西南交通大学学报

Dynamic Performance Analysis and Design of Fuel Cell Hybrid Locomotive

CHEN Weirong, ZHANG Guorui, MENG Xiang, BU Qingyuan, LI Qi

2017, 30(1): 1-8. doi: 10.3969/j.issn.0258-2724.2017.01.001

[Abstract](682)

Abstract:
Fuel cells (FCs) for hybrid locomotives have slow dynamic responses and soft output characteristics, and are incapable of recovering regenerative energy in the braking process. In order to cope with these issues and improve the dynamic and economic performance of FC hybrid locomotives, a locomotive composed of two motor units and one trailer unit was used as a prototype on the Matlab platform to analyze the power and energy requirements of the locomotive when it is powered by FC, battery (B) and super-capacitor (SC) in typical cases, of the maximum speed, acceleration and slop. According to the analysis results, six configuration schemes of hybrid power were proposed, and their feasibility were discussed. The results show that the configuration with 2 sets of FC systems, 800 batteries and 108 super-capacitors is a feasible, reasonable and economic scheme to satisfy the power requirement of the locomotive to speed up to 30 km/h with 1 m/s2 acceleration and then continuously up to 70 km/h. This may provide a reference for the model selection in design of the same kind FC hybrid locomotives.

Frequency-Domain Dielectric Spectroscopy Characteristics of Generator Epoxy/Mica Insulation

GAO Bo, HAO Changjin, LI Shuaibing, YIN Xiaobing, YU Xiaofeng, WU Guangning

2017, 30(1): 9-15. doi: 10.3969/j.issn.0258-2724.2017.01.002

[Abstract](551)

Abstract:
To apply frequency domain dielectric spectroscopy technology (FDS) to the non-destructive diagnosis of epoxy/mica insulation, a generator winding bar sample was given an accelerated multi-stress aging treatment by combined use of thermal, electrical, and mechanical (vibration) aging methods, and its FDS parameters at different aging periods were measured experimentally. Based on these PDF parameters, a double relaxation Cole-Cole model with modified DC conductivity was established and effects of the insulation aging on the complex dielectric constant and relaxation Cole-Cole model parameters were analyzed. The results show that the real part and imaginary part of the complex dielectric constant increases gradually with aging time, and the increase tendency is more significant in the low-frequency band at 0.001-1.000 Hz. The mechanism of relaxation is changed by the aging of insulation, leading to a new relaxation process. Because of the new relaxation, the description of relaxation in the double relaxation Cole-Cole model of the first two periods is incoherent with that of the last three periods. The test values of the dielectric spectrum can be well fitted by the double relaxation Cole-Cole model. With the aging, the DC conductivity and interfacial polarization increases quickly, and the interfacial polarization relaxation time constant tends to decrease. The study provides a new idea for aging status assessment of generator using FDS method.

Fatigue Life Prediction on Rib-to-Deck Welded Joints of Steel Bridge Deck Based on LEFM

WEI Xing, JIANG Su

2017, 30(1): 16-22. doi: 10.3969/j.issn.0258-2724.2017.01.003

[Abstract](546)

Abstract:
In order to explore the fatigue performance of U-shaped rib-to-deck welded joints of orthotropic steel bridge deck under cyclic loading, based on linear elastic fracture mechanics (LEFM), fatigue life evaluation was carried out using finite element method (FEM). According to the structure features of rib-to-deck welded joints of orthotropic steel bridge deck, 2D FEM model with 3 U-shaped ribs was built using ANSYS software. Presetting 4 kinds of initial cracks for weld detail, the equivalent stress intensity factors (ESIF) at each crack with 2 loading cases were calculated. The relationship between stress intensity factor and influential parameters, including initial cracks length, thickness of deck plate, height and thickness of U-shaped rib, was analyzed. In accordance with weld detail category of orthotropic steel bridge deck in Eurocode 3, ESIF at every crack were obtained, and fatigue life prediction method of weld joint of orthotropic steel deck were proposed based on fatigue crack propagation model in LEFM theory. Results show that fatigue life calculated with LEFM is greater than the value in Eurocode 3, and fatigue life of the welded joint will be enhanced when the deck plate thickness is 16-18 mm and initial crack length is less than 0.1 mm.

