Table of Content

    15 March 2017, Volume 49 Issue 2
    Chen Shijiang, Zhu Wancheng, Wang Chuangye, Zhang Fei
    2017, 49(2):  239-256.  DOI: 10.6052/0459-1879-16-255
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    The joint roughness coefficient (JRC) method was suggested by International Society for Rock Mechanics to estimate joint roughness in 1978. Although this method is widely used in engineering practices, there is a shortcoming of subjectivity and experience relied on investigator. So, the research works about quantifying joint roughness were developed by authors in the world. In this article, firstly, we introduced the research progress about quantitative characterization on both joint profiles and discontinuities roughness, and summarized the results of relationship between the parameters and JRC. Secondly, we evaluated the essential properties and applicability of each parameter, pointed out the problems about the parameters in obtained process including sampling interval influence, deciding triangulation of an elementary surface and determining the weight of each parameter in the comprehensive parameters method. At the same time, we gave the author's ideas of solving the problems. In addition, we discussed anisotropy and size effect of surface roughness in detail, on which are focused by researchers. Finally, we predict that fractal dimension remain a method to describe surface roughness and 3D printing technology can be helpful to research anisotropy and size effect of rock discontinuities roughness.

    Chen Rongqian, Nie Deming
    2017, 49(2):  257-267.  DOI: 10.6052/0459-1879-16-002
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    A thorough understanding of the behavior of particles freely suspended in a shear flow is fundamentally important for understanding and predicting flow behavior of particle suspensions. The motion of particles is very complex when the fluid inertia is taken into account. In the present study, the lattice Boltzmann method has been used to simulate the rotation of an elliptical particle in simple shear flow at intermediate Reynolds numbers. Firstly, the effect of the Reynolds number (0 < Re ≤ 170) has been studied. Results show that the particle rotates periodically when Re is smaller than a critical value. The orientation of the particle at which the particle has its minimum angular velocity decreases as Re increases, which has a piecewise linear relationship with Re. Moreover, the rotation period has a power-law relationship with Re. The larger Re is, the larger the rotation period is. However, when Re is greater than the critical value, the elliptical particle will reach a steady state. Results show that the final orientation of the elliptical particle has a power-law relationship with Re for the steady state. The larger Re is, the smaller the orientation is. Secondly, the effect of the ratio of major axis/minor axis α (1 ≤ α ≤ 10) has also been studied. It shows that there is also a power-law relationship between the rotation period and α. The larger the value of α is, the smaller the rotation period is. Similarly, when α is greater than a critical value, the elliptical particle does not rotate. The final orientation of the elliptical particle has a power-law relationship with α. The larger the value of α is, the smaller the orientation is. Furthermore, it also shows that the overshoot is observed when the elliptical particle is rotating if Re is larger enough.

    Fang Yishen, Hu Zongmin, Teng Honghui, Jiang Zonglin
    2017, 49(2):  268-273.  DOI: 10.6052/0459-1879-16-143
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    The oblique detonation wave engine is a new kind of engine which has a simple structure, low cost, and high specific impulse. In order to ensure the initiation, blunt body is used to induce the oblique detonation wave. The oblique detonation wave flow field induced by spheres in supersonic hydrogen/air mixture is numerically simulated, based on the Euler equations and a detailed hydrogen-oxygen chemical reaction model. Unlike the oblique detonation wave induced by a wedge, the reacting flow around a sphere is much more complex. First, a normal shock wave/detonation wave is formed, then oblique shock wave/detonation wave is developed in the presence of a rarefaction wave. The numerical simulation results show that after the gases being compressed by the blunt body and reaching the auto-ignition temperature, two kinds of flowfileds will appear. When Mach numbers are low, the combustion will be quenched and can not appear downstream of the blunt body due to the influence of the rarefaction wave. When Mach numbers are high, combustion can spread to the downstream region. When the scales of blunt body are small, energy around the stationary point is not enough to induce detonation initiation and an obvious decoupling of combustion and shock wave is formed. As the sphere becomes large enough, decoupling of combustion and shock wave will not appear in the flow and this feature is indpendent of the Mach number. By adjusting the spheric diameter, the flow structures with partial coupling of shock wave and combustion zone was obtained which does not exist in a wedgy-induced oblique detonation. The present investigations suggest that the interaction between rarefaction wave and detonation wavefront is the key issue for detonation initiation induced by a spheric body.

