西南交通大学学报

Characteristics of Co-seismic Landslides Triggered by the Lushan Ms7.0 Earthquake on the 20th of April, Sichuan Province, China

HUANG Runqiu, WANG Yunsheng, PEI Xiangjun, LI Yusheng, LI Weile, LUO Yonghong

2013, 26(4): 581-589. doi: 10.3969/j.issn.0258-2724.2013.04.001

[Abstract](1229)

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In order to reveal the distribution laws of the secondary geohazards during the Lushan Ms7.0 earthquake, field investigations and interpretation of aerial photos after the earthquake were carried out to analyze the risk of the co-seismic geohazards. The results show that rockfall was the main type of the co-seismic geohazards. The rockfalls were mainly small-scaled ones and distributed along the area of the Shuangshi-Dachuan fault zone and the NW-strike gorges, such as the Lushan-Baoxing gorge, Lushan-Shuangshi gorge, and Lushan-Taiping gorge, in which the rockfalls occurred most densely in the area near the epicenter, such as Taiping, Baosheng, and Longmen. The source areas of rockfalls in the cross section of the valleys were mainly located at the middle and upper parts of a hill slope and the spur of a hill. The accumulation was mainly composed of blocks and gravel, which buried the roads, became a great risk to vehicles and houses at the toe of slopes, and would threaten the normal operation of the road in the near future. As the potential unstable slopes and small slides increase the source in the valleys and ramp during the earthquake, the debris flow would happen frequently. The PGA (peak ground acceleration) magnitude and topographic amplification was the main reason of the geohazards, and the slope structures and weathering was the second factor.

Debris Flow Characteristics and Movement Process of Dayanbeng Landslide in Tianquan County Triggered by “4·20” Lushan Earthquake

HU Xiewen, GU Chengzhuang, NIU Yanbo, LIANG Jingxuan, PAN Cong, WU Jianli, LIN Jinhui, CHEN Dingcai

2013, 26(4): 590-598. doi: 10.3969/j.issn.0258-2724.2013.04.002

[Abstract](1144)

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The secondary geological disasters triggered by "4·20" Lushan strong earthquake were dominated by rockfalls rather than landslides, and their scales were not large. However, there was a large-scale landslide in Damiao Village, Laochang Township, Tianquan County, the only large-scale landslide in the disaster area. There were about 35.2×104 and 42.0×104 m3 strongly weathered dolomitic limestone sliding out quickly from high places along both sides of thin ridge in Dayanbeng mountain, moving along grooves on both sides with a high speed, then sliding about 504 and 740 m respectively along the left and right ditches, hitting with their main channels and climbing about 35 and 26 m respectively in the left bank of Chunjianwo ditch and the right bank of Gangoutou main ditch. Afterwards they slid about 763 and 409 m respectively and intersected 409 m away from the impact point in Gangoutou ditch, then they slid about 223 m because of gentle slopes to form two small dammed lakes with volumes of 8 000 and 600 m3, causing no casualties and property loss because of no inhabitants along the ditch. On the basis of detailed geological survey and combining with field mapping, prospecting and other means, the basic features of Dayanbeng landslide were researched thoroughly, and the causes of the landslide were analysed preliminarily. The research result shows that the thin ridge, weathered dolomitic limestone and favorable structures are the basic conditions of the landslide, and vibration effect of "4·20" Lushan earthquake is the direct cause of the landslide.

Trigger Effect of Earthquake Geohazards around Baoxing County Induced by Lushan 4·20 Strong Earthquake

HU Xiewen, LIN Jinhui, ZHANG Maochun, XU Hao, LÜ, Junlei, GU Chengzhuang

2013, 26(4): 599-608. doi: 10.3969/j.issn.0258-2724.2013.04.003

[Abstract](1100)

