西南交通大学学报

Experimental Study on Voltage Uniformity of 14.4 kW PEMFC Stack Single Cell

CHEN Weirong, LIU Jiawei, GUO Ai, LI Yan, LIU Zhixiang, ZHANG Xuexia

2017, 30(3): 429-438. doi: 10.3969/j.issn.0258-2724.2017.03.001

[Abstract](726)

Abstract:
Proton exchange membrane fuel cell (PEMFC) stack is superimposed by multi single cells in series. Many factors such as material, process and flow field distribution may lead to the performance degradation of single cells. The service life of the stack depends on the single cell with the lowest voltage. Therefore, the single-cell voltage uniformity is an important factor affecting the fuel cell life. The existing voltage uniformity evaluation methods can not fully reflect the voltage consistency of fuel cells. To address this, experiments for single-cell voltage uniformity were conducted on 14.4 kW PEMFC stack test platform to explore the influences of stack current, flow field distribution and the spatial location on the single-cell voltage fluctuation rate. In the experiments, constant frequency and amplitude was adopted as the loading control strategy, the interval of loading was set as 20 ms, and the loading current amplitude was 2 A. When the steady state current was increased from 10 to 180 A with a step of 10 A and the transient state current was dynamically loaded from 47 to 112 A, the voltage fluctuation rates of single cell were tested respectively. Firstly, the data of steady state current loaded from 10 to 180 A were processed according to the statistical principle of discarding the samples at the high and low end. The functional relation between the voltage fluctuation rate and current of single cells were respectively Fourier trinomial and Gaussian binomial before (after) eliminating the end data of single cell. Then, as the voltage fluctuation rate of single cell can not be used for analyzing the voltage amplitude difference and stack fault, an improved evaluation method for voltage uniformity was proposed, which combines the voltage fluctuation amplitude of the single cell, variation ratio, minimum distance and mean deviation of voltage. The voltage fluctuation amplitude of the single cell was used to infer the fluctuation range of stack voltage. The proportion of the cells with large voltage deviation to all single cells was described by the variation ratio. The minimum distance represents the degree of the lowest voltage of the single cell offsetting from the average voltage of the stack. The mean deviation of voltage indicates the fluctuation range of stack voltage. Finally, by using the example of the voltage distribution of 75 single cells when the stack was dynamically loaded from 47 to 112 A, a comparison was made between the traditional voltage fluctuation rate of single cell and the improved evaluation method of voltage uniformity. Although the traditional voltage fluctuation rate of single cell is 0.77, it is difficult to determine the deviation degree of the stack voltage from the voltage fluctuation rate. The improved voltage uniformity evaluation method, however, can overall evaluate the voltage uniformity according to the voltage fluctuation amplitude of the single cell, variation ratio, the minimum distance and mean deviation of the stack voltage. In the comparison experiments, the values of the above parameters are 40.00, 0.04, 14.33 and 2.60 mV respectively, which indicates that the voltage amplitude difference of the stack is relatively large, and there is accidentally a small number of single cells with large voltage fluctuation. The degree of the lowest voltage of the single cell offsetting from the average voltage of the stack is small. These suggest that the overall uniformity of the stack is good.

New Algorithm of Wide-Area Protection Based on Current Polarity and Energy Relative Entropy

WU Hao, LI Qunzhan, LIU Wei

2017, 30(3): 439-449. doi: 10.3969/j.issn.0258-2724.2017.03.002

[Abstract](492)

Abstract:
In order to improve the fault tolerance and sensitivity of wide-area relay protection, a new algorithm of wide-area relay protection based on current polarity and energy relative entropy was proposed. It combines bus-bar sampling value protection with differential protection principle for fault component of lines. Firstly, the protection correlative domain of line IED was divided, so that the fault component currents of positive sequence frequency were extracted accurately according to different correlative domains. Meanwhile, the concepts of boundary current, synthetic calculated current and synthetic virtual current were presented. Secondly, the energy relative entropy of the synthetic current sample was defined to quantify the difference of the synthetic current. At the same time, the angle between the boundary currents of the correlative domain was calculated to characterize the polarity relation of the boundary current, and the correlation between the current sample energy entropy and the polarity relation was utilized to identify the inner and outer faults of the correlative domain. Finally, utilizing IEEE 3-machine and 9-bus system constructed by the software of PSCAD/EMTDC, different fault types were set at different fault points to test eh algorithm performanc. The results reveal that when fault occurs in the correlative domain, the synthetic current is almost the same, with the relative entropy being very small, close to 0, and the angle between the boundary currents is less than /2 with approximate polarity. When the fault is outside the domain, the synthetic current waveform is significantly different from sampling value, with the relative entropy larger than 1, and the angle between the boundary currents is close to , with nearly opposite polarity. The distinction between the faults inside and outside the domain is obvious. Simulation results show that when single-phase earth fault occurs in the domain, the maximum relative entropy is 0.428 and the maximum angle is 0.388 in the condition of high resistance of 800 , which still meets the reliable criterion and has high sensitivity. The experimental results verify that the algorithm performance is basically not affected by the transition resistance, and can overcome the influence of unfavorable factors such as TA saturation and data distortion.

