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1
Gidel, Floriane Marie Pauline. "Variational water-wave models and pyramidal freak waves." Thesis, University of Leeds, 2018. http://etheses.whiterose.ac.uk/21730/.
Повний текст джерелаАнотація:
A little-known fact is that, every week, two ships weighing over 100 tonnes sink in oceans, sometimes with tragic consequences. This alarming observation suggests that maritime structures may be struck by stronger waves than those they were designed to withstand. These are the legendary rogue (or freak) waves, i.e., suddenly appearing huge waves that have traumatised mariners for centuries and currently remain an unavoidable threat to ships, and to their crews and passengers. Thus motivated, an EU-funded collaboration between the Department of Applied Mathematics (Leeds University) and the Maritime Research Institute Netherlands (MARIN) supported this project, in which the ultimate goal, of importance to the international maritime sector, is to develop reliable damage-prediction tools, leading to beneficial impact in terms of both safety and costs. To understand the behaviour of rogue waves, cost-effective water-wave models are derived in both deep and shallow water. Novel mathematical and numerical strategies are introduced to capture the dynamic air-water interface and to ensure conservation of important properties. Specifically, advanced variational Galerkin finite-element methods are used to provide stable simulations of potential-flow water waves in a basin with wavemakers and seabed topography, which allows reliable simulations of rogue waves in a target area. For optimised computational speed, wave absorption is considered with a beach on which waves break and dissipate energy. Robust integrators are therefore introduced to couple the potential-flow model to shallow-water wave dynamics at the beach. Experimental validation of the numerical tank is conducted at Delft University of Technology to ensure accuracy of the simulations from the wavemaker to the beach. The numerical tank is designed for subsequent use by MARIN to investigate the damage caused by rogue waves on structures in order to update maritime design practice and to ensure safety of ships, therefore leading to a competitive commercial advantage across Europe.
2
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.
Повний текст джерелаАнотація:
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 tool<br>differences 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.
3
Mei, Zhongtao. "Wave Functions of Integrable Models." University of Cincinnati / OhioLINK, 2018. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1530880774625297.
Повний текст джерела
4
Du, Chenguang. "How Well Can Two-Wave Models Recover the Three-Wave Second Order Latent Model Parameters?" Diss., Virginia Tech, 2021. http://hdl.handle.net/10919/103856.
Повний текст джерелаАнотація:
Although previous studies on structural equation modeling (SEM) have indicated that the
second-order latent growth model (SOLGM) is a more appropriate approach to
longitudinal intervention effects, its application still requires researchers to collect at least
three-wave data (e.g. randomized pretest, posttest, and follow-up design). However, in
some circumstances, researchers can only collect two-wave data for resource limitations.
With only two-wave data, the SOLGM can not be identified and researchers often choose
alternative SEM models to fit two-wave data. Recent studies show that the two-wave
longitudinal common factor model (2W-LCFM) and latent change score model
(2W-LCSM) can perform well for comparing latent change between groups. However, there
still lacks empirical evidence about how accurately these two-wave models can estimate the
group effects of latent change obtained by three-wave SOLGM (3W-SOLGM). The main
purpose of this dissertation, therefore, is trying to examine to what extent the fixed effects
of the tree-wave SOLGM can be recovered from the parameter estimates of the two-wave
LCFM and LCSM given different simulation conditions.
Fundamentally, the supplementary study (study 2) using three-wave LCFM was
established to help justify the logistics of different model comparisons in our main study
(study 1). The data generating model in both studies is 3W-SOLGM and there are in total
5 simulation factors (sample size, group differences in intercept and slope, the covariance
between the slope and intercept, size of time-specific residual, change the pattern of
time-specific residual). Three main types of evaluation indices were used to assess the
quality of estimation (bias/relative bias, standard error, and power/type I error rate). The
results in the supplementary study show that the performance of 3W-LCFM and
3W-LCSM are equivalent, which further justifies the different models' comparison in the
main study. The point estimates for the fixed effect parameters obtained from the two-wave
models are unbiased or identical to the ones from the three-wave model. However, using
two-wave models could reduce the estimation precision and statistical power when the
time-specific residual variance is large and changing pattern is heteroscedastic
(non-constant). Finally, two real datasets were used to illustrate the simulation results<br>Doctor of Philosophy<br>To collect and analyze the longitudinal data is a very important approach to understand
the phenomenon of development in the real world. Ideally, researchers who are interested
in using a longitudinal framework would prefer collecting data at more than two points in
time because it can provide a deeper understanding of the developmental processes.
However, in real scenarios, data may only be collected at two-time points. With only
two-wave data, the second-order latent growth model (SOLGM) could not be used. The
current dissertation compared the performance of two-wave models (longitudinal common
factor model and latent change score model) with the three-wave SOLGM in order to
better understand how the estimation quality of two-wave models could be comparable to
the tree-wave model. The results show that on average, the estimation from two-wave
models is identical to the ones from the three-wave model. So in real data analysis with
only one sample, the point estimate by two-wave models should be very closed to that of
the three-wave model. But this estimation may not be as accurate as it is obtained by the
three-wave model when the latent variable has large variability in the first or last time
point. This latent variable is more likely to exist as a statelike construct in the real world.
Therefore, the current study could provide a reference framework for substantial
researchers who could only have access to two-wave data but are still interested in
estimating the growth effect that supposed to obtain by three-wave SOLGM.
5
Hill, David J. Saffman P. G. Saffman P. G. "Part I. Vortex dynamics in wake models. : Part II. Wave generation /." Diss., Pasadena, Calif. : California Institute of Technology, 1998. http://resolver.caltech.edu/CaltechETD:etd-04052007-141032.
Повний текст джерела
6
Murray, Stuart William. "Wave radiation in simple geophysical models." Thesis, University of Edinburgh, 2013. http://hdl.handle.net/1842/7922.
Повний текст джерелаАнотація:
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.
7
Timmermans, Ben. "Uncertainty in numerical wind-wave models." Thesis, University of Southampton, 2015. https://eprints.soton.ac.uk/378996/.