Fragility Analysis of Large-Span Continuous Rigid Bridge Considering Wave Passage Effectt

CHEN Zhiwei, PU Qianhui, LI Xi, CHEN Zhiqiang, JIA Hongyu

2017, 30(1): 23-29,37. doi: 10.3969/j.issn.0258-2724.2017.01.004

[Abstract](586)

Abstract:
To study wave passage effect on the fragility of the large-span continuous rigid bridge (LSCRB) in mountainous area, an actual LSCRB in southwest area was chosen as the study object. Twenty earthquake records were selected using the spectra-compatible method. Then, incremental dynamic analysis (IDA) of the bridge structure was conducted under uniform excitations and non-uniform excitations to obtain the fragility curves. The analysis results show that the relative displacements of the piers increase with the height of piers, and the relative displacement of the highest pier is around 1.03-2.81 times that of low pier, but the seismic design of low piers should be paid more attention because the damage probability of low piers is greater than that of high piers. Compared with the case under uniform excitations, the wave passage effect may reduce the probabilities of slight and moderate damages of low piers, and increase those of high piers. Furthermore the probability of extensive damage may be increased by the wave passage effect both for the low and high piers. As a result, in the seismic design of the high-pier bridges, it is necessary to consider the effect of wave passage on bridge structure, especially for the high-intensity zones.

Experimental Research on Deformation Characteristics of Piled Raft Foundation under Flexible Load

SHAO Guoxia, SU Qian, CHEN Shangyong, BAI Hao, WANG Wubin

2017, 30(1): 30-37. doi: 10.3969/j.issn.0258-2724.2017.01.005

[Abstract](571)

Abstract:
To study the pile-raft foundation in thick soft clay ground, total settlements of foundation surface, layered settlements, lateral deformations, and pore water pressures of foundation soil for pile-raft foundation and natural foundation were observed and analyzed by long-time in-situ test. The load and deformation mechanism of pile-raft foundation under flexible load was proposed by the comparative analysis of the deformation differences between the two types of foundations. The results show that the total settlement of pile-raft foundation is reduced to be the 24% total settlement of the natural foundation, and the differential settlement is reduce to be 0.9%. This means that the pile-raft foundation has lager integral rigidity, which can homogenize the load and restrict the lateral deformation, and lead to the reduction in the total settlement and differential settlement. The settlement of the pile-raft foundation in substratum is the main part of total settlement, which accounts for the 90% total settlement. The pile-raft structure bears the most subgrade load. Compared with that of the natural foundation, the excess pore water pressure of the pile-raft foundation is reduced by about 70%; therefore, the settlement of foundation is reduced.

Deformation and Mechanical Performance of Buried HDPE Pipes Reinforced by Geogrids

XIAO Chengzhi, WANG Jiayong, YANG Yaxin, ZHOU Xia

2017, 30(1): 38-44,68. doi: 10.3969/j.issn.0258-2724.2017.01.006

[Abstract](549)

Abstract:
To analyze load reduction performance of buried pipes reinforced by geogrids, the influence of embedment depth of the uppermost geogrid, length of geogrid, geogrid layers, sand surrounding buried pipes and buried depth of pipes on the deformation and mechanism of pipes was studied through static loading plate tests. The results show that when the length of geogrids changes from 0 to 4D (D denotes the external diameter of pipes), relative density of sand varies from 45% to 75% and reinforcement layers change from 0 to 3 or 4, the ultimate bearing capacities of load plate are respectively 1.4, 1.6 and 2.52 times the one without reinforcement. Moreover, the hoop strain plays a dominant role in buried pipes, ranging from -1.0% to 0.5%. Deformation in vertical direction is greater than that in horizontal direction. The optimal load reduction performance of pipes reinforced by geogrids was obtained when the embedment depth of the uppermost geogrid is 0.4B (B is width of loading plate), geogrid length is 4D, and geogrid layers is 3-4.

Performance-Based Experiment Research on Three-Story Concrete-filled Steel Tubular Frame

WEN Yang, MENG Chuncai, GUO Hongling

2017, 30(1): 45-53. doi: 10.3969/j.issn.0258-2724.2017.01.007

[Abstract](524)

Abstract:
To study the seismic performance of concrete-filled steel tubular(CFST) frame structure, the quasi-static test on a three-story frame structure consisting of square CFST column and rectangular CFST beam was carried out. The hysteretic behavior, ductility, bearing capacity, stiffness degradation, energy dissipation capacity and other performance indicators were studied, and finite element simulation was used to analyze the mechanical behavior of concrete-filled rectangular steel tubular beams. Results show that the hysteretic curve of concrete-filled steel tubular frame structure is plump. Its ductility coefficient is greater than 3. The inter-story drift ratio falls in the range of 1/43 to 1/27. The inter-story plastic deformation capacity decreases with the increase of slenderness ratio of frame column and the stiffness ratio of the beam and column. The equivalent viscous damping coefficient is within the range of 0.115 to 0.441. The strength degradation is not obvious, but the stiffness degradation is more obvious. With the increase of load, if the beam or column yields, the neutral axis gradually moves to compressive zone; and the tension zone of concrete reaches the maximum area when load reaches the maximum.

