西南交通大学学报

Simulation Study on Multiline Vehicle-Bridge Coupled Vibration

CUI Sheng'ai, LIU Pin, CAO Yibin, SU Jiao, ZHU Bing

2017, 30(5): 835-843. doi: 10.3969/j.issn.0258-2724.2017.05.001

[Abstract](582)

Abstract:
In order to evaluate the safety and comfort of trains for high-speed multiline railway bridges, it is necessary to perform a simulation research on coupled vibrations for multiline railway vehicle-bridges. For this study, the three-dimensional space dynamic models of CRH3 motor car and trailer were set up using a multibody system dynamics software SIMPACK, and the train dynamics model was assembled via the established CRH3 motor and trailer model by the substructure technology of SIMPACK. The dynamic analytical model of bridge was established by using finite element software ANSYS, for calculating the natural characteristics. Then, according to the deformation compatibility condition and force balance condition between the train system and bridge system, the data transfer of the displacement and force on the wheel-rail contact surface was conducted. The simulation study of multiline vehicle-bridge coupled vibrations was carried out by co-simulation based on SIMPACK and ANSYS for the first time. Meanwhile, the dynamic indexes of the bridge, comfort indexes, and safety indexes of the train were analysed to explore the general rules and influences of coupled vibrations on multiline vehicle-bridges. The research results are as follows:(1) The corresponding vehicle safety indexes (derailment coefficient, wheel unloading ratio, and wheel/rail lateral force) under the combined action of three line trains are almost the same as those only under single line action. As for the vehicle comfort indexes (vertical body acceleration, lateral body acceleration, vertical comfort index, and lateral comfort index), most of the corresponding indexes under single line and three line action are very close (within 1% difference), the only exception being individual vertical body acceleration with slightly larger difference (about 10%) between them. Hence, these comparisons show that the influence of bridge vibrations on the dynamic indexes of trains is small owing to the great stiffness of bridge structures. Thereby the values of corresponding dynamic indicators between single line condition and multiline condition are very close, i.e. the dynamic indexes of vehicles under multiline conditions can be speculated by those under single line conditions. (2) The midspan vertical displacement under the combined action of three lines is slightly larger than the algebra superposition displacement of single line, but less than 1%, and the influence coefficient of vertical displacement is between 1.001-1.006. The midspan lateral displacement under the combined action of three lines is close to the single line superposition displacement with about 10% difference, and the influence coefficient of vertical displacement is about 1.000. Therefore, the midspan vertical and lateral displacements under the multiline condition can be speculated by superposing all single lines. (3) The absolute value of midspan vertical acceleration under the action of three line trains is smaller than that of algebraic superposition for single lines with influence coefficients between 0.636-0.771; hence, it is feasible to conservatively evaluate the vertical acceleration of a bridge under multiline condition referring to the superposition of all single lines. The absolute value of midspan lateral acceleration under the action of three line trains is smaller than the maximum value among the absolute values of the lateral accelerations of each single line; thus, the lateral acceleration of a bridge under multiline condition can be evaluated referring to its single line lateral acceleration.

Optimization of Energy Efficiency of Train Travelling Along Slope Using Sequential Quadratic Programming

LI Chuan, PU Yun, ZHANG Jie

2017, 30(5): 844-851,918. doi: 10.3969/j.issn.0258-2724.2017.05.002

[Abstract](617)

Abstract:
A train energy consumption model was developed to optimize the operation curve of trains travelling along a local steep slope section where the decision variables are continuous variables. The model was developed based on the fundamental theory of train dynamics, taking into account the constraints of train operation. Velocity, distance, and power were chosen as control variables whereas running time and train speed were chosen as constraints. The objective function of the model was to minimize the total energy consumption of the train travelling along the local steep slope sections. The problem was first discretized and then the initial position of the train and kinetic energy of the train as it travels uphill were determined using the sequential quadratic programming algorithm. Simulations were carried out to obtain the energy-efficient train operation curve, with witch the energy consumption could be further saved by 1.771 8% on the basis of existing optimization. The results show that the proposed algorithm can be used to maximize the energy efficiency of trains travelling along local steep slope sections within the given constraints.

