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    23 July 2014, Volume 46 Issue 4
    SCALE ADAPTIVE SIMULATION OF FLOWS AROUND A CIRCULAR CYLINDER AT HIGH SUB-CRITICAL REYNOLDS NUMBER
    Du Lei, Ning Fangfei
    2014, 46(4):  487-496.  DOI: 10.6052/0459-1879-13-384
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    Combining with γ-Reθ transition model, scale adaptive simulation (SAS) is successfully applied on the laminar separation flow past a circular cylinder at high sub-critical Reynolds number (Re=1.4×105). Numerical results are statistically closed to experimental data, and especially the agreement of pressure recovery in separation zone is fairly well. The major error comes from the inaccurate prediction of the separation position. Transient flows indicate that there are spanwise instabilities in the shear layer of laminar separation flow, and they will grow to be fully turbulence when transporting downstream. Comparing to laminar separation, because of the lack of the unsteadiness related to the shear layer instability, the scale resolving capability of SST-SAS is weaker for turbulent separation flow. Therefore, the scale of turbulent structures resolved by SAS in the wake of turbulent separation is much larger than the laminar separation.

    ACTIVE SEPARATION CONTROL FOR THE FLYING-WING UAV USING SYNTHETIC JET
    Xu Xiaoping, Zhou Zhou
    2014, 46(4):  497-504.  DOI: 10.6052/0459-1879-13-344
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    The numerical simulation is conducted on the low-aspect-ratio flying-wing UAV model based on synthetic jet technology. Effectiveness of the synthetic jet active flow control technique for improving the longitudinal aerodynamic characteristics of model at low speed is explored and validated. The actuators produced significant shifts in the lift curve up to 25%. The flow characteristics analyses reveal that the disturbance caused by synthetic jet can transfer the higher moment flow to the boundary layer and reenergized the unstable boundary layer. The numerical results show that the synthetic jet technology can effectively improve flow separation at the middle and high angle of attack flight conditions.
    INVESTIGATION ON THE ATTENUATION OF A ROTATING LIQUID MOTION IN A CYLINDER WITH BOUNDARY RESISTANCE
    Wan Wuyi, Yu Yunqi, Bai Hao
    2014, 46(4):  505-511.  DOI: 10.6052/0459-1879-14-009
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    In order to study the attenuation process of a rotating liquid motion with boundary resistance, the laminar and turbulent flow friction models are used to calculate the head less, as well as a relative experiment is conducted to verify the mathematical approach. Based on equivalent wetted perimeter, a theoretical formula is established to calculate the energy loss due to wall resistance, in which the wall roughness, rotation radius, static water depth and rotation velocity are considered. Then, the attenuation of liquid rotating is measured in a circular cylinder, and the result agree with the theoretical model well. Based on the verified theoretical formula, the influences of various diameters and roughness coefficients on the attenuation are analyzed. The results show that the wall resistance and the cylinder size are the major factors to determine the attenuation process of the rotating liquid movement. The attenuation processes become more conspicuous with more roughness and less diameter.
    ON SHOALING PROPERTY OF A SET OFFOURTH DISPERSIVE BOUSSINESQ MODEL
    Liu Zhongbo, Fang Kezhaoy, Sun Zhaocheny
    2014, 46(4):  512-518.  DOI: 10.6052/0459-1879-13-414
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    When Boussinesq model is applied to compute wave transformation from deep water to shallow water, the proper shoaling effect is essentially important for accurately predicting wave evolution. Improper shoaling parameters value results in bad shoaling property, and decreases the applicability of the Boussinesq model. Based on a fourth order dispersive Boussinesq equations proposed by Madsen and Schäffer (1998), theoretical analysis was reinvestigated, and we pointed out that the α2 and β2 values in the reference of Madsen and Schäffer was not proper and re-determined their values. Numerical model was established in staggered grids, and a composite fourth order Adams-Bashforth-Moulton scheme was applied to solve time integration and the model was solved by a predictor-corrector-iteration algorithm in finite difference method. Numerical simulations were applied to two typical cases: One was linear wave propagation over a slow-varying depth, and the other was nonlinear wave evolution over a submerged sill. The computed results with present parameter values were compared against the relevant analytical solution and experimental measurements. Both of the agreements are quite good, which validates the theoretical shoaling analysis numerically.
