西南交通大学学报

Modal Parameter Identification of Reinforced Concrete Arch Bridge under Ambient Excitation

PU Qianhui, QIN Shiqiang, SHI Zhou, WANG Qiuping, GOU Hongye

2012, 25(4): 539-545. doi: 10.3969/j.issn.0258-2724.2012.04.001

[Abstract](1206)

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Abstract:
An ambient vibration test was conducted on a reinforced concrete arch bridge to correctly choose a modal parameter identification method. Modal parameters were identified using frequency domain, time domain and time-frequency analysis methods. They are the peak-picking, the stochastic subspace identification and the EMD-RDT method based on empirical mode decomposition (EMD) and random decrement technique (RDT), respectively. The comparisons between the results get from the above different methods and the finite element method (FEM) were carried out. The research result shows that the peak-picking has a very high identification speed and can identify natural frequencies reliably, but it needs a lot manual intervention. The stochastic subspace identification has a complete theoretic system and suits for programming realization, and its identification process can neutralize the influence of noises in dynamic tests. Because of mode mixing, the identification results of the EMD-RDT method have some random properties.

DEA-Based Evaluation of Wind Shielding Effect of Wind Barrier for Railway Bridges

XIANG Huoyue, LI Yongle, LIAO Haili

2012, 25(4): 546-550,566. doi: 10.3969/j.issn.0258-2724.2012.04.002

[Abstract](1120)

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In order to evaluate the wind shielding effect of wind barrier for railway bridges, aerodynamic coefficients of a train and two trains passing each other on a railway bridge installed wind barrier with different heights were measured by wind tunnel tests. On the basis of the test results, it was put forward that the aerodynamic coefficients of a train can be used to assess the effect of sudden change of vehicle wind load, and the magnitudes of sudden change of vehicle wind load at different tracks can be considered as the evaluation index. Moreover, the DEA (data envelopment analysis) method was adopted to evaluate the wind shielding effect of wind barrier. The research result shows that the DEA method is feasible to evaluate the wind shielding effect of wind barrier for railway bridges, and the preferable height of wind barrier is 1.72 m.

Accurate Calculation and Adjustment Methods for Cable Forces of Anchor-Span Strands for Suspension Bridges

ZHANG Xingbiao, SHEN Ruili, TANG Maolin, YE Huawen

2012, 25(4): 551-557. doi: 10.3969/j.issn.0258-2724.2012.04.003

[Abstract](1794)

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In order to accurately obtain the cable forces of anchor-span strands for suspension bridges to easily control the cable forces in construction course, a refinement model was established using nonlinear analysis software BNLAS and based on identified parameters of anchor-span strands of Taizhou Yangtze River bridge. A series of cable force-frequency data was obtained by assigning different initial cable forces of cable strands in the model. The explicit expression of cable force-frequency relationship was obtained by the regression analysis of the data to give a method of cable force calculation and avoid solving a transcendental equation by iteration to gain the cable forces. Based on elasticity theory calculation, a measure of cable force adjustment was put forward, that is cable force adjustment is transformed into screw pitch adjustment. The research results show that the method of cable force calculation has an error of less than 3%, and the measure of cable force adjustment is reliable and can meet the need of cable force control during the construction.

Analytical Investigation of Bridge Seismic Vulnerability in Wenchuan Earthquake

CHEN Libo, ZHENG Kaifeng, ZHUANG Weilin, MA Hongsheng, ZHANG Jianjing

2012, 25(4): 558-566. doi: 10.3969/j.issn.0258-2724.2012.04.004

[Abstract](1437)

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In order to evaluate the seismic loss risk of highway bridge systems in Wenchuan area, Sichuan, China, statistical seismic vulnerability models of bridges were established based on the collected bridge damage data from the Wenchuan earthquake. A modified Wenchuan earthquake attenuation model was developed for estimating the ground motion parameter, i.e., peak ground acceleration (PGA), at various bridge sites. Two-parameter lognormal distribution functions were assumed to be suitable for developing fragility functions. Combined with the surveyed earthquake damage data, two different statistical models were then used to estimate the parameters based on the maximum likelihood method, and the bridge seismic fragility curves corresponding to four damage states (including minor, moderate, major, and collapse) were generated. According to the type and configuration of bridges, the surveyed bridge samples were categorized and distinct fragility curves of the sub-sample bridges were established. Goodness of fit test of the statistical results was carried out. The results show that the fragility functions cannot be rejected under the 10% significance level.

