Home About us Contact
|
Home About us Contact | ||
|
|
||
Simplified Approach (simplified + approach)
Selected AbstractsSimulating turbulent Dean flow in Cartesian coordinatesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 3 2009George K. El Khoury Abstract A simplified approach to simulate turbulent flows in curved channels is proposed. A set of governing equations of motion in Cartesian coordinates is derived from the full Navier,Stokes equations in cylindrical coordinates. Terms to first order in the dimensionless curvature parameter are retained, whereas higher-order terms are neglected. The curvature terms are implemented in a conventional Navier,Stokes code using Cartesian coordinates. Direct numerical simulations (DNS) of turbulent flow in weakly curved channels are performed. The pronounced asymmetries in the mean flow and the turbulence statistics observed in earlier DNS studies are faithfully reproduced by the present simplified Navier,Stokes model. It is particularly rewarding that also distinct pairs of counter-rotating streamwise-oriented vortices are embedded in the simulated flow field. Copyright © 2008 John Wiley & Sons, Ltd. [source] A need for a simplified approach to venous thromboembolism prophylaxis in acute medical inpatientsINTERNATIONAL JOURNAL OF CLINICAL PRACTICE, Issue 2 2007D. P. J. Howard Summary Venous thromboembolism (VTE) is a major cause of morbidity and mortality in the UK. Studies have shown that pulmonary embolism causes or contributes to approximately 1 in 10 hospital deaths of medical patients admitted to general hospitals in the UK (Lindblad B, Sternby NH, Bergqvist D. BMJ 1991; 302: 709,11), with pulmonary embolus being the most common preventable cause of hospital death. Thromboprophylaxis is safe, highly effective and cost effective, but despite various current clinical guidelines, physicians fail to prescribe prophylaxis for the majority of medical inpatients at risk of VTE. This article outlines the current evidence for VTE prophylaxis in medical patients and discusses the reasons behind the insufficient use of prophylaxis in the acute medical setting. [source] Behaviour modelling of a PEMFC operating on diluted hydrogen feedINTERNATIONAL JOURNAL OF ENERGY RESEARCH, Issue 14 2008M. Minutillo Abstract The polymer electrolyte membrane fuel cell (PEMFC) using reformate gas as fuel is regarded as an attractive solution for the near-term introduction of fuel cells in stationary or mobile power generation market. With respect to hydrogen feeding, the reformate gas fuelling involves additional polarization losses because of the hydrogen dilution and the impurities contained in the gas. In this paper a one-dimensional model has been developed to investigate the behaviour of a PEMFC operating with reformate gas mixture. The model, based on a semi-empirical approach, considers the kinetic reactions in the anode side taking into account the effect of reverse water,gas shift (RWGS) due to the presence of CO2 in the fuel. As it is well known, the exhaust stream from fuel reformers can contain a high carbon dioxide concentration (>20%) that can have a detrimental effect on the fuel cell performance because of the combination of the dilution and the formation of CO by the RWGS reaction. The numerical simulation results have been compared with the experimental data, obtained in the test room of Industrial Engineering Department of Cassino University, and a good match has been observed. The model has been developed by using a simplified approach that, nevertheless, can allow to obtain a good numerical prediction of the fuel cell performance reducing the simulation time and computational efforts. Copyright © 2008 John Wiley & Sons, Ltd. [source] Theoretical facet and experimental results of harmonic tuned PAsINTERNATIONAL JOURNAL OF RF AND MICROWAVE COMPUTER-AIDED ENGINEERING, Issue 6 2003Paolo Colantonio Abstract High-efficiency power amplifier design criteria imply a synthesis of input and output networks with particular emphasis on their harmonic behavior. In this article, a simplified approach to clarify the relevance of such terminations is presented. Starting from the implications of power balance for stage performance, design criteria to improve the efficiency of high-frequency applications are presented. In order to validate the approach, comparisons among the performances of single-stage amplifiers, all operated at 5 GHz under a sinusoidal driving signal and synthesized by utilizing different design methodologies, are presented. Drain efficiencies at 1-dB compression of 44.5%, 53.3%, and 61.56% have been measured respectively for the tuned load and harmonically manipulated (2nd and 2nd & 3rd) realized amplifiers, compared with a simulated drain efficiency of 55% using the Class E approach. © 2003 Wiley Periodicals, Inc. Int J RF and Microwave CAE 13: 459,472, 2003. [source] Air Current Segregation of Alumina PowderPARTICLE & PARTICLE SYSTEMS CHARACTERIZATION, Issue 2 2007Stefan Zigan Abstract This paper outlines the industrial problem of air current segregation in alumina storage silos which occurs with the handling of the feedstock alumina in aluminium plants and investigates the parameters that affect the severity of the segregation. Bates [1] stated that the feeding rate influences segregation which we can confirm with own experimental findings. Higher