力学学报

RESEARCH PROGRESS ON KINETICS OF CELL SPREADING

Li Jianjun, Zhao Yapu

The interaction between cell and extracellular matrix (ECM) is essential in many cellular processes,such as cell migration,differentiation and apoptosis.As the first step of cell-ECM interaction,cell spreading has been widely investigated.In this review,the biological background of cell spreading process is first introduced,including a brief overview of involved genes and proteins.Polymerization force,adhesive force and membrane tension are introduced in a coherent framework of cell spreading dynamics from mechanics point of view.The existing physical and/or mechanical models are reviewed based on principles of either viscous flow of cells or mechanical equilibrium at cell periphery.We also discuss the modeling approaches,open questions,and potential opportunities of cell spreading dynamics.

2012, 44(5): 807-823. doi: 10.6052/0459-1879-12-104

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INVESTIGATING INTO TECHNIQUES FOR EXTENDING THE TEST-DURATION OF DETONATION-DRIVEN SHOCK TUNNELS

Jiang Zonglin, Li Jinping, Zhao Wei, Liu Yunfeng, Yu Hongru

Ground test is the important and indispensable method for the research and development of hypersonic vehicle,and the acquisition of the high-enthalpy test flow with long enough test time in the test is one of the key challenges for the shock tunnel.Based on detonation-driven shock tunnel,several factors that are of significant influences on the test time are discussed and the corresponding solutions for extending test time are proposed in this paper,including the tailored condition,the shock starting process in the nozzle and the interaction of reflected shock and boundary layer,aiming to meet the requirement for the test time of supersonic combustion experiments.Through the application of the proposed methods,a large detonation-driven shock tunnel has been successfully developed,which can provide the test time of more than 100 microseconds and are capable of duplicating the hypersonic flight conditions.

2012, 44(5): 824-831. doi: 10.6052/0459-1879-12-160

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EXACT DYNAMICAL MODEL OF AXIALLY MOVING BEAM WITH LARGE DEFORMATION

Liu Yanzhu

The lateral vibration of an axially moving beam is a dynamics problem with practical engineering background.In this paper the Cosserat's model of elastic rod was applied to discuss the dynamics modeling and stability of an axially moving beam with circular cross section.The arc-coordinate along the center line of the beam was used instead of the fixed coordinate.The deformation process of the beam was expressed by the attitude motion of the cross section with the variation of the arc-coordinate and time.Considering the inertial effect and shear strain of the cross section,the dynamics equations of the beam with large deformation were established from the view point of the concept of velocity field of Euler.The three-dimensional motion of an axially moving Timoshenko's beam can be regarded as a special case of small deformation.The stability problem of quasi-stationary state of the axially moving beam was discussed in the static and dynamic states,and the critical axial velocity before buckling was derived.It was proved that the Euler's stability conditions of the moving beam in the space domain are the necessary conditions of Lyapunov's stability in the time domain.

2012, 44(5): 832-838. doi: 10.6052/0459-1879-12-117

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DIRECT FORMULATION OF QUADRILATERAL PLANE ELEMENT WITH QUASI-CONFORMING METHOD——INTO THE FORBIDDEN ZONE OF FEM

Xia Yang, Hu Ping, Tang Limin

The direct formulation of quadrilateral plane element in rectangular Cartesian coordinate system has been a forbidden zone for finite element method.In this paper,the quasi-conforming finite element method is applied on this problem and a bilinear element as well as complete second-order element is constructed.Meanwhile,the convergence analysis of the elements is carried out with "Taylor expansion test" and the comparative study with isoparametric element is also considered.The results show the direct formulation of quadrilateral plane elements is feasible within the quasi-conforming framework,and there is not any convergence problem with these elements.Therefore the finite element theory concerning plane element can be unified by quasi-conforming framework.Compared with isoparametric elements,the bilinear element present in this paper is easy to formulate,with stable performance and explicit stiffness matrix for the plane problem analysis.

2012, 44(5): 839-850. doi: 10.6052/0459-1879-12-105

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NEAR-CIRCULAR LOW-EARTH-ORBIT SPACECRAFT FORMATION CONTROL WITH LORENTZ FORCE

Peng Chao, Gao Yang

Based on the physical law that charged particle experiences Lorentz force in magnetic field,we have analyzed the long-term averaged changes in classical orbital elements with two different charging modes:(1) The spacecraft is charged constantly;(2) The spacecraft is charged in the first half orbital revolution and uncharged in the second half.It is found that,in the first mode,the long-term changes in the longitude of ascending node,argument of periapsis and mean anomaly,can be effectively controlled by Lorentz force,while semi-major axis,eccentricity,and inclination can not be.Meanwhile,the eccentricity can be varied in the second mode.Based on the averaged evolution of the orbital element difference between two spacecrafts in formation-one is charged deputy and the other is uncharged chief,we proposed a new propellantless means for formation control-adjusting the size of fly-around elliptical relative orbit and formation center,when the chief spacecraft's reference orbit is near-circular.The required charge-to-mass ratio for formation control is derived analytically and the effectiveness of Lorentz-force formation control is verified by numerical simulations.

