力学学报

An experimental study on forebody vortex flow control technique using combined perturbation

Yankui Wang, Zhanfeng Wei, Xueying Deng, Tao Huang, Xingzhi Ding

The control capability of aircraft forebody asymmetric vorticeswith micro-triangle and the effect of blowing on lee side on asymmetricvortices are discussed in this paper. A new kind of active controltechnique, the perturbation-combined active control technique, whichcombines the micro-triangle and micro-blowing perturbation, is proposed onthe basis of the above discussion. The test was conducted in the D4 wind tunnel inBeijing University of Aeronautics and Astronautics. The result shows thatthis perturbation-combined control technique is effective forcontrolling the side-force of aircraft with a high attack angle.

2007, 23(4): 433-441. doi: 10.6052/0459-1879-2007-4-2006-171

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Investigation of the performance of a new recipe of spacer for sea-water drilling fluids by means of laboratory and in-situ experiments

Jifu Zhou, Dongqing Liu

Spacer is one of the crucial factors influencing the quality of wellcementing. It is particularly important to choose right ingredients of the spacerfor well cementing in sea-water drilling fluid. The paper proposes a new recipe of spacer and studies itsperformance in laboratory. The experimental results demonstrate that the newspacer works well with the environmental fluids, such as sea-water drillingmud, cement slurry and salty water. It can stabilize the wall ofthe well. And, with carefully chosen solid particles and surfactantsin the recipe, the spacer fluid can efficiently used to wash the wall of thewell, especially, for the mud cake. Furthermore, in-situ experimentswereconducted in Shengli Oilfield, Shangdong Province, China. The results showthat the new spacer fluids can shorten the mixing length of the drilling mudand the cement slurry, and can evidently improve the quality of the secondinterface of the cement annulus.

2007, 23(4): 442-448. doi: 10.6052/0459-1879-2007-4-2006-275

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Hamiltonian formulation of axisymmetrical liquid jets

Zhi Li

It is shown that the governing equations describing thepotential motion of axisymmetrical liquid jets have a Hamiltonian structure.Round and annular jets are discussed. The Hamiltonian is the total energy ofthe jet, and the expressions for the canonical variables are given.

2007, 23(4): 449-454. doi: 10.6052/0459-1879-2007-4-2005-508

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The characteristic of precursor film in Navier-Stokes equations frame

Xiongping Luo

This paper studies a model for a fluid lumpspreading with a precursor film. In the description, the fluid lump and theprecursor film are calculated as a whole using order parameter coupledNavier-Stokes equations, CHW (Cahn, Hilliard and van der Waales) equationand GNBC (Generalized Navier boundary condition). The fluid lump spreads underthe actions of certain long-range force -VW (van der Waals) intermolecularlong-range force, surface tension and viscous force. A film of nanoscopicthickness emerges as VW force reaches a certain value. The profile of thefilm after spreading a long time approaches to $1/x$ power law, which agreeswell with the theoretical results of Ref.[1]. The frontal position of thefilm is found to has a power-law dependence on time, which is also shown inthe results of some experiments[6]. The interfacial stretching has apower-law dependence on time as well. The exponent of the later is a littlebigger than that of the former.

2007, 23(4): 455-459. doi: 10.6052/0459-1879-2007-4-2006-437

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Effect of silane on ignition characteristics of JP10 and kerosene as shown in shock tube study

