西南交通大学学报

Cusp Point Condition for Estimating Ultimate Load of Pile Foundation Based on Strength Reduction Method

DONG Tianwen, ZHENG Yingren, TANG Xiaosong

2014, 27(3): 373-378. doi: 10.3969/j.issn.0258-2724.2014.03.001

[Abstract](938)

Abstract:
In order to estimate the ultimate load of pile foundation by the strength reduction method, based on the Zeeman machine of cusp catastrophe, the bearing capacity functional of pile foundation and the theory of direct shear test the catastrophe's critical condition of bearing capacity of pile foundation was advanced, and the relation between incremental displacement gradient and geotechnical material shear strength was established. And a method based on cusp-catastrophic curve was put forward to estimate the ultimate load of pile foundation. The analysis of examples shows that the cusp-catastrophic curve is almost vertical to the axis of strength reduction factor after the cusp point. A micro increment of strength reduction factor will result in the quick increase of incremental displacement gradient, indicating that the plastic deformation of geotechnical materials occurs. So the strength reduction factor corresponding to the cusp point may be determined as the strength reduction factor under ultimate load condition. The ultimate loads estimated by a cusp-catastrophic curve and a reduction factor-settlement curve are almost the same, but the physical meaning and cusp point of the former are still clearer.

Bearing Behaviour of Composite Foundation with Rigid-Flexible and Long-Short Piles under Embankment Load

ZUO Shen, LIU Weizheng, ZHANG Ruikun, ZHANG Hao, ZHANG Junhui

2014, 27(3): 379-385. doi: 10.3969/j.issn.0258-2724.2014.03.002

[Abstract](1371)

Abstract:
In order to study the bearing characteristics of the composite foundation with rigid-flexible and long-short piles under embankment loading, a field test of a foundation improved by the capped pre-stressed thin-wall concrete (PTC) piles and soil cement deep mixed (CDM) columns was conducted in a bridgehead transition section. The variation laws of pile-soil stress ratio, load sharing ratio and pile-soil differential settlement were analyzed. Furthermore, the embankment load transfer characteristics of long-short-pile composite foundation were numerically simulated. The test and simulation results indicate that soil pressure between piles and stress on the top of CDM pile increase slowly with the increase of embankment load, while the pressure on the top of PTC pile cap increases faster. Due to the effect of soil arching caused by differential settlements between the piles and the soil, a large part of embankment load is shifted to the rigid-long piles. And the maximum values of stress ratio between rigid-long pile as well as flexible-short pile and soil are 7.5 and 2.1, respectively. The location of the neutral point of rigid-long pile shaft gradually ascends up during the embankment filling and soil consolidation due to the existence of short piles, and the pile-top pressure and pile shaft friction resistance of rigid-long pile decrease. The change of short pile length makes no difference to embankment settlement when it becomes larger than a certain value. Therefore, the length of short pile can be designed to be the critical value that satisfies the requirement of ground bearing capacity.

Structural Internal Force of Shield Tunnel in Expansive Soil Underlying Sandy Pebble Layer

FANG Yong, HE Chuan, QI Chun, ZHANG Ming

2014, 27(3): 386-392. doi: 10.3969/j.issn.0258-2724.2014.03.003

[Abstract](931)

Abstract:
The Chengdu metro line 2 partly passes through the complex strata of sandy pebble and expansive soil. In order to obtain the influence law of expansive force resulted from partial expansion on shield tunnel lining structure load in complex layers, the influence of partial expansion with various ranges and expansion forces on the contact pressure of tunnel lining structure was analyzed with a numerical method. Load distribution and internal forces of tunnel lining structure at the stage of grouting and after tunnel transfixion were obtained by field tests and compared with the calculated structural internal forces under different expansion loads. The research show that the expansion thickness and range have a little effect on the increment of pressure on the lining structure, but the expansion force has a great influence on the increment. The existence of partial expansion will increase the bending moment of segment and is harmful to the lining structure. The negative bending moment becomes the control factor of tunnel structure design in the complex layers. When structure internal forces in complex layers of sandy pebble and expansive soil are calculated, the influence of expansion load should be considered and it is better to use a numerical method to determine its value.