Effects of Contact Strips Wear on Service Performance of Pantograph System

SONG Dongli, JIANG Yanan, ZHANG Weihua

2017, 30(3): 450-457. doi: 10.3969/j.issn.0258-2724.2017.03.003

[Abstract](584)

Abstract:
To realize the parametric description of contact strips wear surface and evaluate the influence of contact strips wear on the service performance of pantograph systems, the effects of contact strips wear on the dynamic and fatigue performance on the pantograph-catenary system were investigated.. Firstly, based on a large amount of measured data of contact strips surface, the quadratic equation was proposed to fit the contact strips surface. Two characteristic quantities were defined, i.e., the surface shape parameter and wear depth, and the rule of characteristic quantities varying with time was obtained. Secondly, the mode superposition method was adopted to build a dynamic pantograph-catenary coupled system model, which takes into account the wear characteristics of contact strips. Based on the model, the effects of contact strips wear on the current collection performance of the coupled system were explored. Finally, a fatigue life prediction model considering the time-varying characteristics of contact strips surface wear was built. The effects of the wear on the fatigue performance of pantograph were analyzed. Results indicate that the wear surface of contact strips enhanced the periodic frequency with wave length of span increasing the amplitude of the dominant frequency. The larger the absolute value of surface shape parameter, the poorer the dynamic performance of the pantograph-catenary coupled system. When considering the contact strips surface wear, the predicted fatigue life of pantograph frame parts was reduced by about 30%-40%, and the upper structure was affected more greatly.

Characteristics and Suppression Neasures for Soft Flutter of Main Girder with П-Shaped Cross Section

ZHENG Shixiong, GUO Junfeng, ZHU Jinbo, TANG Yu

2017, 30(3): 458-465. doi: 10.3969/j.issn.0258-2724.2017.03.004

[Abstract](574)

Abstract:
Main girder with П-shaped cross section has aerodynamic blunt body structure, and under the nonlinear self-excited force, it is vulnerable to soft flutter. To study the effects of various aerodynamic measures on soft flutter performance of this main girder, the aerodynamic performance of a cable-stayed bridge was used through wind tunnel test of sectional model. The results show that soft flutter of the main girder is a coupled two-degree-of-freedom torsional-bending vibration with single frequency. With the increase of wind speed, the degree of vertical vibration decreases first and then increases. Setting wind fairings can increase the value of R. The amplitude of soft flutter follows a normal distribution, and the amplitude range varies with wind speed and angle of attack. Soft flutter is most likely to occur when the angle of attack is negative. Setting auxiliary facilities on the bridge deck can enlarge the critical velocity, and reduce the soft flutter amplitude and the amplitude growth rate. Setting wind fairings can reduce the vibration response of soft flutter, and the soft flutter performance can be improved by sharpening wind fairings. With the wind fairing angle sharpening, the critical velocity of soft flutter tend to rise but the amplitude of soft flutter tend to fall. Setting the central stabilizer at the base of the bridge deck has am unobvious effect on the soft flutter performance of the main girder.

In-Situ Measurement and Numerical Simulation of Wave Pressure on Marine Bridge Cofferdam

TI Zilong, LI Yongle, QIN Shunquan, MEI Dapeng

2017, 30(3): 466-473,531. doi: 10.3969/j.issn.0258-2724.2017.03.005

[Abstract](585)

Abstract:
To study the wave pressure distribution on the cofferdam under wave loads, an in-situ measurement and several numerical simulations of the wave pressure on a large-scale steel cofferdam used for construction of a marine bridge were carried out. Through the regular wave simulation of measured significant wave height based on 3D diffraction analysis and representative method, the distribution pattern of peak wave pressures along the surface of the cofferdam and along water depth was obtained and compared with the measured results. Meanwhile, the dynamic wave pressure distribution along the surface of the cofferdam was analyzed and compared with the measured values as well. The results show that the 3D diffraction analysis gives reasonable results about the pressure distribution along the cofferdam. Under the influence of wave diffraction, the peak wave pressure and peak dynamic wave pressure presents a large value at the up-wave side, while a small value at the down-wave side. The maximum difference of dynamic pressure is up to 125%. The measured pressure increases with depth of water, while the peak dynamic wave pressure decreases with depth.

