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1
Maldonado, Theresa A. « Analysis of electro-optic/gyrotropic biaxial crystals for bulk and waveguide applications ». Diss., Georgia Institute of Technology, 1990. http://hdl.handle.net/1853/15851.
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2
Jafari, Alireza. « Analysis and Prediction of Wave Transformation from Offshore into the Surfzone under Storm Condition ». Thesis, Griffith University, 2013. http://hdl.handle.net/10072/366745.
Texte intégralRésumé :
Surfzone wave transformation under storm conditions is investigated through field and laboratory
measurements in this study. The observations have been used to examine currently available
models of wave energy dissipation.
Detailed field data has been collected by means of a novel method which was first introduced by
Nielsen (1988). This method has been utilised through a common program between Griffith
University and The University of Queensland at The Spit on the Gold Coast in Southeast
Queensland. The facility primarily consists of a manometer tube array with 12 different manometer
tube lengths varying from 60 m to 500 m offshore and a concrete manhole excavated into the dune
system to house the monitoring station. Accordingly, this system has enabled the monitoring of a
detailed wave height profile across the surfzone under any conditions from the safety of the
“bunker” on land.
The findings of new laboratory experiments on the frequency response of the semi-rigid
manometer tubes are also presented which extend and improve upon the previous work of Nielsen
et al. (1993). Testing was conducted over a range of frequencies (0.0067 Hz< f <2 Hz) and tube
lengths (10 m< L <900 m). New frequency response factors are determined by fitting the semiempirical
gain function of Nielsen et al. (1993) to the observed gain data. As a result, new
predictive formulas for the empirical coefficients as a function of tube parameters are provided in
this study.
Wave induced pore pressure in the surfzone seabed is investigated based on the recorded field data.
Two well-known models, i.e. Hsu and Jeng (1994) and Sleath (1970), are assessed against the
field measurements. The findings validate the accuracy of the models and indicate that the extent of
energy dissipation due to the overlying sand is less than 5% and depends on the incident wave
length.Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Engineering
Science, Environment, Engineering and Technology
Full Text
3
Gotthardsson, Björn. « Analysis and Evaluation of the Wavebox Wave Energy Converter ». Thesis, Uppsala universitet, Elektricitetslära, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-149364.
Texte intégralRésumé :
Increasing attention to climate change in combination with ever-growing energy consumption worldwide has boosted the demand for new green energy sources. Wave power is developing in many different branches to become part of the new era of electricity production. This thesis deals with a wave power system in its primary stages of development. The system was investigated in order to estimate its potential to produce electric power from sea waves. It is a system consisting of a moored buoy to which the energy is transferred when the wave tilts the buoy in the pitch direction. Due to the increased pitch angle, an amount of liquid contained inside the buoy is allowed to flow via ramps to an upper container, from where it flows down through a hydroelectric turbine. A computer program was used to calculate the properties of the buoy in sea waves. Another program was written in MATLAB to simulate the movements in sea waves and from a set of given parameters calculate the power output. A brief economic study was made to determine if the power output was large enough for the concept to be of financial interest to any future investors. The results show that the wave power system produced 0.9 kW in a wave climate equal to that off the coast of Hanstholm, Denmark, and 1.6 kW in a wave climate off the coast of San Diego, USA. The economic study shows that the power output needed to be improved by a factor of at least five to have a chance of being economically viable. A number of enhancements were suggested to increase the power output of the system, and further investigation could be of use to improve the concept. The created computer simulation model, as well as the results in this thesis could be valuable in any future research on the concept.
4
Lindblom, Ove. « Investigations of bending waves in plates and properties of nonlinear wave equations ». Licentiate thesis, Luleå tekniska universitet, 1997. http://urn.kb.se/resolve?urn=urn:nbn:se:ltu:diva-16895.
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5
Lopez, Guiomar. « Evaluation, analysis, and application of HF radar wave and current measurements ». Thesis, University of Plymouth, 2017. http://hdl.handle.net/10026.1/9291.
Texte intégralRésumé :
This study investigates the accuracy of the wave products retrieved by a 12-MHz high-frequency (HF) phased-array radar, and establishes their potential to characterise wave-current interactions. The two stations composing the system were deployed in 2011 to overlook the Wave Hub, a test site for marine renewable energy devices located on the south-western coast of the United Kingdom. The system was conceived and configured to reduce the inaccuracies introduced by short time averaging and minimal overlap between stations, both associated with the most traditional HF radar deployments, whose primary activity is current measurement. Wave spectra were retrieved by two independent inversion algorithms, which were evaluated both independently and relative to each other. This process helped determining the errors associated to the algorithm used, and differentiated them from those inherent to the radar technology itself. The first method investigated was a semi-empirical algorithm distributed with Wellen Radars (WERA), which was calibrated using in situ measurements collected within the radar footprint. Evaluated through comparison against measurements acquired by three in situ devices, the results revealed estimates of significant wave height with biases below 9 cm, Pearson correlations higher than 0.9, and RMS errors that range from 29 to 44 cm. The relative error of wave energy period comparisons was within 10% for periods between 8 and 13 s, while both under- and overestimations were observed above and below that range, respectively. The validation demonstrated that when locally calibrated, the algorithm performs better than in its original form in all metrics considered. Observed discrepancies were mainly attributable to single-site estimations, antenna sidelobes, and the effect of the second-harmonic peaks of the Doppler spectrum. As opposed to the semi-empirical inversion, the second method evaluated in this work provides estimates of the full directional spectrum. Compared against the in situ measurements, the radar spectra were more spread over frequencies and directions, and had a lower energy content at the peak of the spectrum. In terms of parameter estimation, this was generally translated in a slight underestimation of wave periods, but accurate estimates of significant wave heights. Pearson correlations between these parameters and the in situ measurements for the bulk of the spectrum were higher than 0.9, and both types of measurements resulted in similar standard deviations. The inversion algorithm showed a high skill estimating mean wave directions, which revealed linear correlations higher than 0.8, when compared to the in situ devices. Overall, the inversion algorithm has shown to be capable of providing accurate estimates of directional spectra and the parameters derived from them, and at present the main drawback of the method is the data return, which due to the high data quality requirements of the algorithm, did not exceed 55% over the 8-month period studied here. In the second part of this work, the validated measurements were examined to determine their ability to reproduce the effects of wave-current interactions. The fine structure of the surface current was first evaluated, and revealed a circulation dominated by tides. The residual flow was seen to respond to the wind, as well as to the stratification present in the area during the spring and summer months. These data were then used to assess their contribution to wave refraction over the radar domain. The results show modulations in the wave phase parameters, which resulted from both the temporal and spatial derivatives of the surface current velocities. The evaluation of HF radar wave measurements provided in this work has shown that, properly configured, this technology can produce accurate estimates of several statistical descriptors of the wave field. Together with the highly accurate surface currents also measured by this device, the spatial wave data obtained has proved to have great potential for studying wave-current interactions; a skill that can be of support to coastal wave modelling.
6
Yamazoe, Shotaro. « Bifurcations and Spectral Stability of Solitary Waves in Nonlinear Wave Equations ». Kyoto University, 2020. http://hdl.handle.net/2433/259759.
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7
Myung, Noh Hoon. « A high frequency analysis of electromagnetic plane wave scattering by perfectly-conducting semi-infinite parallel plate and rectangular waveguides with absorber coated inner walls / ». The Ohio State University, 1986. http://rave.ohiolink.edu/etdc/view?acc_num=osu1487267546980859.
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Freij, Nabil. « The identification and analysis of MHD waves in localised solar atmospheric wave guides ». Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/11904/.