Setting-out Mechanism of Landslide Induced by Earthquake

GU Chengzhuang, HU Xiewen, LUO Gang, NIU Yanbo, HU Hengyang

2012, 25(4): 567-572. doi: 10.3969/j.issn.0258-2724.2012.04.005

[Abstract](1024)

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The starting mechanism of earthquake-induced landslides was investigated in order to make a further research on the complex dynamics mechanism of landslide setting out. Based on the analysis of aggregated elastic strain energy, the expression of the setting-out velocity of seismic landslides was derived with the theory of energy conversion and by considering the vertical and horizontal accelerations of an earthquake together. The research result shows that the slope failure caused by earthquake is due to the comprehensive effect of "fluctuating oscillation chain", and seismic landslides go through a process from starting to accelerating to setting-out in the whole setting-out stage. The relative difference between calculated setting-out velocities based on the above expression and the momentum transfer method is about 3% to Donghekou landslide induced by the Wenchuan earthquake.

Seismic Dynamic Responses of No.19 Grotto's West Side Cave of Yungang Grottoes

SUN Bo, PENG Ningbo, WANG Fengrui

2012, 25(4): 573-579. doi: 10.3969/j.issn.0258-2724.2012.04.006

[Abstract](1636)

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A three-dimensional entity model for the 19th grotto's west side cave of Yungang Grottoes was built in order to explore the seismic dynamic responses of grottoes. A finite difference software, FLAC3D, was used to numerically simulate the displacement, acceleration amplification factor, stress distribution and acceleration Fourier spectrum of its chamber and surrounding rock. The simulation results show that its external cliff has a trend of outward collapse, and the main failure mode of rock mass is shear failure. Seismic waves are reflected and superimposed on each other in the region near the chamber, and large energy is absorbed by rock mass, so earthquake acceleration in the region should be augmented in antiseismic strengthening design.

Determination of Optimal Sand Content for Improving High Liquid Limit Soil

CHENG Tao, HONG Baoning, LIU Xin, HUANG Man

2012, 25(4): 580-585,596. doi: 10.3969/j.issn.0258-2724.2012.04.007

[Abstract](1041)

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In order to determine the optimal sand content, high liquid limit soils were classified respectively based on fine particle content, liquid limit and soil CBR (California bearing ratio) value, the range of the optimal sand content for different types of high liquid limit soils were ascertained. The classification standard is that CBR value of improved soils is equal to 6. The optimal sand content was determined by comprehensively considering the three different factors. The experimental result shows that compared with liquid limit and clay-silt ratio, the effect of fine particle content on CBR value is great. The CBR value decreases with the increase of clay-silt ratio. The optimal sand content of high liquid limit soil along Yunfu-Luoding expressway is about 20%. To high liquid limit soils with different properties, different treatment measures should be adopted.

Experimental Research on Onset of Muddy Clay Exposed to Unidirectional Flow

YANG Bing, CAI Ruiqing, TANG Chi, MA Jianlin, HUHE Aode

2012, 25(4): 586-590. doi: 10.3969/j.issn.0258-2724.2012.04.008

[Abstract](992)

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In order to investigate the onset law of muddy clay, the onset characteristics of muddy clay with different sedimentary densities were investigated experimentally by the synchronous measurement of water grey level and flow velocity. The experimental results show that the phenomenon of the onset of muddy clay can be divided into weak onset and general onset. To the weak onset, the rate of erosion on the muddy bed is low and the variation of water grey level is about 10. While to the general onset, the rate of erosion corresponding to a sudden change in the curve of water grey level increases evidently and the variation of water grey level is usually more than 20. The flow velocity of the general onset is 1.5 times as much as that of the weak onset.