Soil-Water and Shear Strength Characteristics of Unsaturated Red Clay

LI Longqi, LUO Shuxue, JIANG Hong, SONG Lei, DING Bingbing, LI Chugen

2014, 27(3): 393-398,431. doi: 10.3969/j.issn.0258-2724.2014.03.004

[Abstract](1063)

Abstract:
In order to study the unsaturated characteristics of red clay, Geo-experts self-balanced pressure plate meter and ZJ direct shear apparatus were used in experiments to investigate the soil-water and shear strength characteristics of the typical undisturbed and remolded red clays under different dry densities. Based on the experimental results, the physical and mechanical features of unsaturated red clay were discussed. The results show that mineral composition and micro-structural changes may be the major factors accounting for the difference between physical and mechanical properties of the undisturbed and remolded red clay. The soil-water characteristics curve of undisturbed unsaturated red clay show three stages, which has the obvious air-entry values and residual moisture content, while the soil-water characteristics curve of remodeled unsaturated clay presents a semi-parabolic variation. For the undisturbed red clay, the maximum cohesion occurs in a low moisture condition, and the corresponding moisture content is about 5% to 10% larger than the residual moisture content. Thus, in this case, increasing the number of test groups can optimize the test results. For the remolded red clay, the range of the significantly reduced internal friction angle can be determined according to the plastic limit.

Dynamic Responses of Groundwater Seepage of Landslide Influenced by Fluctuation of Reservoir Water Level

XIA Min, REN Guangming, MA Xinlei, DONG Qingzhi, HUANG Bangzhi, SUN Renxian

2014, 27(3): 399-405. doi: 10.3969/j.issn.0258-2724.2014.03.005

[Abstract](927)

Abstract:
In order to investigate the impact of reservoir water level fluctuation on the dynamic responses of groundwater seepage of landslide. The transient seepage of Shiliushubao landslide as a research object was discussed under five different water level fluctuation rates and different seepage coefficient magnitudes. The research results show that the groundwater seepage line is affected by water level fluctuation rate and permeability coefficient. Under the condition of the rise of water level, landslide appears generally as a synchronous impoundment type when permeability coefficient is above 1×10-4 m/s and greater than the water level rising rate. Under the condition of the descend of water level, seepage line will be characterized by a sudden drawdown when the permeability coefficient is less than 1×10-6 m/s; reservoir water level will drop slowly if the coefficient is from 1×10-4 to 1×10-5 m/s; and seepage line and reservoir water level will descend synchronously as the coefficient exceeds 1×10-4 m/s.

Analysis of Dynamic Characteristics of Railway Subgrade Based on Three-Dimensional Numerical Simulation

KONG Xianghui, JIANG Guanlu, LI Anhong, XIAO Dong

2014, 27(3): 406-411. doi: 10.3969/j.issn.0258-2724.2014.03.006

[Abstract](1309)

Abstract:
To discuss the effect of train axle load and speed on the dynamic characteristics of soil subgrade, a 3D dynamic simulation of the ballast track-subgrade system was made using ANSYS and FLAC3D. In the calculation process, the hysteretic damping was used to simulate the nonlinear characteristics of soil under cyclic dynamic loading. The proposed method was then used to calculate the dynamic stress of subgrade in the field cyclic loading test of the Dazhou-Chendu railway, and the simulation results showed a good agreement with the field measurements. In the conversion between the load vibration frequency and the passenger train speed, the distance between the peaks of the adjacent dynamic stress was simplified as the two bogie spacing of adjacent compartments. On this basis, the effect of passenger train speed on the dynamic property of soil subgrade was investigated. The results indicate that train axle load and speed has a large impact on the dynamic stress of subgrade surface. With an increase in axle load and speed, the saddle-shaped distribution of dynamic stress of subgrade surface is more obvious. However, train speed has little effect on the attenuation law of dynamic stress along the subgrade depth. The dynamic stress is attenuated by 42%-46% in the subgrade surface layer, and the attenuation value can reach 79%-82% after the diffusion of subgrade bottom layer at different speeds.

