Number of found documents: 2902
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Experimental and finite element analysis of composite gun barrels
Mochar, Dominik; Trnka, Jan; Chlada, Milan; Valeš, František; Gabriel, Dušan; Červ, Jan; Vtípil, J.
2018 - English
In this work experimental and numerical investigation of composite gun barrels was studied. The history of the stress-induced deformations located at the center of gun barrels on the outer surface generated by impact loading was measured for six types of barrels. The obtained signals were subsequently evaluated using wavelet transformation. Finally, the finite element analysis in Abaqus and MARC software for optimum composite material M46J was performed. Keywords: composite gun barrels; contact-impact analysis; drop weight tester; air cannon Available at various institutes of the ASCR
Experimental and finite element analysis of composite gun barrels

In this work experimental and numerical investigation of composite gun barrels was studied. The history of the stress-induced deformations located at the center of gun barrels on the outer surface ...

Mochar, Dominik; Trnka, Jan; Chlada, Milan; Valeš, František; Gabriel, Dušan; Červ, Jan; Vtípil, J.
Ústav termomechaniky, 2018

Fast estimation of flutter parameters of steam turbine blades using boundary element methods
Prasad, Chandra Shekhar; Pešek, Luděk
2018 - English
In the present paper the classical flutter parameters in turbomachinery cascade such as aerodynamic damping estimation using fast numerical method is described. The unsteady aerodynamic loading and the aerodynamic damping (AD) coefficient of the vibrating cascades is estimated by 2D boundary elementmethod such as source and doublet panel method (PM). To estimate the flutter parameters aerodynamic influence coefficient traveling wave mode (TWM)method is adopted. The experimental aerodynamic damping is compared against simulated results. The result demonstrate that potential flow based boundary elements method can estimate the AD with desired accuracy and less computational time. Keywords: turbomachinary; aeroelasticity; classical flutter; unsteady panel method; aerodynamic damping; traveling wave mode Available at various institutes of the ASCR
Fast estimation of flutter parameters of steam turbine blades using boundary element methods

In the present paper the classical flutter parameters in turbomachinery cascade such as aerodynamic damping estimation using fast numerical method is described. The unsteady aerodynamic loading and ...

Prasad, Chandra Shekhar; Pešek, Luděk
Ústav termomechaniky, 2018

Low Cost Laser Rangefinder Evaluation
Krejsa, Jiří; Věchet, Stanislav
2018 - English
Laser rangefinders are essential tools in indoor mobile robot navigation. Lately several low-cost models become available, enabling the use of this type of sensor in broader range of applications. This paper evaluates the properties of currently (2018) the cheapest sensor available, particularly RPLidar A1M8, in order to determine whether it is usable in mobile robot development. As the sensor is based on triangulation principle, the increase of errors with the measured distance was expected; the experiments proved these expectations. Furthermore, the increasing, but linear trend in absolute measurement error was observed. The influence of surface material and color was also evaluated. The measurements indicate that RPLidar A1M8 can serve as a useful alternative for more expensive types of laser rangefinders. Keywords: laser rangefinder; mobile robot; localization Fulltext is available at external website.
Low Cost Laser Rangefinder Evaluation

Laser rangefinders are essential tools in indoor mobile robot navigation. Lately several low-cost models become available, enabling the use of this type of sensor in broader range of applications. ...