Su Wang, Bingcheng Fan, Yuzhong He, Jiping Cui

On the basis of the ignition experiments of JP10 and kerosene, experimentswere carried out to study the effect of silane addition on ignitioncharacteristics of these two typical heavy hydrocarbon fuels behindreflected shock waves over the temperature range of 880$\sim$1800K and pressurerange of 0.16~0.53MPa.A longer observation time is required as the ignition time increases at thelower temperature region. The shock tube worked under conditions for atailored interface, resulting in an observation time of about 7ms, and thelower temperature bound of experiments was extended in the current study.The uncertainty in the concentration of the fuel vapor due to the adsorptionof the fuel vapor on the shock tube wall is one of the largest sources oferrors in ignition time measurements of heavy hydrocarbon fuels, thus thegaseous concentrations of JP10 and kerosene were determined in the shocktube by measuring the gas pressure with a high-precision vacuum gaugecombined with gas chromatography. Since kerosene is a complex mixture ofmany hydrocarbon components, the adsorption content of differentcomponents differs, so the gas composition different from the liquidcomposition. In the present study, a simulant modified fuel for kerosene wasprepared by adding some heavy hydrocarbon components into the originalkerosene in proportion to the adsorption content to compensate the loss inthe gas phase through the adsorption. To minimize the degree of adsorptionand increase the test fuel vapor pressure, the shock tube was preheated andmaintained at 70 C throughout the experiments. The conditions behindthe reflected shock were calculated from the incident shock speed using theone-dimensional shock relations. A quartz window was installed on thesidewall very close to the endplate of the driven section to monitor theemission from the ignition process in the reflected shock region. Theemission focused through a lens was detected by using a photomultiplierafter passing through a monochromator centered at the emission line of OHradical at 306.5nm as a marker to identify the instant of ignition.When the molar ratio of the added silane with the fuel was in the range of10%$\sim$15{%}, the corresponding mass ratio was 2%~3{%}, a significantreduction in the ignition delay time was observed experimentally. Anincrease of the additionof silane shortened the ignition delay for JP10 at the lower endof temperature range studied. Specifically, the ignition time for JP10decreased from 3.7 to 0.87ms at 1100K and from 0.17 to 0.10ms at1500K. By contrast, the addition of silane shortened the ignition delay for kerosenethroughout the temperature range considered. Specifically, the ignition timefor kerosene decreased from 3.6 to 0.91ms at 1000K and from 0.75to 0.16ms at 1220K. The results presented herein are useful for the engine design andfuel selection in supersonic combustion researches, and also can be used tovalidate chemical kinetics models of heavy hydrocarbon fuel combustion withsilane addition.

2007, 23(4): 460-465. doi: 10.6052/0459-1879-2007-4-2006-462

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Simulation of flame spread over thin solid fuel under microgravity using narrow channel on ground

Xia Zhang

The simulation of flame spread over thin solid fuel undermicrogravity with narrow channel was analyzed with dimesion theory and validated experimentally by using flame spread picture recording. The resultshows that the qualitative simulation of microgravity combustion on groundcan be achieved with reducing the size of test section. The trends of theflame spread rate varying with flow velocity in vertical and horizontalnarrow channels are quite different. The natural convection in horizontalnarrow channel is effectively suppressed, while that in vertical channel isnot.

2007, 23(4): 466-472. doi: 10.6052/0459-1879-2007-4-2005-555

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Mixed finite element method for generalized convection-diffusion equations based on implicit characteristic-based algorithm

Wenhua Wu, Xikui Li

A mixed finite element method for generalized convection-diffusion equationsis proposed. The primitive variable with its spatial gradient and thediffusion flux are interpolated as independent variables. The variational(weak) form of the governing equations is given on the basis of the extendedHu-Washizu three-field variational principle. The mixed element isformulated with stabilized one point quadrature scheme and particularlyimplicit characteristic-based algorithm for eliminating spurious numericaloscillations. The numerical results show good performances in accuracyand efficiency of the proposed mixed element in comparison with a standardfinite element.

2007, 23(4): 473-478. doi: 10.6052/0459-1879-2007-4-2006-257

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Three-point microbend size effects for pure Ni foils

Xiuyan Feng, Xianghua Guo, Daining Fang, Ziqiang Wang

The three-point microbend tests are performed for the pureNi foils with different thicknesses. The deflection and load are measured byemploying the sequence pulse counting method and a high sensitive microload-sensor, respectively. All experimental results are analyzed usingcouple stress theory by Fleck and Hutchinson in which only rotation gradientis considered. Based on the plane-strain model we have derived the differentialequations and boundary conditions, which include the effect of couplestress. The differential equations are solved by the Runge-Kutta method. Thenumerical results are compared with the experimental data. There is no anyfitting parameter in the present theoretical calculation. All materialparameters are taken from the experimental measurements. The length scale istaken from the work of Stolken and Evans [2]. The present theoreticalpredictions are in good agreement with the experimental data.

2007, 23(4): 479-485. doi: 10.6052/0459-1879-2007-4-2006-274

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3D flanging and blank shape prediction for sheet metal based on one-step inverse FEM

Xiangkui Zhang, Yidong Bao, Ping Hu, Sibo Hu, Zhikui Lang, Yu Wang

In this paper, a fast simulation scheme for 3D curve binderflanging and blank shape prediction for sheet metal based on one-step inversefinite element method is proposed, in which the total deformation plasticity theory andproportional loading assumption are used. The scheme can be actually used tosimulate 3D flanging with complex curve binder shape, and suitable forsimulating any type of flanging model by numerically determining the flangingheight and flanging lines. Two typical 3D curve binder flangingprocesses includingstretch and shrink characters are simulated at the same time by using thepresent scheme and incremental FE non-inverse algorithm based on incrementalplasticity theory, which show the validity and high efficiency of thepresent scheme.

