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1
Dickson, William S. "Wave reflections from breakwaters." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 1994. http://handle.dtic.mil/100.2/ADA283483.
Texte intégralRésumé :
Thesis (M.S. in (Meteorology and Physical Oceanography)) Naval Postgraduate School, June 1994.<br>Thesis advisor(s): Thomas H. C. Herbers, Edward B. Thornton. "June 1994." Bibliography: p. 37. Also available online.
2
Karenowska, Alexy Davison. "Some magnetic reflections on wave dynamics." Thesis, University of Oxford, 2011. http://ora.ox.ac.uk/objects/uuid:d31bd222-a948-45f8-9617-40507f4f96c6.
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3
Karimi, Hussain H. (Hussain Habibullah). "Oblique reflections of internal gravity wave beams." Thesis, Massachusetts Institute of Technology, 2012. http://hdl.handle.net/1721.1/74673.
Texte intégralRésumé :
Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2012.<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Cataloged from student submitted PDF version of thesis.<br>Includes bibliographical references (p. 99-100).<br>We study nonlinear effects in reflections of internal gravity wave beams in a continuously stratified liquid which are incident upon a uniform slope at an oblique angle. Wave motion in a stratified fluid medium is unique in the sense that the anisotropy of stratification directs energy transport in a manner specified by the frequency of the driving mechanism. Since there is no spatial variation along the direction of the flow field, plane waves are exact nonlinear solutions of the governing equations. In general, energy is carried in the form of a wave beam, which is a superposition of plane waves having parallel wavevectors. However, beams incident upon a surface interact with the re reflected beam in a locally confined region. Nonlinear interactions in the vicinity of the reflection site where the incident and reflected beams overlap act as a source for the generation of higher order harmonics. Employing small-amplitude expansions, we determine the directions of propagation and the strength of primary and second-harmonic reflected beams. The energy associated with the secondary beam during steady-state conditions is also computed. We find that in-plane reflections produce the strongest nonlinear reflections and that larger spatial variations of the incident beam profile produce stronger secondary beams.<br>by Hussain H. Karimi.<br>S.M.
4
Birtel, Philip [Verfasser]. "Inclusion of Multi-Reflections in the Beam-Wave Interaction Simulation of Traveling Wave Tubes / Philip Birtel." München : Verlag Dr. Hut, 2011. http://d-nb.info/1013526538/34.
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Papandreou, Benjamin David. "On the detection of shallow buried objects using seismic wave reflections." Thesis, University of Southampton, 2011. https://eprints.soton.ac.uk/334160/.
Texte intégralRésumé :
This thesis is concerned with a methodology for the detection of shallow (of order 1 metre) objects buried in soil using seismic waves. Possible objects of interest include infrastructure, archaeological artefacts and ordinance. A mathematical analysis of an idealised system is performed to gain understanding of both seismic wave propagation and the generation of these waves by surface sources. The mathematical techniques used in the existing analysis of a point vertical source are applied to the desired problem of a point horizontal surface traction. Results are displayed in a graphically concise form. An experimental methodology, capable of forming two-dimensional images through the ground, is described. The use of shear waves is shown preferable. The advantages and implementation of using time extended, rather than impulsive, excitation signals are described. Additional signal processing techniques, such as generalised cross-correlation functions, are also detailed. Simple numerical simulations are undertaken with the aim of both validating the post-processing algorithms and evaluating its robustness against non-ideal conditions. Simulated time histories are created by defining signals in the frequency domain and then modifying their amplitude and phase to replicate attenuation and propagation. Non-ideal conditions focus mainly on variation in the wavespeed as a function of depth. Simulations indicate that the imaging method fails for sufficiently large variations of wavespeed, particularly for objects buried below significant discontinuities in material properties. As shear waves are used for the imaging method, a source was designed and constructed to preferentially generate shear waves and was verified using field experimentation. The imaging methodology is applied to data from three experimental sites and is able to detect the target objects with some success. Problems, however, remain with the measurement of a wavespeed that is consistent and indicative of the propagation speed at depth, and in consistently obtaining a sufficiently large reflected wave from the object.
6
BATTAGLIA, ENZO. "Seismic reflection imaging of near surface structures using the Common Reflection Surface (CRS) Stack Method." Doctoral thesis, Università degli Studi di Cagliari, 2014. http://hdl.handle.net/11584/266406.
Texte intégralRésumé :
This PhD thesis aims to evaluate whether the
Common-Refl
ection-Surface (CRS) stack method can be considered as a more cost efficient processing alternative to the conventionally used Common Midpoint (CMP) stack method for processing of shallow and ultrashallow reflection data.
The CRS stack is a seismic imaging method established for oil and gas exploration that is similar in concept to the conventional CMP stack method. Unlike the CMP stack,
the CRS stack process is not confined to single CMP gathers (offset direction), but also includes neighbouring CMPs (midpoint direction) into the so-called CRS supergathers.