Texte intégralRésumé :
There have been ubiquitous observations of wave-like motions in the solar atmosphere for decades and the presence of magnetoacoustic waves in magnetic structures in the solar atmosphere is well-documented. By using high-resolution data sets taken from several solar telescopes, the aim was to identify magnetohydrodynamics (MHD) wave modes in the cross-sectional area of these magnetic structures. Two sunspots and four pores were chosen as good examples of MHD wave guides in the lower solar atmosphere. To achieve this aim, the cross-sectional area and total intensity was measured through time, then this signal was analysed with three signal analysis methods, namely, wavelets, empirical mode decomposition (EMD) and the fast Fourier transform (FFT). Many characteristic periods were found within the cross-sectional area and total intensity time series. To identify what MHD wave mode these oscillations are, previously derived linear MHD theory details that each MHD wave mode perturbs the cross-sectional area and total intensity differently. This phase difference is used to separate the possible MHD wave modes. These oscillations were identified as slow sausage MHD waves, as the phase difference between the cross-sectional area and total intensity was in phase which is the signature of slow sausage MHD waves. Furthermore, several properties of these oscillations such as the radial velocity perturbation, magnetic field perturbation and vertical wavenumber were determined using magneto-seismology. The calculated range of the wavenumbers reveals that these oscillations are trapped within these magnetic structures and are standing harmonics. This allowed the calculation of the expansion factor of the wave guides by employing further magneto-seismology theory. Finally was the analysis of Running Penumbral Waves (RPWs). Here, RPWs within a pore are observed for the first time and are interpreted as Upwardly Propagating Waves (UPWs) due to the lack of a penumbra that is required to support RPWs. These UPWs are also observed co-spatially and co-temporally within two emission lines that sample the Transition Region and low corona. The estimated energy of the waves is around 150 W m$^{-2}$, which is on the lower bounds required to heat the quiet Sun corona.
9
Casadei, Filippo. « Multiscale analysis of wave propagation in heterogeneous structures ». Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/44889.
Texte intégralRésumé :
The analysis of wave propagation in solids with complex microstructures, and local heterogeneities finds extensive applications in areas such as material characterization, structural health monitoring (SHM), and metamaterial design. Within continuum mechanics, sources of heterogeneities are typically associated to localized defects in structural components, or to periodic microstructures in phononic crystals and acoustic metamaterials. Numerical analysis often requires computational meshes which are refined enough to resolve the wavelengths of deformation and to properly capture the fine geometrical features of the heterogeneities. It is common for the size of the microstructure to be small compared to the dimensions of the structural component under investigation, which suggests multiscale analysis as an effective approach to minimize computational costs while retaining predictive accuracy.
This research proposes a multiscale framework for the efficient analysis of the dynamic behavior of heterogeneous solids. The developed methodology, called Geometric Multiscale Finite Element Method (GMsFEM), is based on the formulation of multi-node elements with numerically computed shape functions. Such shape functions are capable to explicitly model the geometry of heterogeneities at sub-elemental length scales, and are computed to automatically satisfy compatibility of the solution across the boundaries of adjacent elements. Numerical examples illustrate the approach and validate it through comparison with available analytical and numerical solutions. The developed methodology is then applied to the analysis of periodic media, structural lattices, and phononic crystal structures. Finally, GMsFEM is exploited to study the interaction of guided elastic waves and defects in plate structures.
10
Cabrera, Gomez Jose Julian. « Velocity-dip analysis in the plane-wave domain ». Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30604.
Texte intégralRésumé :
Plane-wave decomposition and slant stack transformation have recently gained much interest as viable routes to perform a variety of prestack processing tasks, such as velocity estimation, migration, filtering, deconvolution, and velocity inversion. To further complement the current advances, the problem of earth model parameter estimation and prestack structural imaging are addressed in this work. Unlike existing methods, the algorithms presented here make a novel and systematic use of the plane-wave domain to determine migration and interval velocities, interface dip angles and common-shot gather reflector images.
To start, a method is developed to estimate migration velocities and interface dip angles in earth models composed of planar, dipping reflecting interfaces separating homogeneous layers, and where straight-ray travelpaths to the reflecting interfaces can be assumed. The method consists of transforming a common-shot gather into the plane-wave domain, where a semblance analysis search along cosinusoid trajectories is performed. Since the cosinusoid trajectories are functions of the migration velocity and interface dip angle, selection of the maximum semblance values yields the best estimates to the desired earth model parameters.
To remove the straight-ray assumption of the velocity-dip analysis method, a recursive technique is developed to estimate
interval velocities and interface dip angles via a ray tracing algorithm. This technique essentially generates plane-wave domain traveltimes for a range of interval velocities and interface dip angles, and computes the error between the generated and observed plane-wave traveltimes. The minimum error determines the best estimates of the earth model parameters.
With the information attained in the velocity-dip analysis algorithm, a plane-wave based imaging method is developed to produce prestack common-shot gather images of the reflecting interfaces. The method consists of transforming a common-shot gather into the plane-wave domain, where a velocity-dip semblance analysis is performed. Then, the plane-wave components are downward extrapolated and recombined via a dip-incorporated inverse slant-stack transformation to produce the spherical-wave field that would have been recorded by receivers placed on the reflecting interfaces. The dip incorporation consists of redefining the angle of emergence of the plane waves. Finally, a simple mapping algorithm converts the offset and time coordinates of the reconstructed wave field to the true horizontal location and two-way vertical time of the reflection points. This results in the desired prestack migrated images of the reflecting interfaces.
In this thesis, a novel algorithm to perform plane-wave decomposition via Fourier transforms is also proposed. This algorithm consists of the application of the double fast Fourier
transform to the input data, followed by complex vector multiplications with essentially the Fourier representation of the Bessel function J0 . A numerical singularity is avoided by applying an analytical expression that approximately accounts for the singular point contribution. An inverse fast Fourier transform from frequency to time gives the desired plane-wave seismogram.
The techniques proposed in this work have yielded encouraging results on synthetic and field data examples. The examples demonstrate, for the first time, the systematic use of the plane-wave domain in processing seismic reflection data from common-shot gather data to the plane-wave domain, to velocity and dip angle analysis and to prestack structural imaging. It is believed that the results from this work will help researchers as well as practising geophysicists to become better acquainted with plane-wave domain processing.Science, Faculty of
Earth, Ocean and Atmospheric Sciences, Department of
Graduate
11
Ashton, Ian Gerard. « Spatial variability of wave fields over the scale of a wave energy test site ». Thesis, University of Exeter, 2011. http://hdl.handle.net/10036/3471.
Texte intégralRésumé :
Accurate wave measurements are required for wave energy applications, including resource assessments and performance assessments. In response, wave data are measured from deployment sites, commonly using wave buoys or other point wave sensors. Spatial variability in the wave field will introduce inaccuracies to the analysis of data captured from a single point to represent a separate location or area. This thesis describes research undertaken to quantify the effect of spatial variability on the accuracy of direct wave measurements taken at a wave energy site. An array of four timesynchronised wave buoys were deployed, separated by 500m, in a location close to the Wave Hub wave energy test site in Cornwall, UK. These data were subject to close scrutiny in terms of data processing and quality control, which raised specific issues regarding data processing and the validation of wave data for a new measurement facility. Specific recommendations are made for data captured from this facility, and bespoke quality control routines were developed. This process minimises the possible contribution of errors to the processed data, which is observed to be of the highest importance when analysing simultaneous data sets, and provides a data set that is particularly suited to the examination of the spatial characteristics of ocean waves. The differences between simultaneous data demonstrated local physical processes to be causing a deterministic difference between the waves at the measurement sites, which contributed to a significant difference between the power statistics at different locations within the site. Instantaneous differences between measurements were observed to agree well with theoretical estimations of random error, based on sampling theory. The culmination of the research is a unique analysis of the spatial properties of ocean wave fields on the scale of a wave energy test site, of direct relevance to the development and monitoring of wave energy test sites.
12
Zomorodian, Seyed Mohammad Ali. « Shear wave velocity of soils by the spectral analysis of surface waves (SASW) method ». Thesis, University of Ottawa (Canada), 1996. http://hdl.handle.net/10393/10395.