Повний текст джерелаАнотація:
The modelling of ocean waves is now carried out routinely at meteorological centres around the world. However, little is know about the source of the uncertainty in the predictions of waves produced, and sources can be numerous depending on the specific application. Historically it was felt that the dominant source of uncertainty originated from incomplete knowledge and expression of forcing winds. However more recent studies have focused on the underlying physical processes and their representations, with some authors questioning whether the limitation of the current modelling approach has been reached. Recently, methods for the statistical analysis of complex computer models, including models such as those used for wave prediction, have been developed. In this thesis these methods are applied to perform the first ever uncertainty analysis of a wave model. These new methods are applied to the state of the art wave model Wavewatch IIIr. This thesis principally explores the effect of tuning parameter uncertainty relating to the “Tolman and Chalikov” input and dissipation parameterisation, the discrete interaction approximation scheme for nonlinear wave-wave interactions and uncertainty about wind forcing, on wave simulation output, in a range of idealised cases, and realistically on Lake Michigan. The effectiveness of the statistical methods is first demonstrated in simple cases, before analysis is performed for progressively more complex simulations. In each case, uncertainty measures are computed with respect to simulation output in terms of summary wave statistics, typically including significant wave height and peak period. The analysis reveals nonlinear response and the relative importance of the various input, which in turn shows the active physical processes, and where the greatest sources of uncertainty lie. Both uncertainty about wind forcing and the process of nonlinear wave-wave interactions are found to be dominant in all cases, although energy dissipation is important in growing sea states. Finally, observational wave height data is used to perform a parameter calibration for simulations of stormy conditions on Lake Michigan, leading to improved performance.
8
Clavica, Francesco. "Computational and experimental time domain, one dimensional models of air wave propagation in human airways." Thesis, Brunel University, 2012. http://bura.brunel.ac.uk/handle/2438/9622.
Повний текст джерелаАнотація:
The scientific literature on airflow in the respiratory system is usually associated with rigid ducts. Many studies have been conducted in the frequency domain to assess respiratory system mechanics. Time-domain analyses appear more independent from the hypotheses of periodicity, required by frequency analysis, providing data that are simpler to interpret since features can be easily associated to time. However, the complexity of the bronchial tree makes 3-D simulations too expensive computationally, limiting the analysis to few generations. 1-D modelling in space-time variables has been extensively applied to simulate blood pressure and flow waveforms in arteries, providing a good compromise between accuracy and computational cost. This work represents the first attempt to apply this formulation to study pulse waveforms in the human bronchial tree. Experiments have been carried out, in this work, to validate the model capabilities in modelling pressure and velocity waveforms when air pulses propagate in flexible tubes with different mechanical and geometrical properties. The experiments have shown that the arrival of reflected air waves occurs in correspondence of the theoretical timing once the wave speed is known. Reflected backward compression waves have generated an increase of pressure (P) and decrease of velocity (U) while expansion backward waves have produced a decrease of P and increase of U according to the linear analysis of wave reflections. The experiments have demonstrated also the capabilities of Wave intensity analysis (WIA), an analytical technique used to study wave propagation in cardiovascular system, in separating forward and backward components of pressure and velocity also for the air case. After validating the 1-D modelling in space and time variables, several models for human airways have been considered starting from simplified versions (bifurcation trachea- main bronchi, series of tubes) to more complex systems up to seven generations of bifurcations according to both symmetrical and asymmetrical models. Calculated pressures waveforms in trachea are shown to change accordingly to both peripheral resistance and compliance variations, suggesting a possible non-invasive assessment of peripheral conditions. A favourable comparison with typical pressure and flow waveforms from impulse oscillometry system, which has recently been introduced as a clinical diagnostic technique, is also shown. The results suggested that a deeper investigation of the mechanisms underlying air wave propagation in lungs could be a useful tool to better understand the differences between normal and pathologic conditions and how pathologies may affect the pattern of pressure and velocity waveforms.
9
Alves, Jose Henrique Gomes de Mattos Mathematics UNSW. "A Saturation-Dependent Dissipation Source Function for Wind-Wave Modelling Applications." Awarded by:University of New South Wales. Mathematics, 2000. http://handle.unsw.edu.au/1959.4/17786.
Повний текст джерелаАнотація:
This study reports on a new formulation of the spectral dissipation source term Sds for wind-wave modelling applications. This new form of Sds features a nonlinear dependence on the local wave spectrum, expressed in terms of the azimuthally integrated saturation parameter B(k)=k^4 F(k). The basic form of this saturation-dependent Sds is based on a new framework for the onset of deep-water wave breaking due to the nonlinear modulation of wave groups. The new form of Sds is succesfully validated through numerical experiments that include exact nonlinear computations of fetch-limited wind-wave evolution and hindcasts of two-dimensional wave fields made with an operational wind-wave model. The newly-proposed form of Sds generates integral spectral parameters that agree more closely with observations when compared to other dissipation source terms used in state-of-the-art wind-wave models. It also provides more flexibility in controlling properties of the wave spectrum within the high wavenumber range. Tests using a variety of wind speeds, three commonly-used wind input source functions and two alternative full-development evolution limits further demonstrate the robustness and flexibility of the new saturation-dependent dissipation source term. Finally, improved wave hindcasts obtained with an implementation of the new form of Sds in a version of the WAM model demonstrate its potential usefulness in operational wind-wave forecasting applications.
10
Poon, Chun-Kin, and 潘俊健. "Numerical simulation of coupled long wave-short wave system with a mismatch in group velocities." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 2005. http://hub.hku.hk/bib/B35381334.
Повний текст джерела
11
Jin, Wenlong. "Kinematic wave models of network vehicular traffic /." For electronic version search Digital dissertations database. Restricted to UC campuses. Access is free to UC campus dissertations, 2003. http://uclibs.org/PID/11984.
Повний текст джерела
12
Tshisaphungo, Mpho. "Validation of high frequency propagation prediction models over Africa." Thesis, Rhodes University, 2010. http://hdl.handle.net/10962/d1015239.
Повний текст джерелаАнотація:
The ionosphere is an important factor in high frequency (HF) radio propagation providing an opportunity to study ionospheric variability as well as the space weather conditions under which HF communication can take place. This thesis presents the validation of HF propagation conditions for the Ionospheric Communication Enhanced Profile Analysis and Circuit (ICEPAC) and Advanced Stand Alone Prediction System (ASAPS) models over Africa by comparing predictions with the measured data obtained from the International Beacon Project (IBP). Since these models were not developed using information on the African region, a more accurate HF propagation prediction tool is required. Two IBP transmitter stations are considered, Ruaraka, Kenya (1.24°S, 36.88°E) and Pretoria, South Africa (25.45°S, 28.10°E) with one beacon receiver station located in Hermanus, South Africa (34.27°S, 19.l2°E). The potential of these models in terms of HF propagation conditions is illustrated. An attempt to draw conclusions for future improvement of the models is also presented. Results show a low prediction accuracy for both ICEPAC and ASAPS models, although ICEPAC provided more accurate predictions for daily HF propagation conditions. This thesis suggests that the development of a new HF propagation prediction tool for the African region or the modification of one of the existing models to accommodate the African region, taking into account the importance of the African ionospheric region, should be considered as an option to ensure more accurate HF Propagation predictions over this region.