    Bai Yuchuan, Ji Ziqing, Xu Haijue
    2017, 49(2):  274-288.  DOI: 10.6052/0459-1879-16-105
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    Configuration of river is closely related with hydrodynamic structures of flows, for the shape of a channel influences the flow structures in it, and the flow structures also affect the developing trend of the channel through the movement of sediment, forming a pair of dialectical interactions in the river system. The natural rivers are different in configurations, which can generally be divided into such types as straight, bending, branching and wandering. Among them, the bending river or the river composed of several curved channels, the result configuration of interaction between the natural river and the complex hydrodynamic flow structure in it, become one of the most important types in the study of river dynamics. As the basis of theoretical research, the establishment of model and the study on flows within a moving channel has become the focus not only from researchers of fluid mechanics, but also from investigators of river dynamics. Therefore, this study first established a theoretic model on the flow in a meandering channel with a moving boundary by using a streamwise-transverse coordinate system. It next discussed the hydro-dynamic instability characteristics of the laminar flow within the sine-generated moving boundaries. Then it quantitatively analyzed the influences of various character parameters to the velocity distributions of main flow. Finally, it obtained the selective influences from the curvature and meandering properties to the flow structure.

    Peng Ningning, Liu Zhifeng, Wang Lianze
    2017, 49(2):  289-298.  DOI: 10.6052/0459-1879-16-247
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    As particulate air pollution has aroused the universal concern of the public, the motion and diffusion law as well as the distribution rule of suspended particles have become research focuses. The suspended particles in air are discrete which are different from continuum medium, and thus the model of particle motion are different from that of continuous fluid. To ascertain the model of particle motion is a critical issue in the research of ambient particulate matter. This paper concentrates on the movement of submicron particles in still air where the particle-sink exists. In this experimental study, submicron particles were generated by combustion, particle-sink was simulated through electrostatic adsorption device, and particles' movements at different intensities of particle-sinks were measured by PIV and LDV. The experimental results show that movements of particles in still air without sink are Brownian motion, and if there is a sink, particles move to the sink at variable velocities which varied inversely as the distance to the sink. It turns out that particles' movements around sink are analogous to that of continuum flow. Also, an empirical formula of particle's twodimensional velocity distribution is given on the basis of PIV experimental data, which shows the motion of particle in small space does not satisfy the continuity equation. Meanwhile, experiments in a bigger space were performed by LDV technique, and the result is identical with previous experimental outcome. Therefore, according to this study, a hypothesis is presented as follows:a non-pneumatic-conveying air purify technology base on sink's action and particle disperse is feasible.

    Liu Liqin, Guo Ying, Zhao Haixiang, Tang Yougang
    2017, 49(2):  299-307.  DOI: 10.6052/0459-1879-16-264
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    This paper presented motion responses of the floating VAWT (vertical axis wind turbine) considering the coupling between aerodynamics and hydrodynamics, the method of aerodynamics of fixed VAWT was improved to calculate the aerodynamics of the floating VAWT. The equations of surge, heave and pitch motions of the floating VAWT were established considering the damping forces, wave forces, wind loads, mooring forces, and so on. The formula of wind loads acting on the blades were deduced by the double-multiple-stream tube theory considering the dynamic stall and motions of the floating foundation, and a computing code was developed. Taking the Sandia 17 m wind turbine as an example, the validity of the aerodynamics computing code was verified. The model tests were carried out, where the wind turbine is Φ-Darrieus type and the foundation is truss Spar type. The results obtained by the model tests were compared with those obtained by the numerical simulation, and the coupling computing code was verified.It is found that, the RAO (response amplitude operator) curves of heave and pitch motions of the floating VAWT obtained by numerical calculation agree well with those obtained by model tests, and the validation of the coupling computing code was verified. However, there is difference between the results of numerical calculation and the model tests. This is because the differences between the numerical model and the model tests, mainly regarding the degrees of freedom of the floating VAWT motions, the damping, and the wind forces.