Texte intégralRésumé :
Spectral analysis of surface waves (SASW) method is an in-situ seismic method used for determining the thickness and elastic properties of soil and pavement. The SASW method is fast and economical to perform since no boreholes are required. The method is suitable for sites where the use of large equipment is difficult or where sublayer conditions make it difficult to perform other seismic tests. The SASW method is also ideal for preliminary field investigations to be conducted prior to more detailed site investigation, and for quality control and monitoring of ground improvement. The purpose of this research was to improve the SASW method by incorporating multi-mode propagation in the backcalculation procedure. In order to facilitate the investigation carried out in this study, two computer programs were developed to simulate SASW tests (and also Steady-State surface wave tests) and to calculate theoretical dispersion curves. The program for calculating theoretical dispersion curves was based on the root-searching procedure used in existing backcalculation methods. The computer programs developed in this study were used in a case study to demonstrate difficulties encountered by existing methods in dealing with multi-mode situations. It was shown that: (i) wavelength filtering criteria used by existing methods yield inconsistent (i.e. erroneous) dispersion curves when more than one propagation mode participate in the wave field, and (ii) backcalculation procedures based on root-searching cannot identify predominant propagation modes and hence fail to yield accurate results in the case of multi-mode propagation. Two developments were made in the present study to overcome the above difficulties. First, a new wavelength filtering criterion was adopted. In this criterion, the dispersion data point for a particular frequency is rejected (i.e. filtered out) if the values of phase velocity obtained from two different receiver-to-receiver spacings are not in close agreement. In this manner, inconsistencies that might result in the dispersion due to multi-mode propagation are avoided. Second, a new procedure to calculate the theoretical dispersion curve was developed. This procedure is based on the maximum vertical flexibility coefficient (at each frequency) of the theoretical layered model. Unlike root-searching methods, the maximum vertical flexibility coefficient method easily identifies predominant propagation modes. A computer program was developed in this study for backcalculation of SASW data based on the flexibility coefficient method. Least-squares optimization using the down-hill simplex method was also implemented in this program to automate the backcalculation process. The accuracy of the above proposed procedures was demonstrated using SASW field tests. The shear wave velocity profiles obtained using the procedures developed in this study are in good agreement with those obtained from other in-situ seismic tests. (Abstract shortened by UMI.)
13
Yoon, Sungsoo. « Array-Based Measurements of Surface Wave Dispersion and Attenuation Using Frequency-Wavenumber Analysis ». Diss., Georgia Institute of Technology, 2005. http://hdl.handle.net/1853/7246.
Texte intégralRésumé :
Surface wave methods have been used to determine dynamic properties of near-surface soils in geotechnical engineering for the past 50 years. Although the capabilities of engineering surface wave methods have improved in recent years due to several advances, several issues including (1) near-field effects, (2) combined active and passive measurements, and (3) accurate measurements of surface wave attenuation still require study to further improve the capabilities of modern surface wave methods.
Near-field effects have been studied for traditional surface wave methods with two receivers and several filtering criteria to mitigate the effects have been recommended. However, these filtering criteria are not applicable to surface wave methods with multiple receivers. Moreover, the criteria are not quantitatively based and do not account for different types of soil profiles, which strongly influence near-field effects. A new study of near-field effects on surface wave methods with multiple receivers was conducted with numerical and experimental methods. Two normalized parameters were developed to capture near-field effects. Quantitatively based near-field effect criteria for an ideal homogeneous half-space and three typical soil profiles are presented.
Combining active and passive surface wave measurements allows developing a shear wave velocity profile to greater depth without sacrificing the near-surface resolution offered by active measurements. Generally, active and passive measurements overlap in the frequency range from approximately 4 to 10 Hz, and there are often systematic differences between the two measurements. The systematic errors in active and passive surface wave methods were explored to explain and resolve the differences, allowing for a more accurate composite dispersion curve.
The accuracy of measured surface wave attenuation is improved by properly accounting for (1) geometric spreading, (2) near-field effects, and (3) ambient noise. In this study, a traditional estimation method and a frequency-wavenumber method utilizing sub-arrays were investigated using displacement data from numerical simulations, focusing on near-field and ambient noise effects. Detailed procedures for the frequency-wavenumber estimation method are developed based on a study of the primary factors affecting attenuation estimates. The two methods are also evaluated using experimental displacement data obtained from surface wave field measurements with three different arrays.
14
McAllister, Mark Laing. « Analysis of laboratory and field measurements of directionally spread nonlinear ocean waves ». Thesis, University of Edinburgh, 2017. http://hdl.handle.net/1842/28762.
Texte intégralRésumé :
Surface gravity waves exist in the oceans as multi-directional nonlinear phenomena. Understanding how these two properties interact is intrinsically important in itself. Furthermore, an understanding of this relationship may be used to gain insight into other oceanic phenomena. This thesis first describes an experimental investigation into the relationship between directionality and non-linearity (Part I). This relationship was then used as a tool to estimate the directional spreading of field data (Part II). Experiments have been conducted in which directionally spread focused wave groups were created in a wave tank. The relationship between the degree of directional spreading and the second-order bound harmonics of the wave groups was examined, in particular the formation of a `set-up'. These measurements were then compared to predictions from second-order theories, finding good agreement. The two-dimensional structure of the bound waves was explored giving new insight into the underlying physics. Experiments were then carried out for directionally spread crossing wave groups. It is believed that the crossing of two sufficiently separated wave groups may be the cause of an anomalous set-up in the second-order bound waves observed for some extreme and potentially freak waves. This set-up is reproduced experimentally. Again, the results of these test agreed very well when compared to second-order theory. The insight gained from the foregoing experiments was then utilised in the analysis of field data. A method, which requires only a single measurement to estimate the observed degree of directional spreading, was applied to a large dataset of field measurements from the North Alwyn platform in the North Sea. This method was then compared to conventional approaches, which require multiple concurrent measurements. The method that requires only a single measurement was shown to be effective, and presents a promising approach to gaining additional insight about the directional spreading of point observations.
15
Jang, Jun-keun. « Study on the Application of Shear-wave Elastography to Thin-layered Media and Tubular Structure : Finite-element Analysis and Experiment Verification ». 京都大学 (Kyoto University), 2016. http://hdl.handle.net/2433/217145.
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16
Johnson, Stuart G. « Applications of global seismic tomography and analysis of variational methods for the solution of the linearly attenuating frequency domain wave equation / ». Diss., Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 1997. http://wwwlib.umi.com/cr/ucsd/fullcit?p9823696.
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Kerber, Florian. « Dispersive Wave Analysis using the Chirplet Transform ». Thesis, Georgia Institute of Technology, 2006. http://hdl.handle.net/1853/14116.
Texte intégralRésumé :
Time-frequency representations (TFR) are a widely used tool to analyze signals of guided waves such as Lamb waves. As a consequence of the uncertainty principle, however, the resolution in time and frequency is limited for all existing TFR methods. Due to the multi-modal and dispersive character of Lamb waves, displacement or energy related quantities can only be allocated to individual modes when they are separated in the time-frequency plane.
The chirplet transform has been introduced as a generalization of both the wavelet and Short-time Fourier transform. It offers additional degrees of freedom to adjust time-frequency atoms which can be exploited in a model-based approach to match the group delay of individual modes.
The objective of the current thesis is to apply the algorithm proposed by Kuttig to a series of candidate nondestructive evaluation problems. The accuracy and robustness of the CT based procedure is examined for each of these example problems and is benchmarked against analytical solutions (if available) and to the conventional STFT.
18
Ratan, Naren. « Complex phase space representation of plasma waves : theory and applications ». Thesis, University of Oxford, 2017. https://ora.ox.ac.uk/objects/uuid:af5654e3-3137-4d9a-b41d-574cd72103b2.