2012, 44(5): 851-860. doi: 10.6052/0459-1879-12-044

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MECHANICAL CHARACTERIZATION AND PREDICTING MODEL FOR CUTTERHEAD INTERFACE LOAD OF SHIELD MACHINE

Zhang Qian, Cai Zongxi, Huang Ganyun, Hou Zhende, Kang Yilan, Zheng Lin

The paper presents a mechanical characterization and predicting model for the cutterhead interface load of shield machine.The interaction between the cutterhead and the soil on the excavation interface is decoupled.The geotechnical yield effect is considered to amend the stress concentration around the edge area on the interface.Then the normal and tangential stress distributions on the cutterhead are presented.In addition,a comprehensive consideration about the interface load with the contributions of the depth burial and the cutterhead topological structure is made.The present study establishes a predicting model of the thrust and the torque acting on the cutterhead interface with the influences of geological parameters,operating parameters,and structural parameters.The effectiveness of the proposed model is verified with a metro engineering instance in China.

2012, 44(5): 861-868. doi: 10.6052/0459-1879-12-057

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THEORETICAL MODELING FOR THE PREDICTION OF THE LOCATION OF PEAK HEAT FLUX FOR HYPERSONIC COMPRESSION RAMP FLOW

Li Bangming, Bao Lin, Tong Binggang

A theoretical model is established to find out why the peak heat flux arises near the reattachment point in hypersonic compression ramp flow and how to predict the location of peak flux.Firstly,the compressible oblique stagnation flow model is set up to describe the nature of flow near reattachment point.Secondly,the approximate solutions of this model reveal that there is a minimum thickness of the boundary layer nearby the reattachment point.Correspondingly,the semi-analytical and semi-numerical method for estimating the location and the magnitude of peak heat flux is presented.Finally,present results are verified by the numerical results,and the extended applications of our theories are discussed.

2012, 44(5): 869-875. doi: 10.6052/0459-1879-12-066

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TEMPORAL INSTABILITY STUDY OF INVISCID FOCUSED JETS UNDER AN ELECTRIC FIELD

Li Guangbin, Si Ting, Yin Xiezhen

A temporal instability analysis of an electrified coaxial liquid-gas jet was performed based on the simplified theoretical model of the flow focusing under an electric field.On the assumption that the fluids are inviscid,an analytical dispersion relation of disturbances growing in the temporal regime was obtained and the effects of main controllable parameters on the unstable modes were analyzed.The results indicate that,only the axisymmetric and the first non-axisymmetric disturbances grow in the temporal regime;the surface tension has two-fold influences on the axisymmetric instabilities and suppresses the non-axisymmetric instabilities;the increases of velocity and density of the external gas streams can definitely promote the jet instabilities.These conclusions are consistent with the experimental results qualitatively.The results also show that the single axial electric field can suppress the jet instability when the initial electric charge density on the jet surface is neglected.On the whole,the theoretical investigation will be helpful for understanding the physical mechanisms of the flow focusing under an electric field and for providing guidance to practical applications.

2012, 44(5): 876-883. doi: 10.6052/0459-1879-12-032

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AN HLLC SCHEME FOR THE SEVEN-EQUATION MULTIPHASE MODEL AND ITS APPLICATION TO COMPRESSIBLE MULTICOMPONENT FLOW

Liang Shan, Liu Wei, Yuan Li

In this paper,the numerical method for the two-pressure and two-velocity seven-equation model presented by Saurel and Abgrall is improved and applied to numerical simulation of compressible multicomponent flows.Based on the operator splitting method given by Saurel et al.and the idea proposed by Abgrall that "for a two phase system,uniformity in velocity and pressure at t=0 will be kept on the same variable during its temporal evolution",discretization for the non-conservative terms and upwind scheme for the volume fraction evolution equation are derived in terms of the underlying HLLC approximate Riemann solver used for the conservation equations.Moreover,the third-order TVD Runge-Kutta method is implemented in conjunction with the operator splitting to obtain a robust procedure by reordering the sequence of operators.Numerical tests with several 1d and 2d compressible gas-liquid multicomponent flow problems with high density and high pressure ratios demonstrate that the present method is more accurate and robust than previous methods.