Model Experiment of Fatigue Deformation Characteristic of Emergency Soil Airfield Pavement

LIU Junzhong, WENG Xingzhong, ZHANG Jun, LI Xianpeng, JI Dongming, GUO Lei

2014, 27(3): 412-418. doi: 10.3969/j.issn.0258-2724.2014.03.007

[Abstract](883)

Abstract:
To investigate the reasonable pavement structure for rapid construction of emergency airfield, fatigue deformation characteristics of soil airfield pavement were researched respectively by manual loading method and electro-hydraulic servo fatigue testing machine. Through a full-scale model test, the variations of cumulative plastic deformation, rebound deflection and deflection basin curve with load, loading frequency and loading times were discussed. The test results show that cumulative plastic deformation increases with loading frequency, and there exists a logarithmic relationship between it and loading times, the deflection basin curve has approximately an S-style curve and can be fitted well by a quartic polynomial equation. The carrying capacity of pavement structure increases fast at an early stage, holistic elastic modulus runs up to from 200 to 500 MPa in 7 to 60 d, the rebound deflections are less than 1 mm under ten thousands traffic times. The fatigue deformation characteristics of the recommended airfield pavement structure composed of compacted subsoil, cement stabilized soil base (or subbase) and functional surface course, can meet the requirements of emergency airfield.

Dynamic Responses of Super-Long-Span Suspension Bridge with CFRP Cables under Different Structural Design Parameters

LI Cuijuan, XU Xun, QIANG Shizhong

2014, 27(3): 419-424. doi: 10.3969/j.issn.0258-2724.2014.03.008

[Abstract](1016)

Abstract:
In order to research the dynamic responses of a super-long span suspension bridge with CFRP cables, a super-long-span suspension bridge with CFRP (carbon-fibre reinforced plastic) cables and having a span of 3 500 m was designed by taking a strait as engineering background. Based on the ANSYS software, its dynamic responses and the effects of structural design parameters on the dynamic responses were analyzed. These structural design parameters are rise-span ratio, main cable safety factor, restraint systems of the stiffening girder and bridge tower stiffness. The research results show that torsional-bending frequency ratio increases proportionately with rise-span ratio, and the main cable safety factor has a little effect on the dynamic responses, and a long span decreases the effect of the restraint system of stiffening girder on the dynamic responses and increases the bending stiffness of bridge tower in the axial direction of bridge and the torsional stiffness are benefit to raise the vertical vibration fundamental frequency and torsional vibration fundamental frequency.

Effects of Axial Force Fluctuations on Seismic Behavior of Steel Box Column

LI Haifeng, LUO Yongfeng, CHEN Lincong, MEI Zhen

2014, 27(3): 425-431. doi: 10.3969/j.issn.0258-2724.2014.03.009

[Abstract](767)

Abstract:
To investigate the influence mechanism of axial force fluctuation on the seismic behaviors of steel box columns, the seismic behaviors of steel box columns under 5 patterns of eccentrically fluctuant axial force were numerically analyzed by finite element simulation. The influence rules of axial force fluctuation on their load-displacement hysteresis loops, skeleton curves, displacement ductility coefficients and energy dissipation capacities were discussed. The research results show that the loading frequency of a fluctuant axial force has an significant effect on the seismic behavior of a steel box column—when the loading frequency increases, the seismic behavior deteriorates rapidly. A large amplitude of the fluctuant axial force results in the severe degeneration of load-bearing capacity of a steel box column. When the width-to-thickness ratio of plates in steel box columns is small, the effects of axial force fluctuation on the seismic behavior become conspicuous. As a result, the adverse effects of axial force fluctuation on the seismic behaviors of the columns should be sufficiently considered when the seismic measures of steel box columns in a large span spatial structure are established.

Influence of Seam in Type Ⅰ Slab Ends on Dynamic Characteristics of Track and Vehicle

YANG Junbin, LIU Xueyi, LIU Yongxiao, DAI Feng

2014, 27(3): 432-437,512. doi: 10.3969/j.issn.0258-2724.2014.03.010

[Abstract](940)

Abstract:
In order to study the influence of the seam between type Ⅰ slab ends and CA mortar on dynamic characteristics of rail, slab, and vehicle under high-speed train load, a vehicle-type Ⅰ slab track vertical coupling dynamic model was established. Through this model, the changes of evaluation indexes such as wheel-rail force, displacement of rail and slab, acceleration of rail, tensile stress of slab, acceleration of slab, and acceleration of vehicle were investigated under various working conditions for different seam lengths and heights at slab ends. The result indicates that with a shorter seam at the slab end, the track slab is easier to bear the force with a void. When the track slab bears the force with a void and a seam length, the seam height equals to the maximum vertical displacement of the track slab with the seam length. The force of track structure and vehicle is influenced by both the seam length and height, but more influenced by seam length. When the seam is less than 0.6 m long, the deformation and stress were deteriorated mainly on the rail and slab. When the seam is longer than 0.6 m, the vibration acceleration of vehicle will exceed the allowable value.