    Xu Xin, Li Shirong
    2017, 49(2):  308-316.  DOI: 10.6052/0459-1879-16-369
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    Based on Euler-Bernoulli beam theory and the one-way coupled heat conduction theory, thermoelastic damping (TED) of functionally graded material (FGM) micro-beams was studied. By assuming the material properties of the rectangular cross-section micro-beams to be varied continuously along the thickness direction as power law functions and ignoring the variation of the temperature gradient in the axial direction, one dimensional and one-way coupled heat conduction equation with variable coefficients was established. By using the layer wise homogenization approach, the heat conduction with variable coefficients was simplified as a series of differential equations defined in each layer. The equation governing flexural free vibration of the FGM micro beams subjected to time dependent non-uniform heating was developed on the basis of classical beam theory. By using the boundary conditions at the top and the bottom surfaces and the continuity conditions at the interfaces, analytical solution of the temperature field in the FGM micro-beams given layer wisely was obtained. Substituting the temperature field into equation of motion of the micro-beams, the complex frequency including TED was achieved, and finally, values of the TED was extracted. Numerical results of the TED were calculated for the given values of physical and geometrical parameters of a metal-ceramic FGM beam. Effects of the material gradient, the geometry, frequency orders and the boundary conditions on TED were analyzed in detail. The results showed that:(1) if the beam length is fixed, one can arrive at the minimum of the TED by changing the volume fraction of the ceramic when the beam thickness is less than a certain value; (2) the orders of the frequency have no influence on the maximum of TED, however, the larger frequency corresponds to the smaller critical thickness (at which the TED reaches the maximum); (3) for different boundary conditions the maximums of TED are same, but the critical thickness is smaller for the stronger end constraints; (4) both the maximum of TED and the critical increase of the FGM micro beams increase along with the increment in the values of the volume fraction of the metal.

    Tan Bingdong, Xu Jinsheng, Jia Yunfei, Yu Jiaquan
    2017, 49(2):  317-323.  DOI: 10.6052/0459-1879-16-324
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    Short fiber reinforced EPDM inhibitor film is used for a new winding coating process, which is mainly to solve the reliable problem in free loading solid rocket grains with complicated structure. Based on fiber reinforced continuum mechanics theory, a simple anisotropic hyperelastic constitutive model is proposed to describe their large deformation, highly non-linear and strongly anisotorpic mechanical behaviors in the work process of solid rocket motor. The unitvolume strain energy function is decomposed into two parts:representing the strain energy from isotropic rubber matrix and anisotropic fiber tensile deformation. By introducing fiber direction to modify fiber strain energy, the specific method of obtaining model parameters by uniaxial and off-axis tension data is presented.Results show that it is highly suitable to characterize their anisotropic mechanical behaviors in the fiber direction from 0° to 45° and the error is less than 5% compared with experimental data. It is concluded that the proposed model is highly accurate and easy to achieve numerical development, which can provide theoretical basis for the structural integrity analysis of solid rocket motor.

