力学学报

INVESTIGATION INTO MECHANISMS UNDERLYING HEAD-ON COLLISION OF DETONATIONS WITH SHOCK WAVES

Dai Xugang, Zhang Deliang, Hu Zongmin, Jiang Zonglin

A 2D numerical study on head-on collision of detonation waves with shock waves of different strengths in the gaseous mixture of hydrogen and oxygen under equivalence-ratio state has been carried out. The NND scheme and chemical model with improved two-step reaction was used and the x-t streak schlieren diagrams and smoke foil photographics were numerically recorded to study the collision process. It was found that the transmitted detonation wave is attenuated firstly and even partially decoupled due to expansion effect. However, the collision of triple points along the detonation front can induce re-coupling which may consequently restore the detonation. In the collision process, the weak transverse waves are generated by inhomogenous combustion in the near wake of the Mach stem. The repeated collision of weak transverse waves can form new cellular structures.

2012, 44(6): 953-961. doi: 10.6052/0459-1879-12-081

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GUST ALLEVIATION OF TRANSONIC WING

Zhang Wei, Zhang Weiwei, Quan Jingge, Ye Zhengyin

Gust response analysis plays an important role in large commercial plane structural design. Gust alleviation by active deflecting control surfaces is a pivotal technique for future aircraft design. Based on CFD/CSD time simulation method, considering gust as the input of the system and the root bending moment as the output, we build a gust response analysis model in state-space by using system identification in transonic flow. Similarly, considering aileron deflexion as the input and the root bending moment as the output, we build an aileron deflexion response analysis model. By coupling the two models, a gust alleviation analysis model is constructed in state-space. Then the optimal control method based on state feedback is used to design the active control law, and an observation device is designed to attain the state variable. Finally, the effectiveness of the designed control law is validated through a numerical simulation. The wing root bending moment can be decreased up to 60%-80%.

2012, 44(6): 962-969. doi: 10.6052/0459-1879-12-087

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AN EXPERIMENT INVESTIGATION ON VIV TRAJECTORIES OF A TWO DEGREE FREE VIBRATION CYLINDER

Kang Zhuang, Jia Lusheng

The paper makes experimental studies on vortex induced vibration of a two degree free vibration cylinder. The cylinder is put horizontally, with the diameter of 5cm and the length of 120cm. The model test could change the frequency of the modeling system vibrating upwards cross and in-line flows by adjusting the number of springs in cross and in-line flows. It has been found the vibrating frequency of the cylinder in in-line flow appears to be "multi-frequency". Under certain vibration frequency and reduced velocity conditions, single-frequency exists in cross flow besides twice-frequency. Consequently, the new trajectories of "egg" and "rain drop" were shown in the tests, different from the traditional trajectories of figure "8" and "new moon", which"" was rarely mentioned in the studies of two degree-of-freedom vortex induced vibration of rigid cylinders with elastic support.

2012, 44(6): 970-980. doi: 10.6052/0459-1879-12-120

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GROUND EXPERIMENTS OF BOUYANT THERMOCAPILLARY CONVECTION OF LARGE SCALE LIQUID BRIDGE WITH LARGE PRANDTL NUMBER

Wu Yongqiang, Duan Li, Li Yongqiang, Kang Qi

Thermocapillary-driven convection in a large scale liquid bridge was investigated by ground experiments in this paper. We used 2 cst silicone oil (Pr=28.571), observed the onset of liquid bridge with different aspect ratios (A=l/d) and volumes, analyzed the transformation of temperature oscillation frequency and phase, discussed the problems of hydrothermal waves. The column diameter of liquid bridge was 20mm. Due to the limit by gravity, we constructed the bridge with 3-4.25mm height. With the help of five azimuthal thermocouples inserted in the bridge interior, we discovered that temperature oscillation in flow field occurs at the same time; bridges with different aspect ratios and volumes have different flow modes, and with the increase of temperature difference, the frequency increases approximately linearly, and oscillation phase of each temperature oscillation curve continuously changes. Bridges with different aspect ratios have different ways to chaos.

2012, 44(6): 981-989. doi: 10.6052/0459-1879-12-148

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FLOW REGIM FOR SHALE GAS IN EXTRA LOW PERMEABILITY POROUS MEDIA

Yao Tongyu, Huang Yanzhang, Li Jishan

The research on flow mechanism and productivity evaluation of shale gas is still in its infancy. Based on the complex pore structure of shale gas reservoir, slip flow and adsorption-desorption of shale gas, Darcy model is modified. Compared with the Darcy model in production steady case, the bottom hole pressure based on non-Darcy flow model is higher than that from the Darcy flow; the pressure from the Darcy flow model decays more exaggerated and than predicted well life was shorter. The modified flowing model can describe and characterize shale gas flowing process more accurately. The results can provide basic parameters for the operation and management of the shale gas reservoir.