The use of CRS supergathers enables stable \data-driven", i.e. without human interactions, velocity analysis and residual static corrections, avoiding the poorly-automated
and time-consuming processing steps that are instead required when implementing conventional CMP processing. This makes the seismic imaging process more compatible
with budgets available for near-surface geophysical investigations. Improving seismic
imaging of near-surface reflection data, while at the same time reducing processing costs and human interaction during processing was the principal objective which guided
my work. To investigate the advantages and limitations of exporting the CRS stack from the hydrocarbon
exploration field to the near-surface scale, I have firstly analysed and adapted the characteristics of the CRS to the requirements of near-surface reflection data. Then, I have compared the results (seismic sections and velocity fields) obtained by processing
with the CMP and the CRS stack methods for two real field datasets (P- and SH-wave)and two synthetic datasets that exhibited very large vertical velocity changes. Finally,
I have proposed some original solutions that overcome several of the issues encountered when using CRS stack with near-surface data. The P-wave dataset was collected as part of a hydrogeological investigation with the aim
of delineating the hydrogeological framework of a paleolake environment to a depth of few hundred metres. Using the CMP method, several nearly horizontal reectors with onsets from 60 to about 250 ms were imaged. The CRS stack produced a stacked section with greater coherency and lateral continuity than the CMP section, but also spurious
alignments of seismic energy which hinder interpretation. Weighing the CRS stacked section with the corresponding CRS coherence and number of CRS stacked traces leads
to a considerable reduction of the spurious alignments, resulting in a seismic section more suited to delineate the aquifer and its confining units. The SH-wave ultrashallow dataset was collected to support a geotechnical study to a
depth of 10 m. The obtained CMP stacked section imaged a dipping bedrock interface below four horizontal re
ectors in unconsolidated, very low velocity sediments. The
vertical and lateral resolution was very high, so that despite the very shallow depth the resulting CMP stacked section showed the well-defined pinchout of two layers at less than 10 m depth. The CRS stack improved the continuity of the shallowest reector but showed an excessive smearing effect with some reector portions, including the pinchout,
unresolved and not as well defined as in the (very detailed) CMP counterpart. Restricting the CRS stack process to single CMP gathers, preserving the CRS-supergather for the search of stacking parameters, produced a time section very similar to the CMP counterpart. In both cases, I swiftly obtained the CRS stacked sections in a fully automatic way,
so with a cost/benefit ratio considerably more advantageous than that of the CMP sections, which required time-consuming prestack velocity analysis as well as residual
static corrections. Moreover, using the kinematic wave field attributes determined for each stacking operation I reconstructed velocity fields matching the ones estimated with the CMP processing, even if this required a greater amount of work than that required to produce the CRS stacked sections. Finally, using two synthetic datasets, I addressed the issue of the crossing reection events that appear in data acquired in soils characterized by strong vertical velocity gradients. Although a matter debate for decades, this is an issue still unresolved by use
of the conventional CMP method. Using the first synthetic dataset I showed that unlike in conventional CMP processing which cannot accurately process crossing reflection events without generating distortions and artefacts, the data-driven CRS stack imaging process considerably restricts their generation, limiting the reduction of signal-to-noise ratio and of temporal resolution in stacked traces. With the second synthetic dataset I simulated a data acquisition reproducing a case history with a high-velocity contrast in the first 5 m depth. The CRS results that I obtained from the modelled data demonstrated
that the CRS stack method may be a reliable alternative for processing crossing reection events, definitely easier and faster than the construction of complicated velocity
functions and/or the separated processing of the crossing events. By comparing these results with those obtained using the CMP method I obtained other interesting
results, which, however, to validate would necessitate the use of real datasets. The findings of this present study demonstrates that the CRS stack could represent a
significant step forward for the reduction of the costs involved in shallow and ultrashallow
seismic reflection data processing, one which does not compromise the quality of results. Both these conditions being essential to the increased acceptance of the seismic reection method as a routine investigation method for use in shallow and ultrashallow seismics.
7
Zhu, Xiang 1970. "3-D numerical modeling of the P and SV wave reflections from fractured reservoirs." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/58162.
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Day, Elizabeth Anne. "Array studies of short period P-wave reflections from boundaries within the deep Earth." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610226.
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Aloi, Daniel Nicholas. "Development and verification of a mathematical model to investigate the effects of earth-surface-based multipath reflections at a differential global positioning system ground reference site." Ohio : Ohio University, 1999. http://www.ohiolink.edu/etd/view.cgi?ohiou1175264170.
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Atef, Ali Hadi Mr. "ANALYSES OF URSEIS MOHO REFLECTIONS BENEATH THE PREURALIAN FOREDEEP OF THE URAL MOUNTAINS, RUSSIA." University of Akron / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=akron1181569948.
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Neto, Celso de Carvalho Noronha. "Matriz de massa de ordem elevada, dispersão de velocidades e reflexões espúrias." Universidade de São Paulo, 2008. http://www.teses.usp.br/teses/disponiveis/18/18134/tde-23092008-091215/.
Texte intégralRésumé :
O assunto principal deste trabalho é qualificar, quantificar e implementar o comportamento numérico de estruturas discretizadas através do método dos elementos finitos. Serão abordados apenas os elementos lineares unidimensionais dinâmicos, porém a aplicabilidade da formulação proposta pode se estender para elementos bi e tridimensionais lineares dinâmicos. Inicia-se com uma introdução ao tema. Com certo desenvolvimento matemático, pode-se isolar analiticamente a parcela relacionada ao erro numérico. Elevando a ordem do erro de truncamento, obtém-se precisão elevada na resposta numérica. Inspirado no integrador temporal de Newmark, projetam-se elementos que apresentam estabilidade incondicional para os chamados efeitos espúrios. O efeito evanescente é um fenômeno espúrio onde a onda se propaga ao longo da estrutura acompanhada de um amortecimento puramente numérico ao longo do domínio do espaço. Outro efeito analisado é a reflexão espúria. Quando dois elementos adjacentes têm comprimentos diferentes, surge uma onda de reflexão (ou duas, no caso do elemento de viga) na interface deles. Tal onda, também de origem puramente matemática, existe devido à diferença entre as massas e as rigidezes absolutas dos elementos envolvidos, independente do fato de que eles tenham as mesmas características físicas. A relação entre o incremento de tempo e o período de oscilação é convenientemente empregada como principal parâmetro para quantificar a discretização no domínio temporal. No domínio do espaço, a relação empregada é entre o comprimento do elemento e o comprimento de onda.<br>The main subject of this work is to qualify, quantify and implement the numerical behavior of discrete structures through the finite element method. It will be investigated only the dynamic onedimensional linear elements, but the applicability of the proposed formulation can be extended to the bi and tri-dimensional cases. It begins with an introduction to the theme. With some mathematical development, the related numerical error can be isolated analytically. Once the truncation error is isolate, a high precision numerical response is obtained. Inspired in the Newmark time integrator, unconditionally stable elements for spurious effects are idealized. The evanescent effect is a spurious phenomenon where the wave propagates along the structure subjected to a numerical damping in the spatial domain. Another effect analyzed here is the spurious wave reflection. When two adjacent elements have different lengths, a reflected wave exists (two waves for the beam element) at their interface. This wave, which meaning is purely mathematical, exists due to the difference of their absolute mass and stiffness between the finite elements involved, even when both elements have the same physical properties. The rate between the time increment and the period of oscillation is conveniently employed as the main parameter to quantify the time discretization. In the spatial domain, the used parameter is the relation between the element and the wave length.
