初始几何缺陷对薄圆环板弹塑性稳定性的影响

本文应用Neale关于增量边界值问题的广义变分原理,考察初始几何缺陷对薄圆环板弹塑性屈曲临界载荷的影响,计算表明,只要在J₂增量理论的解中计入初始几何缺陷的影响,所得的结果与几何理想圆环板在塑性形变理论下的分支性屈曲载荷十分接近.     

Nonexistence of a Globally Stable Supersonic Conic Shock Wave for the Steady Supersonic Isothermal Euler Flow

In this paper, for the full Euler system of the isothermal gas, we show that a globally stable supersonic conic shock wave solution does not exist when a uniform supersonic incoming flow hits an infinitely long and curved sharp conic body.     

Aerodynamic Interaction of Systems of Bodies in a Supersonic Flow

Use of numerical experiment methods gives broad opportunities for studying complex flows by rather simple and inexpensive means. This work is devoted to researches on aerodynamic interference of bodies in supersonic flows. Interest to similar problems is shown in a number of areas of modern mechanics: meteoritics, movement of multiphase media, applied fields. The head shock wave before a configuration of spheres with growth of distance h monotonously breaks up to individual shock waves before spheres of forward lines. The basic conclusion of this research is the following: distortion of supersonic stream around systems of bodies as though is transferred downstream, i.e. the influence of back bodies on the flow nearby forward bodies is small. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

超音速平板边界层转捩中层流突变为湍流的机理研究

采用空间模式,对来流Mach数为4.5的平板边界层转捩过程做了直接数值模拟．对结果进行的分析发现,在层流-湍流转捩的突变(breakdown)过程中,层流剖面得以快速转变为湍流剖面的机理在于平均剖面的修正导致了其稳定性特征的显著变化．虽然在层流下第2模态T-S波更不稳定,但在层流突变为湍流的过程中,第1模态不稳定波也起了重要作用．     

桩侧摩阻力对打入桩定向稳定性的影响

在本文中,把打桩时桩顶的锤击力作为一种周期荷载而导得Mathieu方程.从该方程的稳定界限,我们可求得桩的临界长度,也讨论了桩侧摩阻力对定向稳定性的影响.     

超声速气流中含灰气体点源流动特性

采用Lagrange方法，研究了超声速气流中含灰气体点源的流动特性，求得了对称轴附近激波层内的流动参数．计算数值模拟结果揭示了大惯性颗粒在激波层内沿着相互交叉的振荡轨迹运动，颗粒分布形成了高、低密度层交错出现的“多层结构”，而且粒子在轨迹包络线附近急剧聚集．     

Global Existence of a Shock for the Supersonic Flow Past a Curved Wedge

This note is devoted to the study of the global existence of a shock wave for the supersonic flow past a curved wedge. When the curved wedge is a small perturbation of a straight wedge and the angle of the wedge is less than some critical value, we show that a shock attached at the wedge will exist globally.     

The Effect of Structural Curvings on the Stress Distribution in a Rigidly Fixed Composite Plate under Forced Vibration

Based on the exact three-dimensional equations of continuum mechanics and the Akbarov-Guz' continuum theory, the problem on forced vibrations of a rectangular plate made of a composite material with a periodically curved structure is formulated. The plate is rigidly fixed along the Ox ₁ axis. Using the semi-analytic method of finite elements, a numerical procedure is elaborated for investigating this problem. The numerical results on the effect of structural curvings on the stress distribution in the plate under forced vibrations are analyzed. It is shown that the disturbances of the stress ₂₂ in a hinge-supported plate are greater than in a rigidly fixed one. Also, it is found that the structural curvings considerably affect the stress distribution in plates both under static and dynamic loading.     

Global Existence of Supersonic Flow Past a Curved Convex Wedge

In this paper we discuss the supersonic flow past a curved convex wedge. Our conclusion is that if the vertex angle of the wedge is less than a critical angle, the shock attached the head of the wedge is weak, and if the wedge is formed by a smooth convex curve, monotonically increasing, then the global solution of such a boundary value problem exists.     