Integrated Classification Method for Vehicle Wheel-set Condition Based on Imbalanced Datasets

AO Yinhui, HUANG Xiaopeng, YUAN Minzheng, CHEN Xijun, FANG Enquan

2017, 30(5): 852-858. doi: 10.3969/j.issn.0258-2724.2017.05.003

[Abstract](489)

Abstract:
The wheel-rail vibration signal of a metro vehicle has the characteristics of being non-linear, non-stationary, and a low value of signal-to-noise ratio. The paper proposes an integrated classifier model based on the imbalanced datasets to achieve the disassembly detection and fault diagnosis of wheel flats. Four typical wheel flat faults, namely tread normal, tread scratch, tread peeling, and circumference wear were studied in the research. Feature extraction of signals was performed by incorporating the variational mode decomposition and fuzzy entropy. Fault datasets were constructed and support vector samples were filtered by employing the bias support vector machines. SMOTE (synthetic minority oversampling technique) oversampling was applied and non-support vector samples were combined. An integrated classifier was then built by incorporating the directed acyclic graph for the fault identification. Finally, the study analyzed the precision and recall ratios to evaluate the classification performance of an integrated classifier the. Experiments were conducted at a depot under no load running test. The experimental results show that the proposed method can achieve over 96% of accuracy for the given 4 fault models, which can be effectively employed in the wheel flat faults diagnosis for the metro vehicles.

Periodic Braking of Freight Trains with HXD2 Locomotive on Long Heavy Down Grade

LIN Xuan, WANG Qingyuan, LIU Qiangqiang, FENG Xiaoyun

2017, 30(5): 859-868. doi: 10.3969/j.issn.0258-2724.2017.05.004

[Abstract](553)

Abstract:
An optimal control model of freight train operation, with focus on the regenerative braking energy, was established, based on the fundamental principles of railway traction and energy consumption analysis. The model was specifically developed for the following conditions:(1) the train travels along the track in the long steep downhill section at a non-constant speed while the air brake is applied. (2) The air recharging time should be guaranteed between two successive braking operations. The model was developed based on a pressure reduction of 50 kPa, which is a typical condition during braking. The optimal control strategies were studied for the case where the train travels along the track in the long steep downhill section. The time allocation for each sub-section between two stations was also studied. The optimality of the periodic braking strategy (full electrical braking-full braking-full electrical braking) was analysed using Pontryagin's maximum principle. The necessary conditions were also analysed for the case where the train enters and then leaves the long steep downhill section. The numerical algorithm used for optimal control of the train travelling along the track in the long steep downhill section and its adjacent section was presented in detail. The proposed model and numerical algorithm were verified by performing simulations of an HXD2 locomotive with 100 fully loaded cars. The simulation results were compared with those of the fuzzy predictive control and field test data. Based on the condition that the train is punctual, it is found that the energy consumption during train operation can be reduced by up to 5.6% and 17.9% with respect to the fuzzy predictive control and field test data, respectively.

Organization and Scheduling Method of 3D Urban Scene Data Driven by Visual Perception

ZHU Qing, CHEN Xingwang, DING Yulin, LIU Mingwei, HE Huagui, YANG Weijun, CHEN Liyan, CAO Zhenyu

2017, 30(5): 869-876. doi: 10.3969/j.issn.0258-2724.2017.05.005

[Abstract](632)

Abstract:
Focusing on the problems of inefficient 3D model scheduling and low visual consistency of complex 3D urban scene visualization, a self-adaptive organization and scheduling method for 3D urban scenes driven by visual perception is proposed. Based on the spatial distribution of 3D city models, the adaptive quadtree partition was used to divide the complex 3D scene into different levels of granularity. Subsequently, traversing the quadtree from bottom to top, levels of detail (LODs) were generated for the intermediate nodes, and the geometric error of each layer was calculated to construct a flexible multi-granularity 3D tile model. Finally, visual perception parameters such as the shape, size, and height of the building model were evaluated by employing the screen error, which was used to constrain the self-adaptive scheduling of LODs. The 3D models of four LODs in Berlin were selected for an interactive 3D roaming test. The experimental results show that the rendering frame rate was more than 40 f/s based on the view-related hierarchical LOD dynamic scheduling, which could ensure efficient dynamic scheduling and visual consistency of the complex 3D urban scene in a network environment.

Optimizing Railway Station Locations in Mountainous Areas Based on Weighted

PU Hao, ZHANG Hong, LI Wei, HU Jianping, HU Guangchang

2017, 30(5): 877-885. doi: 10.3969/j.issn.0258-2724.2017.05.006

[Abstract](575)

Abstract:
To solve the problem of automatically setting railway station locations in the case where no alternatives can be selected, a method named "weighted mask transform" was proposed. This method is based on the grey correlation analysis theory and the coupling between railway alignment and station locations. First, the range of the station area was simplified as a rectangular mask of a given length and width. The locations of station centers were searched by moving the rectangular mask, while the stations directions were determined by rotating the mask. Then, an evaluation system including land use cost, earthwork cost, distance from residential areas, and the coupling degree of railway alignment and station locations was established. The weights of these evaluation indicators were assigned using the gray correlation analysis. Finally, calculations and ranking of the comprehensive costs of the station locations, which are obtained by moving and rotating the rectangular mask, were carried out to realize the optimization of station locations in continuous areas. The effectiveness of the proposed method was verified by applying it in an actual railway station in the southwest mountainous areas of China. Forty-nine alternatives were generated and ranked from low to high according to the comprehensive cost. The result shows that the method can assist the designers by automatically generating optimized railway station locations in complex mountainous regions.