12
Srikasem, Suthum. "Wave reflection in uniaxially anisotropic media." Ohio : Ohio University, 1987. http://www.ohiolink.edu/etd/view.cgi?ohiou1183062033.
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Chen, Yu. "Spherical wave reflection and transmission." Thesis, Open University, 1991. http://oro.open.ac.uk/57346/.
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This study is concerned with the reflection and transmission of spherical waves at a plane interface between two different media. The phenomenon of the reflection and transmission of spherical waves has been studied by means of analytical methods, numerical computation, and experimental tests. A new integral representation for a spherical wave is obtained by transforming Lamb/Sommerfeld's integral representation. The new integral has no singularity so it allows more accurate numerical integration. A new proof of Lamb/Sommerfeld's integral representation for a spherical wave is presented based on the new integral. By using the new form of solutions for reflected waves and existing solutions for transmitted waves, numerical studies have been carried out to examine. the phenomenon of reflection and transmission. of spherical waves at plane surfaces of discontinuity in material properties. It is shown that the effective critical angle for the total reflection of a spherical wave is greater than that of a plane wave at a hard boundary, and that when the source height increases the effective critical angle for the total reflection of a spherical wave tends to that of a plane wave. It is shown that recent predictions of spherical wave reflection and transmission coefficients greater than 1 at normal incidence under certain condition are probably due to numerical integration error. It also has been found that for spherical wave reflection and transmission, the time average energy flux, normal to a plane parallel to the plane of discontinuity, may locally be in the direction opposite to that of the direction of energy transmission over the plane as a whole. This so-called "backward wave" occurs in an interference between the direct and reflected waves, as well as in a transmitted wave. An indirect test on the theory has been performed to check the pressure field, above a rigid boundary, predicted by the spherical wave theory. Theoretical and experimental results were in good agreement.
14
Liu, Faqi. "Surface multiple attenuation operators in the plane wave domain : theory and applications /." Digital version accessible at:, 1999. http://wwwlib.umi.com/cr/utexas/main.
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Azam, Md Ali. "Wave reflection from a lossy uniaxial media." Ohio : Ohio University, 1995. http://www.ohiolink.edu/etd/view.cgi?ohiou1179854582.
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Jackson, Ruth P. "PIN diodes : Requirements for millimetre-wave reflection." Thesis, Queen's University Belfast, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.534723.
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Grooth, Pieter Jan. "Wave reflection by a flat plate cascade." Thesis, Massachusetts Institute of Technology, 1990. http://hdl.handle.net/1721.1/42459.
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Helfrich, L. Cody. "Estimating oceanic internal wave energy from seismic reflector slope spectra." Laramie, Wyo. : University of Wyoming, 2008. http://proquest.umi.com/pqdweb?did=1594476671&sid=1&Fmt=2&clientId=18949&RQT=309&VName=PQD.
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Watson, David H. "Wave Reflection on a Two-Slope Steep Beach." Thesis, Monterey, California. Naval Postgraduate School, 2012. http://hdl.handle.net/10945/6884.
Texte intégralRésumé :
Wave reflection of sea-swell (0.050.20 Hz) energy on a two-slope (1/7.6 nearshore and 1/19 offshore) steep beach with no subaqueous sandbar is studied. The dataset were collected using a cross-shore array of 4 Acoustic Doppler Current Profilers measuring velocity and pressure at 1 Hz continuously for 40 days. Measurement of pressure and velocity at the same location allows data to be decomposed into onshore and offshore components to determine reflection. The long data set captured a wide range of wave conditions at various tidal stages. Observations show low amplitude long period waves produced energy reflection coefficients up to 80%, with most in the 3050% range. There was a measured increase in the number of nodes and anti-nodes at higher frequencies and observations farther offshore consistent with theory. Field data were compared to an analytical two-slope model that predicts the cross-shore nodal structure of standing waves. The predicted locations of nodes and anti-nodes are in good agreement with observations.
20
Lee, Seung-Kyu. "Wave reflection, transmission and propagation in structural waveguides." Thesis, University of Southampton, 2006. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.430485.
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Cao, Jun. "Toward a wave-equation based true-reflection imaging /." Diss., Digital Dissertations Database. Restricted to UC campuses, 2008. http://uclibs.org/PID/11984.
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Guy, Erich D. "Analysis and modeling of high-resolution multicomponent seismic refelction data." The Ohio State University, 2003. http://rave.ohiolink.edu/etdc/view?acc_num=osu1044983175.
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Barnes, Crispin Henry William. "Reflection of waves from disordered media." Thesis, Imperial College London, 1990. http://hdl.handle.net/10044/1/47763.
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Appelö, Daniel. "Non-reflecting Boundary Conditions for Wave Propagation Problems." Licentiate thesis, KTH, Numerical Analysis and Computer Science, NADA, 2003. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-1664.
Texte intégralRésumé :
<p>We consider two aspects of non-reflecting boundaryconditions for wave propagation problems. First we evaluate aproposed Perfectly Matched Layer (PML) method for thesimulation of advective acoustics. It is shown that theproposed PML becomes unstable for a certain combination ofparameters. A stabilizing procedure is proposed andimplemented. By numerical experiments the performance of thePML for a problem with nonuniform flow is investigated. Furtherthe performance for different types of waves, vorticity andsound waves, are investigated.</p><p>The second aspect concerns spurious waves, which areintroduced by any discretization procedure. We constructdiscrete boundary conditions, that are nonreflecting for bothphysical and spurious waves, when combined with a fourth orderaccurate explicit discretization of one-way wave equations. Theboundary condition is shown to be GKS-stable. The boundaryconditions are extended to hyperbolic systems in two spacedimensions, by combining exact continuous non-reflectingboundary conditions and the one dimensional discretelynon-reflecting boundary condition. The resulting boundarycondition is localized by the standard Pad´eapproximation.</p><p>Numerical experiments reveal that the resulting methodsuffers from boundary instabilities. Analysis of a relatedcontinuous problem suggests that the discrete boundarycondition can be stabilized by adding tangential viscosity atthe boundary. For the lowest order Pad´e approximation weare able to stabilize the discrete boundary condition.</p>
25
Seaman, Roy C. "Beach response in front of wave-reflecting structures." Thesis, University of Aberdeen, 1998. http://digitool.abdn.ac.uk/R?func=search-advanced-go&find_code1=WSN&request1=AAIU105978.