Comprehensive Assessment Method for Health Status of Subgrade in Existing Line Speed-Raising Reconstruction

FANG Tao, LIU Xinrong, GENG Daxin, DIAO Xinhong

2012, 25(4): 591-596. doi: 10.3969/j.issn.0258-2724.2012.04.009

[Abstract](1118)

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To deal with the speed-raising reconstruction for an existing railway line, the health status of the subgrade of the line need to be assessed first. On the basis of a field investigation of the subgrade damage, the subgrade was divided into 24 segments to be tested according to the severity of subgrade damage, filling material, and the structure of subgrade bed. A total of 754 groups of compaction tests, 345 groups of dynamic elastic modulus tests, and 1 311 groups of light dynamic penetration tests on different positions were conducted, and the test results were analyzed. The analysis indicates that the comprehensive assessment method for health status of subgrade, which combines light dynamic penetration and compaction tests with dynamic elastic modulus tests based on a field investigation, can adequately reflect the strength, rigidity, and durability of subgrade. This method is proved to be reliable, and the test results by it can be directly applied to the design of the technical scheme of subgrade reconstruction.

Wheel-Rail Force Continuous Measurement Based on Combinational Forecast Model

LI Yifan, LIN Jianhui, LIU Jianxin

2012, 25(4): 597-604. doi: 10.3969/j.issn.0258-2724.2012.04.010

[Abstract](1598)

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In order to accurately judge vehicle operation state, a wheel-rail force continuous measure method was put forward. Based on the wheel-rail interaction characteristics, the available data of wheel-rail force were extracted from test data by using the threshold value judgmental method. From the uncertainty and time variation of a wheel-rail force measurement system, a dynamic measurement sequence was regarded as a grey process, so the grey theory was used to continuously measure wheel-rail force. In order to improve prediction accuracy, the traditional GM(1,1) model was improved by combining the genetic algorithm and neural network. Ten prediction models were established to predict respectively, and then the predicted values with high accuracy were imported into series grey neural network to predict once again to improve the prediction accuracy and stability. The 10 prediction models were applied to wheel-rail force continuous measurement. The results show that the combination model based on the grey system, genetic algorithm and neural network has a high accuracy, and the average relative error is less than 2%. This combination forecast model can meet the requirement of wheel-rail force continuous measurement and reduce the influence of sensor failures on measurement results.

Design Method for Rigid Frog Based on Wheel/Rail Contact Parameters

CAO Yang, WANG Ping, ZHAO Weihua

2012, 25(4): 605-610,617. doi: 10.3969/j.issn.0258-2724.2012.04.011

[Abstract](1153)

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A design method of rigid frog structure based on contact parameters was proposed in order to improve its wheel/rail interaction relationship. Using the method, the top profiles of nose rail and wing rail of No.12 rigid frog were optimized. The results show that the wheel/rail relationship can be improved effectively by lowering the height of the nose-rail section with the head width of 20 mm by 4 mm, eliminating the 1∶20 cross slope of the wing-rail head, and modifying the wing-rail head rising scope to be from the throat to the nose-rail section with the head width of 50 mm. Therefore, the proposed method is feasible and valid.

Dynamic Parameter Design Method for Turnout and Its Application in Switch Design

LIU Zhe, WANG Ping, CHEN Rong, QUAN Shunxi

2012, 25(4): 611-617. doi: 10.3969/j.issn.0258-2724.2012.04.012

[Abstract](1295)

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In order to design the wheel-rail relation in turnout intuitively and quickly, a dynamic parameter design method for turnout was put forward based on the static contact theory of wheel-rail in turnout and by analyzing the vertical vibration of independent wheel and the hunting motion of single wheelset. No.18 high-speed turnout with the design of gauge widening switch was analyzed by this method, and a better scheme of gauge widening switch was obtained. In this scheme, the maximum value of gauge widening is 15 mm, the maximum value of gauge widening is located in the 30 mm width of the top surface of switch, and the range of gauge widening is 21.743 m. Train-turnout system dynamics verification and operation practice demonstrate the correctness of the method.

Detection of Residual Stress in Aluminum Alloy Carbody of High-Speed Train Using X-ray Diffraction Technology

GOU Guoqing, HUANG Nan, CHEN Hui, TIAN Aiqin

2012, 25(4): 618-622. doi: 10.3969/j.issn.0258-2724.2012.04.013

[Abstract](1301)

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In order to test the surface residual stress in the aluminum alloy carbody of high-speed trains accurately, quickly, and non-destructively, the tensile test of an equal strength rod was used to calibrate the measurement of X-ray diffraction (XRD) method. The residual stress values of welded joints in the aluminum alloy carbody of a high speed train were detected separately by XRD method, blind hole-drilling method, and finite element method (FEM), and then compared with each other. The results show that during the tensile test of the equal strength rod sample, the stress value measured by XRD method well accords with the tensile loading stress in the range of 10 to 70 MPa, and hence the XRD method can be used for testing the residual stress in the key parts of the aluminum alloy carbody of high speed trains. In addition, the numerical values of residual stress detected by XRD method are slightly higher than those obtained by theoretical calculation and electrical measuring method. The maximum residual stress of welded joints in high speed train aluminum alloy vehicle roof is approximately 146.3 MPa. The residual stress results detected by XRD method are in good agreement with those by the equal strength rod tensile calibration, blind hole-drilling method, and FEM.