Element Stiffness Matrix Analysis for Variable Curvature Curved Beam

DONG Changjun, LIU Shizhong, LI Aijun

2017, 30(3): 474-481. doi: 10.3969/j.issn.0258-2724.2017.03.006

[Abstract](625)

Abstract:
Most element stiffness matrixes are implicit functions, and hence are inconvenient to apply directly. To overcome this deficiency, assuming that the shear center of a variable-curvature curved beam coincides with its centroid, an explicit analytical solution formula for flexibility matrix of a kind of variable-curvature curved beam element with cantilever end condition is derived in polar coordinates by Castigliano's displacement theorem. First, the flexibility matrix is degraded to classical forms. Then, the stiffness matrix of the variable-curvature curved beam element with cantilever end condition is obtained by inversion of the flexibility matrix. Finally, according to conditions of static balance and arbitrariness of node displacement, the element stiffness matrix is obtained. In addition, taking a curved girder with two clamped ends as an example, comparisons are conducted between the calculation results by MATLAB program and those by ANSYS. The results show that the values of vertical displacement and torsion angle generated by MATLAB deviate from those by ANSYS within 5%, the small error between them verifying the effectiveness of the stiffness matrix in calculations of variable-curvature curved beam. What's more, elements in the matrix can be expressed as explicit functions of parameters and all the parameters can be directly referenced, which also proves the correctness of the element stiffness matrix.

Experimental Study of Interface Behavior of Geogrids with Different Aperture Shapes

ZHENG Junjie, ZHOU Yanjun, CAO Wenzhao, LAI Hanjiang, YANG Youbin

2017, 30(3): 482-488. doi: 10.3969/j.issn.0258-2724.2017.03.007

[Abstract](579)

Abstract:
In order to investigate the effect of aperture shape on the geogrid-soil interface behavior, tensile tests were conducted using two kinds of geogrids with triangular apertures and rectangular apertures, which are of similar aperture size and mechanical properties. The effect of aperture shape on the geogrid-soil interface behavior under different normal pressures and pullout test directions were analyzed in terms of the pullout resistance, shear strength of geogrid-soil interface, apparent friction coefficient and geogrid rib deformation. The results show that the geogrid with triangular apertures plays a better role than the geogrid with rectangular apertures in restraining the lateral displacement of soil. For the geogrid with triangular apertures, the peak values of friction angle in cases TX_0 and TX_90 were 48.2 and 38.2, respectively, while the peak value of friction angle in case SS20 case was only 35.9. The flexural deformation of different degrees was observed in the horizontal and diagonal ribs of the geogrid with triangular apertures during the pullout test, while the ribs of the geogrid with rectangular apertures mainly presented a tensile deformation.

Joint Reinforcement Design Method of Tieback Anchors on Slope Surface and Anti-Slide Piles at Slope Toe

ZHAO Xiaoyan, HUANG Jinhe, ZHOU Yiwen, LI Yulong, JIANG Chusheng, YUE Zongyu

2017, 30(3): 489-495. doi: 10.3969/j.issn.0258-2724.2017.03.008

[Abstract](618)

Abstract:
In the reinforcement of high and steep slopes, joint uses of tieback anchors of the second-grade and upper-grade slopes and anti-slide piles of the first-grade slope toe are frequent. However, the design method for these combinations remains immature. In this work, a method for optimizing joint reinforcement design was proposed. Firstly the effects of the preload of a single tieback on each slice of the sliding body, and then the residual thrust and load on the anti-piles was determined by the stability calculation of the reinforced slope by tieback anchors. Thus the coordination between the preload of tieback anchors and passive load of anti-slide piles can be achieved. The proposed method is validated by an example of a slope on the Guangtong-Dali railway. The results show that the preload of the tieback anchors is suggested as 40% of the total residual thrust, and the control conditions include 5.0-8.0 m spacing between the centers of anti-slide piles, 2.0-3.0 m width and 1.5-4.0 m height of pile section, and 1/3-1/2 of the total pile length for stable layer length.

Shaking Table Model Tests for Composite Reinforced Slopes

LI Lihua, REN Zengle, LI Guangxin, XIAO Henglin, YANG Zhiyong, YANG Chao, CUI Feilong

2017, 30(3): 496-504. doi: 10.3969/j.issn.0258-2724.2017.03.009

[Abstract](540)

Abstract:
Waste tires and triaxial geogrids can be used as new reinforcement materials in geotechnical engineering, with merits of excellent mechanical performance, economy and environmental friendliness. Shaking table tests were conducted to study the dynamic performances including distribution of acceleration amplification factor under various conditions such as different earthquake waves, peak ground accelerations(PGA)and reinforcement methods.The slope models include unreinforced slope,triaxial geogrid reinforced slope,triaxial geogrid-waste tire composite reinforced slope,waste tire-tire shred composite reinforced slope. The experimental results show that the seismic performance of the reinforced slopes is significantly improved.Compared with unreinforced slopes, the maximum decrease of acceleration magnification for triaxial geogrid reinforced slope is 37.5%, 30.0% for triaxial geogrid-waste tire composite reinforced slope and 21.0% for waste tire-tire shred composite reinforced slope under Wenchuan wave excitation. The average acceleration magnification reduction of triaxial geogrid reinforced slope is 1.4 and 2 times greater than those of the latter two types of the slopes. Acceleration amplification factor of the reinforced slopes increases with the seismic excitation in a nonlinear way. Compared with the unreinforced slopes,the increasing amplitude of acceleration amplification factor decrease with the input of PGA.Along the surface of the slope about 1/3 of the slope elevation,acceleration magnification factor of the reinforced slopes increase gradually with the elevation,and reaches the maximum at the slope top.The acceleration response induced by Qianan wave is significantly stronger than those induced by other three types of seismic excitations.