Autonomous-Positioning Information Aided Train Integrity Detection Risk Analysis Method

LI Sihui, CAI Baigen, XU Aiguo, SHANGGUAN Wei, WEN Yinghong, WANG Jian

2017, 30(5): 886-892. doi: 10.3969/j.issn.0258-2724.2017.05.007

[Abstract](534)

Abstract:
Autonomous-positioning information error and failure can lead to a safety risk in train integrity detection. In this study, the problem of train integrity detection, which determines whether a train remains intact in terms of relative position, velocity and acceleration, was investigated. A Bayesian risk-based train integrity detection risk analysis model was proposed to determine both the false-alarm rate and failure rate of autonomous-positioning information based train integrity detection. In this model, both the misdetection probability and failure probability of each autonomous-positioning information were applied to find the misdetection rate and false-alarm rate of train integrity detection. Then, a simulation based on field data was conducted to verify the train integrity detection risk analysis method. The results show that the risk of false alarms is 10-1.8, which is larger than the risk of misdetection (10-5.5) in the complete train scenario. In contrast, in the train break scenario, the risk of misdetection is 10-1.8 when cruising and 1 when accelerating, which are larger than the risk of false alarms (10-4.5 when cruising and 0 when accelerating). The results conform to the train integrity states, indicating that the risk analysis model has sufficient capability to calculate the risk of autonomous-positioning information aided train integrity detection.

Effect of Slope Gradient on Wind Pressure of High-Rise Buildings during Thunderstorm

WANG Zhisong, FANG Zhiyuan, LIU Ya'nan

2017, 30(5): 893-901. doi: 10.3969/j.issn.0258-2724.2017.05.008

[Abstract](525)

Abstract:
To analyze the effects of thunderstorm downburst wind on the surface wind load of high-rise buildings and provide a reference for the design of high-rise buildings, the wind pressure distribution on the surface of high-rise buildings on flat and sloped terrains was investigated using an impinging jet device in wind tunnel tests. The computational fluid dynamics software FLUENT was used to simulate and supplement the test cases, analyze the characteristics of surface wind pressure on high-rise buildings over flat terrain and slope, and determine how the slope gradient affects the wind pressure on high-rise buildings. The results show that on flat terrain, the resistance coefficient distribution of each layer of a high-rise building along the vertical direction has the same changing law at different radial positions and the resistance of each layer decreases with an increase in the radial distance. For radial distances from 1.0 times the diameter of the jet nozzle to 3.0 times. the average maximum layer resistance coefficient decreased from 1.3 to approximately 0.3. The wind pressure on the building gradually decreased with an increase in the slope gradient. On slope terrain, there is negative correlation between windward pressure and the increase of the slope angle, and the height of the extreme wind pressure also decreases with the increase in the slope angle. From a flat ground to a 90° slope, the extreme wind pressure coefficient decreased by more than 0.7, and the height of the maximum wind pressure decreased from the 1/4 of building height down to the bottom of building.

Method to Predict Vibrations Induced in Ancient Wooden Structures by Traffic Loads and its Validation

ZHANG Yunshi, ZHANG Nan, FAN Hua, CAO Yanmei, XIA He

2017, 30(5): 902-909. doi: 10.3969/j.issn.0258-2724.2017.05.009

[Abstract](544)

Abstract:
The aim of this work is to establish a method for predicting vibrations induced in ancient wooden structures by traffic loads. First, a field test was performed at the Buddhist sutra depositary at Yangzhou Zhunti Temple, based on the prediction method. The modal parameters were identified from the experimental data, and the FE model was established using ANSYS. Next, the efficiency of the prediction method was validated by comparing the predicted values of the traffic load-induced vibrations of the Buddhist sutra depositary with the corresponding experimental data. Finally, the vibration response of the Buddhist sutra depositary under the influence of heavy traffic load moving at high speed was predicted. The comparison between experimental data and numerical calculations reveals that the relative error between the predicted value and the experimental data of the peak acceleration induced by a typical vehicle is as small as 1.47%. This indicates that the vibration response of a certain structure under the influence of traffic load can be effectively predicted by the proposed method.