Numerical Simulation of Heat Exchange Performance of Radiator Module in Construction Vehicles

LIU Jiaxin, QIN Sicheng, XU Zhenyuan, ZHANG Ao, XI Yu, ZHANG Xuelin

2012, 25(4): 623-628. doi: 10.3969/j.issn.0258-2724.2012.04.014

[Abstract](1247)

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In order to study the performance law of a construction vehicle radiator under different working conditions and ensure its working stability, a 3D physical model of the vehicle engine cabin was built based on original drawings with the software UG NX7.0, in which a heat exchange module was adopted to represent the radiator group. Then, the engine cabin model in a virtual tunnel was simulated using the computational fluid dynamics (CFD) numerical method, and the heat exchange performance of the radiator module was analyzed under various working conditions. Finally, the simulation results were verified experimentally. The results show that the heat exchange process has a gradient temperature change in each working condition, and increasing the temperature of the hot-air backflow will lower the radiator efficiency. When the radiator efficiency can not meet the need of the whole vehicle system, system overheating and performance instability occur. The error between simulation and experimental results is between 2.83% and 4.07%.

Fretting Wear Behavior of Angular Contact Ball Bearings

WANG Siming, GAO Hongli, XU Mingheng

2012, 25(4): 629-633. doi: 10.3969/j.issn.0258-2724.2012.04.015

[Abstract](968)

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In order to investigate the fretting wear behavior of angular contact ball bearings under different loads, oscillation angles, and number of cycles, a series of tests for angular contact ball bearings (QJ208) were performed under dry condition on a self-made bearing fretting wear test rig with four axial loads (2.5, 5.0, 10.0, and 20.0 kN), three oscillation angles (0.88?, 1.21?, and 1.54?) and two cycle numbers (2?104 and 12?104). The fretting wear behavior was analyzed in combination with microscopic examinations on worn scars. The results show that the fretting wear on the outer ring reduces with the increasing load, but increases with the increasing oscillation angle. As the number of cycles increases, the growth rate of wear slows down. In addition, the wear mechanism is dominated by fatigue wear at the oscillation angle of 0.88?, and by abrasive wear at the oscillation angle of 1.54?. For each ball, the wear damage on the outer ring is more serious than that on the inner ring.

Effects of Internal Heat Exchanger on Performance of Transcritical CO2 Heat Pump System

JIN Dongxu, WANG Ping, KOYAMA Shigeru, TAKATA Nobuo

2012, 25(4): 634-638. doi: 10.3969/j.issn.0258-2724.2012.04.016

[Abstract](1231)

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The performance of a transcritical CO2 heat pump system applied for hot water supply was experimentally investigated under various refrigerant charging conditions to clarify the effects of the heat transfer area of an internal heat exchanger (IHX) on the system performance. Experiments were conducted in the condition of constant heating capacity and evaporator outlet superheat by adjusting the compressor frequency and the opening of electronic expansion valve. Experimental results show that, at the optimum refrigerant charge, the compression ratio decreases while the discharge and suction temperatures increase with an increase in the IHX heat transfer area. Adopting an IHX can increase the maximum heating COP (coefficient of performance), and an improvement of about 3.2%- 5.1% is obtained by using an IHX with a dimensionless heat transfer area of 0.2.