Texte intégralRésumé :
Several studies have previously demonstrated that sediment transported as bed load under a standing wave will be moved from between node and antinode towards the node where it accumulates. The end result is the generation of areas of scour in the bed between node and antinode and areas of sediment accretion around the node. However, these studies have failed to provide an adequate description of the mechanisms which led to this so-called "N-type" response. Consequently it has been the purpose of this study to examine the phenomenon of N-type beach response in some detail. As a first step an experimental programme was conducted in a random wave flume using a model beach and vertical, impermeable wall N-type conditions were produced, observations are made on the mechanisms of sediment transport and flow-field measurements are also reported. The experimental results demonstrate that N-type beach response is the direct result of an asymmetry in the main flow-field caused by the superposition of incident and reflected non-linear waves. A second experimental programme examines the N-type equilibrium profile shape using measurements of profiles generated under a range of wave conditions. An equation defined for a given profile amplitude and profile limits is found to predict the underlying characteristic N-type profile shape very well. Finally, a model of N-type beach response is developed. This model follows a relatively simple "grab-and-dump" concept with coefficients based on the understanding gained of the N-type response processes. It is shown that N-type profiles can be predicted reasonably well for the range of wave conditions used in the experiments here. Outside of this range predictions are less good, suggesting a re-examination of the model coefficients is required.
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Uhrig, Matthias Pascal. "Numerical simulation of nonlinear Rayleigh wave beams evaluating diffraction, attenuation and reflection effects in non-contact measurements." Thesis, Georgia Institute of Technology, 2015. http://hdl.handle.net/1853/54368.
Texte intégralRésumé :
Although several studies have proven the accuracy of using a non-contact, air-coupled receiver in nonlinear ultrasonic (NLU) Rayleigh wave measurements, inconsistent results have been observed when working with narrow specimens. The objectives of this research are first, to develop a 3D numerical finite element (FE) model which predicts nonlinear ultrasonic measurements and second, to apply the validated model on the narrow waveguide to determine causes of the previously observed experimental issues. The commercial FE-solver ABAQUS is used to perform these simulations. Constitutive law and excitation source properties are adjusted to match experiments conducted, considering inherent effects of the non-contact detection, such as frequency dependent pressure wave attenuation and signal averaging. Comparison of “infinite” and narrow width simulations outlines various influences which impair the nonlinear Rayleigh wave measurements. When the wave expansion is restricted, amplitudes of the fundamental and second harmonic components decrease more significantly and the Rayleigh wavefronts show an oscillating interaction with the boundary. Because of the air-coupled receiver’s finite width, it is sensitive to these edge effects which alter the observed signal. Thus, the narrow specimen adversely affects key factors needed for consistent measurement of material nonlinearity with an air-coupled, non-contact receiver.
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Teh, Hee Min. "Hydrodynamic performance of free surface semicircular breakwaters." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7652.
Texte intégralRésumé :
Different types of breakwaters have been developed in the past for the protection of valuable coastal property, commercial activity and beach morphology. Among these, gravity-type breakwaters are the most common and provide good surface wave attenuation. However, these breakwaters are not always suitable due to their adverse impact on the coastal environment. To alleviate the problem, free surface breakwaters with a variety of caisson designs have been proposed and developed. The main advantages of such breakwaters are low capital cost, freedom from silting and scouring, short construction period, circulation of water beneath the breakwater and exertion of relatively low hydrodynamic forces on the structure as compared to conventional breakwaters. However, complete tranquillity on the lee side is not likely to occur due to wave energy transfer through the permeable parts of the breakwater. The degree of wave attenuation primarily depends on the configuration of the breakwater, the water depth and the incident wave conditions. The hydrodynamic performance of such free surface breakwaters is the subject of this thesis. Semicircular breakwaters mounted on a low-crested rubble mound structure were successfully built for harbour protection in Japan and China. However, the concept of having semicircular structures as free surface breakwaters has not yet been explored by the research community. As a result, this research is initiated with the aim of developing a free surface semicircular breakwater (SCB) that would serve as an anti-reflection barrier and provide reasonably good wave protection to coastal and marine infrastructures. To meet this research goal, a free surface SCB models were constructed and tested in a wave flume under various wave conditions. The experiments were conducted in three stages. For the first stage, the SCB model was initially tested without any perforations on the curved surface (i.e. a solid SCB) for different depths of immersion from the still water level in the wave flume. For the second stage, the front curved wall of the model was subsequently perforated with rectangular openings of different dimensions, producing front wall porosity of 9, 18 and 27%. Following this, two rows of rectangular openings near the crest of the rear curved wall were provided so as to facilitate water infiltration and escape of the run-up waves. For the third stage, additional effort was made to extend the draft of the breakwater by adding a wave screen at the front or/and rear. The screen porosity was 25, 40 and 50%. The hydrodynamic characteristics of the SCB models were investigated in both regular and irregular seas through a series of systematic experimental programme. The water surface elevations were measured at different locations upstream and downstream of the models to determine the coefficients of wave transmission (CT), reflection (CR) and energy dissipation (CL) as well as the wave climate coefficients in front and inside the breakwater chamber. The horizontal wave forces exerted on the SCB models and the wave screen(s) were also measured and subsequently normalised to yield the force coefficients in the analysis. These hydrodynamic coefficients for the respective test cases are presented and discussed in this thesis. The experimental results revealed that even though the solid SCB was a better wave attenuator than the perforated ones, it produced a considerable amount of wave reflection. The perforated SCB with 9% porosity of the front wall (denoted as SCB9) outperformed the other perforated breakwater models; however, it produced high wave transmission when the draft was limited and subjected to longer period waves. Hence, wave screens were added to further enhance the performance of the SCB9. The SCB9 with double screens of 25% porosity was found to provide the highest hydraulic performance. Empirical equations were developed using a multiple regression technique to provide design formulae for wave transmission, wave reflection and horizontal wave forces. The proposed empirical equations showed good agreement with the experimental data. These equations are intended to be of direct use to engineers in predicting the hydrodynamic performance of free surface SCBs. However, sensible engineering judgement must be taken while using these equations as they are based on small scale laboratory tests.
