Acta Polytechnica 2005/1
Deformation Stress State of Elastic Bodies
The theory of the deformation stress state is based on the actual corpuscular structure of matter characterized in terms of mechanics by the fact that an increase in the distance of two adjacent atoms is accompanied by the origin of an attractive force and a reduction in their distance by the origin of a repulsive force. These forces differ significantly from the classical internal forces, which are the forces of the mechanics of perfectly solid bodies. These express the equilibrium of forces with reference to the given area within the loaded body, and have no direct deformation effect. This paper defines the quantities of the deformation stress state – the deformation force and the deformation stress – the direct manifestation of which is a deformation. The author introduces the term of deformation stress state theory (DSS theory) to the field of the theory of elasticity dealing with the stress state of deformable bodies. The quantities and the equations of this theory also form the basis for the formulation of the theory of failure, which makes it possible to determine reliably the safety margin and the strength of a multiaxially loaded body from the stress state described by the static quantities (stress tensor) and uniaxial strength.
Keywords: deformation force, deformation stress, effective stress, effective strength, proportionality principle
A Progress Report on Numerical Solutions of Least Squares Adjustment in GNU Project Gama
A. Čepek, J. Pytel
GNU project Gama for adjustment of geodetic networks is presented. Numerical solution of Least Squares Adjustment in the project is based on Singular Value Decomposition (SVD) and General Orthogonalization Algorithm (GSO). Both algorithms enable solution of singular systems resulting from adjustment of free geodetic networks.
Keywords: geodesy, least square adjustment, local geodetic network
Heating and Cooling Anomaly of a Rotating Body
O. Brůha, T. Brůha
This paper deals with an effect which appears when heating or cooling a rotating body. No external forces acting on the body are supposed. Due to thermal expansion, the moment of inertia of the body varies together with the temperature changes. In agreement with the principle of conservation of angular momentum , the angular momentum is constant. This results in angular velocity changes and subsequently in kinetic energy changes. Also the stress energy varies together with the changes in thermal dimension. To satisfy the principle of energy conservation we have to suppose that the changes in kinetic and stress energy are compensated by the changes in internal energy, which is correlated with temperature changes of the body. This means that the rules for the heating or cooling process of a rotating body are not the same as those for a body at rest. This idea, applied to a cylinder rotating around its geometric axis under specific parameters, has been mathematically treated. As a result, the difference between the final temperature of the rotating cylinder and the temperature of the cylinder at rest has been found.
Keywords: angular momentum, energy conservation, rotating body, thermal expansion
Schema Management for Data Integration: A Short Survey
A. Almarimi, J. Pokorný
Schema management is a basic problem in many database application domains such as data integration systems. Users need to access and manipulate data from several databases. In this context, in order to integrate data from distributed heterogeneous database sources, data integration systems demand the resolution of several issues that arise in managing schemas. In this paper, we present a brief survey of the problem of schema matching which is used for solving problems of schema integration processing. Moreover, we propose a technique for integrating and querying distributed heterogeneous XML schemas.
Keywords: schema matching, schema integration, data integration
A Complexity and Quality Evaluation of Block Based Motion Estimation Algorithms
S. Usama, M. Montaser, O. Ahmed
Motion estimation is a method, by which temporal redundancies are reduced, which is an important aspect of video compression algorithms. In this paper we present a comparison among some of the well-known block based motion estimation algorithms. A performance evaluation of these algorithms is proposed to decide the best algorithm from the point of view of complexity and quality for noise-free video sequences and also for noisy video sequences.
Keywords: motion estimation, block matching, quality evaluation, complexity evaluation
Comparison of the Capacitance Method and the Microwave Impulse Method for Determination of Moisture Profiles in Building Materials
P. Tesárek, J. Pavlík, R. Černý
A comparison of the capacitance method and the microwave impulse method for the determination of moisture profiles in three typical porous building materials is presented in this paper. The basic principles of the measuring methods are given. The calibration process is described in detail. On the basis of the measured results, it can be concluded that the capacitance method provides better accuracy in the range of lower moisture content than to the microwave impulse method, which is more accurate for the highest values of moisture content.
Keywords: Moisture profiles, capacitance method, microwave impulse method, building materials
3D Information System of Historical Site – Proposal and Realisation of a Functional Prototype
The development of methods for 3D data acquisition, together with progress in information technologies raises the question of creating and using 3D models and 3D information systems (IS) of historical sites and buildings. This paper presents the current state of the “Live Theatre” project. The theme of the project is the proposal and realisation of a 3D IS of the baroque theatre at Český Krumlov castle (UNESCO site).The project is divided into three main stages – creation of a 3D model, proposal of a conception for a 3D IS, and realisation of a functional prototype. 3D data was acquired by means of photogrammetric and surveying methods. An accurate 3D model (photo-realistic, textured) was built up with MicroStation CAD system. The proposal of a conception of a 3D IS was the main outcome of the author’s dissertation. The essential feature of the proposed conception is the creation of subsystems targeted on three spheres – management, research and presentation of the site. The functionality of each subsystem is connected with its related sphere; however, each subsystem uses the same database. The present stage of the project involves making a functional prototype (with sample data). During this stage we are working on several basic technological topics. At present we are concerned with 3D data, its formats, format conversions (e.g. DGN Ţ VRML) and its connection to other types of data. After that, we will be seeking a convenient technical solution based on network technologies (Internet) and an appropriate layout for the data (database). The project is being carried out in close co-operation with the administration of the castle and some other partners. This stage of the project will be completed in December 2005.A functional prototype and the information acquired by testing it will form the basis for the final proposal of a complex IS of a historical site. The final proposal and appropriate technology will be the outcome of the project. The realisation of a complex 3D IS will then follow. The results will be exploitable both for site management and for organisations working in the area of presenting historical sites and creating multimedia shows.
Keywords: cultural heritage, 3D information sciences, system, project, proposal, development, virtual reality, Internet/web
Influence of Ring Stiffeners on a Steel Cylindrical Shell
D. Lemák, J. Studnička
Shell structures are usually formed from concrete, steel and nowadays also from many others materials. Steel is typically used in the structures of chimneys, reservoirs, silos, pipelines, etc. Unlike concrete shells, steel shells are regularly stiffened with the help of longitudinal and/or ring stiffeners.The authors of this paper investigated steel cylindrical shells and their stiffening with the use of ring stiffeners. The more complete the stiffening, the more closely the shell will act to beam theory, and the calculations will be much easier. However, this would make realization of the structure more expensive and more laborious. The target of the study is to find the limits of ring stiffeners for cylindrical shells. Adequate stiffeners will eliminate semi-bending action of the shells in such way that the shell structures can be analyzed with the use of numerical models of the struts (e.g., by beam theory) without significant divergences from reality. Recommendations are made for the design of ring stiffeners, especially for the distances between stiffeners and for their bending stiffness.
Keywords: shell, cylindrical shell, chimney, steel structure, wind load, ring stiffener, distance of stiffeners, stiffness of ring stiffener, design