Ústav matematiky a deskriptivní geometrie

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    Flexure response of thermal loaded concrete specimens by acoustic emission method
    (EDP Sciences – Web of Conferences, 2017-05-24) Pazdera, Luboš; Topolář, Libor; Mikulášek, Karel; Smutný, Jaroslav; Hoduláková, Michaela; Chobola, Zdeněk; Seelmann, Herbert
    The response to fire of concrete structural members depends on the thermal, mechanical, and deformation properties of concrete. These properties vary significantly with temperature depending on the composition and characteristics of the concrete batch mix as well as heating rate and other environmental conditions. The paper presents the effects of a high temperature on selected physical properties of concrete. The main aim of the article is the evaluation of monitoring concrete properties loaded in a few thermal steps up to 1200 °C. Therefore, the concrete specimens were heated in a programmable laboratory furnace at a heating rate of 5 °C/min. The specimens were loaded at six temperatures, 200 °C, 400 °C, 600 °C, 800 °C, 1000 °C, and 1200 °C maintained for 60 minutes. The acoustic emission activity and some material characteristics were evaluated in a three-point bending test.
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    Stabilization of Lure-type Nonlinear Control Systems by Lyapunov-Krasovskii Functionals
    (Springer Nature, 2012-10-24) Shatyrko, Andrej; Diblík, Josef; Khusainov, Denys; Růžičková, Miroslava
    The paper deals with the stabilization problem of Lure-type nonlinear indirect control systems with time-delay argument. The sufficient conditions for absolute stability of the control system are established in the form of matrix algebraic inequalities and are obtained by the direct Lyapunov method.
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    An efficient new perturbative Laplace method for space-time fractional telegraph equations
    (Springer Nature, 2012-11-27) Khan, Yasir; Diblík, Josef; Faraz, Naeem; Šmarda, Zdeněk
    In this paper, we propose a new technique for solving space-time fractional telegraph equations. This method isbased on perturbation theory and the Laplace transformation.
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    Multiplicity of solutions for nonlinear coercive problems
    (Elsevier, 2023-12-01) Diblík, Josef; Galewski, Marek; Radulescu, Vicentiu; Šmarda, Zdeněk
    We are concerned in this paper with problems that involve nonlinear potential mappings satisfying condition (S) and whose potentials are coercive. We first provide mild sufficient conditions for the minimizing sequence in the Weierstrass-Tonelli theorem in order to have strongly convergent subsequences. Next, we establish a three critical point theorem which is based on the Pucci-Serrin type mountain pass lemma and which is an infinite dimensional counterpart of the Courant theorem. Ricceri-type three critical point results then follow. Some applications to Dirichlet boundary value problems driven by the perturbed Laplacian are given in the final part of this paper.
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    Use of cohesive approaches for modelling critical states in fibre-reinforced structural materials
    (MDPI, 2024-07-01) Kozák, Vladislav; Vala, Jiří
    During the operation of structures, stress and deformation fields occur inside the materials used, which often ends in fatal damage of the entire structure. Therefore, the modelling of this damage, including the possible formation and growth of cracks, is at the forefront of numerical and applied mathematics. The finite element method (FEM) and its modification will allow us to predict the behaviour of these structural materials. Furthermore, some practical applications based on cohesive approach are tested. The main effort is devoted to composites with fibres and searching for procedures for their accurate modelling, mainly in the area where damage can be expected to occur. The use of the cohesive approach of elements that represent the physical nature of energy release in front of the crack front has proven to be promising not only in the direct use of cohesive elements, but also in combination with modified methods of standard finite elements.