powder flow rates tend to reduce air current segregation. Cooper et al. [2] pointed out that the air extraction rate affects the content of fine particles (dust) in the circulating air currents and we confirm his finding. The importance of the effect of different feeding rates on air current segregation was discovered in a two dimensional apparatus. The investigation of the influence of air extraction rate was realised in a cylindrical silo. Both experiments show a strong relationship between the strength of the particle-air flow in the silo and air current segregation. It is found that an increase of the powder feeding rate or the air extraction rate reduces air current segregation in the experimental equipment. The aim of our experiments was to find all significant parameters and to apply dimensional analysis to develop a method which scales the findings from small scale experiments to large industrial alumina silos. Five dimensionless groups were obtained, which is unwieldy. To reduce the number of dimensionless groups, physical properties were lumped into the terminal velocity. This simplified approach gives three dimensionless groups. Experiments in a water model and an air model justify more research using this simplified scaling method. [source] A simplified approach to modeling the co-movement of asset returnsTHE JOURNAL OF FUTURES MARKETS, Issue 6 2007Richard D. F. Harris The authors propose a simplified multivariate GARCH (generalized autoregressive conditional heteroscedasticity) model (the S-GARCH model), which involves the estimation of only univariate GARCH models, both for the individual return series and for the sum and difference of each pair of series. The covariance between each pair of return series is then imputed from these variance estimates. The proposed model is considerably easier to estimate than existing multivariate GARCH models and does not suffer from the convergence problems that characterize many of these models. Moreover, the model can be easily extended to include more complex dynamics or alternative forms of the GARCH specification. The S-GARCH model is used to estimate the minimum-variance hedge ratio for the FTSE (Financial Times and the London Stock Exchange) 100 Index portfolio, hedged using index futures, and compared to four of the most widely used multivariate GARCH models. Using both statistical and economic evaluation criteria, it was found that the S-GARCH model performs at least as well as the other models that were considered, and in some cases it was better. © 2007 Wiley Periodicals, Inc. Jrl Fut Mark 27:575,598, 2007 [source] Recent advances in research relevant to electric and magnetic field exposure guidelinesBIOELECTROMAGNETICS, Issue 7 2008Robert Kavet Abstract Limits on exposures to extremely low-frequency electric fields, magnetic fields and contact currents, designated as voluntary guidelines or standards by several organizations worldwide, are specified so as to minimize the possibility of neural stimulation. The limits, which we refer to as guidelines, derive from "basic restrictions" either on electric fields or current density within tissue, or on avoidance of annoying or startling interactions that may be experienced with spark discharge or contact current. Further, the guidelines specify more conservative permissible doses and exposure levels for the general public than for exposures in controlled environments, which most typically involve occupational settings. In 2001 we published an update on guideline science. This paper covers more recent developments that are relevant to the formulation and implementation of the next generation of guidelines. The paper deals with neurostimulation thresholds and the relevance of magnetophosphenes to setting guideline levels; dosimetry associated with contact current benchmarked against basic restrictions; tissue and cellular dosimetry from spark discharge; assessment of exposures to high electric fields in realistic situations (e.g., line worker in a transmission tower); a simplified approach to magnetic field assessment in non-uniform magnetic fields; and a quantitative approach to sampling workplace exposure for assessing compliance. Bioelectromagnetics 29:499,526, 2008. © 2008 Wiley-Liss, Inc. [source] Direct assessment of structural resistance against pressurized fractureINTERNATIONAL JOURNAL FOR NUMERICAL AND ANALYTICAL METHODS IN GEOMECHANICS, Issue 5 2003G. Bolzon Abstract The determination of the load bearing capacity of hydraulic structures such as dams, reservoirs and retaining walls requires the consideration of mixed-mode fracture, possibly driven by the fluid pressure, in correspondence to artificial and natural joints (or cracks, in the latter case). A friction-cohesive softening interface model with coupled degradation of normal and tangential strength is introduced here to account for the essential features of the joint behaviour; its predictive capability is assessed through extensive calculations. Alternative numerical techniques resting on the discrete-crack approach are considered, focusing on simplified approaches for the direct appraisal of the structural resistance. Comparison is made with the results of evolutionary analyses, based on a priori piecewise linearization of the interface model and on ,exact integration'. Copyright © 2003 John Wiley & Sons, Ltd. [source] | ||||||||||