Texte intégralRésumé :
This thesis presents results on the description of plasma waves in terms of wavepackets. The wave field is decomposed into a distribution of wavepackets in a space of position, wavevector, time, and frequency. A complex structure joining each pair of Fourier conjugate variables into a single complex coordinate allows the efficient derivation of equations of motion for the phase space distribution by exploiting its analytic properties. The Wick symbol calculus, a mathematical tool generalizing many convenient properties of the Fourier transform to a local setting, is used to derive new exact phase space equations which maintain full information on the phase of the waves and include effects nonlocal in phase space such as harmonic generation. A general purpose asymptotic expansion of the Wick symbol product formula is used to treat dispersion, refraction, photon acceleration, and ponderomotive forces. Examples studied include the nonlinear Schrödinger equation, mode conversion, and the Vlasov equation. The structure of partially coherent wave fields is understood in terms of zeros in the phase space distribution caused by dislocations in its complex phase which are shown to be correlated with the field entropy. Simulations of plasma heating by crossing electron beams are understood by representing the resulting plasma waves in phase space. The local coherence properties of the beam driven Langmuir waves are studied numerically.
19
Tom, Tracey Hiroto Alena. « Development of Wave Prediction and Virtual Buoy Systems ». 京都大学 (Kyoto University), 2010. http://hdl.handle.net/2433/120845.
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Cheung, Kwok Fa. « Time-domain solution for second-order wave diffraction ». Thesis, University of British Columbia, 1991. http://hdl.handle.net/2429/30987.
Texte intégralRésumé :
A numerical method based on potential flow theory is developed for simulating transient, second-order interactions of ocean waves with large fixed bodies of arbitrary shape in two and three dimensions. The physical problem is represented by a mathematical model composed of a fluid domain bounded by the body surface, the still water surface, the seabed, and a control surface truncating the infinite fluid region.
The nonlinear free surface boundary conditions defined on the instantaneous free surface are expanded about the still water level by a Stokes expansion procedure. The flow potential to second order is thereby defined with respect to a time-independent boundary which includes the still water surface, and its solution involves a numerical discretization of an integral equation. With the potential separated into incident and scattered components, the Sommerfeld radiation condition applied to the scattered potential is modified to incorporate a time-dependent celerity to account for the transient and second-order effects. The free surface boundary conditions and the radiation condition are then satisfied to second order by a numerical integration in time.
An alternative second-order solution is derived based on a different expansion procedure in which the nonlinear free surface boundary conditions and an integral equation defined on the instantaneous free surface are both expanded by a Taylor series, and terms up to second order are retained. The two approaches give rise to identical first-order problems, but give rise to second-order problems which are apparently different. The discrepancy arises from the second-order integral equation in which additional second-order terms are retained. The physical interpretations and limitations of these terms are explored and their effects on the evaluations of wave forces are assessed.
Applications of the present method are made to studies of regular wave diffraction around a fully submerged and a semi-submerged circular cylinder in two dimensions, and around a bottom-mounted surface-piercing circular cylinder in three dimensions. The stability and
numerical accuracy of the proposed solution and the treatment of the radiation condition to second order are examined. Comparisons of computed wave forces and runup are made with previous theoretical and experimental results and these indicate favourable agreement.Applied Science, Faculty of
Civil Engineering, Department of
Graduate
21
Wu, Xiong-Jian. « Motion and wave load analyses of large offshore structures and special vessels in waves ». Thesis, Brunel University, 1990. http://bura.brunel.ac.uk/handle/2438/7865.
Texte intégralRésumé :
Predictions of the environmental loading and induced motional and structural responses are among the most important aspects in the overall design process of offshore structures and ships. In this thesis, attention is focused on the wave loads and excited bodily motion responses of large offshore structures and special vessels. With the aim of improving the existing theoretical methods to provide techniques of theoretical effectiveness, computational efficiency, and engineering practicality in marine and offshore applications, the thesis concentrates upon describing fundamental and essential aspects in the physical phenomenon associated with wave-structure interactions and deriving new methods and techniques to analyse offshore structures and unconventional ships of practical interest. The total wave force arising from such a wave-structural interaction is assumed to be a simple superposition of the potential and the viscous flow force components. The linear potential forces are solved by the Green function integral equation whilst the viscous forces are estimated based on the Morison's damping formula. Forms of the Green function integral equation and the associated Green function are given systematically for various practical cases. The relevant two-dimensional versions are then derived by a transformation procedure. Techniques are developed to solve the integral equation numerically including the interior integral formulation and, in particular, to tackle the mathematical difficulties at irregular frequencies. In applying the integral equations to solve problems with various offshore structures and special vessels, some modified, improved or simplified methods are proposed. At first, simplified method is derived for predictions of the surge, sway and yaw motions of elongated bodies of full sectional geometry or structures with shallow draft. Then, a new shallow draft theory is described for both three- and two-dimensional cases with inclusion of the finite draft effect. Furthermore, a three-dimensional strip method is formulated where the end effects of the body are fully taken into account. Finally, an approximation to the horizontal mean drift forces of multi-column offshore structures are presented. Some new findings are also discussed including the multiple resonances occurring in the motions of multi-hulled marine structures due to the wave-body interaction, the mutual cancellation effect of the diffraction and the radiation forces arising from a full shaped slender body, and so on. Further to those verification studies for individual methods developed, more comprehensive example investigations are given related to two industrial applications. One is a derrick barge semi-submersible with zero forward speed; and the other, a SWATH ship with considerable speed. By correlation of all the proposed approaches with available analytical, numerical and experimental data, the thesis tries to demonstrate a principle that as long as principal physical aspects in the wave-structure interaction problem are properly treated, an appropriately modified or simplified method works, performs well and, sometimes, even better.
22
Rosenblad, Brent Lyndon. « Experimental and theoretical studies in support of implementing the spectral-analysis-of-surface-wave (SASW) method offshore / ». Digital version accessible at:, 2000. http://wwwlib.umi.com/cr/utexas/main.
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Lowery, Kristen Mary. « Dynamic Analysis of an Inflatable Dam Subjected to a Flood ». Thesis, Virginia Tech, 1997. http://hdl.handle.net/10919/35802.
Texte intégralRésumé :
A dynamic simulation of the response of an inflatable dam subjected to a flood was carried out to determine the survivability envelope of the dam where it can operate without rupture, or overflow. A fully nonlinear free-surface flow was applied in two dimensions using a mixed Eulerian-Lagrangian formulation.
An ABAQUS finite element model was used to determine the dynamic structural response of the dam. The problem was solved in the time domain which allows the prediction of a number of transient phenomena such as the generation of upstream advancing waves, and dynamic structural collapse. Stresses in the dam material were monitored to determine when rupture occurs. An iterative study was performed to find the service envelope of the dam in terms of the internal pressure and the flood Froude number for two flood depths. It was found that the driving parameter governing failure of the dam was the internal pressure. If this pressure is too low, the dam overflows; if this pressure is too high, the dam ruptures. The fully nonlinear free-surface flow over a semi-circular bottom obstruction was studied numerically in two dimensions using a similar solution formulation as that used in the previous study. A parametric study was performed for a range of values of the depth-based Froude number up to 2.5 and non-dimensional obstacle heights up to 0.9. When wave breaking does not occur, three distinct flow regimes were identified: subcritical, transcritical and supercritical. When breaking occurs it may be of any type: spilling, plunging or surging. In addition, for values of the Froude number close to 1, the upstream solitary waves break. A systematic study was undertaken, to define the boundaries of each type of breaking and non-breaking pattern, and to determine the drag and lift coefficients, free surface profile characteristics and transient behavior.
Master of Science
24
Crowder, Jefferson Osborn. « Data analysis for space-based gravitational wave detectors ». Diss., Montana State University, 2006. http://etd.lib.montana.edu/etd/2006/crowder/CrowderJ0506.pdf.
Texte intégral
25
Gholami, Ghadikolaei Iraj. « Data analysis of continuous gravitational waves ». Phd thesis, Universität Potsdam, 2007. http://opus.kobv.de/ubp/volltexte/2008/1880/.
Texte intégralRésumé :
This thesis describes two main projects; the first one is the optimization of a hierarchical search strategy to search for unknown pulsars. This project is divided into two parts; the first part (and the main part) is the semi-coherent hierarchical optimization strategy. The second part is a coherent hierarchical optimization strategy which can be used in a project like Einstein@Home. In both strategies we have found that the 3-stages search is the optimum strategy to search for unknown pulsars.
