Direct Statistical Simulation of a Supersonic Flow of a Binary Mixture of Rarefied Gases around a Transversely Positioned Cylinder

A supersonic flow of a binary mixture of gases in a wide range of rarefaction (from a flow with a Knudsen number K _n = 0.1 to a free-molecular flow) around a cylinder is studied by means of direct statistical Monte Carlo simulations (DSMC method). The influence of a small fraction of heavy particles in a light gas flow on the region of significant nonequilibrium near the cylinder and on the heat flux is considered.__________Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 5, pp. 53–59, September–October, 2005.     

Subgrid models preserving the symmetry group of the Navier–Stokes equations

In order to preserve the physical properties of the flow (scaling laws, conservation laws, …) during the simulation, a class of subgrid models respecting the symmetry group of the Navier–Stokes equations is built. The class is then refined such that models satisfy the second law of thermodynamics and are suited to take into account the inverse energy cascade. A simple model belonging to the class is tested and a better result than those provided by Smagorinsky and dynamic models is obtained. To cite this article: D. Razafindralandy, A. Hamdouni, C. R. Mecanique 333 (2005).     

Stochastic Hopf bifurcation in quasi-integrable-Hamiltonian systems

A new procedure is developed to study the stochastic Hopf bifurcation in quasiintegrable-Hamiltonian systems under the Gaussian white noise excitation. Firstly, the singular boundaries of the first-class and their asymptotic stable conditions in probability are given for the averaged Ito differential equations about all the sub-system‘s energy levels with respect to the stochastic averaging method. Secondly, the stochastic Hopf bifurcation for the coupled sub-systems are discussed by defining a suitable bounded torus region in the space of the energy levels and employing the theory of the torus region when the singular boundaries turn into the unstable ones. Lastly, a quasi-integrable-Hamiltonian system with two degrees of freedom is studied in detail to illustrate the above procedure.Moreover, simulations by the Monte-Carlo method are performed for the illustrative example to verify the proposed procedure. It is shown that the attenuation motions and the stochastic Hopf bifurcation of two oscillators and the stochastic Hopf bifurcation of a single oscillator may occur in the system for some system‘s parameters. Therefore, one can see that the numerical results are consistent with the theoretical predictions.     

Solution of Müller's paradox of frame dependence in mixtures of polymeric liquid crystals

Recently, there appeared in this journal a short review article by Müller ((2002), 14: 227–229), in which it was argued that the internal energy of a reacting mixture of liquid crystals should not be an objective quantity (i.e., a quantity independent of the referential frame). Such a paradoxical conclusion has revealed the urging necessity for a better comprehension of the interactions taking place in structured mixtures, specially when referred to non-inertial observers. This work shows that Müller's paradox is avoided when all inertial effects are carefully accounted for. Further, it predicts interesting phenomena without analogue in reacting mixtures of structureless fluids: internal inertial effects, produced by a combination of mass exchanges (e.g. by chemical reactions or phase changes) with the extra degrees of freedom posed by the microstructure. Such effects clarify the reasons why inertial forces and couples acting on a mixture do not always coincide with the sum of the inertial forces and couples exerted upon its individual constituents. The present conclusions establish a reinterpretation of some fundamental concepts of continuum mechanics and thermodynamics, including a deeper understanding of the manner in which total energy and momenta are conserved in complex media. Received: July 25, 2002 / Published online: February 17, 2003 Communicated by Kolumban Hutter, Darmstadt e-mail: faria@mechanik.tu-darmstadt.de     

Experimental dynamic analysis of elastic-plastic shear frames with secondary structures

Various experimental models are developed to study the influence of lightweight secondary structures on the dynamic response of elastic and elastic-plastic shear frames. Small-scale two-story model frames, with an elastic single-degree-of-freedom secondary structure attached, are considered for sinusoidal and random in-plane support excitation. Both elastic and elastic-plastic responses are recorded by varying the material properties of the columns of a distinguished floor. Parametric studies are performed by varying the secondary structure's fundamental frequency and damping. Experimental results are compared with those obtained by computational simulations. Experimental and numerical results are in excellent agreement, however they show that the material properties have to be determined very carefully. The statistic response of randomly excited elastic-plastic structures is not much affected by the motion of tuned secondary structures. However, this dynamic behavior is not true for elastic main structures. In this case, an optimally tuned secondary structure decreases the structural response up to 25%.     

Diffusion in isotropic and anisotropic porous systems: Three-dimensional calculations

Effective diffusion coefficients were calculated numerically for three-dimensional unit cells representative of different unconsolidated porous media. These numerical results were compared with the experimental results of Kim for packed beds of glass spheres, mica particles, and an artificial porous medium composed of mylar disks. These three-dimensional numerical results confirm that the porosity is the essential parameter for the determination of the effective diffusion coefficient in the case of unconsolidated isotropic systems. In the case of anisotropic systems, better agreement is obtained between numerical predictions and actual data when the unit cell is three-dimensional rather than twodimensional. This emphasizes the fact that three-dimensional unit cells feature more realistic geometrical properties which are needed to accurately describe anisotropic systems.     

Effect of microhydration on the atmospherically important metastable carbonyl sulfide anion: Structure,energetic, and infrared study

Structure, energetics, and vibrational frequency of the microhydrated carbonyl sulfide anion [OCS^?? (H₂O)_n (n = 1–6)] have been explored by the systematic ab initio study to have a comprehensive understanding about the hydration‐induced stabilization phenomenon of OCS^?. Water binds with the OCS^? in single hydrogen‐bonded (SHB) or double hydrogen‐bonded (DHB) fashion with O? H S and O? H O contacts. Maximum five water molecules can stay in a cyclic water network of these hydrated clusters forming interwater hydrogen bonding (IHB) with each other and out of this, maximum of two water molecules can bind directly to the OCS^? in (DHB) arrangement. The stabilization energy values of OCS^?? (H₂O)_n depict that ion–water interaction is significant up to four water molecules and beyond that OCS^? is stabilized by IHB between the water molecules. The CO stretching frequency of OCS^? gets red shifted, whereas CS stretching frequency gets blue shifted on hydration. Charge analysis of hydrated clusters of OCS^? indicates that negative charge moves toward oxygen from sulfur on hydration. © 2015 Wiley Periodicals, Inc.     

Addendum to “Volumetric properties of binary liquid-phase mixture of (water + glycerol) at temperatures of (278.15 to 323.15) K and pressures of (0.1 to 100) MPa” [J. Chem. Thermodyn. 79 (2014) 135–158]: Effect of pressure on excess thermodynamic characteristics of mixture water + glycerol

Experimentally determined volumetric properties of the liquid binary mixture of {water (1) + glycerol (2)} were processed to calculate the changes of the following thermodynamic parameters with pressure: excess molar Gibbs free energy, ${\mathrm{\Delta }}_{P_o\to P}{G}_m^E$, excess molar entropy, ${\mathrm{\Delta }}_{P_o\to P}{S}_m^E$, excess molar enthalpy, ${\mathrm{\Delta }}_{P_o\to P}{H}_m^E$, as well as the enthalpy of mixing of water and glycerol, $H_m^E$, at 100 MPa. The mixing enthalpies of water and glycerol, $H_m^E$, became more exothermic with pressure increasing at all temperatures studied.