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Liu, Yan-Qiang. "Analysis of P-wave seismic reflection data for azimuthal anisotrophy." Thesis, University of Edinburgh, 2003. http://hdl.handle.net/1842/12444.
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Linton, C. M. "Wave reflection by submerged bodies in water of finite depth." Thesis, University of Bristol, 1988. http://hdl.handle.net/1983/4f92efdb-190a-4c58-bd4d-6906362c5883.
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Petzer, J. M. "A study of water wave reflection using close range photogrammetry." Master's thesis, University of Cape Town, 1989. http://hdl.handle.net/11427/18789.
Texte intégralRésumé :
The intention of this investigation is to investigate the various forms of water wave reflection to a high degree of accuracy. Close range photogrammetry is the technique that is used to measure the water surface profile, as it produces an accurate and comprehensive analysis of the water surface profiles. Conventional photogrammetry techniques (photography) were used in preference to near real time photogrammetry (digital). Although near real time photogrammetry has the advantage of a far higher rate of data acquisition, it does not achieve the same degree of accuracy as can be achieved by conventional photogrammetry, the technique finally used for this investigation. For the generation of the desired wave patterns, certain equipment was developed and modified. To test the various angles of incidence a moveable reflecting wall was built. Due to the small size of the wave basin, an efficient wave absorber was required to absorb the reflected wave generated when oblique wave reflection was investigated. It was observed that a very poor quality wave was being generated by the wave generator, as a result of its flexibility. Consequently the wave generator was stiffened considerably which improved the wave generated. Interesting information was obtained from the analysis of the standing wave. A coefficient of reflection of 1,6 at the reflection wall was obtained, this places new emphasis on the relationship between the standing wave and overtopping. The oblique wave reflection resu1ts corresponded well with theoretical predictions, while no well-defined trends were established for the mach wave. The data for the mace wave did however suggest that previously established trends for the mach wave may not be correct. Close range photogrammetry produced accurate results, and is an excellent method for water surface profile measurement. The results obtained showed that the wave generator was not generating a pure wave, which lead to unknown errors in the results of spot heights. Conventional photogrammetry is a slow process, so not enough data was acquired to adequately analyse the reflection trends. This suggests that in order for the trends to be well-established, near real time photogrammetry should be used once these systems have developed sufficient accuracy.
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Hinis, Mehmet Ali Weggel J. Richard. "Cnoidal and sinusoidal wave reflection from a laboratory sand beach /." Philadelphia : Drexel University, 2003. http://dspace.library.drexel.edu/handle/1721.1/100.
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Gongora, Orozco Nalleli. "Experimental studies on internal shock wave phenomena and interactions." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/experimental-studies-on-internal-shock-wave-phenomena-and-interactions(6325f185-76a1-483a-9d14-606a6a48374e).html.
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Unsteady shock waves are formed by the coalescence of pressure waves. The attenuationof pressure and shock waves in general is of great importance in a wide varietyof application such as vehicle performance, health and safety. Previous researcheshave been carried out on a variety of geometries to understand the physics. Theaim of this project is to advance the previous-state-of-the-art and to shed furtherlight into the fundamental physics associated with the shock wave interactions andphenomena. Shock wave attenuation was studied by using rough walls in a three-pipe system. The roughness at the walls is added by placing grooves on the upper and lower wallsof the junctions. The angles of the branch pipe were varied from 30 to 150 degrees. Shock wave interactions with a co-flow jet were also examined. All the experimentswere performed for driver gas (air) pressures of 4, 8, and 12 bar and atmosphericpressure within the driven section, giving theoretical Mach number of 1.34, 1.54, and1.66, respectively. Three different velocities, 114, 138, and 178 m/s, were used forthe co-flow jet. High-speed schlieren photography, particle image velocimetry (PIV),and pressure measurements techniques were employed to visualise and quantify theflow field. Expansion and compression waves produced by the grooves led to a highly unsteadyflow field, an increase to the pressure upstream, and the formation of asecondary shock wave. The pressure of the incident shock front was reduced by anestimated 20%. A maximum of 10% reduction of velocity of the shock front at theexit was achieved. The shock vortex/ structure led to multiple reflections, distortionof the vortical field, a lambda-shock configuration and pressure fluctuations. Theinfluence of the co-flow jet dissipated the shock/vortex structure, and attenuatedthe pressure peaks caused by multiple reflections. Complementing this investigation the testing of pressure sensitive paints (PSP)for the use of unsteady and high speed flows was carried out. The results showedthat the use of luminophores with high intensity output, and pressure sensitivityapplied on a porous material were the most suitable PSPs for these applications.
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Xie, Jishi. "Acoustic reflection from temperature microstructure." Thesis, The University of Sydney, 1989. https://hdl.handle.net/2123/26377.
Texte intégralRésumé :
This thesis develops a numerical technique to predict the acoustic reflection from an arbitrary sound speed microstructure in the ocean (or a temperature microstructure in the fresh water). This numerical technique is able to reproduce the theoretical formulas for calculating the reflection coefficients of two analytically defined transition layers.
The 50 kHz acoustic reflection coefficients from the temperature The 50 kHz acoustic reflection coefficients from the temperature microstructure measured in a fresh-water reservoir was predicted to be less than -90 dB and was found to be much weaker than the observed volume scattering which was due to the biological activities.