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Even though Lushan 4·20 strong earthquake has characteristics of high seismic magnitude and strong destructiveness, its secondary geological disasters are dominated by rockfalls rather than landslides. Compared with secondary geological disasters induced by 5·12 Wenchuan earthquake, their size and number are both mild. However, Baoxing County, which is in the earthquake-affected zone, is an exception. Rockfalls and landslides develop well around the county because of steep mountains. Geological field investigations of the geohazards around Baoxing County before and after the earthquake show that after earthquake the number of rockfall, landslide and debris flood changes into 21, 1, and 3 from 3, 1, and 3, respectively; geohazards development density and modulus change into 2.02 km-1 and 5.59×104 m3/km from 0.38 km-1 and 3.4×103 m3/km, respectively, which are 5.3 and 16.4 times that before the earthquake; and the effect of slope failure induced by the earthquake is significant. Based on the investigation, the following recognitions are obtained by segmental analysis: Seismic geological disasters occur mainly at thin ridges and steep slopes, rockfalls occur mostly at rock slopes, and landslides occur at loose deposited slopes, but large-scale landslides are rare. The overall revival of large-scale loose deposits is not caused by the earthquake, and only some collapse or vibration cracks take place in some parts of steep-gentle junctions. Thus, the loose deposited ancient landslides are stable. This suggests that strong earthquake may not induce overall revival of ancient landslides.

Distribution Law of Landslides Triggered by Earthquake Based on Cellular Automata

HUANG Yidan, YAO Lingkan, GUO Chenwen

2013, 26(4): 609-615. doi: 10.3969/j.issn.0258-2724.2013.04.004

[Abstract](991)

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In order to interpret the mechanism of distribution of landslides triggered by earthquake from a physical point of view, typical sections in earthquake zones in the Wenchuan earthquake were investigated, and related remote sensing data was interpreted. The result shows that there exists a negative power-law relationship between the volume and number of landslides in IX seismic intensity zone of the Wenchuan earthquake, and the same is true between the area and frequency of landslides in X intensity seismic zone. However, the relationship changes into a lognormal distribution in XI seismic intensity zone. In addition, cellular automata was used to simulate landslides. The cellular automaton simulation reveals that with the change of disturbance intensity, the dynamical mechanism of sand-pile model is from a strong power-law to a weak power law, then to a lognormal distribution. Under the conceptual framework of self-organized criticality, it is proved that the distribution model of landslides in different seismic intensity zones has a universal law. The research results may not only be used to guide inventory of landslides triggered by the Wenchuan earthquake, but also provide a scientific basis for mountain disaster assessment in high seismic intensity zones.

Generalized Nonlinear Unified Strength Theory of Rock

ZAN Yuewen, YU Maohong

2013, 26(4): 616-624. doi: 10.3969/j.issn.0258-2724.2013.04.005

[Abstract](1005)

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The generalized Hoek-Brown strength criterion is used widely in rock engineering. The effect of the intermediate principal stress, however, is not taken into account in the Hoek-Brown criterion. The twin-shear models and the generalized Hoek-Brown strength criterion were generalized and combined into a generalized nonlinear unified strength theory. The serial limit surfaces of the generalized nonlinear unified strength theory cover the whole convex region, and encompasses the generalized Hoek-Brown strength criterion and the generalized nonlinear twin shear strength criterion as two special cases. In the stress space, the inner bound of limit surface of the generalized nonlinear unified strength theory is the generalized Hoek-Brown strength criterion, and the outer bound is the generalized twin shear strength criterion. A series of new limit surfaces cover the all region between these two bounds. As a result, the unified yield criterion, the unified strength theory, the rock nonlinear unified strength theory can be linked with the generalized nonlinear unified strength theory.

Bending Bearing Capacity Calculation of Prestressed Steel Reinforced Concrete Beam under Fire

FU Chuanguo, SHANG Shengqiang, WANG Yuzhuo, LI Shibo

2013, 26(4): 625-631,658. doi: 10.3969/j.issn.0258-2724.2013.04.006

[Abstract](1299)

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Based on the bearing performance of prestressed steel reinforced concrete beam at normal temperature,the simplified calculation formula for the bending bearing capacity of the prestressed steel reinforced concrete beam under high temperatures is established by means of the cross-sectional finite element method. The relationship between the beam bending capacity and the standard heating time during the whole process is obtained. The relationship curve reveals a degradation rule that the bending bearing capacity of the cross section is decreased significantly with the increase of heating time. The comparison between the calculated bending capacity and the measured one shows a good agreement with a relative error of 9.3%.

