No (6379)
Yes (946)
Number of found documents:
7325
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A new blade cascade for flutter studies
Šnábl, Pavel; Pešek, Luděk; Procházka, Pavel P.; Skála, V.
2023 - English
In this paper, a new blade cascade, developed in the Institute of Thermomechanics, is presented. The geometry of the cascade was modified so now the stall flutter can occur. It has some major construction improvements over the original cascade which now allow more precise and reliable measurements. The stability of the new blade cascade with five NACA 0010 profiles with rotational degree of freedom is assessed by Travelling Wave Mode approach and Aerodynamic Influence Coefficient approach.
Keywords:
blade cascade; stability; travelling wave mode; aerodynamic influence coefficient
Available at various institutes of the ASCR
A new blade cascade for flutter studies
In this paper, a new blade cascade, developed in the Institute of Thermomechanics, is presented. The geometry of the cascade was modified so now the stall flutter can occur. It has some major ...
Bohl-Marek decomposition applied to a class of biochemical networks with conservation properties
Papáček, Štěpán; Matonoha, Ctirad; Duintjer Tebbens, Jurjen
2023 - English
This study presents an application of one special technique, further called as Bohl-Marek decomposition, related to the mathematical modeling of biochemical networks with mass conservation properties. We continue in direction of papers devoted to inverse problems of parameter estimation for mathematical models describing the drug-induced enzyme production networks [3]. However, being aware of the complexity of general physiologically based pharmacokinetic (PBPK) models, here we focus on the case of enzyme-catalyzed reactions with a substrate transport chain [5]. Although our ultimate goal is to develop a reliable method for fitting the model parameters to given experimental data, here we study certain numerical issues within the framework of optimal experimental design [6]. Before starting an experiment on a real biochemical network, we formulate an optimization problem aiming to maximize the information content of the corresponding experiment. For the above-sketched optimization problem, the computational costs related to the two formulations of the same biochemical network, being (i) the classical formulation x˙(t) = Ax(t) + b(t) and (ii) the 'quasi-linear' Bohl-Marek formulation x˙M(t) = M(x(t)) xM(t), can be determined and compared.
Keywords:
Mathematical modeling; Biochemical network; Pharmacokinetic (PBPK) models
Fulltext is available at external website.
Bohl-Marek decomposition applied to a class of biochemical networks with conservation properties
This study presents an application of one special technique, further called as Bohl-Marek decomposition, related to the mathematical modeling of biochemical networks with mass conservation properties. ...
Validation of numerical simulations of a simple immersed boundary solver for fluid flow in branching channels
Keslerová, R.; Lancmanová, Anna; Bodnár, Tomáš
2023 - English
This work deals with the flow of incompressible viscous fluids in a two-dimensional branching channel. Using the immersed boundary method, a new finite difference solver was developed to interpret the channel geometry. The numerical results obtained by this new solver are compared with the numerical simulations of the older finite volume method code and with the results obtained with OpenFOAM. The aim of this work is to verify whether the immersed boundary method is suitable for fluid flow in channels with more complex geometries with difficult grid generation.
Keywords:
immersed boundary method; finite volume method; OpenFOAM
Available in digital repository of the ASCR
Validation of numerical simulations of a simple immersed boundary solver for fluid flow in branching channels
This work deals with the flow of incompressible viscous fluids in a two-dimensional branching channel. Using the immersed boundary method, a new finite difference solver was developed to interpret the ...
Rooting algebraic vertices of convergent sequences
Hartman, David; Hons, T.; Nešetřil, J.
2023 - English
Structural convergence is a framework for convergence of graphs by Nešetřil and Ossona de Mendez that unifies the dense (left) graph convergence and Benjamini-Schramm convergence. They posed a problem asking whether for a given sequence of graphs (Gn) converging to a limit L and a vertex r of L it is possible to find a sequence of vertices (rn) such that L rooted at r is the limit of the graphs Gn rooted at rn. A counterexample was found by Christofides and Král’, but they showed that the statement holds for almost all vertices r of L. We offer another perspective to the original problem by considering the size of definable sets to which the root r belongs. We prove that if r is an algebraic vertex (i.e. belongs to a finite definable set), the sequence of roots (rn) always exists.
Keywords:
rooting; algebraic vertices; convergent sequences
Available in digital repository of the ASCR
Rooting algebraic vertices of convergent sequences
Structural convergence is a framework for convergence of graphs by Nešetřil and Ossona de Mendez that unifies the dense (left) graph convergence and Benjamini-Schramm convergence. They posed a problem ...
Effect of aging on mechanical properties of 3D printed samples using stereolithography
Drechslerová, V.; Falta, J.; Fíla, T.; Dvořák, R.; Kytýř, Daniel
2023 - English
This paper focuses on stereolithography (an additive manufacturing technology working on the principle of curing liquid resins layer by layer using ultraviolet radiation) and the effect of aging on the mechanical properties of the material and printed samples. The aging of the material could be a problem for its subsequent use as the stability of the mechanical properties would not be maintained and unwanted deterioration of the material could occur. As part of the research, sets of samples were printed and subjected to different aging methods and subsequently subjected to quasi-static and dynamic uni-axial load tests. From the data obtained, the basic mechanical properties of the material were calculated and compared with each other. The aim of this paper was to investigate whether aging process causes significant changes in the mechanical properties of the materials used, which could have a consequential impact on their use in different industries.