13
LOPES, DANIEL T. "Caracterização de estruturas de ondas lentas helicoidais para utilização em, TWT de potência." reponame:Repositório Institucional do IPEN, 2007. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11596.
Повний текст джерелаАнотація:
Made available in DSpace on 2014-10-09T12:53:40Z (GMT). No. of bitstreams: 0<br>Made available in DSpace on 2014-10-09T13:58:44Z (GMT). No. of bitstreams: 0<br>Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)<br>Dissertação (Mestrado)<br>IPEN/D<br>Instituto de Pesquisas Energéticas e Nucleares - IPEN-CNEN/SP<br>FAPESP:05/03612-0
14
Bucca, Steven E. "Wave propagation in lossy waveguide structures." Thesis, Virginia Tech, 1989. http://hdl.handle.net/10919/44110.
Повний текст джерелаАнотація:
In this thesis a numerical technique is developed determining the propagation constant
in waveguides and transmission lines. The technique accounts for both dielectric and conductor
losses in a guide having an arbitrary cross section and uses a full-wave solution process. A set of
coupled, vector integral equations which characterize the system are derived. The equations
enforce the necessary boundary conditions on the tangential electric and magnetic fields at the
boundaries separating the conductors and dielectrics.
The method of moments (MOM) technique is used to cast the equations into a
numerically solvable form. Computed results for various waveguide structures are compared to
known or perturbed results for three well-known structures. However, the program is more
general and may be applied to other cross-sections. Finally, possible future extensions of the
work is presented.<br>Master of Science
15
Closson, Taunia Lydia Lynn, and University of Lethbridge Faculty of Arts and Science. "Biological models with a square wave driving force." Thesis, Lethbridge, Alta. : University of Lethbridge, Faculty of Arts and Science, 2002, 2002. http://hdl.handle.net/10133/146.
Повний текст джерелаАнотація:
Systems that require a driving force of some kind are very common in physical and biological settings. Driving forces in a biological context are usually referred to as rhythms, pulses or clocks. Here we are interested in the effect of adding a square wave periodic driving force to a biological model. This is intended to model inputs from biological circuits with all-or-none or switch-like resposes. We study a model of cell division proposed by Novak and Tyson. Our switched input is intended to model the interaction of the mitotic oscillator with an ultradian clock. We thoroughly characterize the behaviour as a function of the durations of the active and inactive phases. We also study a model of vein formation in plant leaves proposed by Mitchison. Pulsed hormonal release greatly accelerates vein formation in this model.<br>x, 105 leaves : ill. (some col.) ; 29 cm.
16
Vetreno, JoAnna Ruth. "ANALYTIC MODELS FOR ACOUSTIC WAVE PROPAGATION IN AIR." NCSU, 2008. http://www.lib.ncsu.edu/theses/available/etd-01032008-114426/.
Повний текст джерелаАнотація:
Ultrasound waves have been used for imaging purposes for many years. However, a liquid interface has always been necessary between the transducer and the object being imaged due to a high mechanical resistance at the air-transducer interface. Recent advances in transducers have made it possible to omit the liquid interface, allowing imaging to be done through air interfaces. Because this is a relatively new field, research into ultrasound propagation in air is very limited. A comprehensive model of how an ultrasound wave propagates through air would expedite the study of air-coupled ultrasound for imaging. This thesis presents a mathematical model of two-dimensional linear acoustic wave propagation in air. The model takes as input the frequency and amplitude of an acoustic signal and outputs the pressure field over varying longitudinal and lateral distances from the source. The benefits of a mathematical model over a finite element model are first discussed, then the mathematical model for acoustic propagation in air is developed using both computer simulations and physical experiments in an anechoic chamber. Results are presented and compared to experimental data to confirm the validity of the mathematical model.
17
De, Villiers Magdaline. "Existence theory for linear vibration models of elastic bodies." Pretoria : [s.n.], 2009. http://upetd.up.ac.za/thesis/available/etd-10072009-201522.
Повний текст джерела
18
Foster, David H. "Fabry-Perot and Whispering Gallery Modes In Realistic Resonator Models." Thesis, view abstract or download file of text, 2006. http://wwwlib.umi.com/cr/uoregon/fullcit?p3211216.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--University of Oregon, 2006.<br>Typescript. Includes vita and abstract. Includes bibliographical references (leaves 204-213). Also available for download via the World Wide Web; free to University of Oregon users.
19
Xu, Hao. "Terrestrial radio wave propagation at millimeter-wave frequencies." Diss., Virginia Tech, 2000. http://hdl.handle.net/10919/27522.
Повний текст джерелаАнотація:
This research focuses on radio wave propagation at millimeter-wave frequencies. A measurement based channel characterization approach is taken in the investigation.
First, measurement techniques are analyzed. Three types of measurement systems are designed, and implemented in measurement campaigns: a narrowband measurement system, a wideband measurement system based on Vector Network Analyzer, and sliding correlator systems at 5.8+AH4AXA-mbox{GHz}, 38+AH4AXA-mbox{GHz} and 60+AH4AXA-mbox{GHz}. The performances of these measurement systems are carefully compared both analytically and experimentally.
Next, radio wave propagation research is performed at 38+AH4AXA-mbox{GHz} for Local Multipoint Distribution Services (LMDS). Wideband measurements are taken on three cross-campus links at Virginia Tech. The goal is to determine weather effects on the wideband channel properties. The measurement results include multipath dispersion, short-term variation and signal attenuation under different weather conditions. A design technique is developed to estimate multipath characteristics based on antenna patterns and site-specific information.
Finally, indoor propagation channels at 60+AH4AXA-mbox{GHz} are studied for Next Generation Internet (NGI) applications. The research mainly focuses on the characterization of space-time channel structure. Multipath components are resolved both in time of arrival (TOA) and angle of arrival (AOA). Results show an excellent correlation between the propagation environments and the channel multipath structure.