2007, 23(4): 486-494. doi: 10.6052/0459-1879-2007-4-2006-500

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A new smeared stiffener theory for grid-stiffened composite panels

Decai Wu, Yuanming Xu, Tianpeng He

An improved basic mechanical hypothesis was proposed toaccount for the mechanical behavior of grid stiffened composite panels.Withsuch hypothesis, a new smeared stiffener approach was developed toeffectively take into consideration the stiffener-skin interaction effects.The parametrized representation of grid unit cell was described, and thecorresponding mechanical model was estabilished. Such generalized model canbe used for global buckling analysis of grid-stiffened structures withdifferent types of grid layouts. Therefore, it is very useful for aerospacestructural design. Using Rayleigh-Ritz method combined with the developedsmeared stiffener approach, the eigen function for the globalbuckling load of grid stiffened panels was derived. Finally, various testexamples with different grid patterns were analyzed and the results werecompared with those obtained with existing methods. It is shown that the developedapproach has better accuracy and thus can be used foroptimal design of grid stiffened composite structures.

2007, 23(4): 495-502. doi: 10.6052/0459-1879-2007-4-2006-221

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Finite element modelling and shape control for piezoelectric composite plates under thermal load

Jianping Jiang, Dongxu Li

The deformation induced by thermal loads in flexible spacestructures may be actively compensated using piezoelectric materials. Inorder to develop the finite element formulations coupled withthermo-mechanical-electric effects, the refined higher order displacement field, thehigh order electrical potential field and the linear temperature field wereadopted. The numerical examples of the piezoelectric bimorph beam andcomposite plate were taken. The parabolic through-thickness distributionof electric potential at the middle of the beam is found by the presentmodel, which is different from the linear distribution assumption. Numericalexamples show that the present model can well predict the thermaldeformation with or without active compensation and the voltage of sensor, all ingood agreement with those from literature. The pyroelectric effects mayinfluence the structural deflection and sensor's voltage significantly.

2007, 23(4): 503-509. doi: 10.6052/0459-1879-2007-4-2006-522

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Application of hypersingular integral equation method to a three-dimensional crack perpendicular to the interface in electromagnetoelastic bimaterials

Bojing Zhu, Taiyan Qin

This paper proposes a hypersingular integral equation method toanalyze the three-dimensional mixed-mode crack perpendicular to theinterface in anisotropic electromagnetoelastic (EME) bimaterials underextended electro-magneto-elastic coupled loads through theoreticalanalysis and numerical simulations. Using the Green's functions, the generalextended displacement solutions of three-dimensional mixed-mode crackmeeting the interface in anisotropic EME bimaterials under extended loads isanalyzed by the boundary element method. Then this crack problem is reduced tosolve a set of hypersingular integral equations coupled with boundaryintegral equations. The exact analytical solution of the extended singularstresses and extended stress intensity factors near the crack front areobtained. At last, a numerical method for the hypersingular integral equationfor a three-dimensional mixed-mode rectangular crack subjected to extendedloads by the body force method is proposed. Numerical solutions of theextended stress intensity factors of some examples are obtained.

2007, 23(4): 510-516. doi: 10.6052/0459-1879-2007-4-2006-417

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Viscoelastic properties of chondrocytes isolated from normal and osteoarthritic rabbit knee cartilage

