Number of found documents: 2861
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Mapping of problematic regions in AE source location
Chlada, Milan; Převorovský, Zdeněk
2017 - English
Similarly to Global Positioning System, location of material defects by acoustic emission method meets the geometrical dilution of precision (GDOP) phenomena. Besides the several attitudes how to mathematically express its measure and compare particular sensor configurations in accordance with desired location precision, recently proposed method brings extended possibilities for detection of critical regions characterized by strong sensitivity of location results to signal arrival time changes or errors. Analogically to GDOP parameter it yields the sensitivity map available even for non-continuous or anisotropic materials. During the computation it uses the algorithm for finding the shortest ways in discretely defined bodies, which furthermore enables to view the problem through the so-called similarity and ambiguity maps. Keywords: acoustic emission; source location; geometrical dilution of precision Available at various institutes of the ASCR
Mapping of problematic regions in AE source location

Similarly to Global Positioning System, location of material defects by acoustic emission method meets the geometrical dilution of precision (GDOP) phenomena. Besides the several attitudes how to ...

Chlada, Milan; Převorovský, Zdeněk
Ústav termomechaniky, 2017

On finite element modelling in time reversal problems
Mračko, Michal; Kober, Jan; Kolman, Radek; Převorovský, Zdeněk; Plešek, Jiří; Masák, Jan; Kruisová, Alena
2017 - English
In this paper we analyse suitability and accuracy of computational techniques in time reversal applications based on finite element method (FEM) for detection and localization of defects, cracks or other acoustic emission sources in bodies and structures. As it is known, a classical explicit integration scheme - central difference is reversible. The central difference scheme as a time integrator is widely used for linear and nonlinear finite element analyses and it is also implemented in commercial and open-source finite element software. In the paper properties of the explicit FEM in time reversal problems are studied and analysed. We use the standard Galerkin FEM formulation with linear shape functions, one-point Gauss integration and lumped mass matrix. Loading by the Ricker pulse was applied for modelling of the acoustic source in an elastic square domain. A special attention is paid to the choice of boundary conditions in reverse problem which keep the reversibility of problems of interest. Finally, we show the quality of refocusing of the original acoustic source. Keywords: time reversal; explicit finite element analysis; elastic wave propagation; non-destructive testing; source reconstruction; refocusing Available at various institutes of the ASCR
On finite element modelling in time reversal problems

In this paper we analyse suitability and accuracy of computational techniques in time reversal applications based on finite element method (FEM) for detection and localization of defects, cracks or ...

Mračko, Michal; Kober, Jan; Kolman, Radek; Převorovský, Zdeněk; Plešek, Jiří; Masák, Jan; Kruisová, Alena
Ústav termomechaniky, 2017

NDT in additive manufacturing of metals
Převorovský, Zdeněk; Krofta, Josef; Kober, Jan
2017 - English
In this study we tested possibilities of nonlinear elastic wave spectroscopy (NEWS) methods to classify two types of artificially created defects in Ti-6Al-4V prismatic samples fabricated by Electron Beam Melting (EBM) system. Two series of samples with variable internal defects were tested: samples with central circular defects (missing material gaps), and samples with gradually growing stochastic porosity. Each group of samples contained also fully compact sample for a comparison. Five ultrasonic NEWS procedures were used to classify defects variability. Relatively simple experimental facility with two piezoelectric transducers allows interrogate samples and record their response. The best results, documented in this paper, were obtained by two modifications of NWMS procedure. Results of NEWS tests indicate that selected NEWS procedures can be used also for online AM monitoring. Keywords: additive manufacturing; 3D printing of metals; nondestructive testing; nonlinear elastic wave spectroscopy Available at various institutes of the ASCR
NDT in additive manufacturing of metals

In this study we tested possibilities of nonlinear elastic wave spectroscopy (NEWS) methods to classify two types of artificially created defects in Ti-6Al-4V prismatic samples fabricated by Electron ...

Převorovský, Zdeněk; Krofta, Josef; Kober, Jan
Ústav termomechaniky, 2017

Parametric identification in mechanical engineering
Kozánek, Jan; Zapoměl, Jaroslav
2017 - English
This paper deals with parametric identification in mechanical engineering, similarly as in [1]. We assume a linear mathematical model of a vibrating machine in matrix form and in frequency domain, defined by stiffness, viscous damping and mass matrices and by the corresponding resolvent matrix. Parametric identification is understood as the evaluation of the measured data from dynamical experiments and its methods can be divided into "indirect" (obtaining spectral and modal properties - modal analysis methods) and "direct" (determination of the coefficient matrices of the mathematical model). Keywords: mathematical model; dynamical experiments; identification Available at various institutes of the ASCR
Parametric identification in mechanical engineering

This paper deals with parametric identification in mechanical engineering, similarly as in [1]. We assume a linear mathematical model of a vibrating machine in matrix form and in frequency domain, ...