    Wang Lujun, Ai Zhiyong
    2017, 49(2):  324-334.  DOI: 10.6052/0459-1879-16-272
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    The thermal consolidation of saturated porous media subjected to a heat source is an important subject in civil engineering and energy engineering. For the complexity of the problem, the porous media are usually treated as homogeneous isotropic media and the heat source is assumed to be a heat source with constant strength in the existing studies. In engineering practice, natural saturated porous media usually show obvious layered characteristics and the heat source is decaying with time. In this case, the extended precise integration method (EPIM) is presented in this study to investigate the thermal consolidation problems of layered saturated porous media subjected to a decaying heat source. The partial differential equations are reduced to ordinary ones by means of the integral transform techniques. Combining the adjacent layer elements and considering the boundary conditions, the EPIM solutions in the transformed domain of the problems are deduced. With the aid of corresponding numerical integral inversion, the temperatures, excess pore pressures and vertical displacements in the physical domain are obtained. A numerical example with the corresponding calculation program is performed to compare with the existing results, which confirm the applicability and validity of the presented method in dealing with the thermal consolidation problems of layered saturated porous media. Finally, numerical examples are carried out to analyse the influence of the heat source's half-life and buried depth, as well as the stratification of medium on the thermal consolidation behaviour. Numerical results show that:the decay period of heat sources has significant influence on the peak values and peak time of temperature and excess pore pressure, the longer the decay period, the greater the peak values and the longer the peak time of temperature and excess pore pressure; burial depths have obvious influence on the variations of excess pore pressure and vertical displacement, the evolutions of vertical displacements against time on both side of the deeply buried heat source are symmetrical, while there is no such phenomenon for the shallow heat source; stratification characteristics of the saturated porous media shows prominent effects on the thermal consolidation.

    Liu Yan, Zhao Chenggang, Li Jian, Cai Guoqing
    2017, 49(2):  335-343.  DOI: 10.6052/0459-1879-16-190
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    Unsaturated soil is a three-phase porous media. The interfaces between every two phases, especially between liquid and gas phase, have important influence on soil behavior. The interfacial form and effect of soil are discussed and the expressions for interfacial work and specific interfacial area are presented. By introducing the interfacial work into the existing work input equation, the Helmholtz free energy of unsaturated soils with interfacial effect can be derived. Based on the free energy equation, the stress variables considering interfacial effect for solid and liquid can be obtained. The influences of interfacial area on flow equation of liquid phase are discussed, and it is pointed out that the gas-liquid interface area should be introduced as a third variable in a complete soil water retention curve (SWRC). The traditional SWRC is a projection of the three-dimensional expression in the (s, Sr) plane. The effective stress considering specific area can be calculated by the relationship between specific area and SWRC. The proposed equation of effective stress is used to simulate experimental data in the literature, and results show our findings are in good accordance with practice. Different from the existing phenomenology studies, the deductive process has a rigorous theoretical basis in this paper. The results shown that the complete expression of effective should consider the effects of internal force in soil, which including not only matric suction, but also the other force related to the specific interfacial area.

    Guo Pengfei, Zhou Shunhua, Yang Longcai, Xiao Junhua
    2017, 49(2):  344-358.  DOI: 10.6052/0459-1879-16-286
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    Based on the dynamic governing equations of unsaturated soil, a continuous medium model regarding vertical dynamic response of rock-socked pile in three-phase unsaturated medium was established in this paper, taking the transverse inertial effect into consideration. The Laplace transformation is then used to solve the dynamic governing equations. In frequency domain, potential function and operator decomposition methods are also used to resolve the governing equations, thus obtained the expressions of soil vertical vibration displacement and shear stress. To solve the soil-pile coupling system, the vertical vibration equation of pile foundation and the continuity conditions are both adopted. Eventually, complex stiffness and admittance of the pile butt, vertical vibration displacement and shear stress of the model are obtained in frequency domain. And the travel curve of vibration velocity under half sine excitation load has also been deducted with the help of Laplace inverse transformation. The model is verified through the comparison with the saturated models. Finally, a case study of dynamic response of a pile in unsaturated soil is presented. The influences of transverse inertial effect, Poisson's ratio, saturation, pile length-diameter ratio and pile-soil modulus ratio on response of pile are investigated. The results show that:(1) Dynamic stiffness, damping and admittance oscillate with the frequency, and the pile resonance occur at the natural frequency of pile. (2) Dynamic response of the pile is sensitive to Poisson's ratio, saturation, pile length-diameter ratio and pile-soil modulus, while the sensitivity with higher frequency. (3) Larger Poisson's ratio causes smaller amplitude of dynamic stiffness, damping and admittance, as well as smaller reflection signal at bottom of the pile in its speed history curve. (4) Larger saturation leads to larger amplitude of pile response and peak value of reflection signal from the pile bottom.