The measurement results and models provide not only guidelines for wireless system design and installation, but also great insights in millimeter-wave propagation.<br>Ph. D.
20
Bashir, Hussam. "Calculation of Wave Propagation for Statistical Energy Analysis Models." Thesis, Uppsala universitet, Tillämpad mekanik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-267928.
Повний текст джерелаАнотація:
This thesis investigates the problems of applying Statistical Energy Analysis (SEA) tomodels that include solid volumes. Three wave types (Rayleigh waves, Pressure wavesand Shear waves) are important to SEA and the mathematics behind them is explainedhere. The transmission coefficients between the wave types are needed for energytransfer in SEA analysis and different approaches to solving the properties of wavepropagation on a solid volume are discussed. For one of the propagation problems, asolution, found in Momoi [6] is discussed, while the other problem remains unsolveddue to the analytical difficulties involved.
21
Meurer, Thomas. "Wave propagation in hysteretic media." Thesis, Georgia Institute of Technology, 2000. http://hdl.handle.net/1853/19090.
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22
Larsson, Ashley Ian. "Mathematical aspects of wave theory for inhomogeneous materials /." Title page, table of contents and summary only, 1991. http://web4.library.adelaide.edu.au/theses/09PH/09phl334.pdf.
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23
Zhang, Jianfeng. "Incoporating rubble mound jetties in elliptic harbor wave models." Texas A&M University, 2003. http://hdl.handle.net/1969.1/5839.
Повний текст джерелаАнотація:
Simulation models based on the elliptic mild or steep slope wave equation are
frequently used to estimate wave properties needed for the engineering calculations of
harbors. To increase the practical applicability of such models, a method is developed to
include the effects of rubble mound structures that may be present along the sides of
entrance channels into harbors.
The results of this method are found to match those of other mathematical models
(i.e. parabolic approximation & three-dimensional solution) under appropriate conditions,
but they also deviate from results of parabolic approximations in some cases because
dissipation can create angular scattering. Comparison with hydraulic model data also
shows that this approach is useful for designing pocket wave absorbers that are used to
reduce wave heights in entrance channels.
24
Canali, Alessandro. "Wave propagation at coast combining numerical and statistical models." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/20247/.
Повний текст джерелаАнотація:
In this work, a hybrid model that combines numerical and statistical models is provided in order to study the propagation of the wave parameters from offshore areas to coastal areas. The methodology utilized involves a preliminary aggregation of 6 buoys data around an island in the Pacific Ocean in a single point. In the ocean environment studies usually the aggregated parameters of significant wave height, peak period and mean direction are utilized: in this work is performed also the separation between swell and wind sea waves. The time-series is 40 years long, thus 500 cases are selected utilizing the maximum dissimilarity algorithm, which represents different scenarios. After that, this cases are propagated utilizing the software SWAN, which is a phase-averaged resolving model. The inputs are the wave parameters of the 500 cases and the wind velocity, while the results are the wave parameters propagated in each point of a map. Three different maps have been used, with increasing resolution of the bathymetry. In the end, the output of a specific point has been extracted and, with the application of the radial basis function algorithm, the original time series has been rebuilt. The values obtained have been validated with the buoy data present. After, two sets of other simulations have been performed varying the mean sea level in order to have a qualitative analysis of the influence of the tide level on the significant wave height inside the lagoon.
25
Blake, Richard John. "Numerical models for Rayleigh wave scattering from surface features." Thesis, University College London (University of London), 1988. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.282401.
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26
Taylor, Peter. "Development of compartment models of epileptic spike-wave discharges." Thesis, University of Manchester, 2013. https://www.research.manchester.ac.uk/portal/en/theses/development-of-compartment-models-of-epileptic-spikewave-discharges(4f6f4ff6-f5cd-451f-a806-39590b58468e).html.
Повний текст джерелаАнотація:
Background: Despite the so-called "generalised" nature of many epileptic seizures, patient specific spatio-temporal properties have been shown using imaging data at the macroscopic level of the cortex. Previous computational models have failed to account for spatial heterogeneities at the scale of the entire cortex. Furthermore, one of they key benefits of developing a model is the ability to easily test stimulation protocols. Previous studies of generalised spike-wave (the hallmark of absence epilepsy) have abstracted away from this.METHODSIn this work we develop a set of models of epileptic activity, one of which is at the scale of the entire cortex and incorporates anatomically relevant connectivity from human subjects. A similar model incorporating physiologically relevant thalamocortical circuitry is developed in order to test hypotheses regarding stimulation protocols.RESULTSWe show that the model can account for large-scale spatio-temporal dynamics similar to those seen in epileptic patients. We demonstrate, using the model of thalamocortical interaction, that such a modelling approach can be used for the evaluation of stimulation protocols which are shown to successfully abort the seizure prematurely.CONCLUSIONThis work highlights the importance of computational modelling to support existing data and to make specific predictions regarding testable hypotheses. For example, a stimulus given at the correct time with the correct amplitude will stop the seizure.
27
Dods, Steven R. A. "A spectral theory for planar dielectric waveguides." Thesis, University of British Columbia, 1990. http://hdl.handle.net/2429/30690.
Повний текст джерелаАнотація:
The problem of electromagnetic wave propagation across the junction of two similar planar
dielectric waveguides is analysed, within the Kirchhoff approximation, by expanding the field into transverse variations of all possible modes. It is proven that the expansion can represent any solution for any planar dielectric waveguide. The spectral function is introduced into the representation, and this helps resolve some of the theoretical problems in passing from the limit of closed waveguides to open waveguides. Using the spectral function and the Gel'fand-Levitan integral equation some new exact solutions to novel dielectric planar waveguides can be found. Examples of waveguiding by total internal reflection or by Bragg reflection (which are physically very different processes) can be generated by changing a single parameter in the formulation. Usually the representation
for an open dielectric waveguide requires the matrix spectral function. However the Gel'fand-Levitan reconstruction is defined for scalar spectral functions. A technique for constructing the spectral matrix and the scattering solutions from two spectral functions is demonstrated. This technique uses a variational formulation of a scattering experiment. The connection between a dielectric structure and the characteristics of propagation on it is obscure. However the connection between these characteristics and the spectral function
is much clearer. It is sometimes possible to make predictions about the properties of the waveguide by looking at its spectral function only. Since the connection between the spectral function and the dielectric structure is well established by inverse spectral theory, introducing the spectral function has been of help in establishing the desired connection between the dielectric structure and the characteristics of propagation on it.