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Niemeyer, Günter Dieter. "Using wave variables in time delayed force reflecting teleoperation." Thesis, Massachusetts Institute of Technology, 1996. http://hdl.handle.net/1721.1/10622.
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Li, Ye. "Propagation and reflection of pulse waves in flexible tubes and relation to wall properties." Thesis, Brunel University, 2011. http://bura.brunel.ac.uk/handle/2438/6554.
Texte intégralRésumé :
The wall properties of the arteries play an important role in cardiovascular function. Stiffness of large artery is predictive of cardiovascular events. To understand the function of the cardiovascular system, special attention should be paid to the understanding of pulse wave propagation, because pulse waves carry information of the cardiovascular function, and provide information which can be useful for the prevention and diagnosis of diseases. This thesis presents a series of in vitro experimental studies of wave propagation, wave reflection and determination of mechanical properties of flexible vessels. In this thesis, several studies have been included: 1) applied and compared foot-to-foot, PU-loop and lnDU-loop methods for determination of wave speed in flexible tubes and calf aortas; 2) investigated the variation of local wave speed determined by PU-loop with proximity to the reflection site; 3) investigated using wave intensity analysis (WIA) as the analytical technique to determine the reflection coefficient; 4) developed a new technique which based on one-point simultaneous measurements of diameter and velocity to determine the mechanical properties of flexible tubes and calf aortas. In the first study, it is found wave speeds determined by PU-loop and lnDU-loop methods are very similar, and smaller than those determined by foot-to-foot method. The timing of arrival time of reflected wave based on diameter and velocity technique highly agreed with the corresponding timing based on pressure and velocity technique. The shapes of forward and backward non-invasive wave intensities based on diameter and velocity are very similar with the corresponding shapes based on pressure and velocity. Although the density term is not part of the equation, the lnDU-loop method for determining local wave speed is sensitive to the fluid density. In the second study, it is found wave speed measured by PU-loop is varied with proximity to the reflection site. The closer the measurement site to the reflection site, the greater the effect upon measured wave speed; a positive reflection caused an increase in measured wave speed; a negative reflection caused a decrease in measured wave speed. Correction iteration process was also considered to correct the affected measured wave speed. In the third study, it is found, reflection coefficient determined by pressure, square roots of wave intensity and wave energy are very close, but they are different from reflection coefficient determined by wave intensity and wave energy. Due to wave dissipation, the closer the measurement site to the reflection site, the greater is the value of the local reflection coefficient. The local reflection coefficient near the reflection site determined by wave intensity and wave energy are very close to the theoretical value of reflection coefficient. In the last study I found that distensibility determined by the new technique which utilising lnDU-loop is in agreement with that determined from the pressure and area which obtained from tensile test in flexible tubes; distensibility determined by the new technique is similar to those determined in the static and dynamic distensibility tests in calf aortas; Young’s modulus determined by the new technique are in agreement with that those determined by tensile tests in both flexible tubes and calf aortas. In conclusion, wave speed determined by PU-loop and lnDU-loop methods are very similar, the new technique lnDU-loop provides an integrated noninvasive system for studying wave propagation; wave speed determined by PU-loop is affected by the reflection, the closer the measurement site to the reflection site, the greater the change in measured wave speed; WIA could be used to determine local reflection coefficient when the measurement site is close to the reflection site; the new technique using measurements of diameter and velocity at one point for determination of mechanical properties of arterial wall could potentially be non-invasive and hence may have advantage in the clinical setting.
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Khalili, Nasser. "Application of Cepstral techniques to the measurement of reflection coefficients for dispersive systems." Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.303060.
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Roy, Matthew S. "Acute effects of facial cooling on arterial stiffness and wave reflection." Access to citation, abstract and download form provided by ProQuest Information and Learning Company; downloadable PDF file, 56 p, 2007. http://proquest.umi.com/pqdweb?did=1397914231&sid=1&Fmt=2&clientId=8331&RQT=309&VName=PQD.
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Li, Xiangyang. "Shear-wave splitting in reflection surveys : theory, methods and case studies." Thesis, University of Edinburgh, 1992. http://hdl.handle.net/1842/12418.
Texte intégralRésumé :
Over the last decade, the use of multi-component seismic reflection data to study shear-wave splitting has become increasingly common within the hydrocarbon industry to determine the crack geometry of oil reservoirs. Thus, it is important to investigate the characteristics of, develop processing techniques for, and carry out case studies of shear-wave splitting in reflection surveys. I have examined the effects of anisotropic symmetry, particularly orthorhombic symmetry, on velocity variations and moveouts of split shear-waves in vertical off-symmetry planes. I have also examined the effects of crack orientation changing with depth on reflection and transmission coefficients of split shear-waves. These theoretical developments in understanding shear-wave splitting in reflection surveys are described in Chapters 2 and 3. Complex component analysis was developed as an alternative to polarization analysis for displaying and identifying shear-wave splitting in large seismic datasets. This complex component analysis allows the calculation of instantaneous amplitudes and instantaneous polarizations for two-component seismic data and of shear-wave splitting sections and polarization logs for four-component data. Four field seismic datasets, including a two- and a four-component VSP, a reflection shot data matrix and a two-component crosshole survey, have been used to verify and illustrate the technique, as described in Chapters 4 and 5. A linear-transform technique was developed as an alternative to rotation analysis for quantifying and processing shear-wave splitting in seismic data. This linear-transform technique allows various attributes to be measured, including the polarizations and time delays of split shear-waves and downhole geophone orientation. It also allows time series of the split shear-waves to be separated deterministically and such separation can be made before stacking in reflection surveys. Three field datasets including a zero-offset VSP, an offset VSP and a reflection shot data matrix, have been used to verify and illustrate the technique, as described in Chapter 6.
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Zhang, Bing. "Joint identification in structural waveguides using wave reflection and transmission coefficients." Thesis, University of Southampton, 2007. https://eprints.soton.ac.uk/50563/.
