Numerical simulation of the collision of two microdroplets with a pseudopotential multiple-relaxation-time lattice Boltzmann model

Collisions of two equally sized liquid microdroplets in gaseous phase are numerically studied by the lattice Boltzmann method (LBM). The multiphase formulation adopted is a pseudopotential model with improved treatment of the equation of state and force incorporation which is then coupled with the multiple-relaxation-time scheme. That allows a detailed investigation into microdroplet collisions characterized by high-density ratios as well as by relevant inertial effects. Simulations related to a wide range of flow parameters (e.g. Weber and Reynolds numbers) are reported, in order to embrace all the collisional regimes presented in previous experimental studies. From surface tension-driven coalescence (both inertial and viscous coalescence have been examined) to catastrophic break-up with the formation of children microdroplets, the simulations demonstrate that the LBM correctly reproduces the collision dynamics and the final outcomes in almost all the regimes. Different break-up mechanisms like end-pinching and capillary wave-induced break-up have been observed. Finally, the initial stages of the inertia-dominated head-on collision process have been studied, showing once more the effectiveness and reliability of this multiphase LBM implementation.     

A Discontinuous Galerkin Scheme Based on a Space–Time Expansion. I. Inviscid Compressible Flow in One Space Dimension

In this paper, we propose an explicit discontinuous Galerkin scheme for conservation laws which is of arbitrary order of accuracy in space and time. The basic idea is to use a Taylor expansion in space and time to define a space–time polynomial in each space–time element. The space derivatives are given by the approximate solution at the old time level, the time derivatives and the mixed space–time derivatives are computed from these space derivatives using the so-called Cauchy–Kovalevskaya procedure. The space–time volume integral is approximated by Gauss quadrature with values at the space–time Gaussian points obtained from the Taylor expansion. The flux in the surface integral is approximated by a numerical flux with arguments given by the Taylor expansions from the left and from the right-hand side of the element interface. The locality of the presented method together with the space–time expansion gives the attractive feature that the time steps may be different in each grid cell. Hence, we drop the common global time levels and propose that every grid zone runs with its own time step which is determined by the local stability restriction. In spite of the local time steps the scheme is locally conservative, fully explicit, and arbitrary order accurate in space and time for transient calculations. Numerical results are shown for the one-dimensional Euler equations with orders of accuracy one up to six in space and time.     

Messung der stabilen Rißverlängerung mit der Elektropotentialmethode

Wesentliche Voraussetzung für eine kostengünstige Ermittlung von Rißzähigkeitskennwerten ist eine einfache und zuverlässige Bestimmung der stabilen Rißausbreitung. Da die Potentialmethode zur Ermittlung der Rißinitiierung und des Rißwachstums vielfach vorgeschlagen wird, sollte die Leistungsfähigkeit der Methode im durchgeführten Ringversuch ermittelt und das Verfahren durch Vergleich der angewandten Versuchstechniken optimiert werden.     

Rosenborg Project: nursing home residents with senile dementia--treatment methods in family therapy

To assess the role of metabolic shifts in pathogenesis of excretory renal dysfunction arising in chronic glomerulonephritis (CGN), two groups of patients were considered. Fourteen patients of group 1 had CGN in a preazotemia stage, thirteen patients of group 2 died of CGN-induced uremia. Cortical nephrobiopsies obtained intravitally (group 1) and renal tissue specimens obtained at autopsies during postmortal hours 0-2 (group 2) were investigated. Apical epithelium of proximal canaliculi in group 1 showed higher levels of acid phosphatase (AP), though much lower of succinate dehydrogenase (SDH) and lactate dehydrogenase (LDH) compared to group 2. In basal proximal nephrothelium of group 1 the activity of LDH and AP was inhibited against these values in group 2. The activity of NADPN2-dehydrogenase, SDH and AP in group 1 surpassed that in group 2 in endothelium of renal cortex peritubular capillaries. These structures LDH and AP proved more active in group 1. The authors observed a series of significant multidirectional correlations between the activity of the enzymes studied and renal excretion. The growing activity of NADN2-dehydrogenase and AP was associated with diminution of electrolyte and water excretion, while enhancing LDH activity exhibited the opposite effect. It is concluded that progression of cortical disorders in the kidneys of CGN patients entails serious metabolic derangement reflected by imbalance in aerobic and anaerobic metabolism. These biochemical shifts result in ambiguous functional sequelae and may contribute both to renal retention of fluid, electrolytes and their excretion. The latter is likely a compensatory mechanism involved in maintenance of water-salt homeostasis in relevant patients.     

The Stress Intensity Factor in Bonded Quarter Planes after a Change in Temperature

High stresses can occur in bonded dissimilar materials after a change in temperature in the vicinity of the intersection of the interface and the free edge. These stresses depend on the thermal expansion and on the elastic constants of the two materials. In bonded quarter planes the stresses near the intersection of the interface and the free edge can be described by the sum of one singular term and one regular term which is independent of the distance to the singular point. With the exception of the stress intensity factor of the singular term, all parameters can be calculated analytically. The stress intensity factor was evaluated numerically using the finite element method. Joints with different ratios of height to length and various material combinations were investigated. An empirical relationship between the stress intensity factor, the elastic constants and the ratios of height to length of the joint is given by exponential and polynomial equations.     

Untersuchungen zum Einfluß des Gefügezustandes auf das Rißausbreitungs-Verhalten bei einsinniger Belastung von TiAl6V4

Investigations on the Effect of Microstructure on Crack Propagation during Unidirectional Loading of TiAl6V4 Fracture mechanics tests were performed with the titanium alloy Ti-6 Al-4 V between ?196°C and room temperatur. Crack propagation behaviour was characterized by the K-Δa-curve, K_Io at the onset of stable crack extension and by K_Q, determined with the 5% secant method. K_Q is strongly dependent on the microstructure, whereas there is a less effect on K_Io. For a material with a microstructure with a low fracture toughness the value K_Q can be increased considerably by vaccum annealing at 750°C. There is only a small decrease of the yield strength.     

Ligament yielding of a plate with semi-elliptical surface cracks under uniform tension

The ligament yielding of a plate with a semi-elliptical surface crack under tension loading is calculated using the Dugdale model. The stress intensity factor for the strip load is obtained using the weight-function method. The necessary crack opening displacement is calculated with an approach proposed by Petroski and Achenbach.     

Effect of specimen type on J-integral at the onset of crack extension

International Journal of Fracture -     

Data base reorganization by clustering method

This paper is concerned with the problem of data re-allocation on a moving-head-disk, in order to minimize the average access time. From the analysis of the chronological accesses to the records during the reference period, the initial exploitation cost of the implementation is situated among all the possible ones, and the benefit of a reorganization may be evaluated. The reorganization itself is a two stage process: at first the file is partitioned by a clustering algorithm, and then, the clusters are allocated to cylinders. By the application of this method on a 11,000-record file, the access mean time was reduced by a factor 2.