2025-04-13
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2025-04-13
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2025-04-13
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2025-03-02
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Weak imposition of potential Dirichlet boundary conditions in piezoelasticity: Numerical study
Cimrman, Robert
Detailed modelling of piezoelastic structures often includes also an external circuit. This is tied with the need for a weak imposition of electric potential Dirichlet boundary conditions and questions of simulation accuracy arise. Several methods allowing the weak imposition, namely the non-symmetric Nitsche’s method, penalty method and their combinations, are evaluated and their numerical convergence w.r.t. uniform mesh refinement for various finite element approximation orders is reported. The numerical study is performed on a geometry corresponding to a piezoelectric sensor.
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2025-02-22
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2025-02-09
00:17 |
Řešení ustálených stavů MMC měničů 3AC1AC a 3ACDC1AC
Kokeš, Petr
Byly řešeny ustálené stavy dvou měničů na bázi MMC topologie (Modular Multilevel Converter), které jsou použitelné jako zdroj 25kV/50Hz pro trakční napájecí stanice: přímého měniče 3AC-1AC a nepřímého měniče 3AC-DC-1AC. Odvodili jsme analytické vztahy pro ustálené řešení napětí a proudu větví, a pro zvlnění napětí na buňkách. Z těchto vztahů jsme vypočetli různé důležité statistiky těchto veličin, jako jsou RMS a špičkové hodnoty, poté jsme numericky vypočetli proudové zatížení spínacích polovodičových prvků v buňce a proudové zatížení kondenzátoru v buňce. Výsledky výpočtů elektrických veličin závisí na účiníku jednofázové zátěže. U přímého měniče rozložení zatížení závisí i na fázovém posunu mezi napětím na vstupní trojfázové straně a výstupní jednofázové straně. V závěru zprávy jsou shrnuty výhody a nevýhody měniče 3AC-1AC vůči 3AC-DC-1AC.\n\n
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2025-02-09
00:17 |
Apparent Young's modulus of human cranial cancellous bone
Votava, T. ; Marcián, P. ; Borák, L. ; Fuis, Vladimír ; Zikmund, T. ; Kaiser, J. ; Wolff, J.
This study investigates the biomechanical behavior of cancellous bone in the os occipitale through finite element modeling. Utilizing micro-computed tomography scans, 47 bone segments were analyzed, and their apparent Young's moduli of each segment were determined in three orthogonal directions. The results revealed strong directional dependencies of Young’s modulus on bone volume fractions. In contrast, nondirectional dependency exhibited a weaker correlation, indicating an orthotropic elasticity. The derived correlation equations offer an efficient means to describe cancellous bone in cranial biomechanical simulations, especially when a detailed trabecular representation is impractical.
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2025-02-09
00:17 |
Influence of Berkovich indenter tilt on the projected contact area at nanoindentation test
Kovář, J. ; Fuis, Vladimír
At the nanoindentation test, the tilt of the indenter or specimen surface can occur. This deviation influences the projected contact area, which is important for the evaluation of the Young modulus and hardness. This paper is aimed on the derivation of the analytical expressions for the projected contact area if the indenter is tilted in 3D space. Then the projected contact area is the same as the area of indenter cross-section by the plane corresponding to the specimen surface. The calculated results for tilted and ideal indenter were compared and the influence of the indenter tilt was evaluated. The cross-sections were plotted for few indenter tilts to better describe the change of the projected contact area. The results show that indenter tilt can have significant impact on the results if the indenter tilt is big enough.
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2025-02-09
00:17 |
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2025-02-09
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