2012, 44(6): 990-995. doi: 10.6052/0459-1879-12-047

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INVESTIGATION ON TRAFFIC FLOW CHARACTERISTICS AROUND A TYPE C WEAVING SECTION BASED ON CELLULAR AUTOMATON MODEL

Jiang Jinsheng, Dong Liyun

The lane-changing rules are proposed on the basis of features of lane-changing behaviours in the two-sided type C weaving section. The multi-lane cellular automata model is adopted to investigate traffic flow in such a weaving section. The phase diagram is obtained by numerical simulation with different weaving lengths. It is shown that the weaving length has negligible effect on traffic states of the weaving section when traffic flows of both main road and on-ramp are free. However, the increase of weaving length can improve the traffic states of on-ramp when the traffic flow of main road or on-ramp is congested. Furthermore, the distributions of density, velocity and lane-changing frequency of vehicles are discussed in the case of free flow of main road and large on-ramp flux. It is found that lane-changing behaviours occur mainly on both merging and diverging areas and lead to local congestion correspondingly.

2012, 44(6): 996-1004. doi: 10.6052/0459-1879-12-030

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STUDY ON NUMERICAL PRECISION OF EXTENDED FINITE ELEMEMT METHODS FOR MODELING WEAK DISCONTINUTIES

Jang Shouyan, Du Chengbin

This paper mainly studies the effects of the enrichment functions on the numerical precision of XFEM when the method is used to model weak discontinuities problems. The dominant reasons for the effects of the enrichment functions on the numerical precision of XFEM are discussed in detail. In the corrected-XFEM, the set of enriched nodes equals to the set of enriched nodes in the standard-XFEM plus their neighboring nodes. The fact is thereby indicated that the increase of enriched nodes can improve the numerical precision of the corrected-XFEM. In this paper, the proposed method is to expand the enriched nodes of the corrected-XFEM, and the expanding enriched nodes is the set of enriched nodes in the corrected-XFEM plus their neighboring nodes. Then, the level set method is used for the description of the inner discontinuous interfaces. The governing equation of XFEM is deduced. A numerical integration scheme is elaborated to integrate the stiffness matrix of enrichment elements. Also a method is introduced for the acquirement of accurate stresses in enrichment elements. The numerical results of two illustrations with single inclusion and multi-inclusions both show that the proposed method of expanding the enriched nodes of the corrected-XFEM can improve evidently the numerical precision of XFEM.

2012, 44(6): 1005-1015. doi: 10.6052/0459-1879-12-102

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SOLUTION OF THE DYNAMIC RESPONSE OF RIGID FOUNDATION OF ARBITRARY SHAPE ON MULTI-LAYERED SOIL

Lin Gao, Han Zejun, Li Jianbo

An approach based on integral transformation, dual form of wave motion equation and precise integration method is proposed for the solution of the dynamic stiffness matrices of rigid foundation of arbitrary shape on multi-layered half-space. Firstly, to take advantage of the axisymmetric property of the load-displacement field of subdisk-element in cylindrical coordinates, the equation of Green's influence function for multi-layered half-space is formulated. Then the dual form of the uncoupled wave motion equation in the frequency-wave number domain for in-plane motion and out-of-plane motion is established. It can be solved quite accurately by the precise integration method. Finally, the contact interface between the rigid foundation and the multi-layered half-space is discretized into a number of subdisk-elements, and the matrix-equation of translational and rotational dynamic stiffnesses of the foundation is evaluated. The proposed method is efficient, accurate and computationally stable. It is well suited to the dynamic interaction analysis of rigid foundation of arbitrary shape on complex multi-layered half-space. Numerical examples clearly demonstrate the superiority of the proposed approach.