Performance-Based Plastic Design Method of Reinforced Concrete Frames

XIONG Ergang, ZHANG Qian

2013, 26(4): 632-638. doi: 10.3969/j.issn.0258-2724.2013.04.007

[Abstract](925)

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In order to desirably predict and control the inelastic activity of reinforced concrete (RC) frames subjected to severe ground motions, on the basis of energy-work balance a performance-based plastic design (PBPD) method for the design of RC frames was presented. In the PBPD method, the design base shear is obtained based on the energy-work balance and pre-selected target drift and yield mechanism. Plastic design was performed to detail the frame members and connections in order to achieve the targeted yield mechanism and behavior. The method was applied to an eight-storey RC frame and validated by inelastic dynamic analyses. The results indicate that the frames develop desired strong column sway mechanisms, and the story drifts are well within the target values to meet the desired performance objectives.

Stability-Based Equivalent Static Wind Loads on Large-Span Snowy Roofs

HUANG Youqin, LIN Junhong, YUE Qizhe, FU Jiyang

2013, 26(4): 639-644. doi: 10.3969/j.issn.0258-2724.2013.04.008

[Abstract](1132)

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To avoid the dynamic instability of roofs in snowstorms, a method of stability-based equivalent static wind loads was presented. Snowdrifts on roofs are firstly simulated by the computational fluid dynamics (CFD) method. The state of dynamic instability of the snowy roof is determined by the Budiansky-Roth criterion. Then, the computational theory of stability-based equivalent static wind loads is constructed by referring to the principle of the gust loading factor method. Finally, the theory is applied to a real double-layer cylindrical reticulated shell. The results show that the snowy roof takes on evident instability under strong winds, and would become dynamically unstable when the wind velocity is 1.0 times the basic wind velocity. The critical wind velocity for wind-induced dynamic instability of snowy roofs, which is 35.8 m/s for the shell, can be obtained by static stability analysis using the proposed method.

Creep of Concrete-Filled Steel Tube Arch Bridge Considering Geometric Nonlinearity and Construction

WU Wenjie, WANG Yuanfeng, MA Yishuo

2013, 26(4): 645-650. doi: 10.3969/j.issn.0258-2724.2013.04.009

[Abstract](1469)

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In order to investigate the creep behavior of long-span concrete filled steel tube (CFST) arch bridges, a finite element model for structural creep was developed using the age-adjusted effective modulus method based on the B3 model for concrete creep. In this framework, the corotational approach for geometric nonlinearity and the technique of element birth and death for simulating different construction stages were also introduced. A long-span half-through CFST arch bridge was analyzed as a numerical application to analyze the impact of geometric nonlinearity and construction process on creep. The calculated results demonstrate that considering the geometric nonlinearity and construction process makes the deflection and stress in steel tube change less than 10%, but leads to a change of 50% in the stress in concrete core. The coupling effect between creep and geometric nonlinearity/construction process is not negligible in the creep analysis of long-span CFST arch bridges.

Experimental Investigation on Deformation Parameters of Silty Clay Based on Local Deformation Measurement

ZHANG Chonglei, JIANG Guanlu, WANG Zhimeng, LI Anhong

2013, 26(4): 651-658. doi: 10.3969/j.issn.0258-2724.2013.04.010

[Abstract](1145)

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In order to investigate the influence of deformation measurement methods on the deformation parameters of undisturbed silty clay, triaxial consolidated-drained shear tests equipped with local deformation measurement transducers were carried out to analyze the behaviors of strain-stress, shear strength parameters and the characteristics of Poisson's ratio and stiffness under small strain. The results show that the effective internal friction angle by using the local deformation measurement, compared with by using the full deformation measurement, decreases about 4.5% to 6.0%, while the effective cohesion increases about 5.7% to 14.0%. The volumetric strains obtained by different measurements are similar before the contraction peak value, after that, the volumetric strain gained by the local deformation measurement is the biggest, followed by the ones via the full deformation measurement and the water measurement. The stiffness gained by the local deformation measurement is twice larger than that based on the full deformation measurement under small strain. When axial strain is smaller than 0.2%, Poisson's ratio increases rapidly with the increase of axial strain in the initial stage, then slows down and becomes stable gradually.