Mechanical Responses of Single-Pressure Arch-Shaped Open Tunnel Structure under Rockfall Impaction

WANG Yusuo, ZHOU Liang, LI Zhenghui, HE Junnan, WANG Tao

2017, 30(3): 505-515. doi: 10.3969/j.issn.0258-2724.2017.03.010

[Abstract](518)

Abstract:
To learn the stress state and provide a design basis for open tunnel structures, the mechanical response of a single-pressure arch-shaped open tunnel structure on a double-line passenger dedicated line is analyzed using dynamic finite element method. Firstly, regarding the vertical drop impaction as the basic condition, interactions between rockfall and backfill soil on the tunnel top, as well as the motion trajectory of rock-fall, are analyzed to study responses of the tunnel structure in terms of stress, strain, strain rate, displacement, velocity and acceleration. Secondly, according to the law of energy conversion and transmission among rockfall, concrete backfill materials and tunnel structure, the mechanisms of backfill soils acting as buffering cushions and concrete-filled materials as structure protection to rockfall impaction are explained through stress responses of the side wall and ground basement, and influences of the structural form of the side wall on the mechanical performance of the ground basement and the inverted arch of open tunnel are also discussed. Finally, the dynamic responses of the tunnel structure under 45 oblique rockfall impaction are analyzed and compared with those in the basic condition. The results show that the designed open tunnel can bear 700 kJ vertical impaction energy of rockfall while substructures such as apex of arch, spandrel, inner side of the arch wall and corner of the ear wall are relatively weak parts in bearing the stress; thus the way of backfill and the structural form of the side wall in the open tunnel need to be further optimized. Strain rates of the open tunnel structure caused by rockfall impaction are found limited in the range of 10-3~10-2 s-1, which is the same as that caused by earthquake. Under the condition of this research, the effect on the open tunnel structure from oblique rockfall impaction is generally less than that from vertical drop impaction.

Structural Features and Engineering Application of Bell-Shaped Mining Caverns in Changyu

YANG Dan, HU Xiewen, SONG Dage, ZHANG Xuan

2017, 30(3): 516-523. doi: 10.3969/j.issn.0258-2724.2017.03.011

[Abstract](547)

Abstract:
Cavern shape and surrounding rock structure are the important factors to cavern stability. In this work, the shape, surrounding rock structure, and rock strength of the deserted bell-shaped caverns without support in Changyu, Wenlin, Zhejiang province were investigated. Then the cavern stability with different shapes, span-depth ratios, inclination angles of sidewall was calculated and analyzed utilizing FLAC. It is shown that the bell-shaped cavern is better than other shaped caverns, such as rectangular cavern, circular cavern and a type of cavern with straight wall and top arch, because the tensile stress area of surrounding rock is smallest and the surrounding rock is more stable with high compressive strength. The smaller the span-depth radio, the smaller tensile stress area of surrounding rock and the more stable the cavern chamber. When the span-depth radio is less than 1.33, there is no tensile stress area on the top of the surrounding rock, which is favorable to the surrounding rock stability. With the decreasing of the inclination angle of sidewall, the tensile stress areas first decrease and then increase. When the inclination angle of sidewall ranges between 70 and 80, the tensile stress area of surrounding rock is small, which is favorable to the surrounding rock stability. In site investigation, 75% of the caverns has the span-depth ratio less than 1.33, while 60% of sidewall angles are between 70and 80.

Failure Mechanism and Shear Capacity of Organic Polymer Shear Connectors

ZHAN Yulin, LI Guifeng, ZHAO Renda, ZOU Zhaoyong, XUE Dengyu

2017, 30(3): 524-531. doi: 10.3969/j.issn.0258-2724.2017.03.012

[Abstract](483)

Abstract:
In order to deal with several weaknesses of metal shear connectors such as original crack, welding residual stress and transfering shear capacity intermittently, the performance of organic polymer shear connectors was introduced to study. Eight sets specimens (total 24 specimens) with different adhesive thickness, Young's modulus and interface roughness of organic polymer shear connectors were investigated by push-out test, the ultimate shear capacity and the failure modes were also observed. Considering the main influence factors such as the adhesive thickness, Young's modulus and interface roughness of organic polymer shear connectors, an computational formula on the ultimate shear capacity was proposed. The results show that: organic polymer and concrete sheared together is the main damage form; ultimate shear capacity of organic polymer shear connectors is between 1.10 and 2.47 Mpa,the analysis and test results both show that the shear capacity of metal and organic polymer shear connectors is the same.

