simulation results show that the coating thickness after optimization meets the coating requirement. Compared with the general method, the proposed method can reduce the error of coating thickness between the maximal and ideal values by 0.4 m, and reduce the error between the minimal and ideal values by 1.0 m. In addition, the above errors are 0.8 and 1.4 m less in combination of synclastic patches than those in combination of inverted patches.

Self-synchronization and Stability of Two-Times Frequency Shaker Excited by Bi-shaft

HOU Yongjun

2012, 25(1): 104-108. doi: 10.3969/j.issn.0258-2724.2012.021.01.017

[Abstract](1834)

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Abstract:
Differential equations of phase angle differences between two exciting shafts of a bi-frequency self-synchronous shaker were derived based on the differential equations of shaker motion and those of rotation of the two exciting shafts. The necessary conditions for self-synchronization of the two shafts was obtained by finding the equilibrium point of the status equations, and the stability condition of the shaker was determined by applying the Lyapunov stability theory. A simulation example was presented. The results show that the second power of ratio of the natural torsional frequency of shaker to the exciting frequency of lower speed shaft is a criterion (4/7 in this example), below the criterion the motion of the shaker is stable.

Two Precise Time-Integration Methods for Structural Dynamic Analysis

FAN Xuanhua, CHEN Pu, MU Wenpin

2012, 25(1): 109-114. doi: 10.3969/j.issn.0258-2724.2012.021.01.018

[Abstract](1546)

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Similarities and differences in solving dynamic equations between precise time-integration method with augmented matrix (PTI-AM) and extended precise time-integration method (EPTI) were analyzed. The explicit, discrete and recursive expressions for both methods were deduced, respectively, with the evolutionary random excitations in a general combined form of polynomial, exponential, and sinusoid/cosine functions. Both recursive expressions can be transformed into polynomial functions corresponding to the integral steps. With the same number of terms in the Taylor series, the recursive expression for EPTI contains additional high-order terms besides all the terms in PTI-AM. Therefore, EPTI has higher precision than PTI-AM does. If those additional high-order terms are neglected, the two methods have an identical discrete and recursive expression. In this respect, the two methods are essentially the same despite of different programming realization. An engineering example was presented, showing that the computing precision of both methods was as high as 10-significant-figures, and the computing time of EPTI was over 1 order of magnitude less than that of PTI-AM.

Design of Photoacoustic Imaging System with High Positioning Accuracy Based on PCI4732

RONG Jian, CHEN Bingzhang, ZHONG Xiaochun, HUANG Lin, JIANG Huabei

2012, 25(1): 115-120. doi: 10.3969/j.issn.0258-2724.2012.021.01.019

[Abstract](1211)

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In order to research the photoacoustic imaging abilities of different absorbers, a photoacoustic imaging system was developed based on Labview software design platform coupled with PCI4732 and high positioning accuracy rotation stage RT-5-10. This system consists of a pulsed laser, an immersion probe and an amplifier and so on, and a PCI (peripheral component interconnect) bus was used to realize the connection between the PCI card and a computer. A high resolution filtered back-projection reconstruction algorithm was used to process the data and obtained high contrast and high resolution images. To verify the practicability of the developed system it was tested using human hairs as objects respectively with 2.25, 5.00 and 10.00 MHz transducers. The result indicates that a 5 MHz transducer can gain clearer images than a 2.25 or 10 MHz transducer to show that certain absorber should correspond to certain frequency of transducer.

Design of 16-Way High Power Divider

ZHANG Jianqiong, LIU Qingxiang, LI Xiangqiang, ZHAO Liu

2012, 25(1): 121-126. doi: 10.3969/j.issn.0258-2724.2012.021.01.020

[Abstract](1228)

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Abstract:
In order to meet the requirement for the feeding system of high power microwave (HPM) radiation antenna and overcome the shortage of current multi-port high power divider, a novel 16-way high power divider was developed. The novel high power divider is composed of coaxial waveguide- 4-way rectangular waveguide, H-T branch and rectangular coaxial waveguide, and the 16 outputs of the divider are characterized of equivalent amplitudes and phases. The 16-way high power divider was designed and tested with a center frequency of 2.85 GHz. The experiment results show that at the center frequency, the insertion loss is about 0.4 dB, the voltage standing wave radio (VSWR) is about 1.3, and the output power and phase imbalances are about 0.7 dB and 5 respectively. In the range of 2.78 to 2.92 GHz (5% bandwidth of the center frequency), the insertion loss and the VSWR are below 0.6 dB and 1.5 respectively. The input coaxial waveguide is the bottleneck of the power capacity of the divider so that this characteristic permits the divider to realize the power dividing of HPM source.