Keywords:
stereolithography; aging; mechanical properties
Available at various institutes of the ASCR
Effect of aging on mechanical properties of 3D printed samples using stereolithography
This paper focuses on stereolithography (an additive manufacturing technology working on the principle of curing liquid resins layer by layer using ultraviolet radiation) and the effect of aging on ...
Computed tomography system with strict real-time synchronization for in-situ 3D analysis of periodically vibrating objects
Rada, Václav; Fíla, Tomáš; Zlámal, Petr; Koudelka_ml., Petr; Šleichrt, Jan; Macháček, Michael; Vavřík, Daniel; Kytýř, Daniel
2023 - English
In the contribution, we present a laboratory system capable of X-ray computed tomography (XCT) scanning of an periodically moving or oscillating object. The system is an in-house developed XCT setup with electromagnetic voice coil actuator mounted on top of the rotary stage of the setup. The strict synchronization of the components, the rotary stage, the electromagnetic actuator movement and the detector readout is accomplished with use of the detector hardware trigger and hard real-time Linux operating system. Cylindrical sample manufactured from epoxy resin with metal particles to enable movement tracking is scanned in a stationary position and during periodical movement induced by the vibration stage. The volumetric data of the scans is compared and the results of this contribution represent an important step towards identification of defects through modal analysis of in-situ harmonically vibrating object.
Keywords:
computed tomography; hardware trigger; harmonic motion; realtime synchronization
Available at various institutes of the ASCR
Computed tomography system with strict real-time synchronization for in-situ 3D analysis of periodically vibrating objects
In the contribution, we present a laboratory system capable of X-ray computed tomography (XCT) scanning of an periodically moving or oscillating object. The system is an in-house developed XCT setup ...
Analysis suggestion for vehicle scanning method
Bayer, Jan
2023 - English
An analytical approach is suggested that can be conveniently applied in the framework of the Vehicle scanning method (VSM). It assumes that the modal parameters of a bridge will be imported from a finite element (FE) program into MATLAB, where the structural response caused by a moving mass and a moving spring mass is solved using coupling equations and numerical integration. A mathematical formulation of the solution is presented together with a short numerical case study that compares the results to a traditional closed form solution. It is shown that when comparing both forms of analysis the suggested approach is more accurate in the case of slow velocities of the passing sprung mass. Other advantages are that the method allows for the mass of the vehicle or (tractor) towing vehicle and a damping \nto be included in the calculation. The user-friendly preprocessing in commercial FE programs can also be considered an advantage.
Keywords:
moving vehicle; vehicle scanning method; natural frequency; finite element analysis
Available at various institutes of the ASCR
Analysis suggestion for vehicle scanning method
An analytical approach is suggested that can be conveniently applied in the framework of the Vehicle scanning method (VSM). It assumes that the modal parameters of a bridge will be imported from a ...
A short study on self-balancing of vertical rotors mounted in passive contactless bearings
Zapoměl, Jaroslav; Kozánek, Jan
2023 - English
Energy losses and wear of the support elements of high-speed rotors can be reduced by mounting the rotors in stable passive contactless bearings, the operation of which is based on magnetic levitation. The goal of the conducted research was to investigate applicability of selfbalancing device added to vertical rotors supported by bearings showing low stiffness and damping, which is a specific property of passive magnetic bearings. This paper deals with applicability and efficiency of self-balancing devices added to vertical rotors supported by bearings having very low stiffness and damping, which corresponds to the properties of magnetic frictionless bearings.
Keywords:
self-balancing of rotors; passive contactless bearings; the influence of external damping
Available at various institutes of the ASCR
A short study on self-balancing of vertical rotors mounted in passive contactless bearings
Energy losses and wear of the support elements of high-speed rotors can be reduced by mounting the rotors in stable passive contactless bearings, the operation of which is based on magnetic ...
Dynamic tensile experiments of hard rubber on instron test machine under finite deformations
Šulc, Petr; Pešek, Luděk; Bula, Vítězslav; Šnábl, Pavel
2023 - English
This paper deals with the first experimental tests of hard rubbers under tensile harmonic loading on the axial-torsional servohydraulic Instron 8852 test machine. The objective of these experiments on cylindrical rubber specimens on this machine is to obtain stress-strain curves of rubber specimens, first considering uniaxial finite longitudinal strains for a single load cycle. Next, the hysteresis loops and their skeleton curves are compared for two selected strain measures as a function of their conjugate stress. It is shown how to obtain the dependence between elongation in the axial direction and constriction in the radial direction, which is used to determine the Cauchy stress in this configuration.
Keywords:
uniaxial harmonic loading; finite deformation; second Piola-Kirchhoff stress; hysteresis loop; Green-Lagrange strain tensor
Available at various institutes of the ASCR
Dynamic tensile experiments of hard rubber on instron test machine under finite deformations
This paper deals with the first experimental tests of hard rubbers under tensile harmonic loading on the axial-torsional servohydraulic Instron 8852 test machine. The objective of these experiments on ...
On the problem of singular limit
Caggio, Matteo; Ducomet, B.; Nečasová, Šárka; Tang, T.
2023 - English
We consider the problem of singular limit of the compressible Euler system confined to a straight layer Ωδ = (0, δ)×R², δ > 0. In the regime of low Mach number limit and reduction of dimension the convergence to the strong solution of the 2D incompressible Euler system is shown.
Keywords:
compressible Euler equations; dissipative measure-valued solutions; low Mach number; thin domain
Available in digital repository of the ASCR
On the problem of singular limit
We consider the problem of singular limit of the compressible Euler system confined to a straight layer Ωδ = (0, δ)×R², δ > 0. In the regime of low Mach number limit and reduction of dimension the ...
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