力学学报

Reflection and transmission of water waves past a rigid vertical thin barrier in a two-layer fluid

2005, 37(5): 529-541. doi: 10.6052/0459-1879-2005-5-2004-242

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Numerical simulations of flow around two circular cylinders in cruciform arrangement and two spheres in tandem arrangement by virtual boundary method

The virtual boundary method was applied to simulate the flow passing around two circular cylinders in cruciform arrangement at Re=150. Spatial structures of the flow wake are different at various spacing ratio. When the spacing ratio is greater than 3, for upstream cylinder, the influence of downstream cylinder is restricted in the region that the wake of downstream cylinder coexists, and out of this region the wake of upstream cylinder maintains a regular Karman vortex street. When the spacing ratio is smaller than or equal to 3, for upstream cylinder, the influence of downstream cylinder is expanded to the whole spanwise of the upstream cylinder wake, and obvious three-dimensional structures can be observed. In the case that spacing ratio smaller than or equal to 3, in the plane in near wake of downstream cylinder, four symmetrical vortices come into being. Other detailed parts of the flow field are addressed in this paper, and some macro-variables such as vortex shedding frequency, lift and drag coefficients are also calculated in this paper.

2005, 37(5): 542-550. doi: 10.6052/0459-1879-2005-5-2004-222

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2005, 37(5): 551-557. doi: 10.6052/0459-1879-2005-5-2004-179

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2005, 37(5): 558-563. doi: 10.6052/0459-1879-2005-5-2003-406

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Multi-Monte Carlo Methods for Inter-particle Collision

In the interest of improving collision arithmetic and decreasing computation cost, a new Multi-Monte Carlo (MMC) method for inter-particle collision is prompted. The particle motion is described by the Langevin equations, which is solved by Monte Carlo (MC) method. On the same time, Inter-particle collision is modeled by Direct Simulation Monte Carlo (DSMC) method. DSMC is coupled with forenamed MC method, as it is called Multi-Monte Carlo method. The simulation particle of MMC method is fictitious particle which number is far less than real particle. In order to form an integrated MMC method for inter-particle collision, a series of methods are developed, which include the restriction of the setting of time step, the guide line to judge in which control volume fictitious collision partner lies, the guide line to judge whether or not inter-particle collision event occurs, the choice rule of fictitious collision partner, and particle collision dynamics based on stochastic collision angle. Fine particles and heavy coarse particles flows are chosen as standard cases to validate MMC method. The simulation results of MMC methods are in good agreement with both theoretical solution and Direct Numerical Simulation (DNS), not only on macroscopical facets such as particle collision frequency but also on microcosmic facets such as the evolvement of particle fields. Numerical simulation proves MMC method for inter-particle collision not only has enough low computation cost but also gets to enough high computation precision.

2005, 37(5): 564-572. doi: 10.6052/0459-1879-2005-5-2004-240

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Asymptotic field of mode I dynamic growing crack in visco-elastic material

2005, 37(5): 573-578. doi: 10.6052/0459-1879-2005-5-2004-191

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Inhomogeneous plane waves and their energy dissipations in a liquid-saturated incompressible viscoelastic porous medium

2005, 37(5): 579-585. doi: 10.6052/0459-1879-2005-5-2004-048

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A new topology description function based approach for material design with prescribed properties

2005, 37(5): 586-592. doi: 10.6052/0459-1879-2005-5-2004-154

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Nonlinear finite element buckling analysis of tubing with weight in constant-curvature wells

2005, 37(5): 593-599. doi: 10.6052/0459-1879-2005-5-2004-116

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Asymptotic Analysis of Interaction of Closely-spaced Cracks

2005, 37(5): 600-605. doi: 10.6052/0459-1879-2005-5-2004-025

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Method of Centers for Multi-objective Optimization of Structures

This paper presents an efficient algorithm for multi-objective optimization of large-scale structures， which is a direct extension of the method of centers for solving general nonlinear programming. At each iteration, we define a 'moving target' for each objective function, to convert it to a level constraint and then the algorithm calculates the center of the intersection of level constraints and original constraints. Some examples are given to illustrate the proposed algorithm.

2005, 37(5): 606-610. doi: 10.6052/0459-1879-2005-5-2004-279

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Dynamic Optimization of Multibody System Dynamics and Adjoint Variable Method for Design Sensitivity Analysis

Dynamic optimization based on multibody system dynamics is a complex process, which composed of traditional analysis and simulation of multibody system dynamics, design sensitivity analysis and iterative processes of optimization. The mixed penalty function method of optimization is presented, which is based on general kinematical, dynamical analysis formulation, general objective functions and adjoint variable method. Finally, an example of simple spring/damper-mass system is given to test the method presented in this paper.