Multi-objective Shape Optimization of Hydrodynamic Journal Bearings Using Non-dorminated Sorting Genetic Algorithm Ⅱ

PANG Xiaoping, CHEN Jin

2012, 25(4): 639-645. doi: 10.3969/j.issn.0258-2724.2012.04.017

[Abstract](1308)

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In order to overcome the shortcoming caused by taking the eccentricity as the initial design variables in the shape optimization model, i.e., the optimized shape was localized in the original shape, a new mathematic model of multi-objective shape optimization for hydrodynamic journal bearings was built through the general film thickness equation based on the Fourier series. In the model, the objective function is minimization of oil leakage and power loss, which is subjected to the minimum oil film thickness and the minimum bearing capacity, and the coefficients of general oil film thickness are design variables. The multi-objective optimization for the profile design of a hydrodynamic journal bearing is accomplished using a modified non-dominated sorting genetic algorithm II (NSGA-Ⅱ). The governing equations based on the general film thickness were solved by Matlab PDE (partial differential equation) toolbox. The results of a case study show that the bearing shape obtained by multi-objective optimization based on the general film thickness equation is not limited by the original shape. In addition,a Pareto-optimal set is obtained, where, for one of the optimized non-circle bearings with the maximum load capacity, the power loss and leakage rate are decreased by 80.8% and three orders of magnitude, respectively, compared with that just taking the load capacity as the objective function.

Formation Mechanism of Hot Spot in Stress Control Cable Terminations under Harmonic Voltages

ZHOU Kai, LI Xutao, HUANG Youcong, WAN Li, ZHAO Wei

2012, 25(4): 646-651. doi: 10.3969/j.issn.0258-2724.2012.04.018

[Abstract](1123)

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In order to investigate the premature failure of a stress control cable termination under high frequency harmonic voltages, the relationship between hot spot and applied voltage frequency was researched to the stress control cable termination. A high frequency harmonic generator was utilized to simulate practical harmonic voltage waveforms in a medium voltage power system. Infrared thermal images and non-linear transient electric field of the termination were analyzed under different frequency harmonic voltages. The research results show that with the rise in harmonic frequency, an obvious hot spot forms in local region on surface of the termination and temperature of the hot spot also rise. The hot spot is mainly connected to the high frequency components resulting in high electric field strength in the local region. From 100 Hz to 20 kHz, the electric field strength and the heating power both increase markedly in the local region on the surface of the termination.

Web Services Evaluation Model Based on Variant Time Utility

YIN Guisheng, CUI Xiaohui, MA Zhiqiang, DONG Hongbin

2012, 25(4): 652-661. doi: 10.3969/j.issn.0258-2724.2012.04.019

[Abstract](986)

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To solve the problems of the KNN (k-nearest neighbor) method in the quantification of time utility, the width of evaluation windows and the control of feedback, a web services evaluation model with variant time utility (WSEM-VTU) was proposed. In WSEM-VTU, the system dynamics is used to investigate the complex quantification method of the time utility to achieve the variant time utility. From the results of the quantification method, the width of the evaluation windows is adaptively calculated. In terms of the statistics of feedbacks, a feedback control strategy is involved. By means of experiments, WSEM-VTU was compared with the current evaluation models, WSEM-E and WSEM-KNN. The experimental results show that the average error of WSEM-VTU is 0.877, being lower 1.020 and 0.135 than the errors of WSEM-E and WSEM-KNN respectively. With the feedback control strategy, malicious ratings are reduced by an average of 67%.

Moving Objects Detection Algorithm Based on Three-Dimensional Gaussian Mixture Codebook Model

HUANG Jin, JIN Weidong, QIN Na

2012, 25(4): 662-668. doi: 10.3969/j.issn.0258-2724.2012.04.020

[Abstract](993)

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In order to solve the difficulty of adjusting parameters for the codebook model and the computational complexity of probability distribution for the Gaussian mixture model in intelligent visual surveillance, a moving objects detection algorithm based on the three-dimensional Gaussian mixture codebook model was proposed. In this algorithm a codebook model based on RGB space is built, and then a three-dimensional Gaussian model based on R, G and B components in codewords is established. In this way, the characteristic of the three-dimensional Gaussian mixture model for the codebook model can be obtained. The experimental results show that the average frame rate of the proposed algorithm is about 23.0 frames per second, while it is about 9.0 frames per second for the iGMM (improved Gaussian mixture model) algorithm, about 6.2 frames per second for the BM (Bayes model) algorithm, and about 10.7 frames per second for CBM (codebook model) algorithm in the comparative experiments. Furthermore, the proposed algorithm can obtain a good detection quantity.