Impact of Partition Method in Pit Construction Adjacent to Existing Metro Shield Tunnel

ZHENG Yuchao, SHI Bowen, SUN Keguo, YANG Tianchun, LI Hui

2017, 30(5): 910-918. doi: 10.3969/j.issn.0258-2724.2017.05.010

[Abstract](531)

Abstract:
In order to ensure the structural safety and normal operation of pit construction occurring adjacent to an existing metro shield tunnel, research on a longitudinal equivalent rigidity model of a shield tunnel was performed to establish the relationship between the tunnel's longitudinal deformation curvature and the bolt's bearing condition, and to set the requirements for a normal operation of the track. Subsequently, the actual engineering conditions of a particular deep-large pit in Shenyang, which is adjacent to an existing subway shield tunnel, were used to create a three-dimensional numerical analog. By changing the spatial position of the newly constructed pit near the existing shield tunnel with pile-anchor support, zoning charts were drawn and divided into zones of strong, weak, or no influence. Settlement measured in the field confirmed the efficiency of zoning standards based on influence and control technology. The results show that the longitudinal deformation curvature of the shield tunnel is the key index for determining the safety and normal operation of pit construction adjacent to the existing metro shield tunnel. Consequently, the tunnel's longitudinal deformation curvature can be used as a zoning standard for the influence of the adjacent subway shield tunnel. Finally, the critical state of the track alignment and the longitudinal deformation curvature of the tunnel joint within the limit state can be used to define the thresholds for zoning charts divided into zones of strong, weak, and no influence.

Model Experimental Study on Dynamic Performance of Special Soil Subgrade Reinforced with Composite Geomembrane Seal Layer

HUANG Junjie, SU Qian, ZHAO Wenhui, WANG Wubin

2017, 30(5): 919-925. doi: 10.3969/j.issn.0258-2724.2017.05.011

[Abstract](488)

Abstract:
To analyze the protective effect of a composite geomembrane seal layer on special soil subgrades, two full-scale models of ballast track-special soil subgrade were developed. In this study, the dynamic performance of ballast track-special soil subgrades with and without a composite geomembrane seal layer were investigated under both soaked and unsoaked conditions. The test results show that the vibration in the model without a composite geomembrane seal layer is more severe than the vibration in the model with a composite geomembrane seal layer for the same loading frequency and level. Under cyclic loading in unsoaked conditions, the accumulative settlement of the models with and without a composite geomembrane seal layer tends to stabilize at cyclic loading greater than 80,000 cycles. Under cyclic loading in soaked conditions, the accumulative settlement of the model without a composite geomembrane seal layer continually increases, while the accumulative settlement of the model with a composite geomembrane seal layer gradually stabilizes. When the cyclic loading reaches 1,400,000 cycles, the moisture content of the special soil is increased by 41%, while the K30 value at the top of the bottom layer of the subgrade is reduced by 39% in the model without a composite geomembrane seal layer. However, the moisture content of the special soil and K30 values for the model with a composite geomembrane seal layer remain basically unchanged. The composite geomembrane used for protecting the special soil of a subgrade bed can effectively intercept water seeping into the subgrade bottom of a bed filled with special soil, which can prevent the special soil from softening. Therefore, the ballast track-special soil subgrade demonstrates favorable long-term dynamic stability when subjected to cyclic loading.

Prediction Soft Soil Settling Using a Combination Method

CUI Kai, YANG Wenheng

2017, 30(5): 926-934. doi: 10.3969/j.issn.0258-2724.2017.05.012

[Abstract](510)

Abstract:
To explore the antecedence and accuracy of predicting soft soil roadbed settlement this study analyzed selected typical sections taking into account field relationships, engineering geological surveys, engineering measurements, and roadbed settlement tests. A combined optimization method for predicting the settling of a soft soil subgrade was proposed. First, three kinds of curve fitting methods were applied. The optimal curve was determined using identification methods for two different evaluation criteria, the minimum mean square and maximum correlation methods. Then, the FLAC3D numerical simulation method was used to predict the settling of a soft soil roadbed. The optimal fitting curve method, FLAC3D numerical simulation method, and measured data were quantitatively analyzed and combined to predict the settlement process. Prior to settling, the laboratory test data were used in the FLAC3D numerical simulation method, and the modeled values were 15% to 20% greater than the observed values. This is considered safe, and the method can be used to predict excessive settlement in early construction processes. When settling occurred, the optimal curve fitting method predicted the roadbed settlement more accurately using the measured engineering data, and the error between the final settlement and measured did not exceed 3%. Compared with the roadbed settlement after reinforcement, the joint method was more accurate; furthermore, the accuracy rate was 5% to 10% higher for the soft soil subgrade with less disturbance.

