Catálogo de publicaciones - libros

Slender vortices of compressible flow are studied, in particular the deceleration of the axial flow to a free stagnation point on the axis, causing bursting or breakdown of the vortex. Steady, inviscid, compressible, axially symmetric flow conditions are assumed to enable a reduction of the Euler equations for a stream tube of small radius. The angular velocity near the axis is shown to be directly proportional to the axial mass flux, indicating that a decelerated axial flow can cause the angular velocity to vanish and breakdown to occur. This behavior is reversed in supersonic flow. A breakdown criterion is derived for a Rankine vortex with isentropic and normal-shock deceleration of the axial flow. The results are compared with available experimental data.

The new approach to construction of monotonic nonlinear difference second order schemes, based on the investigation of the differential approximation of a scheme, is presented. One of possible formulas for the definition of approximating viscosity is given, which leads to the coincidence of the constructed scheme with the Harten’s TVD scheme. The known and widely used TVD schemes with other limiters can be also obtained using the presented approach.

With the increase of processor performance numerical simulation has become a ubiquitous technology both in science and industry. In both fields it is part of a workflow or a process chain in which it has to be integrated in a seamless way. In research this integration is sometimes referred to as e-science. The term indicates that electronic means change the way scientists work. In industry the key words are information lifecycle management (ILM) and product lifecycle management (PLM). They describe the fact that information processes are integrated via a coordinated software solution into processes and work flows. Simulation and its results have to become a part of this context. The paper presented focuses on simulations carried out on supercomputing systems. The special problems of their integration both in the scientific work and the industrial process are discussed.

The current results of the joint project of the Institute of Computational Technologies of the Siberian Branch of the Russian Academy of Sciences (ICT SB RAS, Novosibirsk, Russia) and the High Performance Computing Center Stuttgart (HLRS, Stuttgart, Germany) are presented. The project is realized within the framework of the activities of the German-Russian Center for Computational Technologies and High Performance Computing.

A boundary value problem for the Navier-Stokes equations for a viscous heat conducting gas in a finite computational domain is considered. The space approximation is constructed with the use of the Bubnov-Galerkin method combined with the method of lines. The parallel realization of this method is discussed for multiprocessor computational system.

Effective iterative algorithms are considered for numerical implementation of the solution of auxiliary differential equations. These equations appear when using splitting schemes, for which convergence theorems are proved and convergence rates are estimated. An effective algorithm is suggested, allowing the grid continuity equation to be satisfied identically.

In this contribution we describe and evaluate an efficient implementation of an adaptive and parallel grid () within the Distributed and Unified Numerics Environment . A generalization of the serial grid interface of , described in [1], to the adaptive and parallel case is discussed and example computations using the grid interface are presented. The computations are compared with computations of the original code, which was optimized for the specific example problem studied here.

The description of the DWD-contribution (DWD - Deutscher Wetterdienst) in the work under the EU-Project “An European Flood Forecasting System” (EUContract EVG1-CT-1999-00011 EFFS) is presented. The aim of the EU-funded project was the development of a prototype version of a medium-range (up to 10 days ahead) flood forecasting system for the whole of Europe. The brief description of methods for preparing input meteorological fields on high performance systems for EU-Project and the complex operational models of an atmosphere used for their construction are given. The used algorithm for numerical analysis of high-resolution analyses of 24h precipitation heights on the basis of surface observations for the four flood events in 1994 (Po, November), 1995 (Rhine/Meuse, January), 1997 (Odra, July) and 2002 (Elbe, August) is presented.

For the numerical simulation of large scale CFD and fluid-structure interaction (FSI) problems efficiency and robustness of the algorithms are two key requirements. In this paper we would like to describe a very simple concept to increase significantly the performance of the element calculation of an arbitrary unstructured finite element mesh on vector computers. By grouping computationally similar elements together the length of the innermost loops and the vector length can be controlled. In addition the effect of different programming languages and different array management techniques will be investigated. A numerical CFD simulation will show the improvement in the overall time-to-solution on vector computers as well as on other architectures.

The main line of application of computational methods in General Relativity is concerned with the determination of the waveforms of the gravitational radiation which is emitted from astrophysical processes. Gravitational wave detectors, currently under construction and calibration, need this information in order to filter out the signals from the noisy background. This contribution describes the basic ideas behind these efforts.