Calculation of Internal Humidity Field of Concrete Based on ANSYS

WANG Yongbao, JIA Yi, ZHAO Renda

2017, 30(1): 54-60. doi: 10.3969/j.issn.0258-2724.2017.01.008

[Abstract](606)

Abstract:
In order to calculate the humidity field of concrete using the temperature field module in finite element program, a comparison between thermal field and humidity field was made of their differences in the differential equations, initial and boundary conditions, etc. Based on the temperature field module in ANSYS, a finite element method was proposed to calculate the humidity field in concrete. From the aspect of self-desiccation and desiccation, this method was verified against the existing test results of the relative humidity in concrete. The values of parameters for ANSYS analysis such as the coefficients of the internal moisture consumption function, moisture diffusion coefficients, and surface factors which affect the humidity field in concrete were analyzed. The results show that the relative humidity, diffusion coefficients, self-desiccation formula, and the coefficient of moisture transfer in surface used in the humidity field calculation can be replaced by the temperature, thermal diffusivity, adiabatic heating function, and the heat transfer coefficient used in the temperature field calculation. Using the temperature field module to analyze the humidity field in concrete, the maximum error between the calculated results and the existing test results is 7.3%, which meets the engineering requirements. The self-desiccation formula obtained from the experimental results can be applied to the moisture field calculation of the concrete with a water cement ratio ranging from 0.28 to 0.68.

Effect of Admixtures on Tensile Behavior of Fiber Reinforced Cementitious Composites

WANG Hailong, LUO Yuejing, PENG Guangyu, SUN Xiaoyan, YING Qiming

2017, 30(1): 61-68. doi: 10.3969/j.issn.0258-2724.2017.01.009

[Abstract](479)

Abstract:
To reduce the material cost and understand the modification effects of admixtures on the tensile properties of polyvinyl alcohol fiber-reinforced engineered cementitious composites (PVA-ECCs), PVA-ECCs were prepared with different mass percentages of silica fume(SF), fly ash(FA) and metakaolin (MK) for replacement of cement. Then, tensile tests were carried out to study the tensile properties of the PVA-ECCs before and after modification, including the ultimate tensile strain, the initial cracking load, the ultimate tensile strength, and the crack development. Furthermore, the influence mechanisms of the admixtures were discussed on the basis of the experiment. The results show that the initial cracking load and the ultimate tensile strength of the composite modified by 65.0% of FA were decreased by 25.5% and 26.0%, respectively,but the deformation ability was twofold enhanced. In addition, fly ash improved the crack width and crack distance in the composite, causing the multiple cracking phenomenon happened more easily in the FA modified composite. For the composite admixed with 50.0% of FA and 15.0% of SF compound, the crack width decreased; however, the deformation ability was increased by 7.6% compared to the composite admixed with 65.0% of FA. When MK was incorporated into the composite, the modified materials had better deformation abilities. For the composites with the incorporation of FA, SF and MK and a moderate fiber volume fraction of 2.0%, an ultimate strain exceeding 2.0% as well as an ultimate strength of 3.99 MPa was achieved. In addition, the material exhibited a high ductility and multiple cracking characteristic. The cracks were controlled well by the material itself, in which the maximum crack width in saturation state was less than 175 m and the average crack width was less than 115 m.

Morphology of Limestone Manufactured Sand Based on Image Processing Technology

ZENG Xiaohui, DAI Yapeng, QU Fulin, YE Yuezhong, XUE Yuan, WANG Zhimeng, ZHENG Yongfei

2017, 30(1): 69-74. doi: 10.3969/j.issn.0258-2724.2017.01.010

[Abstract](511)

Abstract:
To quantitatively study the morphological characteristics and regularity of limestone manufactured sand with different particle sizes, digital images of 6 size fractions in total, 4.750-2.360, 2.360-1.180, 1.180-0.600, 0.600-0.300, 0.300-0.150 mm and 0.150-0.075 mm (sample size of each size fraction is 500), were collected by digital camera and stereomicroscope. Based on digital image processing (DIP), the circularity,aspect ratio and sphericity of samples were quantitatively determined using software Image-Pro Plus. While the fractal dimension of limestone manufactured sand was calculated according to fractal theory. Besides, statistical analysis was used for the morphology characteristics, and the morphology parameters of limestone manufactured sand and river sand were compared. The results indicate that the circularity,aspect ratio and sphericity of limestone manufactured sand with different sizes basically obey the normal distribution. For different size fractions,the changes of circularity,aspect ratio,sphericity and fractal dimension are consistent,signifying that the morphology parameters of limestone manufactured sand or river sand can be characterized by either one of these parameters.The circularity,aspect ratio and sphericity of limestone manufactured sand are 0.834-0.857, 0.693-0.705 and 0.793-0.799, less than those of river sand by 5.0%,7.2% and 3.3%, respectively,while its fractal dimension reaches 1.046-1.056, higher than that of the river sand by 3.2%. Finally, the recommended ranges of roundness, aspect ratio, sphericity and fractal dimension in the process of manufactured sand shaping were provided, i.e., 0.880-1.000,0.740-1.000, 0.820-1.000 and 1.010-1.025.