Krejsa, Jiří; Věchet, Stanislav
Ústav termomechaniky, 2018

Deformation energy of Yeoh hyperelastic model and constant hyperelastic proportional damping
Šulc, Petr; Pešek, Luděk; Bula, Vítězslav; Košina, Jan; Cibulka, Jan
2018 - English
The paper deals with a proposal of the dissipated energy of hard rubbers as a function of the deformation energy expressed by the Yeoh hyperelastic model. Then the deformation energy may be dependent only on the first invariant of deformation. Based on the experiment, a “hyperelastic proportional damping” (HPD) is proposed for hard rubbers under finite strains. It is analogical to the model of proportional damping in the elastic theory, i.e. the dissipated energy is proportional to the deformation energy multiplied by the frequency of dynamic harmonic loading. The Yeoh model is chosen since the deformation function is dependent only on the first strain invariant for a description of the simple shear of a surface cylinder. The constants are used to an enumeration of the deformation energy of the Yeoh model for the specific cases of tested rubbers. The coefficients of hyperelastic proportional damping are evaluated on the basis of experimental results,too. Keywords: Yeoh model; hyperelastic proportional damping; deformation energy Available at various institutes of the ASCR
Deformation energy of Yeoh hyperelastic model and constant hyperelastic proportional damping

The paper deals with a proposal of the dissipated energy of hard rubbers as a function of the deformation energy expressed by the Yeoh hyperelastic model. Then the deformation energy may be dependent ...

Šulc, Petr; Pešek, Luděk; Bula, Vítězslav; Košina, Jan; Cibulka, Jan
Ústav termomechaniky, 2018

Computational time reversal method based on finite element method: influence of temperature
Mračko, Michal; Kolman, Radek; Kober, Jan; Převorovský, Zdeněk; Plešek, Jiří
2018 - English
Time reversal method is used to focus elastic waves to the location of the original source and reconstruct its source time function. The procedure consists of two steps: Frontal task and Reversal task. In the Frontal task, the medium is excited by an arbitrary source, elastic waves propagate through a body of interest and the dynamic response at few points on boundary is recorded. In the second step (say the Reversal task) the response signal is reversed in time and transmitted back into the medium resulting in focusing in the original source location. It is of practical importance to investigate a case when the medium changes its properties between the frontal and reversal wave propagation steps. An example is a problem of transferring experimentally recorded data to a computational model, where discrepancies in geometry, elastic properties and boundary conditions are expected. Our motivation is to develop a methodology for computation of time reversal problems in commercial finite element software. The results prove that this method is extremely sensitive to the change of temperature and one have to pay special attention to tuning of elastic parameters relevant to the\nexperiment. Keywords: time reversal method; elastic wave propagation; finite element method; temperature sensitivity; refocusing Available at various institutes of the ASCR
Computational time reversal method based on finite element method: influence of temperature

Time reversal method is used to focus elastic waves to the location of the original source and reconstruct its source time function. The procedure consists of two steps: Frontal task and Reversal ...

Mračko, Michal; Kolman, Radek; Kober, Jan; Převorovský, Zdeněk; Plešek, Jiří
Ústav termomechaniky, 2018

Dynamical analysis of bistable mechanical oscillator
Byrtus, M.; Půst, Ladislav
2018 - English
The contribution deals with analysis of dynamical properties of 1 DOF bistable mechanical oscillator. First the mathematical model is formulated. The original mathematical model is approximated by Duffing equation as it is commonly used. These two models are compared and it is shown how they differ in both static and dynamical response. The dynamical response is studied using bifurcation analysis performed by brute force numerical integration in time domain to detect area of interest from dynamical point of view. Such a bistable mechanical system can appear in many technical applications and therefore the proper modelling plays a significant role. Keywords: bistable system; vibration; bifurcation; stability Available at various institutes of the ASCR
Dynamical analysis of bistable mechanical oscillator

The contribution deals with analysis of dynamical properties of 1 DOF bistable mechanical oscillator. First the mathematical model is formulated. The original mathematical model is approximated by ...

Byrtus, M.; Půst, Ladislav
Ústav termomechaniky, 2018

The influence of permanent magnetic rings on the loss power, vibration and stability of vertical rotors
Zapoměl, Jaroslav; Ferfecki, P.; Sudhakar, A.; Kozánek, Jan
2018 - English
Lifting the vertical rotors by permanent magnets is an advanced technological solution for\nreducing energy losses in the supports. The disadvantage of this design is the instable interaction between the magnetic rings, which may destabilize the rotor oscillations. The performed research was focused on the development of computational procedures for analysis of energy losses in the supports of magnetically lifted vertical rotors mounted in rolling element bearings and on analysis of stability of their vibration in a wide range of operating speeds. The computational simulations proved efficiency of the magnetic suspension. Keywords: lifting vertical rotors; magnetic rings; energy losses reduction; vibration stability evaluation Available at various institutes of the ASCR
The influence of permanent magnetic rings on the loss power, vibration and stability of vertical rotors

Lifting the vertical rotors by permanent magnets is an advanced technological solution for\nreducing energy losses in the supports. The disadvantage of this design is the instable interaction between ...

