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Effect of aspect ratio on triaxial compression of multi-sphere ellipsoid assemblies simulated using a discrete element method

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Particuology 2017年第3期15卷 49-62页

作者： Jian gong Jun Liu State Key Laboratory of Coastal and Offshore Engineering Dalian University of Technology Dalian 116024 China

Here, we present a numerical investigation of the mechanical behavior of ellipsoids under triaxial com- pression for a range of aspect ratios. Our simulations use a multi-sphere approach in a three-dimensional discrete element method. All assemblies were prepared at their densest condition, and triaxial compres- sion tests were performed up to extremely large strains, until a critical state was reached. The stress-strain relationship and the void ratio-strain behavior were evaluated. We found that the stress-dilatancy rela- tionship of ellipsoids with different aspect ratios could be expressed as a linear equation. In particular, the aspect ratio influenced the position of the critical state lines for these assemblies. Particle-scale char- acteristics at the critical state indicate that particles tend to be flat lying, and the obstruction of particle rotation that occurs with longer particles affects their contact mechanics. Lastly, anisotropic coefficients related to aspect ratio were investigated to probe the microscopic origins of the macroscopic behavior. A detailed analysis of geometrical and mechanical anisotropies revealed the microscopic mechanisms underlying the dependency of peak and residual strengths on aspect ratio.

关键词： EllipsoidsAspect ratio DEM Triaxial compression Particle shape Macro-micro response

SURFACE SELF-DIFFUSION ANISOTROPY OF TUNGSTEN ATOMS ON W(112) PLANE

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Chinese Physics Letters 1990年第12期7卷 537-540页

作者： gong Yunming Department of Radio-Electronics Peking UniversityBeijing 100871

Surface self-diffusion anisotropy of tungsten on W(112)plane has been measured along(Ⅱ)and across(丄)channels existed on this plane by using the field emission fluctuation method in two forms of the *** the round probehole the thermal activation energy E=13.0kcal,and the prefactor of the surface self-diffusion coefficient Dq=^.5X 70_7cm2s-1;in the long narrow rectangular slit,E(Ⅱ)=13.2kcal,D0(Ⅱ)=7.1×10-7crr^and E(丄)=6.2kcal,Do(丄)=1.8×10^(-9)cm^(2)s^(-1) at T=*** experimental data suggest that a W atom diffusing across channels should not climb over the channel wall,which would certainly require a much higher activation energy,but instead,displace an atom in the *** process reqwes a much smaller activation energy;however,since it involves concerted motion of at least two atoms,it will also have a much smaller prefactor.

关键词： activation diffusion SURFACE

Full Power Hydraulic Brake System Based on Double Pipelines for Heavy Vehicles

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Chinese Journal of Mechanical Engineering 2011年第5期24卷 790-797页

作者： gong Mingde WEI Hailong College of Mechanical Science and Engineering Jilin University Changchun 130025 China

The hydraulic caliper disc brake system with air-over-oil is widely adopted at present for heavy vehicles,which makes use of air pressure system propelling the hydraulic pressure system acting on friction plates divided and combined for *** are some disadvantages such as pneumatic components failure,dust polluted and produce lots of heat in hydraulic caliper disc brake ***,considering the demands of the high speed,heavy weight,heavy load and fast brake of heavy vehicles,the full power hydraulic brake system based on double pipelines for heavy vehicles is designed and analyzed in this *** scheme of the full power hydraulic brake system,in which the triloculare cylinder is controlled by dual brake valve,is adopted in the brake *** full power hydraulic brake system can accomplish steering brake,parking brake and emergent brake for heavy ***,electronic control system that is responsible for coordinating the work of hydraulic decelerator and hydraulic brake system is developed for different speed *** on the analysis of the influence of composed unit and connecting pipeline on braking performance,the nonlinear mathematic model is established for the full power hydraulic brake *** braking completion time and braking pressure in braking performance of the double-pipeline steering brake and parking brake are discussed by means of simulation experiments based on Matlab/Simulink,and the simulation results prove that the braking performance of steering brake and parking brake meets the designing requirement of the full power hydraulic brake ***,the test-bed experiments of the brake system for heavy vehicles are carried *** experimental data prove that the braking performance achieves the goal of the design,and that the full power hydraulic brake system based on double pipelines can effectively enhance braking performance,ensure braking reliability and security for heavy vehicles.