    Long Kai, Wang Xuan, Han Dan
    2017, 49(2):  359-366.  DOI: 10.6052/0459-1879-16-262
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    In topology optimization problems of structures containing multiphase materials, it is common practice to set the volume constraint of each constituent phase or total mass of entire constituent phase constraint to control the final material usage. On the practical engineering background for lightweight design, it is of significance that the minimized weight is taken as the objective in optimal model from the engineering point of view. To solve the topology optimization problem of steady heat conductive with the multiple candidate materials, a new modeling method of weight minimization with the given thermal compliance constraint under multiple load cases is proposed. Following the modeling manner of independent continuous mapping method, two sets of independent topological variables are employed to identify elemental thermal conductive matrix and elemental weight, respectively. The sensitivities of thermal compliance and global weight with respect to the design variable are derived, and their approximate expressions are calculated based on the first-order and second-order Taylor expansion. To eliminate checkerboard patterns and mesh-dependence, the first term of the constraint function is filtered as a solution of the partial differential equation, which also ensures the constraint equation is consistent. The approximate optimal model with the objective and constraint in the form of quadratic and linear function is established. The topological optimization model is solved by dual sequential quadratic programming. Various effects such as the constraint value of thermal compliance, the selection of multiple materials, and the multiple constraints in multiple load cases on the optimal result are discussed in four 3D numerical examples. The results demonstrate the feasibility and effectiveness of the proposed optimization approach regarding structural light design using multi-material in steady heat conduction.

    Xing Haojie, Li Hongjing
    2017, 49(2):  367-379.  DOI: 10.6052/0459-1879-16-282
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    Multi-transmitting formula (MTF) is considered to be a universal local artificial boundary condition, which is generally employed in finite element simulation of near-field wave motion. Due to the great difference between spectral element method (SEM) and finite element method (FEM), the traditional numerical scheme of MTF cannot be simply adopted in SEM without any change. In order to make use of the advantages of MTF, i.e., clear physical mechanism and controllable accuracy, basic problems involved in the combination of MTF and SEM are discussed in this paper, then the feasibility of spatial or temporal interpolation schemes are investigated, respectively. From the view of spatial interpolation scheme, a set of numerical formulas of MTF based on Lagrange polynomial are proposed, where the higherorder MTF is implemented via a simple iteration process. The accuracy and stability of the above MTF schemes are examined by a standard 1-D spectral element model of wave motion. The numerical results show that all schemes have comparable accuracy for 1st- and 2nd-order MTF, and the MTF scheme based on spectral element displacement mode is superior to others for 3rd- or 4th-order MTF. On the contrary, the stability threshold descends with the growth of interpolation polynomials' order of different MTF schemes, but instabilities only occur under the unusual condition that artificial wave speed is far beyond the physical wave speed.

    Wu Manqiao, Zhu Jihong, Yang Kaike, Zhang Weihong
    2017, 49(2):  380-389.  DOI: 10.6052/0459-1879-16-273
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    Smart structures are those equipped with sensors/actuators made of smart materials, which have the capability to control structure movement in such a way that makes the design more efficient. However, due to systematic complexity and multidisciplinary objectives, the optimization design of such structures in accurate shape control becomes very challenging. This paper proposes an integrated layout and topology optimization design method for accurate shape control of smart structures with surface bonded piezoelectric actuators. The multi-point constraints (MPC) method is used to simulate the bonding connections between movable piezoelectric actuators and host supporting structures. A new weighted shape error function based on desired deflections of observation points is defined to fulfill accurate shape control of piezoelectric smart structure. Through the proposed method, the optimal position and orientation of each piezoelectric actuator as well as the topology configuration of host supporting structure are founded, which significantly improves the systematic actuating and morphing performance of piezoelectric smart structures. Further studies on the relationships of structural stiffness with shape morphing constraint and volume fraction constraint are carried out, and distortions of load carrying path in optimized designs are illustrated. With several numerical results, the proposed integrated optimization method is proved to be an efficient way to decrease the error between computed and desired surface and achieve the accurate shape control of piezoelectric smart structures.