Analysis of Dynamic Interaction between Hole Embedded in Saturated Soil and Moving Loads Using 2.5D Boundary Element Method

XU Bin, GAO Liang, LEI Xiaoyan, XU Manqing, LIU Linya

2013, 26(4): 659-665. doi: 10.3969/j.issn.0258-2724.2013.04.011

[Abstract](928)

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To study the mechanism of interaction between the saturated soil with complex surface and moving loads, a specific 2.5D boundary element method (BEM) for the problem of dynamic responses of the hole embedded in the saturated soil under a moving load was derived systematically. Based on Biot's theory, the frequency wave number domain Green's function for saturated porous media was developed using the Fourier transform method and the potential decomposition approach. Then, dynamic responses in the time-space domain solution were further obtained by synthesizing the wave number solution via inverse fast Fourier transform (IFFT). The results show that using the frequency wave-number boundary integrated equations established by the consistency of the directions of moving load, a 3D spatial model for the dynamic interaction between the holes embedded in the saturated soil with moving loads is convertible to a 2D planar model in the frequency domain, and the 3D complex boundary can be simplified to a problem of 2D boundary element. Thus, the complicated boundary planes can be transformed into computed lines using the 2.5D wave number domain BEM formulation, consequently reducing the amount of computation to a manageable size.

LOD Algorithm of Terrain Based on Conservative Screen Error and Isolated Division of Quad-tree

ZHANG Junfeng, YAO Zhihong

2013, 26(4): 666-671,677. doi: 10.3969/j.issn.0258-2724.2013.04.012

[Abstract](957)

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In order to deal with the problems of enormous data redundancy, single evaluation standard of precision and strong scene of jumping at level switch in static and dynamic level of detail models, an algorithm for regular square grid was proposed. This algorithm reduces the complex computation in real-time expression through terrain tile partition and data pre-progressing, and eliminates dependencies between nodes using isolated division of quad-tree. By building up an evaluation standard based on conservative screen error, jumping feeling is weakened greatly. Finally, cracks between adjacent tiles and nodes are eliminated easily by adding split points and averaging elevation value. Experiment results show that this algorithm has abilities to overcome the shortcoming of the conventional methods and meets the requirements of 3D real-time expression of large-scale terrain. Furthermore, amount of calculation for real-time display is small and frame speed is within 0.03 s.

Rutting Model Considering Shear Behavior of Asphalt Pavement

CHEN Guangwei, LIU Liping, SU Kai, TANG Wen, CHEN Rongsheng

2013, 26(4): 672-677. doi: 10.3969/j.issn.0258-2724.2013.04.013

[Abstract](902)

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To provide a reference for the design of asphalt pavement, a rutting model considering shear behavior of asphalt pavement was established using the observed data from a circular road test, and this model was compared with the current rutting models. To verify the established rutting model, data observed from two expressways was used to analyze the relationship between the predicted and observed rutting values. The comparison result shows that compared with the current rutting models, the established rutting model is more satisfactory, and when correction factor is 0.361 3, there is a good match between the predicted and observed rutting values in the two expressways.

Effect of Geometric Features of Simple Curves on Steering Behavior of Passenger Car

XU Jin, PENG Qiyuan, LUO Qing, SHAO Yiming

2013, 26(4): 678-687. doi: 10.3969/j.issn.0258-2724.2013.04.014

[Abstract](909)