Crack Propagation Law of Segment Tendon under Jacking Forces

LU Daiyue, HE Chuan, WANG Shimin

2017, 30(1): 75-82. doi: 10.3969/j.issn.0258-2724.2017.01.011

[Abstract](496)

Abstract:
To explore the cracking and local damage of tenon segment that easily occurs during the construction of shield-driven tunnels, a model of standard tenon segment was built using the extend finite element method (XFEM) with ABAQUS. The initiation location, propagation direction and distribution of segment cracks were analyzed in a dozen of working conditions including non-uniform jacking forces, asynchronous jacking and eccentric jacking loads. Numerical results indicate that bad construction load is the main cause of cracks. Areas burden with large loads and that the jacks first contact are liable to crack. Cracks are easier to initiate and propagate at the central area of the top surface of segment than at both ends, and at the intrados than at outer surface. Three factors, if sorted in a descending order by their damage severity to a tenon segment, are eccentric jacking loads, asynchronous jacking and non-uniform jacking forces.

Experimental Study of Spectral Characteristics of Fluctuating Wind Loads on High-Rise Building with Rectangular Section

ZENG Jiadong, LI Mingshui

2017, 30(1): 83-90. doi: 10.3969/j.issn.0258-2724.2017.01.012

[Abstract](559)

Abstract:
In order to study the effects of wind field characteristics and side ratio of rectangular section on the spectral characteristics of fluctuating wind loads for rectangular high-rise buildings, the pressure fluctuations on a stationary rigid model with cross configurations of 1:2 and 2:1 were measured by wind tunnel test for synchronous pressure measurement in simulated atmospheric boundary layer. Referring to the spectral model given by the Architectural Institute of Japan (AIJ), a simplified spectral expression of fluctuating across-wind loading of rectangular high-rise building was proposed by fitting the measured results. The experimental results show that the fluctuating along-wind load is mainly caused by longitudinal turbulence, and the spectrum of fluctuating along-wind load is consistent with those of incident turbulence. The formation mechanism of fluctuating across-wind loads is more complex, and there is vortex shedding, separation or reattachment on the sides of the rectangular prism. The dimensionless power spectral density and the Strouhal numbers are almost constant along the height. The values of Strouhal number are 0.128 and 0.069 7 respectively for the side ratios of 2:1 and 1:2.

New Methodology for Stability Analysis on Repeated Measurement of CPⅢ Vertical Control Network

LIU Chenglong, LIU Zhujun, YANG Xuefeng, LIU Zhi

2017, 30(1): 91-97. doi: 10.3969/j.issn.0258-2724.2017.01.013

[Abstract](562)

Abstract:
In the current code on the stability analysis of repeated measurements for the CPⅢ vertical control network of high-speed railways, the divergence tolerance of elevation between original and repeated measurements should be no more than 2 mm, which is not reasonable due to misjudging stable points. Besides, there is also poor evidence to set the altitude difference between original and repeated measurements to be no more than 3 mm. Thus, more reasonable divergence tolerance of elevation and altitude difference between the original and repeated measurements were deduced, and a new method on the stability analysis of CPⅢ vertical control network was proposed. This new method calculates the altitude difference for every segment of the CPⅢ vertical control network and detects unstable segments in the whole network according to the original and repeated measurement limits. Then, for the two CPⅢ points on each unstable segment, the divergence tolerances of elevation were computed respectively to detect the unstable CPⅢ points of the unstable segments and analyze the stability of CPⅢ vertical control network. Both the theoretical and test data show that when the divergence tolerance of elevation between original and repeated measurements for the neighboring points is less than 1.4 mm, the proposed method can reliably detect the unstable points from the CPⅢ vertical control network.

Effect of Regional Distribution and Degradation of Ballast Resistance on Longitudinal Force of Rail

LIU Hao, XIE Kaize, WANG Ping, XIAO Jieling, CHEN Rong

2017, 30(1): 98-105. doi: 10.3969/j.issn.0258-2724.2017.01.014

[Abstract](513)

Abstract:
In order to explore the effect of ballast resistance evolution on the mechanical behavior of the continuously welded rail (CWR) on bridge, tests were conducted for the longitudinal and lateral ballast resistances on bridge and roadbed sections. Taking an example of an extra-large double-line continuous beam bridge commonly used in railway, the track resistance distribution characteristics on bridge were obtained, and the local ballast resistance degradation was discovered in the ballast service. On this basis, the longitudinal mechanics behavior model of CWR on bridge was established, which takes into account the non-uniform distribution and degradation of ballast resistance. The results show that the distribution of ballast longitudinal resistance on bridge shows significant regional distribution characteristics, the maximum longitudinal resistance was 31.8 kN per sleeper at the central span of bridge, and the longitudinal resistance near the beam joint was relatively small, 21.7 kN per sleeper, demonstrating obvious ballast resistance degradation. The lateral resistance distribution on bridge also has moderate regional distribution characteristics, the lateral resistance at the central span of bridge was 31.7 kN per sleeper and the lateral resistance near the beam joint was 25.5 kN per sleeper, while the degradation does not obvious. As thermal load leads to beam expansions and the dynamic loads of trains cause bridge vibration displacement and rotation angles at the beam support, the crushed-stone ballast dynamically changes between tension and compression, and the ballast resistance shows obvious degradation characteristics. When there is ballast resistance degradation, the rail longitudinal force, rail displacement and relative displacement between bridge and track under thermal loading has a certain attenuation. Thus, the maximum rail longitudinal additional force with the temperature span of 140 m was reduced by about 11.7%, and the attenuation rate increases linearly with the increase of temperature span. The beam-rail interaction is relatively large if it is calculated according to specifications.