For the second project we have developed a computer software for a coherent Multi-IFO (Interferometer Observatory) search. To validate our software, we have worked on simulated data as well as hardware injected signals of pulsars in the fourth LIGO science run (S4). While with the current sensitivity of our detectors we do not expect to detect any true Gravitational Wave signals in our data, we can still set upper limits on the strength of the gravitational waves signals. These upper limits, in fact, tell us how weak a signal strength we would detect. We have also used our software to set upper limits on the signal strength of known isolated pulsars using LIGO fifth science run (S5) data.Diese Dissertation besteht aus zwei Projekten: Im ersten Projekt wird die Optimierung einer hierarchischen Strategie zum Auffinden von 'unbekannten' Pulsaren beschrieben. Der erste Teil besteht dabei aus einer semi-kohärenten und der zweite Teil aus einer kohärenten Optimierungsstrategie, wie sie in Projekten wie Einstein@Home verwendet werden kann. In beiden Ansätzen erwies sich eine 3-Stufensuche als optimale Suchstrategie für 'unbekannte' Pulsare. Für das zweite Projekt entwickelten wir eine Software für eine kohärente Multi-IFO (Interferometer Observatory) Suche. Zum Validieren der Software verwendeten wir sowohl simulierte Daten als auch Hardware induzierte Signale von Pulsaren aus dem vierten 'LIGO Science run' (S4). Wir erwarten nicht, mit der aktuellen Empfindlichkeit unserer Detektoren echte GW- Signale aufzunehmen, können jedoch obere Grenzen für die Stärke der Gravitationswellen-Signale bestimmen. Diese oberen Grenzen geben uns an, wie schwach ein gerade noch detektierbares Signal werden kann. Ferner benutzten wir die Software um eine obere Grenze für bekannte, isolierte Pulsare zu bestimmen, wobei wir Daten aus dem fünften 'LIGO Science run (S5) verwendeten.
26
Semedo, Alvaro A. M. « The North Atlantic oscillation influence on the wave regime in Portugal : an extreme wave event analysis / ». Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2005. http://library.nps.navy.mil/uhtbin/hyperion/05Mar%5FSemedo.pdf.
Texte intégral
27
Phillips, William Scott. « The separation of source, path and site effects on high frequency seismic waves : an analysis using coda wave techniques ». Thesis, Massachusetts Institute of Technology, 1985. http://hdl.handle.net/1721.1/59037.
Texte intégralRésumé :
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric and Planetary Sciences, 1985.Microfiche copy available in Archives and Science.
Bibliography: leaves 178-185.
by William Scott Phillips.
Ph.D.
28
Lange, Martin, et Christoph Jacobi. « Analysis of gravity waves from radio occultation measurements ». Universitätsbibliothek Leipzig, 2017. http://nbn-resolving.de/urn:nbn:de:bsz:15-qucosa-217072.
Texte intégralRésumé :
In the height range 10–30 km atmospheric gravity waves lead to periodic perturbations of the background temperature field in the order of 2-3 K, that are resolved in temperature profiles derived from radio occultation measurements. Due to the spherical symmetry assumption in the retrieval algorithm and the low horizontal resolution of the measurement damping in the amplitude and phase shift of the waves occurs leading to remarkable errors in the retrieved temperatures. The influence of the geometric wave parameters and the measurement geometry on plane gravity waves in the range 100-1000 km horizontal and 1-10 km vertical wavelength is investigated with a 2D model ranging ±1000 km around the tangent point and 10-50 km in height. The investigation shows, that with radio occultation measurements more than 90 % of the simulated waves can be resolved and more than 50% with amplitudes above 90%. But the geometrical parameters cannot be identified, since one signal can be attributed to different combinations of wave parameters and view angle. Even short waves with horizontal wavelengths below 200 km can be derived correctly in amplitude and phase if the vertical tilt is small or the view angle of the receiver satellite is in direction of the wave crestsAtmosphärische Schwerewellen führen im Höhenbereich 10-30 km zu periodischen Störungendes Hintergrundtemperaturfeldes in der Größenordnung von 2-3 K, die in Temperaturprofilen aus Radiookkultationsmessungen aufgelöst werden. Aufgrund der sphärischen Symmetrieannahme im Retrievalverfahren und durch die niedrige horizontale Auflösung des Messverfahrens werden Phasenverschiebungen und Dämpfung der Amplitude verursacht, die zu beachtlichen Fehlern bei den abgeleiteten Temperaturen führen. Der Einfluss der geometrischen Wellenparameter und der Messgeometrie auf ebene Schwerewellen im Bereich 100-1000 km horizontale und 1-10 km vertikale Wellenlänge wird untersucht mit einem 2D-Modell, dass sich auf ein Gebiet von ±1000 km um den Tangentenpunkt und von 10-50 km in der Höhe erstreckt. Die Untersuchung zeigt, dass mit Radiookkultationsmessungen mehr als 90% der simulierten Wellen aufgelöst werden und mehr als 50% mit Amplituden oberhalb von 90% der ursprünglichen. Die geometrischen Parameter können jedoch nicht aus Einzelmessungen abgeleitet werden, da ein Signal zu verschiedenen Kombinationen von Wellenparametern und Sichtwinkel zugeordnet werden kann. Auch relativ kurze Wellen mit horizontalen Wellenlängen unterhalb von 200 km können korrekt in der Amplitude und Phase aufgelöst werden, falls die Neigung des Wellenvektors gegen die vertikale gering ist oder der Sichtwinkel des Empfängersatelliten in Richtung der Wellenberge ist
29
Yildirim, Baran. « Acoustic Wave Analysis Using Different Wave Propagation Models ». Master's thesis, METU, 2008. http://etd.lib.metu.edu.tr/upload/3/12609527/index.pdf.
Texte intégralRésumé :
In this study in order to simulate the acoustic waves, Ray Theory and Normal Mode models are used. These methods are analyzed using MATLAB simulation tooldifferences between two models are examined and a region with a known bottom profile and sound velocity profiles is investigated. The Ray Theory is used in acoustic systems which is the one of the applications of wave modeling. Ray theory is solved with standard Ordinary Differential Equation solvers and normal mode with finite element method. Different bottom profiles and sound velocity profiles previously taken are interpolated to form an environment and examined in the case study. in the case study.
30
Nielson, Kevin Derek. « Analysis and gyrokinetic simulation of MHD Alfvén wave interactions ». Diss., University of Iowa, 2012. https://ir.uiowa.edu/etd/3504.
Texte intégralRésumé :
The study of low-frequency turbulence in magnetized plasmas is a difficult problem due to both the enormous range of scales involved and the variety of physics encompassed over this range. Much of the progress that has been made in turbulence theory is based upon a result from incompressible magnetohydrodynamics (MHD), in which energy is only transferred from large scales to small via the collision of Alfv ́n waves propagating oppositely along the mean magnetic field. Improvements in laboratory devices and satellite measurements have demonstrated that, while theories based on this premise are useful over inertial ranges, describing turbulence at scales that approach particle gyroscales requires new theory.
In this thesis, we examine the limits of incompressible MHD theory in describing collisions between pairs of Alfvén waves. This interaction represents the fundamental unit of plasma turbulence. To study this interaction, we develop an analytic theory describing the nonlinear evolution of interacting Alfv ́n waves and compare this theory to simulations performed using the gyrokinetic code AstroGK. Gyrokinetics captures a much richer set of physics than that described by incompressible MHD, and is well-suited to describing Alfvénic turbulence around the ion gyroscale. We demonstrate that AstroGK is well suited to the study of physical Alfvén waves by reproducing laboratory Alfvén dispersion data collected using the LAPD. Additionally, we have developed an initialization alogrithm for use with AstroGK that allows exact Alfvén eigenmodes to be initialized with user specified amplitudes and phases.