Vibration Response of Vehicle with Stochastic Structural Parameters under Random Excitation

JIA Aiqin, CHEN Jianjun, CAO Hongjun

2014, 27(3): 438-443. doi: 10.3969/j.issn.0258-2724.2014.03.011

[Abstract](919)

Abstract:
To investigate the influence of random structure parameters on vehicle vibration responses, the random vibration responses of a vehicle system with uncertain parameters under random road excitations were investigated using a quarter-vehicle model. A dynamic model for the system was established. In this model, sprung mass, unsprung mass, suspension damping, suspension and tyre stiffness are considered as random variables, springs between tires and vehicle body are thought to be nonlinear, and road irregularity is considered to be a white noise process. The nonlinear vehicle system was linearized by the energy difference method, a stationary covariance matrix for the random vibration responses was obtained by solving the Lyapunov equations, and the stable equivalent linear system parameters of vehicle were gained through iterations. The example calculation results show that this method can improve the accuracy and efficiency of computation—the relative error of displacement is 6.841 5% to the energy difference method, while it is 8.150 5% to the equation difference method; solving the variance value of random responses using the energy difference method uses only 0.8 s, and while simulating 1 000 times using the Monte Carlo method 70 min.

Actions of Derailed Train on Structures in Eurocode：Impact Mechanism and Design Strategy

LIU Yanhui, ZHAO Shichun, Manfred Keuser

2014, 27(3): 444-449. doi: 10.3969/j.issn.0258-2724.2014.03.012

[Abstract](1063)

Abstract:
In order to study the impact mechanism and design method for a derailed train impacting against adjacent structures that are applicable to Chinese high-speed train, the UK Railway Group Standards GC/RT5112 and International Union of Railways leaflet UIC777-2R are analyzed, which are the basis to develop the Eurocode EN1991-1-7 in terms of the impact from the derailed train against the nearby structures, including the danger zone on both sides of the track, impact loads, preventive measures, etc. Then, the design strategy of accidental loads in Eurocode EN1991-1-7 is introduced; the main research achivements that have important influence on Eurcode about the impact mechanism from the derailed train against structures are reviewed. The results show that the research methods and design strategies of the Eurocode about the impact of a derailed train on adjacent structures are worth learning, but Chinese railways are different from European ones in aspects of structural features of high-speed rail stations, running speed, production methods of railroad track bed, train marshalling, etc., it is necessary to study the impact problems from derailed train against structures according to Chinese situations.

DC Bus Capacitor Voltage Balancing Circuits in Diode-Clamped Multilevel Converter

DING Na, SHU Zeliang

2014, 27(3): 450-454. doi: 10.3969/j.issn.0258-2724.2014.03.013

[Abstract](744)

Abstract:
In order to solve the imbalance of DC bus capacitor voltages in the diode-clamped multilevel converter, a balancing circuit with two-layer auxiliary inductors was designed. With this circuit, the voltages of all the DC-side capacitors in the multilevel converter can be balanced by a simple control. On the basis of analysis of the circuit structure and control principle, the ranges of inductor parameters were analyzed from the viewpoint of energy conversion. Taking a five-level converter as an example, a Matlab/Simulink simulation model and an experimental prototype were built, and the balance characteristics of DC bus capacitor voltages were compared between the proposed two-layer auxiliary circuit and the traditional one-layer circuit. Experimental results verify that the proposed two-layer circuit could effectively balance all the DC bus capacitor voltages within 20 ms, and the capacitor voltage ripple was less than 3%.