Effect of Rolling Direction Reversal on Friction and Wear Behavior of Wheel Steel

ZHANG Mingyuan, LU Liantao, ZENG Dongfang, CHEN Gang, ZHANG Jiwang

2017, 30(1): 106-111,126. doi: 10.3969/j.issn.0258-2724.2017.01.015

[Abstract](431)

Abstract:
In order to improve the wear resistance of wheel steel in rolling contact conditions, friction and wear tests were conducted on a rolling-sliding wear test machine to measure the friction coefficients and wear rates of wheel specimens before and after their rolling direction reversal (RDR) at the transition and steady wear states. The surface damages of the wheel specimens were observed by scanning electron microscopy (SEM), and the deformed structures of the wheel specimens were observed by laser scanning confocal microscopy and SEM. The results show that the friction coefficients of the specimens were all around 0.495 before and after RDR, so the RDR has no effect on the friction coefficient of the friction pairs. After test, the wear rate of the wheel specimen whose RDR occurred at the transition state was 16.09 g/m, while the wear rates of the wheel specimens whose RDR occurred at the steady state were 13.65 g/m and 13.94 g/m, respectively, suggesting that the RDR at the transition wear state improves the wear resistance less than that at the steady state. For the wheel specimen with higher strain hardening rate before RDR, the depth of the wavy structure was shallower and the pearlite interlamellar spacing became smaller after wear test, and hence the wear resistance was improved more significantly.

Influence of Wheelset Structure and Fastener Stiffness on Rail Corrugation

CUI Xiaolu, CHEN Guangxiong, YANG Hongguang

2017, 30(1): 112-117. doi: 10.3969/j.issn.0258-2724.2017.01.016

[Abstract](575)

Abstract:
In order to study the formation mechanism and influence factors of rail corrugations on a sharp curved track of metro line, a finite element model for a wheelset-track system on a sharp curved track, which consists of a power wheelset, two rails and a series of sleepers, is established from the viewpoint of friction-induced vibration causing rail corrugation. Using this model, the stability and dynamic performance of the wheelset-track system are analyzed by the complex eigenvalue analysis and transient dynamic analysis. The simulation results show that the friction-induced vibration of the wheelset-track system is more likely to occur under the effect of the saturated creep force, which is able to cause rail corrugation. Meanwhile, the gearbox location on the leading wheelset has a little influence on the self-excited vibration of the system. The lateral stiffness of the fastener has a little influence, while the vertical stiffness has a significant influence on self-excited vibration. As the vertical stiffness of fastener increases, the unstable vibration of the wheelset-track system presents a trend of first increase and then decrease. When the vertical stiffness is about 20 MN/mm, rail corrugation is most likely to occur.

Design of Magnetic Levitation Controller and Static Stability Analysis

WANG Keren, LUO Shihui, ZHANG Jiye

2017, 30(1): 118-126. doi: 10.3969/j.issn.0258-2724.2017.01.017

[Abstract](692)

Abstract:
In order to realize the stable suspension of the maglev train in the condition of low track beam stiffness, and reduce construction cost of track beam, a electromagnet-elastic-track-carbody model was established based on Newton's second law. Firstly, the vibration information of electromagnet, track beam and carbody was introduced into the control system by the designed state observer; then the feedback gain matrix was obtained using linear matrix inequality. Next, both were utilized for the dynamic simulation by MATLAB to derive the optimal track beam stiffness and quality, which are 200 kN/m and 325 kg, respectively. The analysis results show that compared with the traditional optimal controller based on the Riccati equation, the controller using linear matrix inequality control algorithm achieves a better quadratic performance index. The control strategy is able to realize the system stable suspension at small stiffness and mass of track beam, and stabilize the system after 0.5 seconds or so. The system is robust to some external disturbances.

