力学学报

EXPERIMENTAL INVESTIGATION ON LIFT INCREMENT OF A PLASMA CIRCULATION CONTROL AIRFOIL

Feng Lihao, Wang Jinjun, Choi Kwing-So

Based on the flow characteristics of the dielectric-barrier-discharge (DBD) plasma actuator, a novel circulation control technique has been proposed, which is used to control flow around a NACA0012 airfoil. Since the trailing edge of the NACA0012 airfoil is not a circular surface, the circulation control technique is constructed from two DBD plasma actuators. One is attached to the suction surface near the trailing edge, with its induced wall jet to the same direction with the free stream. The other is attached to the pressure surface near the trailing edge, with its induced wall jet to the opposite direction with the free stream. Time-resolved PIV is employed to measure the velocity field in the near-wake region, with the Reynolds number based on the airfoil chord length Re=20000. With the plasma circulation control, a steady recirculation region could be formed on the pressure surface near the trailing edge, acting as the virtual aeroshaping effect, thus the flow over the suction surface is accelerated, while the velocity over the pressure surface is reduced. Thus both the suction and pressure over the airfoil are enhanced, increasing the circulation over the airfoil. The dynamic force balance measurements further validate the efficiency of the lift improvement by the present plasma circulation control. The plasma control increases the lift coefficients over the entire angles of attack.

2013, 45(6): 815-821. doi: 10.6052/0459-1879-13-012

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A HIGH RESOLUTION CELL-CENTERED ALE METHOD FOR LARGE DEFORMATION MULTIMATERIAL INTERFACE

Liu Yan, Tian Baolin, Shen Weidong

For the large dissipation problem of the multimaterial Global ALE method based on the Euler equation with integral form combined with the mass fraction equation, we use the high resolution anti-diffusive idea for interface based on the Euler equation with differential form to control the numerical diffusion at interface, and then we developed a multimaterial cell-centered ALE method based on the Euler equation with integral form combined with the mass fraction equation and volume fraction equation in plane coordinate to simulate the large deformation multimaterial interface with high resolution.

2013, 45(6): 822-832. doi: 10.6052/0459-1879-13-164

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MOVEMENT AND SPLASHING OF A DROPLET IMPACTING ON A WET WALL

Song Yunchao, Ning Zhi, Sun Chunhua, Lü Ming, Yan Kai, Fu Juan

The liquid layer has an important effect on the movement of a droplet after impacting on a wet wall. The numerical solution of the movement of a droplet impacting on a wet wall was realized by using the combined Level Set-VOF method for gas-liquid interface tracking and the wall wetting model, and the movement of a droplet impacting on a wet wall was researched. The results show that there are several different movement forms after a droplet impacting on a wet wall under different impacting velocities, such as adhesion spreading, wave, crown and splashing, and the pressure distribution induced by the impacting is the main reason of different movement forms. The movement of splashing is a special form of crown movement under certain conditions, and its formation satisfies the theory of capillary breaking. The effect of the impacting velocity on the movement direction of splashing is small, while the effect of the thickness of the liquid layer is bigger. Both impacting velocity and liquid layer have certain influence on the droplet shape, splashing separation position, splashing velocity and splashing occurrence time.

2013, 45(6): 833-842. doi: 10.6052/0459-1879-13-053

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EXPERIMENTS ON EVOLUTION CHARACTERISTICS FOR THE MUSHROOM-LIKE VORTEX STRUCTURE GENERATED BY A SUBMERGED LAMINAR ROUND JET