We demonstrate that our analytic theory based upon incompressible MHD gives excellent agreement with gyrokinetic simulations for weakly turbulent collisions in the limit that k⊥ ρi << 1. In this limit, agreement is observed in the time evolution of nonlinear products, and in the strength of nonlinear interaction with respect to polarization and scale. We also examine the effect of wave amplitude upon the validity of our analytic solution, exploring the nature of strong turbulence. In the kinetic limit where k⊥ ρi ≥ 1 where incompressible MHD is no longer a valid description, we illustrate how the nonlinear evolution departs from our analytic expression.
The analytic theory we develop provides a framework from which more sophisticated of weak and strong inertial-range turbulence theories may be developed. Characterization of the limits of this theory may provide guidance in the development of kinetic Alfvén wave turbulence.
31
Kalinski, Michael E. « Determination of in situ V[subscript s] and G[subscript max] using surface wave measurements in cased and uncased boreholes / ». Digital version accessible at:, 1998. http://wwwlib.umi.com/cr/utexas/main.
Texte intégral
32
Sajjadi, S. G. « A mechanism for the transfer of energy from wind to water waves ». Thesis, Coventry University, 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.382219.
Texte intégral
33
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.
Texte intégral
34
Norton, Andrew David. « Analysis of Ionospheric Data Sets to Identify Periodic Signatures Matching Atmospheric Planetary Waves ». Thesis, Virginia Tech, 2021. http://hdl.handle.net/10919/101791.
Texte intégralRésumé :
Atmospheric planetary waves play a role in introducing variability to the low-latitude ionosphere. To better understand this coupling, this study investigates times when oscillations seen in both atmospheric planetary waves and ionospheric data-sets have similar periodicity. The planetary wave data-set used are temperature observations made by Sounding of the Atmosphere using Broadband Emission Radiometry (SABER). These highlight periods during which 2-Day westward propagating wave-number 3 waves are evident in the mesosphere and lower thermosphere. The ionospheric data-set is Total Electron Content (TEC), which is used to identify periods during which the ionosphere appears to respond to the planetary waves. Data from KP and F10.7 indices are used to determine events that may be of external origin. A 17-year time-span from 2002 to 2018 is used for this analysis so that both times of solar minimum and maximum can be studied. To extract the periods of this collection of data a Morlet Wavelet analysis is used, along with thresholding to indicate events when similar periods are seen in each data-set. Trends are then determined, which can lead to verification of previous assumptions and new discoveries.Master of Science
The thermosphere and ionosphere are impacted by many sources. The sun and the magnetosphere externally impact this system. Planetary waves, which originate in the lower atmosphere, internally impact this system. This interaction leads to periodic signatures in the ionosphere that reflect periodic signatures seen in the lower atmosphere, the sun and the magnetosphere. This study identifies these times of similar oscillations in the neutral atmosphere, the ionosphere, and the sun, in order to characterize these interactions. Events are cataloged through wavelet analysis and thresholding techniques. Using a time-span of 17 years, trends are identified using histograms and percentages. From these trends, the characteristics of this coupling can be concluded. This study is meant to confirm the theory and provide new insights that will hopefully lead to further investigation through modeling. The goal of this study is to gain a better understanding of the role that planetary waves have on the interaction of the atmosphere and the ionosphere.
35
Millasseau, Sandrine. « Arterial pulse wave analysis ». Thesis, King's College London (University of London), 2003. https://kclpure.kcl.ac.uk/portal/en/theses/arterial-pulse-wave-analysis(5002b38b-53de-4c76-af89-db21c08fea68).html.
Texte intégral
36
Lange, Martin, et Christoph Jacobi. « Analysis of gravity waves from radio occultation measurements ». Wissenschaftliche Mitteilungen des Leipziger Instituts für Meteorologie ; 26 = Meteorologische Arbeiten aus Leipzig ; 7 (2002), S. 101-108, 2002. https://ul.qucosa.de/id/qucosa%3A15225.
Texte intégralRésumé :
In the height range 10–30 km atmospheric gravity waves lead to periodic perturbations of the background temperature field in the order of 2-3 K, that are resolved in temperature profiles derived from radio occultation measurements. Due to the spherical symmetry assumption in
the retrieval algorithm and the low horizontal resolution of the measurement damping in the amplitude and phase shift of the waves occurs leading to remarkable errors in the retrieved temperatures. The influence of the geometric wave parameters and the measurement geometry on plane gravity waves in the range 100-1000 km horizontal and 1-10 km vertical wavelength is investigated with a 2D model ranging ±1000 km around the tangent point and 10-50 km in height. The investigation shows, that with radio occultation measurements more than 90 % of the simulated waves can be resolved and more than 50% with amplitudes above 90%. But the geometrical parameters cannot be identified, since one signal can be attributed to different combinations of wave parameters and view angle. Even short waves with horizontal wavelengths below 200 km can be derived correctly in amplitude and phase if the vertical tilt is small or the view angle of the receiver satellite is in direction of the wave crests.Atmosphärische Schwerewellen führen im Höhenbereich 10-30 km zu periodischen Störungendes Hintergrundtemperaturfeldes in der Größenordnung von 2-3 K, die in Temperaturprofilen aus Radiookkultationsmessungen aufgelöst werden. Aufgrund der sphärischen Symmetrieannahme im Retrievalverfahren und durch die niedrige horizontale Auflösung des Messverfahrens werden Phasenverschiebungen und Dämpfung der Amplitude verursacht, die zu beachtlichen Fehlern bei den abgeleiteten Temperaturen führen. Der Einfluss der geometrischen Wellenparameter und der Messgeometrie auf ebene Schwerewellen im Bereich 100-1000 km horizontale und 1-10 km vertikale Wellenlänge wird untersucht mit einem 2D-Modell, dass sich auf ein Gebiet von ±1000 km um den Tangentenpunkt und von 10-50 km in der Höhe erstreckt. Die Untersuchung zeigt, dass mit Radiookkultationsmessungen mehr als 90% der simulierten Wellen aufgelöst werden und mehr als 50% mit Amplituden oberhalb von 90% der ursprünglichen. Die geometrischen Parameter können jedoch nicht aus Einzelmessungen abgeleitet werden, da ein Signal zu verschiedenen Kombinationen von Wellenparametern und Sichtwinkel zugeordnet werden kann. Auch relativ kurze Wellen mit horizontalen Wellenlängen unterhalb von 200 km können korrekt in der Amplitude und Phase aufgelöst werden, falls die Neigung des Wellenvektors gegen die vertikale gering ist oder der Sichtwinkel des Empfängersatelliten in Richtung der Wellenberge ist.
37
Dupuy, Mi-Song. « Analysis of the projector augmented-wave method for electronic structure calculations in periodic settings ». Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC073/document.