2012, 44(5): 884-895. doi: 10.6052/0459-1879-12-022

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A NUMERICAL MODEL FOR INTERNAL WAVE PROPAGATION IN CONTINUOUSLY STRATIFIED OCEAN

Zhang Hongsheng, Gu Junbo, Jia Haiqing, Gu Biao

Based on the Euler equations,the finite volume method is employed to develop a numerical model for the internal wave propagation in continuously stratified ocean with variable water depth.The convection terms are discretized with the total variation diminishing (TVD) scheme to make the numerical scheme accurate up to second order,and the SIMPLE algorithm is used in the present numerical scheme.In order to simplify the calculation process and easily adapt to different TVD schemes,the adopted semi-implicit method for pressure linked equations (SIMPLE) algorithm is modified.The predicted velocity fields are calculated with the explicit scheme,instead of the implicit scheme,which is traditionally adopted in the SIMPLE algorithm.Also,the varieties of the hydrostatic pressure due to the density disturbances are not involved in the original SIMPLE algorithm,but they are involved and resolved in this paper.Thus,the SIMPLE algorithm is further developed.The open boundary at the far end is dealt with a sponge layer combined with the Sommerfield's radiation condition.The numerical results with constant depth are compared to the analytical solutions and good agreements are found,and the calculated spatial distributions of the density fields with a submerged dike at different moments are analyzed in details.It is shown that the present numerical model can effectively simulate the propagation of internal wave.

2012, 44(5): 896-903. doi: 10.6052/0459-1879-12-195

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A SELF-ADAPTIVE NEWMARK METHOD WITH PARAMETERS DEPENDENT UPON STRUCTURAL DYNAMIC CHARACTERISTICS

Xing Yufeng, Guo Jing

This paper presents a self-adaptive Newmark method whose parameters are dependent upon the structural dynamic characteristics,and the parameters can be analytically determined based on the conditions of minimizing the numerical dispersion and dissipation.The phase error of the proposed method is exactly zero for linear single degree-of-freedom (DOF) dynamic system.Moreover,the proposed method is the most accurate method among the second order integration methods for multi-DOF system and nonlinear system.Numerical simulations validate the present method and the theoretical results.

2012, 44(5): 904-911. doi: 10.6052/0459-1879-12-033

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ALGORITHM FOR X-RAY PULSAR-BASED NAVIGATION USING A SINGLE DETECTOR IN THE DEEP SPACE EXPLORATION

Wang Yidi, Tang Geshi, Zheng Wei, Li Li

Algorithm for X-ray pulsar-based navigation using a single detector in the deep space exploration is proposed.The measurement information obtained from a single detector at different measurement times is used to establish an improved measurement model,and then deep space spacecraft need not to carry many X-ray detectors to navigate.The obsevabiltiy of the navigation system with available measurement schemes is investigated using a linear obsevability analysis.The analysis shows that spacecraft should measure various X-ray pulsars at different measurement times in order to get a desirable performance of the navigation system.Corresponding simulations are given.The results of the simulations show that the navigation accuracy of the algorithm is similar with that of traditional algorithm.The results of this work show that the quality of an X-ray pulsar-based navigation system can be reduced greatly by using this algorithm and that this algorithm can provide a possible method of the industrialization of X-ray pulsar-based navigation.

2012, 44(5): 912-918. doi: 10.6052/0459-1879-12-005

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THE FIRST EXPLORATION OF THE DYNAMIC RELATION BETWEEN NERVOUS ENERGY AND NEURAL INFORMATION

Zheng Jinchao, Wang Rubin, Zhang Zhikang

In accordance with the basic principles and methods of Information Theory,this article proposes to research and analyze neural coding by using the minimum mutual information principle and the maximum entropy principle.In this paper,firstly,we elaborate their basic principles.Next,we highlight how the minimum mutual information and maximum entropy principle are used to measure the information in neural responses.Studies show that neural information expression and energy utilization rate are closely related,and the fact that highly evolved nervous system on energy consumption is strictly compliance with the two basic principles-economy and efficiency.In order to verify the relation between the neural information processing and energy utilization,this paper put forward a new concept used to measure the efficiency on energy utilization when the neural system follows the maximum entropy principles.Finally,we demonstrate a conjecture that the consumed energy in nervous system reflects the inherent law of neural information energy through the numeric calculation.It lays an important foundation for the further study of a new neural information processing principle—energy neural coding.

2012, 44(5): 919-927. doi: 10.6052/0459-1879-12-046

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INFLUENCE OF DEFORMATION MODES ON SHPB EXPERIMENTAL RESULTS OF CELLULAR METAL

Wang Pengfei, Xu Songlin, Zheng Hang, Hu Shisheng

Two types of improved Hopkinson bar were used to measure the stress on the impact and support ends of a cellular metal specimen.The experimental results and high-speed photography showed,as the impact velocity increased,the stress on the impact end increased,while the stress on the support end didn't change.The stress uniformity of two ends became worse when the impact velocity increased.Based on the experimental results we infer that under the shock mode,the stress on two ends is unrelated to the thickness of the specimen,but related to the density of the materials.In the high-strain-rate experiment of cellular metal,axial inertia (wave) effect will lead to stress non-uniformity.The results would be the coupling of axial inertia effect and strain rate effect and could not represent the dynamic mechanical properties of the materials.