Chen Ke, You Yunxiang, Chen Yunxiang, Hu Tianqun

A constant-pressure spillover system is designed to produce a submerged Laminar round jet with the constant outlet velocity, the flow patterns are visualized by dyed liquid, the evolution mechanism and characteristics due to the jet momentum in viscous uniform fluid is conducted experimentally for different combinations of the injection time and Reynolds number, where three non-dimensional parameters for the mushroom-like vortex structure generated by such a submerged laminar round jet, including the length of the jet L^*, the radius of the mushroom-like vortex R^* and the length of vortex circulation d^*, are defined and the variation characteristics of these parameters with non-dimensional time t^* are quantitatively analyzed. Serial experimental results show that the formation and evolution process of such a mushroom-like vortex can be described as three stages: starting, developing and decaying stages. In starting stage, L^* and d^* increase linearly with t^*, while R^* approximately remains a constant. In developing stage, the mushroom-like vortex structure shows a significant self-similarity, where L^*, R^* and d^* are approximately proportional to t^*1/2 for different combinations of the injection time and Reynolds number, the experimental results agree well with the theoretical solution based on stokes approximation. In decaying stage, two kinds of decay cases will happen for the mushroom-like vortex structure. In the first case, the decay happens after the end of the submerged round jet, where L^* and R^* are related to t^*1/5, and d^* approximately remains a constant. In the second case, the decay happens before the end of the submerged round jet, where some broken phenomenon will occur for the mushroom-like vortex structure after the jet momentum reaches the critical value.

2013, 45(6): 843-853. doi: 10.6052/0459-1879-12-370

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THE MICROSTURCTURE AND LINEAR VISCOELASTICITY OF OTAC/NASAL WORMLIKE MICELLES

Wang Zhiguo, Wang Shuzhong, Sun Xiao, Jing Zefeng, Wu Jinqiao, He Jing

The formation, microstructure and linear viscoelasticity of wormlike micelles with octadecyl trimetryl ammoium chloride (OTAC)/sodium salicylate (NaSal) were analyzed with the method of rheology and freeze-fracture transmission electron microscopy (FF-TEM). It is shown that the long wormlike micelles with several micrometers are obtained if the mass ratio of the OTAC master solution to NaSal is 5:1. The linear micelle is dominated when the OTAC master solution weight content is 1.4%. The micelles begin to entangle with the increase of the OTAC solution concentration. When the weight content of OTAC master solution is 4% at a constant mass ratio, 5:1 of OTAC to NaSal, the minimum of entanglement length, l_e, may occur and the solution shows good viscoelasticity with a longer relaxtion time, 2.86 second. The entanglement wormlike micelles show the Maxwellian behavior at low frequency and the deviation occurs at high oscillation frequency. The deviation shows that the "breathing" and "Rouse-like" motions of wormlike micelles will dominate the stress relaxation process for the entanglements of micelles. It is a solely characteristic stress relaxation mechanism of wormlike micelles at high oscillation frequency.

2013, 45(6): 854-860. doi: 10.6052/0459-1879-13-062

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INVESTIGATION OF BUBBLE-BUBBLE INTERACTION EFFECT DURING THE COLLAPSE OF MULTI-BUBBLE SYSTEM

Zhang Lingxin, Wen Zhongqing, Shao Xueming

The collapse stage of 3D bubbles in higher surrounding pressure is studied using direct numerical simulation based on the volume of fluid (VOF) method. The numerical results show that the collapse of central bubble in multi-bubble system is different from single bubble collapse significantly, which contains delay stage and acceleration stage. Increasing the number of neighboring bubbles or decreasing the distance between bubbles leads to a longer collapse time and a higher pressure peak of central bubble. According to theoretical analysis, the bubble's radial motion is driven not only by the liquid pressure in the far field but also by the pressures emitted from the neighboring bubbles. The pressures from the neighboring bubbles first decrease and then increase. This leads to the delay and acceleration characteristics of central bubbles.