    RESEARCH ON THE COLLISION EFFICIENCY OF NANO-PARTICLE-TO-WALL WITH EXTERNAL ELECTRIC FIELD
    Zhang Kai, Sheng Bingying, Mi Xiaojing, Yan Weiwei
    2014, 46(4):  519-524.  DOI: 10.6052/0459-1879-13-423
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    In this paper, we focus on the effect of surface repulsive force on the collision efficiency of particle under the action of electric field. We first solve the dynamic equations of the compression and spring-back of particle-wall collision by using the Runge-Kutta method in Matlab, and then obtain the collision efficiency based on the integral of Maxwell speed distribution. The results indicate that the particle collision efficiency increases with the increasing of collision angle, and finally it will reach a critical value for the collision efficiency when particles are completely coagulated. In addition, we find that the particle collision efficiency will decrease when the surface repulsive force is considered, which illustrates that the surface repulsive force will partly hinder the coagulation of particles.
    FORCE EVALUATION USING MOMENTUM-EXCHANGEMETHOD IN POROUS MEDIA
    Meng Xuhui, Wang Liang, Guo Zhaoli
    2014, 46(4):  525-532.  DOI: 10.6052/0459-1879-13-359
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    Flows over porous media are frequently encountered in industrial applications such as chemical engineering process and porous particles suspension. It's of great importance to evaluate the force between the fluid and the objects accurately. The momentum exchange method which is efficient and easy for implementation is widely used to determine the force in lattice Boltzmann method. In this work we propose an efficient momentum exchange method to calculate the force by analyzing the exchange process of the fluid and the object. The method is validated by simulating the flows over a porous object at the pore scale, and the method is also extended for fluid-object interaction at scale. Simulations of flows over a square cylinder at different Reynolds numbers are conducted, and the viability of the method is confirmed by the numerical results.
    NUMERICAL ANALYSIS ON THE VELOCITY AND PRESSURE FIELDS INDUCED BYMULTI-OSCILLATIONS OF AN UNDERWATER EXPLOSION BUBBLE
    Li Shuai, Zhang Aman, Han Rui
    2014, 46(4):  533-543.  DOI: 10.6052/0459-1879-13-321
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    The gas inside the underwater explosion bubble is assumed to undergo adiabatic expansion and compression. The water flow induced is assumed to be inviscid, irrotational and incompressible, which is simulated based on potential flow theory coupled with the boundary element method (BEM). Much attention was paid to the character of the pulsating pressure and the flow velocity, and the related theory and numerical method were given in detail. The validity and convergence of numerical model were confirmed by comparing the calculations with experimental and analytical results, so our BEM codes were used to simulate underwater explosion bubbles under different conditions. During the expansion phase of the bubble, the fluid pressure along the radius direction may first increase and then decrease. To simulate the subsequent motion after the bubble jet impact, a vortex ring was put inside the bubble, thus the flow field could be decomposed into two parts: an irrotational flow field and a vortex field. Besides, some numerical techniques were adopted to handle the topology of the bubble which made it possible to simulate multi-oscillations of bubbles. It's noted that there were two high-pressure regions formed around the top and the bottom of the toroidal bubble while its fast rise proceeded. It can also be found that the top region had a greater peak value, while the bottom region covered a larger area. Meanwhile, the flow velocity in the jet direction accelerated inside the toroidal bubble, but decelerated rapidly near the top of the bubble.
    NUMERICAL STUDY ON THE EFFECTS OF SMALL-AMPLITUDE INITIAL PERTURBATIONS ON RM INSTABILITY
    Jiang Hua, Dong Gang, Chen xiao
    2014, 46(4):  544-552.  DOI: 10.6052/0459-1879-13-347
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    Two-dimensional simulations of Richtmyer-Meshkov (RM) instability of small-amplitude initial perturbed interface induced by shock waves are performed by using Navier-Stokes equations. The evolution of interface mixing zone, which is considered as a combination of a bubble and a spike before and after the passages of reshock wave, is analyzed under the single-mode and random multi-mode initial perturbed conditions. The results show that the perturbation growth is influenced by the initial patterns of interface before and after the passages of reshock wave. The information of initial perturbed interface pattern can be transmitted to that of the interface after reshock wave by transforming between the bubble and spike. The growth rate of spike on the interface dominates the whole growth rate of the mixing zone. The developed spike with crown shape before the passage of reshock is transformed into the complex bubble structure that drags the development of spike after the passage of reshock wave. The evolution of random multi-mode perturbed interface shows the similar behavior as that of single-mode perturbed interface. However, the asymmetric feature of complex bubble structure on random multi-mode interface weakens the drag effect on the development of spike, and thus gives rise to the faster growth of the random multi-mode interface than that of the single-mode interface, under the conditions of similar initial wave length for both interfaces.