Simulation of Airbag Ejection Acceleration Process on a Train Collision Testbed

LIU Zhongbin, XIAO Shoune, LUO Shihui

2017, 30(1): 127-132. doi: 10.3969/j.issn.0258-2724.2017.01.018

[Abstract](524)

Abstract:
To solve the driving problem with great energy for a train collision testbed, the airbag with a self-growth variable boundary was proposed. The airbag with high-pressure gas can work effectively in a long distance under the condition of constraint and un-blasting. Based on the control volume method, an ejection model of the circlewise folding airbag was built using the simulation software LS-PrePost and LS-DYNA. The influence of the ejection process and structural features of multilevel airbags on the ejection behavior and energy was studied under conditions of initial compression and a certain pressure, respectively. The results show that the ejection model of the circlewise folding airbag can reflect the basic characteristics of the airbag ejection acceleration method, and the airbag ejection acceleration is stable and continuous. The number of airbags has a significant effect on the ejection distance, the output energy, and the stability of the airbag collision testbed. A more number of airbags means a greater ejection distance and more effective energy output. The energy of a three-airbag catapult is 6 times than that of a one-airbag catapult. The more the number of airbags is, the larger the lateral displacement of the airbag ends is. However, the swing displacement of a three-airbag catapult is not more than 7 mm, and hence a good stability can be ensured in the airbag ejection process.

Generalized Multi-step Explicit Integration Method in Structural Dynamics

YANG Chao, ZHU Tao, YANG Bing, YANG Guangwu, LU Liantao, XIAO Shoune

2017, 30(1): 133-140. doi: 10.3969/j.issn.0258-2724.2017.01.019

[Abstract](516)

Abstract:
In order to develop new time integration algorithms, a generalized multi-step explicit integration method (GMEM) was proposed by means of weighting independent variables, accelerations. Firstly, a general integration format was provided based on the acceleration explicit method. Furthermore, the stability, numerical dissipation, numerical dispersion and accuracy were analyzed. Finally, two numerical examples were employed to contrastively analyze three kinds of GMEMs (GMEM1, GMEM2 and GMEM3-2), the HHT- method and the Newmark method. The results indicate that the GMEM is conditionally stable. The spectral radius is identically equal to 1 in the system without damping. The GMEM of three steps can achieve the highest accuracy of three order. There is not numerical dissipation for the GMEM of three steps in undamped systems. The root mean square error of the GMEM2 is approximately half of that of the Newmark method, and 1.8 times that of the GMEM3-2 approximately.

Abrasion Process Modeling of Abrasive Belt Grinding in Rail Maintenance

WANG Wenxi, LI Jianyong, FAN Wengang, HE Zhe

2017, 30(1): 141-147. doi: 10.3969/j.issn.0258-2724.2017.01.020

[Abstract](497)

Abstract:
Considering the contact area state under elastic contact of curved surfaces, an abrasive belt wear process model for rail grinding was established using the Archard equation and Heltzian contact theory to investigate the influence of technological parameters on the belt service life. The curves of wear height and belt service life were calculated through numerical simulations under different grinding forces, belt speeds, running car speeds, rail surface curvature radius and average variances of grit protrusion height. The rationality of the model was proved by comparing the simulational curves with existing experimental results. Simulation analysis illustrates that the wear contour of abrasive belt surface typically presents as a half ellipsoid, and the belt service life reduces exponentially with an increase in both the contact pressure and belt speed, but rise approximate linearly with the growth of running car speed. Taking the 60 kg/m rail as an example, under the same process conditions, the belt wear for grinding the R13 segment is clearly worse than that for both R80 and R300 segments. In the range of allowable rail surface roughness, a large grit protrusion height variance would be helpful to prolonging the abrasive belt service life.

OFDM based DFT Scrambling Vector Code Division Multiple Access

ZHOU Gao, FAN Pingzhi, HAO Li

2017, 30(1): 148-155. doi: 10.3969/j.issn.0258-2724.2017.01.021

[Abstract](406)

Abstract:
Channel spectral nulls (or deep fades) on some sub-carriers will degrade the performance of multiple access systems based on multiple access OFDM. To improve the performance, a novel DFT scrambling vector multi-carrier DS-CDMA was proposed based on the theory of matrix permutation. Using the decomposability of tensor product (or named Kronecker product), the new system rearranges the transmission signals with the help of vector OFDM (V-OFDM), uses channel diversity resulted from by matrix vector decomposition of Kronecker product to restrain the single sub-carrier deep fading, and lowers the system complexity and peak-to-average power ratio (PAPR) by DFT spread and pre-scrambling based on analyzing decomposition characteristics of r-cyclical matrix. Simulation results show that the novel system is better than traditional multi-carrier accesses. For example, at high signal-to-noise ratio (Eb/N0), such as 20 dB, compared with a typical uplink access, i.e., multi-carrier direct-sequence code division multiple access (MC-DS-CDMA), the new system performance is upgraded by 6 dB averagely, and is slightly 0.5 dB better than a typical downlink access, multi-carrier code division multiple access (MC-CDMA). It achieves full channel diversity order theoretically. Moreover, the new system lowers PAPR and promotes spectrum efficiency compared with the two traditional accesses. For instance, with 64 sub-carriers, 8 blocks and 12 guard intervals, the proposed system reduces PAPR with 2 dB, and gains more 10% spectrum too.