Weiyi Chen, Quanyou Zhang, Xiaochun Wei, Xiaohu Wang, Xiaona Li

This study uses the micropipette aspiration techniquecoupled with a viscoelastic solid model to investigate the viscoelasticproperties of chondrocytes isolated from normal and osteoarthritic rabbitarticular cartilage. Rabbit osteoarthritic model obtained by anteriorcruciate ligament (ACL) transection is used to simulate the pathologicalevents associated with OA. The average grades for normal and osteoarthriticcartilages are found to be higher in the ACL transection joints than in normal joints($p<0.005$). The experimental results show that the mean diameters ofchondrocytes from normal and OA cartilage are 14.85$\pm $2.218$\mu$m and14.38$\pm$1.909$\mu$m, respectively, and are not significantly different($p>0.05$), however, OA chondrocytes see a significantly lowerequilibrium modulus, instantaneous modulus and apparent viscosity($E_{\infty }=0.257\pm 0.091$\,kPa, $E_{0}=0.455\pm 0.182$\,kPa,$\mu =0.386\pm 0.136$\,kPa$\cdot $s, $n=67$) compared with normal chondrocytes($E_{\infty }=0.366 \pm 0.07$\,kPa, $E_{0}=0.653\pm 0.095\,1$\,kPa,$\mu =6.360\pm 1.121$\,kPa$\cdot $s, $n=52$) ($p<0.000\,1$). Theanalyses of correlation indicate no dependence of the viscoelasticparameters on the cell diameter or on the ratio of cell diameter tomicropipette diameter for cells from normal or OA chondrocytes($p>0.05$) except for the equilibrium modulus ($E_{\infty }$) of normal chondrocytes($p<0.05$).

2007, 23(4): 517-521. doi: 10.6052/0459-1879-2007-4-2006-466

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Relative motion around displaced solar orbit

Shengping Gong, Junfeng Li, Yunfeng Gao, Hexi Baoyin

This paper investigates the formation flying around a displaced orbit.The equation for relative motion is derived. Since the displacement betweentwo different solar sails is very small compared with the displacement fromthe sails to the sun, the equation of motion is linearized around thenominal displaced solar orbit to obtain a linear equation. Based onthe linear equation, three formation control strategies are discussed,including the passive control strategy. This strategy has the advantagesof simplicity and large stable region. Simulations based on thenonlinear equaiton are given. The results show that strategies canrealize the formation around the displaced solar orbit.

2007, 23(4): 522-527. doi: 10.6052/0459-1879-2007-4-2006-254

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Nonlinear behaviors of a drop undergoing large amplitude oscillatory shear flow

Quan Chen, Wei Yu, Chixing Zhou

Nonlinear viscoelastic behavior of immiscible polymer blends in largeamplitude oscillatory shear flow (LAOS) is partly due to nonlinearmorphological evolution of its interface. In order to understand theinterfacial evolution of immiscible polymer blends in LAOS, aconstitutive model by Yu and Bousmina$^{[5]}$ is used. Its predictingresults are compared with both the experimental and theoretical resultsof previous studies. As a result, it is found that YB model canreasonably reproduce the experimental results in the evolution of droplength and orientation angle. In addition, a detailed discussion isgiven on the evaluation of nonlinearity of the interface.

2007, 23(4): 528-532. doi: 10.6052/0459-1879-2007-4-2006-346

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Gigahertz oscillation of coaxial cylindrical tubes driven by Casimir and electrostatic forces

Haijun Li, Wanlin Guo

With the development of nano electromechanical systems,ultrahigh frequency mechanical oscillators are in great demand. Tomeet this demand, a mechanical oscillator model of double-walled coaxialcylindrical tubes is proposed. The oscillation frequencies of the modeldriven by Casimir and electrostatic forces are evaluated, respectively, bycontinuum mechanics. It is found that when the tube gap of the model reaches1 nanometer scale, the frequencies of the model can reach or even exceed theorder of GHz under ideal situations, whether driven by Casimir force or byelectrostatic force. The present work proves that it is feasible in theoryto achieve GHz oscillators driven by Casimir force or electrostatic force.

2007, 23(4): 533-537. doi: 10.6052/0459-1879-2007-4-2006-381

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Propagation Characteristic of High Frequency Longitudinal Guided Waves in Steel Rod

Cunfu He, Yaxin Sun, Bin Wu, Xiuyan Wang, Zenhua Liu

The attenuation dispersion curve and group velocitydispersion curve of ultrasonic guided waves in steel rod are calculatedwith consideration of the attenuation. Propagation characteristics of highfrequency longitudinal modes between 1MHz~3MHz in steel rod arestudied. In theory, there is one attenuation minimum in every high orderlongitudinal mode whose attenuation is the smallest in all modes at thespecial high frequency. The high order mode at this special frequency canpropagate a longer distance than other modes at the same frequency. Thisindicates that high frequency low attenuation longitudinal mode at thisspecial high frequency can be used for the inspection of steel rod. Theexperiments on steel rod of 22mm in diameter, 2m in length arecarried out usingultrasonic guided wave. Guided wave signals are excited andreceived by the same probe at the same end of the rod. The group velocityand amplitude curves of first endreflection against frequency are obtained. The experimental curves areconsistent with those dispersion curves of theory. This indicates that thedispersion curve of steel rod with consideration of attenuationcharacteristics can be a guidance to experiment.

