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Accuracy Analysis (accuracy + analysis)
Selected AbstractsAccuracy analysis of super compact scheme in non-uniform grid with application to parabolized stability equationsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2004V. Esfahanian Abstract A brief derivation of the super compact finite difference method (SCFDM) in non-uniform grid points is presented. To investigate the accuracy of the SCFDM in non-uniform grid points the Fourier analysis is performed. The Fourier analysis shows that the grid aspect ratio plays a crucial role in the accuracy of the SCFDM in a non-uniform grid. It is also found that the accuracy of the higher order relations of the SCFDM is more sensitive to grid aspect ratio than the lower order relations. In addition, to obtain a mathematical representation of the accuracy and making clear the role of the aspect ratio in the accuracy of the SCFDM in non-uniform grids, the modified equation approach is used. For the sake of demonstrating the analytical results obtained from the Fourier analysis and the modified equation approach, the super compact finite difference method is applied to solve the Blasius boundary layer and the non-linear parabolized stability equations as numerical examples indicating the difficulty with non-uniform grid spacing using the super compact scheme. Copyright © 2004 John Wiley & Sons, Ltd. [source] Do tests of malingering concur?BEHAVIORAL SCIENCES & THE LAW, Issue 5 2006Concordance among malingering measures Malingering test accuracy is increasingly a major issue in psychology and law. Integrating results across measures might offset limitations of a single test, but the practical benefits of using several tests depend on the extent to which they misclassify the same individuals. Data from 66 evaluatees were used to assess the degree of overlap and consistency of classification among several commonly used malingering instruments. Although correlative data indicated that measures were highly redundant even across symptom domains, classification accuracy analyses revealed that findings based on conjunctions of these scales may not overlap to the degree that the correlations might suggest. Copyright © 2006 John Wiley & Sons, Ltd. [source] Prognostic ability of simplified nuclear grading of renal cell carcinomaCANCER, Issue 5 2007Nathalie Rioux-Leclercq MD Abstract BACKGROUND. The Fuhrman grading system is an established predictor of survival in patients with renal cell carcinoma (RCC). The predictive accuracy of various Fuhrman grading schemes was tested with the intent of improving the prediction of RCC-specific survival (RCC-SS). METHODS. The analyses targeted 5453 patients from 14 institutions. Univariable, multivariable, and predictive accuracy analyses addressed RCC-SS. The statistical significance of the gain in predictive accuracy was quantified with the Mantel-Haenszel test. RESULTS. The median follow-up time was 4.5 years. In both univariable and multivariable analyses, Fuhrman grade achieved independent predictor status regardless of the coding scheme. When Fuhrman grade was not considered in multivariable analyses, the predictive accuracy was 83.8%. Addition of Fuhrman grade to the multivariable model resulted in predictive accuracy gains of 0.8% for all 3 grading schemes tested. CONCLUSION. Fuhrman grade must to be considered when RCC-SS is assessed. However, modified or conventional Fuhrman grading schemes perform equally well as the conventional grading system. Cancer 2007 © 2007 American Cancer Society. [source] Parameter estimation accuracy analysis for induction motorsEUROPEAN TRANSACTIONS ON ELECTRICAL POWER, Issue 2 2005E. Laroche Abstract Various analytical dynamic models of induction machines, some of which take magnetic saturation and iron loss into account, are available in the literature. When parameter estimation is required, models must not only be theoretically identifiable but allow for accurate parameter estimation as well. This paper presents a comparison of parameter estimation accuracies obtained using different models and sets of measurements in the case of steady-state sinusoidal measurements. An explicit expression of estimation error is established and evaluated with respect to several measurement and modelling errors. This study will show that certain models are better suited for identification purposes than others and that certain sensors are bound to be more accurate than others. Lastly, an optimal experimental design procedure is implemented in order to derive an improved measurement set that leads to reduced estimation errors. Copyright © 2005 John Wiley & Sons, Ltd. [source] Stability and accuracy analysis of a discrete model reference adaptive controller without and with time delayINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 9 2010Oreste S. Bursi Abstract Adaptive control techniques can be applied to dynamical systems whose parameters are unknown. We propose a technique based on control and numerical analysis approaches to the study of the stability and accuracy of adaptive control algorithms affected by time delay. In particular, we consider the adaptive minimal control synthesis (MCS) algorithm applied to linear time-invariant plants, due to which, the whole controlled system generated from state and control equations discretized by the zero-order-hold (ZOH) sampling is nonlinear. Hence, we propose two linearization procedures for it: the first is via what we term as physical insight and the second is via Taylor series expansion. The physical insight scheme results in useful methods for a priori selection of the controller parameters