In this work results of numerical simulations and experimental measurements related to the high frequency dynamics of an aluminium Timoshenko periodic beam are presented. It was assumed by the ...authors that the source of beam structural periodicity comes from periodical alterations to its geometry due to the presence of appropriately arranged drill-holes. As a consequence of these alterations dynamic characteristics of the beam are changed revealing a set of frequency band gaps. The presence of the frequency band gaps can help in the design process of effective sound filters or sound barriers that can selectively attenuate propagating wave signals of certain frequency contents. In order to achieve this a combination of three numerical techniques were employed by the authors. They comprise the application of the Time-domain Spectral Finite Element Method in the case of analysis of finite and semi-infinite computational domains, damage modelling in the case of analysis of drill-hole influence, as well as the Bloch reduction in the case of analysis of periodic computational domains. As an experimental technique the Scanning Laser Doppler Vibrometry was chosen. A combined application of all these numerical and experimental techniques appears as new for this purpose and not reported in the literature available.
•In the work dynamics of an isotropic Timoshenko periodic beam is investigated.•Periodicity of the beam comes from evenly spaced drill-holes along its length.•Periodicity results in the emergence of frequency band gaps in the beam spectrum.•These frequency band gaps allow to apply the beam a sound barrier or filter.•Numerical results by TD-SFEM agree well with experimental ones by 1D-SLDV.
Damage identification by wavelet analysis Grabowska, J.; Palacz, M.; Krawczuk, M.
Mechanical systems and signal processing,
10/2008, Letnik:
22, Številka:
7
Journal Article
Recenzirano
Structural health monitoring (SHM) has been related to damage monitoring with operational loads playing a significant role in terms of fatigue life and damage accumulation prognostics. A lot of ...different techniques like acoustic emission, ultrasonic, acousto-ultrasonic, guided ultrasonic waves or Lamb waves are nowadays investigated in terms of efficient and user-friendly damage identification system. Every damage identification system available consists of the hardware and software. This paper deals with the latter which is based on propagating Lamb wave measurements. It has been developed especially for distinguishing different kinds of damages. The reason for that research is that for example small voids in material, classified as damage, do not influence its overall strength. The literature gives enormous number of application of wavelets and Lamb waves but only for detecting the damage. Distinguishing seems not to be a subject of wide interest. The usage of wavelet transformation with propagating Lamb waves for distinguishing between different failures is the most important novelty of the research done. To obtain the presented results for modelling, the FFT-based spectral element method has been used. For signal processing, the wavelet analysis has been employed. The proper results are given and future of this research direction is discussed.
The aim of this paper is to introduce a new finite spectral element of a cracked Timoshenko beam for modal and elastic wave propagation analysis. The proposed approach deals with the spectral element ...method. This method is suitable for analyzing wave propagation problems as well as for calculating modal parameters of the structure. In the paper, the results of the change in modal parameters due to crack appearance are presented. The influence of the crack parameters, especially of the changing location of the crack, on the wave propagation is examined. Responses obtained at different points of the beam are presented. Proper analysis of these responses allows one to indicate the crack location in a very precise way. This fact is very promising for the future work in the damage detection field.
The lifetimes of the low-lying excited states 2+ and 4+ have been directly measured in the neutron-deficient 106,108Sn isotopes. The nuclei were populated via a deep-inelastic reaction and the ...lifetime measurement was performed employing a differential plunger device. The emitted γ rays were detected by the AGATA array, while the reaction products were uniquely identified by the VAMOS++ magnetic spectrometer. Large-Scale Shell-Model calculations with realistic forces indicate that, independently of the pairing content of the interaction, the quadrupole force is dominant in the B(E2;21+→0g.s.+) values and it describes well the experimental pattern for 104−114Sn; the B(E2;41+→21+) values, measured here for the first time, depend critically on a delicate pairing-quadrupole balance, disclosed by the very precise results in 108Sn.
The paper presents analysis and assessment of operating power of vacuum induction furnace in relation to the efficiency of lead removal from Cu-Pb alloy in VIM (vacuum induction melting) technology. ...Thermodynamic analysis of the process is performed as well.