2013, 45(6): 861-867. doi: 10.6052/0459-1879-13-067

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ANALYSIS OF SHIP MANEUVERING PERFORMANCES AND ICE LOADS ON SHIP HULL WITH DISCRETE ELEMENT MODEL IN BROKEN-ICE FIELDS

Li Zilin, Liu Yu, Sun Shanshan, Lu Yunliang, Ji Shunying

With the development of navigation channels in Arctic regions and oil/gas exploitations in cold fields, the investigation of ice load on ship hull is required urgently in offshore engineering under various ice and maneuvering conditions. In this paper, the discrete element method (DEM) is adopted to simulate the interactions between drifting ice floes and a moving ship. The pancake ice floes are modeled with three-dimensional discrete elements considering the buoyancy, drag force and added mass of current. The ship hull is constructed with triangle elements. The interaction between ice floe and ship hull is determined through element contact detection and impact force calculation. The influences of ice conditions (current velocities and directions, ice thicknesses, concentrations and ice floe sizes) and navigational speed on the dynamic ice forces of ship hull are examined. This work is of reference value to the ship structure design and the navigation security in ice-covered fields reseaches.

2013, 45(6): 868-877. doi: 10.6052/0459-1879-13-020

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A VARIATIONAL INEQUALITY APPROACH FOR NON-STEADY SEEPAGE FLOW THROUGH THREE-DIMENSIONAL FRACTURE NETWORK

Ye Zuyang, Jiang Qinghui, Yao Chi, Zhou Chuangbing

To solve non-steady seepage flow problems with free surface in fractured rock masses, Darcy's law is extended to the entire domain. A parabolic variational inequality (PVI) formulation, in which a Signorini's type of boundary condition enforced on the potential seepage surface, is established for transforming the flux condition on the potential seepage surface into natural boundary conditions, and then proved to be equivalent to the partial differential equation (PDE) formulation, and then the difficulty in solving this problem is reduced. Finite element numerical solution of the PVI formulation is proposed, and the validity of the numerical approach is verified by comparison of theoretical and calculated results for cross fracture model. Finally, the proposed approach is applied for non-steady seepage flow behaviors in a complex fractured rock slope, and the calculation results validate the reliability and robustness of this method well.

2013, 45(6): 878-887. doi: 10.6052/0459-1879-13-055

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DYNAMIC MODEL OF SELF-OSCILLATING GELS AND THE CONTROLLABILITY ANALYSIS

Wang Pengfei, Liu Shaobao, Zhou Jinxiong, Lu Tianjian, Xu Feng

Self-oscillating gels, i.e., BZ gels, are a typical branch of soft smart materials with a large periodic deformation of shrinking and swelling driven by the Belousov-Zhabotinsky chemical reaction (BZ reaction). BZ gels could be widely applied in the fields of actuators, sensors, drug release and bionic system. Based on the Oregonator model of the BZ reaction and the mechanical equilibrium of the gel deformation, a simplified dynamic model, only consisting of a second order differential equation, is given to reformulate the complicated process of the oscillatory deformation. It is demonstrated that the phase space trajectory of BZ gels presents a limit-cycle oscillation (i.e., steady-state periodic oscillation). Subsequently, the periodic solution of oscillation is obtained by adopting an improved shooting method and the influence of some adjustable system parameters on the mechanical characters of the oscillatory deformation(i.e., pattern, period, amplitude) is systematically investigated, where the system parameters are dependent on the concentration of reactants, catalyst efficiency and hydrophobicity of polymers. The conclusion demonstrates that the system maintains a limit-cycle oscillation in the case of certain selected values of the system parameters and the mechanical characters of the system appear predictable changes while the parameters are changed. This study theoretically supports the controllability of self-oscillating gels and their potential applications.

2013, 45(6): 888-896. doi: 10.6052/0459-1879-13-073

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A NEW SEMI-ANALYTIC ALGORITHM OF NEARLY SINGULAR INTEGRALS IN HIGH ORDER BOUNDARY ELEMENT ANALYSIS OF 2D ELASTICITY