Self-Recovery E-evidence Image Watermarking Algorithm Based on Binary features of Important Blocks

YIN Bangxu, CHEN Fan, WEI Wei, WANG Hongxia

2017, 30(1): 156-163,208. doi: 10.3969/j.issn.0258-2724.2017.01.022

[Abstract](479)

Abstract:
Existing self-recovery watermarking algorithms are generally designed for natural images, which have a large watermark embedding capacity and cannot clearly recover the text information. To deal with this, a self-recovery watermarking algorithm for E-evidence image authentication was proposed, which can reach a balance between watermark embedding capacity and recovery quality. Firstly, according to the characteristics of an E-evidence image, all image blocks in the test E-evidence image were categorized into three types:important block, unimportant one and blank one. Then, to ensure the correctness of the type code, the type code is permutated and encoded by RS coding to generate a partial-recovery watermark that is randomly embedded in all blocks. At the same time, another recovery watermark is generated by coding the binary features of important blocks and randomly embedded in the least significant bit of unimportant or blank blocks based on secret key. At last, the performances of the proposed scheme and the alterable-capacity watermarking algorithms were compared by using seven E-evidence images. Results show that the watermark embedding capacity of the proposed scheme is reduced to 0.64 bit per pixel, compared with two literature results of 1.73 and 2.99, and the peak signal to noise ratio (PSNR) of the watermarked E-evidence image by the proposed scheme is about 8 dB and 23 dB higher than those obtained from literature, while the performance of tamper detection and tamper recovery is not worsened. This is mainly because the proposed scheme adopts classification code and only encodes the important blocks.

Algorithm for Reconstructing Polyhedral Objects from Single Axonometric Line Drawing Based on Rotation Transformation

TIAN Huaiwen, GUO Shizhang, YANG Ningxue

2017, 30(1): 164-170. doi: 10.3969/j.issn.0258-2724.2017.01.023

[Abstract](482)

Abstract:
The divide-and-conquer strategy is adopted to improve the efficiency of 3D reconstruction of a single line drawing and guarantee the convergence of the optimization algorithm for polyhedral objects. First, the single line drawing is divided into a lot of closed polygons, then all closed polygons are grouped according to their connection relationships, and finally all faces represented by the closed polygons in one group are reconstructed into 3D. In this way, a normal global optimization problem is resolved in a step-by-step fashion. Based on this strategy, several local optimization criteria are discussed, and a step resolving algorithm for 3D reconstruction by use of the rotation transformation are proposed. By rotating the child face against its parent face until some local optimization criteria are met, all child faces in the same level can be resolved in 3D space. Utilizing the top-down linkage relationships among faces represented by the loops on the drawing, all the child faces will be reconstructed step by step. Case studies indicate that this method is suitable for 3D reconstruction of multi-face objects and the efficiency can be improved by 20% compared with typical global optimization methods.

Research on Nonlinear Characteristics of Air Traffic Flows on Converging Air Routes

WANG Chao, ZHENG Xufang, WANG Lei

2017, 30(1): 171-178. doi: 10.3969/j.issn.0258-2724.2017.01.024

[Abstract](616)

Abstract:
Insights into the temporal and spatial characteristics of air traffic flow is the prerequisite of air traffic flow simulation, prediction and control. Nonlinear characteristics of traffic flow time series on converging air routes were explored from the chaotic and fractal views. First, a traffic flow identification method based on air route network structure was proposed, and air traffic flow time series were constructed on different time scales. Then, based on the reconstruction of phase space, chaos existing in air traffic flow was quantitatively analyzed by the max Lyapunov exponent, and the chaotic characteristics of traffic flow time series on different time scales were analyzed by recurrent maps. Finally, the fractal characteristics of traffic flow time series on different time scales were analyzed using the correlation dimension. The results show that chaos does exist in traffic flow time series on different time scales. The chaotic characteristic of traffic flow time series is the most obvious at the time scale of 5 min. With time scales increasing, the randomness of air traffic flow time series increases, and the ability to show the system complexity becomes weak.

Collaborative Aircrafts Scheduling Strategy in Metroplex Terminal Area Based on FS-MOPSO

WANG Zhan, WU Yi

2017, 30(1): 179-185. doi: 10.3969/j.issn.0258-2724.2017.01.025

[Abstract](522)

Abstract:
To solve the collaborative scheduling problem for arrival aircrafts in metroplex terminals, a discrete optimization model was proposed under ration-by-schedule (RBS). The model focuses on improving scheduling fairness between airlines based on collaborative decision-making (CDM) to seek a best scheduling strategy. By analyzing the fix and runway double restraints and keeping the RBS order as far as possible by minimizing the number of each flight's reversals, the model realized the muilt-objectives of improving the scheduling fairness and minimizing the total delay and the total amount of flights overtaking. In addition, fuzzy self-correction multi-objectives particle swarm optimization (FS-MOPSO) was used to solve the model. As a case study, the scheduling problem for arrival aircrafts in Shanghai metroplex was simulated by the proposed method to verify its effectiveness. The results show that the collaborative scheduling strategy can reduce the total delay time by 22.53% compared to the traditional strategy, and the decrease the variance of reversals by 26.31% compared to the genetic algorithm aimed at minimizing the delay time only.

