Number of found documents: 2718
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Effect of oscillating blade on tonal noise of blade cascade with five NACA 0010 profiles
Šnábl, Pavel; Pešek, Luděk; Radolf, Vojtěch; Antoš, Pavel; Procházka, Pavel P.; Prasad, Chandra Shekhar
2022 - English
The airfoil tonal noise is a well known phenomenon which appears on single airfoils in moderate Reynolds numbers at low angles of attack. It can appear on small aircrafts, fans, wind turbines etc. In thispaper, it was observed on a blade cascade consisting of five NACA 0010 profiles placed in a closed rectangular channel with hard walls when for given conditions, i.e. flow velocity and angle of attack, the cascade tunes to one single frequency. During the middle blade oscillation, the single tone splits up to several tones with lower intensity modulated by the excitation frequency. Thus, the oscillation of one blade suppresses the tonal noise generation in the cascade. Keywords: aeroacoustics; blade cascade; trailing edge noise; tonal noise; NACA 0010 Fulltext is available at external website.
Effect of oscillating blade on tonal noise of blade cascade with five NACA 0010 profiles

The airfoil tonal noise is a well known phenomenon which appears on single airfoils in moderate Reynolds numbers at low angles of attack. It can appear on small aircrafts, fans, wind turbines etc. In ...

Šnábl, Pavel; Pešek, Luděk; Radolf, Vojtěch; Antoš, Pavel; Procházka, Pavel P.; Prasad, Chandra Shekhar
Ústav termomechaniky, 2022

Problematics of aerodynamic damping calculation from measured data of 5-blade cascade
Šnábl, Pavel; Pešek, Luděk; Prasad, Chandra Shekhar; Chindada, Sony
2022 - English
Aerodynamic damping as a function of inter-blade phase angle (IBPA), so called S-curve, is crucial for assessment of aeroelastic stability of blade cascades, e.g. turbines, compressors, etc.\nFor constructing the S-curve, the motion-induced controlled flutter is introduced to the bladesof the cascade. As decribed in [1], two testing methods exist: aerodynamic influence coefficient\n(AIC) approach and travelling wave mode (TWM) approach. In TWM approach, all blades in a row oscillate with the same frequency and amplitude with various IBPAs. The response is\nmeasured only on the reference blade. With this approach, several measurements with different IPBAs are needed to construct the S-curve. On the other hand, AIC uses single oscillating\nblade and principle of linear superimposition of aerodynamic influence responses measured on all blades in a cascade. The result of one single measurement can be used for estimation of\naerodynamic damping for any IBPA. In the past year a new 5-blade cascade with rotating symmetrical NACA 0010 profiles was designed and built. The blades of the cascade were placed further apart and thus we are now able to reach stall flutter. Also, the suspension of the blades and sensors were significantly improved. Now, our goal is to evaluate S-curves using AIC approach for different flow conditions and oscillation frequencies. Keywords: aerodynamic damping; S-curve; blade cascade Available at various institutes of the ASCR
Problematics of aerodynamic damping calculation from measured data of 5-blade cascade

Aerodynamic damping as a function of inter-blade phase angle (IBPA), so called S-curve, is crucial for assessment of aeroelastic stability of blade cascades, e.g. turbines, compressors, etc.\nFor ...

Šnábl, Pavel; Pešek, Luděk; Prasad, Chandra Shekhar; Chindada, Sony
Ústav termomechaniky, 2022

Wake Behind a Cylinder: An Overview of Spatio-Temporal Aspects
Uruba, Václav
2022 - English
A circular cylinder in crossflow is subjected to the overview study from the point of view spatial and temporal characteristics. It represents itself a typical engineering problem, appearing in practice frequently in various forms. In fluid mechanics, this case is considered to be a typical canonical case, with relatively simple and straightforward definition, but complex and dynamical flow topology. The typical dynamics is characterized by quasi-periodic behavior called von Kármán – Bénard vortex street with a typical frequency expressed in dimensionless number called Strouhal number. The wake flow structure is considered to be characterized by a single frequency and 2D topology, homogeneous along the cylinder axis, very often. The presented paper concentrates on differences between this commonly accepted model and physical reality. Both temporal and spatial aspects of the flow in the wake behind a cylinder are to be addressed. The turbulent subcritical wake characterized by Reynolds number about 5 thousand will be considered, as this situation is a typical case in mechanical engineering applications. Keywords: circular cylinder; wake; vortex; dynamics; 3D structure Fulltext is available at external website.
Wake Behind a Cylinder: An Overview of Spatio-Temporal Aspects

A circular cylinder in crossflow is subjected to the overview study from the point of view spatial and temporal characteristics. It represents itself a typical engineering problem, appearing in ...