Texte intégralRésumé :
The dynamic modelling of one-dimensional jointed structures is relevant to many engineering applications, such as pipe systems and beam networks in constructions. Currently available techniques are undermined by inadequate ability to model the joints and other discontinuities due to uncertainty in their properties. Measured modal data can be used to update joint models, but often with limited success. In this thesis a wave approach is employed to investigate the reflection and transmission coefficients of various joint models in structural waveguides. The reflection and transmission coefficients are potentially more sensitive to the parameters of the joint models. Numerical simulations and experiments have been performed on three types of jointed waveguides. Appropriate models have been identified for these cases and sensitivities of the scattering coefficients to joint parameters have been investigated. Accurate measurement of the reflection and transmission coefficients is desired in order to estimate joint parameters. A noise model is developed and a perturbation method is used to study the influence of measurement noise on the estimated reflection and transmission coefficients. An iterative method is examined to solve the non-linear problem of estimating the parameters of a joint from measured reflection and transmission coefficients, in a leastsquares sense. Issues concerning the iteration process, such as the selection of objective functions and frequency ranges, are examined in accordance with the sensitivity of the objective function to unknown parameters. The parameter identification method is validated by numerical simulation case studies and then verified by using measured data for mass discontinuities on beams, a supported straight pipe and a right-angled pipe bend. The case studies demonstrate that parameter identification of discontinuities in waveguides by using the wave approach is a success where modal methods are inappropriate.
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Berumen, Cantu Jorge Alberto. "Kinetic picture of ion acoustic wave reflection using laser-induced fluorescence." Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6368.
Texte intégralRésumé :
An examination of the first laser-induced fluorescence measurements of ion-acoustic wave reflection is presented in this dissertation. The experiment is performed in a multipole cylinindrical chamber using singly-ionized argon (ArII) plasma produced by a means of a hot cathode. Ion-acoustic waves are launched from a mesh antenna and reflected/absorbed by a biased, solid boundary (electrode). A kinetic analysis of wave reflection is carried out through LIF's ability of resolving ion phase-space. A comparison between Langmuir probe and LIF diagnostics is presented, with complementary Electric-field probe measurements.
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Shin, Chang Soo. "Nonlinear elastic wave inversion by blocky parameterization /." Access abstract and link to full text, 1988. http://0-wwwlib.umi.com.library.utulsa.edu/dissertations/fullcit/8810420.
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Tuerxunjiang, Abulikemu. "FDTD measurement of the reflection coefficient associated with total internal reflection from gainy Lorentzian media." Pullman, Wash. : Washington State University, 2008. http://www.dissertations.wsu.edu/Thesis/Fall2008/A_Tuerxunjiang_120108.pdf.
Texte intégralRésumé :
Thesis (M.S. in physics)--Washington State University, December 2008.<br>Title from PDF title page (viewed on July 10, 2009). "Department of Physics and Astronomy." Includes bibliographical references (p. 64-68).
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Jiao, Junru. "Residual migration velocity analysis in the plane wave domain : theory and applications /." Access restricted to users with UT Austin EID Full text (PDF) from UMI/Dissertation Abstracts International, 2001. http://wwwlib.umi.com/cr/utexas/fullcit?p3023551.
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Kürschner, Dierk, and Christoph Jacobi. "Long-term behaviour of E-region nighttime LF reflection heights." Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-217519.
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The nighttime reflection height of low-frequency (LF) radio waves at oblique incidence is measured at Collm Observatory using 1.8 kHz sideband phase comparisons between the sky wave and the ground wave of a commercial 177 kHz LF transmitter. The measurements have been carried out continuously since September 1982, now allowing the analysis of trends and regular variations of the reflection height. In the time series is found a) a long-term negative trend and b) a solar cycle dependence, both confirming earlier measurements and theoretical estimations. Moreover, a significant oscillation of quasi-biennial period is visible in LF reflection heights, indicating a reaction of the midlatitude mesosphere/lower thermosphere region on the equatorial quasi biennial oscillation<br>Am Observatorium Collm der Universität Leipzig werden die nächtlichen Reflexionshöhen von Langwellen auf 177 kHz unter Verwendung von Seitenbandinformationen in einem kleinen Bereich um 1.8 kHz gemessen. Die Messungen werden seit September 1982 durchgeführt und erlauben nunmehr Analysen von Langzeittrends und regulären Variationen der unteren Ionosphäre. Bei der Untersuchung der Zeitreihen fallen die folgenden Zusammenhänge auf: a)es existiert ein negativer Trend, welcher mit der Abkühlung der Stratosphäre in Zusammenhang steht, b) die Reflexionshöhe weist eine Modulation mit dem 11-Jährigen Sonnenfleckenzyklus auf und c) es ist eine deutliche quasi-zweijährige Schwingung sichtbar, die auf eine Kopplung der Mesosphäre und unteren Thermosphäre mit der äquatorialen Stratosphäre hinweist
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Ward, Gavin Stuart. "Deep reflection seismics using S-waves on land." Thesis, University of Cambridge, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.387057.
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Thomson, James M. (James McArthur). "Infragravity waves over topography: generation, dissipation, and reflection." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/39222.
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Thesis (Ph. D.)--Joint Program in Physical Oceanography (Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences; and the Woods Hole Oceanographic Institution), 2006.<br>This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.<br>Includes bibliographical references.<br>Ocean surface infragravity waves (periods from 20 to 200 s) observed along the southern California coast are shown to be sensitive to the bottom topography of the shelf region, where propagation is linear, and of the nearshore region, where nonlinearity is important. Infragravity waves exchange energy with swell and wind waves (periods from 5 to 200 s) via conservative nonlinear interactions that approach resonance with decreasing water depth. Consistent with previous results, it is shown here that as waves shoal into water less than a few meters deep, energy is transfered from swell to infragravity waves. In addition, it is shown here that the apparent dissipation of infragravity energy observed in the surfzone is the result of nonlinear energy transfers from infragravity waves back to swell and wind waves. The energy transfers are sensitive to the shallow water bottom topography. On nonplanar beach profiles the transfers, and thus the amount of infragravity energy available for reflection from the shoreline, change with the tide, resulting in the tidal modulation of infragravity energy observed in bottom-pressure records on the continental shelf. The observed wave propagation over the shelf topography is dominated by refraction, and the observed partial reflection from, and transmission across, a steep-walled submarine canyon is consistent with long-wave theory. A generalized regional model incorporating these results predicts the observed infragravity wave amplitudes over variable bottom topography.<br>by James M. Thomson.<br>Ph.D.