Such considerations suggest one of the above waveguides is sensitive to small perturbations
and could be used as an electro-optic modulator. Detailed calculations confirm the hypothesis.<br>Applied Science, Faculty of<br>Electrical and Computer Engineering, Department of<br>Graduate
28
Wingeart, Karen M. "Validation of operational global wave prediction models with spectral buoy data." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2001. http://handle.dtic.mil/100.2/ADA401720.
Повний текст джерелаАнотація:
Thesis (M.S. in Meteorology and Physical Oceanography) Naval Postgraduate School, December 2001.<br>"December 2001". Thesis advisor(s): Herbers, Thomas H.C.; Wittmann, Paul A. Includes bibliographical references (p. 39). Also available online.
29
Pinilla, Camilo Ernesto. "Numerical simulation of shear instability in shallow shear flows." Thesis, McGill University, 2008. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=115697.
Повний текст джерелаАнотація:
The instabilities of shallow shear flows are analyzed to study exchanges processes across shear flows in inland and coastal waters, coastal and ocean currents, and winds across the thermal-and-moisture fronts. These shear flows observed in nature are driven by gravity and governed by the shallow water equations (SWE). A highly accurate, and robust, computational scheme has been developed to solve these SWE. Time integration of the SWE was carried out using the fourth-order Runge-Kutta scheme. A third-order upwind bias finite difference approximation known as QUICK (Quadratic Upstream Interpolation of Convective Kinematics) was employed for the spatial discretization. The numerical oscillations were controlled using flux limiters for Total Variation Diminishing (TVD). Direct numerical simulations (DNS) were conducted for the base flow with the TANH velocity profile, and the base flow in the form of a jet with the SECH velocity profile. The depth across the base flows was selected for the' balance of the driving forces. In the rotating flow simulation, the Coriolis force in the lateral direction was perfectly in balance with the pressure gradient across the shear flow during the simulation. The development of instabilities in the shear flows was considered for a range of convective Froude number, friction number, and Rossby number. The DNS of the SWE has produced linear results that are consistent with classical stability analyses based on the normal mode approach, and new results that had not been determined by the classical method. The formation of eddies, and the generation of shocklets subsequent to the linear instabilities were computed as part of the DNS. Without modelling the small scales, the simulation was able to produce the correct turbulent spreading rate in agreement with the experimental observations. The simulations have identified radiation damping, in addition to friction damping, as a primary factor of influence on the instability of the shear flows admissible to waves. A convective Froude number correlated the energy lost due to radiation damping. The friction number determined the energy lost due to friction. A significant fraction of available energy produced by the shear flow is lost due the radiation of waves at high convective Froude number. This radiation of gravity waves in shallow gravity-stratified shear flow, and its dependence on the convective Froude number, is shown to be analogous to the Mach-number effect in compressible flow. Furthermore, and most significantly, is the discovery from the simulation the crucial role of the radiation damping in the development of shear flows in the rotating earth. Rings and eddies were produced by the rotating-flow simulations in a range of Rossby numbers, as they were observed in the Gulf Stream of the Atlantic, Jet Stream in the atmosphere, and various fronts across currents in coastal waters.
30
Chen, Jack. "Numerical study of tsunami wave propagation and runup on islands." Thesis, University of Cambridge, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.610080.
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Leadbetter, Jeffrey. "High order numerical models for high amplitude ultrasonic wave propagation." Thesis, McGill University, 2011. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=104880.
Повний текст джерелаАнотація:
The application of high-order numerical modeling to nonlinear ultrasonic wave propagation in fluids is discussed. This work is motivated by ongoing developments with Wave Phase Conjugating (WPC) transducers, which are able to greatly amplify and re-emit incident acoustic energy back to a source location. As a result of the high amplification factors, conjugate wave magnitudes may exceed linear acoustic thresholds, leading to progressive nonlinear distortion and shock wave formation. In this work, a numerical model is formulated and coded for the simulation of the high amplitude nonlinear wave-fields produced by WPC transducers. At ultrasonic frequencies (> 1 MHz) wavelengths are short relative to propagation distances, making accurate numerical methods a requirement. The implemented numerical scheme uses high-order Weighted Essentially Non-Oscillatory (WENO) techniques. Novel analysis is presented on the WENO schemes' spectral accuracy and on their capability to model progressive wave distortion. Details on the integration of a WPC transducer model into the numerical framework are also provided. This combination of modeling capabilities offers a new advancement in the simulation of WPC transducers and the high amplitude sound fields they produce. Using a simplified one-dimensional representation, the numerical model is applied and preliminary results investigating the influence of nonlinear acoustic response in ultrasonic WPC are presented.<br>L'application de schémas numériques d'ordre supérieur à la propagation d'ondes ultrasonores non-linéaires dans les fluides sera discutée. Cette recherche est motivée par les développements continus relatifs à de la conjugaison de phase acoustique, procédé qui permet d'amplifier et de renvoyer l'énergie acoustique incidente vers son lieu d'émission. Pour cette raison, les amplitudes des ondes conjuguées peuvent dépasser les seuils de validité de l'acoustique linéaire, conduisant à une distorsion non-linéaire progressive et à la formation d'ondes de choc. Dans ce travail, un modèle numérique a été élaboré et codé pour simuler les champs induits par des ondes non-linéaires issues d'une conjugaison de phase acoustique. A des fréquences ultrasonores (> 1 MHz) les longueurs d'ondes sont courtes devant la distance de propagation, ce qui rend nécessaire l'usage de méthodes numériques précises. La modélisation numérique implémentée dans cette recherche utilise une technique de schémas d'ordre supérieur intitulée: "Weighted Essentially Non-Oscillatory". Les analyses faites sur la précision spectrale des schémas seront confrontées aux résultats des calculs de propagation d' ondes ultrasonores. Les détails de l'intégration du modèle de fluide non-linéaire avec celui d'un transducteur à conjugaison de phase acoustique seront présentés ainsi que les résultats préliminaires sur le comportement de la conjugaison de phase en milieu non linéaire.
32
Plowman, Joseph Eugene. "Constraining massive black hole population models with gravitational wave observations." Thesis, Montana State University, 2010. http://etd.lib.montana.edu/etd/2010/plowman/PlowmanJ0510.pdf.