    INVESTIGATION OF MOLECULAR SPRING ON VIBRATION ISOLATION MECHANISM AND MECHANICAL PROPERTIES
    Yu Muchun, Chen Qian, Gao Xue, Zhang Shuzhen
    2014, 46(4):  553-560.  DOI: 10.6052/0459-1879-13-362
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    Molecular spring is a kind of vibration isolation and shock absorption medium which consists of water and hydrophobic zeolites. In the case of vibration and impact, loading and unloading take turns. Water intrudes into and extrudes from hydrophobic pores of zeolites and at the same time stores, releases and dissipates energy. Force equilibrium of water column in pore and interfacial layer thermodynamic equilibrium are used separately to establish the mechanics model of water intruding into a single hydrophobic pore. Then water flowing into large numbers of hydrophobic pores is calculated considering that contact angle distribution is Gaussian and aperture is uniform. And force-displacement curve of molecular spring is derived. The theoretical result shows good agreement with quasi-static experimental data. Finally, the vibration isolation property is assessed by energy transmissibility. The result shows that the stiffness of molecular spring mixture is piecewise nonlinear with high-low-high three parts and the system with molecular spring isolator has low nature frequency during working. Therefore, molecular spring is suitable for heavy equipment with low frequencies.
    GPU-BASED DISCRETE ELEMENT MODELLING OF INTERACTION BETWEEN SEA ICE AND JACK-UP PLATFORM STRUCTURE
    Di Shaocheng, Ji Shunying
    2014, 46(4):  561-571.  DOI: 10.6052/0459-1879-13-400
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    During the interaction between sea ice and jack-up platform, the ice load is the key factor affecting vibration response and fatigue life of the structure. In this study, a discrete element method (DEM) with bonding-breaking function is developed to simulate the breakage characteristics of ice cover and the relative ice load on platform structure. According to the demand in the large scale DEM simulation between the sea ice and the jack-up platform structure with multi-legs, a parallel algorithm with high efficiency is established based on GPU (Graphical Processing Units) technique. In this algorithm, the element neighbor lists are generated with the sorting approach of cell index. The contact modes and contact forces between element-element and element-structure are determined. Meanwhile, the global ice load on jack-up structure can also be obtained. Moreover, the contact models between spherical element and cylindrical structure are also developed to determine the interaction between ice cover and jack-up structure. To validate this GPU-based DEM, the interaction between sea ice and conical jacket offshore structure is simulated and compared well with the field data in the Bohai Sea. Moreover, the ice loads on jack-up structure with multi-legs are simulated. The breakage characteristics of sea ice during the dynamic interaction and the ice loads on each structure legs are obtained. This GPU-based DEM can be applied to determine the ice loads on different offshore structures for ice-resisted structure design and ice-induced structure fatigue analysis.
    AN INTERNAL STATE VARIABLE VISCOELASTIC-VISCOPLASTIC CONSTITUTIVE EQUATION WITH DAMAGE
    Zhang Long, Liu Yaoru, Yang Qiang, Xue Lijuny
    2014, 46(4):  572-581.  DOI: 10.6052/0459-1879-13-387
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    Based on Rice internal state variable thermodynamics, the creep damage is discussed in constrained configuration space. An internal state variable viscoelastic-viscoplastic constitutive equation with damage under constant stress and temperature conditions is derived by giving specific complementary energy density function and evolution functions of internal state variables. Parameters identification and model validation are conducted under one dimensional scene through uniaxial creep test of analogue material by load and unload method. The proposed constitutive equation can describe viscoelastic strain and three phases of creep preferably. Different stages accompany with different energy dissipation processes. The material system without damage tends to thermodynamic equilibrium state or steady state after disturbing by stress. During creep damage process, the material system has a tendency that is from closing to equilibrium state or steady state to departing from equilibrium state. The energy dissipation rate can be a measure of distance between current state and equilibrium state of material system; the time derivative of energy dissipation rate can characterize development trend of system, and their integral value in domain can be regarded as indexes to evaluate the long-term stability of structure.