关键词： heavy vehicle full power hydraulic brake system double-pipeline brake triloculare cylinder braking performance

Generating test data for both path coverage and fault detection using genetic algorithms

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Frontiers of Computer Science 2013年第6期7卷 822-837页

作者： Dunwei gong Yan ZHANG School of Information and Electrical Engineering China University of Mining and Technology Xuzhou 221116 China School of Technology Mudanjiang Normal University Mudanjiang 157012 China

The aim of software testing is to find faults in a program under test, so generating test data that can expose the faults of a program is very important. To date, current stud- ies on generating test data for path coverage do not perform well in detecting low probability faults on the covered path. The automatic generation of test data for both path coverage and fault detection using genetic algorithms is the focus of this study. To this end, the problem is first formulated as a bi-objective optimization problem with one constraint whose objectives are the number of faults detected in the traversed path and the risk level of these faults, and whose constraint is that the traversed path must be the target path. An evolution- ary algorithm is employed to solve the formulated model, and several types of fault detection methods are given. Finally, the proposed method is applied to several real-world programs, and compared with a random method and evolutionary opti- mization method in the following three aspects： the number of generations and the time consumption needed to generate desired test data, and the success rate of detecting faults. The experimental results confirm that the proposed method can effectively generate test data that not only traverse the target path but also detect faults lying in it.

关键词： software testing path coverage fault detection test data multi-objective optimization genetic algorithms

Delay-dependent robust H_∞control of convex polyhedral uncertain fuzzy systems

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Journal of Systems Engineering and Electronics 2008年第6期19卷 1191-1198页

作者： gong Cheng Su Baoku Dept. of Control Theory and Control Engeering Harbin Inst. of Technology Harbin 150001 P. R. China

The robust H∞ control problem for a class of uncertain Takagi-Sugeno fuzzy systems with timevarying state delays is studied. The uncertain parameters are supposed to reside in a polytope. Based on the delay-dependent Lyapunov functional method, a new delay-dependent robust H∞ fuzzy controller, which depends on the size of the delays and the derivative of the delays, is presented in term of linear matrix inequalities （LMIs）. For all admissible uncertainties and delays, the controller guarantees not only the asymptotic stability of the system but also the prescribed H∞ attenuation level. In addition, the effectiveness of the proposed design method is demonstrated by a numerical example.

关键词： robust H∞ control delay-dependent polyhedral uncertainty fuzzy systems

Bus holding strategy based on shuffled complex evolution method

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Frontiers of Computer Science 2012年第4期6卷 462-468页

作者： Yu JIANG Shuli gong College of Civil Aviation Nanjing University of Aeronautics and AstronauticsNanjing 210016China

Holding strategies are among the most commonly used operation control strategies. This paper presents an improved holding strategy. In the strategy, a mathematical model aiming to minimize the total waiting times of pas- sengers at the current stop and at the following stops is con- structed and a new heuristic algorithm, shuffled complex evo- lution method developed at the University of Arizona （SCE- UA）, is adopted to optimize the holding times of early buses. Results show that the improved holding strategy can provide better performance compared with a traditional schedule- based holding strategy and no-control strategy. The compu- tational results are also evidence of the feasibility of using SCE-UA in optimizing the holding times of early buses at a stop.

