1/2001

Contents:

• K.W.Wojciechowski and V.V.Novikov, Negative Poisson's Ratio and Some Multi-Connected Structures - abstract | full text
• V.Konopinska, S.Telega and J.Sienkiewicz, Electron-Argon Scattering: a High Angle Minimum in Differential Cross Sections - abstract | full text
• A.Herman and A.Jankowski, Wind- and Density-Driven Water Circulation in the Southern Baltic Sea - a Numerical Analysis - abstract | full text
• R.Gorecki, M.Mars, W.Alda, L.Fioretti and J.Rybicki, Simulation of Fluid Flow with Interacting Particles - abstract | full text
• N.Egidi, L.Misici and R.Piergallini, Laminar Mixing Flow in a Stirred Vessel - abstract | full text
• M.Rychcik, J.Bosko, J.Rybicki, W.Alda, W.Dzwinel, G.Mancini and L.Fioretti, 2D Simulations of Liquid Percolation through Model Porous Media: Preliminary MD and DPD Results - abstract | full text
• L.Fioretti and M.Conti, Heat Transfer Analysis for the Hydraulic Circuit of an Expresso-Coffee Machine - abstract | full text

• A.Januszajtis, Secrets of Golden Vodka

Abstracts:

• K.W.Wojciechowski and V.V.Novikov, Negative Poisson's Ratio and Some Multi-Connected Structures

  Elastic properties of non-uniform, two-component systems are studied in frames of a model of percolation on a simple cubic lattice. It is shown that as the ratio of the bulk moduli of the components tends to zero, κ = K_s/K_h --> 0 (where s, h denote the softer and harder phase, respectively), the Poisson's ratio of the system tends to 0.2 at the percolation threshold of the harder phase, no matter what are the values of the Poisson's ratios of the components. A qualitatively new, collective mechanism leading to negative Poisson's ratio is suggested.

• V.Konopinska, S.Telega and J.Sienkiewicz, Electron-Argon Scattering: a High Angle Minimum in Differential Cross Sections

  Ab initio relativistic calculations of the high angle differential cross section minimum have been presented. Theoretical method is based on the Dirac-Hartree-Fock scattering equation. Ab initio polarization and exact exchange have been included. Calculations have been performed for the low energy elastic scattering from argon. A very good agreement with the recent experimental data has been found.

• A.Herman and A.Jankowski, Wind- and Density-Driven Water Circulation in the Southern Baltic Sea - a Numerical Analysis

  The study focuses on the hydrodynamic processes in the southern Baltic Sea, with special interest in the Stolpe Channel - the only deep water connection between Bornholm Basin to the west and Gdansk and Gotland Basins to the east. The Channel is an area of strong interactions of wind- and density-driven currents that may lead to a complex flow structure. A three-dimensional numerical model was applied to an analysis of processes mentioned above. Three model versions of different spatial resolution (5, 3 and 1Nm) were used to investigate an influence of this parameter on the model results. The simulations were performed for four main wind directions, for a variable in time wind speed. It was shown that water circulation in the southern Baltic is to a high degree dependent on local anemobaric conditions. The results confirm the hypothesis of Krauss and Brugge that the flow in the Channel is opposite to the wind direction. Numerical grid step can have a decisive influence on the modeled circulation patterns, especially when barotropic andbaroclinic flow components counteract. In such situations - when the flow is bidirectional and mesoscale eddies are generated - high resolution of the model is particularly important.

• R.Gorecki, M.Mars, W.Alda, L.Fioretti and J.Rybicki, Simulation of Fluid Flow with Interacting Particles

  In the paper a method for modeling flows in the presence of interacting particles is briefly presented. The method is based on merging classical, continuous approach of numerical solution of Navier-Stokes equations on the 2D mesh with discrete particles interacting with the fluid and among themselves by means of central and friction forces. Several sample simulations presenting the flow through porous medium and convection flow driven by sedimentation.

• N.Egidi, L.Misici and R.Piergallini, Laminar Mixing Flow in a Stirred Vessel

  Using finite element method we study the transient motion of fluid particles in a 3D cavity, when the fluid is incompressible viscous and with uniform density. The fluid is mixed under the action of four blades turbine that is simulated by a velocity function. The mixing quality of the fluid is studied giving a qualitative visualization and a quantitative measure of the indices of diffusion and dispersion.

• M.Rychcik, J.Bosko, J.Rybicki, W.Alda, W.Dzwinel, G.Mancini and L.Fioretti, 2D Simulations of Liquid Percolation through Model Porous Media: Preliminary MD and DPD Results

  In the paper we make a short overview of computer models based on particle approach, which can be suitable for the simulation of fluid flow through porous media. We concentrate on Molecular Dynamics (MD) and Dissipative Particle Dynamics (DPD) methods. We describe main features of our simulation programs, and present and discuss preliminary results of MD and DPD simulations of 2D fluid flow through a simple model rigid porous media. The paper aims at the evaluation of the applicability of MD and DPD methods for simulations of liquid flows in media of complicated geometry.

• L.Fioretti and M.Conti, Heat Transfer Analysis for the Hydraulic Circuit of an Expresso-Coffee Machine

  An Espresso-Coffee Machine supplies water which temperature must be confined within a narrow range in different operating conditions; this requires an accurate design at the component as well as the system level. In the present paper we develop a mathematical model to analyse the performances of the heating circuit of such a machine; our aim is to capture the main operating characteristics of the system with the maximum of simplicity. The governing equations of the model have been solved with the finite difference technique, and the first results have been compared with some experimental data.