Kozánek, Jan; Zapoměl, Jaroslav
Ústav termomechaniky, 2017

Running flutter waves in blades cascade
Půst, Ladislav; Pešek, Luděk
2017 - English
The simplified mathematical model of dynamic properties of bladed cascade excited by wakes of flowing steam from the stationary cascade is derived. Interaction of this kind of forced excitation with aero-elastic self-excitation described by Van der Pol formula causes origin of flutter and its. running waves. It is shown that the velocity, direction of flutter running waves and mode of vibration depend on the blades’ number ratio and on kind of self-excitation forces on individual blade or on inter-blade distance. Keywords: running waves; flutter; self-excitation; wakes; ratio of blade numbers Available at various institutes of the ASCR
Running flutter waves in blades cascade

The simplified mathematical model of dynamic properties of bladed cascade excited by wakes of flowing steam from the stationary cascade is derived. Interaction of this kind of forced excitation with ...

Půst, Ladislav; Pešek, Luděk
Ústav termomechaniky, 2017

Some energy relations of the self-excited profile vibration in flowing fluid
Vlček, Václav; Zolotarev, Igor; Kozánek, Jan; Šidlof, Petr; Štěpán, M.
2017 - English
The aeroelastic measurements on the oscillating NACA0015 profile vibrating as the dynamic system with two degrees of freedom (pitch and plunge) were realized within the interval of Mach numbers M = 0.08 to 0.45 and Reynolds numbers Re = (1 – 5) 105 in the wind tunnel of the Institute of Thermomechanics of the CAS. Frequency and amplitude characteristics of the vibrating profile and values of elastic strain energy corresponding maximum pitch and plunge displacements of the studied profile were detected. Keywords: airfoil NACA 0015; aeroelasticity; stall flutter; dynamic stall; limit cycle oscillation Available at various institutes of the ASCR
Some energy relations of the self-excited profile vibration in flowing fluid

The aeroelastic measurements on the oscillating NACA0015 profile vibrating as the dynamic system with two degrees of freedom (pitch and plunge) were realized within the interval of Mach numbers M = ...

Vlček, Václav; Zolotarev, Igor; Kozánek, Jan; Šidlof, Petr; Štěpán, M.
Ústav termomechaniky, 2017

Měření tepelné vodivosti izolačních materiálů
Čenský, Miroslav
2017 - Czech
Cílem této práce bylo zjištění tepelných vodivostí dvou typů izolačních materiálů dodaných firmou Škoda Auto. Za pokojové teploty byly naměřeny tepelné vodivosti izolačních materiálů EKV/2 a EPA/1. The aim of this work was to determine the thermal conductivity of two types of insulating materials supplied by Škoda Auto. The thermal conductivity of the EKV / 2 and EPA / 1 insulation materials was measured at room temperature. Keywords: thermal conductivity; insulating materia; automotive industry Available at various institutes of the ASCR
Měření tepelné vodivosti izolačních materiálů

Cílem této práce bylo zjištění tepelných vodivostí dvou typů izolačních materiálů dodaných firmou Škoda Auto. Za pokojové teploty byly naměřeny tepelné vodivosti izolačních materiálů EKV/2 a ...

Čenský, Miroslav
Ústav termomechaniky, 2017

Explicit dynamic finite element analysis of a firing pin assembly
Mochar, Dominik; Gabriel, Dušan; Masák, Jan; Kopačka, Ján; Kolman, Radek; Plešek, Jiří; Hynek, P.; Vtípil, J.
2017 - English
In this paper, explicit dynamic finite element analysis of a firing pin assembly was performed. Two different geometries of the firing pin were considered using the finite element software PMD and Abaqus. For both variants there was evaluated a stress distribution at the critical point of a tested component, that is going to be later used for a fatigue analysis of the firing pin. Keywords: firing pin; explicit dynamic analysis; FEM; fatigue Available at various institutes of the ASCR
Explicit dynamic finite element analysis of a firing pin assembly

In this paper, explicit dynamic finite element analysis of a firing pin assembly was performed. Two different geometries of the firing pin were considered using the finite element software PMD and ...

