Vol. 13, No 4, 2009 < Volumes
(ISSN 1428-6394)

Contents:

  • Leonardo Pasini and Sandro Feliziani Simulators of VOIP Traffic in P2P Networks   abstract | full text
  • Mirosław Gajer Specialized Fully Automatic Machine Translation System Delivering High Quality of Translated Texts   abstract | full text
  • Mirosław Gajer Examining the Impact of Positive and Negative Constant Learning on the Evolution Rate   abstract | full text
  • Andrzej Czy/zewski and Maciej Szczodrak Software for Calculation of Noise Maps Implemented on Supercomputer   abstract | full text
  • Tomasz /Lusiak, Adam Dziubiński and Kazimierz Szumański Interference between Helicopter and Its Surroundings, Experimental and Numerical Analysis   abstract | full text
  • Patryk Chaja and Tadeusz Koronowicz Towards the Design of Low Noise Level Wind Turbines   abstract | full text
  • Paweł Sosnowski and Jacek Pozorski Open-Source CFD Analysis of Multi-domain Unsteady Heating with Natural Convection   abstract | full text

Abstracts:

hLeonardo Pasini and Sandro Feliziani Simulators of VOIP Traffic in P2P Networks

This study is included in a research programme developed by the authors at the University of Studies in Camerino for the construction of traffic flow simulators in computer and telecommunication networks [1–4]. The article contains the definition of a library of object types whose architecture is based on the queue networks, for a simulation of the VOIP traffic in P2P networks. Basing on this library, we simulate the traffic in a P2P network that is locally implemented with three different technology types: 1. Fast Ethernet, 2. Wireless, 3. ADSL2+. In this context, we simulate traffic flows due to file-sharing applications in the network and due to voice communications through the VOIP technology. Thus, we evaluate the impact of the VOIP traffic for procedures of file-sharing in a P2P network.

 

hMirosław Gajer Specialized Fully Automatic Machine Translation System Delivering High Quality of Translated Texts

The paper concerns machine translation systems that form a discipline of computer science and are aimed at writing computer programs that are able to translate text between natural languages. In the paper the author argues that it is not possible to build a machine translation system that would be able to translate any kind of documents with a sufficiently high quality. Instead, the author proposes a specialized machine translation system the aim of which is to translate financial reports concerning the global currency exchange market – forex. For the purpose of building the above mentioned system, the author has proposed his own machine translation method of translation patterns. The translation patterns allow transferring the translation process from the level of single words to the level of words chunks. The translation patterns play a very important role in the case of such an inflectional language as Polish because they make it possible to choose the correct form of Polish translation of foreign phrases depending whether they perform the verb or object function in the sentence. The high quality of the specialized machine translation system developed by the author was proved with many experiments the results of which are demonstrated in the paper. The quality of translation is so high that the Polish translations of English reports from the global currency exchange market can be published on Web pages without any additional changes. Thus, it is possible to totally eliminate the human translator from the process of translation of texts which are highly stereotypical and oriented to a selected and narrow domain.

 

hMirosław Gajer Examining the Impact of Positive and Negative Constant Learning on the Evolution Rate

The paper discusses the influence of learning on evolutionary processes. In biological sciences it is a well-known fact that the rate of evolution can be effected by learning and the same phenomena can also be observed in artificial evolutionary systems, however, their nature is still not sufficiently well understood. In the paper the influence of constant learning on the rate of evolution is examined. The constant learning is a kind of learning during which the genotype of the individual being taught is moved toward the global optimum over a constant value. If the fitness function is monotonic, it can be concluded from the mathematical theory that such kind of learning should decelerate evolution. However, this fact is highly counterintuitive and for this reason it should be proved by numerical experiments. In the article the results of numerical simulations are presented. They prove that evolution is indeed decelerated by learning in case of the sigmoid fitness function. Moreover, two cases of constant learning were examined in the paper. These are the positive and negative constant learning. It was demonstrated that in the case of the negative constant learning the evolution was decelerated to a larger extent than in the case of the positive constant learning. The obtained results can help explain certain phenomena concerning the impact of learning on the evolution both in natural and artificial evolutionary systems.

 

hAndrzej Czy/zewski and Maciej Szczodrak Software for Calculation of Noise Maps Implemented on Supercomputer

Investigation results relevant to the implementation of algorithms for calculation of noise maps are presented in this paper. The aim of implementing the algorithms on a computer cluster is explained. Selected implementation details of the software called Noise Propagation Model are described. The software interaction with the data acquisition system is presented. Noise maps obtained using the described software are presented. A comparison between the outcomes of the implemented models and the simulation results of a commercial program is presented. An analysis of the computation efficiency is described. A discussion concerning dynamic presentation of noise maps is also presented.

 

hTomasz /Lusiak, Adam Dziubiński and Kazimierz Szumański Interference between Helicopter and Its Surroundings, Experimental and Numerical Analysis

The paper describes the phenomenon of the occurrence of aerodynamic interference between a helicopter and an object in its near vicinity. Such situations occur during rescue missions as well as during police and military operations when the helicopter flies near such objects as buildings and ships. The specific shape of the example object, a typical town courtyard, is discussed below. The influence of the interference on the rotor and fuselage loading, air flow and flying qualities was analyzed for these special cases of helicopter operations. The results of the computations performed using the FLUENT software in terms of the dynamic response to disturbances on the simulation model of a helicopter rotor have been presented. The model used in these calculations made it possible to analyze flexible rotor blades. The results of the experimental tests of interference between the helicopter model and different shapes have been attached, as well.

 

hPatryk Chaja and Tadeusz Koronowicz Towards the Design of Low Noise Level Wind Turbines

According to the authors' hypothesis generation of high intensity noise is caused by generation of vorticity structures inducing velocities that can be locally higher than the velocity of sound. The localization and magnitude of vorticity concentration can be precisely defined on the basis of a double layer vortex model. Knowing the localization and mechanism of generation of significantly high induced velocities, turbine blades can be shaped in such a way so as to decrease the concentration of vorticity in these zones. According to the hypothesis described in this paper, a modification of turbine blades at the design stage results in their quieter operation for higher loads and wind velocities. The authors base their hypothesis on the experience from design works concerning low noise ship propellers. The following paper focuses on these tasks.

 

hPaweł Sosnowski and Jacek Pozorski Open-Source CFD Analysis of Multi-domain Unsteady Heating with Natural Convection

The paper presents the capabilities of open-source programs used for numerical simulation of fluid flow and heat transfer phenomena. These tools are applied for unsteady problems with natural convection and, in particular, the heating of an automotive headlight. To perform these studies, a solver was created using an open-source C++ library OpenFOAM. The implementation problems encountered were, inter alia, dealing with multi-domain computation and coupling of sub-domains. The presented simulation results clearly show that open-source software can readily be applied also to engineering problems and can compete with commercial packages.

 

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