Vol. 6, No 3, 2002 < Volumes
(ISSN 1428-6394)

Contents:

  • Zofia Kowalska Modelling and Simulation of Dynamic Unilateral Elasto-plastic Contact of Compact Hard Bodies   abstract | full text
  • Roman Bogacz, Michał Kocjan and Włodzimierz Kurnik Dynamics of Wheel-Tyre Subjected to Moving Oscillating Force   abstract | full text
  • Zdzisław Gałkowski An Analysis of Influence of SMA Material on Dynamic Properties of a Spring Taking into Account Constructional Friction   abstract | full text
  • Marek Pietrzakowski A Design of Piezoelectric Vibration Absorber with the Capacitive Adjustment   abstract | full text
  • Anita Usciłowska and Jan A. Kołodziej Chaotic Motion of a Multi-articulated Tower Immersed in Waving Fluid: Numerical Experiment   abstract | full text
  • Szymon Opoka and Henryk Walukiewicz Informational Entropy in Simulation of One-dimensional Random Fields   abstract | full text
  • Jacek Tejchman Evolution of Shear Localisation in Earth Pressure Problems of a Retaining Wall   abstract | full text
  • Tomasz Majewski and Jacek Tejchman Numerical Analysis of Behaviour of Reinforced Concrete Elements under Eccentric Compression   abstract | full text
  • Jan Kozicki and Jacek Tejchman Application of a Cellular Automata Model to Granular Flow   abstract | full text
  • Jerzy Bobiński and Jacek Tejchman A Non-local Elasto-plastic Model to Describe Localisations of Deformation in Concrete   abstract | full text
  • Marcin Kujawa, Tomasz Mikulski and Czesław Szymczak Numerical Simulation of Behaviour of Thin-walled Frames Subjected to Static Loads   abstract | full text
  • Ireneusz Kreja and Czesław Szymczak Numerical Simulation of a Thin-walled Beam with Warping Stiffeners Undergoing Torsion   abstract | full text
  • Marek Litniewski Influence of Step Errors (Truncation Errors) on Results of Molecular Dynamics Simulations   abstract | full text
  • Jacek Leluk, Monika Sobczyk and /Lukasz Becella Correlated Mutations in Selected Protein Families   abstract | full text
  • Wojciech Kwedlo and Marek Kr/etowski Learning Decision Rules Using a Distributed Evolutionary Algorithm   abstract | full text
  • Sławomir T. Wierzchoń Function Optimization by the Immune Metaphor   abstract | full text
  • Marek Kozłowski and Sławomir T. Wierzchoń Evolutionary Algorithm for Learning Bayesian Structures from Data   abstract | full text
  • Mirosław Gajer The Implementation of the Example-based Machine Translation Technique for French-to-Polish Automatic Translation System   abstract | full text
  • Andrzej Januszajtis The Library of the Technical University of Gdansk in Bremen   abstract | full text

Abstracts:

hZofia Kowalska Modelling and Simulation of Dynamic Unilateral Elasto-plastic Contact of Compact Hard Bodies

The problems of modelling, simulation and analysis of vibro-impact motion of compact hard bodies are considered. In particular, dynamic elasto-plastic contact is simulated by using Johnson's analytical model of spherical bodies' contact. The results are compared with behaviour of the system with discrete linear-perfectly plastic model of contact.

 

hRoman Bogacz, Michał Kocjan and Włodzimierz Kurnik Dynamics of Wheel-Tyre Subjected to Moving Oscillating Force

The subject of the paper is analysis of wheel of a moving railway vehicle which is subjected to a moving oscillating force. Rail ring is treated as a beam of small curvature connected to wheel axle with a Winkler foundation. Bernoulli-Euler and Timoshenko beam model is used. Results are gained using Fourier transformation. Space and space-time graphs, showing wave propagation in subcritical and supercritical zones of excitation, concerning resonance of transverse vibrations, are included.

 

hZdzisław Gałkowski An Analysis of Influence of SMA Material on Dynamic Properties of a Spring Taking into Account Constructional Friction

In this paper, an analysis of forced transverse harmonic vibration with constant changes of the exciting force in a dynamic system consisting of two beams is presented together with a model of a leaf spring. In this junction both beams are made of shape memory material (SMA). The constructional friction is also taken into account. For the purpose of the analysis an equivalent linearization of the elasticity-damping features of the beams was conducted. As an effect of linearization a junction was acquired with both stiffness of elements and viscosity damping. The obtained differential equations were solved using the asymptotic Bogolubov-Krylov-Mitropolski method. The results of the conducted simulation are presented on graphs, showing the influence of unitary pressure on the system's damping properties.

 

hMarek Pietrzakowski A Design of Piezoelectric Vibration Absorber with the Capacitive Adjustment

In the paper the problem of vibration damping via piezoelectric absorbers capacitively shunted is studied. The considered system is a simply supported beam with the absorber composed of piezoceramic patches joined by means of brackets in a uniform distance from the beam surface, symmetrically on both sides of the beam. Due to the applied damping strategy piezoceramic actuators are shunted with a changeable capacitor in the external circuit to tune the resonance frequencies of the system. The analysis is completed with results of numerical simulations.