    THE NMM-BASED EFG METHOD AND SIMULATION OF CRACK PROPAGATION
    Liu Feng, Zheng Hong, Li Chunguang
    2014, 46(4):  582-590.  DOI: 10.6052/0459-1879-13-430
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    In order to solve continuum and discontinuous problems in a uniform way, the numerical manifold method (NMM) introduces two cover systems, i.e., the mathematical cover (MC) and the physical cover (PC). By constructing the MC with the node influence domains in moving least squares interpolation (MLS) as the mathematical cover, the Element Free Galerkin method in the setting of NMM is proposed, named NMM-EFG. The NMM-EFG can easily deal with continuum and discontinuous problems while the pre-processing becomes very easy. A scheme for simulating crack propagation under the small deformation and the large deformation conditions is developed. By the treatment of kinked cracks, the crack can grow at arbitrarily small step without mesh refinement. Compared with results from large deformation, the results from small deformation might be prone to unsafe evaluation.
    A PROBABILITY AND INTERVAL HYBRID STRUCTURAL RELIABILITY ANALYSIS METHOD CONSIDERING PARAMETERS’ CORRELATION
    Jiang Chao, Zheng Jing, Han Xu, Zhang Qingfei
    2014, 46(4):  591-600.  DOI: 10.6052/0459-1879-14-025
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    This paper proposes a mixed probability-interval uncertainty model considering correlation and a structural reliability analysis method which can solve problems of relevant variables. First, relevant angles of probability variables, probability-interval variables and interval variables are defined respectively in order to quantitatively describe the correlation between variables. Then through affine coordinates relevant variables are transformed into independent variables. A reliability analysis model is put forward, and a highly efficient method is built to solve the reliability index and failure probability interval. Finally two numerical examples are provided to verify the validity of the method.
    INVESTIGATION OF THE RELATION OF IMPORTANCE ANALYSIS INDICES FOR MODEL WITH CORRELATED INPUTS
    Song Jingwen, Lü Zhenzhou
    2014, 46(4):  601-610.  DOI: 10.6052/0459-1879-13-369
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    Nowadays, several importance analysis methods have been developed for model with correlated inputs. For choosing the most appropriate analysis methods to meet different requirements, it is necessary to make differences among these existing methods. In this paper, the importance indices, including the total, the structural and the correlative contributions, derived from the covariance decomposition, are firstly derived for the quadratic polynomial without interaction terms and the one with interaction terms. Then, based on these derived analytical solutions, the relation between the traditional variance based method and the newly covariance based method is explored. The results derived from the quadratic polynomials are then extended to general cases, and validated from the point of high dimensional model representation. Three examples are introduced for investigating the relation between the two groups of importance indices, and relative merits of each. The conclusions are instructive and meaningful to importance analysis and engineering design when the model inputs are correlated.
    A HIERARCHICAL PARALLEL COMPUTING APPROACH FOR STRUCTURAL STATIC FINITE ELEMENT ANALYSIS
    Miao Xinqiang, Jin Xianlong, Ding Junhong
    2014, 46(4):  611-618.  DOI: 10.6052/0459-1879-13-335
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    According to the architecture characteristics of distributed memory parallel computers, a hierarchical parallel computing approach for structural static finite element analysis is proposed. Based on the two-level partitioning and twice condensation strategies, the proposed method not only improves memory access rate through the distributed storage of a large amount of data, but also significantly improves communication rate with the three-layer parallelization of the computational procedure. Moreover, the interface equations' size is further reduced and its solution time is considerably reduced. Thus, it can improve the efficiency rates of parallel computing of large-scale problems by fully exploiting the architecture characteristics of distributed memory parallel computers. Finally, typical numerical experiments were used to validate the correctness and efficiency of the proposed method.
    PREDICTION OF MECHANICAL PROPERTIES OF FISH MUSCLE IN VIVO DURING STEADY SWIMMING
    Zhang Wei, Yu Yongliang, Tong Binggang
    2014, 46(4):  619-625.  DOI: 10.6052/0459-1879-14-053
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    This paper is a comparison study of the mechanical performance of the red muscle in vivo in cruise swimming of anguilliform and carangiform fishes, based on a global modeling of the integrated swimming mechanics. Given a lateral undulatory motion of the fish body, this modeling method could ascertain the external fluid force and the inertia force, and then indirectly predict the in vivo internal active muscle force and viscoelastic force due to the passive deformation of biological tissues. The results suggest that the strength of the caudal red muscle is significantly lower than that of the anterior in an anguilliform swimmer, while in a carangiform swimmer, the strength of red muscle is roughly equal in caudal and anterior part of the body. A higher energy efficiency is observed for a carangiform swimmer as a result of the different external forces experienced in the two swimming modes. It is also found that in both swimming modes, there exists an energy transmission from the anterior to the posterior, and the distribution of the net power produced by the active muscle along the fish body is characterized by a bell-shaped curve. Generally, the positive net power is produced at each axial position.
