Catálogo de publicaciones - libros

An efficient approach for the numerical simulation of arbitrary shaped bodies using cartesian grids is presented. The method is applied to the simulation of an airfoil at Re=20 000 and high angle of attack. Results of different flow configurations are compared.

Computational Fluid Dynamics (CFD) simulations in a Virtual Reality (VR) environment allow a very flexible analysis of complex flow phenomena, supporting the planning process of a building with respect to fluid mechanical aspects. In this paper a prototype application of a CFD-based computational steering system is presented.

Simple geometries can be modified interactively in a Virtual Reality system consisting of a stereoscopic projection unit and a wand device and are sent to a high performance supercomputer. The underlying CFD simulation is performed by a Lattice-Boltzmann kernel, which shows excellent parallel efficiency. State-of-the-art visualization techniques allow for an intuitive investigation of the transient nature of the corresponding flow field.

The area of application primarily covers the analysis of indoor air flow and the optimization of Heat Ventilation Air Conditioning (HVAC) systems.

To study the effect of free-stream fluctuations on laminar flow separation a series of Direct Numerical Simulations (DNS) is performed. The three largest computations have been carried out on the Hitachi SR8000 F1 at the Leibniz Computing Centre (LRZ) in Munich using 256 processors. The level of the free-stream disturbances in the oncoming flow is found to have a significant impact on the size of the Laminar Separation Bubble (LSB). Downstream of the separation bubble, the near wall turbulent flow is found to only slowly assume the ”normal” characteristics of a turbulent boundary layer.

Parallel multigrid methods belong to the most prominent tools for solving huge systems of (non-)linear equations arising from the discretisation of PDEs, as for instance in Computational Fluid Dynamics (CFD). However, the quality of (parallel) multigrid methods in regard of numerical and computational complexity mainly stands and falls with the smoothing algorithms (“smoother”) used. Since the inherent highly recursive character of many global smoothers (SOR, ILU) often impedes a direct parallelisation, the application of block smoothers is an alternative. However, due to the weakened recursive character, the resulting parallel efficiency may decrease in comparison to the sequential performance, due to a weaker total numerical efficiency. Within this paper, we show the consequences of such a strategy for the resulting total efficiency on the Hitachi SR8000-F1 if incorporated into the parallel CFD solver for 3D incompressible flow. Moreover, we analyse the numerical losses of parallel efficiency due to communication costs and numerical efficiency on several modern parallel computer platforms.

Quantum-Chromodynamics (QCD) is the theory of quarks, gluons and their interaction. It has an important almost exact symmetry, the so-called chiral symmetry (which is actually broken spontaneously). This symmetry plays a major role in all low-energy hadronic processes. For traditional formulations of lattice QCD, CPU-time and memory limitations prevent simulations with light quarks and this symmetry is seriously violated. During the last years successful implementations of the chiral symmetry for lattice QCD have been constructed. We use two approximate implementations (both of them in the quenched approximation) with different specific advantages. We have also made progress towards the development of a practical algorithm to allow for simulations with dynamical quarks. In 2003 a series of discoveries of a new class of particles, called pentaquarks, has created very strong interest in lattice studies of resonance states. We have performed such studies with a specific method for the N* resonances with very satisfying results and are currently working on similar calculations for the pentaquarks. We have also addressed the question, which type of gauge field configurations is responsible for confinement and chiral symmetry breaking. Finally we are calculating three-point functions. We hope that for the small quark masses which we reach the results will not only be of direct phenomenological interest, but will also test predictions from chiral perturbation theory.

In deformations of polynomial functions one may encounter “singularity exchange at infinity” when singular points disappear from the space and produce “virtual” singularities which have an influence on the topology of the limit polynomial. We find several rules of this exchange phenomenon, in which the total quantity of singularity turns out to be not conserved in general.

We present a density functional study of structures and reactivities of [VO(O)(Im)], a model peroxovanadium(V) complex with a biogenic ligand, and its potential use as catalyst in biomimetic oxidations of organic substrates. The mechanism of olefin epoxidation mediated by this complex is studied in detail for the gas-phase. In addition, structures and energetics of key intermediates in the catalytic cycle are simulated in solution using the Car-Parrinello molecular dynamics (CPMD) technique. The rate-limiting step is indicated to be oxo transfer from a peroxo moiety of the catalyst to the substrate. In a second part, the standard used for V NMR spectroscopy, VOCl, is modeled as neat liquid by means of CPMD simulations. According to preliminary results for the magnetic shieldings averaged along the trajectory, the V nucleus is deshielded by ca. 40 ppm.

We use molecular dynamics simulations in order to understand the dissolution and diffusion of water in bulk amorphous silica. These simulations are driven in the liquid state at temperatures where the systems can be brought to equilibrium. In the equilibrated state we are able to investigate hydrogen diffusion mechanisms in the time window present days' molecular dynamics simulations can offer. Quenches of selected configurations to ambient temperatures allow comparisons of the obtained structure with experimental results. In this article we describe the setup of such kind of simulation on the Hitachi SR8000-F1 and give a brief overview of some results that have already been presented in two scientific articles [1, 2].

In this report we present dynamical simulations of ultrafast electron transfer (ET) reactions in mixed valence compounds in solution and at dye-semiconductor interfaces. The dynamical calculations are based on the self-consistent hybrid approach. To study the ET dynamics we consider the population dynamics of the donor/acceptor states as well as pump-probe spectra for these reactions. In addition, results of electronic structure calculations for small models of dye-semiconductor complexes are presented.

In deformations of polynomial functions one may encounter “singularity exchange at infinity” when singular points disappear from the space and produce “virtual” singularities which have an influence on the topology of the limit polynomial. We find several rules of this exchange phenomenon, in which the total quantity of singularity turns out to be not conserved in general.