Texte intégralRésumé :
Cette thèse est consacrée à l'étude de la méthode PAW (projector augmented-wave) et d'une de ses modifications, baptisée méthode PAW variationnelle (VPAW), pour le calcul de l'état fondamental d'Hamiltoniens en géométrie périodique. Ces méthodes visent à améliorer la vitesse de convergence des méthodes d'ondes planes (ou méthodes de Fourier) en appliquant une transformation inversible au problème aux valeurs propres initial agissant au voisinage de chaque site atomique. Cette transformation permet de capter une partie des difficultés dues aux singularités coulombiennes. La méthode VPAW est analysée pour un opérateur de Schr\"odinger unidimensionnel avec des potentiels de Dirac. Les fonctions propres de ce modèle comprennent des sauts de dérivées similaires aux cusps électroniques. Le saut de dérivée des fonctions propres du problème aux valeurs propres issu de la méthode VPAW est réduit de façon importante. Cela entraîne une accélération de convergence en ondes planes du calcul des valeurs propres corroborée par une étude numérique. Une étude de la méthode VPAW est conduite pour des Hamiltoniens 3D périodiques avec des singularités coulombiennes, parvenant à des conclusions similaires. Pour la méthode PAW, la transformation inversible comporte des sommes infinies qui sont tronquées en pratique. Ceci introduit une erreur, qui est rarement quantifiée en pratique. Elle est analysée dans le cas de l'opérateur de Schrödinger unidimensionnel avec des potentiels de Dirac. Des bornes sur la plus basse valeur propre en fonction des paramètres PAW sont prouvées conformes aux tests numériquesThis thesis is devoted to the study of the PAW method (projector augmented-wave) and of a variant called the variational PAW method (VPAW). These methods aim to accelerate the convergence of plane-wave methods in electronic structure calculations. They rely on an invertible transformation applied to the eigenvalue problem, which acts in a neighborhood of each atomic site. The transformation captures some difficulties caused by the Coulomb singularities. The VPAW method is applied to a periodic one-dimensional Schr\"odinger operator with Dirac potentials and analyzed in this setting. Eigenfunctions of this model have derivative jumps similar to the electronic cusps. The derivative jumps of eigenfunctions of the VPAW eigenvalue problem are significantly reduced. Hence, a smaller plane-wave cut-off is required for a given accuracy level. The study of the VPAW method is also carried out for 3D periodic Hamiltonians with Coulomb singularities yielding similar results. In the PAW method, the invertible transformation has infinite sums that are truncated in practice. The induced error is analyzed in the case of the periodic one-dimensional Schrödinger operator with Dirac potentials. Error bounds on the lowest eigenvalue are proved depending on the PAW parameters
38
Pile, David Fujio Pelleas. « Extremely asymmetrical scattering of waves in periodic Bragg arrays ». Thesis, Queensland University of Technology, 2003. https://eprints.qut.edu.au/15794/1/David_Pile_Thesis.pdf.
Texte intégralRésumé :
This thesis fills in the gaps in the existing theory of wave phenomena in thick diffraction gratings at extreme angles of scattering, i.e. when the scattered wave propagates parallel or almost parallel to the grating boundaries. A consistent theory of a new type of Bragg scattering of bulk and guided optical modes in thick uniform and non-uniform, dissipative and non-dissipative, slanted periodic gratings has been developed. This type of scattering is
called extremely asymmetrical scattering (EAS).
One of the main distinctive features of EAS is the strong resonant increase of the scattered wave amplitude compared to the amplitude of the incident wave. Several unique combinations of strong resonances shaping a complex multi-resonant pattern of EAS in different types of gratings have been predicted and investigated theoretically and numerically. This includes the prediction of a new resonant wave effect in non-uniform gratings with varying phase – double-resonant EAS, the discovery of several sharp and strong resonances with respect to scattering angle in gratings with the scattered wave
propagating almost parallel to the grating boundaries (grazing-angle scattering (GAS)) for the case of second-order scattering, and the prediction of a new type of eigenmode in gratings with second-order scattering (especially in gratings with large amplitude). In addition, several other important practical problems that may be crucial for the experimental observation and application of EAS and GAS have been solved. These are the determination of the tolerance of EAS to small grating imperfections, e.g., fluctuations of the grating amplitude, prediction
of unusually high sensitivity of second-order EAS to small variations of mean structural parameters, determination of the effect of weak dissipation on EAS, etc. Physical reasons for the predicted resonances and effects are explained. In particular, the crucial role of the diffractional divergence for EAS and GAS has been revealed, especially for non-uniform gratings.
Methods of analysis involve the approximate and rigorous approaches. The approximate method is based on understanding the role of the diffractional divergence in the geometry of EAS and the two-wave approximation (valid for any types of waves). The rigorous approach is based on the rigorous coupled-wave analysis (RCWA) and, in particular, the known enhanced T-matrix
algorithm (by Moharam, et al.) that is numerically stable for narrow and wide gratings with arbitrary amplitude (valid only for bulk electromagnetic waves).
39
Pile, David Fujio Pelleas. « Extremely asymmetrical scattering of waves in periodic Bragg arrays ». Queensland University of Technology, 2003. http://eprints.qut.edu.au/15794/.
Texte intégralRésumé :
This thesis fills in the gaps in the existing theory of wave phenomena in thick diffraction gratings at extreme angles of scattering, i.e. when the scattered wave propagates parallel or almost parallel to the grating boundaries. A consistent theory of a new type of Bragg scattering of bulk and guided optical modes in thick uniform and non-uniform, dissipative and non-dissipative, slanted periodic gratings has been developed. This type of scattering is
called extremely asymmetrical scattering (EAS).
One of the main distinctive features of EAS is the strong resonant increase of the scattered wave amplitude compared to the amplitude of the incident wave. Several unique combinations of strong resonances shaping a complex multi-resonant pattern of EAS in different types of gratings have been predicted and investigated theoretically and numerically. This includes the prediction of a new resonant wave effect in non-uniform gratings with varying phase – double-resonant EAS, the discovery of several sharp and strong resonances with respect to scattering angle in gratings with the scattered wave
propagating almost parallel to the grating boundaries (grazing-angle scattering (GAS)) for the case of second-order scattering, and the prediction of a new type of eigenmode in gratings with second-order scattering (especially in gratings with large amplitude). In addition, several other important practical problems that may be crucial for the experimental observation and application of EAS and GAS have been solved. These are the determination of the tolerance of EAS to small grating imperfections, e.g., fluctuations of the grating amplitude, prediction
of unusually high sensitivity of second-order EAS to small variations of mean structural parameters, determination of the effect of weak dissipation on EAS, etc. Physical reasons for the predicted resonances and effects are explained. In particular, the crucial role of the diffractional divergence for EAS and GAS has been revealed, especially for non-uniform gratings.
Methods of analysis involve the approximate and rigorous approaches. The approximate method is based on understanding the role of the diffractional divergence in the geometry of EAS and the two-wave approximation (valid for any types of waves). The rigorous approach is based on the rigorous coupled-wave analysis (RCWA) and, in particular, the known enhanced T-matrix
algorithm (by Moharam, et al.) that is numerically stable for narrow and wide gratings with arbitrary amplitude (valid only for bulk electromagnetic waves).
40
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.
41
Yilmaz, Nihal. « Spectral Characteristics Of Wind Waves In The Eastern Black Sea ». Phd thesis, METU, 2007. http://etd.lib.metu.edu.tr/upload/3/12608614/index.pdf.
Texte intégralRésumé :
Wind waves are highly complex, random phenomena. One way to describe the irregular nature of the sea surface is the use of wave energy spectrum. Spectral information for wind waves in the Black Sea is extremely limited. Knowledge on spectral characteristics of wind waves would contribute to scientific, engineering and operational coastal and marine activities in the Black Sea. The aim of the present thesis is to investigate characteristics of wind wave spectra for the Eastern Black Sea. This would allow detailed understanding of the nature of the waves occurring in this enclosed basin. Long-term wave measurements obtained by directional buoys deployed offshore at Sinop, Hopa and Gelendzhik were utilized as the three sets of wave data. Records were analyzed to identify them as uni-modal or multi-modal spectra, and occurrences of spectral peaks were computed. Single peaked spectra were studied as belonging to fully arisen or developing sea states. Model parameters of JONSWAP and PM spectra were estimated for the observed spectra by using a least square error method. The records of developing seas were further analyzed to select the ones belonging to stable wind conditions. Fetch dependencies of non-dimensional spectral variables, mean parameters of JONSWAP model spectrum and the envelop of dimensionless spectra were investigated for this data sub-set.
42
Mortola, Giuseppe. « Nonlinear analysis of waves induces motions and loads in large amplitude waves ». Thesis, University of Strathclyde, 2013. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=20838.