Full-Scale Tests on Seismic Behavior of RC Frames Infilled with Hollow Bricks

SU Qiwang, ZHANG Yan, XU Ziyi, CAI Hongru

2017, 30(3): 532-539. doi: 10.3969/j.issn.0258-2724.2017.03.013

[Abstract](593)

Abstract:
In order to study the seismic behavior of RC frames infilled by hollow bricks, full-scale tests of one-story single-bay hollow bricks infilled frame structure and one-story single-bay hollow bricks infilled frame structure with the opening under low cyclic reversed loading were carried out. Then, the indexes were studied including failure modes, load-displacement hysteretic loops, skeleton curves, bear capacity, displacement ductility, energy dissipation, strength degradation and rigidity degradation. Besides, according to test data from the literatures on one-story single-bay hollow bricks infilled frame structure, the reduction formulae for describing the effects of the openings on strength and rigidity degradation were also proposed. The experimental results show that the peak load of the frame without window and door is increased by 70% at early loading stage in contrast to the frame with window and door, and the peak loads of two structures will become much closer after story drift ratio reaches 1%. It can be found that the openings in infills reduce the ultimate bearing capacity, whereas the structural deformation capacity improves greatly. As a result, the damage of infills lessens.

Bond-Slip Performance of Steel Tubular Composite Piles

ZHANG Min, MA Jianlin, ZHANG Zhengxin, DU Can

2017, 30(3): 540-545,553. doi: 10.3969/j.issn.0258-2724.2017.03.014

[Abstract](510)

Abstract:
To investigate the bond-slip performance of steel tubular composite (STC) piles with shear ring, drilling mud skin and anti-corrosion coating, a new bond-slip constitutive model of the STC piles was proposed assuming an exponential trend of adhesion stress along the length of interface. The correctness of the model was then verified using five push-out tests of STC piles conducted in construction of the Hong Kong-Zhuhai-Macao Bridge, among which two tests adopted pile samples with shear ring. Results showed that under the external load the theoretical predictions of the bond-slip displacement between steel tube and concrete and the stress of steel pipes were consistent with the experimental results. The relative slip displacement between steel tube and concrete was less than 0.2 mm when the failure of piles was induced by the bond-slip behavior. The adhesion stress between the steel tubes and concrete was reduced by drilling mud skin and anti-corrosion coating. The average bond strength of STC piles was increased by 50% because of the shear ring when the spacing of shear ring was 1D (where D is the diameter of the pile), while adverse effects of drilling mud skin and anti-corrosion coating would be ignored under this condition. In addition, the exponential relationship between adhesion stress and the length of interface was observed.

In-Situ Test on Dynamic Responses of Reinforced Soil Retaining Walls for High-Speed Railways

WU Lianhai, YANG Guangqing, ZHANG Qingbo, SUN Hongwei, ZHANG Liguo, JIAO Ruiling, SU Qian

2017, 30(3): 546-553. doi: 10.3969/j.issn.0258-2724.2017.03.015

[Abstract](576)

Abstract:
In order to study the dynamic responses and mechanism of geogrid reinforced soil retaining wall under the loads of high-speed vehicles, in-situ vibration excitation tests were conducted to obtain distributions of acceleration and dynamic soil pressure in geogrid reinforced soil retaining wall. The dynamic responses of different wall faces were compared. The results show that, with the increase of load cycles, the vertical acceleration of reinforced soil is nearly unchanged. The dynamic soil pressure near wall surface in the horizontal direction has a single-peak distribution and its max-value is located at 2/3 of the wall height. The vertical dynamic soil pressure has a little increase with the number of load cycles. In the range from wall top to 1/3 wall height, the vertical acceleration attenuates 87%-91%and the vertical dynamic soil pressure attenuates 86%. The reinforced soil retaining wall with block panel has the merits of large rigidity, small deformation and strong integrity.

Genesis Mechanism and Distribution of Gently-Dipping Brittle Discontinuities in Rock Slope

ZHU Lei, YAN Ming, Huang Runqiu, Gao Feng

2017, 30(3): 554-562. doi: 10.3969/j.issn.0258-2724.2017.03.016

[Abstract](540)

Abstract:
A rock slope in Nujiang River (China) was taken as an example to better understand the distribution of the gently-dipping discontinuities subjected to river incision. Based on field surveys, geological analysis and numerical simulation, a study on the density and evolution of the gently-dipping discontinuities was carried out to reveal the distribution and genesis mechanism. The results indicate that the gently-dipping discontinuities in the epigenetic reworking stage have evolved to distribute at irregular intervals: the discontinuities concentrate in certain zones (i.e., high-density zones), separated by some low-density zones. Totally, there are three to four high-density evolution zones of gently-dipping discontinuities. The density of discontinuities in these high-density zones ranges from 10 to 18 per 10 square meters, while the value in the low-density zones is 5 to 8 per 10 square meters. Moreover, the geometry and kinematic analyses of the system of discontinuities suggest that the genesis of the discontinuities can be synthesized into a progressive evolution model. The model suggests that the joint starts with the formation of an array of en-echelon cracks, with continued crack elongation and shearing; then they approach one another and interact, forming a complex joint system finally. According to the history of river valley evolution, a view is proposed that the river intermittent incision was the main factor resulting in the intermittently concentrated distribution of the gently-dipping discontinuities.