On-Board Software Self-recovery Technique for Defending MBU Effect

BAO Haichao, YANG Genqing, ZHANG Yuning

2012, 25(4): 669-674. doi: 10.3969/j.issn.0258-2724.2012.04.021

[Abstract](921)

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A software self-recovery technique was proposed to mitigate the effect of multi-bit upsets (MBUs) on on-board computers to guarantee satellite safety. This technique takes advantages of the inherent multi-bit error detection capability of hardware EDAC (error detection and correction) and self-recovery feature of fault-tolerant technology to capture MBU and selectively starts system self-recovery to prevent on-board computer problems caused by MBUs. Key data index is set up to refrain from unnecessary self-recoveries. A division hash table and a novel moderate recovering strategy are applied to minimize the interrupt processing time. SEU (single event upset) hazard analysis and flight data show that the proposed technique can decrease the probability of satellite failures caused by SEUs by more than 90%. The technique has been successfully applied to XX02 satellites.

Security Analysis of Video Hashing

LIU Li, WANG Yongqing

2012, 25(4): 675-679. doi: 10.3969/j.issn.0258-2724.2012.04.022

[Abstract](876)

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In order to analyze the security of robust multimedia hashing quantitatively, Shannon's unicity distance was adopted to explain the security of robust multimedia hashing. A typical robust video hashing algorithm was used as an example, and a mathematics model for randomized feature extraction of the algorithm was found. Attacks for the typical video hashing algorithm were classified, and unicity distance, a concept proposed by Shannon, was adopted to measure the security level of the typical video hashing algorithm and analyze its security quantitatively. Theoretical analysis results show that the repeated use number of times of a robust video hashing algorithm's key cannot exceed the unicity distance, otherwise the key can be estimated.

Aircraft Departure Slot Control Method Based on Multi-objective Optimization

WANG Fei, MU Weiwei, DONG Jiankang

2012, 25(4): 680-685. doi: 10.3969/j.issn.0258-2724.2012.04.023

[Abstract](1402)

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In order to balance efficiency and equity and make best use of slot resources, aircraft departure slots were allocated. According to the decision-making targets of airport control operation departments and airline companies, three kinds of multi-objective optimization methods were established through different combinations of optimization objectives, including flight punctuality rate, passenger delay, flight delay cost, and Gini coefficient. Aiming at the application background of aircraft release in the airport control, an improved artificial fish school algorithm was used to solve the models. When flight delay cost and flight punctuality rate are optimization goals, two Pareto solutions are obtained; compared with those obtained by the ration-by-schedule (RBS) allocation algorithm, the flight delay cost is decreased by 52.9% and 48.6%, and the flight punctuality rate is improved by 62.5% and 75.0%. When flight delay cost and passenger delay are optimization goals, only one solution is obtained; compared with those by the RBS allocation algorithm, the flight delay cost and the passenger delay are reduced by 52.9% and 37.5%, respectively. When efficiency and equity are optimization goals, with the equity being improved, the efficiency was gradually weakened. The method presented in this paper can overcome the defect of the existing methods only considering the efficiency, and it can provide more alternative decision-making programs.

Dynamic Reroute Planning under Uncertain Severe Convective Weather

MENG Linghang, XU Xiaohao, LI Shanmei, GENG Zengxian

2012, 25(4): 686-691. doi: 10.3969/j.issn.0258-2724.2012.04.024

[Abstract](1562)

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In order to solve the reroute planning problem with uncertain severe convective weather, a state transition matrix was built using the uncertain measure of forecasting state and the random error of extrapolating position for rainstorm cloud cluster. The matrix was then used to predict the time-varying delay conditions of the reroute planning network. On this basis, a dynamic reroute planning model, with the least expected rerouting cost as its optimized objective, was developed under the constraints of path continuity and maximum penetrating risk, and solved by the generic algorithm subsequently. Finally, two kinds of weather scenarios with 16 initial states of cloud cluster were set up in a case study to verify the proposed model. Simulation results show that the rerouting paths will strategically penetrate clouds with unsafe initial state or detour clouds with safe initial state, by predicting the uncertain changes of cloud cluster states in uncertain weather scenarios. In addition, with the dynamic rerouting strategy under an uncertain scenario, the detouring distance decreases by 40% and the penetrating count decreases by 30.8%, compared with those under a certain weather scenario. Therefore, both safety and economy of rerouting paths are improved effectively.