Variable Width Pulse Train Controlled DCM Buck Converter

WU Songrong, ZHONG Shu, XU Jianping, SHA Jin

2014, 27(3): 455-461. doi: 10.3969/j.issn.0258-2724.2014.03.014

[Abstract](752)

Abstract:
In order to solve the problem that DC-DC converter switch has a large steady-state output voltage ripple in pulse train (PT) control, a variable width pulse train (VWPT) control method was proposed after analysis of the generating mechanism of large output voltage ripples. The VWPT control method is based on a buck converter operated in discontinuous conduction mode (DCM). According to the load power change, the duty ratios of high and low power pulses can be regulated dynamically by digital control, and then the converter can be controlled by two drive pulses with small energy discrepancy. Thus, the characteristics of output voltage ripple in VWPT control are obviously better than in PT control. The experimental results show that the steady-state output voltage ripple in VWPT control can be reduced about 50% compared with that in PT control.

Optimization Design of Mathematical Morphology Filter Based on Quantum Genetic Algorithm

ZHANG Xiaochen, GAO Hongli, HUANG Haifeng, GUO Liang, XIAO Shide

2014, 27(3): 462-469. doi: 10.3969/j.issn.0258-2724.2014.03.015

[Abstract](1458)

Abstract:
To deal with the structuring element optimization of mathematical morphology filter, an optimization design method of mathematical morphology filter based on quantum genetic algorithm was proposed. The quantum genetic population was initialized according to the characteristic of mathematical morphology structuring element parameters. The population evolution was realized by quantum crossover, variation and quantum rotation gate based on expansion coefficient, thus obtaining the best parameters of the mathematical morphology filter. The performances of optimization algorithm under different proportions of random noise and power frequency interference noise were studied. The simulation results show that the performance of mathematical morphology filter is greatly improved after being optimized. The signal-to-noise ratio of the signal with random noise is improved from -0.98 dB to 5.23 dB, and that of the signal with mixed noise is improved from -3.05 dB to 0.41 dB. It means that the optimized mathematical morphology filter could remove both random noise and mixed noise with power frequency interference effectively.

Dynamic Behaviors Analysis of a Class of Complex-Valued Neural Networks with Mixed Time Delays

XU Xiaohui, ZHANG Jiye, ZHAO Ling

2014, 27(3): 470-476. doi: 10.3969/j.issn.0258-2724.2014.03.016

[Abstract](1064)

Abstract:
To apply the complex-valued neural networks to pattern recognition, the dynamical behaviors of the equilibrium point of a class of complex-valued networks with mixed time delays were investigated. Assuming that the activation functions satisfy the global Lipschitz condition, some sufficient conditions for assuring the existence, uniqueness and exponential stability of the equilibrium point of the system were obtained by using homeomorphism mapping lemma and the vector Lyapunov function methods. The results show that the judgment matrices constructed using weighted coefficients, self-feedback functions and activation functions of the system were M matrix. Finally, a numerical example was presented to show the correctness of the obtained results.

Real-Time Object Tracking Based on Hough Ferns

QUAN Wei, CHEN Jinxiong, JIANG Yongquan, YU Nanyang

2014, 27(3): 477-484. doi: 10.3969/j.issn.0258-2724.2014.03.017

[Abstract](799)

Abstract:
In order to deal with the tough problem of providing high accuracy and meanwhile achieving real-time tracking using Hough-based approaches under very limited samples for training, a Hough ferns based method was proposed for object tracking. This method uses the random ferns as the basic detector. It samples the local appearances of object as training set, and computes and saves the Hough votes for each leaf-node. The detector and object model were learned online at runtime to adapt to the variation of object and the TLD (tracking-learning-detection) was improved to achieve long-term visual tracking in unconstrained environment. Experimental results on Babenko sequences demonstrate that the average running speed of the tracker based on the proposed approach on a normal PC is 3fps and the average accuracy rate is 87.1%, showing its better tracking performance than several state-of-the-art methods.