AnalysisofAirFlowFieldinAirConditioningSystem andCompartmentsofHigh-SpeedTrains

LIU Jie, LI Renxian, CHEN Lin, LI Shudian

2012, 25(1): 127-132. doi: 10.3969/j.issn.0258-2724.2012.021.01.021

[Abstract](1781)

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In order to test the rationality of the air-conditioning system design of high-speed trains, an entire geometry model for compartment and air-conditioning system of high-speed trains was built considering the characteristics of negative pressure at fresh-air inlet, complicated air-conditioning pipes and good airtightness. The airflow field in the entire geometry was simulated by solving the governing differential functions of computational fluid dynamics (CFD) using the finite volume method. The distributions of velocity field, temperature field, humidity field, and CO2 concentration in the chamber were obtained, and the thermal comfort was evaluated by flow field indexes and comfort indexes. The results show that when a train is running at 350 km/h in summer, the temperature distribution is uniform in compartments; the average value of CO2 concentration is 0.07% to meet the demand for comfort (less than 0.15%); because of the high wind velocity, effective temperature difference at aisle is -4.5 ℃, which is 2.8 ℃ below the standard value of the thermal comfort index; and an appropriate air supply and recycle mode is crucial to obtain uniform flow field and good thermal comfort.

Experimental Study on Electrochemical Corrosion Mechanism of Welded Bogies

YU Xinian, WANG Baoyan, LIU Jun

2012, 25(1): 133-138. doi: 10.3969/j.issn.0258-2724.2012.021.01.022

[Abstract](1410)

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In order to reveal the corrosion law of welded bogies, three types of steel plates and their welded specimens used for welded bogies were put in 3.5%NaCl solution, and their corrosion potentials and AC impedances were analyzed. Polarization curves of the specimens were obtained through potentiodynamic scanning. Meanwhile, galvanic corrosion tests were carried out to detect the potential distributions in welds and at a different location on the both sides of weld seams. The results show that the lowest corrosion potential and the worst corrosion resistance were in weld seams, and high corrosion potentials occurred at the steel plate around the weld seams. Among the test specimens, the highest corrosion potential and the best corrosion resistance, happened in the welded steel plate of 09CuPCrNi-A, where the highest value of potential was -0.458 V, and the highest value of galvanic current was 1.76 A/cm2, which was equivalent to a corrosion rate of 0.018 mm/a. Therefore, the electrochemical corrosion of welded bogies should be given sufficient attention.

Quantitative Analysis of Parameters of Vascular Bioreactor

LIU Yanqiu, HUANG Nan, ZOU Yuanwen, HUANG Xuejin, LI Jinchuan, FAN Yubo

2012, 25(1): 139-143,150. doi: 10.3969/j.issn.0258-2724.2012.021.01.023

[Abstract](1349)

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A vascular bioreactor was designed and constructed by Beihang University and Sichuan University for Southwest Jiaotong University for simulating in vivo environments. The performance indicators of the bioreactor including shearing stress, the state of laminar flow, and pulse pressure were analyzed quantitatively through theoretical derivation of hydromechanics and orthogonal experiment range analysis. The results show that for blood vessels of different diameters, the bioreactor could provide shearing stress ranging from 0.08 to 70.51 Pa. In order to maintain a laminar flow condition of the perfusate, the maximum flow rate in the tubes of five kinds of diameters should not exceed 4.36 cm3/s when the inlet tube length of the culture chamber was 18 cm, and the viscosity coefficient and fluid density of the perfusate were fixed. The operating distance of the pulsation generator had a bigger effect on the difference between systolic and diastolic blood pressures than the flow and frequency, while the effect of pressure was the smallest.

Prediction of Railway Freight Volumes Based on Grey Adaptive Particle Swarm Least Squares Support Vector Machine Model

GENG Liyan, LIANG Yigang

2012, 25(1): 144-150. doi: 10.3969/j.issn.0258-2724.2012.021.01.024

[Abstract](1450)

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In order to improve the forecasting accuracy and the modeling speed for railway freight volumes, the grey forecasting model GM (1, 1) and the adaptive particle swarm optimization (APSO) were both introduced into the least squares support vector machines (LSSVMs). Thus, a new model, the grey APSO least squares support vector machine (GM-APSO-LSSVM) model, was built. The new model weakens the stochastic factor in the original sequence and exploits the regularity of data using the grey sequence operator of the grey model in the first stage. Then, the new data are forecasted with the LSSVM featured by simple calculation, fast solving speed, and powerful non-linear mapping ability. At the same time, the parameters of LSSVM are optimized by the APSO. An empirical analysis was performed to verify the proposed model using the freight volumes data in China. The results show that the proposed model has a superior prediction performance to the existing models, and its performance indices RMSE, MAE, MPE, and Theil are 0.062 8, 0.052 3, 0.016 2, and 0.010 7, respectively, all less than those of the other models. The searching time for the optimal LSSVM parameters using the APSO is 55.656 s, which is 10.462 s less than the time spent by the conventional cross-validation method. The relative prediction errors of the model in predicting the railway freight volumes from 2006 to 2009 are 0.39%, -1.67%, 1.44% and 4.75%, respectively; therefore, the proposed model is more suitable for short-term railway freight volumes forecasting.

