Experimental and numerical studies of liquid dispersal from a soft projectile impacting a wall

A medium-scale IMPACT test programme is currently being implemented at the Technical Research Centre of Finland (VTT). In these tests, deformable cylindrical steel or aluminium projectiles impact a solid concrete wall or a steel force plate. One part of the test is conducted with a missile filled with liquid water to study liquid dispersal phenomena (i.e., wet missile tests).The fluid-filled missile ranged in length from 0.5 to 1.5 m, the water mass inside the missile from 15 to 68 kg, and the impact velocity of missile from 70 to 177 m/s.This paper describes the methods used to measure the liquid dispersal processes, and presents the main results for preliminary simulations of liquid spread. Because the IMPACT tests have focused on structural aspects, it was necessary to develop cost-effective methods for measuring liquid phenomena. The tests measured some important parameters associated with liquid: the discharge speed and direction of the liquid core released from the ruptured missile, propagation speed of the spray front, liquid pooling on the floor, extent of liquid dispersal away from the target, and the drop size of the liquid spray.The experimental findings indicate that the liquid release starts along the surface almost perpendicularly to the incoming direction of the missile and forms a fairly “flat” and uniform splash pattern around the missile. Although the discharge speed of the liquid core may be initially much higher than the impact velocity of the missile, the propagation speed of the spray front decreases rapidly with increasing distance from the source. Results of the preliminary simulations show that the Fire Dynamic Simulator (FDS) program is a usable tool for simulating two-phase flows involving high-speed droplets, provided that the initial conditions (angle and speed of liquid release, droplet size, and initial air speed) can be specified appropriately. Given these requirements, FDS can reasonably well predict the formation of the water spray cloud and final distribution of water.     

Capillary zone electrophoresis of some extremely weak bases in acetonitrile

In water capillary zone electrophoresis cannot be used to investigate basic compounds, which are so weak that their pK(a,HB+) values are less than zero. In acetonitrile the basic strength of such compounds is increased by many orders of magnitude. Accordingly, several extremely weak bases are protonated at low pH in acetonitrile, thus, allowing their investigation by CZE. In this work the CZE separation of thioacetamide, acetamide, thiourea, benzamide, and 4-nitrobenzamide as well as that of N-methylformamide, N,N-dimethylformamide, formamide, and dimethyl sulfoxide is demonstrated in acetonitrile using 10 mmol/L perchloric acid as an electrolyte. The effect of BGE additives, like water and acetic acid, on the CZE performance is discussed. The problem of finding a suitable electroosmotic flow marker at low pH in acetonitrile is addressed, and nitromethane is shown to be a proper marker compound under such extreme conditions. This work demonstrates how organic solvents can enlarge the field of application of CZE.     

The patch test—a condition for assessing FEM convergence

This paper discusses various forms of the Irons patch test and shows again that its satisfaction is a necessary convergence condition being equivalent to consistency, Further, it is shown that the test can be applied for verification of stability requirements, thus providing also a sufficient condition of convergence. The patch test is useful in testing the order of asymptotic convergence and the satisfaction of the test gives a guide for development of certain incompatible element forms.     

An analysis of strong discontinuities induced by strain-softening in rate-independent inelastic solids

Ket qualitative features of solutions exhibiting strong discontinuities in rate-independent inelastic solids are identified and exploited in the design of a new class of finite element approximations. The analysis shows that the softening law must be re-interpreted in a distributional sense for the continuum solutions to make mathematical sense and provides a precise physical interpretation to the softening modulus. These results are verified by numerical simulations employing a regularized discontinuous finite element method which circumvent the strong mesh-dependence exhibited by conventional methods, without resorting to viscosity or introducing additional ad-hoc parameters. The analysis is extended to a new class of anisotropic rate-independent damage models for brittle materials.     

Subgroup differentiation and subgroup bias among Latinos as a function of familiarity and positive distinctiveness.