 

hAnita Usciłowska and Jan A. Kołodziej Chaotic Motion of a Multi-articulated Tower Immersed in Waving Fluid: Numerical Experiment

The offshore structures, such as multi-articulated towers, manipulators working in waving fluid are more and more popular structures. Commonly they are modelled as an inverted pendulum. The motion of such tower immersed in waving fluid is under consideration. It is assumed that the tower is hinged to the seabed by the hinge with friction. The joint of tower elements is the hinge with friction, as well. Motion of tower loaded by regular wave fluid force is considered. The numerical experiment shows that the multi-potential systems may move chaotically for some parameters of the tower and the fluid.

 

hSzymon Opoka and Henryk Walukiewicz Informational Entropy in Simulation of One-dimensional Random Fields

The entropy H of a continuous distribution with probability density function f (•) is defined as a function of the number of nodes (n) in a one-dimensional scalar random field. For the second order theory this entropy is expressed by the determinants of the covariance matrices and simulated for several types of correlation functions. In the numerical example the propagation of the entropy for the static response of linear elastic, randomly loaded beam has been considered. Two unexpected results have been observed: • function H(n) is entirely different for differentiable (m. s.) and non-differentiable fields, with the same parameters in the correlation functions, • in some cases, the greater randomness at the input (measured by the entropy) does not lead to the greater randomness at the output.

 

hJacek Tejchman Evolution of Shear Localisation in Earth Pressure Problems of a Retaining Wall

The paper deals with numerical investigations of the evolution of shear localisation in granular bodies for earth pressure problems of a retaining wall in conditions of plane strain. The passive and active failure of a retaining wall in sand is discussed. The calculations are carried out with a rigid and very rough retaining wall undergoing horizontal translation, rotation around the top and rotation around the bottom. The behaviour of dry sand is numerically modelled with a finite element method using a hypoplastic constitutive relation within a polar (Cosserat) continuum. The constitutive relation is obtained through extension by polar quantities, viz. rotations, curvatures and couple stresses, using the mean grain diameter as a characteristic length. During FE-calculations, the attention is laid on the influence of different wall movements on shear localisation. In addition, the effects of the initial void ratio, distribution of the initial void ratio and mean grain diameter, pressure level and size of the sand body and retaining wall is investigated in the case of a passive wall translation. The FE-results are compared with corresponding experimental results of laboratory model tests.

 

hTomasz Majewski and Jacek Tejchman Numerical Analysis of Behaviour of Reinforced Concrete Elements under Eccentric Compression

Paper presents results of numerical modelling of behaviour of plane strain reinforced concrete elements under eccentric compression. In the analysis, a finite element method was used based on an elasto-plastic constitutive law by Drucker-Prager with hardening and softening for concrete and an elasto-plastic constitutive law by von Mises for reinforcement. The effects of boundary conditions at the element ends, eccentricity of the compressive load, element slenderness, area of the longitudinal and horizontal reinforcement on the load bearing capacity of elements were studied. The effect of the mesh refinement on the bearing capacity of elements was also analysed. A satisfactory agreement with model tests was achieved.

 

hJan Kozicki and Jacek Tejchman Application of a Cellular Automata Model to Granular Flow

Paper presents the results of simulations of granular flow with a cellular automata model. Flow of granular material behind a moving retaining wall and in a silo with inserts was numerically analysed. Two different migration schemes during flow were assumed. Advantages and limits of the model were outlined.

 

hJerzy Bobiński and Jacek Tejchman A Non-local Elasto-plastic Model to Describe Localisations of Deformation in Concrete

The paper presents numerical simulations of behaviour of concrete elements subjected to uniaxial compression for plane strain. FE-calculations are performed with two different elasto-plastic constitutive laws for concrete. Numerical results obtained suffer from mesh sensivity due to the presence of material softening. To obtain a well-posed boundary problem and a mesh independent solution, conventional constitutive laws with softening require an extension (called regularisation) to describe properly the localisations of deformations. In this paper elasto-plastic constitutive laws are extended by non-local strain terms. Owing to them, localisations of deformations are realistically captured.

 

hMarcin Kujawa, Tomasz Mikulski and Czesław Szymczak Numerical Simulation of Behaviour of Thin-walled Frames Subjected to Static Loads

In this paper we are discussing the problem of behaviour of frames composed of thinwalled members with bisymmetric open cross-section. We present results of computer simulations of behaviour of the frame subjected to torsional loads. The main problem of the simulation is bimoment distribution in the frame node. The new approach using the node superelement is proposed to carry out static analysis of the frame. Numerical examples of the frame analysis subjected to a torque are given.

