Catálogo de publicaciones - libros

In this Paper we will present a set of modules and plugins developed for the COVISE visualization system which allow setting up interactive CFD simulations. Real objects can be moved in a model and thus provide an easy to use interface to modify the geometry of the simulation.

We address the problem of detecting deviations of a binary sequence from randomness, which is very important for ra ndom number (RNA) and pseudorandom number generators (PRNG) and their applications to cryptography. Namely, we consider a hypothesis that a given bit sequence is generated by the Bernoulli source with equal probabilities of 0’s and 1’s and the alternative hypothesis that the sequence is generated by a stationary and ergodic source which differs from the source under . We show that data compression methods can be used as a basis for such testing and describe two new tests for randomness, which are based on ideas of universal coding. Known statistical tests and suggested ones are applied for testing PRNGs which are used in practice. The experiments show that the power of the new tests is greater than of many known algorithms.

We discuss basic optimization and parallelization strategies for current cache-based microprocessors (Intel Itanium2, Intel Netburst and AMD64 variants) in single-CPU and shared memory environments. Using selected kernel benchmarks representing data intensive applications we focus on the effective bandwidths attainable, which is still suboptimal using current compilers.We stress the need for a subtle OpenMP implementation even for simple benchmark programs, to exploit the high aggregate memory bandwidth available nowadays on ccNUMA systems. If the quality of main memory access is the measure, classical vector systems such as the NEC SX6+ are still a class of their own and are able to sustain the performance level of in-cache operations of modern microprocessors even with arbitrarily large data sets.

‘Virtual Organizations’ belong to the key concepts in the Grid computing community. They are currently evolving from basically static to dynamic solutions that are created ad-hoc in reaction to a market demand. This paper provides a defi- nition of ‘dynamic Virtual Organizations’ in order to assess specific challenges of an abstract collaborative engineering scenario. The paper concludes with a description of an evolving architecture enabling such dynamic virtual organizations.

The performance of algorithms dependents on a whole bunch of parameters, not only frequency of the processor but also its architecture, bandwidth and different latencies for getting data. Also the implementation of the algorithm is essential. We try to identify some important parameters by the analysis of the delivered performance of some typical algorithms and to show the differences between architectures.

This paper presents the design and implementation of the Science Grid Modeling Laboratory (SGM-Lab), an automated parametric modeling system for performing complex dynamically-controlled parameter studies. Nowadays, simulation programs are used not only in research but also during the development of products, often to optimize their quality. Typically, this involves repeated execution of the simulation codes, whereby for each run some of the input data is varied. As a result, many different jobs have to be launched and a huge amount of output data has to be administered. A grid environment can provide, and enable the exploitation of the necessary resources for this computation. However, in order to be able to use a grid environment effectively, tool support is required to automatically generate the parameter sets, issue jobs, control the successful operation and termination of jobs, and collect results. Support is also needed to generate new parameter sets based on previous results in order to obtain a functional optimum, after which the parameter study should terminate. The SGM-Lab software described in this paper offers a unified framework for such large-scale optimization problems.

Canonical flows like homogeneous, irrotationally strained or linearly sheared turbulence, or developed plane channel turbulence have been studied for many years. Direct numerical simulations have produced reliable data at moderate Reynolds numbers in some of these flows, where homogeneity and symmetry allows for substantial reduction of the computational effort. But flows possessing less symmetries, such as grid–generated turbulence or simple flows combining features of several canonical ones, have remained difficult to treat with such simulations. Motivated by specific industrial design applications, we have investigated by direct and large–eddy simulations several flows of that kind.