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Acoustic emission of cyclical loaded aircraft structures
Blaháček, Michal ; Skála, J.
Aircraft structures fatigue failure is considerable risk of today´s aviation safety. The problem is usually solved by critical parts preventive replacement, regardless of parts real state. It is very expensive and uneconomical solution. NDT method capable to find the changes in the part, that are indication of crack creation and growth, would be very useful and money saving.Acoustic emission (AE) is a NDT procedure that is candidate for the method. In the Aeronautical Research and Test Institute (VZLÚ) set of cyclical fatigue tests was done. During the test, loaded sample AE activity was monitored, during the loading sequence pauses, the sample state was checked using NDT methods such us ultrasound, eddy current, optical methods, non-linear ultrasound, etc. Presented paper attends to desription and analysis of AE measurement on cyclical loaded aircraft structure.
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Nelineární časově reversní ultrazvuková-tomografie
Převorovský, Zdeněk ; Krofta, Josef ; Převorovský, David
Nonlinear Elastic Wave Spectroscopy (NEWS) becomes new effective method for non-destructive testing of complex structures providing high sensitivity of damage detection. One of the most promising NEWS procedures is Nonlinear Time Reversal Acoustics (NLTRA) realizable in a lot of different ways. Common NLTRA procedure is mostly global, which means that localization of defect by this procedure can be often difficult. A modification of NLTRA is proposed in this paper, based on similar arrangement as ultrasonic tomography. Computer controlled switching between transmitting and receiving transducers is realized by specially designed high-voltage relay multiplexer.
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Expertní detekce příchodu signálu AE
Chlada, Milan
Accurate acoustic emission (AE) source location is the primary goal of the defect anylysis following the AE signal detection. The source localization is mostly based on arrival time differences of signals recorded by several transducers. Considerable signal distortion happens during the wave propagation through the solid. Inaccurate determination of signal onset and arrival time differences respectively, are the greatest sources of localization errors.Especially, in a case of figher requirements on accuracy and robustness, the results of currently used localization methods appear to be insufficient. In the paper, recently improved version of the new signal-shape based algorithm, modelling an expert system of the elastic wave arrival detection, is introduced. In many applications, this method, based on signal energy and local gravity center evolution, has been proved as rugged enough, fast and easily applicable.
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Modelování klasické námrazy na profilu křídla
Horák, V. ; Hoření, Bohumír
The paper presents the rime ice accretion prediction code. Model includes the calculation of a velocity distribution, droplet motion equations and detetrmination of a water mass flux impacting on the wing airfoil surface. Changing the airfoil shape is illustrated in compare of experimental results.
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Sensitivity Analysis of Neural Networks and the Correction of Emission Parameters to One Reference Source Location
Chlada, Milan ; Převorovský, Zdeněk
In the report, detailed description of neural network sensitivity analysis - the method for insignificant input parameters reduction - is mentioned. The starting point of any AE signal parameterization is the signal onset detection. The results of currently used localization methods appear to be insufficient. Hence, the new signal-shape based algorithm, modeling an expert system of the elastic wave arrival detection, has been proposed and tested. It is described in the first part of the report. The last part is located to the correction of AE signal parameters to one reference location in source vicinity. To illustrate the new partial inverse problem solution method, the numerical models with artificial emission sources and both theoretical and practically recorded Green's functions are discussed.
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Numerical simulation of interaction of a vibrating airfoil with turbulent flax
Dubcová, L. ; Feistauer, M. ; Horáček, Jaromír ; Sváček, Petr
The report deals with numerical simulations of 2D viscous incompressible flow around a rotationaly vibrating profile. The flow is described by continuity and Navier-Stokes equations. Solution of the partial differential equations is based on finite element method. Because the Reynolds numbers higher than 10 000 are considered the solution is stabilized by SUPG method. Alge-braic turbulence model is taken into account and for simulations of the flow on moving grids the ALE method is used. the method was applied on harmonie vibrations of the profil NACA 0012 and the results are in good agreement with the experimental data obtained in ARTI.
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