2012, 44(6): 1016-1027. doi: 10.6052/0459-1879-12-101

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MULTI-SCALE DYNAMIC ANALYSIS METHOD FOR UNDERGROUND STRUCTURES

Yu Haitao, Yuan Yong

Underground structures suffered great damages frequently in recent earthquakes. A number of researchers have developed studies on seismic analysis of underground structures, but failed to address the existing multi-scale dynamic problems. In this paper, a multi-scale method is proposed for the dynamic response analysis of underground structures subjected to dynamic loadings. This method does not result in spurious wave reflections and does not need additional filtering or damping. Based on the bridging coupling theory, Lagrangian multipliers are introduced to append the constraints into the dynamic equations, and the dynamic control equations are deduced for the multi-scale subdomains using the energy potential function. Based on the central differential method, a multi-scale dynamic explicit algorithm is proposed to solve the established multi-scale dynamic coupling systems. As an application, the presented method is used in an existing underground structure. The advantage of the multiscale modeling method in minimizing spurious reflections is verified by providing comparisons with the displacement-coupled method. The research is of great benefit to seismic analysis theories and methods of underground structures, and also provides instructions for dynamic calculation and analysis of underground structures.

2012, 44(6): 1028-1036. doi: 10.6052/0459-1879-12-133

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DYNAMIC TOLOGICAL OPTIMAL DESIGN OF THREE-DIMENSIONAL CONTINUUM STRUCTURES WITH FREQUENCIES CONSTRAINTS

Ye Hongling, Shen Jingxian, Sui Yunkang

The purpose of present work is to study structural optimal design of dynamics for three-dimensional (3D) continuum structures, and to aim at constructing topological optimal formulation by using ICM method, which is considering weight as object function and fundamental eigenfrequency as constraints. An explicit expression of frequency-constraint(s) with respect to topological variables is obtained based on Rayleigh's quotient and first-order Taylor expansion. And two types of models with filter functions including power function and exponential function are standardized. As a result, the topology optimization problem is solved by the dual quadratic programming. Localized mode and mode switching often occurred in structural optimization with natural frequency constraints are handled by using filter functions and moving constraints in the optimal process. Finally, several numerical examples applying different filter functions in the optimal model are analyzed and discussed to demonstrate the feasibility and efficiency of the proposed method.

2012, 44(6): 1037-1045. doi: 10.6052/0459-1879-12-069

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A PSEUDO-STEADY STATE METHOD FOR ANALYZING RANDOM RESPONSES OF COUPLED VEHICLE-TRACK SYSTEMS

Zhang Youwei, Xiang Pan, Zhao Yan, Lin Jiahao

A pseudo-steady state method for analyzing random responses of coupled vehicle-track systems subjected to track irregularities is developed. The vehicle is simplified as a three dimensional multi-rigid body dynamic system and the track is modeled by the generalized finite element method. Assume that the sleeper spans are uniform, and then the equation of motion of the coupled system is periodically time-varying. Pseudo-excitation method (PEM) is used to transform the three types of rail irregularities into harmonic pseudo-excitations; the differential equations theory and the Schur decomposition scheme are then applied to develop a pseudo-steady state method for solving the above equation of motion. In this method, a linear equation set with an upper triangular coefficient matrix is established to replace the conventional step-by-step integration process when calculating the pseudo-responses of PEM which considerably reduces the computational effort. The random response of a three-dimensional coupled vehicle-track system is analyzed in the numerical example and the transmission mechanism of random vibration in the coupled system is investigated.

2012, 44(6): 1046-1056. doi: 10.6052/0459-1879-12-041

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ROBUST CONTROL AND VIBRATION SUPPRESSION OF FREE-FLOATING FLEXIBLE SPACE ROBOT

Xie Limin, Chen Li

The dynamics modeling, algorithm design of motion control and step active suppression of joint-link double flexible vibration of free-floating flexible space robot are discussed. The system dynamic equations are established according to system momentum conservation, angular momentum conservation and Lagrange-assumed mode method. Based on singular perturbation method, the system is decomposed into a slow subsystem (represents the system's rigid motion), a fast subsystem 1 (represents the system's flexible motion caused by flexible-link), and a fast subsystem 2 (represents the system's flexible motion caused by flexible-joint). For the slow subsystem, a robust controller is proposed to compensate the uncertain parameters and rotation errors, and to realize the asymptotic tracking of the system's motion trajectory. For the fast subsystem 1, linear quadric regulator (LQR) is used to suppress the flexible vibration caused by flexible-link. For the fast subsystem 2, a feedback controller based on the velocity difference between the link and the motor is used to suppress the flexible vibration caused by flexible-joint. So the system's controller is a synthesize controller by the three controllers. The simulation results prove the controller's efficiency.