Variable Weight Method for Multi-objective Optimization of Freight Flow Allocation in Logistics Network

ZHOU Xiao, ZHANG Jin, ZHANG Fei, LIU Sijing

2012, 25(1): 151-157. doi: 10.3969/j.issn.0258-2724.2012.021.01.025

[Abstract](1320)

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To overcome the shortness of traditional weighted-sum method (WSM) for multi-objective optimization of freight flow allocation in logistics network, a variable weight method was proposed, in which the weights of optimization objectives are variable. The variable weights are determined by preset weights and state values of logistics network elements including the nodes, lines and paths. Those state values are obtained with a WSM based on the attribute values of the elements. The proposed method was applied to an optimization example of logistics network where the restraints are the capacities of transport lines and logistics nodes, and the objectives are the minimum logistics cost, shortest one-way delivery time, and the maximum utilization ratio of the logistics network.

Following Phenomenon and Air Freeway Flow Model

WANG Lili, ZHANG Xinyu, ZHANG Zhaoning

2012, 25(1): 158-162. doi: 10.3969/j.issn.0258-2724.2012.021.01.026

[Abstract](1527)

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Air freeways connecting long-distance city-pairs with heavy traffic flow in the next generation aviation transportation system (NGATS) are characterized by monolayer route with single direction, no crossover, aircraft performance limitation, and high density of operation. In order to study the traffic flow operation on the air freeways, a microscopic aircraft-following model for single-layer route of air freeways was established using the car-following theory, based on the civil aviation operation rules of NGATS. Through analysis of the relationship between air traffic flow and density, the model was then extended to a macroscopic traffic flow model for air freeways. The macroscopic model can be used for air route flow optimization, safety analysis, and capacity evaluation. Simulation results of the microscopic aircraft-following model show that the aircraft-following response of a posterior aircraft intensifies when the separation distance from its anterior aircraft is nearer, the speed of flight in the route is faster, or the respond intensity of the posterior aircraft is weaker. Simulation results of the macroscopic air traffic flow model show that the air traffic flow variation is more remarkable when the aircraft separation distance is smaller or the initial velocity is larger.

Arrival-Departure Capacity and Its Influencing Factors

HU Jun, HU Haibo

2012, 25(1): 163-168. doi: 10.3969/j.issn.0258-2724.2012.021.01.027

[Abstract](1470)

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In order to mitigate flight delays caused by airport capacity limitation, a novel arrival-departure capacity model was built with the maximum flow as the objective. In this model, a discrete-time mixed queuing algorithm is employed to form the transition probability matrix for potential conflicts, and a conflict factor is adopted to adjust the transition probability matrix for optimization of model performance. The mathematic formula for arrival-departure capacity is then derived, and calculation procedures of the capacity algorithm are designed. A simulation was conducted using the actual data collected from Chengdu Shuangliu international airport. The results show that the standard deviation between the calculated number of flights and the actual data are 1.552 and 1.436, respectively, when the arrival and departure rates of flights are 0.6 and 0.5, and the throughput rate of airport (TRA) is 0.8. When the arrival requests obey Poisson distribution, the number of rejected requests decreases with an increase in TRA, and the relationship between arrival capacity and TRA shows a positive correlation trend.

Removal of Heavy Metals from Sludge by Bio-leaching

XU Youze, MA Chao, CHENG Yingxiang, WANG Qiangqiang, ZHONG Zhenyu

2012, 25(1): 169-174. doi: 10.3969/j.issn.0258-2724.2012.021.01.028

[Abstract](1068)

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In order to reduce the harm of heavy metals in sludge to environment, the effect of medium pH, microorganism inoculation amount, leaching temperature, and cycle leaching time on removal of heavy metals was studied by single factor experiment, and the content change of heavy metals in the process of leaching under the optimal conditions was analyzed. The results show that the leaching liquid pH decreased as the process of removal of heavy metals progresses, and that the optimal medium pH, microorganism inoculation amount, leaching temperature, and cycle leaching time was 1.0, 15.0%, 30 ℃, and 24 h/d, respectively. Under the optimal conditions, the removal rate of Cd, Mn, Cu, Pb, and Zn was 88.0%, 88.0%, 69.0%, 67.0%, and 83.0%, respectively.

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2012 Vol. 25, No. 1