Mechanical Behaviours of Typical Asphalt Pavement Structures under Wheel Loads

WU Yu, JIANG Xin, LIANG Xuejiao, FENG Wenqing

2017, 30(3): 563-570. doi: 10.3969/j.issn.0258-2724.2017.03.017

[Abstract](665)

Abstract:
The mechanical behaviours of three typical asphalt pavements including semi-rigid base, inverted and composite asphalt pavement under wheel loads were analyzed and compared based on the tests on the asphalt pavement test section constructed in Chengdu-Deyang-Nanchong expressway. Comparing with static deflection of pavement surface obtained by Beckman beam test , static analysis based on elastic multi-layered theory was carried out. Pre-plugged asphalt strain gauges were used for the three asphalt pavement test section to measure in-situ dynamic responses caused by moving vehicle with different axle loads or at different speeds. The results show that fatigue cracking is more likely to appear in the transverse direction of asphalt pavement. The peak values of tensile strain in the vehicle traveling direction and the transverse direction of bottom of inverted asphalt surface are respectively 1.24 and 1.30 times those of composite asphalt pavement, and 2.37 and 2.67 times those of semi-rigid base asphalt pavement respectively.For pavement structures of the same thickness, semi-rigid base asphalt pavement has great advantage in decreasing fatigue cracking of asphalt surface and permanent deformation, and the force bearing capacity of the composite asphalt pavement is close that of the semi-rigid base asphalt pavement, which thus can be replaced by the composite asphalt pavement partially. Although the inverted asphalt pavement is less sensitive to axle load than other pavement structures, the thickness of its asphalt surface or asphalt treated base should be increased appropriately to improve force bearing capacity, and moreover the tensile stress of the asphalt treated base should be controlled strictly to decrease the fatigue damage of the inverted and composite asphalt pavements.

Seismic Dynamic Response and Instability Mechanism of Slopes in Nyingchi-Bome Section of G318 Highway, Tibet

WU Xiaofei, WANG Ying, YE Tangjin, YANG Zhong, JIANG Yu

2017, 30(3): 571-577. doi: 10.3969/j.issn.0258-2724.2017.03.018

[Abstract](545)

Abstract:
Strata structures and dynamic responses of slopes are significant factors in slope failures. In order to elucidate the dynamic response differences and dynamic response patterns of slopes with different stratum structures, a numerical simulation model of slope with Kobe seismic wave is established in FLAC3D to analyze typical slopes of four types of strata structures in the Nyingchi-Bome section of G318 highway, Tibet. Through this model, dynamic responses of strain, horizontal displacement and acceleration at the monitoring points located in different parts of slopes (on slope surface and in slope body) are calculated and analyzed under the Kobe seismic wave. Results show that in the soil-rock slopes, the amplification factor of peak ground acceleration (PGA) on the slope surface increases with slope height and reaches a maximum at a certain height. The PGA amplification factor of the slope body increases linearly with slope height, with a maximum value of 10.7, and is bigger in phyllitic slopes than other type of slopes. The horizontal displacements of slopes on both sides of the rock-soil contact zone show great differences between soil and rock, even to nearly one order of magnitude. The deformation inconsistency caused by horizontal displacement is the primary reason for sliding in the rock-soil contact zone. Moreover, the horizontal displacement and PGA amplification factors for different soil slopes are obviously different, and the instability of soil-rock slopes is chiefly controlled by soil textures.

Topology Optimization of Heat Conduction Structures Based on Probabilistic and Non-probabilistic Hybrid Reliability

YOU Fang, CHEN Jianjun, LIN Feng, CAO Hongjun

2017, 30(3): 578-583,599. doi: 10.3969/j.issn.0258-2724.2017.03.019

[Abstract](560)

Abstract:
Topology optimization design of heat conduction structures with interval variables and random variables was studied. Firstly, structural physical parameters and applied loads were regarded as interval variables and random variables. The probabilistic reliability and the non-probabilistic reliability were utilized as the measurement of hybrid structural reliability. Secondly, the optimization mathematical model was constructed, in which the relative thermal conductivity of elements was taken as design variables, minimum volume of heat conductive material was taken as objective function and the hybrid reliability index for dissipation of heat transport potential capacity was taken as the constraint. Lastly, the evolutionary structural optimization method was used in the optimization. In the two numerical examples, the probabilities of hybrid reliability of optimal topology structures are 0.94476 and 0.944476, which are larger than the given probability of 0.928650 and 0.933129, respectively, validating the feasibility and effectiveness of the optimal model and solving strategy.

DEM Co-registration Algorithm Based on Gauss-Newton Method

ZHANG Tonggang, WANG Kunlun, JIN Guoqing

2017, 30(3): 584-592. doi: 10.3969/j.issn.0258-2724.2017.03.020

[Abstract](654)

Abstract:
To improve the efficiency of DEM (digital elevation model) co-registration, a fast algorithm based on Gauss-Newton method was proposed. This algorithm uses Gauss-Newton method instead of the least squares method, to solve the objective equation of the DEM co-registration model, and greatly accelerates the iterative convergence. During the iterations of the new algorithm, matching parameters approach the target values by following the direction of maximal gradient, which significantly reduces the number of iterations. Moreover, the iterative convergence is more stable and the algorithm operation efficiency is greatly enhanced. The new algorithm was tested with several groups of simulated datasets, and compared with the representative iterative closest points (ICP) algorithm. The experimental results show that the average convergence rate of the proposed algorithm is improved by 42.1%, and the computation time for matching is reduced by about 74.9%.