Barrier-Free Design of Passenger Trains in China

XIANG Zerui, XU Bochu, ZHI Jinyi, DONG Shiyu, GUO Xiaofeng, ZHANG Yong

2014, 27(3): 485-493. doi: 10.3969/j.issn.0258-2724.2014.03.018

[Abstract](1347)

Abstract:
To find out the solution for barrier-free design of passenger trains in China, three models were proposed by analyzing the passengers' special needs, including the demand model of passenger with reduced mobility, the accessible passageway model of coach, and the basic layout model of wheelchair accessible zone. Then, the theoretically optimal layout was obtained by comparing the all schemes. By both human tests and virtual simulations, some key dimensions were determined for barrier-free design of passenger trains, such as wheelchair turning space, passage width, and the controllable range of wheelchair users' hands. Further, the accessibility information symbols in passenger trains were introduced and some suggestions were provided for their places. The results show that trains should be equipped with priority seats, accessible coach and accessibility information symbols. Wheelchair accessible seat and individual washroom for wheelchair users should be arranged on both sides of the coach entrances. The number of the priority seats is no less than 5% of the seats. When the number of the coaches is no more than 8, one wheelchair accessible seat is required. But when the number of the coaches is more than 8, two wheelchair accessible seats are required. The diameter of wheelchair turning area is no less than Φ1 500 mm, and there should be one at the every corner of the accessible passageway. The passage width for passengers with reduced mobility is no less than 950 mm. All of the controllers should be installed on the wall with 389-1 354 mm far away from the floor. The depth of the table surface should be less than 423 mm.

Stability Research for Parallel Operation of Diesel Generator Sets

LI Donghui, ZHANG Jundong, JI Yulong

2014, 27(3): 494-498. doi: 10.3969/j.issn.0258-2724.2014.03.019

[Abstract](1104)

Abstract:
In order to analyze quantitatively the stability of parallel operation of diesel generator sets and monitor the state of generators being out of step during development of a simulator for the ship power system, calculation formulae for parameters of the swing angle were deduced. An on-line algorithm for calculating the parameters of swing curves of generators was presented, and the parametric exponents of the curve were calculated by solving high-order state differential equations. In addition, the stability degree of parallel operation (SDPO) was defined, and the Simulink tool box was used to set up a simulation system to verify the algorithm. The results of simulation examples show that the SDPO can indicate the stability allowance of parallel operation of diesel generator sets. The parameters obtained by the algorithm can reflect the stability of parallel operation in real time during the simulator training. The parameters of the swing curve can be determined by differentiation of the curve from the first to the forth order. When the exponents change with time or the data of the curve are discrete, the parametric exponent can be obtained by derivation using the five-point interpolation method.

Scheme for Optimal Energy-Efficient and Resource Allocation in OFDM-Based DF Relay Link

HUANG Gaoyong, FANG Xuming, HUANG Bo, CHEN Yu

2014, 27(3): 499-506. doi: 10.3969/j.issn.0258-2724.2014.03.020

[Abstract](793)

Abstract:
The resource allocation problem in OFDM-based DF-Relayed link was formulated as a joint optimization of subcarrier pairing and power allocation while maximizing energy efficiency (EE) with both the minimum rate and the total transmission power constraints. It is proved that the optimal energy-efficient solution under the minimum rate and maximum transmit power constraints for the OFDM-based DF-Relayed link is globally unique. Subsequently, a resource allocation scheme with low complexity was proposed. Simulation results show that compared with the fixed subcarrier pairing strategy, the data rate and EE of the proposed scheme with the subcarriers pairing strategy are respectively increased by 2.3% and 3.1% when the relay node is located at the midpoint position between the source and destination nodes, and Rmin=1.5 Mbit/s. Compared with the traditional equal power allocation scheme, rate maximization and waterfilling power minimization schemes, the proposed scheme achieves the optimal EE while guaranteeing minimum rate requirements and maximum total transmission power constraints.

Reliability Model for Failure Dependence Direction of Mechanical Components

LIANG Hongqin, TANG Jiayin, HE Ping, WANG Jianpeng

2014, 27(3): 507-512. doi: 10.3969/j.issn.0258-2724.2014.03.021

[Abstract](886)

Abstract:
In order to determine the dependence direction of correlated failures in the reliability calculation of mechanical structural systems, a reliability variable determination model was established under a linear regression background according to properties of the linear dependent coefficient. Using the Copula regression function, the model was expanded to determine directions of correlated failures in the general asymmetrical structures. To verify its validity, the expanded model was applied to a locomotive axle to determine the correlated failure direction of wear failure and deformation failure of the axle. The calculated Skewness coefficients of wear loss and deformation were 2.362×10-6 and 9.665×10-33 respectively. The results indicate that the wear failure was the dominant mechanism, which is consistent with the actual failure form of the axle. This verifies the effectiveness of the model.