Phase Field Modeling of Internal Convection and Free Interface Deformation of Levitated Droplet of Molten Silicon

SHI Wanyuan, ZHANG Fengchao, TIAN Xiaohong, TSUKADA Takao

2012, 25(4): 692-697. doi: 10.3969/j.issn.0258-2724.2012.04.025

[Abstract](1147)

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In order to simulate the two-phase flow with high density ratio, the algorithm of Newton iteration was utilized to solve a discretized semi-implicit Cahn-Hilliard equation. The dam-break flow problem and the interface deformation of a rising air bubble in water were numerically simulated using the phase field method. The result exhibits that when the water flow reaches the right side wall, it flows upward along the solid wall. Driven by the buoyant force, the spherical bubble rises up, and deforms into a spherical-cap shape gradually. The results agree well with those obtained by the front tracking method, which indicates the validity of the numerical algorithm. By the phase field method, the internal convection and interface deformation of a levitated droplet of molten silicon is simulated with a given initial amplitude. The result shows that the droplet gradually shrinks and the internal convection occurs, driven by the surface tension force. After a while, the droplet extends again, and four vortexes locate in the droplet, aligning along the vertical direction.

Improved Particle Swarm Optimization Algorithm for Sound Absorption Model with Polyurea Coating

ZHANG Wencheng, ZHOU Suihua, QU Yang

2012, 25(4): 698-704. doi: 10.3969/j.issn.0258-2724.2012.04.026

[Abstract](1335)

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To improve the stealth performance of small underwater targets with anechoic coating, a reflection coefficient formula was deduced based on a basic sound absorption model for multilayer structure with polyurea coating. According to the application requirements of material optimization, a modified dynamic mixing particle swarm optimization (PSO) algorithm was proposed by improving the PSO strategy and combining the global algorithm with the local algorithm, to improve the convergence capability and search precision. Then, the material parameters of the model were optimized using the improved algorithm. The optimization results show that the model has optimal performance when the material Young's modulus is a piecewise linear function of frequency. On this basis, a theoretic method to improve the sound absorption performance of the absorption model was provided, and then verified experimentally. The application results show that the target strength of the optimized model is decreased by more than 10 dB in the range of 140 to 500 kHz.

Random Lattice Order Group Decision-Making Based on Interval Probability Preferences

GUO Chunxiang, GUO Qiang, GUO Yaohuang

2012, 25(4): 705-711. doi: 10.3969/j.issn.0258-2724.2012.04.027

[Abstract](1182)

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To solve the random lattice order group decision-making problems where preference relations are random and probability of random events is described by interval values, a decision-making method based on the preferences of decision makers subject to an interval probability distribution is proposed. First, the preference relations are extended from four kinds (preference, inferior, indifference, and incomparability) to seven kinds (preference, inferior, indifference, incomparability, incomparability with a minimum upper bound, incomparability with a maximum lower bound, and incomparability with a minimum upper bound and a maximum lower bound). Second, the probability distribution of lattice order preference relations is defined on the basis of the concept and property of interval probability, and the operation rules of interval numbers. Third, the probability maximization objective function of preference relation of any pair of alternatives is established, and individual preferences are aggregated to group preferences according to priority rules and intersection rules. Finally, the steps of the group decision-making method are listed through a case study, and the feasibility and effectiveness of the method is validated.

Multi-attribute Group Decision-Making Method for Interval Number Decision Information

YOU Houxing, LIN Jie

2012, 25(4): 712-718. doi: 10.3969/j.issn.0258-2724.2012.04.028

[Abstract](1207)

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In the process of group decision-making, it is difficult to determine accurate index weight and expert weight coefficients, and obtain precise decision-making information. To solve this problem, a group decision-making method was presented based on a set-valued statistics model and the information axiom. In this method, individual decision information for each index is expressed by interval numbers, the comprehensive evaluation value of each index is calculated using the set-valued statistics model for decision-making group, and the availability of comprehensive evaluation values is determined through the viewpoint divergence degree. Taking the effective comprehensive evaluation values as the index design range of decision group expectation, the information content of each alternative scheme is calculated by using the information axiom. According to the information content, the ranking of alternatives was judged, and the concrete evaluation steps are given for this method. Finally, the validity of the proposed method was demonstrated through a case study. The experimental data analysis shows that this method can avoid the complex calculation process of determining weight coefficients, reducing the decision-making complexity, and fitting decision makers' thinking habits.

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2012 Vol. 25, No. 4