Low Temperature Performance and Evaluation Index of Epoxy Asphalt Mixture

RAN Wuping, LING Jianming, GU Zhifeng

2017, 30(5): 935-942. doi: 10.3969/j.issn.0258-2724.2017.05.013

[Abstract](608)

Abstract:
In order to establish a theoretical basis for the design of epoxy asphalt pavement under low temperature conditions, in this study, the cracking performance and evaluation indexes of epoxy asphalt mixtures under low temperature conditions were investigated through laboratory tests. Based on the applicability analysis results of various low temperature evaluation indexes of asphalt mixtures, splitting strength is recommended as an index for evaluating the low temperature resistance of epoxy asphalt mixtures. In the design of new epoxy asphalt pavement structures for cold regions, -31℃ is set as the critical cracking temperature design index of the surface layer at low temperatures, whereas low temperature splitting strength is regarded as the structural design control index. Results show that in epoxy asphalt mixtures, low temperature creep rate is small and low temperature plastic deformation ability is low, but low temperature anti-cracking performance is improved. The observed epoxy asphalt tensile strength is 1.3-2.0 times larger and stiffness modulus is 1.3-1.9 times larger than the corresponding properties of a similar type of modified asphalt mixture.

Study on Design Parameters of Aggregate Based on Surface Texture Characteristic of HMA

CHEN De, HAN Sen, SU Qian

2017, 30(5): 943-948. doi: 10.3969/j.issn.0258-2724.2017.05.014

[Abstract](522)

Abstract:
In order to realise an optimised asphalt mixture design according to surface texture properties, the distributions along with wavelengths of the surface texture of asphalt mixtures, having different aggregate design parameters, were analysed using the testing method of levels and distributions of asphalt mixture surface texture, which was developed based on image analysis techniques. The indicators (i.e., characteristic wavelength and level of characteristic wavelength) were proposed, to characterise the overall properties of the asphalt mixture surface texture. The correlations between the aggregate sizes in different passing ratios and asphalt mixture surface texture levels were analysed. The irregularity and fragments of aggregate gradation were obtained according to the fractal theory. Following this, the shapes and distributions of aggregates in the asphalt mixture were studied. The results indicate that D90, which is the sieve size in the 90% passing ratio, is an ideal index for representing the entire aggregate particle size. Furthermore, factual dimensions can reflect the irregularity and fragments of aggregate gradation. The regularity and sine of the aggregate direction angle can be used to represent the aggregate shape and distribution in the asphalt mixture.

Application of Railway Engineering Survey Based on Remote Sensing Technology for Realistic Scenes

MENG Xianglian, ZHOU Fujun

2017, 30(5): 949-955. doi: 10.3969/j.issn.0258-2724.2017.05.015

[Abstract](596)

Abstract:
In order to promote the application of remote sensing technology in railway engineering surveys, the limitations of traditional remote sensing technology were analysed, and a novel remote sensing technology is proposed for realistic scenes. A complete remote sensing modelling method and production application process were established, based on the disparity function and double stereo orthoimages. Because the parallax and model baseline are in the same direction and the angle is eliminated, a dimensional model provides greater accuracy. Data from different professions transfer in both directions, based on a collaborative design platform. In various research and engineering practices, remote sensing technology for realistic scenes is widely applicable for different majors in railway engineering surveys, and it is effectual for unfavourable geological condition surveys as well as railway line selection. A work time saving of approximately 50% is achieved during the site survey period, and of approximately 20% during the interior design period. The proposed technology offers potential value for similar engineering applications and projects.

Forming Rules and Performances of Laser-MAG Hybrid Welding Joints of SUS301L-MT Stainless Steel

HAN Xiaohui, ZHAO Yanqiang, YANG Xiaoyi, CHEN Hui, GOU Guoqing

2017, 30(5): 956-961. doi: 10.3969/j.issn.0258-2724.2017.05.016

[Abstract](510)

Abstract:
This study focusses on 6 mm-thick SUS301L-MT austenitic stainless steel, which will be used for the manufacture of next-generation city rail trains. In order to establish the technical foundation for the manufacture of city rail trains, the forming rules and performances of 6 mm-thick SUS301L-MT austenitic stainless steel laser-MAG (metal active gas welding) hybrid welding T-joints were studied using weld cross-section analysis, metallographic observation, X-ray diffraction residual stress tests, etc. The increase of laser power and defocusing distance can improve the width of the weld top surface. When welding speed increases, the widths of the weld middle section and weld bottom surface significantly decrease. The width of the weld cross-section increases significantly with the increase in defocusing distance. The microstructure of the weld zone is austenite mixed with ferrite. The maximum longitudinal residual stress appears at the center of the joint, with a value of 330 MPa.