Повний текст джерелаАнотація:
A number of scenarios have been proposed for the origin of the supermassive black holes (SMBHs) that are found in the centres of most galaxies. Many such scenarios predict a high-redshift population of massive black holes (MBHs), with masses in the range 10² to 10ⵠtimes that of the Sun. When the Laser Interferometer Space Antenna (LISA) is finally operational, it is likely that it will detect on the order of 100 of these MBH binaries as they merge. The differences between proposed population models produce appreciable effects in the portion of the population which is detectable by LISA, so it is likely that the LISA observations will allow us to place constraints on them. However, gravitational wave detectors such as LISA will not be able to detect all such mergers nor assign precise black hole parameters to the merger, due to weak gravitational wave signal strengths. This dissertation explores LISA's ability to distinguish between several MBH population models. In this way, we go beyond predicting a LISA observed population and consider the extent to which LISA observations could inform astrophysical modelers. The errors in LISA parameter estimation are applied in two ways, with an 'Error Kernel' that is marginalized over astrophysically uninteresting 'sample' parameters, and with a more direct method which generates random sample parameters for each source in a population realization. We consider how the distinguishability varies depending on the choice of source parameters (1 or 2 parameters chosen from masses, redshift or spins) used to characterize the model distributions, with confidence levels determined by 1 or 2-dimensional tests based on the Kolmogorov-Smirnov test.
33
Song, Qingyang [Verfasser]. "Assimilation and application of nearshore ocean wave models / Qingyang Song." Kiel : Universitätsbibliothek Kiel, 2018. http://d-nb.info/1160235457/34.
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Siddons, Lee Anthony. "Data assimilation of HF radar data into coastal wave models." Thesis, University of Sheffield, 2007. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.444578.
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35
Jin, Won Tae. "Circuit models for a millimeter-wave suspended-microstrip line discontinuity." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA240906.
Повний текст джерелаАнотація:
Thesis (M.S. in Systems Engineering (Electronic Warfare))--Naval Postgraduate School, September 1990.<br>Thesis Advisor(s): Atwater, Harry A. Second Reader: Janaswamy, Rama. "September 1990." Description based on title screen as viewed on December 29, 2009. DTIC Identifier(s): Suspended striplines, microstrip lines, equivalent circuits, program listings, theses. Author(s) subject terms: Suspended-microstrip line, step discontinuity, equivalent circuit model, step-change. Includes bibliographical references (p. 60). Also available in print.
36
Nghiem, Son V. (Son Van). "Electromagnetic wave models for polarimetric remote sensing of geophysical media." Thesis, Massachusetts Institute of Technology, 1991. http://hdl.handle.net/1721.1/13879.
Повний текст джерелаАнотація:
Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1991.<br>Vita.<br>Includes bibliographical references (p. 239-245).<br>by Son V. Nghiem.<br>Ph.D.
37
Valentino, Eric. "The Design of Passive Networks with Full-Wave Component Models." Scholar Commons, 2019. https://scholarcommons.usf.edu/etd/7979.
Повний текст джерелаАнотація:
In this thesis, the design of passive networks with the aid of full-wave simulation software and geometry-based models of lumped elements is investigated. This is done by examining the results of a number of simulation examples, as well as measured data from manufactured designs to compare against simulated equivalents. One such example is a chip antenna evaluation board design, in which the PCB, antenna, matching components and connector are all modeled. When measured, the simulation agreed with the board’s best matched frequency of 5.5 GHz to within 20 MHz. In another, a new antenna layout is generated from an existing evaluation design which, produced a match of about -15 dB at the design frequency with a similar bandwidth to that shown on the antenna datasheet on the first attempt at manufacture. Additionally, a statistical experiment was conducted in order to provide insight into the phenomenon of coupling between lumped components, and to define clearly when it starts to become an important effect to consider. For both chip capacitors and inductors, a behavioral model of how much crosstalk is present in a prospective circuit was developed which takes into account angle and distance between components, as well as case size. Finally, a simple discrete gradient descent was implemented in a commercial full-wave simulation software in order to assist in the refinement of designs containing 3-D geometry-defined component models.
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Stott, Jonathon D. "Developing realistic models of the atrium and the p-wave." Thesis, University of Manchester, 2009. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.509024.
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39
Yip, Man-kit, and 葉文傑. "Frequency dependent admittance in one and two dimensions." Thesis, The University of Hong Kong (Pokfulam, Hong Kong), 1999. http://hub.hku.hk/bib/B31239675.
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40
Hodge, Steven Eric. "Discrete-time closed-loop control of a hinged wavemaker." Thesis, University of British Columbia, 1986. http://hdl.handle.net/2429/26704.
Повний текст джерелаАнотація:
The waves produced by a flap-type wavemaker, hinged in the middle, are modelled using first-order linear wavemaker theory. A simplified closed-loop, discrete-time system is proposed. This includes a proportional
plus integral plus derivative (PID) controller, and the wavemaker in order to compare the actual wave spectral density with the desired wave spectral density at a single frequency. Conventional discrete-time control theory is used with the major difference being the use of a relatively long timestep duration between changes in waveboard motion.
The system response is calculated for many controller gain combinations
by the computer simulation program CBGANES. System stability is analyzed for the gain combinations by using two different methods. One method is an extension of the Routh criterion to discrete-time and the other is a state-space eigenvalue approach. The computer simulation and the stability analysis provide a means for selecting possible controller gains for use at a specific frequency in an actual wave tank experiment.
The computer simulation performance response and the two stability analyses predict the same results for varying controller gains. It is evident that integral control is essential in order to achieve a desired response for this long duration timestep application. The variation in discrete timestep duration and in desired spectral density (an indirect indication of frequency variation) provide variation in the constraints on controller gain selection. The controller gain combinations yielding the fastest stable response at a single frequency are for large proportional gain and small integral and derivative gains.<br>Applied Science, Faculty of<br>Mechanical Engineering, Department of<br>Graduate
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Phlips, P. J. "Models of the heat-induced circulation in the tropical atmosphere." Thesis, University of Oxford, 1986. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.371572.
Повний текст джерела
42
Conn, Ariel. "Q Models for Lg Wave Attenuation in the Central United States." Thesis, Virginia Tech, 2013. http://hdl.handle.net/10919/19317.