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To study the kinematics characteristic and driver behaviors of vehicle driving on simple curves, a dynamic model of passenger car was built with ADAMS software to perform virtual driving tests on simple curves under the driving patterns of curve-cutting and curve-following. On the basis of the angle change of the steering wheel, a steering process was divided into three stages: entering the curve, maintaining the steering wheel, and exiting the curve. Parameters of steering behavior at the three stages were collected separately for the two driving patterns, such as steering distance and steering time when the vehicle entered or exited the simple curve, and the effects of deflection angle and vehicle wheelbase on vehicle steering behavior were analyzed. The result shows that: steering angle, steering distance, and steering time increase with the deflection angle when deflection angle is smaller than a critical value, especially for the curve-cutting pattern; steering distance of vehicle entering or departing a curve increases as the curve radius when the radius is shorter than 550 m; different driving patterns can lead to different steering distances, and the steering distance of the curve-cutting pattern is about twice as long as that of the curve-following pattern; for the curve-cutting pattern, the profile of steering time against curve radius increases first then decreases, namely, it takes on a parabolic shape, while the profile of the curve-following pattern falls in a monotone manner, and the average steering time of two patterns is approximately 3.75 s.

A Bi-Layer Cooperative Simulation Model of Bi-Directional Pedestrian Flows

TONG Weiping, CHENG Lin

2013, 26(4): 688-693,744. doi: 10.3969/j.issn.0258-2724.2013.04.015

[Abstract](1004)

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Pedestrian behavioral characteristics in metro interchange passageways were analyzed by means of the site observation data at Xinjiekou Station of Nanjing Subway. A comprehensive bi-layer cooperative model for bi-directional pedestrian flows was developed to eliminate the drawbacks in the existing models in terms of behavioral characteristics, the spatial structure expression, dynamic storage and transformation of spatial unit states, and the simulation visualization. In the model, the layer of passageways was first rasterized using GIS technology and then the data were stored in the spatial database and finally output to the GUI by visualization engine in the post-simulation stage scene. In the layer of pedestrian behaviors, a decision model was established on the basis of the Multi-agent and CA theories. The model defined the agent with the consideration of pedestrian's characteristics and actions. The simulation results obtained from the model exercise illustrated the density-speed curve and the time interval and speed curve. The simulation shows that the model can reproduce the typical phenomena observed in reality such as formation of bi-directional pedestrian flows and the phase transition.

Railway Passenger Station Operation Combined Simulation Model Based on TCPN

LU Gongyuan, YAN Haifeng, XU Jin

2013, 26(4): 694-701. doi: 10.3969/j.issn.0258-2724.2013.04.016

[Abstract](1025)

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A timed colored Petri net (TCPN) simulation model is presented to describe the operating process of railway passenger stations. The TCPN model uses a route conflicting graph to define the station yard in order to solve the problems such as complex modeling process, limited applicable range, and inefficiency, in the system simulation of the current railway station operation. The results of the simulation example show that the TCPN model has the advantages of stability and reusability, and can be widely used in the simulation and optimization of passenger railway stations including high-speed railway stations; the conflicting graph is an accurate presentation of station yard routes, which has the same accuracy as the design of station yard construction, and its precision can reach a millimeter level; compared to the traditional modeling method, the progress of the conflicting graph modeling is more efficient. In the given example, maximum loading rates at station throat area and arrival-departure tracks are 70% and 35%, respectively; on-schedule rates of arrival and departure are 100% and 91%, respectively.

Mechanical Properties of High-Speed Turnout Switching and Locking Device

XU Jingmang, WANG Ping, CHEN Rong, XU Hao

2013, 26(4): 702-707. doi: 10.3969/j.issn.0258-2724.2013.04.017

[Abstract](1154)

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In order to optimize the design of high-speed switching and locking device, a lateral force calculation model for switching and locking device was established according to the wheel-rail system coupled dynamics using the finite element method. Taking the external locking device of 60 kg/m rail No.18 turnout in passenger dedicated line as an example, the influences of some main factors, including the speed through turnout, scant displacement of switch rail, and the gap between point switch and block, on the mechanical properties of switching and locking device were analyzed. The computational results show that the speed through turnout has significant effect on the mechanical properties of locking hook; when the speed through the turnout was 250 km/h, the lateral force and displacement was at maximum; a certain scant displacement of switch rail is favorable for the force of locking hook; as the gap between point switch and jacking block increases, the force of locking hook increases almost linearly, and the gap should be avoided to the greatest extent during the operation of turnout.

