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Static and dynamic analysis of plain and fiber-reinforced concrete using discrete meso-scale model
Květoň, Josef ; Vorel,, Jan (oponent) ; Šejnoha,, Michal (oponent) ; Eliáš, Jan (vedoucí práce)
The presented thesis is devoted to mathematical modeling of concrete fracture. A special type of model called discrete particle model is used. The concrete meso-structure is simplified as a system of interconnected polyhedral particles. The particle interaction is prescribed at their contacts. Solution of discrete displacement field is obtained under the assumption of small deformations and rigid body movement of particles. Two modifications of the static version of the discrete meso-scale model are presented: (i) representation of short fiber reinforcement and (ii) implicit dynamic solver. The first main part of the thesis is devoted to modelling of short fiber reinforcement, which is used to improve poor tensile performance of concrete. This material modification leads to more efficient material use and crack width reduction. Short fibers are represented in the discrete model indirectly, taking into account the frictional forces between fiber and cement matrix. The fiber forces are applied at particle contacts working against the crack opening. This modification is able to capture the strain hardening behavior and the multiple cracking of the fiber reinforced composites. The second main part of the thesis addresses dynamic material behavior. Concrete resistance varies under different strain-rates. For slow, quasi-static loading rates, the initial micro-cracks localize into a macro-crack. For fast loading rates, the energy is not consumed by one crack only, but multiple cracking and crack branching occurs. The inertia typically dominates in fast processes. Even though the meso-scale model accounts for the inertia and the crack branching, the cracking at lower scale is not addressed. Therefore additional phenomenological rate-dependency of the constitutive law is adopted. Numerical simulations on various geometries under various loading rates are performed and compared to experimental evidence from literature.
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Static and dynamic analysis of plain and fiber-reinforced concrete using discrete meso-scale model
Květoň, Josef ; Vorel,, Jan (oponent) ; Šejnoha,, Michal (oponent) ; Eliáš, Jan (vedoucí práce)
The presented thesis is devoted to mathematical modeling of concrete fracture. A special type of model called discrete particle model is used. The concrete meso-structure is simplified as a system of interconnected polyhedral particles. The particle interaction is prescribed at their contacts. Solution of discrete displacement field is obtained under the assumption of small deformations and rigid body movement of particles. Two modifications of the static version of the discrete meso-scale model are presented: (i) representation of short fiber reinforcement and (ii) implicit dynamic solver. The first main part of the thesis is devoted to modelling of short fiber reinforcement, which is used to improve poor tensile performance of concrete. This material modification leads to more efficient material use and crack width reduction. Short fibers are represented in the discrete model indirectly, taking into account the frictional forces between fiber and cement matrix. The fiber forces are applied at particle contacts working against the crack opening. This modification is able to capture the strain hardening behavior and the multiple cracking of the fiber reinforced composites. The second main part of the thesis addresses dynamic material behavior. Concrete resistance varies under different strain-rates. For slow, quasi-static loading rates, the initial micro-cracks localize into a macro-crack. For fast loading rates, the energy is not consumed by one crack only, but multiple cracking and crack branching occurs. The inertia typically dominates in fast processes. Even though the meso-scale model accounts for the inertia and the crack branching, the cracking at lower scale is not addressed. Therefore additional phenomenological rate-dependency of the constitutive law is adopted. Numerical simulations on various geometries under various loading rates are performed and compared to experimental evidence from literature.
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Neutrally stratified flow modelling over complex terrain at meso-scale: open-cut coal mine study
Nosek, Štěpán ; Jaňour, Zbyněk ; Jurčáková, Klára ; Kellnerová, Radka ; Kukačka, Libor
The objective of this case study was to determine the influence of the coal mine cavity and its vicinity on the main flow field with respect to prevailing wind direction. In order to model the neutrally stratified flow over extremely huge open-cut coal mine Libouš situated at north-west of Czech Republic the laminar flow analogy was applied. The model was scaled down to 1:9000 according to dimensions of wind-tunnel and selected coal mine surroundings. The measurements of longitudinal and lateral velocity components in selected vertical, resp. horizontal planes were performed by LDA. The measured data will be used for validation of CFD simulation and for selections of area of interest at bigger scales where turbulent flow modelling will be performed. The results revealed that not only of cavity shape and deepness but also the surroundings orography has influence on flow pattern, hence on ventilation, within the area of interest.
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