Niu Zhongrong, Hu Zongjun, Ge Renyu, Cheng Changzheng

The calculation of the nearly singular integrals on high order elements is difficult in boundary element method (BEM) at present. In this paper, a new semi-analytic algorithm is established to deal with the nearly strongly singular and hyper-singular integrals for high order elements in two dimensional (2D) BEM. By analyzing the geometric feature of high order elements by local coordinates, the relative distance from a source point to the element is defined. For the nearly singular integrals of the high order elements, the leading singular part of the integral kernel function is separated into the explicit formulation by a series of deduction. Then the nearly singular integrals on the high order elements close to the source point are transformed to both the non-singular part and singular part by the subtraction, where the former is computed by the numerical quadrature and the later is evaluated by the analytic algorithm. Consequently, the quadratic element with the new semi-analytic algorithm was applied to calculate the displacements and stresses very close to the boundary and thin-walled structures in the boundary element analysis of 2D elasticity. Three examples were given to demonstrate that the computed results of the quadratic element with the semi-analytic algorithm are more accurate than those of the linear element with the analytic algorithm for the nearly singular integrals. In fact, the boundary element analysis with the linear element has been greatly more advantageous compared with the finite element method in analyzing the thin bodies.

2013, 45(6): 897-907. doi: 10.6052/0459-1879-13-215

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A GENERAL ALGORITHM FOR CALCULATING NEARLY SINGULAR INTEGRALS OVER HIGH-ORDER ELEMENTS IN 3D BEM

Zhang Yaoming, Li Xiaochao, Vladimir Sladek, Jan Sladek

This work presents a general methodology to compute nearly singular integrals arising in 3D BEM using the eight-node second-order quadrilateral and six-node second-order triangular surface elements. The proposed method constructs a new distance function. The exponential transformation, which was proposed by present authors and is accurate and easy to implement according to extensive applications of 2D BEM, will be extended to 3D BEM to remove the near singularities of integrands. Several numerical examples are given to verify the high efficiency and the stability of the proposed scheme.

2013, 45(6): 908-918. doi: 10.6052/0459-1879-13-057

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INTERACTION MODEL OF THE ENCLOSED AIR AND THE OUTER MEMBRANE

Li Peng, Yang Qingshan

The enclosed air in inflatable membrane structures is assumed as potential flow in this paper. The wave equation of enclosed air was derived, and the finite element dynamic equation was obtained by using Galerkin method. The relation between nodal potential of air elements and nodal displacement of membrane elements was established through the introduction of interface coupling conditions. Then the interaction model of the inflatable membrane structure system was obtained by combining the dynamic equations of both the enclosed air and the membrane. On the basis of the interaction model, two typical inflatable structures were modeled and analyzed to verify the accuracy and rationality of the interaction model by comparing the numerical results with the experimental results.

2013, 45(6): 919-927. doi: 10.6052/0459-1879-13-019

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IMPROVEMENTS OF GEOMETRICALLY NONLINEAR ANALYSIS ALGORITHMS FOR SPATIAL FRAME STRUCTURES

Li Wenxiong, Ma Haitao, Chen Taicong

Two spatial beam elements based on the geometrically exact beam theory are developed using high order Lagrange interpolation and Hermite interpolation. An element-level equilibrium iteration procedure is proposed for condensing out internal degrees of freedom, enhancing the applicability of the elements to general-purposed finite element software. A geometrically nonlinear analysis algorithm with both load control and cylindrical arc-length control is developed for spatial frame structures. The presented results of numerical examples show that the proposed approach is effective both to increase the computational efficiency and to achieve better numerical stability. Especially, the proposed element based on the Hermite cubic interpolation performs better in the numerical tests and is therefore well suited for the post-buckling analysis of frame structures.

2013, 45(6): 928-935. doi: 10.6052/0459-1879-13-018

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COHESIVE ZONE MODELING OF INTERGRANULAR CRACKING OF INTERMETALLIC COMPOUNDS IN SOLDER JOINTS

An Tong, Qin Fei

In order to investigate the effect of the microstructure of intermetallic compound (IMC) on the micro and macro mechanical behaviors of solder joints, a finite element based numerical approach is developed to simulate initiation, propagation and coalescence of microcracks along the grain boundaries in the IMC layer. In the approach, the topological microstructure of IMC grains is generated by Voronoi tessellations, and the proposed cohesive interface elements are embedded between the grain boundaries. By the proposed approach, the effect of grain shape and randomly distributed grain interfacial defects on the microcrack pattern and the overall response, and the effect of IMC microstructure on the strength and the failure mode of solder joints, are investigated. The results indicate that the grain shape has little effect on the overall mechanical response, but affects the cracking path. In the model with Weibull distributed grain interfacial strength, the weak grain interface plays a key role in the overall strength. The thickness of the IMC layer has a significant influence on the strength and failure mode of solder joints, while the roughness of the solder/IMC interface has an influence on the failure mode only.

