306 research outputs found
READ @your library Beny Neta (bookmark)
No full textA project of the Dudley Knox Library at the Naval Postgraduate School
READ @your library Beny Neta (poster)
No full textA project of the Dudley Knox Library at the Naval Postgraduate School
A new sixth-order scheme for nonlinear equations
No full textApplied Math. Letters, 25, (2012), 185–189, doi:10.1016/j.aml.2011.08.012.The article of record as published may be located at http://dx.doi.org/10.1016/j.aml.2011.08.012In this paper we present a new efficient sixth-order scheme for nonlinear equations. The method is compared to several members of the family of methods developed by Neta (1979) [B. Neta, A sixth-order family of methods for nonlinear equations, Int. J. Comput. Math. 7 (1979) 157–161]. It is shown that the new method is an improvement over this well known scheme
Software for the staggered and unstaggered Turkel-Zwas schemes for the shallow water equations on the sphere
No full textA linear analysis of the shallow water equations in spherical coordinates for the Turkel-Zwas1 explicit large time-step scheme was presented by Neta, Giraldo and Navon2 as well as the unstaggered1 Turkel-Zwas scheme for the solution of the shallow water equations on the sphere.Approved for public release; distribution is unlimited
Application of Higdon non-reflecting boundary conditions to shallow water models
No full textIn many applications involving wave propagation, problem domains are often very large or unbounded. A common numerical method used to solve such problems is to truncate the domain via artificial boundaries to form a finite computational domain. To accomplish this, Non-Reflecting Boundary Conditions (NRBC's) which minimize spurious wave reflections are imposed. The quality of the solution strongly depends on the properties of both the NRBC and the wave behavior. This dissertation explores the use of Higdon NRBC's to solve shallow water equations (SWE's) in a dispersive environment. A linearized SWE model is developed that includes stratification and advection effects. Initially a single NRBC is used to truncate a semi-infinite channel. Later four NRBC's are used to restrict an infinite plane. In both cases finite rectangular domains are formed. A scheme developed by Neta and Givoli is used to rapidly discretize high-order Higdon NRBC's. Finite difference methods and are used in all numerical schemes, which are solved explicitly when possible. Results will show that Higdon NRBC's can be used effectively to restrict large rectangular domains when solving SWE's that include the before mentioned effects.Approved for public release; distribution is unlimited.Commander, United States Navyhttp://archive.org/details/applicationofhig109451104
Unstructured high-order galerkin-temporal-boundary methods for the klein-gordon equation with non-reflecting boundary conditions
No full textA reduced shallow water model under constant, non-zero advection in infinite domains is considered. High-Order Givoli-Neta (G-N) and Hagstrom-Hariharan (H-H) non-reflecting boundary conditions (NRBCs) are introduced to create a finite computational space and solved using a spectral element formulation with high-order time integration. Numerical examples are used to demonstrate the synergy of using high-order spatial, time and boundary discretizations. Several alternatives are also presented for solving open domain problems. These alternatives include adjustments to the G-N NRBC based on physical arguments as well as formulating the boundary condition for arbitrary domains using unstructured grids. The H-H polar NRBC is also formulated in an unstructured grid setting and extended to include dispersive effects. Results show that by balancing all numerical errors involved, high-order accuracy can be achieved for unbounded channel problems. Further, the adjustments to the G-N and H-H NRBCs to operate in an unstructured grid setting are shown to significantly reduce errors over first order non-reflecting boundary schemes when operating in an open domain configuration.Major, United States Armyhttp://archive.org/details/unstructuredhigh109451052
Parallelization of the Naval Space Surveillance Center (NAVSPASUR) satellite motion model
No full textThe Naval Space Surveillance Center (NAVSPASUR) uses an analytic satellite motion model based on the Brouwer-Lyddane theory to assist in tracking over 6000 objects in orbit around the earth. The satellite motion model is implemented by a Fortran subroutine, PPT2. Due to the increasing number of objects required to be tracked, NAVSPASUR desires a method to reduce the computation time of this satellite motion model. Parallel computing offers one method to achieve this objective. This thesis investigates the parallel computing potential of the MAVSPASUR model using the Intel iPSC/2 hypercube multi-computer. The thesis developed several parallel algorithms for the NAVSPASUR satellite motion model using the various methods of parallelization, applies these algorithms to the hypercube, and reports on each algorithm's potential reduction in computation time. A diskette containing the Fortran software is available upon request from [email protected] for public release; distribution is unlimited.Captain, United States Armyhttp://archive.org/details/parallelizationo109452400
Stability analysis for Eulerian and semi-Lagrangian finite-element formulation of the advection-diffusion equation
No full textThe article of record as published may be located at http://dx.doi.org/10.1016/S0898-1221(99)00185-6This paper analyzes the stability of the finite-element approximation to the linearized two-dimensional advection-diffusion equation. Bilinear basis functions on rectangular elements are considered. This is one of the two best schemes as was shown by Neta and Williams [1]. Time is discretized with the theta algorithms that yield the explicit (theta = 0), semi-implicit (theta = 1/2), and implicit (theta = 1) methods. This paper extends the results of Neta and Williams [1] for the advection equation. Giraldo and Neta [2] have numerically compared the Eulerian and semi-Lagrangian finite-element approximation for the advection-diffusion equation. This paper analyzes the finite element schemes used there. The stability analysis shows that the semi-Lagrangian method is unconditionally stable for all values of a while the Eulerian method is only unconditionally stable for 1/2 < theta < 1. This analysis also shows that the best methods are the semi-implicit ones (theta = 1/2). In essence this paper analytically compares a semi-implicit Eulerian method with a semi-implicit semi-Lagrangian method. It is concluded that (for small or no diffusion) the semi-implicit semi-Lagrangian method exhibits better amplitude, dispersion and group velocity errors than the semi-implicit Eulerian method thereby achieving better results. In the case the diffusion coefficient is large, the semi-Lagrangian loses its competitiveness. Published by Elsevier Science Ltd
- …
