2024-09-22
00:06 |
Role of submembrane spaces in the control of transmembrane ion flux and cellular inotropic state in a model of human ventricular cardiomyocyte
Pásek, Michal ; Bébarová, M. ; Christé, G.
We have recently developed a model of a human ventricular cardiomyocyte incorporating the t-tubular and surface submembrane spaces and restricted ion exchange between these spaces and cytosol. After incorporating the experimental finding that the majority of Na+-Ca2+ exchanger proteins are located at the t-tubular membrane of human ventricular cardiomyocytes, we explored the consequences of ion concentration changes in the submembrane spaces on the electrophysiological activity of these cells. Consistently with published experimental and modelling studies, our model predicts an increased Ca2+ extrusion during the action potential. However, our model also predicts a significant reduction of Ca2+ extrusion throughout the diastole, which can ultimately lead to an increase in cellular inotropy.
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2024-05-12
00:02 |
Flow simulations approach for flocculation tanks
Idžakovičová, Kristýna ; Bílek, V. ; Haidl, J. ; Isoz, Martin ; Pivokonský, M.
Flocculation in water treatment facilities plays a key role in the separation of colloidal inorganic and organic substances. Its optimization leads to a significant increase in its efficiency and savings of operational costs. However, it is currently based on trial-and-error experimental approaches. In this contribution, we focus on flow modeling in stirred flocculation tanks that would, after coupling with a calibrated model of particle aggregation, enable simulationbased flocculation optimization. Despite the abundance of literature on stirred tank modeling, there is no universal agreement on the methodology used to describe turbulence nor on the approach to the computational mesh creation. Consequently, there is no unified methodology for simulations and their validation. To address this, we present a best-practice methodology for economical, yet reliable flow simulations in the said device. This methodology includes the choice of the turbulence model, the approach to the design of a high quality mesh suitable for arbitrary geometries, and results evaluation. It is developed based on an extensive literature review, a multitude of flow simulations using several meshes of progressively higher quality and resolution, and various strategies to converge to steady-state flow conditions. The simulation quality indicators used here involve comparison with the experimental data on fluid velocity, stirrer power output, and flow rate through the impeller zone. Additionally, the resulting flow simulation models are compared using tracer transport simulations, hinting at their potential for coupling with particle aggregation models.
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2024-04-15
12:40 |
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2024-04-15
12:40 |
Computational and experimental assessment of natural frequencies in a bladed disk system
Mekhalfia, Mohammed Lamine ; Procházka, Pavel ; Maturkanič, Dušan ; Voronova, Evgeniya ; Hodboď, Robert
This paper examines the modal characteristics of a bladed disk in rotating machinery systems using a combination of analytical and experimental modal analysis methods. The analysis involves measuring natural frequencies and mode shapes under different operational conditions. A comparative analysis is conducted to assess modal properties obtained from both analytical and experimental approaches, while also considering the influence of rotation speed. Additionally, Finite Element Method (FEM) outputs are used to accurately position the strain gauge. Integrating these techniques provides a comprehensive understanding of the bladed disk's behaviour under varying rotational speeds, enhancing result accuracy and facilitating thorough investigation within rotating machinery systems.
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2024-04-15
12:40 |
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2024-04-15
12:40 |
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2024-04-15
12:32 |
Non-linear Vibration of Planar Case of Three-blade Bundle with Dry Friction Contacts
Šnábl, Pavel ; Pešek, Luděk ; Půst, Ladislav
Using dry friction couplings (so called tie-bosses) between the blades in turbine rotors can be used to suppress dangerous resonant vibrations of turbine blades and it has been studied on our institute on various models. Experimental setup of three-blade bundle was built along with bladed wheel. The first set-up of the bundle was with blades turned 45 degrees to the disc plane. In that case the deformation of the blades causes turning of the ends of tie-bosses and edge contact together with multi-directional slip occurs. The experimental set-up was simplified herein so that the blades are parallel to the disc plane and in-line slip occurs. Although single electromagnet was used to excite the system, the first mode of vibration with no slip in tie-bosses just occurred. In case of bladed wheel, all blades have coupling through tie-bosses with neighbouring blades which stiffen them and raise their eigenfrequency. In our case, a mistuning by reducing mass of side blades caused similar behaviour. Steel to steel contact pair was used for the first tests.
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2024-04-15
12:32 |
Numerical and Experimental Investigation of the Flow Field in Five Blade Linear Cascade in Subsonic Flow
Šnábl, Pavel ; Chindada, Sony ; Bublík, O. ; Procházka, Pavel P. ; Prasad, Chandra Shekhar
In large steam turbines, last stage blades are very long and must be designed very thin and with no shroud to minimize the centrifugal force which leads to low eigenfrequencies and low structural damping. In this case, aero-elastic damping plays important role on last stage bladed disc’s dynamics. Three major aero-elastic issues found in turbomachinery are forced response, non-synchronous vibrations, and flutter. Flutter is an unstable, self-excited vibration resulting from coupling between the structural vibrations and unsteady aerodynamic forces. It is clear that this unstable behaviour must be avoided and predictions of flutter behaviour need to be performed during design stage of the turbine.\n
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2024-04-15
12:32 |
Modelling of pulse-triggered running waves on a blade cascade
Šnábl, Pavel ; Pešek, Luděk
An experimental cascade of five NACA 0010 blades with pitch degrees of freedom is excited by a moment pulse to one of the blades. Depending on the flow conditions, such as wind speed and the angle of attack of the wind on the blades, the vibration of the excited blade is transmitted by the wind to the other blades. This can result in a running wave that diminishes over time or in a flutter running wave. A simplified spring-mass-damper model with inter-blade connections and non-linear van der Pol dampers is tuned to match experimentally obtained stability curves and tested to see if it can qualitatively model the response of the cascade to the pulse excitation.\n
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2024-04-15
12:31 |
Střední úroveň řízení měniče FB-MMC s topologií Delta
Kokeš, Petr
Regulace modulárního vícehladinového měniče (Modular Multilevel Converter, MMC) je technicky podstatně komplikovanější, než měniče klasického, a to nejen kvůli velkému počtu jednotlivých buněk. Na rozdíl od klasického měniče se zde musíme zabývat další úrovní řízení, která představuje balancování napětí mezi větvemi měniče a řízení kruhových proudů uvnitř měniče. Ve zprávě je analyzována vhodná metoda a navržena regulační struktura pro balancování napětí mezi všemi třemi větvemi MMC v zapojení do trojúhelníku (Delta) s buňkami typu úplného můstku (Full H-bridge, FB). Následně byla ověřována činnost tohoto balancování pomocí počítačových simulací a praktických zkoušek na dvou fyzikálních modelech MMC pro sítě 400V a 6kV s implementovanou funkcí aktivního filtru.
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