Mechanical model of lung parenchyma as a two-phase porous medium

The anatomy and geometry of the lung at the micro- and macroscopic level have been described briefly. A notion of lung parenchyma — a macroscopically continuous medium whose mechanical properties result from those of microstructural components — has been adapted. Simplifying assumptions propounded in the constitutive model have been discussed. Two phases have been distinguished in the medium: the solid phase — a highly deformable, nonlinearly elastic skeleton in the form of a thin-walled tissue structure on the micro-scale — and the fluid phase — perfect gas (air) filterating through the structure. General constitutive relations for both phases and their mechanical interactions have ben formulated. Further, the fundamental set of differential equations of the quasi-static coupled problem has been developed. Large deformations, material nonlinearities, and dependence of permeability on skeleton deformation have been included. Matrix formulation of the problem has been presented from the point of view of the finite element method. An implicit iterative time integration scheme has been proposed. The algorithm has been illustrated with results of simple numerical tests.     

Electrophoresis of a 2-particle cluster near a plane boundaryElectrophorèse de deux particules en présence d'une paroi plane

Particle–boundary and particle–particle interactions in Electrophoresis are examined by considering a 2-particle cluster near a plane boundary. The advocated treatment holds for two insulating particles of arbitrary shapes and zeta potential functions and resorts to 13 boundary-integral equations. Preliminary results reveal that, depending upon the addressed velocity nature (translational or angular), wall–particle may be stronger or weaker than particle–particle interactions. To cite this article: A. Sellier, C. R. Mecanique 331 (2003).     

Mechanics Applied to Skeletal Ontogeny and Phylogeny

The musculo-skeletal system serves the mechanical function of creating motion and transmitting loads. It is made up mainly of four components: bone, cartilage, muscle and fibrous connective tissue. These have evolved over millions of years into the complex and diverse shapes of the animal skeleton. The skeleton, however, is not built to a static plan: it can adapt to mechanical forces during growth, it can remodel if the forces change, and it can regenerate if it is damaged. In this paper, the regulation of skeletal construction by mechanical forces is analyzed from both ontogenetic and phylogenetic standpoints. In the first part, models of biomechanical processes that act during skeletal ontogenesis – tissue differentiation and bone remodeling – are presented and, in the second, the evolution of the middle ear is used as an example of biomechanical change in skeletal phylogenesis. Because the constitutive laws for skeletal tissues are relatively well understood, and because the skeleton is preserved in the fossil record, application of mechanics to skeletal evolution seems to present a good opportunity to explore the relationships governing ontogenetic adaptations and phylogenetic change.     

零维物质体和微态物质体

在这篇文章里,R.G Muncaster的零维弹性体被推广到一般的高阶零维物质体。从非极连续介质力学理论出发,我们推出了零维物质体的所有平衡方程和热力学不等式。再从这些方程和不等式推出微态物质体的相应平衡方程和热力学不等式。这样,我们在零维物质体理论和微态物质体理论之间建立了一个类似于刚性质点力学和古典非极连续介质力学之间关系的关系。     

Turbulent boundary layer manipulation by outer-layer devices

A turbulent boundary layer manipulated by outer-layer devices has been studied. Experiments have been conducted in the 0.70 by 0.50 m² low speed wind tunnel of the Modesto Panetti Aeronautical Laboratory of the Politecnico di Torino. Mean values and turbulent quantities measured in the natural and manipulated boundary layers are shown for comparison. The mechanisms to explain the observed skin friction and turbulence reduction are discussed. The manipulator wake effect, consisting in decoupling the wall-region from the boundary layer outer-region, is stressed in the present results.

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Sommario Viene studiato uno strato limite turbolento manipolato, utilizzando la tecnica degli outer-layer devices. Gli esperimenti sono stati condotti nella galleria del vento 0.70×0.50 m² del Laboratorio di Aeronautica Modesto Panetti del Politecnico di Torino. Sono confrontati risultati relativi ai casi di flusso non manipolato e manipolato. Vengono discussi i meccanismi che conducono alla riduzione dello sforzo di attrito a parete e delle quantità turbolente; in particolare si punta l'attenzione sull'effetto decorrelante della scia del manipolatore.