    Yue Baozeng, Yu Jiarui, Wu Wenjun
    2017, 49(2):  390-396.  DOI: 10.6052/0459-1879-16-342
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    The compound control methods are widely used to control the orbit translation and attitude maneuver of liquidfilled spacecraft with high accuracy. The dynamic boundary conditions on curved liquid free surface under low-gravity environment are transformed to general simple differential equations by using Fourier-Bessel series expansion method and the state vectors of coupled liquid sloshing equations are composed by the modal coordinates of relative potential function and the modal coordinates of wave height. The coupled dynamic equations for the rigid platform motion and liquid fuel sloshing are obtained by means of Lagrange equations in terms of general quasi-coordinates. The expressions of the sloshing forces and moments are obtained by analyzing the liquid model. An adaptive fast terminal sliding mode controller and a composite controller that combines the adaptive fast terminal sliding mode strategy and the input shaping technology are respectively designed to control spacecraft orbit translation and attitude maneuver for two cases. In the first case, the spacecraft carries one partially liquid-filled propellant tank. In the second, the spacecraft carries four partially liquid-filled propellant tanks. The efficiency and the accuracy of the controllers are examined through numerical simulations. The results indicate that liquid-control-spacecraft coupled resonance can appear in the controlled spacecraft system if the sloshing effects have not been sufficiently taken accounted of during designing attitude and orbit controller for spacecraft with multiple propellant tanks, and this resonance will result in the instability of the spacecraft attitude. Nevertheless, such disadvantages have been efficiently inhibited by using presented composite adaptive terminal sliding mode controller.

    Zhang Min, Xu Jian
    2017, 49(2):  397-409.  DOI: 10.6052/0459-1879-16-367
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    In recent years, with the wide application of the industrial robot, the development of the mobile robot has attracted more and more attention. In order to finish the work accurately in some complex environments, vibrationdriven system has been proposed and researched by scholars. At the presence of anisotropic viscous friction, this paper investigates the motion law of a vibration-driven locomotion system in which two internal masses vibrate sinusoidally in two parallel guides and puts forward a design method to conduct the tasks like obstacle avoiding. Firstly, by using the second-kind Lagrange's equation, dynamical equations of the system are established; then, the motion law is numerically analyzed, the relationship between the internal drive parameters and the system trajectory and the system velocity are obtained by using the velocity-verlet algorithm; finally, based on the motion law of the vibration-driven locomotion system, the drive design method is proposed to make the system move along a prescribed path and realize the obstacle avoidance. To make the mobile system move along a prescribed path, the motion trajectory of the system could be obtained by curve discretization. Then, by changing the driving parameters of the internal mass block, the system could move along the preset path. In order to make the mobile system reach the goal position in the obstacle environment, an optimized path planning method based on the grid method, Floyd algorithm and the minimum vertex circle method is proposed, and the optimal motion path of the vibration-driven mobile system is obtained. Finally, obstacle avoiding can be realized through changing the driving parameters of the internal mass block.

    Gu Huaguang
    2017, 49(2):  410-420.  DOI: 10.6052/0459-1879-16-315
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    The nervous systems achieve information processing and biological functions with dynamic electronic activities. The firing rhythms and spatiotemporal behaviour of nervous systems are the dynamical characteristics of the achievement of the functions. Combined electrophysiological experiments with theoretical models, diverse rhythm patterns such as periodic, chaotic, and stochastic firing patterns, and complex rhythm transition regularities modulated by the external signal, parameter, and noise were identified with help of the bifurcations. The rhythm information (blood pressure signal and pathological pain) coding mechanism for sensory nervous system and the effect and different classes of synaptic noise to enhance information transmission capability in single pyramidal neurons of the brain were identified. The results are helpful to enhance the ability to enhance information detection and provide guidance for analgesia. The drug-modulated spiral waves/epilepsy observed in the brain cortex and synchronization transitions of firing patterns/abnormal functions of motor network were interpreted with the dynamics of single neurons such as the bifurcations and the fast-slow dynamics of the bursting pattern, which provide the way to modulate the functions of the nervous system. The spatiotemporal behaviour of the functional network of brain of the patients with autism can be acquired with big-data analysis and it was that the synchronous degree between brain regions related to the symptoms of autism reduced, which may be used as the potential diagnostic criteria. The results of the present paper provide new experimental observations, new mathematical model, new analysis method, and new viewpoints, and present identification of the complex dynamics of nervous system and deep understanding for the information processing mechanism and abnormal biological functions/diseases, which are of important scientific values and potential applications.