Investigation on Effect of Torque on Fretting Damage of Test Facility Shaft

WEN Guang, HE Chenggang, WANG Wenjian, ZHOU Guiyuan, LIU Qiyue

2017, 30(5): 962-969. doi: 10.3969/j.issn.0258-2724.2017.05.017

[Abstract](462)

Abstract:
The effect of torque on the fretting damage of an interface fit between the shaft and inner surface of bearings was investigated on the JD-1 wheel/rail simulation test facility with different loads. The fretting damage mechanism of the shaft surface was analyzed by observing the wear scar and microstructure of the cross-section of specimens by using a laser scanning confocal microscope and scanning electronic microscopy. The results indicate that the fretting damage appears on the interface fit between the shaft and inner surface of bearings under vertical load and braking torque, the wear is in the form of adhesive wear and abrasive wear. With an increase in braking torque, the wear on the surfaces of shaft is more serious, the plastic deformation layer is thicker by approximately 75%, the fretting damage becomes more severe. Moreover, the wear and plastic deformation on the left surface are more severe than those on the right, and the plastic layer is uneven. Micro cracks appear on the interface fit, and there are more cracks on the left interface fit than those on the right, the number of micro cracks increase by approximately six times with the increase of the braking torque, and the crack propagation angle also increases by approximately 50%.

Drawbead Optimisation in Stamping Using SA-RBF Neural Networks

XIE Yanmin, TANG Wei, HUANG Renyong, XIONG Wencheng, ZHUO Dezhi

2017, 30(5): 970-976,993. doi: 10.3969/j.issn.0258-2724.2017.05.018

[Abstract](528)

Abstract:
The structure of a radial basis function (RBF) neural network based on the k-means clustering algorithm was optimised by employing the simulated annealing algorithm for improving the prediction accuracy. The NUMISHEET 02 fender was considered as the object of research and six equivalent drawbead forces were used as input variables. Based on Spearman correlation analysis and Latin hypercube sampling, the data which had smaller correlation coefficient values were chosen as training samples for the simulated annealing-radial basis function (SA-RBF) neural network. The numerical simulations of training samples were performed by employing the Dynaform software package. The evaluation functions of forming quality were established based on the wrinkling defects and crack defects. The nonlinear relationship between the equivalent drawbead force and the associated objective function was established by incorporating a SA-RBF neural network. NSGA-Ⅱ algorithm was employed to achieve the Pareto frontier and the best equivalent drawbead forces were determined by applying grey correlation analysis theory. Finally, the numerical simulation of fender forming was performed based on the optimised drawbead forces. The resultant forming limit diagram (FLD) indicates decreased wrinkles in the optimised forming part and greater uniformity in the plastic deformation, thereby leading to improvement in the quality of fender forming.

Axial Rigidity of Unstiffened Transverse Plate-to-Circular Hollow Section (CHS) Joints

ZHAO Bida, LIU Chengqing, YU Congdi, CHEN Anhua

2017, 30(5): 977-984. doi: 10.3969/j.issn.0258-2724.2017.05.019

[Abstract](546)

Abstract:
To study the initial axial rigidity of transverse plate-to-circular hollow section (CHS) joint, a semicircular arch and circular ring models for the rigidity calculation of T-type and cross shaped-type plate-to-CHS joints were developed based on the analysis of force transferring mechanism and local deformation characteristics. Utilizing maclaurin series expansion and multiple nonlinear regression analysis, the complex theoretical formula was simplified to the product of an exponential function and a power function. A calculation formula for the initial axial rigidity was established by introducing the neglected influential factor, plate-to-CHS thickness ratio. The results indicate that the initial axial rigidity of joints is directly proportional to CHS diameter and elastic modulus, and it has a logarithmic relationship with plate-to-CHS thickness ratio, showing power function with CHS diameter-to-thickness ratio and exponential function with plate width-to-CHS diameter ratio. The last two ratios affect each other. The rigidity is not affected by bending and shear when the joints is under the elastic stress, and the relative errors between the theoretical rigidities calculated by the proposed formula and the finite element analysis (FEA) are less than 10%.