2007, 23(4): 538-543. doi: 10.6052/0459-1879-2007-4-2006-271

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Dynamic response of viscoelastic half-space under moving loads

Huafei Zhou, Jianqun Jiang

To investigate high-speed train induced subground vibrations,viscoelastic half-space under moving loads was used to model thesubground under passing trains. Analytical solutions for displacements ofthe viscoelatic half-space were obtained using Green's function method forvarious moving loads, including constant and harmonic point, line and areaload. All velocity cases including the subsonic, transonic and supersonicvelocities were considered. Coupled IFFT algorithm and adaptive quadraturealgorithm were employed to compute double integrals in the analyticalsolutions. Numerical results for displacements induced by constant movingpoint load were presented in this paper as examples. The effects ofvelocity on the distribution and the maximum value of displacements were discussed. Itis found that the distribution and the maximum value of displacements varysignificantly as velocity increases beyond Rayleigh wave speed.

2007, 23(4): 545-553. doi: 10.6052/0459-1879-2007-4-2005-460

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The ICM method for continuum structural topology optimization with condensation of stress constraints

Yunkang Sui, Hongling Ye, Xirong Peng, Xuesheng Zhang

In order to overcome the difficulties of large number ofstress constraints and high cost in calculating the stress sensitivitiesin the topology optimization with stress constraints, this paper proposesthe ICM method for structural topology optimization with condensation ofstress constraints. Using the theory of Mises strength totransform stress constraints into strain energy constraints, two approachesare proposed for condensation of stress constraints. One is globalization ofstress constraints, the other is integration of stress constraints. Thenthe optimal model with a weight objective and condensed strain energyconstraint is established, and the dual theory is used in the optimal model ofcontinuum structure to obtain the numerical solution. Four examples show thatthe method has high computational efficiency and a reasonable optimaltopology can be obtained. In addition, this method is valid not only fortwo dimensionalcontinuum structure but also for three dimensional continuum structure.

2007, 23(4): 554-563. doi: 10.6052/0459-1879-2007-4-2006-043

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Reliability sensitivity algorithm based on line sampling

Shufang Song, Zhenzhou Lu, Lin Fu

In this paper, reliability sensitivity algorithm based online sampling is presented. In the line sampling for structural reliabilityanalysis, the failure probability Pf of structure is calculated byaveraging the failure probability Pfj (j=1,...,N) corresponding toeach simulated sample. From Pf in the linesampling, the reliability sensitivity of Pf with respect to thedistribution parameter \theta , i.e. \partial Pf / \partial \theta , canbe calculated by averaging \partial Pfj / \partial \theta , and\partial Pfj / \partial \theta can be obtained by using the analyticalrelationship between Pfj and \theta . The expressions of \partialPfj / \partial \theta and \partial Pf / \partial \theta are derivedin detail. With the use of the line sampling, reliability sensitivity algorithmenjoys the advantages of the line sampling, such as high precision,high efficiency and wide applicability in high dimensions and multiplefailure modes. Examples are used to show the advantages of thepresented reliability sensitivity algorithm.

2007, 23(4): 564-570. doi: 10.6052/0459-1879-2007-4-2006-220

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Molecular dynamics simulations of interfacial crack nucleation and propagation

Fulin Shang, Takayuki Kitamura

Molecular dynamics (MD) simulations are carried out to studythe critical conditions for crack nucleation at the interface edges andfor crack propagation along the interface, and theirrelations. MD method is employed to examine the fracturebehaviors near the apexes of the interface edges and near the tip of theinterface crack, with the outer boundaries of the simulation cellsbeingconstrained by the elastic finite element displacement fields. Thesimulation results show that, at the instant of fracture initiation, themaximum stresses along the interfaces reach the ideal strength of theinterface; also their interface energies can just overcome the intrinsiccohesive energy of the interface material. Therefore, thefracture conditions for crack nucleation at the interface edges and forcrack propagation along the interface could be correlated through either theideal strength or the cohesive energy of the interface. Further, a unifiedcriterion for interface fracture initiation is proposed based on thesimulation results.

2007, 23(4): 571-576. doi: 10.6052/0459-1879-2007-4-2006-199

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