    Zhang Zhen, Li Jiachun
    2017, 49(2):  421-430.  DOI: 10.6052/0459-1879-16-287
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    The regenerator filled with solid matrix is one of the major components in the PTC (pulse tube cryocooler). In this paper, a new source/sink model instead of porous medium assumption, which is merely applicable for low frequency apparatus, is established to simulate the flow and transport in the regenerator. The new model also is a non-thermal equilibrium model. Based on some assumptions, the analytic solution of the filled solid temperature can be obtained. The new model can reduce the computational workload because the model does not require the establishment of the energy equation of solid. We also propose a method to calculate the value of convective heat transfer coefficient under the alternating flow conditions. According to the comparison with the experimental data, the new model is verified. Then the model is used to analyze the heat transfer mechanism between the working fluids and the solid fillers in the regenerator.The regenerator heat transfer performance are optimized under different mesh screen geometries and properties with numerical simulation.

    Shao Chuanping, Zhu Yuanyuan
    2017, 49(2):  431-440.  DOI: 10.6052/0459-1879-16-179
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    The study of aerodynamic and solid-fluid coupling characteristics of tree leaves is of significance in tree protection, new power generation technology and solar panel design. Vogel first observed that a tree leaf could reconfigure itself at high winds to avoid damage. Vogel's leaf was freely supported at its petiole end, which is quite different from the natural way of petiole-branch connection. In our study, the leaf was clamped at the end of its petiole. The lamina was vertically hanging, with its front or back surface facing wind. Two types of lamina steady status, i.e, wing steady and conic steady, three types of lamina vibration, i.e, low frequency sway, 1st and 2nd high frequency vibration, and 5 critical wind speeds were observed in the range of wind speed 0~27 m/s. The probability of existance of every status and the expected value of each critical wind speed were obtained by statistics of the results of more than 70 leaves. The phenomenon of vortex shedding from a deformed leaf was found by flow visualization. Wind tunnel balance measurement revealed that the leaf drag coefficient decreased with the increase of lamina Re, and finally reached 0.1. A cantilevered beam model was introduced, and the measured aerodynamic force on the lamina was used to simulate the static bending curve of a petiole. Results showed that, the downstream bending increased rapidly with the increase of wind speed from 0 to 5 m/s, but it slowed down from 5 m/s to higher ones.

    Deng Kaiwen, Chen Haixin
    2017, 49(2):  441-455.  DOI: 10.6052/0459-1879-16-285
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    A new hybrid optimization algorithm HSADE(hybrid self-adaptive differential evolution) based on differential evolution and radial basis function response surface was proposed aiming at aerodynamic optimization problems. Through combing the merits of response surface method's fast local searching ability and differential evolution's powerful global searching ability, the overall local and global search efficiency of HSADE were simultaneously enhanced. Several improvements were made on certain logics and strategies embedded in the processes of each sub-algorithm by proposing and utilizing strategies such as selection strategy based on double elimination and self-adaptive parameters. Having applied HSADE and several other typical optimization algorithms-NSGA-II, MOPSO and multi-objective differential evolution to several benchmark functions, the results indicated HSADE was superior to other algorithms in most of the cases regarding local search ability represented by generation distance and global search ability symbolled by hyper volume ratio, which validated the effectiveness of above improvements. Applying HSADE along with basic DE and NARSGA to an airfoil optimization problem and a hypersonic nozzle expansion surface optimization problem, the results showed HSADE was able to obtain airfoils with extra 0.5 count drag reduction and nozzles with better performance than other two algorithms under approximately 1000 function evaluations, which indicated high engineering application potential of HSADE.