Zapoměl, Jaroslav; Ferfecki, P.; Sudhakar, A.; Kozánek, Jan
Ústav termomechaniky, 2018

The experimental study of aeroelastic coupling of the moveable blade grid with the flow field at Reynolds number up to 150 000
Procházka, Pavel; Uruba, Václav; Pešek, Luděk; Bula, Vítězslav
2018 - English
This experimental study was conducted to help clarify an aeroelastic coupling in the case of rotational periodic bodies. The blade grid was placed behind the outlet of the blow-down wind tunnel. Three of five blades were constructed to allow vertical position changing by the action of three shakers. Particle Image Velocimetry was used to study the flow field statistical and dynamical parameter. The parameters, whose presence indicates the aeroelastic coupling, are searched. Keywords: blade cascade; time-resolved PIV; aeroelasticity Available at various institutes of the ASCR
The experimental study of aeroelastic coupling of the moveable blade grid with the flow field at Reynolds number up to 150 000

This experimental study was conducted to help clarify an aeroelastic coupling in the case of rotational periodic bodies. The blade grid was placed behind the outlet of the blow-down wind tunnel. Three ...

Procházka, Pavel; Uruba, Václav; Pešek, Luděk; Bula, Vítězslav
Ústav termomechaniky, 2018

Flow Dynamics in the Vicinity of Tandem Buildings
Gnatowska, R.; Kellnerová, Radka; Uruba, Václav
2017 - English
The flow-field in the vicinity of tandem building model in a wind tunnel will be subjected to analysis of dynamics. The model is 3D consisting of the two blocks of different sizes arranged in a streamwise direction. Experiments were performed using time-resolved PIV technique in several measuring planes to capture both spatial and dynamical features. Keywords: PIV experiment; tandem building arrangement; wind tunnel Available at various institutes of the ASCR
Flow Dynamics in the Vicinity of Tandem Buildings

The flow-field in the vicinity of tandem building model in a wind tunnel will be subjected to analysis of dynamics. The model is 3D consisting of the two blocks of different sizes arranged in a ...

Gnatowska, R.; Kellnerová, Radka; Uruba, Václav
Ústav termomechaniky, 2017

Impact of Turbulence Generators on Turbulent Characteristics and Structures
Kellnerová, Radka; Jurčáková, Klára; Jaňour, Zbyněk
2017 - English
The turbulent generators are routinely used to produce very turbulent flows. Special type of vertically slenderize spires are applied to enhance turbulent diffusion from the surface upwards in order to increase the boundary layer depth. This paper studies the influence of variable upstream distance of generators on formation of both vortical and non-vortical organized structures within a test section. The 2-component 2-dimensional time-resolved particle image velocimetry measurement of the flow was performed in the wind channel with very rough surface. Intermittent flow dynamics was evaluated by means of higher order moments, vorticity, quadrant and wavelet analysis. The downstream evolution of the flow suggests that equilibrium between roughness- and spires-produced turbulence was reached at the distance of 7 spires height.\n Keywords: turbulence generator; wind channel; vorticity; quadrant analysis Fulltext is available at external website.
Impact of Turbulence Generators on Turbulent Characteristics and Structures

The turbulent generators are routinely used to produce very turbulent flows. Special type of vertically slenderize spires are applied to enhance turbulent diffusion from the surface upwards in order ...

Kellnerová, Radka; Jurčáková, Klára; Jaňour, Zbyněk
Ústav termomechaniky, 2017

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