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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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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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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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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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Middle-level control of FB-MMC converter in Delta connection
Kokeš, Petr
Control of a modular multilevel converter (MMC) is technically far more complicated than control of a standard 2-level converter. It is not only because of a great number of series-connected cells. For a MMC converter we need to cope with another control level (mentioned here as the middle-level control), which means balancing of voltages among MMC branches and the control of currents circulating inside this converter. For the Delta connected MMC with full H–bridge (FH) cells a convenient method for voltage balancing among all three MMC branches has been analysed and the appropriate control structure has been designed. Then the functionality of this balancing method has been verified using computer simulations and also tested with two MMC physical models operating as active power filters on 400V and 6kV grids.
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Asynchronous time integration while achieving zero interface energy
Dvořák, Radim ; Kolman, Radek ; Falta, J. ; Neühauserová, M.
This contribution deals with an asynchronous direct time integration of the finite-element model. The proposed method is applied to the phenomenon of wave propagation through an elastic linear continuum. The numerical model is partitioned into individual subdomains using the domain decomposition method by means of localized Lagrange multipliers. For each subdomain, different time discretizations are used. No restrictions for relation between subdomain’s time steps are imposed. The coupling of the subdomains is forced by an acceleration continuity condition. Additionally, we use the a posteriori technique to also provide the displacement and velocity continuity at the interfaces, and hence we obtain exact continuity of all three kinematic fields. The proposed method is experimentally validated using the modified SHPB (split Hopkinson pressure bar) setup.
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Předběžné výsledky měření na HVAC jednotce pro H2-Bus s chladivy R454C a R513A
Blahut, Aleš ; Kordík, Jozef ; Šulc, V. ; Vinš, Václav
Technická zpráva shrnuje předběžné vyhodnocení experimentálních zkoušek chladící jednotky a tepelného čerpadla (HVAC) pro vodíkový autobus s chladivy R454C a R513A. V klimakomoře Elektrotechnického zkušebního ústavu, s. p. v Praze Troji byla v říjnu 2023 podrobně testována zkušební HVAC jednotka v režimech klimatizace a tepelného čerpadla při teplotách okolí od -25 °C do +45 °C. Ve zprávě jsou analyzovány základní výkonové parametry HVAC jednotky zahrnující topný a chladící výkon na kondenzátoru, resp. výparníku, topné a chladící faktory okruhu a izoentropickou účinnost kompresoru.
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