Rutting Behavior of Flexible Pavement in Airport Turning Area under Temperature Field

CAI Jing, LI Yue, SUN Qingang

2017, 30(1): 186-194. doi: 10.3969/j.issn.0258-2724.2017.01.026

[Abstract](485)

Abstract:
Since the lateral shearing effect of aircraft wheels during low-speed turning may aggravate the rutting defects of flexible pavement and jeopardize the driving safety, a numerical analysis model of flexible pavement structure coupled with a continuous alternating temperature field was established on the ABAQUS platform. In this model, the low speed turning performance of aircraft wheel on the ground was formulated and analyzed, and the laws of rutting formation in straight-line and turning areas of flexible pavement were compared. According to the deformation characteristics of pavement in turning area, a new evaluation index of rutting depth was proposed, whereby parametrical influences of traffic load and meteorological conditions on the rutting formation were analyzed. The results indicate that the transverse thrust of aircraft wheel load will lead to a notable lateral tensile deformation at the bottom of the pavement surface layer. The vertical stress at the loading position in the turning area is smaller than in the straight line area, which is in good accordance with the distribution of rutting depth. As the upheaval deformation at the external side of the outside wheel increases in the turning area, the upheaval deformation at the internal side of the inside wheel decreases and merges with the settlement basin together. The deformation can be reflected by the index of composite rutting depth and it presents a tendency to increase with the aircraft's turning speed, with a maximum amplification of nearly 50%. With the turning speed increasing, the accumulative action time of wheel load shortens, and the rutting depth at wheel marks decreases with a maximum amplitude of 30%. In addition, the continuous high temperature of surface layer of flexible pavement during daytime is a vital environmental reason for the rapid development of rutting formation in the initial stage. The sensitive temperature of rutting formation in the flexible pavement under study is around 30℃. The rutting deformation of the turning area can be remarkably reduced by limiting the minimum taxiing speed in high temperature conditions.

Integrated Navigation Grid Model and Its Applications in Smart Tourism Routing

ZHU Qing, WANG Yeping, ZHANG Junxiao, CHEN Chongtai, CAO Zhenyu

2017, 30(1): 195-201. doi: 10.3969/j.issn.0258-2724.2017.01.027

[Abstract](480)

Abstract:
Aiming at the personalized navigation requirements of the tourists in complex scenic environments, an integrated navigation grid model is proposed to comprehensively represent the tourist preference and multidimensional dynamic environmental factors like the terrain, weather, tourist behaviors and related events. Based on this model, an A* algorithm of the dynamic routing for smart tourism is designed. The grid model of integrated multidimensional dynamic environmental information breaks through the limitation of the traditional tourist maps, which mainly depend on the static road network models, and supports the dynamic routing with an ability to perceive the real time environment and to adapt to tourist preference. To verify its effectiveness, the model was applied to the Dujiangyan scenic spot in a case study. The results show that the optimal route obtained by the proposed algorithm is 17.6% shorter than the recommended path in the integrated distance, and favors providing the dynamic, intelligent, precise and integrative location information service for tourists.

GBSAR Atmospheric Turbulence Calibration Based on Weighted Stable Points

HUANG Qihuan, YUE Jianping

2017, 30(1): 202-208. doi: 10.3969/j.issn.0258-2724.2017.01.028

[Abstract](493)

Abstract:
Atmospheric disturbance is one of the key factors affecting the accuracy of ground based synthetic aperture radar (GBSAR) interferometry for deformation monitoring. Considering the correlation of atmosphere delay with azimuth direction, a new GBSAR atmospheric turbulence calibration method based on distance-weighted stable points is proposed. In this method, the atmospheric disturbance factor is first calculated from the stable points, and the images which are severely affected by atmospheric disturbance are removed using the length of the atmospheric disturbance factor. Then, the atmospheric disturbance factor of unstable pixels are obtained by distance-weighting of stable points to calibrate the atmospheric disturbance on unstable pixels and derive the final product of deformation information. As a case study, the proposed method was applied to the deformation monitoring of Geheyan dam using the IBIS-L GBSAR system. The results show that the maximum deformation affected by the atmospheric disturbance along the radar line of sight (LOS) reaches 75 mm, but the influence is significantly reduced after the calibration with the presented method. The accuracy of the deformation monitoring was improved to 1 mm, and the monitored deformation trend has a good agreement with the plummet measurements.

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2017 Vol. 30, No. 1