Повний текст джерелаАнотація:
A series of small- to moderate-sized earthquakes occurred in Arkansas, Oklahoma and Texas from 2010 to 2012, coinciding with the arrival of the EarthScope Transportable Array (TA). The data the TA recorded from those earthquakes provide a unique opportunity to study attenuation of the Lg phase in the mid-continent and Gulf Coastal region. <br />The TA data reveal previously unrecognized regional variability of ground motion propagation in the central United States. A study of the Fourier amplitude spectra shows the Lg phase exhibiting strong attenuation for ray paths from Arkansas, southwest through the Ouachita Orogenic Belt and into central Texas, and south into the Gulf Coastal region. Less attenuation is seen in central Texas for ray paths extending directly south from Oklahoma, though attenuation remains strong along the Gulf Coast. In contrast, ray paths to the north, regardless of source location, exhibit very little attenuation, especially in northern Missouri and southern Iowa. <br />Regression models that incorporate near-receiver (distance-independent) attenuation due to thick sediments in the Gulf Coastal Plain successfully reduce path-related bias in the regression residuals for stations near the Gulf Coast. Dividing the central United States into three regions (the Gulf Coastal Plain, the Great Plains and the Midwest) further reduced bias, and allowed for the development of Q models in the Gulf Coastal Plain and the Great Plains. In the Gulf Coastal Plain, the Q model for that part of the ray path through the basement, from the earthquake to the base of the sediment deposits below the receiver, was found to be Q=(295±11)*f^(0.645±0.029). The model for attenuation in the sediment section near the receiver in the Gulf Coastal Plain is Q=(72±6.7)*f^(0.32±0.06) (velocity through the sediments is unconfirmed but thought to be approximately 1 km/s). The Q model for the Great Plains is Q=(692±61.3)*f^(0.43±0.07). The Midwest region exhibited extremely complicated behavior: the data indicate little or no attenuation of amplitudes in the frequency band from approximately 0.7 to 2.0 Hz. As a consequence, Q in the Midwest region in that frequency range could not be realistically determined. <br /><br>Master of Science
43
Andre, Daniel Batista. "Weyl expansion for multicomponent wave equations." Thesis, University of Bristol, 2000. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.310887.
Повний текст джерела
44
Drysdale, Euain Fraser. "Modelling of equatorial wave motions in the middle atmosphere." Thesis, University of Oxford, 1998. http://ora.ox.ac.uk/objects/uuid:9ae75869-a15b-465e-af64-c608cca8b34c.
Повний текст джерелаАнотація:
A three-dimensional mechanistic model of the middle atmosphere is used to model various classes of equatorial wave motions that are observed in the atmosphere. These waves are thought to be largely responsible for the forcing of the quasi-biennial oscillation (QBO) in the tropical lower stratosphere. By generating a combination of different classes of equatorial waves in the model, an oscillation which has many similarities to the observed QBO is produced in the model. The numerical model used is run in a variety of configurations, including running it at different vertical resolutions and with two different radiation parameterisation schemes. It is found that model used in the project must be modified to allow the accurate modelling of equatorial waves. Several modelling problems are encountered while applying the modifications necessary in the model; the steps necessary to rectify these problems are detailed in this thesis. Equatorial waves are then forced in this modified model under a range of conditions and their interaction with the mean flow is observed. Their dissipation mechanisms and the influence of changes in model conditions on these waves are investigated. The model is found to be generally very successful in modelling these equatorial waves. Modelling of the QBO is one of the principle aims of this project and a QBO is successfully generated in a variety of model configurations. The modelled QBO is found to be sensitive to changes in the temperature structure of the model (brought about by changes in the model's radiation scheme) and several experiments are performed in order to learn what processes affect this sensitivity. A QBO is then generated in series of model runs where the state of the model is varied from very idealised (where temperatures in the model are relaxed towards an isothermal state by the radiation scheme) to a state that is far more realistic (a perpetual January run with realistic boundary information). A fairly realistic QBO is generated throughout many of the experiments. The properties of this QBO are investigated and compared to the observed QBO. The model is then run with planetary waves forced in addition to the QBO. The interaction between the planetary waves and the QBO is investigated. It is found that the planetary waves have little effect on the QBO propagation. The QBO however has a fairly strong modulating effect on the planetary waves in certain regions.
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Olivares, Nicole Michelle. "Accuracy of Wave Speeds Computed from the DPG and HDG Methods for Electromagnetic and Acoustic Waves." PDXScholar, 2016. http://pdxscholar.library.pdx.edu/open_access_etds/2920.
Повний текст джерелаАнотація:
We study two finite element methods for solving time-harmonic electromagnetic and acoustic problems: the discontinuous Petrov-Galerkin (DPG) method and the hybrid discontinuous Galerkin (HDG) method.
The DPG method for the Helmholtz equation is studied using a test space normed by a modified graph norm. The modification scales one of the terms in the graph norm by an arbitrary positive scaling parameter. We find that, as the parameter approaches zero, better results are obtained, under some circumstances. A dispersion analysis on the multiple interacting stencils that form the DPG method shows that the discrete wavenumbers of the method are complex, explaining the numerically observed artificial dissipation in the computed wave approximations. Since the DPG method is a nonstandard least-squares Galerkin method, its performance is compared with a standard least-squares method having a similar stencil.
We study the HDG method for complex wavenumber cases and show how the HDG stabilization parameter must be chosen in relation to the wavenumber. We show that the commonly chosen HDG stabilization parameter values can give rise to singular systems for some complex wavenumbers. However, this failure is remedied if the real part of the stabilization parameter has the opposite sign of the imaginary part of the wavenumber. For real wavenumbers, results from a dispersion analysis for the Helmholtz case are presented. An asymptotic expansion of the dispersion relation, as the number of mesh elements per wave increase, reveal values of the stabilization parameter that asymptotically minimize the HDG wavenumber errors. Finally, a dispersion analysis of the mixed hybrid Raviart-Thomas method shows that its wavenumber errors are an order smaller than those of the HDG method.
We conclude by presenting some contributions to the development of software tools for using the DPG method and their application to a terahertz photonic structure. We attempt to simulate field enhancements recently observed in a novel arrangement of annular nanogaps.
46
Sherkat, Navid. "Approximation of Antenna Patterns With Gaussian Beams in Wave Propagation Models." Thesis, Linnéuniversitetet, Institutionen för datavetenskap, fysik och matematik, DFM, 2011. http://urn.kb.se/resolve?urn=urn:nbn:se:lnu:diva-14437.