2013, 45(6): 936-947. doi: 10.6052/0459-1879-13-004

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COMPUTATIONAL METHOD FOR DYNAMICS SIMULATION OF PAYLOAD SEPARATION FROM SATELLITE WITH RAIL CLEARANCE

Zhao Ganglian, Jiang Yi, Chen Yujun, Dong Xiaotong

Traditional researches on payload separation from spacecraft don't consider actual contacts in rail clearance, and separation velocity of payload can't be assessed accurately. According to two semicircle rails, characteristics of contacts between spatial rail and director were investigated. A method for detecting potential contact points between director and rail with relative movements was presented based on the structural features. Spatial angle between the director and the rail is calculated to detect contact exactly in the later stage of separation. The normal contact force was modeled using the continuous approach proposed by Lankarani and Nikravesh, and the tangent friction was calculated by a modified Coulomb's friction law. Validity of the methodology is proved through a free-floating flexible spacecraft model. And the results show that rail clearance causes high contact forces, and velocity vertical to the separation direction increases with clearance size. Further more, clearance aggravates the coupling between the appendages and the base, and effects spacecraft's stability.

2013, 45(6): 948-956. doi: 10.6052/0459-1879-13-193

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FREE VIBRATION OF TAUT CABLE WITH DAMPER AND PARALLEL SPRING

Zhou Haijun, Zhu Yafeng, Sun Limin

This paper studied free vibration of taut cable with damper and parallel spring. The complex frequency equation of taut cable with damper and parallel spring system was derived. The equation was further expanded to real and imaginary parts. The special limiting solutions were derived. The modal frequency and modal damping in each specific region were further discussed. The second mode vibration frequency, damping ratio and mode shape were given for each specific region. The modal crossing phenomena were addressed. The sag effect on 1st modal frequency and frequency was further addressed. It was found that modal frequency and modal damping were dependent on damper and parallel spring location. The cable vibration frequency and damping were greatly increased after damper and parallel spring installation.

2013, 45(6): 957-964. doi: 10.6052/0459-1879-13-006

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NONLINEAR VIBRATIONS OF AXIALLY ACCELERATING VISCOELASTIC TIMOSHENKO BEAMS

Tang Youqi

Nonlinear parametric vibrations are investigated for axially accelerating viscoelastic Timoshenko beams subject to parametric excitations resulting from longitudinally varying tensions and axial accelerations. The dependence of the tension on the finite axial support rigidity is also considered. The governing equations of coupled planar vibration of the Timoshenko beam and the associated boundary conditions are established from the generalized Hamilton principle and the Kelvin viscoelastic constitutive relation. The governing equation of transverse vibration is simplified into a nonlinear integro-partial-differential equation with time-dependent and space-dependent coefficients. The method of multiple scales is employed to investigate parametric resonances with the focus on steady-state responses. Some numerical examples are presented to demonstrate the effects of the viscosity coefficient, the mean axial speed, the axial speed fluctuation amplitude, the large rotary inertia, the rotary inertia, and the small nonlinear coefficient on the amplitudes of the steady-state oscillating response.