关键词： public transportation improved holding strategy schedule heuristic algorithm-shuffled complex evolution

Horn–Schunck optical flow applied to deformation measurement of a birdlike airfoil

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Chinese Journal of Aeronautics 2015年第5期28卷 1305-1315页

作者： gong Xiaoliang Stephan Bansmer School of Aeronautics Northwestern Polytechnical University Institute of Fluid Mechanics Technische Universitt Braunschweig

Current deformation measurement techniques suffer from limited spatial resolution. In this work, a highly accurate and high-resolution Horn Schunck optical flow method is developed and then applied to measuring the static deformation of a birdlike flexible airfoil at a series of angles of attack at Reynolds number 100,000 in a low speed, low noise wind tunnel. To allow relatively large displacements, a nonlinear Horn-Schunck model and a coarse-to-fine warping process are adopted. To preserve optical flow discontinuities, a nonquadratic penalization function, a multi- cue driven bilateral filtering and a principle component analysis of local image patterns are used. First, the accuracy and convergence of this Horn-Schunck technique are verified on a benchmark. Then, the maximum displacement that can be reliably calculated by this technique is studied on synthetic images. Both studies are compared with the performance of a Lucas-Kanade optical flow method. Finally, the Horn-Schunck technique is used to estimate the 3-D deformation of the birdlike airfoil through a stereoscopic camera setup. The results are compared with those computed by Lucas-Kanade optical flow, image correlation and numerical simulation.

关键词： Deformation measurementsFlexible airfoil Horn-Schunck Optical flow Stereoscopic

On Optimal Priority Modelling of Group Intuitionistic Fuzzy Preference Relations with Normal Uncertainty Distribution

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Journal of Systems Science and Systems Engineering 2019年第4期28卷 510-525页

作者： Lihong Wang Zaiwu gong College of Management Science and Engineering Nanjing University of Information Science and TechnologyNanjing 210044 China

The uncertainty distribution can more effectively express the uncertainty of decision makers' judgments during a pairwise comparison of any alternatives. This paper investigates the priority models of group intuitionistic fuzzy preference relations with normal uncertainty distribution. The mathematical equivalence between the membership, non-membership degree interval fuzzy preference relation and the intuitionistic fuzzy preference relation is constructed, showing that there exists an inverse relationship between the priority of alternatives using these two types of interval preference relations. The new optimal models regarded the event that the deviation between the ideal judgement meeting the multiplicative consistency and the actual judgement obeying normal uncertainty distribution shall not exceed a threshold value under the given belief degree as a constraint, and regarded the minimum sum of all the threshold values as the objective function. The chance constraint was introduced to measure the degree to which multiplicative consistency can be realized under different belief degrees. The priority model provides a new method for simulating uncertainty and fuzziness in the real-world decision making environment.

关键词： Group decisions and negotiations intuitionistic fuzzy preference relation multiplicative consistency normal uncertainty distribution chance constraint programming

Safety Analysis of Flow Parameters in a Rotor-stator Cavity

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Chinese Journal of Aeronautics 2012年第6期25卷 831-838页

作者： ZHANG gong DING Shuiting Airworthiness Technologies Research Center Beihang University Beijing 100191 China National Key Laboratory of Science and Technology on Aero-Engine Aero-thermodynamics School of Jet Propulsion Bei hang University Beij ing 100191 China

In order to ensure the safety of engine life limited parts （ELLP） according to airworthiness regulations, a numerical approach integrating one-way fluid structure interaction （FSI） and probabilistic risk assessment （PRA） is developed, by which the variation of flow parameters in a rotor-stator cavity on the safety of gas turbine disks is investigated. The results indicate that the flow parameters affect the probability of fracture of a gas turbine disk since they can change the distribution of stress and temperature of the disk. The failure probability of the disk rises with increasing rotation Reynolds number and Chebyshev number, but descends with increasing inlet Reynolds number. In addition, a sampling based sensitivity analysis with finite difference method is conducted to determine the sensitivities of the safety with respect to the flow parameters. The sensitivity estimates show that the rotation Reynolds number is the dominant variable in safety analysis of a rotor-stator cavity among the flow parameters.

关键词： airworthiness aircraft engines engine life limited parts safety analysis rotor-stator cavity risk assessment