    Liu Haibo, Jiang Chao, Zheng Jing, Wei Xinpeng, Huang Zhiliang
    2017, 49(2):  456-466.  DOI: 10.6052/0459-1879-16-294
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    There are a large number of inherently uncertain parameters in the problem of system reliability. Traditional system reliability analysis methods are usually based on the probability model assumption. Probability distribution function of uncertain parameters can be easily obtained with sufficient samples, but in practical engineering problems, it is often difficult to get the precise probability distribution function with limited data or test conditions. In this paper, the uncertain variables of the system based on sufficient information are taken as the random variables, while others with limited information can only be given variation intervals. This paper proposes a new system reliability analysis method for structures with probability and interval mixed uncertainty. Firstly, the minimum reliability index of each failure mode is obtained based on an efficient solution method. Then the system reliability model under multiple failure modes with probability and interval mixed uncertainty is provided. Considering the dependence between different failure modes of systems, a correlation coefficient matrix is obtained by the linear correlation calculated method. Finally, the maximum failure probabilities are calculated for series and parallel system. Three numerical examples show that the present method can effectively deal with the system reliability problems of multiple nonlinear failure modes with probability and interval mixed uncertainty. Compared to the traditional probabilistic reliability analysis method, the presented method can ensure the security of system well and it only needs less uncertain information, and hence it seems suitable for reliability analysis and design of many complex engineering structures or systems.

    Shan Renliang, Bai Yao, Huang Pengcheng, Song Yongwei, Guo Xiang
    2017, 49(2):  467-477.  DOI: 10.6052/0459-1879-16-364
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    In order to know the mechanical properties of frozen wall which contain ice, solve the ice-rock coupling problems, provide believable parameters for ice engineering design and numerical simulation analysis, it is necessary to research the ice mechanics under triaxial compressive stress. Taking the frozen shaft construction of Shilawusu coal mine in Inner Mongolia Autonomous region Dongsheng coal field as the project background of the research. The similarity columnar ice specimens are fabricated in the laboratory based on the field data. A series of tests were performed on artificial freshwater columnar ice under triaxial compression at 4 group temperatures and 7 group confining pressures by using the TDW-200 frozen soil triaxial test system. The loading rate of the series of tests is 0.5 mm/min, and the loading direction is perpendicular to the crystal axis of ice. The results show that, when the experimental temperature is constant, the plasticity of columnar ice increases with increasing confining pressures. When the experimental confining pressure is constant, the brittleness of columnar ice increases with decreasing temperature. Within the range of test temperature, the strength of columnar ice and polycrystalline ice increase with the increase of confining pressure and temperature. The strength of columnar ice is higher than polycrystalline ice at the same conditions. The non-linear relationship between deviatoric stress and confining pressures is explained by D-A model or Teardrop model. From the point of view of integrated advisement, the D-A failure criteria is more reasonable to describe the failure characteristics of the freshwater ice. The conclusions can provide some scientific references for ice-rock coupling research and numerical simulation under the same conditions.

    Zhan Shige, Zhang Panfeng
    2017, 49(2):  478-483.  DOI: 10.6052/0459-1879-17-061
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    The manuscript generally introduced the discipline characteristic and the strategic position of mechanics according to NSFC development strategy plan on mechanics during the 13th Five-Year. The supported region and guiding pricinple on mechanics were alos presented. The project application and funding issues are presented in details, which include the General Program, Young Scientists Fund, Key Program from 2006 to 2015, and National Science Fund for Distinguished Young Scholars, Excellent Young Scientists Fund from begining to 2015. The role of NSFC fundings to promote mechanics development was discussed. At last, the suggestion to discipline development and NSFC funding policy were given.