2005, 37(5): 611-619. doi: 10.6052/0459-1879-2005-5-2004-113

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First-passage problem for Coupled Duffing-van der Pol Systems Subject to Gaussian Excitation

In this paper, the stochastic average method for stochastic and dissipative quasi-non-integrable Hamiltonian system is applied to study the first-passage problem of coupled Duffing-van der Pol system subject to Gaussian white noise excitation. First, a backward Kolmogorov equation for the conditional reliability function and a generalized Pontryagin equation for the conditional moment of the first-passage time are established. Then according to the classification of the boundary conditions and initial conditions of these two kinds of equations, the reliability of system response under external excitation combined with parametric excitation and pure parametric excitation are analyzed respectively in detail. At last, numerical results for reliability function, the probability of first-passage time and mean first-passage time of system in virtue of figures.

2005, 37(5): 620-626. doi: 10.6052/0459-1879-2005-5-2004-372

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2005, 37(5): 627-631. doi: 10.6052/0459-1879-2005-5-2003-354

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Simulation of Supersonic or Hypersonic Aeroelasticity Basing on Local Piston Theory

Existing piston theory for supersonic flow can only deal with thin supersonic wing with sharp leading edge at small angles of attack. The unsteady CFD technology basing on Euler/N-S equations can solve the unsteady aerodynamic loads precisely, but it often needs much computational time even just for a simple 3D shapes. Local piston theory basing on steady CFD technology has a good precision and high efficiency to compute the supersonic or hypersonic unsteady pressure by comparing the piston theory and unsteady Euler code. Coupling the structure equations, the supersonic or hypersonic aeroelasticity is simulated in time domain. The computed flutter precision of local piston theory is higher than original piston theory by comparing with the experimental data. The non-linear characteristics of the flutter speed with increasing Mach number and increasing anger of attack of a typical wing are studied. The computed flutter results by local piston theory agree with the theoretic analysis and are better than original piston theory at high Ma numbers.

2005, 37(5): 632-639. doi: 10.6052/0459-1879-2005-5-2004-263

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In this paper, numerical simulation results of turbulent supercavitating flow were presented, which were using the Navier-Stokes equations with two equations' turbulence model and the developed Kubota cavity model. To assess our numerical method, several cavitating flows over the hydrofoil were computed and the numerical results were compared with experimental results. It shows that the numerical results by the present cavity model agreed with the experimental results very well. Then, the wonderful phenomenons of cavitating and supercavitating flows around the NACA0015 hydrofoil and an axisymmetric body were displayed.

2005, 37(5): 640-644. doi: 10.6052/0459-1879-2005-5-2004-272

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Comments on the calibration technique of the projected contact area of nanoindentation tester

The nanoindentation test techniques especially the O&P method are analyzed and the nanoindentation tests are implemented. The analysis focuses on the determination of the contact area and the depth region of the application. Analysis results show that a common area formula for all materials justified only at large indentation depth, and such a universal formula may lead to larger errors at small depth. Hence hardness values measured at small indentation depth based on O&P method must be used with care.

2005, 37(5): 645-652. doi: 10.6052/0459-1879-2005-5-2004-304

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2005, 37(5): 653-657. doi: 10.6052/0459-1879-2005-5-2003-121

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Dynamics characteristics of edge dislocation in Mo by molecular dynamics

This investigation simulates the dynamics characteristics of edge dislocation in BCC crystal Mo under different temperature and abrupt shear strains by molecular dynamics (MD) simulation. Results show a decrease of mobility with increasing temperature, namely the drag force increased with increasing temperature and decrease with increasing loading. A stationary dislocation can surmount the wave velocity under an abrupt shear strain in crystal Mo in this simulation. Results indicate that there are three wave speeds in the [111] direction in which the dislocation moved. The movement of the edge dislocation when it surmounts the transverse wave speed and drops to subsonic is pictured.

2005, 37(5): 658-661. doi: 10.6052/0459-1879-2005-5-2004-430

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Failure theory and reliability analysis of structural system considering static strength and fatigue

The elements of structural system subjected to dead and fatigue load will be dead or fatigue load failure by any possibility. Based on the understanding of passive impact of accumulated damage induced by fatigue load on ultimate bearing capacity, the ultimate bearing capacity reliability analysis method for structures subjected to fatigue load was presented. The paper analyzed dead or fatigue load failure of every element of structural system and considered the relativity of two failure modes influencing on the element reliability. The paper discussed the failure theory of structural system subjected to dead and fatigue load and gave the method of reliability analysis considering static strength and fatigue. A numerical example is analyzed. It is indicated that the influence on the structural system by dead and fatigue load is different at the different using state, the failure forms of elements in the significant failure paths have dead and fatigue load failure. It is suitable for engineering case.

2005, 37(5): 662-666. doi: 10.6052/0459-1879-2005-5-2004-531

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A homotopy technique with the parameter expansion and its application

2005, 37(5): 667-672. doi: 10.6052/0459-1879-2005-5-2004-129

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2005 Vol. 37, No. 5

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