Corrosion Rate Test of Cable Wires of Large Span Bridge

MIAO Changqing, WEI Tinghua, WANG Yichun, WANG Man

2014, 27(3): 513-518. doi: 10.3969/j.issn.0258-2724.2014.03.022

[Abstract](1005)

Abstract:
In order to explore the corrosion law of large span bridge cables, cylindrical corrosion electrodes were prepared according to the actual corrosion state of bridge cable wires, and the electrochemical corrosion rate of the high strength-steel wires were investigated by orthogonal experiment design and electrochemical experiments. The influence of temperature, salinity, pH value, and their interaction on steel corrosion rate were studied through intuitive analysis and variance analysis of the test results. The result shows that the environmental impact factors can be ordered descendingly by their importance in affecting the corrosion rate of cable wires as NaCl concentration > temperature > interaction between temperature and pH value > pH value > interaction between temperature and NaCl concentration > interaction between NaCl concentration and pH value. In addition, temperature and NaCl concentration bear a monotonic relationship with the corrosion rate and pH value bears a nonmonotonic relationship with the corrosion rate.

Verification of Stent Mechanical Formulas by “Planar Stent” Experiment

YANG Jie, YANG Ji, XU Jiang, LIU Yujie, HUANG Nan

2014, 27(3): 519-524. doi: 10.3969/j.issn.0258-2724.2014.03.023

[Abstract](749)

Abstract:
To verify the formulas of elastic radial stiffness and plastic limit pressure of stents, the conception of "planar stent cell" was proposed and a planar stent specimen was produced according to the real curved structure of an intravascular stent. Tensile experiments of "planar stent cell" were then performed using MTS (material test system) equipment, and the experimental pressure-radial curves were compared with the ones predicted by formulas of elastic radial stiffness and plastic limit pressure. The results show that at the elastic stage of stent expansion, the difference of elastic radial stiffness between experimental measurements and formula-calculated values was less than 3%; at the plastic stage, the two curves obtained by experiment and formula were close. The experiments confirmed the accuracy and precision of the two formulas.

Chaos Control of Lauwerier Mapping

GUO Feng, XIE Jianhua, YUE Yuan

2014, 27(3): 525-529. doi: 10.3969/j.issn.0258-2724.2014.03.024

[Abstract](747)

Abstract:
In order to overcome the defect that the properties of the original system is changed in the process of chaos control with external excitation or damping, the OGY control method is combined with the pole placement technique of the linear control theory to establish a linear mapping. By applying the pole placement technique to select a small time-dependent perturbation of the control parameter, a new method is proposed to control the chaos movement of Lauwerier mapping. According to the ergodicity of chaos movement, the unstable periodic orbits are embedded into the chaotic attractor. The unstable period-1 and period-2 orbits are selected as the control targets. When map points wander to the neighborhood of these periodic orbits, a small perturbation is added to the system control parameter, and the unstable period-1 and period-2 orbits are controlled to be stable. In addition, the influence of different regulator poles on the control time is analyzed. The results show that when the two poles are 1/8 and 0, respectively, the unstable period-1 orbit is controlled at the fixed point after 230 iterations; and when the two poles are 1/6 and -1/4, the chaos control is achieved after 3 300 iterations. The dynamic properties of the original system is not changed in the process of the chaos control.

Accelerated Fatigue Test in Vitro of the New Mechanical Heart Valve

WU Liangliang, ZHOU Feng, SUN Hong, WANG Jin, LIU Li, HUANG Nan

2014, 27(3): 530-535. doi: 10.3969/j.issn.0258-2724.2014.03.025

[Abstract](840)

Abstract:
In order to evaluate the opening and closing states and fatigue properties of a new type of polyoxymethylene heart valve, accelerated fatigue tests were performed on the polyoxymethylene heart valve and an ON-X heart valve using the heart valve prostheses fatigue tester (TH-2200). The opening and the closing positions of the leaflets were tracked using the high speed camera, and the instantaneous motion states of valves were investigated. The results show that the new heart valve had a similar opening-closing cycle at the same frequency with the ON-X heart valve in in vitro accelerated fatigue experiments, and the leaflets of both the valves would generate jitters when they opened to the limit position. After 3×108 cycles of fatigue tests, no obvious wear was found on the valve ring, the valve leaflets rotated flexibly, and the heart valve was working properly.