2012, 44(5): 928-932. doi: 10.6052/0459-1879-11-354

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THE FREQUENCY-DEPENDENT STUDY ON VISCOSITY COEFFICIENT AND LOSS TANGENT OF VISCOELASTIC MATERIALS

Liang Chaofeng, Liu Tiejun, Zou Dujian, Yang Qiuwei

According to the relationship between viscosity coefficient of viscoelastic damping model and loss tangent of complex damping model,and the consistency of structural vibration response,the general expression of viscosity coefficient and loss tangent of viscoelatic material was deduced by SDOF's dynamic analysis when the system was in steady-state harmonic vibration or free vibration.Furthermore,the experimental investigation was carried out to study the frequency-dependent viscosity coefficient and loss tangent of fiber reinforced concrete material.It has been shown that,for the steady-state harmonic vibration and free vibration,the expressions of viscosity coefficient and loss tangent were identical except the given vales of frequency.The loss tangent and viscoelastic coefficient of fiber reinforced concrete was decreased with increasing frequency,and decreased shapely among 0.5 to 1.0Hz,then decreased smoothly.Compared with the control plain concrete,the influence of frequency on loss tangent and viscoelastic coefficient of fiber reinforced concrete was more significant.The frequency-dependent viscosity coefficient and loss tangent and the deduced two parameters expression,validated by experiments,are significant important for building damping coefficient or damping matrix which have explicit physical meaning and is convenient for structural vibration response analysis.

2012, 44(5): 933-937. doi: 10.6052/0459-1879-12-031

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DYNAMIC STRESS CONCENTRATIONS BY USING REFINED EQUATIONS OF PLATE BENDING

Hu Chao, Zhou Chuanping, Fai Ma, Liu Diankui

In this paper,based on the refined dynamic equation of plate bending,elastic wave scattering and dynamic stress concentrations in plates with a circular cutout were studied.Numerical results of dynamic moment concentration factors at the edge of cutouts in plates were obtained at given parameters by the Mindlin theory and the refined equation of plates,respectively.The comparison of the numerical results was made and discussed.It is shown that at a higher frequency,the numerical results,which are from the Mindlin theory and the refined theory,respectively,are different.Especially,as the cutout radius ratio to the thickness a/h is smaller 0.10,using the refined equation,the dynamic moment factor may approach to the maximum value,which is over 16% compared to that from Mindlin theory.The results are more accurate because the refined equation is derivative without using any engineering hypotheses.

2012, 44(5): 938-942. doi: 10.6052/0459-1879-12-048

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TRANSIENT DYNAMIC ANALYSIS OF GRADIENT FLUID-SATURATED SOIL

Zhou Fengxi, Lai Yuanming

Based on the Biot's theory of porous media,the calculation formula of reverberation ray matrix method is established for one-dimensional transient response of fluid-saturated soil,where the non-homogeneous,inertial,viscous and the compressible of solid particles and fluid are taken into account.The present methodology is validated by comparing solutions with some known result.As numerical examples,assuming that the material properties of the saturated soil have an exponential law distribution along the thickness-coordinate,the transient response,in terms of displacement,stress and pore press,are examined using numerical inverse Laplace transform.The effect of non-homogeneous on transient responses of gradient saturated soil is demonstrated and discussed.

2012, 44(5): 943-947. doi: 10.6052/0459-1879-12-003

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NEW GENERALIZED-α METHOD FOR OVER-DETERMINED MOTION EQUATIONS IN MULTIBODY DYNAMICS

Ma Xiuteng, Zhai Yanbo, Luo Shuqiang

Motion equations of multibody systems with holonomic constraints via the first kind of Lagrange's equations are index-3 differential-algebraic equations (DAEs).As for the velocity-constrained equations are considered,over-determined motion equations can be obtained and named as index-2 over-determined differential-algebraic equations (ODAEs).Generalized-α method,which is used in the structural dynamics simulation,is extended to the numerical integration of motion equations in the form of index-2 ODAEs.For the new generalized-α method,the number of nonlinear equations from discretization is not increased compared with other integration methods for the index-2 ODAEs.The new method is validated by numerical experiments.There are no accuracy reductions for the new method in the integration of index-2 ODAEs and it is second-order accuracy.In addition,the numerical dissipation is controllable.In the end,new generalized-α method for motion equations in the form of ODAEs is compared with other methods from the point view of the CPU time.

2012, 44(5): 948-952. doi: 10.6052/0459-1879-12-028

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