The Experts below are selected from a list of 192 Experts worldwide ranked by ideXlab platform

Colin C. Mcandrew - One of the best experts on this subject based on the ideXlab platform.

  • Surface Potential Equation for bulk MOSFET
    Solid-State Electronics, 2009
    Co-Authors: Gennady Gildenblat, Z. Zhu, Colin C. Mcandrew
    Abstract:

    The physical background of the commonly used approximate MOSFET surface Potential Equation is explained by comparison with the exact result. A new well-conditioned surface Potential Equation over the extended temperature range essential for cryogenic CMOS applications is obtained by explicitly accounting for incomplete impurity ionization simultaneously with the imref splitting present in MOS transistors.

  • physics based mathematical conditioning of the mosfet surface Potential Equation
    IEEE Transactions on Electron Devices, 2004
    Co-Authors: Weimin Wu, Gennady Gildenblat, Tenlon Chen, Colin C. Mcandrew
    Abstract:

    The traditional form of the implicit Equation for the surface Potential (/spl phi//sub s/) in metal-oxide-semiconductor field-effect transistors (MOSFETs) works well except near the flatband point /spl phi//sub s/=0 where it is both unphysical and ill-conditioned mathematically. This represents a significant difficulty for recent surface Potential-based models, which require /spl phi//sub s/ evaluation from the accumulation to the strong inversion region. Detailed physical analysis combined with two-dimensional numerical simulations is used to develop a physics-based well-conditioned version of the surface Potential Equation.

Terry L. Holst - One of the best experts on this subject based on the ideXlab platform.

  • Chimera Donor Cell Search Algorithm Suitable for Solving the Full Potential Equation
    Journal of Aircraft, 2000
    Co-Authors: Terry L. Holst
    Abstract:

    An approximate iterative search algorithm for finding donor cells associated with the chimera zonal grid approach is presented. This new algorithm is both fast and simple. It is used in conjunction with a chimera-based full Potential solver for computing transonic flow solutions about wing and wing/fuselage configurations. Within each grid zone a fully implicit approximate factorization scheme is used to advance the solution one iteration. This is followed by the explicit advance of all common intergrid boundaries using a trilinear interpolation of the velocity Potential. The presentation is highlighted with numerical result comparisons, a grid refinement study, and parametric variation of pertinent algorithm parameters. The new search algorithm produces donor cells for the two-zone wing problem at a rate in excess of 60,000 cells/s (single processor Cray C90). The approximate nature of the search algorithm, which causes some of the donor cells to be approximated by nearest neighbor cells, does not cause any impact on solution accuracy. Overall the results indicate that the present chimera zonal grid approach is a viable technique for solving the full Potential Equation for aerodynamic applications

  • On Approximate Factorization Schemes for Solving the Full Potential Equation
    1997
    Co-Authors: Terry L. Holst
    Abstract:

    An approximate factorization scheme based on the AF2 algorithm is presented for solving the three-dimensional full Potential Equation for the transonic flow about isolated wings. Two spatial discretization variations are presented, one using a hybrid first-order/second-order-accurate scheme and the second using a fully second-order-accurate scheme. The present algorithm utilizes a C-H grid topology to map the flow field about the wing. One version of the AF2 iteration scheme is used on the upper wing surface and another slightly modified version is used on the lower surface. These two algorithm variations are then connected at the wing leading edge using a local iteration technique. The resulting scheme has improved linear stability characteristics and improved time-like damping characteristics relative to previous implementations of the AF2 algorithm. The presentation is highlighted with a grid refinement study and a number of numerical results.

  • Numerical solution of the full Potential Equation using a chimera grid approach
    AIAA Journal, 1997
    Co-Authors: Terry L. Holst
    Abstract:

    HE purpose of this Note is to present results from a new algorithm for solving the full Potential Equation based on a chimera grid approach. The long term objective of this work is to develop a chimera-based full Potential flow solver that will be compatible with the well-established OVERFLOW Euler/Navier-Stokes flow solver.1"3 Thus, the user will have an option of which flow solver to use in the chimera-based zonal grid approach: full Potential, Euler, or Navier-Stokes. Of course, the full Potential option will not be applicable for all applications, but for those applications where the full Potential Equation is valid, the execution time should be up to two orders of magnitude less than for the Navier-Stokes formulation. Indeed, a chimera-based full Potential solver should have modest execution times on even moderate-speed workstations. In a parametric study, the bulk of the required computations could utilize the full Potential approach and then a few selected conditions could be checked with a more complete, and thus more accurate, Euler or Navier-Stokes simulation. Such an approach would be extremely cost effective especially considering that all of these approaches would utilize the same problem setup and postprocessing software and to a large extent the same grid generation software. For most chimera zonal grid applications, there is not much information on error analysis. The questions of how much error the interpolation process produces and what the effect is of this error on various aspects of the solution away from the interface boundary have not been generally addressed. One notable exception to this is the work of Meakin,4 in which a chimera scheme error analysis was performed for a number of steady and unsteady transonic airfoil cases. Results from this study demonstrated the viability of the chimera approach for the Euler formulation being used. The purpose of the present study is to investigate the prior two questions in the context of a chimera full Potential solver.

