Eléments finis stochastiques en élasticité linéaireA stochastic finite element method in linear mechanics

The stochastic finite element method presented in this Note consists in representing in a probabilistic form the response of a linear mechanical system whose material properties and loading are random. Each input random variable is expanded into a Hermite polynomial series in standard normal random variables. The response (e.g., the nodal displacement vector) is expanded onto the so-called polynomial chaos. The coefficients of the expansion are obtained by a Galerkin-type method in the space of probability. To cite this article: B. Sudret et al., C. R. Mecanique 332 (2004).     

考虑施工进程的高层建筑结构计算程序

本文克服了以往在计算高层建筑结构内力怀变形时由于只考虑整体一次加载而造成的误差，今采用结构逐层形成、逐层加载的计算模式，较好地模拟耻实际施工的进程，使计算结果能更好地任命真实的内力分布情况，同时在编制程序中，对总刚的分解作了适当处理，以避免许多重复计算，使结构逐层形成和结构整体一次加载下的计算能有机结合起来，从而提高了程序的运行速度。同时又可大大提高程序的使用范围，使得程序能在ＩＢＭＰＣ２８６及以     

Heat conduction in a rock mass with an annular hot water store

Vast subterranean caverns may be used for hot water storage in distinct heating schemes; such caverns can be annular, with a central pillar. This paper considers the quasi-steady solution of the heat conduction equation for this geometry with periodic temperature variations     

Force–displacement relationship in micro-metric pantographs: Experiments and numerical simulations

In this paper, we reveal that the mathematical discrete model of Hencky type, introduced in [1], is appropriate for describing the mechanical behavior of micro-metric pantographic elementary modules. This behavior does not differ remarkably from what has been observed for milli-metric modules, as we prove with suitably designed experiments. Therefore, we conclude that the concept of pantographic microstructure seems feasible for micro-metrically architected microstructured (meta)materials as well. These results are particularly indicative of the possibility of fabricating materials that can have an underlying pantographic microstructure at micrometric scale, so that its unique behavior can be exploited in a larger range of technological applications.     

The Kinematics of Plate Models: A Geometrical Deduction

We present a deduction of the Kirchhoff–Love and Reissner–Mindlin kinematics of a simply-connected plate by using the formal asymptotic development method applied to the compatibility conditions of Saint-Venant and the formula of Cesàro–Volterra. This formal deduction is purely geometrical because we do not use any information coming from the loading or the constitutive behavior.      

Point-source spark shadowgraphy at the historic birthplace of supersonic transportation

About a decade after its foundation, the most advanced ballistics laboratory in Germany at the time, the Kruppsche Schiessplatz, was utilized by Ernst Mach in 1888. His intent was to validate his pioneering shock wave research using military shells as supersonic vehicles. The 125th anniversary of the Schiessplatz was celebrated in 2002. Along with Machs research, it served to initiate the field of supersonic transportation technology. The specific subject of this paper is the application of point-source spark shadowgraphy at the same laboratory in the 1970s to visualize gas flow over aeroballistic projectiles. However, different from Machs original interest, the new purpose of spark photography at that time in the ballistic ranges of the German Bundeswehr was to find technical solutions to aeroballistic problems when field-testing gave incomplete answers. Both a qualitative and a quantitative understanding of the principles of aeroballistics were sought in this research.Received: 3 February 2003, Accepted: 30 June 2003, Published online: 2 September 2003An abridged version of this paper was presented at the 13th American Physical Society Topical Conference on Shock Compression of Condensed Matter at Portland, Oregon, from July 20 to 25, 2003     