Modeling and Verification of Temporary Speed Restriction of CTC-S3 Train Control System

YUAN Lei, WANG Junfeng, KANG Renwei, LÜ, Jidong

2013, 26(4): 708-714. doi: 10.3969/j.issn.0258-2724.2013.04.018

[Abstract](1046)

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In order to meet the real-time performance requirement of a temporary speed restriction (TSR) system of Chinese train control system level 3 (CTCS-3), timed automata sub-models of each equipment of the train control system were established for the working process of TSR, and a timed automata network model was built through parallel composition of the sub-models to valuate the sub-models using the parametric configuration of the specification of CTCS-3. Then, the properties of the TSR system such as safety and bounded liveness were expressed in Backus-Naur form (BNF) and validated through formal verification simulation using the UPPAAL integrated tool. The results show that compared with the parameters defined in the system specifications, the modified time parameters can fix the deadlock problem of the system, and improve the real-time performance of the TSR system on the premise of keeping the system properties such as safety and bounded liveness. The TSR system can respond to inputs within 5 s and meet the system specifications.

Decision Models and Coordinative Strategy of Closed-Loop Supply Chain Based on CVaR Criterion

XU Bing, JIA Yanli

2013, 26(4): 715-723. doi: 10.3969/j.issn.0258-2724.2013.04.019

[Abstract](918)

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The paper proposes the decentralized decision and centralized decision models of a closed-loop supply chain (CLSC) with stochastic demand, consisting of one risk-neutral manufacturer and one risk-averse retailer, with the use of the game theory and the conditional value-at-risk(CVaR) criterion. The purpose is to characterize the impact of the risk-averse degree of retailer on the order-quantity decision and the profit of supply chain, and analyze the effect of inferior-products' repairing and remanufacturing. Based on the contract theory, a profit sharing contract was put forward to coordinate the CLSC. The study reveals that the decentralized order-quantity is lower than the centralized order-quantity; the two decision models of the CLSC with the risk-averse retailer generalize the corresponding models of the CLSC with the risk-neutral retailer, and the classic newsvendor model is a special case of the decentralized models; the profit-sharing contract can coordinate the CLSC and generate a win-win situation between the manufacturer and the retailer. Sensitivity analysis shows that the retailer being more risk-averse makes fewer order quantities; but the lower rate of regular products leads to higher order quantities; under both circumstances the profits of the manufacturer, the retailer and the whole supply chain will reduce.

Improved Ant Colony Algorithm for Two-Sided Assembly Line Balancing Problem of Type I

ZHANG Zeqiang, HU Junyi, CHENG Wenming

2013, 26(4): 724-730. doi: 10.3969/j.issn.0258-2724.2013.04.020

[Abstract](1333)

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To overcome the disadvantages of traditional algorithms in solving large-scale two-sided assembly line balancing problems (TALBPs), such as long computing time and unstable results, an improved ant colony algorithm (ACO) was proposed for solving the TALBP of type I. In the proposed algorithm, a task sequence was generated first, and a feasible solution was then obtained by the heuristic assignment method; in addition, the pheromone summation rule and a global pheromone updating rule were adopted to avoid the ants falling into the locally optimal solutions. A series of numerical experiments were conducted on 30 test problems of different size using the proposed ACO algorithm, the standard ant colony algorithm, and the tabu search algorithm for comparison. The results indicate that the proposed ACO algorithm obtained 29 optimal solutions for the 30 test problems, and obtained 6 and 3 more optimal solutions than the standard ant colony algorithm and the tabu search algorithm, respectively. Finally, the proposed ACO algorithm was applied to a real car assembly line and obtained the satisfactory solutions within 21.01 s, saving 9.14 s and improving the computational efficiency by 30.3% when compared with the traditional ACO under the same line efficiency.