Tensile Behaviour of Hollo-bolts Embedded in Concrete

QU Hui, PAN Hongwei, LIU Yanzhi, TAN Ding

2017, 30(5): 985-993. doi: 10.3969/j.issn.0258-2724.2017.05.020

[Abstract](463)

Abstract:
To examine the tensile response of Hollo-bolts considering the bonding effect of concrete, a new device to perform pullout tests was used to investigate the tensile behaviour of Hollo-bolts embedded in concrete. First, the tensile force-displacement relationships for all specimens under different experimental conditions were obtained. Then, the failure modes and the tensile force-displacement relationship curves were compared and analysed to examine the influence of the tested experimental variables, which include the concrete strength grade and tubular sections with or without concrete filling, on the initial stiffness, strength, and ductility of the structure. Finally, the tension loading-bearing mechanism of Hollo-bolts was analysed considering the bonding effect of concrete. In addition, reasonable measures to improve the tensile-behaviour of Hollo-bolts were subsequently suggested. The test results revealed that the bonding effect of concrete changes the tension loading-bearing mechanism of Hollo-bolts, as the load on the Hollo-bolt eventually shifts from the bolt sleeve to focus on the centre screw. Accordingly, the failure model of the Hollo-bolt changes from sleeve failure to centre screw failure. Furthermore, it was determined that the concrete strength grade significantly influences the stiffness of Hollo-bolts. When the concrete strength grade increased from C30 to C50, the initial stiffness increased from 15.1% to 35.7% and the post-yield stiffness improved 1.27 and 1.64 times compared to the specimens for which the bonding effect of concrete was not considered. However, the findings indicate that the yield tensile strength and ductility of Hollo-bolts are primarily determined by the capacity of the sleeve, while the ultimate tensile strength of Hollo-bolts is influenced by the capacity of the centre screw, as the concrete grade shows no significant effect on the tensile strength of Hollo-bolts.

Numerical Simulation Analysis of RC Beams Strengthened with CFRP Using Viscoelasticity Constitutive

XU Baishun, MA Ming, QIAN Yongjiu, TANG Jishun, ZHANG Fang

2017, 30(5): 994-1000. doi: 10.3969/j.issn.0258-2724.2017.05.021

[Abstract](536)

Abstract:
In order to investigate the mechanical behavior influence of the adhesive viscoelastic on reiforced concrete beams strengthened with the carbon fiber reinforced polymer, the Burger model was used to describe the stress-strain-time relation for the adhesive. The relaxation shear modulus with Prony series forms of Burger model was derived by the mathematical method of Laplace transform and inverse Laplace transform. The finite element software ABAQUS was used to simulate RC beams strengthened with the CFRP. The influence of the adhesive viscoelastic on the stresses of the adhesive, the axial force of the CFRP, the moment of RC beams and the deflection of the reinforced beam were analyzed. The results show that the adhesive viscoelastic affect the mechanical behavior of the reinforced beam to a certain degree. With the increasing of the loading time, the shear stresses and normal stresses peak value of the adhesive decrease, the axial force of the CFRP decrease, the bending moment of the RC beam increase and the deflection of the reinforced beam increase. When the adhesive layer thickness is 0.2 mm, and the reinforced beam has been loaded for 30 d. The peak shear stress decreases by 40.1%, the normal peak stress decreases by 33.0%, the deflection of the reinforced beam increase by 3.7 ‰. On the cross section 20 mm away from the end of the CFRP, the CFRP axial force decreases by 15.8% and the bending moment of the RC beam increases by 17.4%.

Study of Ramp Control Method for Urban Expressways Using Improvised ALINEA Algorithm

QIAO Yanfu, ZHAO Bin, FANG Chuanwu, YAO Zhihong

2017, 30(5): 1001-1007. doi: 10.3969/j.issn.0258-2724.2017.05.022

[Abstract](792)

Abstract:
The traditional ALINEA (asservissement linéaire d'entrée autoroutière) ramp control algorithm does not take into consideration the ramp queue overflow of urban expressways, and may thus cause traffic congestion at the apposite expressway intersection. By incorporating the classical ALINEA ramp control algorithm, a new on-ramp control method for urban expressways has been proposed, based on traffic-flow prediction for urban expressways. The proposed method focuses on developing a wavelet neural network optimized by a genetic algorithm (GA-WNN) for predicting the traffic-flow of an urban expressway. The gap acceptance theory and the grading principle of ramp queues have also been introduced in the proposed methodology, thus leading to the realization of dynamic regulation of the ramp control rate for urban expressways. The control effects of the classical ALINEA and the proposed algorithm were compared through a micro-simulation experiment, and the results show that the proposed model can effectively improve the capacity of the arterial road, and can reduce the average trip time of the ramp by approximately 24.8%.