K Kamemoto - One of the best experts on this subject based on the ideXlab platform.

  • A fast higher-order integral Equation method for solution of the full Potential Equation around airfoils
    Engineering Analysis with Boundary Elements, 2000
    Co-Authors: Mehmet Sahin, K Kamemoto
    Abstract:

    A method based on an integral Equation formulation is described for solution of the full Potential Equation in terms of the velocity field. In addition to the conventional distribution of singularities over the boundaries of field, a field source distribution is added in the flow region in order to represent the non-linear compressibility effect. The unknown source distribution in the field is calculated from the full Potential Equation by iteratively updating the normal velocity boundary conditions. In order to treat more complex configurations, local transformations provided by higher-order elements are used. Computation time required for integration of the domain is improved by using a domain decomposition. Results of calculations demonstrate substantial improvement in computation time and are in good agreement with independent results.

C Srinivasa - One of the best experts on this subject based on the ideXlab platform.

  • Multigrid Technique Applied for the Full Potential Equation Over An Airfoil
    1995
    Co-Authors: C Srinivasa
    Abstract:

    The Multigrid technique is 'employed to,get the fast convergence of solutions for the algorithms particularly, to flow applications. In ihis paper the technique is used for the solution of 'full Potential Equation, over a symmetrical airfoil. The Equation is of non-conservative form in - a cartesion -grid sy8tem. This paper describes the solution obtained upto three levels and for different angle of inci- dences. CPU times obtained fo ' r all the cases have been'tabulated, which shows reasonable reduction of CPU times for more number of levels as compared to non-multigrid single grid level solution. The reduction' of equivalent number 'If iterations is also presented here. Vie olution 'did not bonverge for higher anlge of incidences and for more number of levels.' The coinputed pressure distriutions for all the converged cases is shown in this paper. Solutions obtained13; or sub critical Mach Number, critical Mach Number,-and super critical Mach umber is reported here. Mesh of higher grid ?ize is - considered in this paper. he effect of the grid size on the Multigrid Technique solutions bave been tried to understand, The pressure dis1ribulions obtained aublished results and found to agree reasonably.

  • Solution of full Potential Equation on an airfoil by multigrid technique
    1993
    Co-Authors: C Srinivasa
    Abstract:

    Multigrid technique is a method which accelerates the convergence and hence reduces the CPU time for a given flow problem. This technique has been used to solve the full Potential Equation for an airfoil in cartesian grid. This report describes the multigrid technique solutions obtained for two to three grid levels and for an angle of attack of zero degree and one degree. This report also gives the grid size details for various levels.

  • Multigrid Technique for Solving the Full Potential Equation on an Airfoil in Cartesian Grid
    1992
    Co-Authors: C Srinivasa
    Abstract:

    Multigrid technique has been tried to solve the Full Potential Equation on an airfoil in Cartesian grid. It has been shown that this technique accelerates the convergence and reduces the CPU time. Some important aspects regarding implementation of multigrid technique have also been highlighted.

Leland A. Carlson - One of the best experts on this subject based on the ideXlab platform.

  • Aerodynamic sensitivity coefficients using the three-dimensional full Potential Equation
    Journal of Aircraft, 1994
    Co-Authors: Hesham M. Elbanna, Leland A. Carlson
    Abstract:

    The quasianalytical (QA) approach is applied to the three-dimensional full Potential Equation to compute wing aerodynamic sensitivity coefficients in the transonic regime. Symbolic manipulation is used and is crucial in reducing the effort associated with obtaining sensitivity Equations, and the large sensitivity system is solved using sparse solver routines such as the iterative conjugate gradient method. The results obtained are almost identical to those obtained by the finite difference (FD) approach and indicate that obtaining the sensitivity derivatives using the QA approach is more efficient than computing the derivatives by the FD method, especially as the number of design variables increases. It is concluded that the QA method is an efficient and accurate approach for obtaining transonic aerodynamic sensitivity coefficients in three dimensions.

  • Determination of aerodynamic sensitivity coefficients based on the three-dimensional full Potential Equation
    10th Applied Aerodynamics Conference, 1992
    Co-Authors: Hesham M. Elbanna, Leland A. Carlson
    Abstract:

    The quasi-analytical approach is applied to the three-dimensional full Potential Equation to compute wing aerodynamic sensitivity coefficients in the transonic regime. Symbolic manipulation is used to reduce the effort associated with obtaining the sensitivity Equations, and the large sensitivity system is solved using 'state of the art' routines. Results are compared to those obtained by the direct finite difference approach and both methods are evaluated to determine their computational accuracy and efficiency. The quasi-analytical approach is shown to be accurate and efficient for large aerodynamic systems.