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A simple algorithm for probes positioning in BTT systems
Tchawou Tchuisseu, Eder Batista; Procházka, Pavel; Maturkanič, Dušan
2020 - anglický
The Blade Tip Timing (BTT), a non-contact method for measuring the blade tip displacement through the time of arrival, is studied in this article. This work proposes a simple algorithm based on the minimization of the coherence and the condition number of the sensingmatrix for defining the best probe positioning in the case of synchronous and asynchronous vibrations.
Klíčová slova:
BTT systems; probe positioning; condition number; coherence
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
A simple algorithm for probes positioning in BTT systems
The Blade Tip Timing (BTT), a non-contact method for measuring the blade tip displacement through the time of arrival, is studied in this article. This work proposes a simple algorithm based on the ...
On the 3D Dynamics of the Wake Behind a Circular Cylinder
Uruba, Václav; Procházka, Pavel P.; Skála, Vladislav
2020 - anglický
Flow in the wake of a circular cylinder is studied experimentally using time-resolved stereo PIV method. Special attention is paid to 3D topology of dynamical structures. While the distribution of statistic quantities along the cylinder is uniform, and i.e. 2D, the instantaneous flow structure is fully 3D. Within the velocity fluctuating flow field the structures containing streamwise vorticity and velocity components are dominant. The POD modes connected with von Kármán vortex street are identified.
Klíčová slova:
circular cylinder; wake; 3D structure; POD
Dokument je dostupný na externích webových stránkách.
On the 3D Dynamics of the Wake Behind a Circular Cylinder
Flow in the wake of a circular cylinder is studied experimentally using time-resolved stereo PIV method. Special attention is paid to 3D topology of dynamical structures. While the distribution of ...
Contribution to HPC FEM calculations of bladed disk dynamics with dry-friction contacts
Pešek, Luděk; Šnábl, Pavel; Bula, Vítězslav
2020 - anglický
The experimental set-up for studying dynamical behaviour of the bladed wheel with pre-stressed dry-friction contacts in tie-bosses was built. The numerical solution of the turbine bladed wheel with tie-bosses based on 3D finite element method with surface to surface dry-friction contact model is proposed. Comparison of experimental and preliminary numerical results of dynamical behaviour and damping estimation of our bladed wheel design yielded a reasonable agreement. Due to dry-friction contacts and non-linear solution of 3D FE model it, however, leads to HPC computations and long computation times. The contribution deals with description of computational strategy for damping evaluation and achieved results, too.
Klíčová slova:
bladed wheel; dry-friction contacts; damping; tie-boss couplings
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Contribution to HPC FEM calculations of bladed disk dynamics with dry-friction contacts
The experimental set-up for studying dynamical behaviour of the bladed wheel with pre-stressed dry-friction contacts in tie-bosses was built. The numerical solution of the turbine bladed wheel with ...
Design of experiment for temperature dependence of rubber samples under torsional harmonic load
Šulc, Petr; Pešek, Luděk; Bula, Vítězslav; Košina, Jan; Cibulka, Jan
2020 - anglický
This work deals with the preparation and methodology of temperature measurement inside the rubber sample. There is a design of a rubber sample with placed temperature sensors and a description with a scheme of temperature measurement under torsional dynamic stress. The reason for these measurements is to determine the temperature dependence and sensitivity of the parameters of the thermal outputs.
Klíčová slova:
heat flow; temperature; Fourier equation
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Design of experiment for temperature dependence of rubber samples under torsional harmonic load
This work deals with the preparation and methodology of temperature measurement inside the rubber sample. There is a design of a rubber sample with placed temperature sensors and a description with a ...
Experimental modelling of vibroacoustics of the human vocal tract with compliant walls
Radolf, Vojtěch; Horáček, Jaromír; Košina, Jan
2020 - anglický
Experimental model of human vocal tract cavities with hard walls has been modified to take into account the compliance of the soft tissue of the human vocal tract. The paper presents the studied acoustic-structural interaction of the vocal tract cavities with a dynamical system originated in vibration of the soft tissue. The experimental results are in qualitative agreement with the results of mathematical modelling. Compliant walls of acoustic cavities generate additional low frequency acoustical-mechanical resonances of the system and increase acoustic resonance frequencies.
Klíčová slova:
biomechanics of voice; vocal tract acoustics; acoustic-structural interaction.
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Experimental modelling of vibroacoustics of the human vocal tract with compliant walls
Experimental model of human vocal tract cavities with hard walls has been modified to take into account the compliance of the soft tissue of the human vocal tract. The paper presents the studied ...