Lattice Boltzmann Simulation of Micro-scale Gas Flows in the Transitional Regime

LIU Jiali, ZHANG Jiye, ZHANG Weihua

2013, 26(4): 731-737. doi: 10.3969/j.issn.0258-2724.2013.04.021

[Abstract](815)

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In order to study the flow characteristics of micro-scale gas in the transitional regime, the relationship between Knudsen number and dimensionless relaxation time was derived based on the gas kinetic theory and the effect of Knudsen layer. Computational formulas for the slip velocity on the wall and the bounce-back fraction were derived under a generalized second-order slip boundary condition using the boundary treatment method proposed by Succi. Then, a lattice Boltzmann model for micro-scale gas flows in the transitional regime was established, and the micro-scale Poiseuille flows in the transitional regime were simulated. Computational results show that when the rarefaction parameter is equal to 1.64, the computed dimensionless velocity profile is in good agreement with the dimensionless velocity profile given by Karniadakis in the whole transitional regime. The dimensionless velocity profile remains essentially a parabolic shape in the transitional regime. As Knudsen number increases, the dimensionless slip velocity rises in the boundary and falls in the center line.

New Special Energy-Absorbing Component at Vehicle End of Rail Vehicles

LEI Cheng, XIAO Shoune, LUO Shihui

2013, 26(4): 738-744. doi: 10.3969/j.issn.0258-2724.2013.04.022

[Abstract](1094)

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In order to improve the crashworthiness of rail vehicles, a new special energy-absorbing component at vehicle end was designed according to the energy-absorbing principle of axial cutting and compression process of thin-walled metal structure. An equivalent three-dimensional finite element model for the absorbing process of energy-absorbing component was established using the explicit finite element software LS-DYNA, based on which a numerical simulation of the energy-absorbing process was made. The influences of cutting depth, tool rake angle, and chip central angle on the performance of the energy-absorbing component were analyzed. The results show that the energy absorption and interface force of the energy-absorbing component was proportional to the cutting depth and chip central angle, and inversely proportional to the tool rake angle, but was little affected by cutting depth. The stroke efficiency of the new energy-absorbing component can arrive at 100%, and its compression efficiency and gross efficiency can reach more than 70%, all higher than those of the existing energy-absorbing component.

Stamp-Forming of Heads of Railway Tank Cars

LUO Zhengzhi, ZENG Jing, HUANG Liebing, QIN Shengmou

2013, 26(4): 745-749,768. doi: 10.3969/j.issn.0258-2724.2013.04.023

[Abstract](903)

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In order to ensure the cold stamping quality of railway tank car heads, die surfaces with three different types of draw bead structures at the die entrance, including round draw bead, rectangular draw bead and no draw bead, were designed for the head stamping process. Then, the head stamping processes for the three types of die entrances were simulated using the finite element method. The simulation results were analyzed and compared in terms of wrinkles, spring-back, and thickness variation. On this basis, a reasonable die structure was selected and manufactured for stamping experiments. The result shows that the die entrance with rectangular draw bead could effectively avoid wrinkles and blowups, and has a smaller spring back. The stamping experiment results with the rectangular draw bead indicate that the stamped heads has no defects; the minimum thickness is 9.6 mm, and the maximum thickness is 10.5 mm, which consist with the computational results. Therefore, adopting the die with rectangular draw bead for cold stamping of railway tank car heads is effective.

On-line Monitoring Method for Short-Circuit Reactance of V/X Wiring Traction Transformer

ZHOU Lijun, HUANG Xiaofeng, LI Xianlang, ZHANG Zhigang

2013, 26(4): 750-755. doi: 10.3969/j.issn.0258-2724.2013.04.024

[Abstract](925)

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Based on the equivalent circuit of V/X wiring traction transformer, a calculation model of short-circuit reactance was established to effectively detect the transformer winding deformation by using the monitoring current and voltage data of each primary phase and the feeder line. According to the relative standard deviation of monitoring data, the precision control method for test results was presented. The results show that even without additional sensor installed on the windings, the tested short-circuit reactances of A-B phase and C-B phase of a V/X wiring traction transformer with the proposed method are 67.31 and 61.18 Ω, respectively, which are very close to the off-line test data of 67.40 and 61.27 Ω, revealing that the proposed on-line monitoring method is effective and practical.