 

hIreneusz Kreja and Czesław Szymczak Numerical Simulation of a Thin-walled Beam with Warping Stiffeners Undergoing Torsion

A new approach to numerical simulation of behavior of thin-walled beams of open crosssection with some warping stiffeners is presented. The structure model consists of one-dimensional finite elements described by the standard theory of thin-walled beams with non-deformable crosssection and FEM superelements with warping stiffeners. Comparative study of different kinds of modeling of the beams is performed; some numerical examples of simulation of I-beams behavior are given.

 

hMarek Litniewski Influence of Step Errors (Truncation Errors) on Results of Molecular Dynamics Simulations

Step errors (local errors, called also truncation errors) of the algorithms used in molecular dynamics simulations may result in non-physical correlations between particle velocities, as well as in errors of thermodynamic properties of simulated systems (energy, pressure). The simulations of the Lennard-Jones liquid showed, that the influence is especially high for the Verlet velocity algorithm. Beeman's technique decreases the correlations between the velocities, but at high densities the values of the errors of general averages are close to that of the Verlet method. The influence of step errors can be decreased by about two orders of magnitude by applying the Cowell-Numerov 4th order implicit method (equivalent to the Gear 4th order method treated as an implicit one). The method is very stable (more stable than the Verlet one), and can be highly optimized by restricting iteration to the closest neighbors of a given particle. As a result, the method becomes more efficient than the higher order explicit symplectic methods.

 

hJacek Leluk, Monika Sobczyk and /Lukasz Becella Correlated Mutations in Selected Protein Families

Four different protein families (two proteinase inhibitor families, myoglobins and lysozymes) were surveyed for correlated mutations with respect to the position distance and their significance in structure stabilization and biological activity. They were chosen for this study in order to verify the currently admitted model of mutational correlation relationship with respect to spatial contact of the residues and contribution in protein biological activity. There was observed high contribution of spatially dispersed residues (which are also not involved in the protein active center) in mutational correlation. Because of the significantly large distance between correlated positions these cases do not correspond explicitly to any mechanism included in current hypotheses. It is suggested that the role of residue spatial contact in structure preservation, intermolecular interaction and active site rescue mechanisms only partially explains the correlation phenomenon.

 

hWojciech Kwedlo and Marek Kr/etowski Learning Decision Rules Using a Distributed Evolutionary Algorithm

A new parallel method for learning decision rules from databases by using an evolutionary algorithm is proposed. We describe an implementation of EDRL-MD system in the cluster of multiprocessor machines connected by Fast Ethernet. Our approach consists in a distribution of the learning set into processors of the cluster. The evolutionary algorithm uses a master-slave model to compute the fitness function in parallel. The remainder of evolutionary algorithm is executed in the master node. The experimental results show, that for large datasets our approach is able to obtain a significant speed-up in comparison to a single processor version.

 

hSławomir T. Wierzchoń Function Optimization by the Immune Metaphor

The main goal of the immune system is to protect an organism against pathogens. To be able to recognize unknown (i.e. never seen) pathogens, the immune system applies a number of methods allowing to maintain sufficient diversity of its receptors. The most important methods are clonal selection and suppression of ineffective receptors. In effect the immune system admits maturation affinity property: during its functioning it continuously improves its ability to recognize new types of pathogens. This idea had found many interesting computer-oriented applications. In this paper a simple and easy to implement algorithm for multi-modal as well as non-stationary functions optimization is proposed. It is based on clonal selection and cells suppression mechanisms. Empirical results confirming its usability for uni-, multi-modal and non-stationary functions optimization are presented, and a review of other immunity-based approaches is given.

 

hMarek Kozłowski and Sławomir T. Wierzchoń Evolutionary Algorithm for Learning Bayesian Structures from Data

In this paper we report an evolutionary approach to learning Bayesian networks from data. We explain reasons, which advocate such a non-deterministic approach. We analyze weaknesses of previous works and come to conclusion that we should operate in the search space native for the problem i.e. in the space of directed acyclic graphs instead of standard space of binary strings. This requires adaptation of evolutionary methodology into very specific needs. We propose quite new data representation and implementation of generalized genetic operators and then we present an efficient algorithm capable of learning complex networks without additional assumptions. We discuss results obtained with this algorithm. The approach presented in this paper can be extended with the possibility to absorb some suggestions from experts or obtained by means of data preprocessing.

 

hMirosław Gajer The Implementation of the Example-based Machine Translation Technique for French-to-Polish Automatic Translation System

High-quality machine translation between human languages has for a long time been an unattainable dream for many computer scientists involved in this fascinating and interdisciplinary field of computer application. The developed quite recently example-based machine translation technique seems to be a serious alternative to the existing automatic translation techniques. In the paper the usage of the example based machine translation technique for the development of system which would be able to translate an unrestricted French text into Polish is proposed. The new approach to the example-based machine translation technique that takes into account the peculiarity of the Polish grammar is developed. The obtained primary results of the development of the proposed system seem to be very promising and appear to be a step made in the right direction towards a fullyautomatic high quality French-into-Polish machine translation system for unrestricted text.

 

hAndrzej Januszajtis The Library of the Technical University of Gdansk in Bremen

 

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