Laminar-Turbulent Transition in View of Flow Separation from Isothermal and Heated Cylinder
Pech, Jan
2020 - anglický
This work presents insight to the laminar-turbulent transition in flow around cylinder through a numerical simulation, both in isothermal and heated case. The flow is modelled directly as a solution to the Navier-Stokes and Navier-Stokes-Fourier system. Reynolds numbers are considered in range 100-20000, ratio of cylinder-wall and upstream temperature is up to 1.5. Curves representing evolution of separation positions in time provide novel insight to vortex formation. Various regimes are recognized and some of them can be assigned to phenomena described formerly in experiment.
Klíčová slova:
transition to turbulence; heated flow; cylinder flow; separation angle; Navier-Stokes- Fourier; spectral/hp element method
Dokument je dostupný na externích webových stránkách.
Laminar-Turbulent Transition in View of Flow Separation from Isothermal and Heated Cylinder
This work presents insight to the laminar-turbulent transition in flow around cylinder through a numerical simulation, both in isothermal and heated case. The flow is modelled directly as a solution ...
Comparison of power control method for B4 converter connected to unbalanced grid
Šimek, Petr; Valouch, Viktor
2020 - anglický
The aim of the paper is to present a power control of a three-phase inverter with only four inverter legs (connections B4) connected to an unbalanced grid. The results obtained by the predictive power control with a finite set of control values, the results obtained using a modified direct power control strategy, and the results obtained using a generalized predictive control are compared and discussed.\n
Klíčová slova:
power control; B4 converter; unbalanced grid
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Comparison of power control method for B4 converter connected to unbalanced grid
The aim of the paper is to present a power control of a three-phase inverter with only four inverter legs (connections B4) connected to an unbalanced grid. The results obtained by the predictive power ...
Dependence of signal strangth on the radial distance and different types of magnets
Procházka, Pavel; Voronova, Evgeniya; Maturkanič, Dušan
2020 - anglický
The paper describes dependence of signal strength on the radial distance between the sensor and the measured object and dependence of signal strength on the different types of magnets. The measurements were performed in the laboratory of the rotational laser vibrometry originated at the Institute of Thermomechanics AS CR, v.v.i.
Klíčová slova:
vibration; diagnostics; sensor; laser; blade; turbine
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Dependence of signal strangth on the radial distance and different types of magnets
The paper describes dependence of signal strength on the radial distance between the sensor and the measured object and dependence of signal strength on the different types of magnets. The ...
Inverse mass matrix for higher-order finite element method in linear free-vibration problems
Kolman, Radek; González, J.G.; Cimrman, Robert; Kopačka, Ján; Cho, S.S.; Park, B.G.
2020 - anglický
In the paper, we present adirect inverse mass matrix in the higher-orderfinite element method forsolid mechanics. The direct inverse mass matrix is sparse, has the same structure as the consistent mass matrixand preserves the total mass. The core of derivation of the semi-discrete mixed form is based on the Hamilton’s principle of leastaction. The cardinal issue is finding the relationship between discretized velocities and discretized linear momentum. Finally, the simple formula for the direct inversemass matrix is presented as well as thechoice of density-weighted dual shape functions for linear momentum with respect to the displacement shape functionwith achoice of the lumping mass method for obtaining the correct and positive definitive velocity-linear momentum operator. The application of Dirichlet boundaryconditions into the direct inversemass matrix forafloating system is achieved usingthe projection operator. The suggested methodology is tested on a free-vibration problem of heterogeneous bar for different ordersof shape functions.
Klíčová slova:
higher-order finite element method; direct inverse mass matrix; consistent and lumped massmatrix; free vibration problem; heterogeneous bar
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Inverse mass matrix for higher-order finite element method in linear free-vibration problems
In the paper, we present adirect inverse mass matrix in the higher-orderfinite element method forsolid mechanics. The direct inverse mass matrix is sparse, has the same structure as the ...
Anomalies detection in time-series data for the internal diagnostics of autonomous mobile robot
Věchet, Stanislav; Krejsa, Jiří; Chen, K.S.
2020 - anglický
Autonomous mobile robots are complex mechatronic machines which consists of numerous hardware and software modules working asynchronously to achieve desired behaviour. As there are many frameworks which helps to overcome the flat learning curve the problem of internal diagnostics arises. While users and developers are able to focus only on solving the high level problem algorithm or methods the internal states of the system is hidden. This helps to separate the users from solving hardware issues, which is helping until everything works properly. We present an algorithm which is able to detect anomalies in time based behaviour of the robot to improve the users confidence that the internal robot framework works correctly and as desired. The algorithm is based on probabilistic patterns detection based on Bayesian probabilistic theory.
Klíčová slova:
anomalies detection; system diagnostic; robot operating system
Plné texty jsou dostupné na jednotlivých ústavech Akademie věd ČR.
Anomalies detection in time-series data for the internal diagnostics of autonomous mobile robot
Autonomous mobile robots are complex mechatronic machines which consists of numerous hardware and software modules working asynchronously to achieve desired behaviour. As there are many frameworks ...
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