Uruba, Václav
Ústav termomechaniky, 2022

Use of active power filter to reduce flicker caused by electric arc furnace operation
Čerňan, Martin; Bejvl, Martin; Šimek, Petr; Valouch, Viktor
2022 - English
Effectiveness of using a parallel active power filter to compensate for the flicker of an electric arc furnace,\nand mitigate the reactive power consumption and terminal\nvoltage variation in the grid is presented and evaluated in the contribution. The model of a power system with the electric arc furnace and parallel active power filter in the frequency domain has been developed. The selected results of simulation in the frequency domain using the data collected from the 60 t EAF are presented and evaluated. Keywords: electric arc furnace; flicker mitigation; active power filter; power system model; simulation in frequency domain Available at various institutes of the ASCR
Use of active power filter to reduce flicker caused by electric arc furnace operation

Effectiveness of using a parallel active power filter to compensate for the flicker of an electric arc furnace,\nand mitigate the reactive power consumption and terminal\nvoltage variation in the grid ...

Čerňan, Martin; Bejvl, Martin; Šimek, Petr; Valouch, Viktor
Ústav termomechaniky, 2022

Identification of the blade tip possition and measurement techniques using the BTT method
Maturkanič, Dušan; Procházka, Pavel; Hodboď, Robert; Mekhalfia, Mohammed Lamine
2022 - English
This paper describes the existing practice in identifying and defining the position of the blade tips and the relevant technique for measuring their vibration during rotation. In connection with the effort to precisely define the position of the vibrating blade, the paper also analysed the possibilities of unambiguous determination of its position. This work creates a parallel branch to signal processing in the complex system of precision measurement and analysis of blade vibration, which was mentioned in previous papers. Keywords: turbine blade; vibration; precision method; modification; harmonic function Available at various institutes of the ASCR
Identification of the blade tip possition and measurement techniques using the BTT method

This paper describes the existing practice in identifying and defining the position of the blade tips and the relevant technique for measuring their vibration during rotation. In connection with the ...

Maturkanič, Dušan; Procházka, Pavel; Hodboď, Robert; Mekhalfia, Mohammed Lamine
Ústav termomechaniky, 2022

Measurement and analysis of vibration and acoustic emissions of a railway wheel under defined dynamic excitations
Pešek, Luděk; Prasad, Chandra Shekhar; Šnábl, Pavel
2022 - English
The paper deals with experimental vibro-acoustics of railway wheel. The methodology for evaluation of effect of vibrational plate dampers was elaborated. The four variants of the wheel was measured and analyse to achieve the optimal solution of the dampers. Keywords: vibro-acoustics; railway wheel; dampers; noise Available at various institutes of the ASCR
Measurement and analysis of vibration and acoustic emissions of a railway wheel under defined dynamic excitations

The paper deals with experimental vibro-acoustics of railway wheel. The methodology for evaluation of effect of vibrational plate dampers was elaborated. The four variants of the wheel was measured ...

Pešek, Luděk; Prasad, Chandra Shekhar; Šnábl, Pavel
Ústav termomechaniky, 2022

Shifted proper orthogonal decomposition and artificial neural networks for time-continuous reduced order models of transport-dominated systems
Kovárnová, A.; Krah, P.; Reiss, J.; Isoz, Martin
2022 - English
Transport-dominated systems are pervasive in both industrial and scientific applications. However, they provide a challenge for common mode-based model order reduction (MOR) approaches, as they often require a large number of linear modes to obtain a sufficiently accurate reduced order model (ROM). In this work, we utilize the shifted proper orthogonal decomposition (sPOD), a methodology tailored for MOR of transport-dominated systems, and combine it with an interpolation based on artificial neural networks (ANN) to obtain a time-continuous ROM usable in engineering practice. The resulting MOR framework is purely data-driven, i.e., it does not require any information on the full order model (FOM) structure, which extends its applicability. On the other hand, compared to the standard projection-based approaches to MOR, the dimensionality reduction utilizing sPOD and ANN is significantly more computationally expensive since it requires a solution of high-dimensional optimization problems. Keywords: model order reduction; shifted POD; CFD-DEM; OpenFOAM Fulltext is available at external website.
Shifted proper orthogonal decomposition and artificial neural networks for time-continuous reduced order models of transport-dominated systems

Transport-dominated systems are pervasive in both industrial and scientific applications. However, they provide a challenge for common mode-based model order reduction (MOR) approaches, as they often ...