Повний текст джерелаАнотація:
The topic of antenna pattern synthesis, in the context of beam shaping, is considered. One approach to this problem is to use the method of point matching. This method can be used to approximate antenna patterns with a set of uniformly spaced sources with suitable directivities. One specifies a desired antenna pattern and approximates it with a combination of beams. This approach results in a linear system of equations that can be solved for a set of beam coefficients. With suitable shifts between the matching points and between the source points, a good agreement between the assumed and the reproduced antenna patterns can be obtained along an observation line. This antenna modelling could be used in the program NERO to compute the field at the receiver antenna for a realistic 2D communication link. It is verified that the final result is not affected by the details of the antenna modelling.
47
Choi, Man Soo. "Computer-aided design models for millimeter-wave suspended-substrate microstrip line." Thesis, Monterey, California : Naval Postgraduate School, 1990. http://handle.dtic.mil/100.2/ADA227259.
Повний текст джерелаАнотація:
Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, March 1990.<br>Thesis Advisor(s): Atwater, H.A. Second Reader: Lee, H. M. "March 1990." Description based on signature page as viewed on August 26, 2009. DTIC Descriptor(s): Strip Transmission Lines, Computer Aided Design, Computerized Simulation, Parameters, Microwave Equipment, Radar, Full Wave Rectifiers, Transmittance, Resonant Frequency, Construction, Wave Propagation, Coefficients, Boundary Value Problems, Resonators, Circuits, Discontinuities, Ka Band, Models, Scattering, Equivalent Circuits, Frequency. Author(s) subject terms: Millimeter wave, suspended substrate, design model. Includes bibliographical references (p. 78-79). Also available online.
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Holt-Phoenix, Marianne S. (Marianne Shue). "Wave propagation in finite element and mass-spring-dashpot lattice models." Thesis, Massachusetts Institute of Technology, 2006. http://hdl.handle.net/1721.1/35683.
Повний текст джерелаАнотація:
Thesis (Nav. E. and S.M.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.<br>Includes bibliographical references (p. 42).<br>Numerical efficiency comparisons of a four-node finite element model (FEM), a mass-spring lattice model (MSLM), and a mass-spring-dashpot lattice model (MSDLM) are investigated. Specifically, the error in the ultrasonic phase speed with variations in Poisson's ratio and angle of incidence is evaluated in each model of an isotropic elastic solid. With regard to phase speed, materials with constant N grid spaces per P-wavelength having Poisson's ratios between 0.0 and 0.25 are modeled more accurately with the MSLM. Materials with Poisson's ratios between 0.35 and 0.5 and N grid spaces per P-wavelength are more accurately modeled with the FEM. Materials whose Poisson's ratio is between 0.25 and 0.35 are modeled equally accurately. With regard to phase speed, viscoelastic materials modeled with FEM and MSDLM show good agreement with known analytical solutions. The computational expense of all three models is also examined. The number of floating point operations (FLOPS) needed to achieve a specified phase speed accuracy is calculated for each different model. While the FEM and MSLM have nearly the same computation cost, the MSDLM is 5 times more costly than either the FEM or MSLM.<br>by Marianne S. Holt-Phoenix.<br>Nav.E.and S.M.
49
Cartledge, Nicholas P. "External and internal magnetohydrostatic models of quiescent solar prominences." Thesis, University of St Andrews, 1996. http://hdl.handle.net/10023/14029.
Повний текст джерелаАнотація:
Quiescent solar prominences are amongst the most interesting and yet least understood of the phenomena observed on the Sun and provide both the theorist and the observer with equally demanding challenges. The theoretical study of prominences is an important branch of solar physics as it contributes significantly to the overall understanding of the Sun and its atmosphere. One only needs to be presented with the illuminating fact that there is more mass contained in these bodies than in the remainder of the entire corona to be convinced of their importance. Although many of the physical mechanisms associated with prominence theory are important in their own right, they are also of much wider relevance for various other astrophysical phenomena. For example, radiative and magnetic instabilities are explored in detail in the context of solar prominences; yet clearly these are important processes that relate to many other branches of astrophysics. Prominences are intimately associated with solar flares which occur when a prominence loses equilibrium. Also, prominence eruptions are very important as they are closely connected with coronal mass ejections. These account for a large fraction of the total mass lost from the Sun and so are extremely important events, particularly when one considers the consequences as this plasma interacts with the Earth's environment. It is the period of global equilibrium of quiescent prominences, though, that is the focus of this thesis. Various models are proposed to help understand both the topology and supporting mechanisms of the external, coronal magnetic field, and also the internal prominence structure and the way in which the two regimes fit together. In Chapter 3 we extend a model for the equilibrium of a prominence sheet in a twisted magnetic flux-tube, given by Ridgway, Priest and Amari (1991), to incorporate a current sheet of finite height. This removes the discontinuity at the edge of the tube and provides a shear-free outer boundary which enables the tube to be matched onto a background potential field. In addition, internal prominence solutions are found by expanding the sheet to a finite width and matching suitable magnetic profiles across this region. Next we consider a global model for the magnetic field structure surrounding a polar-crown prominence. We examine potential configurations generated from typical distributions of photospheric flux, and select solutions for which there is a location of dipped magnetic field where prominence material may collect and form. Once such a configuration is available, it is necessary to construct the ensuing prominence solution. We achieve this in Chapter 4 by considering a simplified form for the photospheric field. We show that the equilibrium contains a weighted, curved prominence sheet supported in the location of dipped magnetic field. The equilibrium requires an enhanced magnetic pressure below the sheet to support the component of weight in the normal direction. The internal equilibrium of curved or inclined prominence material has not been considered previously and so we formulate, in Chapter 6, a simple one-dimensional isothermal solution for a cut across the prominence. This is developed to allow for variations along the sheet and in this way an internal solution for the curved prominence of Chapter 4 is given, which matches onto the external potential polar-crown field. Finally, in Chapter 7, we rewrite this solution in terms of its constituent internal and external components and show how the composite solution switches between the two in a region of overlap, or transition region. From this, the internal plasma properties are deduced and realistic profiles for the pressure, density and temperature are obtained.
50
Wiese, Anne Jasmin [Verfasser]. "Assessing and Reducing the Uncertainty in Regional Wave and Coupled Wave-Atmosphere Models during Extreme Events / Anne Jasmin Wiese." Hamburg : Staats- und Universitätsbibliothek Hamburg Carl von Ossietzky, 2020. http://d-nb.info/1236695313/34.
Повний текст джерела