The existence of subgroup differentiation and its impact on the development of in-group bias were explored among Latinos. Consistent with prior evidence, Cubans, Mexicans, and Puerto Ricans were more likely than Anglos to distinguish between Latino subgroups. However, Latinos did not distinguish equally between Cubans, Mexicans, and Puerto Ricans. Latinos differentiated their own subgroup from others but were no more likely than Anglos to differentiate between Latino subgroups to which they did not belong. Latinos even regarded the term Hispanic as more applicable to members of their own subgroup than to members of other subgroups. This tendency among Latinos to view their own subgroup as distinct from others was also linked to a bias for fellow subgroup members but not for Latinos overall. Moreover, results suggested that subgroup differentiation was based more on a desire for positive distinctiveness than on familiarity with members of different Latino subgroups. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Stable and time-dissipative finite element methods for the incompressible Navier–Stokes equations in advection dominated flows

This paper examines a new Galerkin method with scaled bubble functions which replicates the exact artificial diffusion methods in the case of 1-D scalar advection–diffusion and that leads to non-oscillatory solutions as the streamline upwinding algorithms for 2-D scalar advection–diffusion and incompressible Navier–Stokes. This method retains the satisfaction of the Babuska–Brezzi condition and, thus, leads to optimal performance in the incompressible limit. This method, when, combined with the recently proposed linear unconditionally stable algorithms of Simo and Armero (1993), yields a method for solution of the incompressible Navier–Stokes equations ideal for either diffusive or advection-dominated flows. Examples from scalar advection–diffusion and the solution of the incompressible Navier–Stokes equations are presented.     

On the coupled thermomechanical treatment of necking problems via finite element methods

The necking process of a bar in an uniaxial tension test is influenced by the heat production due to inelastic deformations. Thus, for an analysis of this problem the thermomechanical coupling has to be considered. A finite element model and an associated algorithm are developed for this purpose. This computational tool allows the study of adiabatic processes as well as processes with heat flux. The analysis of the necking process of a perfectly cylindrical specimen shows that, in contrast to isothermal and adiabatic cases, no bifurcation occurs in the case where heat flux is considered.     

Improved versions of assumed enhanced strain tri-linear elements for 3D finite deformation problems

Improved three-dimensional tri-linear elements for finite deformation problems are developed based on an assumed enhanced strain methodology which, in the linear regime, incorporates the classical method of incompatible modes as a particular case. Three crucial modifications of a recently proposed element, which reduces to Wilson's brick in the linear regime, are introduced to prevent locking response in distorted configurations and to maintain proper rank, while preserving excellent performance in bending dominated and localization problems: (i) a modified quadrature rule; (ii) an additional enhancement of the divergence term; and (iii) a modification of the isoparametric shape function derivatives for the three-dimensional problem. Moreover, these modified shape function derivatives are shown to improve the performance of the standard tri-linear brick in distorted configurations. In addition, a strategy is described to circumvent the memory storage requirements in the static condensation procedure of the enhanced strain parameters. The excellent performance of the improved methodology is illustrated in representative numerical simulations.     

Charakterisierung des strukturviskosen Verhaltens von Schmierstoffen durch Kombination von Experiment und EHD-Simulation mithilfe des Carreau-Modells

In the present work, the fluid friction in the gap between two discs was examined under full fluid film lubrication conditions. The investigation was both experimental and simulative, whereby input variables for the simulative investigation were obtained from the experimental test series. The experimental examination of fluid friction was carried out on the MEGT’s twin-disk-machine, whereby the load and slide-to-roll-ratio were varied at constant hydrodynamic velocity and oil inlet temperature. The reference oil FVA-3 was used as lubricant. As a result of the experimental investigation, traction curves are obtained which show the change in the coefficient of friction or the shear stress as a function of the slide-to-roll-ratio. The maximum and critical shear stress can be determined from the measured traction curves. These represent input variables for the simulative determination of friction in the gap.     

基于虚拟同步电机控制的微电网稳定性分析

随着微电网中电力电子器件的大量接入,多电源与负荷的动态特性相互耦合,使得微电网系统中稳定分析问题成为研究热点。针对基于虚拟同步电机控制的微电网系统,提出了一种含多分布式电源的系统非线性状态空间建模方法。建立了含分布式电源、线路和负荷的微电网统一状态空间方程。基于所建立的状态空间方程,运用特征根分析法研究了影响微电网系统稳定性的因素。并利用分岔理论研究了虚拟同步电机控制关键参数和系统拓扑结构参数对系统稳定性的影响。在PSCAD/ETMDC仿真平台搭建了基于虚拟同步电机控制的微电网模型,验证了所提方法的正确性和有效性。