673 research outputs found
Electromagnetic Wave Theory and Applications
Contains reports on twelve research projects.Joint Services Electronics Program (Contract DAALO3-86-K-0002)National Science Foundation (Grant ECS 85-04381)National Aeronautics and Space Administration/Goddard Space Flight Center (Contract NAG5-270)National Aeronautics and Space Administration/Goddard Space Flight Center (Contract NAG5-725)U.S. Navy - Office of Naval Research (Contract N00014-83-K-0258)U.S. Navy - Office of Naval Research (Contract N00014-86-K-0533)U.S. Army - Research Office Durham (Contract DAAG29-85-K-0079)International Business Machines, Inc.National Aeronautics and Space Administration/Goddard Space Flight Center (Contract NAG5-269)Simulation TechnologiesSchlumberger-Doll Researc
Time-Dependent Wave-Structure Interaction Revisited: Thermo-piezoelectric Scatterers
In this paper, we are concerned with a time-dependent transmission problem
for a thermo-piezoelectric elastic body immersed in a compressible fluid. It is
shown that the problem can be treated by the boundary-field equation method,
provided an appropriate scaling factor is employed. As usual, based on
estimates for solutions in the Laplace-transformed domain, we may obtain
properties of corresponding solutions in the time-domain without having to
perform the inversion of the Laplace-domain solutions
Modeling for the Computer-Aided Design of Long Interconnects
L'abstract è presente nell'allegato / the abstract is in the attachmen
Evaluating the industrial application of non-destructive inspection of composites using transient thermography
Thesis (MEng)--Stellenbosch University, 2016.ENGLISH ABSTRACT: Transient thermography is a non-destructive testing method used in the detection
and visualization of sub-surface flaws. Transient thermography could
use one of two heating methods: step and square-pulse heating. Both these
methods rely on observing the temperature rise of a surface that is subjected
to a constant heat flux, while square pulse thermography also observes the
subsequent thermal decay after the heat has been removed.
The transient methods have not been thoroughly explored in literature with
respect to the more popular methods, such as pulsed and lock-in thermography.
Particular interest has been placed on investigating transient thermography on
fiber-reinforced polymer (FRP) materials and its application in industry.
Composites are prone to flaws such as delaminations, voids and inclusions
that do not accurately represent flat-bottom holes, which are commonly evaluated
in experimental work. Therefore, the inspection of thin artificial air-gaps
and Teflon® delaminations were investigated. These artificial flaws can be
considered to represent either a fully-separated or contacting delamination. A
significant reduction in defect contrast and definition was observed for the thin
delaminations, which is ascribed to the lower thermal resistance than that for
flat-bottom holes.
Further studies investigated the qualitative and quantitative performance
of thermographic inspection on defective samples provided by an industrial
partner. Experimental results demonstrated that variability in core geometry,
ply arrangement, surface and sub-surface anomalies could be identiffied.
The smallest detectable anomaly was found to be 1 mm wide, which was a
spatial resolution limitation of the infrared camera. The investigated samples exhibited small radius and low resistance defects. It was found that current
techniques to quantify defect depth are inadequate, especially if an accurate
reference depth cannot be found.
Thermography data is typically associated with subtle defect signatures
that are strongly affected by non-uniform heating and surface variability. Advanced
processing methods have been shown to help mitigate these effects.
Various processing methods are reviewed from literature. Several methods
were tested here for the first time, such as: multiscale retinex, matched filters,
Markov error contrast and modified differential absolute contrast (IDAC) for
step thermography.
Transient thermography has shown to be a strong competitor amongst
other thermographic methods for its simple application, relatively fast inspection
times, and high thermal contrast for low defect resistance cases. It further
enables the use of an entry-level infrared camera. The ndings of the artificial
samples reported a maximum defect depth up to 7 mm was observed for clear
Plexiglas®. The clear Plexiglas® can be considered to be the least optimal
case of heating with optical excitation and has a low thermal emissivity. For
the carbon and glass fibre reinforced polymers, a maximum detectable defect
depth of 5 mm was observed, which is considered to be comparative or even
better than pulsed thermography. The method was particularly better for low
diffusivity materials, such as glass fibre composites.AFRIKAANSE OPSOMMING: Oorgangstermografie is 'n nie-destruktiewe tegniek om defekte onder die oppervlak
waar te neem en te visualiseer. Oorgangstermografie kan een van twee
verhittingsmetodes gebruik: stap en vierkant puls verhitting. Beide tegnieke
is gebaseer op die waarneming van die temperatuur styging van 'n oppervlak
onderwerp aan 'n konstante warmtelas, terwyl vierkant puls verhitting ook die
temperatuur daling waarneem nadat die warmtelas verwyder is.
In vergelyking met meer populêre metodes, soos gepulseerde en geslote
termografie, is die oorgangsmetodes nog nie ewe deeglik beskryf in die literatuur
nie. Daar is veral belangstelling in ondersoeke na oorgangstermografie
vir veselversterkte polimere en die toepassing daarvan in industrie.
Saamgesteldemateriale is geneig om defekte soos delaminasie, leemtes en
inklusies te hê wat nie goed voorgestel word deur plat bodem gate nie, soos
algemeen gebruik in eksperimentele werk. Hier is die gebruik van dun, kunsmatige,
luggapings en Te on® delaminasies ondersoek. 'n Beduidende verlaging
in kontras en definisie is waargeneem vir dun delaminasies wat toegeskryf kan
word aan die feit dat dit 'n laer termiese weerstand het as plat bodem gate.
