Small response surface designs for metamodel estimation

WOS: 000180099100017The primary objective of this study is to provide the novice researchers in simulation metamodeling with guidance on how to use small designs for metamodel estimation especially when cost effectiveness is a concern. This study was carried out in three phases: First, a group of second-order small designs were evaluated with respect to various criteria. Next, the metamodel of a time-shared computer system was estimated using these designs. Finally, the predictive capabilities of these small designs in giving the best metamodel fit were investigated, and also, the performance of small designs was compared with two large size standard designs. Results indicate that the metamodel estimated using the hybrid design has the best predictive capability among the small designs, and its performance competes with that of the standard designs studied. (C) 2002 Published by Elsevier Science B.V

Dealing with the least squares regression assumptions in simulation metamodeling

WOS: 000090012300007The aim of this study is twofold. The first is to estimate a metamodel for a time-shared computer system using a sequential design procedure, The second is to deal extensively with the least squares regression assumptions during the metamodel development. In the first stage of the experimentation, a first-order metamodel is estimated using the two-level factorial design. Later, the design is augmented with replicated center points for curvature check. Upon the detection of the significance of the curvature, a central composite design is used for fitting a second-order metamodel, which explains the relation between the levels of the input factors, and the response of interest. In both stages, various diagnostic statistical tests such as normality test, variance homogeneity test, lack-of-fit test and etc, are carried out to make sure that the method of least squares is properly and efficiently applied. (C) 2000 Elsevier Science Ltd. All rights reserved

Second-order experimental designs for simulation metamodeling

WOS: 000181725900001The main purpose of this study is to compare the performance of a group of second-order designs such as Box-Behnken, face-center cube, three-level factorial, central composite, minimum bias, and minimum variance plus bias for estimating a quadratic metamodel. A time-shared computer system is used to demonstrate the ability of the designs in providing good fit of the metamodel to the simulation response. First, for various numbers of center runs, these designs are compared with respect to their efficiency, rotatability, orthogonality, robustness, bias, and prediction variance. Next, second-order metamodels are fit to the data collected using these designs. Metamodel fit is investigated using criteria such as average absolute error, PRESS, and the C-p statistic. Results indicate that the minimum variance plus bias design is the most promising design to estimate a metamodel for the case studied

A metamodeling methodology involving both qualitative and quantitative input factors

This paper suggests a methodology for developing a simulation metamodel involving both quantitative and qualitative factors. The methodology mainly deals with various strategic issues involved in metamodel estimation, analysis, comparison, and validation. To illustrate how to apply the methodology, a regression metamodel is developed for a client-server computer system. In particular, we studied how the response time is affected by the quantum interval, the buffer size. and the total number of terminals when different queuing disciplines are employed in the operation of the round-robin queue with a limited buffer. The results of the study indicate that the relationship between the response time and the quantitative factors cannot be adequately described by a single metamodel for all queuing disciplines

End effect evaluation in rheological measurement of drilling fluids using Coutte coaxial cylinder viscometer

This paper demonstrates the order of influence of end effects on the application of a theory to determine and correct the end effects in Couette coaxial cylinder rotational viscometers, which are commonly used for the rheological evaluation of drilling fluids. It is found that higher shear stresses are measured due to end effects and, consequently, this error bearing shear stress-shear rate data leads to unreliable predictions of the rheological parameters. Evaluation of the shear stress-shear rate data obtained from various drilling fluids indicates that the flow curve corrected for end effects deviates significantly from the measured curve. A parametric analysis for the rheological models, such as the Bingham plastic, power law, and yield-pseudo-plastic models, is also performed with the parameters of the selected rheological model

Silver Leaching from Lead-Zinc Process Tailings in Balya Mines

Some silver and other valuable metallic elements accumulate inside tailings of lead-zinc flotation process in Balya mines. It is therefore investigated in this paper to recover silver by leaching from the tailings fraction of the flotation plant. Representative tailing samples were systematically provided from the actual lead-zinc flotation circuits in order to obtain composites before leaching with hydrochloric acid (HCl), nitric acid (HNO3) and oxalic acid (H2C2O4). Within this study, effects of different types of acids with variable dosages, solid ratio, leaching duration and temperature were investigated. Optimal leaching efficiency was calculated according to silver recovery in acid-leachates. The obtained results showed that the optimal conditions for the leaching tests were as 30% solid concentration, 2 mmol/dm(3) HNO3 addition, 120 min leaching time at 60 degrees C temperature. As a result, dissolution efficiency for silver from the lead-zinc process tailings in Balya mines was calculated as 60.12%