Objective Evaluation Method of Speech Quality Based on Auditory Perceptual Properties

TAN Xiaoheng, XU Ke, QIN Jiwei

2013, 26(4): 756-760. doi: 10.3969/j.issn.0258-2724.2013.04.025

[Abstract](992)

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Based on Mel-frequency cepstral coefficients (MFCC), Mel-cepstral distance measure (Mel-CD) algorithm used for the objective evaluation of speech quality was analyzed. According to the theory of psychoacoustics, a human auditory model proposed by Johannesma and nonlinear compression were applied to extracting MFCC. Gammatone filter bank was used to simulate the basilar membrane. Mel-cepstral gammatone filter bank distance measure (Mel-GD) based on the improved MFCC was proposed, which was more in accordance with the auditory perceptual properties. Performance testing results showed that the proposed algorithm compared favorably with the Mel-CD in time complexity, the correlation degree between objective evaluation and subjective evaluation was improved by 4.9%, and estimation bias was decreased by 45.5%.

Performance Analysis of Multi-Channel Slotted ALOHA Protocol Based on Power Capture and Backoff

YANG Liu, FAN Pingzhi, HAO Li

2013, 26(4): 761-768. doi: 10.3969/j.issn.0258-2724.2013.04.026

[Abstract](1176)

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Abstract:
To extend the theoretical analysis in multi-channel slotted ALOHA protocol based on power capture and backoff, some important performance measures including access success ratio, throughput and delay performance were analyzed. The protocol performance is dependent on channel load, power capture radio, the number of channels and the number of terminals. By the numerical simulation, the parameter influence on the system performance was analyzed. It is shown that smaller power capture radio lead to larger throughput, shorter delay and higher access success ratio; the larger number of channels also results in larger throughput, shorter delay and higher access success ratio. The impact of the number of terminals on throughput and access success ratio is small, and for smaller the number of terminals, delay is longer. The relative error between the theoretical results and the simulation ones was less than 2%.

Blind Sources Separation of Non-stationary Signals Based on Adaptive Maximum Signal-to-Noise Ratio Method

ZHANG Jie

2013, 26(4): 769-775. doi: 10.3969/j.issn.0258-2724.2013.04.027

[Abstract](993)

PDF 702KB(395)

Abstract:
In order to improve the blind separation performance of non-stationary signals, a new blind source separation algorithm named adaptive maximum signal-to-noise ratio algorithm was proposed. This algorithm uses the signal noise ratio function as the cost function parameter and an improved multinomial coefficient autoregressive model to estimate the best length of moving average window. Simulations showed that FastICA algorithm needs to assume the probability density function (PDF) of the sources to approximate their un-Gaussian features by choosing the appropriate nonlinear function. If the assumed PDF considerably deviates from the true one, the sources could not be separated correctly. In the case of the sources with identical kurtosis, the separation algorithm using cumulants failed to separate the sources. The comparison between the proposed method, the classical FastICA algorithm, and the separation algorithm using cumulants showed that the proposed method could retrieve the time-varying non-stationary source signals accurately, and the separation performance of the proposed method was not influenced by the PDF and the kurtosis of the source signals.

Cartesian Mesh Generator for Parallel Finite-Difference Time-Domain Method

CHEN Linglu, ZHOU Haijing, LI Hanyu, FU Haijun, LIAO Cheng

2013, 26(4): 776-782. doi: 10.3969/j.issn.0258-2724.2013.04.028

[Abstract](1041)

PDF 818KB(482)

Abstract:
In order to generate discrete geometric-model that can be solved by the finite-difference time-domain (FDTD) method, and avoid complicated manual operations, an efficient parallel mesh generation technique for massively parallel FDTD simulation was presented. The parallel mesh generator is capable of dissecting arbitrary 3D multi-material models, with triangle-facet computer aided design files as input data. Without the need for excessive data communication between the processors, its parallel efficiency was close to 100% in the test. The coupling effect of a simple computer case with a microstrip board was simulated by the FDTD method, based on this mesh generator. The results by the FDTD coincided with the ones calculated by the commercial electromagnetic simulation software, demonstrating the correctness of this mesh dissection method. Finally, when dissecting a real computer case with 250 processors and the grid number of 0.6 billion, the CPU time was only about 0.2 s. This efficient mesh dissection indicates that the proposed parallel mesh generation technique can efficiently solve the modeling in massively parallel FDTD simulation.

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2013 Vol. 26, No. 4