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Murray, Stuart William. "Wave radiation in simple geophysical models." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7922.
Texte intégralRésumé :
Wave radiation is an important process in many geophysical flows. In particular, it is by wave radiation that flows may adjust to a state for which the dynamics is slow. Such a state is described as “balanced”, meaning there is an approximate balance between the Coriolis force and horizontal pressure gradients, and between buoyancy and vertical pressure gradients. In this thesis, wave radiation processes relevant to these enormously complex flows are studied through the use of some highly simplified models, and a parallel aim is to develop accurate numerical techniques for doing so. This thesis is divided into three main parts. 1. We consider accurate numerical boundary conditions for various equations which support wave radiation to infinity. Particular attention is given to discretely non-reflecting boundary conditions, which are derived directly from a discretised scheme. Such a boundary condition is studied in the case of the 1-d Klein-Gordon equation. The limitations concerning the practical implementation of this scheme are explored and some possible improvements are suggested. A stability analysis is developed which yields a simple stability criterion that is useful when tuning the boundary condition. The practical use of higher-order boundary conditions for the 2-d shallow water equations is also explored; the accuracy of such a method is assessed when combined with a particular interior scheme, and an analysis based on matrix pseudospectra reveals something of the stability of such a method. 2. Large-scale atmospheric and oceanic flows are examples of systems with a wide timescale separation, determined by a small parameter. In addition they both undergo constant random forcing. The five component Lorenz-Krishnamurthy system is a system with a timescale separation controlled by a small parameter, and we employ it as a model of the forced ocean by further adding a random forcing of the slow variables, and introduce wave radiation to infinity by the addition of a dispersive PDE. The dynamics are reduced by deriving balance relations, and numerical experiments are used to assess the effects of energy radiation by fast waves. 3. We study quasimodes, which demonstrate the existence of associated Landau poles of a system. In this thesis, we consider a simple model of wave radiation that exhibits quasimodes, that allows us to derive some explicit analytical results, as opposed to physically realistic geophysical fluid systems for which such results are often unavailable, necessitating recourse to numerical techniques. The growth rates obtained for this system, which is an extension of one considered by Lamb, are confirmed using numerical experiments.
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John, Gelleta. "Three-dimensional Coupled-wave Analysis of External Reflection in Photonic Crystal Lasers." Kyoto University, 2017. http://hdl.handle.net/2433/218016.
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Charonko, John James. "A Nondimensional Scaling Parameter for Predicting Pressure Wave Reflection in Stented Arteries." Thesis, Virginia Tech, 2005. http://hdl.handle.net/10919/31906.
Texte intégralRésumé :
Coronary stents have become a very popular treatment for cardiovascular disease, historically the leading cause of death in the United States. Stents, while successful in the short term, are subject to high failure rates (up to 24% in the first six months) due to wall regrowth and clotting, probably due to a combination of abnormal mechanical stresses and disruption of the arterial blood flow.
The goal of this research was to develop recommendations concerning ways in which stent design might be improved, focusing on the problem of pressure wave reflections. A one-dimensional finite-difference model was developed to predict these reflections, and effects of variations in stent and vessel properties were examined, including stent stiffness, length, and compliance transition region, as well as vessel radius and wall thickness. The model was solved using a combination of Weighted Essentially Non-Oscillatory (WENO) and Runge-Kutta methods. Over 100 cases were tested. Results showed that reasonable variations in these parameters could induce changes in reflection magnitude of up to ±50%. It was also discovered that the relationship between each of these properties and the resulting wave reflection could be described simply, and the effect of all of them together could in fact be encompassed by a single non-dimensional parameter. This parameter was titled â Stent Authority,â and several variations were proposed. It is believed this parameter is a novel way of relating the energy imposed upon the arterial wall by the stent, to the fraction of the incident pressure energy which is reflected from the stented region.<br>Master of Science
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Li, Gavin Sun Man. "Experimental investigation of weak irregular shock wave reflections." Thesis, 2010. http://hdl.handle.net/10539/7800.
Texte intégralRésumé :
An experimental investigation of weak shock wave reflections was conducted with the large
scale shock tube in the Flow Research Unit, in the Mechanical Engineering Laboratory, at the
University of the Witwatersrand, Johannesburg. The purpose of the study was to expand the
current understanding of irregular shock wave reflections, especially the von Neumann
reflection (vNR) and the Guderley reflection (GR). The experiments were conducted using a
high sensitivity schlieren system for three Mach numbers in the region around M 1.10 with
single-frame and multiple-frame cameras. The single-frame photographs were taken to
visualise the sequences of expansion fans and shocklets behind the reflected shock wave,
while the multiple-frame photographs were taken using a million-frame per second camera
for the velocity calculation in the region near the triple point indicated in oblique shock wave
theory. Most of the single-frame photographs show the first set of expansion fans and
associated shocklet clearly, while a few of them show signs of the second set of expansion
fans and shocklet. The third expansion fan is not very clear on some photographs, and there is
no sign of the third shocklet at all. Most of the multiple-frame photographs were useful for the
oblique shock calculations. The work done is the first time to obtain quantitative data on flow
through a Guderley reflection. The lower burst pressure (1.8 bar) tests were proven to be most
successful for the study while the higher burst pressure (3 bar) tests showed contradictions to
the physical meaning of the flow behind the reflected shock wave. This is due to the
assumption of plane shock waves in the oblique shock calculations, recognizing that the
physical shock wave has a very large curvature and the substantial weakness of the reflected
wave, being close to sonic conditions. Some primary computational fluid dynamics (CFD)
simulations using an Euler code, were also conducted to inform the design of a new insert to
vary the angle of the divergent section of the shock tube to improve the visibility of the
expansion fans and shocklets behind the reflected shock wave. The new insert has not been
tested due to time constraint.