     

Application of ‘Operational Quadrature Methods’ in Time Domain Boundary Element Methods

The usual time domain Boundary Element Method (BEM) contains fundamentalsolutions which are convoluted with time-dependent boundary data andintegrated over the boundary surface. Here, a new approach for theevaluation of the convolution integrals, the so-called OperationalQuadrature Methods developed by Lubich, is presented. In thisformulation, the convolution integral is numerically approximated by aquadrature formula whose weights are determined using the Laplacetransform of the fundamental solution and a linear multisep method. Tostudy the behaviour of the method, the numerical convolution of afundamental solution with a unit step function is compared with theanalytical result. Then, a time domain Boundary Element formulationapplying the Operational Quadrature Methods is derived. For thisformulation only the fundamental solutions in Laplace domain arenecessary. The properties of the new formulation are studied with anumerical example.     

Contrôle par rotation ou par aspiration de l'écoulement autour d'un cylindre calculé par Simulation des Grandes Échelles

Control of the flow around a circular cylinder is studied using Large Eddy Simulation. The influence of control by rotation and suction on the flow characteristics is considered for several Reynolds numbers. Comparisons with experiments were conducted at $\mathit{Re}={10}^5$ for the flow with and without control. A drag reduction up to 30% is obtained for an usual suction intensity. To cite this article: G. Fournier et al., C. R. Mecanique 333 (2005).     

Turbulence in cooling channels of rocket engines: Large Eddy Simulations

The aim of this Note is to predict by means of large eddy simulations the three-dimensional structures and secondary mass and heat fluxes which develop within a heated curved duct, for applications to rocket engines cooling channels. We show the existence of unsteady Görtler-type vortices above the concave wall, as well as intense secondary vortices taking the shape of two quasi-steady counter-rotating cells of Ekman type close to the convex wall. These cells control heat exchanges. They induce ejections and sweeps close to the convex wall when it is heated. In this case the Nusselt number undergoes strong transverse fluctuations which might induce material alterations. To cite this article: C. Münch, O. Métais, C. R. Mecanique 333 (2005).     

THE IMPACT MECHANICAL PROPERTIES OF COAL CONTAINING GAS1)

为得出含瓦斯煤体的冲击力学特性,采用类单轴压缩试验方法,对吸附瓦斯压力在0 MPa, 2 MPa, 4 MPa, 6 MPa等情况下的煤样力学特性进行了研究。研究得出：随着吸附瓦斯压力的增大,煤样的抗压强度、弹性模量、冲击能指数均近似线性降低,峰值应变近似线性增大。随着吸附瓦斯压力的增大,煤体的破坏类型由脆性向延性破坏转变,破坏的分选性增强。吸附瓦斯的作用加速了煤体失稳破坏的进程,并使煤岩瓦斯动力灾害类型呈现由冲击地压主导型向煤与瓦斯突出主导型转变的趋势。     

Multiscale Modeling of the Active Site of [Fe] Hydrogenase: The H2 Binding Site in Open and Closed Protein Conformations

A series of QM/MM optimizations of the full protein of [Fe] hydrogenase were performed. The FeGP cofactor has been optimized in the water‐bound resting state ( 1 ), with a side‐on bound dihydrogen ( 2 ), or as a hydride intermediate ( 3 ). For inclusion of H₄ MPT in the closed structure, advanced multiscale modeling appears to be necessary, especially to obtain reliable distances between CH‐H₄MPT⁺ and the dihydrogen (H₂) or hydride (H^?) ligand in the FeGP cofactor. Inclusion of the full protein is further important for the relative energies of the two intermediates 2 and 3 . We finally find that hydride transfer from 3 has a significantly higher barrier than found in previous studies neglecting the full protein environment.