2012, 44(6): 1057-1065. doi: 10.6052/0459-1879-12-156

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A MECHANICAL MODEL OF POROUS MEDIA AND ITS APPLICATION IN CEMENT MATERIALS

Kan Jin, Wang Jianxiang

A new mechanical model is established in this paper on the basic theories of fracture mechanics and meso-mechanics. The mechanical properties of porous media are analyzed. Based on the geometric descriptions and morphological parameters of the pores in porous media such as porosity, shapes and scales, effective elastic equation can be established by equivalent inclusion theory. The final variables of effective elastic equation are stress, strain and morphological parameters of the pores. Mechanical energy, elastic strain energy and potential energy of the porous media are calculated and the energy conservation equation is established. The final variables of energy conservation equation are also stress, strain and morphological parameters of the pores. So the stress-strain relationship of porous media can be obtained by the two equations. Applying the mechanical model in cement material, the mechanical properties can be calculated. The results obtained are consistent with conclusion of the literatures.

2012, 44(6): 1066-1070. doi: 10.6052/0459-1879-12-053

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SOME QUALITATIVE PROPERTIES OF MODESOF DISCRETE SYSTEM OF BEAM WITH OVERHANG

Wang Qishen, Zhang Lihua, Wang Dajun

Base on the basic oscillating properties of the frequencies and the displacement modes in the discrete system of the beam with overhang, it is proved that the stiffness matrices of conjugated system of a two-span beam with one cantilever is to be sign-oscillated. Then, the sign interchanges number of the flexural moment modes of a beam with one cantilever are determined. Furthermore, some qualitative propertiesof its displacement modes, rotation modes, moment modes and shearing force mode are given. The basic oscillating properties about two-span and three-span continuous beams having middle pinned are obtained practically in this paper as well.

2012, 44(6): 1071-1074. doi: 10.6052/0459-1879-12-023

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RESEARCH ON OPTICAL AUTONOMOUS NAVIGATION FOR MARS EXPLORATION BASED ON ASTEROIDS' LIGHT-OF-VIEW

Cui Wen, BaoYin Hexi, Li Junfeng

Based on the upcoming self-Mars Exploration Program of China, the whole process of the optical auto-navi during the Mars exploration cruise segment is studied in this paper. Using the design orbit of the cruise section, the selection criteria and the asteroids sequence for optical navigation are given. The length of observation data arc is set to 30 days, and the period of the observation data is 5 days. Using the weighted least squares algorithm, the position error is from 100km to 400km and the velocity error is less than 0.25m/s when the length of observation data arc is 30 days.

2012, 44(6): 1075-1078. doi: 10.6052/0459-1879-12-071

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THE GLOBAL OPTIMIZATION OF SPACE EXPLORATION TRAJECTORY DESIGN BASED ON DIFFERENTIAL EVOLUTION ALGORITHM

Zhang Renyong, Luo Jianjun, Cheng Yu, Tang Geshi, Cao Jing, Su Erlong, Feng Jinglang

In this paper, a new global optimization method is proposed to solve the multi-target space exploration trajectory design problem. The variables of targets selection, visiting sequences and launch windows are synchronously optimized. In the context of two-body model in which the central gravity of the sun is only considered with the thrust as impulse, the patched-conic method accompanied with differential evolution (DE) algorithm are applied to solve the global optimization trajectory design problem. Then the method is utilized to solve the problem of the Third National Design Competition for Deep Space Exploration and the example missions of the ACT of ESA. It proves that the global trajectory optimization design method is feasible and valuable for the problem of multi-target and multi-mission space trajectory design.

2012, 44(6): 1079-1083. doi: 10.6052/0459-1879-12-012

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3D COMPUTER RECONSTRUCTION OF RAT MICROVESSEL NETWORK BASING ON THE IN-VITRO OBSERVATION USING TRANSPARENT DORSAL SKIN FOLD CHAMBER

Mu Lizhong, Tang Yuanliang, He Ying, Wang Jin

Microcirculation is the basic structure and function unit in the circulatory system, and it is prominent to keep the body's normal physiological function. Many diseases also start from the microcirculation. Therefore, the aim of this paper is to combine dorsal skin fold chamber with image processing and construct the three-dimension model of microcirculation to lay a foundation in in-vitro experiments and numerical analysis of the microcirculation. Stents with round chambers that can be loaded free were designed and fixed on the back of rats, then structure of the vessels in the chamber was observed by the stereomicroscope. In order to obtain vascular structures of microcirculation information such as boundaries and centerline, a series of image processing were employed. Meanwhile, the connections of bifurcation were determined according to the information of intersection in bifurcation. At the stage of the mesh, the improved transfinite interpolation algorithm was applied to build a three-dimensional finite element mesh model of the vascular network, and reconstruction of the three-dimensional model of any branch of the vascular network was achieved.

2012, 44(6): 1084-1088. doi: 10.6052/0459-1879-12-180

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2012 Vol. 44, No. 6

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