Institute for Computational Mechanics in Propulsion (ICOMP)

The Institute for Computational Mechanics in Propulsion (ICOMP) is operated by the Ohio Aerospace Institute (OAI) and the NASA Lewis Research Center in Cleveland, Ohio. The purpose of ICOMP is to develop techniques to improve problem-solving capabilities in all aspects of computational mechanics related to propulsion. This report describes the accomplishments and activities at ICOMP during 1993

Seventh Copper Mountain Conference on Multigrid Methods

The Seventh Copper Mountain Conference on Multigrid Methods was held on April 2-7, 1995 at Copper Mountain, Colorado. This book is a collection of many of the papers presented at the conference and so represents the conference proceedings. NASA Langley graciously provided printing of this document so that all of the papers could be presented in a single forum. Each paper was reviewed by a member of the conference organizing committee under the coordination of the editors. The vibrancy and diversity in this field are amply expressed in these important papers, and the collection clearly shows the continuing rapid growth of the use of multigrid acceleration techniques

Prolongationsoperatoren für ein nichtlineares Mehrgitterverfahren auf unstrukturierten Gittern

In dieser Studienarbeit wurde innerhalb des nichtlinearen Mehrgitters im unstrukturierten Strömungslöser CODA der Einfluss der Prolongationsordnung und der Ordnung der Grobgitterdiskretisierung auf die Beschleunigung und die Robustheit untersucht. Darüber hinaus wurde eine positivitätserhaltende Grobgitterkorrektur implementiert und untersucht. Diese modifizierte Grobgitterkorrektur soll verhindern, dass notwendigerweise positive Größen wie die Dichte nach der Korrektur auf dem feinen Gitter negativ werden. Anhand von zwei zweidimensionalen Testfällen konnte eine eine Verringerung der Iterationen und der Rechenzeit aufgrund einer erhöhten Prolongationsordnung gezeigt werden. Eine genauere Grobgitterdiskretisierung führte für die turbulente, reibungsbehaftete Strömung ebenfalls zu einer Verringerung von Rechenzeit und Iterationen. Für den untersuchten reibungslosen Fall zeigte sich diese Beschleunigung nicht. Die Trends wurden zusätzlich an einem dreidimensionalen, reibungsbehafteten Testfall bestätigt. Die Robustheit nahm durch eine Grobgitterdiskretisierung 2. Ordnung gegenüber einer Diskretisierung 1. Ordnung ab, sodass das Beschleunigungspotential durch einen Verringerung der Robustheit erkauft werden müsste. Eine höhere Prolongationsordnung hatte hingegen einen deutlich geringeren Einfluss auf die Robustheit, welcher ohne erkennbaren Trend war. Für die positivitätserhaltende Grobgitterkorrektur ergab sich ein sehr geringer Einfluss auf das Konvergenzverhalten. Durch eine Variation von der physikalischen Randbedingungen konnten anhand eines reibungslosen Testfalls gezeigt werden, dass es Fälle gibt, in denen eine positivitätserhaltende Grobgitterkorrektur die Stabilität des Lösungsprozesses verbessern kann

SciCADE 95: International conference on scientific computation and differential equations

This report consists of abstracts from the conference. Topics include algorithms, computer codes, and numerical solutions for differential equations. Linear and nonlinear as well as boundary-value and initial-value problems are covered. Various applications of these problems are also included

Consideration of Lie Symmetry Groups in Computational Fluid Dynamics

Lie symmetries are fundamental properties of differential equations that are often not actively considered in construction of numerical schemes relevant to computational fluid dynamics (CFD). While many of these numerical schemes in CFD are constructed based on consideration of a desired order of accuracy and have shown promising results, these schemes usually do not accurately represent fundamental symmetry (or invariance) properties of underlying governing equations. The overall objective of this dissertation is to address this limitation via development of numerical schemes that not only preserve Lie symmetries of underlying differential equations but also ensure a desired order of accuracy. In this regard, novel methodologies for construction of high order accurate invariant numerical schemes, based on the method of equivariant moving frames, are introduced. Formulation of high order accurate invariant schemes presented in this work involves consideration of (a) modified equations (via perturbation or defect correction) and/or (b) compact schemes. Modified forms of equations are used not only to achieve a desired order of accuracy in associated invariant schemes but also to systematically select convenient moving frames. Further, in the construction of invariant compact schemes, extended symmetry groups of differential equations are considered where point transformations based on these extended groups are used to transform existing base schemes to their invariant forms. Construction and performance of symmetry preserving numerical schemes are discussed for a variety of linear and nonlinear canonical problems (such as linear advection-diffusion equation in 1D/2D, inviscid Burgers' equation, viscous Burgers' equation along with application to Euler equations in 1D/2D). The overall quality of results obtained from constructed invariant numerical schemes is often found to be notably better than that of standard, non-invariant base numerical schemes. Such improvements in results are particularly more significant when error measures based on symmetry properties of underlying differential equations are considered

Bibliography of Lewis Research Center technical publications announced in 1993

This compilation of abstracts describes and indexes the technical reporting that resulted from the scientific and engineering work performed and managed by the Lewis Research Center in 1993. All the publications were announced in the 1993 issues of STAR (Scientific and Technical Aerospace Reports) and/or IAA (International Aerospace Abstracts). Included are research reports, journal articles, conference presentations, patents and patent applications, and theses

Aeronautical Engineering, A Continuing Bibliography With Indexes

This bibliography lists 693 reports, articles and other documents introduced into the NASA scientific and technical information system in September 1984