    STUDY ON AEROTHERMOELASTICITY OF A HYPERSONIC ALL-MOVABLE CONTROL SURFACE
    Yang Xiangwen, Wu Jie, Ye Kun, Ye Zhengyin
    2014, 46(4):  626-630.  DOI: 10.6052/0459-1879-13-415
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    An aerothermoelastic analysis of a hypersonic all-movable control surface, in which the effects of the axis and the gap were considered, was carried out based on the hierarchical solution process. The CFD (Computational Fluid Dynamics) method was firstly used to solve the N-S (Navier-Stokes) equations and get the thermal environment around the control surface. Then the wall heat flux was calculated based on the surrounding temperature and the wall temperature. The heat conduction was solved using Fourier's law to obtain the structural temperature distribution. In addition, the structural inherent characteristics considering thermal stress and material degradation were analyzed. The unsteady aerodynamic forces were calculated through local flow piston theory based on CFD. Lastly the flutter was analyzed by state space method. The results show that changes of natural frequencies and pitches between the bending frequencies and the torsion frequencies due to the aerodynamic heating result in changes of the flutter speeds and the flutter frequencies; with heat conduction going on, the natural frequencies and the flutter frequencies become unchanged after a rapid decrease, and the pitches increase slowly after a rapid decrease; the natural frequencies and the flutter frequencies as well as the flutter speeds firstly decrease and then increase with time when only thermal stress takes effect; the axis and the gap can lead to decrease in the natural frequencies, the flutter frequencies and the flutter speeds and the maximum reduction reaches to 6%.
    PIV EXPERIMENTS ON FLOWFIELD CHARACTERISTICS OF ROTOR AIRFOIL DYNAMIC STALL AND MODIFICATIONS OF L-B MODEL
    Wang Qing, Zhao Qijun, Zhao Guoqing
    2014, 46(4):  631-635.  DOI: 10.6052/0459-1879-13-389
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    To investigate the flowfiled characteristics of airfoil dynamic stall, the advanced 3D-PIV technology was employed to measure the dynamic stall flowfield of helicopter rotor airfoil SC1095. It was found that the leading edge vortex convective velocity changed with the location of vortex. The dimensionless vortex velocity was 0.39 when the vortex was moving on airfoil surface, and was 0.55 at airfoil wake zone. Based on the different leading-edge vortex convective velocities, classical Leishman-Beddoes model was then modified, in which the vortex time constant in classical model is replaced by a time varying function. Comparing with the classical model, the peak of airfoil normal force coefficient calculated by the modified model was increased about 5%, and the negative peak of airfoil moment coefficient was promoted about 13%; both of these had better agreements with the experimental data, and it was demonstrated that the modified model gave a more reasonable physical meaning of airfoil leading edge vortex.
    RESEARCH OF AERO-DAMPING FOR BLUNT WITH SPIKE
    Ran Jinghong, Liu Ziqiang, Hu Jing, Zhao Zhenjun, Quan Xiaobo
    2014, 46(4):  636-641.  DOI: 10.6052/0459-1879-13-419
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    Basing on modal shape data, the aero-damping analysis method has been constructed with quasi-steady aerodynamics theory. The dynamic derivative experiments for a rigid model have been accomplished simultaneously for verification and validation of the present method. Then the computation of aero-damping and characteristics analysis have been carried out under the assigned conditions. It can be concluded that the method can be used for aero-damping analysis of spike, and all results are positive in research, which will repress the vibration of the system. There are some factors leading to negative aero-damping, and the factors have different contributions to the aero-damping values.
    A BRIEF INTRODUCTION OF COMPLETED KEY PROGRAM PROJECTS ON MECHANICS IN 2013
    Zhang Panfeng, Zhan Shige, Wang Lifeng, Xu Xianghong
    2014, 46(4):  642-646.  DOI: 10.6052/0459-1879-14-193
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    The paper brief introduced the completion and evaluation of 12 NSFC key program projects on mechanics in 2013. The detail projects list and the evaluation assessments provided by expert committee are given.