Mochar, Dominik; Gabriel, Dušan; Masák, Jan; Kopačka, Ján; Kolman, Radek; Plešek, Jiří; Hynek, P.; Vtípil, J.
Ústav termomechaniky, 2017

Frekvenční a modální spektrum planetové převodovky Wikov
Půst, Ladislav; Pešek, Luděk; Radolfová, Alena
2017 - Czech
Zpráva navazuje na dřívější publikace, vydané v rámci spolupráce mezi Wikov Gear, s.r.o. a ÚT AVČR a zaměřené na výzkum dynamických vlastností čtyř-planetové převodovky se stojícím unášečem planetových kol. Lineární matematický model dynamického chování převodovky vychází z předpokladu tuhých těles ozubených kol, konstantních tuhostí v ložiskách i v uložení planet. Jako konstantní jsou uvažovány také kontaktní poddajnosti v ozubení a to střední hodnotou se zanedbáním periodické proměnnosti kontaktní tuhosti, což u širokého šikmého ozubení s vícenásobným dotykem je přípustné. Velmi měkké uložení osy centrálního kola a pružné uložení planet i kola korunového umožňuje obecný rovinný pohyb všech kol. \nStrukturní periodičnost čtyř-planetové převodovky má za následek, že odpovídající frekvenční spektrum obsahuje několik vícenásobných frekvencí. Poněvadž převodovka nikdy nepracuje samostatně, ale vždy ve spojení s dalšími agregáty, byly na vstupní a výstupní hřídel připojeny jednoduché modely hnacího a brzdicího systému. Pro tuto soustavu o 20 stupních volnosti jsou určeny vlastní frekvence, příslušné tvary kmitání a přenosové funkce mezi jednotlivými prvky. Numerický výpočet je doplněn grafickými záznamy jak vlastních tvarů kmitání, tak i přenosových funkcí.\n This report is a continuation of previous publications edited within the cooperation between Wikov Gear, s.r.o and IT ASCR and oriented on investigation of dynamic properties of four-planetary gearing box with fixed carrier of planet gears. Linear computing model of dynamic behaviour of gearing box is based on the assumption of solid gearing’s wheels, constant stiffness of bearings and of planets’ pins. Also the contact stiffness in gearings are supposed to be constant with the mean value. Due to the vide helical gearing with manifold contacts the periodical variability of contact stiffness is neglected. The very week support of sun wheel and elastic supports of planets and ring wheels results in the general plane motion of all wheels.\nStructural periodicity of four-planetary gearing results in existence of several multiple eigen-frequencies in frequency spectrum. As the gearing box works always in connection with other aggregates, the simple models of driving and breaking systems were jointed to the input and output shafts. Eigen-frequency spectrum corresponding modes of vibrations and transfer functions among all elements were ascertained for this 20 DOF system. Numerical computing is completed by graphical records of eigen-modes as well as of transfer functions. \n Keywords: four-planetary gearing box; eigen-frequencies and eigen-modes spectra; transfer functions Available at various institutes of the ASCR
Frekvenční a modální spektrum planetové převodovky Wikov

Zpráva navazuje na dřívější publikace, vydané v rámci spolupráce mezi Wikov Gear, s.r.o. a ÚT AVČR a zaměřené na výzkum dynamických vlastností čtyř-planetové převodovky se stojícím unášečem ...

Půst, Ladislav; Pešek, Luděk; Radolfová, Alena
Ústav termomechaniky, 2017

Simulation of Transonic Flow Through a Mid-span Turbine Blade Cascade for Various Mach Numbers
Straka, P.; Příhoda, Jaromír; Fenderl, D.
2017 - English
The contribution deals with the numerical simulation of 2D transonic flow through a mid-span turbine blade cascade for several Mach numbers by means of the EARSM turbulence model of Hellsten (2004) connected with the algebraic bypass transition model of Straka and Příhoda (2014). Both models are implemented into an in-house numerical code based on the finite volume method. The gamma-transition model of Menter et al. (2015) with SST turbulence model accessible in the commercial code ANSYS Fluent was used for the comparison. Keywords: turbine cascade; transition model; shock wave-boundary layer interaction Available at various institutes of the ASCR
Simulation of Transonic Flow Through a Mid-span Turbine Blade Cascade for Various Mach Numbers

The contribution deals with the numerical simulation of 2D transonic flow through a mid-span turbine blade cascade for several Mach numbers by means of the EARSM turbulence model of Hellsten (2004) ...

Straka, P.; Příhoda, Jaromír; Fenderl, D.
Ústav termomechaniky, 2017

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