Finite element discrete models of various engineering 1D structures may be considered as structures of certain periodic characteristics. The source of this periodicity comes from the discontinuity of ...stress/strain field between the elements. This behaviour remains unnoticeable, when low frequency dynamics of these structures is investigated. At high frequency regimes, however, its influence may be strong enough to dominate calculated structural responses distorting or even falsifying them completely. In this paper, certain computational aspects of structural periodicity of 1D FE discrete models are discussed by the authors. In this discussion, the authors focus their attention on an exemplary problem of 1D rod modelled according to the elementary theory.
The main objective of this paper is to show the effectiveness and usefulness of the concept of an absorbing layer with increasing damping (ALID) in numerical investigations of elastic wave ...propagation in unbounded engineering structures. This has been achieved by the authors by a careful investigation of three different types of structures characterised by gradually increasing geometrical and mathematical description complexities. The analysis includes propagation of longitudinal elastic waves in a 1-D semi-infinite isotropic rod, modelled according to the classical 1-mode theory of rods, propagation of coupled shear and flexural elastic waves in a 1-D semi-infinite isotropic beam modelled according to the Timoshenko beam theory, as well as propagation of elastic waves in a 3-D semi-infinite isotropic half-pipe shell modelled by a 6-mode theory of shells. The concept of the ALID has been not only presented by the authors, but certain relations between the ALID properties and the characteristics of propagating elastic waves have been given that can help to maximise the ALID performance in terms of its damping capability. All results of numerical calculations presented by the authors in this work have been obtained by the use of the Time-domain Spectral Finite Element Method (TD-SFEM).
•The effectiveness of an absorbing layer with increasing damping has been shown.•The layer can be used for mimicking semi-infinite boundary conditions.•It can be applied for wave propagation related problems in 1-D, 2-D and 3-D.•Its properties should be correlated with the characteristics of propagating waves.•Its concept can be utilised by the Time-domain Spectral Finite Element Method.
A study of the dimensions and performance of a single detector of the future neutron detector array NEDA was performed by means of Monte Carlo simulations, using GEANT4. Two different liquid ...scintillators were evaluated: the hydrogen based BC501A and the deuterated BC537. The efficiency and the probability that one neutron will trigger a signal in more than one detector were investigated as a function of the detector size. The simulations were validated comparing the results to experimental measurements performed with two existing neutron detectors, with different geometries, based on the liquid scintillator BC501.
A comparative study of the neutron–γ discrimination performance of a liquid scintillator detector BC501A coupled to four different 5in. photomultiplier tubes (ET9390kb, R11833-100, XP4512 and R4144) ...was carried out. Both the Charge Comparison method and the Integrated Rise-Time method were implemented digitally to discriminate between neutrons and γ rays emitted by a 252Cf source. In both methods, the neutron–γ discrimination capabilities of the four photomultiplier tubes were quantitatively compared by evaluating their figure-of-merit values at different energy regions between 50keVee and 1000keVee. Additionally, the results were further verified qualitatively using time-of-flight to distinguish γ rays and neutrons. The results consistently show that photomultiplier tubes R11833-100 and ET9390kb generally perform best regarding neutron–γ discrimination with only slight differences in figure-of-merit values. This superiority can be explained by their relatively higher photoelectron yield, which indicates that a scintillator detector coupled to a photomultiplier tube with higher photoelectron yield tends to result in better neutron–γ discrimination performance. The results of this work will provide reference for the choice of photomultiplier tubes for future neutron detector arrays like NEDA.
Digital pulse-timing technique for the neutron detector array NEDA Modamio, V.; Valiente-Dobón, J.J.; Jaworski, G. ...
Nuclear instruments & methods in physics research. Section A, Accelerators, spectrometers, detectors and associated equipment,
03/2015, Letnik:
775
Journal Article
Recenzirano
A new digital pulse-timing algorithm, to be used with the future neutron detector array NEDA, has been developed and tested. The time resolution of four 5in. diameter photomultiplier tubes (XP4512, ...R4144, R11833-100, and ET9390-kb), coupled to a cylindrical 5in. by 5in. BC501A liquid scintillator detector was measured by employing digital sampling electronics and a constant fraction discriminator (CFD) algorithm. The zero crossing of the CFD algorithm was obtained with a cubic spline interpolation, which was continuous up to the second derivative. The performance of the algorithm was studied at sampling rates of 500MS/s and 200MS/s. The time resolution obtained with the digital electronics was compared to the values acquired with a standard analog CFD. The result of this comparison shows that the time resolution from the analog and the digital measurements at 500MS/s and at 200MS/s are within 15% for all the tested photomultiplier tubes.
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