and of the discrete-time step. As there is an inherent sampling delay in the process, a fixed one-step delay in the discrete-time MCS controller is introduced. This results in a reduction of both the absolute stability regions and the controller performance. Owing to the shortcomings of ZOH sampling in coping with high-frequency disturbances, a linearly implicit L-stable integrator is also used within a two degree-of-freedom controlled system. The effectiveness of the methodology is confirmed both by simulations and by experimental tests. Copyright © 2009 John Wiley & Sons, Ltd. [source] A partition-of-unity-based finite element method for level setsINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN ENGINEERING, Issue 10 2008Stéphane Valance Abstract Level set methods have recently gained much popularity to capture discontinuities, including their possible propagation. Typically, the partial differential equations that arise in level set methods, in particular the Hamilton,Jacobi equation, are solved by finite difference methods. However, finite difference methods are less suited for irregular domains. Moreover, it seems slightly awkward to use finite differences for the capturing of a discontinuity, while in a subsequent stress analysis finite elements are normally used. For this reason, we here present a finite element approach to solving the governing equations of level set methods. After a review of the governing equations, the initialization of the level sets, the discretization on a finite domain, and the stabilization of the resulting finite element method will be discussed. Special attention will be given to the proper treatment of the internal boundary condition, which is achieved by exploiting the partition-of-unity property of finite element shape functions. Finally, a quantitative analysis including accuracy analysis is given for a one-dimensional example and a qualitative example is given for a two-dimensional case with a curved discontinuity. Copyright © 2008 John Wiley & Sons, Ltd. [source] Temporal accuracy analysis of phase change convection simulations using the JFNK-SIMPLE algorithmINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 7 2007Katherine J. Evans Abstract The incompressible Navier,Stokes and energy conservation equations with phase change effects are applied to two benchmark problems: (1) non-dimensional freezing with convection; and (2) pure gallium melting. Using a Jacobian-free Newton,Krylov (JFNK) fully implicit solution method preconditioned with the SIMPLE (Numerical Heat Transfer and Fluid Flow. Hemisphere: New York, 1980) algorithm using centred discretization in space and three-level discretization in time converges with second-order accuracy for these problems. In the case of non-dimensional freezing, the temporal accuracy is sensitive to the choice of velocity attenuation parameter. By comparing to solutions with first-order backward Euler discretization in time, it is shown that the second-order accuracy in time is required to resolve the fine-scale convection structure during early gallium melting. Qualitative discrepancies develop over time for both the first-order temporal discretized simulation using the JFNK-SIMPLE algorithm that converges the nonlinearities and a SIMPLE-based algorithm that converges to a more common mass balance condition. The discrepancies in the JFNK-SIMPLE simulations using only first-order rather than second-order accurate temporal discretization for a given time step size appear to be offset in time. Copyright © 2007 John Wiley & Sons, Ltd. [source] Development of a large parallel-cable manipulator for the feed-supporting system of a next-generation large radio telescopeJOURNAL OF FIELD ROBOTICS (FORMERLY JOURNAL OF ROBOTIC SYSTEMS), Issue 11 2001Y. X. Su A large parallel-cable manipulator for the feed-supporting system of a next-generation large radio telescope is presented in this paper. The approximate kinematics model of the system is developed to improve real-time controllability, and the rationality of this approximation is validated by a kinematics accuracy analysis. In order to guarantee the effectiveness of control, the singularity of the large parallel-cable manipulator is analyzed (including kinematics and force singularities). The control strategy of the parallel-cable feed-supporting system is also proposed. © 2001 John Wiley & Sons, Inc. [source] Core casting accuracy analysis via a boundary tensorial techniqueJOURNAL OF PROSTHODONTICS, Issue 4 2002Jung Y. Lee DMD [source] Comparison of gas chromatography and liquid chromatography mass spectrometric measurements for high accuracy analysis of cholesterol in human serum by isotope dilution mass spectrometryRAPID COMMUNICATIONS IN MASS SPECTROMETRY, Issue 9 2002Céline S. J. Wolff Briche Cholesterol measurements are of vital clinical importance and reliable reference materials are essential for method validation. Gas chromatography with mass spectrometry (GC/MS) is usually used for the high accuracy analysis of cholesterol by isotope dilution. A certified reference material for cholesterol content in human serum was analysed by isotope dilution utilising GC/MS and liquid chromatography mass spectrometry (LC/MS). The use of LC/MS avoided the need for a derivatisation step. Both LC/MS and GC/MS produced results on the measurement of cholesterol that agreed within 0.5% of the certified value. Moreover, the precision obtained for ratio measurement using both techniques are comparable and lead to relative expanded standard uncertainties (with a coverage factor of 2) varying between 0.2 and 0.5%. Copyright © 2002 John Wiley & Sons, Ltd. [source] | |||||||||||||