Clock Synchronization Algorithm Based on Particle Swarm Optimization with Natural Selection

JIANG Yilin, ZHANG Fangyuan

2017, 30(3): 593-599. doi: 10.3969/j.issn.0258-2724.2017.03.021

[Abstract](526)

Abstract:
In order to improve the clock synchronization accuracy of wireless sensor network (WSN) and avoid the synchronization error caused by the unreliable data and the change of the network topology structure in the synchronization process, a simulation model of particle swarm optimization (PSO) algorithm based on natural selection was established. Firstly, using Kalman filtering algorithm to locally filter the measurement data of multiple sensors, the redundant information in the bottom of the measurement data could be removed so that the accuracy of measurement data is improved. Then, particle swarm optimization algorithm based on natural selection was used to set up a data fusion model and calculate the optimal fused estimation. Finally,the simulation results of the fusion model of PSO algorithm based on natural selection show that the fusion algorithm can effectively realize the fusion of five node clock in the networks, and improve the fusion accuracy of time offset and frequency offset of node crystal oscillating, producing a virtual clock of high stability. The concentration ranges of fusion accuracy of time offset and frequency offset are 10-5 and 10-7, respectively. Compared with traditional adaptive fusion algorithms, the concentration ranges of fusion accuracy of time offset and frequency offset are improved by one order of magnitude.

Information Estimation on Wheelset State and Track Features of Railway Vehicles

SUN Xiaojie, YANG Junqi

2017, 30(3): 600-606. doi: 10.3969/j.issn.0258-2724.2017.03.022

[Abstract](500)

Abstract:
In order to get the wheelset state and track feature used for rail vehicle wheelset active control in an easy and economical way, an information estimation scheme based on state observers is proposed to simultaneously estimate the wheelset state and unknown track feature. The scheme obtains wheelset yaw velocity and lateral acceleration signal using some inertia sensors (accelerator and gyros). In addition, a single independent rotating wheelset model is set up to simulate and verify the proposed estimation scheme. Simulations show that the estimation system using a reduced order observer and a higher-order sliding mode observer presents good estimating performance, and is hardly affected by track irregularity. Errors of wheelset state estimation are less than 0.10%. In the ideal track, the error of the estimated track curvature and superelevation in curved track is no more than 0.26% and 13.40%, respectively. In the real track with irregularity, the error of the estimated track curvature is no more than 9.10%, but the filter fluctuation error should be removed when using this scheme in practical applications.

Coupled Thermo-Elastic Deformation of Swing Movable Teeth Transmission

LIANG Shangming, LI Lei

2017, 30(3): 607-611. doi: 10.3969/j.issn.0258-2724.2017.03.023

[Abstract](481)

Abstract:
To improve the transmission performance of swing movable teeth transmission, the contact heat transfer process between the movable teeth and internal gear was analyzed and the calculation method of the friction heat flux generated by the meshing pair was proposed according to the meshing principle of swing movable teeth transmission. Then, a finite element analysis model of the internal gear was established, based on which calculation methods of the body temperature field distribution, contact elastic deformation, and coupled thermo-elastic deformation of the internal gear during swing movable teeth transmission were put forward. The results of a case study show that the highest temperature in the internal gear appears near the inflection point of the internal gear profile curve; and the thermal deformation of the internal gear increases its tooth thickness, providing a certain compensation for the elastic deformation of the internal gear. In addition, the coupled thermo-elastic deformation of the internal gear obtained by the proposed method conforms with the actual working condition, and the maximum value is 0.045 mm.

Technological Experiment and Regression Analysis of Surface Residual Stress in Ultrasonic Grinding

HE Yuhui, ZHOU Jianjie, ZHOU Qun, TANG Chu, WAN Rongqiao, TANG Jinyuan

2017, 30(3): 612-617. doi: 10.3969/j.issn.0258-2724.2017.03.024

[Abstract](482)

Abstract:
In order to explore the process features of ultrasonic grinding, an experimental investigation was conducted on 45 steel using a self-developed axial ultrasonic grinding apparatus, and the surface residual stress of workpieces was measured using an iXRD residual stress analyzer. Based on the experimental results, influences of grinding process parameters on the residual stress were analyzed, and regression equations of residual stress against the grinding depth, the ultrasonic vibration amplitude, and the circular linear speed of the grinding wheel were established, with which the residual stress was predicted. Results show that residual compressive stress is produced in workpiece surface in both the ordinary grinding and ultrasonic grinding, and the residual stress in the axial direction is significantly greater than that in the grinding direction. In addition, the residual compressive stress increases with an increase in grinding depth and ultrasonic vibration amplitude, but decreases with an increase in the circular linear speed of the grinding wheel. The maximum relative error between the predicted value and test value is less than 5%, which proves that the predictive regression model can effectively predict the surface residual stresses in ultrasonic grinding.