2013, 45(6): 965-973. doi: 10.6052/0459-1879-13-099

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MICRO-SCALE NUMERICAL STUDY OF THE EFFECT OF ERYTHROCYTE MECHANICAL PROPERTIES ON THE NEAR-WALL MOTION OF PLATELET

Xu Jing, Wang Xiaolong, Liu Yunqiao, Gong Xiaobo

The effect of erythrocyte mechanical properties on the near-wall motion of platelet was numerically studied with the immersed boundary method. Cells were modeled as viscous-fluid-filled capsules surrounded by a hyper-elastic membrane with negligible thickness. The numerical results show that with the increase in hematocrit, the near-wall approaching is enhanced; platelet exhibits larger deformation and orientation (angle of its near-wall tank-treading motion); the lateral force pushing platelet to the wall is increased with larger fluctuation amplitude of lateral force, while the near-wall approaching is reduced by increasing the stiffness of erythrocytes.

2013, 45(6): 974-981. doi: 10.6052/0459-1879-13-045

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AERODYNAMIC OPTIMIZATION OF HIGH-SPEED TRAIN BASED ON RBF MESH DEFORMATION

Yao Shuanbao, Guo Dilong, Yang Guowei

An aerodynamic drag reduction optimization design study of high-speed train head is carried out based on the three-dimensional parametric approach of local shape function, improved ant colony algorithm and improved Kriging surrogate model. To avoid repeated generation of ten millions of meshes in the case of large deformation with complex geometry and improve the optimization efficiency of high-speed train head, we introduce mesh deformation techniques of the reduced control points based on radial basis functions (RBF). The optimization results show that: RBF mesh deformation method could largely shorten the time-consuming of mesh deformation without reducing the quality of meshes, and can be used for aerodynamic optimization design of complex geometry. Under the design space given in this article, the six key design parameters that control the nose shape have effects on the aerodynamic drag of the train with a kind of monotonically increasing relationship. After optimization under the constraints, the total aerodynamic drag of the simplify shape is reduced by 5.68%. The aerodynamic drag of leading and trailing cars reduced a lot, while the aerodynamic drag of middle car changes little.

2013, 45(6): 982-986. doi: 10.6052/0459-1879-13-111

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HIGH-ORDER DISCONTINUOUS GALERKIN SOLUTION OF N-S EQUATIONS ON HYBRID MESH

Qin Wanglong, Lü Hongqiang, Wu Yizhao

A high-order discontinuous Galerkin method (DGM) based on hybrid mesh was developed to solve the laminar NS equations. Details on high order approximation of the real solid boundary were given. Newton method was used to solve the resulting nonlinear system after the DG discretization. In each Newton loop, preconditioned GMRES method was adopted to solve the large sparse linear systems. Numerical results indicate that the developed DG method on hybrid mesh is a promising way to solve viscous flow cases.

2013, 45(6): 987-991. doi: 10.6052/0459-1879-13-151

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IDENTIFICATION OF NONLINEAR VIBRATION SYSTEMS BASED ON PARAMETRIC TFA

Deng Yang, Peng Zhike, Yang Yang, Zhang Wenming, Meng Guang

In this paper, we used the technique of the polynomial chirplet transform (PCT) to extract the instantaneous characteristics of the output response of the nonlinear system. Combined with estimation methods of instantaneous parameters in the PREEVIB and FROCEVIB methods, we acquired the back-bone curve and damping curve which reflects nonlinearities of the system. Then based on fitting of the identified average nonlinear characteristic forces, the specific parameters can be obtained. Numerical simulations results validate the effectiveness of this method, and it has advantages on high accuracy and good tolerance to noise.

2013, 45(6): 992-996. doi: 10.6052/0459-1879-13-125

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REVIEW OF THE SEVENTH NATIONAL SYMPOSIUM ON DYNAMICS AND CONTROL FOR YOUNG SCHOLARS

Wei Kexiang, Wang Lifeng, Zhan Shige, Zhang Panfeng, Xu Jian

This paper brief introduced the seventh national symposium on dynamics and control for young scholars. Reports of this symposium were reviewed, and some constructive suggestions were put forward.

2013, 45(6): 997-1002. doi: 10.6052/0459-1879-13-348

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2013 Vol. 45, No. 6

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