Structural Changes in the Surface Friction Layer of a Polymeric Endoprosthesis Cup

A concept of creation of a polymeric insert for hip joint endoprostheses with the physiological and biomechanical properties typical of natural cartilage is proposed. The spherical friction surface of the insert is coated with a microporous layer imitating cartilage. This layer carries an electret charge, which improves the lubrication of the endoprosthesis with synovia and serves as a carrier of drugs, thus ensuring their prolonged discharge into the operation wound. Tribotechnical characteristics of an endoprosthesis with such an insert are investigated. It is shown that a drop in the friction coefficient of such a pair is accompanied by a change in the microrelief of the friction surface and in the degree of crystallinity of the material of the porous layer.     

The Initial Structure of Wing-Body Interaction in Supersonic Flow

A rigorous asymptotic expansion describing the initial structureof wing-body interaction in steady inviscid supersonic flowis obtained from the exact solution of a canonical problem.A further term is found for the velocity potential on the rootchord, and it is shown how two different asymptotic expansionsdue to Stewartson may be derived from an asymptotic expansionwhich is uniformly valid right up to the root chord.     

柱状固粒两相边界层流场稳定性研究

从运动方程和本构方程出发,推导得到了含柱状粒子两相流场的修正Orr-Sommerfeld方程,然后在边界层流场中,采用数值计算方法,得到了含柱状粒子流场的稳定性中性曲线,给出了流场失稳的临界雷诺数.结果表明在所述情况下,柱状粒子对流场起着抑制失稳的作用,而且抑制的程度随着柱状粒子体积分数和长径比的增加而提高.     

Damping of Vibrations in a SystemWith Two Beams by Structural Friction

This paper presents the results of tests on free and forced harmonic vibrations in a system with two beams with structural friction taken into account. The beams are clamped together with uniform unitary pressure. The hysteresis loop describing the frictional-elastic properties of the system has a form of a parallelogram. The autor created a mathematical model of the vibrating system with two beams. During free vibrations of the system, its damping characteristics were tested by a digital simulation method. The vibration damping decrement as a function of amplitude displacement was determined. When vibrations were harmonically forced, the amplitude - frequency characteristics of the system were determined numerically. The system was used as a nonlinear vibration damper in a linear system with a harmonic force. The equations of motion of the nonlinear two-degree of freedom system were solved by means of a digital simulation method. (© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)     

超声速流场中6自由度物体运动的模拟研究

物体在流场中自由运动的模拟有很广泛的应用,文章描述计算6自由度(6DOF)刚体在超声速流场中自由运动的一种方法.流体部分求解LES方程,亚网格模型为拉伸涡模型.激波和刚体边界周围区域采用迎风型WENO格式,湍流区域采用低数值耗散的TCD格式.时间推进采用三阶的SSP R-K法.刚体采用6自由度模型,刚体姿态用四元数来表示,控制方程为常微分方程,采用四阶Runge-Kutta法求解.文章给出若干算例来验证程序的有效性,结果理想.     

超声速流中含间隙和立方非线性二元机翼的动力学分析

研究超声速流中含间隙和立方非线性二元机翼的气动弹性响应．首先由二阶活塞理论得到了双楔机翼的气动力和气动力矩．然后由平均法得到了气动弹性方程的极限环响应,并用Floquet理论分析了极限环的稳定性．结果表明,间隙系统在超临界Hopf分岔的条件下也存在Fold分岔和幅值的跳跃现象．而后,数值解与平均法的结果进行了对比,两者吻合得很好．最后,详细研究了间隙参数对气动弹性响应的影响．     

Structural Stability for Two Convection Models in a Reacting Fluid with Magnetic Field Effect

This paper deals with two fundamental models for convection in a reacting fluid and porous medium with magnetic field effect. We demonstrate that the solution depends continuously on changes in the chemical reaction and the electrical conductivity coefficients. The continuous dependence is unconditional in two dimensions but conditional in three dimensions.     

Stability of the Poiseuille Flow in a Channel with Comb Grooves

The stability of the Poiseuille flow in a channel with longitudinal comb grooves on the lower wall is studied numerically. Dependences of the linear and energy critical Reynolds numbers on the groove spacing and height are obtained and analyzed. The results are compared with data available for wavy grooves, which tend to comb grooves as one of the groove parameters approaches infinity.