Kovárnová, A.; Krah, P.; Reiss, J.; Isoz, Martin
Ústav termomechaniky, 2022

Analysis of vibration of rotors with a thick rigid disc on the overhanging end supported by hydrodynamic bearings and loaded by uncertain unbalance effects
Zapoměl, Jaroslav; Ferfecki, P.; Molčan, M.; Kozánek, Jan
2022 - English
Rotors of some rotating machines consist of a shaft and a rigid disc attached to its overhanging end. Because of manufacturing and assembling inaccuracies, the disc is unbalanced. In general case, the disc principal axis of inertia deviates from the shaft axis (both axes are skew lines) and the disc center of gravity is not situated on the shaft center line. Then the disc inertia effects are the source inducing the rotor lateral vibration. As magnitude of parameters specifying the disc unbalance is uncertain, application of an adequate method is required to perform the analysis. In addition, if the rotor is supported by hydrodynamic bearings, their nonlinear properties lead to rising complexity of the system vibration and to reducing its predictability. In the presented paper, the motion equation of a rigid disc has been derived. The shaft was represented by a beam body that was discretized into finite elements. The stiffness and damping parameters of the hydrodynamic bearings were linearized in vicinity of the rotor equilibrium position. Then vibration of the rotor is governed by a set of linearized motion equations. The fuzzy numbers were applied to consider uncertainty of the disc unbalance parameters. The presented procedure provides the approach to computational analysis of rotating machines with the rotor having a disc attached to its overhanging end and the geometrical, mechanical, or technological parameters of which have uncertain values. Keywords: rotors; hydrodynamic bearings; rigid discs on overhanging end; uncertain unbalance parameters; fuzzy number approach Fulltext is available at external website.
Analysis of vibration of rotors with a thick rigid disc on the overhanging end supported by hydrodynamic bearings and loaded by uncertain unbalance effects

Rotors of some rotating machines consist of a shaft and a rigid disc attached to its overhanging end. Because of manufacturing and assembling inaccuracies, the disc is unbalanced. In general case, the ...

Zapoměl, Jaroslav; Ferfecki, P.; Molčan, M.; Kozánek, Jan
Ústav termomechaniky, 2022

Study of the oscillation of a pendulum in a magnetic field
Zapoměl, Jaroslav; Kozánek, Jan; Košina, Jan; Cibulka, Jan
2022 - English
Realization of some technological processes requires application of rotating machines with a vertical rotor mounted in rolling element bearings. One of the requirements put on their operation is minimization of energy losses in the support elements. The proposed design variant consists in supporting the vertical rotor by one rolling element bearing placed at its upper part and by one axial magnetic bearing mounted in its lower end. The magnetic bearing is composed of an electric coil coupled with the stationary part and of a permanent magnet attached to the rotating part. The magnetic force attracts the permanent magnet, which reduces radial displacement of the lower end of the rotor. The magnetic field between the magnets represents a force coupling between the rotor and the stationary part, which shows some stiffness and affects the system natural frequencies. The controlled change of the stiffness makes it possible to reduce the rotor lateral oscillations in the resonance area. The investigated pendulum is coupled with the frame by a revolute joint at its upper end. The permanent magnet is attached to its lower end. The electric coil is coupled with the stationary part and placed under the pendulum. The system is excited by a moment of harmonic time history, which sets the pendulum into a seesaw motion.\n\n Keywords: vertical rotor; pendulum; axial magnetic bearings; lateral oscillations; resonance Available at various institutes of the ASCR
Study of the oscillation of a pendulum in a magnetic field

Realization of some technological processes requires application of rotating machines with a vertical rotor mounted in rolling element bearings. One of the requirements put on their operation is ...

Zapoměl, Jaroslav; Kozánek, Jan; Košina, Jan; Cibulka, Jan
Ústav termomechaniky, 2022

Localized formulation of bipenalty method in contact-impact problems
Kolman, Radek; González, J. A.; Dvořák, Radim; Kopačka, Ján; Park, K.C.
2022 - English
Often, the finite element method together with direct time integration is used for modelling of contact-impact problems of bodies. For direct time integration, the implicit or explicit time stepping are gen-\nerally employed. It is well known that the time step size in explicit time integration is limited by the stability limit. Further, the trouble comes with the task of impact of bodies with different critical time step sizes for each body in contact. In this case, this numerical strategy based on explicit time stepping with the same time step size for both bodies is not effective and is not accurate due to the dispersion behaviour and spurious stress oscillations. For that reason, a numerical methodology, which allows independent time stepping for each body with its time step size, is needed to develop. In this paper, we introduce the localized variant of the bipenalty method in contact-impact problems with the governing equations derived based on the Hamilton’s principle. The localized bipenalty method is applied into the impact problems of bars as an one-dimensional problem. The definition of localized gaps is presented and applied into the full concept of the localized bipenalty method. Keywords: contact-impact problem; explicit time integration; bipenalty formulation; ocalized lagrange multipliers; stability analysis Available at various institutes of the ASCR
Localized formulation of bipenalty method in contact-impact problems

Often, the finite element method together with direct time integration is used for modelling of contact-impact problems of bodies. For direct time integration, the implicit or explicit time stepping ...

Kolman, Radek; González, J. A.; Dvořák, Radim; Kopačka, Ján; Park, K.C.
Ústav termomechaniky, 2022

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