Backstepping Control of Attitude Adjustment Servo Platform Based on LS_SVM

HUANG Xiaorong, GAO Hongli, MAO Run, LI Shichao, WEN Juan

2017, 30(3): 618-625. doi: 10.3969/j.issn.0258-2724.2017.03.025

[Abstract](514)

Abstract:
To improve the performance of high-precision servo systems with compound disturbance problem, two least squares support vector machine (LS_SVM) systems were employed to approximate the compound disturbance of the high precision servo systems. The kernel functions and regularization parameters of LS_SVM were attained by particle swarm optimization (PSO) algorithm offline. An adaptive backstepping control system based on the LS_SVM method was designed by using the backstepping control theory and choosing Lyapunov function in turn. The stability of the developed system was proved through the stability of Lyapunov. Simulations show that the compound disturbance of the system could be effectively compensated by LS_SVM. Without considering the compound disturbance, the proposed controller could reduce its response time by 20% compared with the classic three-loop PID controller. However, when considering the compound disturbance, the proposed controller could reduce its response time by 25%, and increase its steady-state precision by 34.09%compared with the classic three-loop PID controller. At the same time, the proposed controller could effectively inhibit the influence on the system performance caused by the change of system parameters, so it has strong robustness.

Design of Vehicle Acceleration Controller Based on Parallel Neural Network PID

LIANG Jun, ZHAO Tongyang, XIONG Xiaoxia, ZHANG Wanwan, CHEN Long, ZHU Ning

2017, 30(3): 626-632. doi: 10.3969/j.issn.0258-2724.2017.03.026

[Abstract](532)

Abstract:
An acceleration control algorithm based on the parallel neural network PID (PNNPID) was proposed to conquer the problems of slow system change identification, poor dynamic performance, and slow adjustment in traditional acceleration control algorithms for adaptive cruise control (ACC). Through analysis of the shortcomings of the traditional serial neural network PID (SNNPID) for direct feedback error, an acceleration controller for vehicles that is based on the parallel control theory is developed using the self-learning function of neural network. In addition, taking into account the vehicle ride comfort, an amplitude limiting scheme of filter is designed to fit driving behavior. Experimental results show that the acceleration controller based on SNNPID can function within a maximum deviation of 0.25 m/s, and is more accurate than the controller based on PNNPID. This new acceleration controller is characterized by small average error, short adjustment time, and good transient property; and the proposed filter amplitude limiting scheme can greatly improve the ride comfort of vehicles.

High-Efficient Preparation of SmBiO3 Buffer Layer for Superconducting Coated Conductors

ZHU Xiaolei, PU Minghua, ZHANG Hong, ZHAO Yong

2017, 30(3): 633-638. doi: 10.3969/j.issn.0258-2724.2017.03.027

[Abstract](456)

Abstract:
In order to shorten the preparation period of buffer layer for high-performance coated conductors, SmBiO3 (SBO) buffer films were efficiently deposited on surface-oxidation epitaxy processed NiO(100)/NiW substrates by chemical solution deposition (CSD) method, using a precursor solution prepared by dissolving samarium nitrate and bismuth nitrate precursors in lactic acid. The effect of sintering temperature on the SBO film was systematically studied. Then, the YBa2Cu3O7- (YBCO) superconductive film was deposited on the SBO buffer layer to test its utility. Results show that a highly textured, smooth and dense SBO thin film was obtained at 798.5 ℃, and the SBO thin film could be prepared within a period of less than 2 h. The YBCO superconductive layer was successfully deposited on the SBO layer with a superconducting transition temperature of 89 K and a critical current density of 1.46 MA/cm2 (77 K, 0 T), which could be used in some electric power applications. Therefore, the proposed method for preparing SBO buffer layer can be used for rapid preparation of coated conductors.

Analysis of Route Choice Behavior of Urban Rail Passengers Considering Transfer Thresholds

YAO Enjian, JIN Fanglei, HU Qianwen, ZHANG Yongsheng, YANG Yang

2017, 30(3): 639-645. doi: 10.3969/j.issn.0258-2724.2017.03.028

[Abstract](585)

Abstract:
In order to investigate the route choice behavior differences of commuters and non-commuters due to different time constraints, the disaggregate theory is employed to construct a route choice model. First, the concept of transfer threshold is proposed, which attempts to analyze the difference of penalty on perception utility of passengers under various conditions of transfers. Then, on the basis of the alternative route set generated from the transit network data of Guangzhou metro, the transfer thresholds are estimated using the revealed preference data of passengers. Finally, based on the estimation results from the proposed path-sized logit (PSL) model, passengers route choice preferences are analyzed. The results show that the parameter values of transfer time with a high number of transfers are 1.114 5 and 1.037 9 times that with a low number of transfers for commuters and non-commuters, respectively, indicating that commuters are more sensitive to transfer time with a high number of transfers.

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2017 Vol. 30, No. 3