Field Measurement of Automobiles’ Lateral Accelerations

XU Jin, YANG Kui, LUO Qing, SHAO Yiming

2014, 27(3): 536-545. doi: 10.3969/j.issn.0258-2724.2014.03.026

[Abstract](1003)

Abstract:
To provide design basis for alignment parameters of different types of highways, the lateral accelerations, speeds, and trajectory curvature radii of passenger cars and buses on 12 highways having different design speed and topography were collected in field survey. The level of driving comfort on each test roads was estimated according to vehicle lateral acceleration. The characteristic percentile value of lateral acceleration on three road types, i.e., six-lane road, four-lane road and double-lane road, were presented. For passenger cars and buses on the three kinds of roads, regression models between lateral acceleration and trajectory radii, and between lateral acceleration and speed were established, including the average value model, the extremum value model, and the 85th percentile value model. The results show the following findings: (1) driving comfort becomes poor as lane numbers decreases. For two-lane highways with a design speed of less than 30km/h, the uncomfortable travel on partial section is unbearable. (2) The inflection point on cumulative probability curve of lateral acceleration appears at the 90-92th percentile, and the maximum value on two-lane highways exceeds 8 m/s2. (3) The distribution of lateral acceleration tends to assemble as the trajectory curvature decreases or the lane number increases, and lateral acceleration distribution of buses is more centralized than the ones of passenger cars. (4) The extremum value model between lateral acceleration and trajectory radii and the 85th percentile value model between lateral acceleration and speed can provide design control for the maximum/minimum value of road geometry elements, and the average value models can control the general value of road geometry elements.

Identification of Prevalent Air Traffic Flow in Terminal Airspace Based on Trajectory Spectral Clustering

WANG Chao, HAN Bangcun, WANG Fei

2014, 27(3): 546-552. doi: 10.3969/j.issn.0258-2724.2014.03.027

[Abstract](1138)

Abstract:
In order to improve the adaptability of terminal airspace and standard arrival/departure routes to real air traffic flows and their spatial distribution, a method for detection of main air traffic flows in massive flight trajectories was addressed. After analysis of the spatial characteristics of trajectories, a trajectory similarity model based on 3D grids was proposed. Flight trajectories were partitioned with spectral clustering algorithm, and an identification method for prevalent air traffic flow and outlier trajectories was proposed through kernel density estimation of trajectories in one cluster. Experiments were carried out from trajectories recorded by air traffic control radar to identify prevalent traffic flows. The results show that 1 476 trajectories were divided into 5 clusters, and 5 prevalent traffic flows were identified; in addition, the identification results were not affected by outliers.

4D Trajectory Prediction Based on BADA and Aircraft Intent

ZHANG Junfeng, JIANG Haihang, WU Xiaoguang, TANG Xinming

2014, 27(3): 553-558. doi: 10.3969/j.issn.0258-2724.2014.03.028

[Abstract](1170)

Abstract:
In order to improve the trajectory prediction accuracy, a new four-dimensional aircraft trajectory prediction approach was presented, which was based on aircraft performance data and aircraft intent. Firstly, through statistical analysis of historical radar data about aircraft trajectories, an aircraft intent model was constructed from the perspective of horizontal trajectory, altitude, and velocity profile. Then the four-dimensional trajectory prediction model was built based on the aircraft intent model in combination with aircraft's kinetic and kinematic models, taking into account the aircraft performance data and meteorological data. Finally, taking arrival flights ACA025 and CES2161 to a domestic airport as examples, a simulation was conducted, in which the error between expected and actual time-of-arrival was chosen as the evaluation criteria. The simulation results show that the proposed trajectory prediction approach can control the error between expected and actual time-of-arrival within 30 s with respect to every passing waypoints.

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2014 Vol. 27, No. 3