Active Longitudinal Control of Wind-Induced Oscillations of a Suspended Cable

Abstract. Active control of oscillations of a suspended cable under transversal wind, described by a constant term and a fluctuating turbulent component, is dealt with. Control of transversal in-plane and out-of-plane oscillations is performed by imposing a longitudinal motion to one support; the control law depends, linearly or quadratically, on measures of displacement and velocity of a selected point. First, the steady-state oscillations around the planar static configuration, determined by the wind constant component, under sinusoidal in-plane and out-of-plane loading are studied, showing the nonlinear behaviour in the regions of primary and parametric resonance and the effects of the control action. Afterwards, attention is focused on the response of the cable to transversal wind turbulence, whose fluctuating component is described by a random process with an assigned spectral density. The effectiveness of longitudinal control is analysed by means of numerical investigations.Sommario. Si analizza il controllo attivo delle oscillazioni di un cavo sospeso, sottoposto all'azione di un vento agente in direzione ortogonale al piano del cavo e descritto mediante un termine di carico costante ed una componente variabile di turbolenza. Il controllo delle oscillazioni piane e spaziali viene realizzato mediante spostamento longitudinale di uno degli appoggi; la legge di controllo dipende linearmente o quadraticamente da misure di spostamento e velocità di un punto prescelto. In una prima fase, vengono studiate le oscillazioni stazionarie sotto carichi sinusoidali agenti rispettivamente nel piano e fuori del piano del cavo, intorno alla configurazione di equilibrio statico determinata dalla presenza della componente costante del vento, mostrando il comportamento nonlineare nelle regioni di risonanza primaria e parametrica e gli effetti dell'azione di controllo. Successivamente, si focalizza l'attenzione sulla risposta del cavo alla componente trasversale di turbolenza del vento, la quale è descritta da un processo stocastico a media nulla con densità spettrale assegnata. L'efficacia del controllo viene analizzata attraverso un'indagine numerica.     

SiC粒子非均布引起铝基复合材料的损伤分析

 根据电镜断面考察结果，以Gurson模型为本构方程的有限单元 法对包体模型及三维非均匀模型进行了详细分析. 为了评价应力-应变 关系及损伤的主要因素，考虑了基体中SiC粒子的体积率和径比的非均 匀分布. 其结果表明，用这种非均匀模型能很好地仿真铝基体在大量塑 性变形之后所发生的韧窝破坏过程. SiC粒子体积率、径比及其位置的 非均匀性，对局部和整体损伤过程与应力-应变关系的影响相当大. 当 Sic粒子径比为1.0，并在基体中均匀分布时，断裂应变会大幅度增大.     

Global stability analysis of a 90°-bend pipe flow

The present work investigates the stability properties of the flow in a 90°-bend pipe with curvature $\delta =R/R_c=1/3$, with R being the radius of the cross-section of the pipe and $R_c$ the radius of curvature at the pipe centreline. Direct numerical simulations (DNS) for values of the bulk Reynolds number ${\mathit{Re}}_b=U_{b}D/\nu$ between 2000 and 3000 are performed. The bulk Reynolds number is based on the bulk velocity $U_b$, the pipe diameter D, and the kinematic viscosity $\nu$. The flow is found to be steady for ${\mathit{Re}}_b⩽2500$, with two main pairs of symmetric, counter-rotating vortices in the section of the pipe downstream of the bend. The presence of two recirculation regions is detected inside the bend: one on the outer wall and the other on the inner side. For ${\mathit{Re}}_b⩾2550$, the flow exhibits a periodic behaviour, oscillating with a fundamental non-dimensional frequency $\mathit{St}=\mathit{fD}/U_b=0.23$. A global stability analysis is performed in order to determine the cause of the transition from the steady to the periodic regime. The spectrum of the linearised Navier-Stokes operator reveals a pair of complex conjugate eigenvalues with positive real part, hence the transition is ascribed to a Hopf bifurcation occurring at ${\mathit{Re}}_{b,\mathit{cr}}\approx 2531$, a value much lower than the critical Reynolds number for the flow in a torus with the same curvature. The velocity components of the unstable direct and adjoint eigenmodes are investigated, and they display a large spatial separation, most likely due to the non-normality of the linearised Navier-Stokes operator. Thus, the core of the instability, also known in the literature as the wavemaker, is sought performing an analysis of the structural sensitivity of the unstable eigenmode to spatially localised feedbacks. The region located 15° downstream of the bend inlet, on the outer wall, is the most receptive to this kind of perturbations, and thus corresponds to where the instability originates. Since this region coincides with the outer-wall separation bubble, it is concluded that the instability is linked to the strong shear by the backflow phenomena. The present results are relevant for technical applications where bent pipes are frequently used, and their stability properties have hitherto not been studied.