Robustness analyses of numerical simulation of fusion welding NeT-TG1 application: “Single weld-bead-on-plate”

This study contributes to the NeT-TG1 European Network formed in 2002. The aim of this study is to predict, by numerical simulation, the residual stresses generated in a test plate by the fusion welding process. The experiment consisted in the deposit of a weld bead along the longitudinal centre-line of an austenitic 316L plate using an automatic Tungsten Inert Gas (TIG) welding process with 316L filler material. During and after thermal cycle, a large quantity of measurement data is obtained that serve to develop a comparison with the results of different numerical models. The comparative thermal and mechanical analysis allows assessment for the general ability of the numerical models to describe the structural behaviour. The importance of the heat-input rate and material characteristics is also investigated. The residual stresses were predicted by the finite element method using the program Code_Aster of EDF and SYSWELD of ESI-GROUP. Finally the numerical results are validated by comparison with experimentally measured data.     

An examination of the role of perceived support and employee commitment in employee-customer encounters.

The authors examined the relationships between perceived organizational support, organizational commitment, commitment to customers, and service quality in a fast-food firm. The research design matched customer responses with individual employees' attitudes, making this study a true test of the service provider-customer encounter. On the basis of a sample of matched employee-customer data (N = 133), hierarchical linear modeling analyses revealed that perceived organizational support had both a unit-level and an employee-level effect on 1 dimension of service quality: helping behavior. Contrary to affective organizational commitment, affective commitment to customers enhanced service quality. The 2 subdimensions of continuance commitment to the organization--perceived high sacrifice and perceived lack of alternatives--exerted effects opposite in sign: The former fostered service quality, whereas the latter reduced it. The implications of these findings are discussed within the context of research on employee-customer encounters. (PsycINFO Database Record (c) 2011 APA, all rights reserved)     

An economic evaluation of photovoltaic grid connected systems (PVGCS) in Flanders for companies: A generic model

In this paper an economic evaluation of photovoltaic grid connected systems (PVGCS) for companies situated in Flanders (Belgium) is conducted by using a generic Excel model. The model is unique in that it includes the dimension of taxation. This inclusion is required, otherwise the fiscal benefit of using solar panels is not accounted for. The model uses the cash flow projection method. This technique allows the calculation of the following classical evaluation criteria: net present value, internal rate of return, payback period, discounted payback period, profitability index, yield unit cost, yield unit revenue and break-even turnkey cost. Their outcome makes it possible to answer the question whether installing a PVGCS in Flanders is a responsible financial investment for companies. Furthermore, the paper estimates whether the corporate environment is ready for a subsidy legislation change. This change has recently been announced and as such it is possible to gauge whether the current market situation is profitable given future legislation.     

Implicit shift scheduling with multiple breaks and work stretch duration restrictions

This paper considers a shift scheduling problem that includes different forms of flexibility in terms of shift starting times, break lengths and break placement. Two particular forms are studied: fractionable breaks and work stretch duration restrictions. Unlike standard breaks, fractionable breaks are not required to be attributed as a whole. They can be divided into fractions of breaks under some conditions. The distribution of breaks within a shift is done with respect to work stretch duration restrictions to ensure a correct mix of periods of work and rest. Two implicit models are proposed. They extend previous work on implicit modeling of break placement to incorporate the concepts of fractionable breaks and work stretch duration restrictions. In this context, we show the merits of using the so-called forward and backward constraints to model work stretch duration restrictions. We also introduce a new formulation of the forward and backward constraints and demonstrate that it considerably reduces the density of the constraint matrix of the two proposed models. Finally, we study the impact of fractionable breaks and work stretch duration restrictions and show that, for some instances, the use of these concepts considerably reduces the workforce size when compared to other traditional approaches.     

Acoustoelastic effect in concrete material under uni-axial compressive loading

This study deals with the general matter of non-destructive evaluation of pre-stressed structures in civil engineering. Usually such structures are composed of concrete and are steel reinforced. Proposed idea is the evaluation of mechanical stress state of a concrete body (instead of steel cables) via ultrasonic non-destructive evaluation (NDE), by using the link between ultrasonic velocities and mechanical stresses provided by the acoustoelasticity theory. Velocities of the ultrasonic waves (longitudinal and transversal with different polarizations) are observed during propagation through a concrete body submitted to uni-axial loading (compressive testing). Obvious variations in velocity are found depending on the mechanical stress state (e.g. Δc=92 m/s at σ=16 MPa for longitudinal waves). Thus acoustoelastic behavior of concrete is demonstrated. Further analyses provide acoustoelastic coefficients of concrete about ten times higher than the common ones of steel. The feasibility of stress evaluation using ultrasounds in concrete structures is proved under laboratory conditions.     

Empirical Game Theoretic Models: Computational Issues

This paper discusses computational issues raised by ageneric solution and estimation methodology applicableto a broad range of empirical game theoretic modelswith incomplete information. By combining the use ofMonte Carlo simulation techniques with that of smoothkernel estimation of empirical distribution functions,the authors develop a numerical algorithm ofunparalleled performance and flexibility applicable,in particular, to models for which no operationalsolutions currently exist. An illustration to a set ofprocurement data from the French aerospace industry isused to illustrate the operation of this algorithm.     

Optimal parametrizations for surface remeshing

We present different linear parametrization techniques for the purpose of surface remeshing: the energy minimizing harmonic map, the convex map, and the least square conformal map. The implementation of those mappings as well as the associated boundary conditions is presented in a unified manner and the issues of triangle flipping and folding that may arise with discrete linear mappings are discussed. We explore the optimality of these parametrizations for surface remeshing by applying several classical 2D meshing algorithms in the parametric space and by comparing the quality of the generated elements. We present various examples that permit to draw guidelines that a user can follow in choosing the best parametrization scheme for a specific topology, geometry, and characteristics of the target output mesh.     

A Mathematical Model for Ultrafine Iron Powder Growth in a Thermal Plasma

ABSTRACT

A two-dimensional model is developed for the growth of ultrafine metal powders in a thermal plasma reactor. The model accounts for particle formation by nucleation, and growth by condensation and Brownian coagulation. Transport of particles occurs by convection, thermophoresis, and Brownian diffusion. The conservation equations for the moments of the particle size distribution are solved, coupled to the equation for the conservation of metal vapor. Elliptic conservation equations result from the consideration of both axial and radial diffusion of the particles. This allows for simulations in complex, recirculating flows, which are likely to occur for numerous reactor configurations and parameters. A progressive grid refining technique is used to accelerate convergence. The model is applied to the case of a typical thermal plasma reactor for the production of ultrafine iron powders. The fields of the macroscopic properties of the aerosol population and the contribution of the different mechanisms are analyzed in various conditions, some of which involve important recirculations. The effect of operating parameters on the properties of the powder generated is studied. The results are compared for some of the conditions to those obtained numerically and experimentally by Girshick et al. (1993).