Flight Taxi-out Time Prediction Based on KNN and SVR

FENG Xia, MENG Jinshuang

2017, 30(5): 1008-1014. doi: 10.3969/j.issn.0258-2724.2017.05.023

[Abstract](442)

Abstract:
Aimed at resolving the possible ground traffic and low operational efficiency issues in a large busy airport caused by the simple aircraft taxi-out time estimation, a two-step aircraft taxi-out time prediction model was constructed based on K-nearest neighbours (KNN) and support vector regression (SVR). First, considering the influence of factors such as taxiing-out distance, the number of taxi-out flights using the same runway and the number of pushback complete flights launched within 15 min of the removal of chocks, the number of departures and arrivals using the same runway during the flight taxiing out was predicted based on KNN. Then, based on the prediction results and other influential factors such as the taxiing-out distance and the average taxi-out time using the same runway within 15 min of the removal of chocks, the taxi-out time was predicted based on SVR. The airport operation data was grouped by arrival and departure traffic flow and the prediction model of the taxi-out time was constructed separately for each group. The experimental results based on the actual operation data of Beijing Capital International Airport show that the average prediction accuracy of the proposed model is up to 79.86% within ±3 min.

Existence Problem of Invariant Torus Particle Motion in Rotating Nonlinear Dynamical Systems

WANG Jing, XIE Jianhua, YUE Yuan

2017, 30(5): 1015-1019. doi: 10.3969/j.issn.0258-2724.2017.05.024

[Abstract](453)

Abstract:
In order to study whether the invariant torus of integrable Hamiltonian systems is retained under small perturbations, we established the Hamiltonian equations in polar coordinates. Using the first integral of the energy conservation equation, the transformation of the second-order state variable from a system with two degrees of freedom into a system with a single degree of freedom was analysed. Secondly, based on the Kolmogorov-Arnold-Moser (KAM) theorem, the existence of invariant tori in the perturbed system was confirmed. Finally, numerical simulations were performed to elucidate the analysis. The results show that the time history curve of the system is periodic, the phase portrait is dense, and the Poincaré map is a closed curve. The system is quasi-periodic, and the invariant torus of the integrable Hamiltonian system is shown to still exist under small perturbations. Moreover, the closed curve Poincaré mapping corresponds to the KAM invariant closed curve.

Adaptive Virtual Impedance Droop Control Method in Load Sharing

WANG Tianhong, LI Qi, CHENG Weirong

2017, 30(5): 1020-1028. doi: 10.3969/j.issn.0258-2724.2017.05.025

[Abstract](669)

Abstract:
An adaptive virtual impedance droop control method considering line impedance is proposed to achieve load sharing of a DC grid system and improve system stability. Based on the output droop characteristics and the principle of virtual impedance, the load voltage and current are taken into consideration in the virtual impedance algorithm. Then, the virtual resistance obtained is modified to realize adaptive correction, which effectively improves the load sharing performance. Finally, experimental measurement and comparison with traditional droop control and traditional virtual impedance droop control are carried out on the experimental platform. The results indicate that the traditional virtual impedance droop control mode and adaptive virtual impedance droop control mode can maintain the load current difference under 0.04 A. Further, the parallel output current difference is small, and the load regulation rate of the adaptive virtual impedance droop control method is 0.1%, which is lower than those of the other two control methods. Given factors such as output current difference, load regulation rate, and bus voltage, the adaptive virtual impedance droop control method has load sharing superiority and system stability.

Effect of Particle Concentration on Dynamic Characteristics of Oil Containing Particles

CHEN Bin, LIU Ge

2017, 30(5): 1029-1036. doi: 10.3969/j.issn.0258-2724.2017.05.026

[Abstract](520)

Abstract:
To reduce the damage caused by particulate matter to equipment operation and to effectively control the particle concentration in oil, the pseudo-homogeneousz-flow mathematical model of suspended particles in oil was established using the continuum theory of liquid-solid two-phase flow. The dynamic characteristics of the oil containing particles were studied; the oil velocity and pressure and the distribution of particle velocity and concentration were analysed for varying particle concentration using the model. The results showed a good agreement between the experimental data and the results attained by the characteristic line method. The jump amplitude value of oil velocity and pressure decreases with increase in particle concentration; however, the jump amplitude value of particle velocity and concentration increases with increase in particle concentration. The distribution of particle concentration is substantially influenced by the oil pressure. The jump moments of the pseudo-homogeneous flow velocity and pressure take place are 1/4 pulsating period odd times, 1/8 pulsating period odd number and 1/4 pulsating period even times, respectively, at the beginning, middle, and end of the pipeline.

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2017 Vol. 30, No. 5