Texte intégralRésumé :
An ocean going vessel, sailing in severe seas, experiences motions and loads that are largely affected by nonlinear phenomena. These effects deviate the responses from the linear prediction, modifying their magnitudes, symmetry and frequency characteristics. The change of the actual wetted geometry due to motions and large ambient waves elevation and the occurrence of impulsive phenomena, such as bottom impact, are some of the main sources of nonlinearities. Current state-of-art in seakeeping, applied to ship design, is based on the assumption of small amplitude motions and linearity between the excitation and the response. These techniques have been proved, during the years, to be reliable for small and moderate sea states, but they are not effective in large amplitude waves. The understanding and prediction of the behaviour of the vessel in rough seas is of crucial importance for its design, and therefore there is a need for better methods and practices. Application of nonlinear seakeeping methods in a every-day design situations is limited. The complexity and the computational cost of some methodologies, together with the absence of standardised procedures, are the main causes for the reduced use of such a methodologies. The work presented in this thesis aims to develop a practical nonlinear seakeeping approach that can be used in a design content to model wave induced motions and loads in large amplitude waves. The wave-body interaction problem is solved using a time domain nonlinear two dimensional approach, that considers the actual wetted hull portion and the relative velocity between the structure and the waves. The vessel is modelled as a flexible body to allow structural dynamics. The proposed formulation takes into account impulsive phenomena due to water impact, on both the bottom and the flare of the hull, using a combination of analytical and empirical techniques. The proposed methodology is applied to the S-175 and the Wils II 13,000 TEU container ships. The validation of the proposed method, conducted in both small and large amplitude regular waves, shows the capability of the technique to correctly predict the behaviour of the vessel also when linear methodologies fail. The analysis demonstrates the importance and the reliability of hydroelastic methods for the prediction of wave induced loads, especially when whipping is relevant. A procedure, which applies the proposed methodology for the evaluation of maximum expected values of wave induced motions and loads is presented. Long term analyses are conducted, using both linear and nonlinear method, to study the e ect of nonlinearities. The comparison between linear and nonlinear approaches shows an increase of maximum load responses when nonlinear hydroelasticity is applied. This study highlights also the dependency of the results on the selection of the return period and operational velocity profile of the vessel.
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Gala, Satya Sumanth Reddy. « Wave and longshore transport studies on Lake Pontchartrain ». ScholarWorks@UNO, 2004. http://louisdl.louislibraries.org/u?/NOD,104.
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Thesis (M.S.)--University of New Orleans, 2004.Title from electronic submission form. "A thesis ... in partial fulfillment of the requirements for the degree of Master of Science in the department of Civil Engineering."--Thesis t.p. Vita. Includes bibliographical references.
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Shimizu, Kenji. « Application of modal analysis to strongly stratified lakes ». University of Western Australia. Faculty of Engineering, Computing and Mathematics, 2009. http://theses.library.uwa.edu.au/adt-WU2009.0079.
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Modal analysis for strongly stratified lakes was extended to obtain a better understanding of the dynamics of the basin-scale motions. By viewing the basin-scale motions as a superposition of modes, that have distinct periods and three-dimensional structures, the method provides a conceptual understanding for the excitation, evolution, and damping of the basin-scale motions. Once the motion has been decomposed into modes, their evolution and energetics may be extracted from hydrodynamic simulation results and field data. The method was applied to Lake Biwa, Japan, and Lake Kinneret, Israel, and used for a theoretical study. The real lake applications showed that winds excited basin-scale motions that had a surface layer velocity structure similar to the wind stress pattern. Three-dimensional hydrodynamics simulations of Lake Biwa indicated that most of the energy input from winds was partitioned into the internal waves that decayed within a few days. The gyres, on the other hand, received much less energy but dominated the dynamics during calm periods due to their slow damping. Analyses of field data from Lake Kinneret suggested that the internal waves, excited by the strong winds every afternoon, were damped over a few days primarily due to bottom friction. Theoretical investigations of damping mechanisms of internal waves revealed that bottom friction induced a velocity anomaly at the top of the boundary layer that drained energy from the nearly inviscid interior by a combination of internal wave cancelling and spin-down. These results indicate that gyres induce long-term horizontal transport near the surface and internal waves transfer energy from winds to near-bottom mixing. Modal structure of dominant basin-scale internal waves can induce large heterogeneity of nearbottom mass transfer processes. The method presented here provides a tool to determine how basin-scale motions impact on biogeochemical processes in stratified lakes.
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Lindley, Edward Andrew. « Analysis of millimetre wave antennas ». Thesis, Queen Mary, University of London, 1990. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.281674.
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Ojima, Hirotaka, Kenji Nagase et Yoshikazu Hayakawa. « Wave-based analysis and wave control of damped mass-spring systems ». IEEE, 2001. http://hdl.handle.net/2237/6856.
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Maling, Ben. « Asymptotic analysis of array-guided waves ». Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/44725.
Texte intégralRésumé :
We develop and apply computational and analytical techniques to study wave-like propagation and resonant effects in periodic and quasi-periodic systems. Two themes that unify the content herein are the guidance and confinement of energy using periodic structures, and the utility of asymptotic analysis to aid computation and produce results that lend physical insight to the problems in question. In the first research chapter, we develop the method of high-frequency homogenisation (HFH) for electromagnetic waves in dielectric media, and apply this to the example of a planar array of dielectric spheres. The theory conveniently describes a range of dynamic effects, including effectively anisotropic behaviour in certain frequency regimes. In the second research chapter, we apply the HFH method to a cylindrical Bragg fibre, and use this to set up an effective eigenvalue problem in which the quasi-periodic system representing the fibre cladding is represented by a single continuous Bessel-like equation. We compare the results with those of direct numerical simulations and discuss how the theory could be developed to aid the study of photonic crystal cavities or fibres. In the remaining chapters, we consider the complex resonances of structures with angular periodicity. We demonstrate the emergence of quasi-normal modes with high Q-factors for the Helmholtz equation in such domains, and explore some of their properties using multiple scale analysis. In the final two chapters, we focus on a particular subset of these domains, and using matched asymptotic expansions show that the Q-factors for certain solutions depend exponentially on the number of inclusions arranged in a circular ring. Finally, we extend this analysis to flexural waves in thin elastic plates, and discuss the possibility of structured-ring resonators based on these solutions.
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Lee, Ray A. « Analysis of Spreading Depolarization as a Traveling Wave in a Neuron-Astrocyte Network ». The Ohio State University, 2017. http://rave.ohiolink.edu/etdc/view?acc_num=osu1503308416771087.
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Weber, Matthew B. « Wave Scattering From Infinite Cylindrical Obstacles of Arbitrary Cross-Section ». Diss., CLICK HERE for online access, 2004. http://contentdm.lib.byu.edu/ETD/image/etd636.pdf.
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Orozco, M. Catalina (Maria Catalina). « Inversion Method for Spectral Analysis of Surface Waves (SASW) ». Diss., Georgia Institute of Technology, 2004. http://hdl.handle.net/1853/5124.
Texte intégralRésumé :
This research focuses on estimating the shear wave velocity (Vs) profile based on the dispersion curve obtained from SASW field test data (i.e., inversion of SASW data). It is common for the person performing the inversion to assume the prior information required to constrain the problem based on his/her own judgment. Additionally, the Vs profile is usually shown as unique without giving a range of possible solutions. For these reasons, this work focuses on: (i) studying the non-uniqueness of the solution to the inverse problem; (ii) implementing an inversion procedure that presents the estimated model parameters in a way that reflects their uncertainties; and (iii) evaluating tools that help choose the appropriate prior information.
One global and one local search procedures were chosen to accomplish these purposes: a pure Monte Carlo method and the maximum likelihood method, respectively. The pure Monte Carlo method was chosen to study the non-uniqueness by looking at the range of acceptable solutions (i.e., Vs profiles) obtained with as few constraints as possible. The maximum likelihood method was chosen because it is a statistical approach, which enables us to estimate the uncertainties of the resulting model parameters and to apply tools such as the Bayesian criterion to help select the prior information objectively.
The above inversion methods were implemented for synthetic data, which was produced with the same forward algorithm used during inversion. This implies that all uncertainties were caused by the nature of the SASW inversion problem (i.e., there were no uncertainties added by experimental errors in data collection, analysis of the data to create the dispersion curve, layered model to represent a real 3-D soil stratification, or wave propagation theory). At the end of the research, the maximum likelihood method of inversion and the tools for the selection of prior information were successfully used with real experimental data obtained in Memphis, Tennessee.