Verdere ondersoeke na die kwalitatiewe en kwantitatiewe vermoë van die
termografiese inspeksie van defektiewe onderdele voorsien deur 'n industriële
vennoot is gedoen. Eksperimentele resultate het getoon dat variasies in die
kern geometrie, laag oriëntasie, oppervlak en sub-oppervlak afwykings geïdenti
fiseer kan word. Die kleinste, waarneembare afwyking was 1 mm wyd, wat
toegeskryf word aan die beperkte ruimtelike resolusie van die infrarooikamera.
Die ondersoekte voorbeelde het klein radius en lae weerstand defekte getoon.
Dit is gevind dat bestaande tegnieke om defek diepte te vind deur die gebruik
van inversie metodes ontoereikend is, veral wanneer 'n verwysingsdiepte
nie akkuraat bepaal kan word nie.
Termografiese data word dikwels geassosieer met fyn defek kenmerke wat
sterk beïnvloed word deur oneweredige verhitting en oppervlakte variasies. Dit
is al gevind dat gevorderde verwerkingsmetodes die effek hiervan kan verminder.
Verskeie van hierdie tegnieke, soos gevind in die literatuur, is oorweeg.
Nuwe metodes, soos multiskaal retinex, bypassende lters, Markov fout kontras
en aangepaste differensiële absolute kontras, word ook beskryf en ge-evalueer.
Die prosesseringsmetodes is geïmplimenteer in 'n oopbron sagteware pakket
en is getoets met voorbeelde uit die industrie.
Dit is getoon dat oorgangstermografie 'n sterk mededinger is in die versameling
termografiese tegnieke vernaamlik as gevolg van die eenvoudige toepassing
daarvan, relatief vinnige inspeksie tye en hoë termiese kontras vir gevalle waar
die termiese weerstand van die defek laag is. Verder is dit moontlik om intreevlak
infrarooikameras te gebruik met hierdie tegnieke. Gebaseer op toetse met
kunsmatige defekte kon foute so diep as 7 mm onder die oppervlak gevind word
in helder Plexiglas®. Helder Plexiglas® is nie 'n ideale materiaal vir hierdie
tegnieke nie as gevolg van die materiaal se lae termiese emmisiwiteit. Defekte
so diep as 5 mm kon gevind word in koolstof- en glasvesel versterkte polimere.
Dit is vergelykbaar met en selfs beter as gepulseerde termografie. Die tegniek
het veral beter resultate gelewer met materiale met lae diffusiwiteit, soos
saamgeselde veselglas materiale
Gravitating discs around black holes
Fluid discs and tori around black holes are discussed within different
approaches and with the emphasis on the role of disc gravity. First reviewed
are the prospects of investigating the gravitational field of a black
hole--disc system by analytical solutions of stationary, axially symmetric
Einstein's equations. Then, more detailed considerations are focused to middle
and outer parts of extended disc-like configurations where relativistic effects
are small and the Newtonian description is adequate.
Within general relativity, only a static case has been analysed in detail.
Results are often very inspiring, however, simplifying assumptions must be
imposed: ad hoc profiles of the disc density are commonly assumed and the
effects of frame-dragging and completely lacking. Astrophysical discs (e.g.
accretion discs in active galactic nuclei) typically extend far beyond the
relativistic domain and are fairly diluted. However, self-gravity is still
essential for their structure and evolution, as well as for their radiation
emission and the impact on the environment around. For example, a nuclear star
cluster in a galactic centre may bear various imprints of mutual star--disc
interactions, which can be recognised in observational properties, such as the
relation between the central mass and stellar velocity dispersion.Comment: Accepted for publication in CQG; high-resolution figures will be
available from http://www.iop.org/EJ/journal/CQ
Wave Propagation in Materials for Modern Applications
In the recent decades, there has been a growing interest in micro- and nanotechnology. The advances in nanotechnology give rise to new applications and new types of materials with unique electromagnetic and mechanical properties. This book is devoted to the modern methods in electrodynamics and acoustics, which have been developed to describe wave propagation in these modern materials and nanodevices. The book consists of original works of leading scientists in the field of wave propagation who produced new theoretical and experimental methods in the research field and obtained new and important results. The first part of the book consists of chapters with general mathematical methods and approaches to the problem of wave propagation. A special attention is attracted to the advanced numerical methods fruitfully applied in the field of wave propagation. The second part of the book is devoted to the problems of wave propagation in newly developed metamaterials, micro- and nanostructures and porous media. In this part the interested reader will find important and fundamental results on electromagnetic wave propagation in media with negative refraction index and electromagnetic imaging in devices based on the materials. The third part of the book is devoted to the problems of wave propagation in elastic and piezoelectric media. In the fourth part, the works on the problems of wave propagation in plasma are collected. The fifth, sixth and seventh parts are devoted to the problems of wave propagation in media with chemical reactions, in nonlinear and disperse media, respectively. And finally, in the eighth part of the book some experimental methods in wave propagations are considered. It is necessary to emphasize that this book is not a textbook. It is important that the results combined in it are taken “from the desks of researchers“. Therefore, I am sure that in this book the interested and actively working readers (scientists, engineers and students) will find many interesting results and new ideas
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