To see the other types of publications on this topic, follow the link: Wave interactions.
Dissertations / Theses on the topic 'Wave interactions'
Create a spot-on reference in APA, MLA, Chicago, Harvard, and other styles
Consult the top 50 dissertations / theses for your research on the topic 'Wave interactions.'
Next to every source in the list of references, there is an 'Add to bibliography' button. Press on it, and we will generate automatically the bibliographic reference to the chosen work in the citation style you need: APA, MLA, Harvard, Chicago, Vancouver, etc.
You can also download the full text of the academic publication as pdf and read online its abstract whenever available in the metadata.
Browse dissertations / theses on a wide variety of disciplines and organise your bibliography correctly.
1
Zhu, Qiang 1970. "Features of nonlinear wave-wave and wave-body interactions." Thesis, Massachusetts Institute of Technology, 2000. http://hdl.handle.net/1721.1/8853.
Full textAbstract:
Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 2000.<br>Includes bibliographical references (leaves 295-302).<br>Although nonlinear water waves have been the subject of decades of research, there are many problems that remain unsolved, especially in the cases when one or more of the following factors are involved: high-order nonlinear effects, moving boundaries, wavestructure interactions and complicated geometries. In this dissertation, a high-order spectral-element (HOSE) method is developed to investigate problems about nonlinear waves. An exponentially converging algorithm, it is able to be applied to solve nonlinear interactions between waves and submerged or surface-piercing bodies with high-order nonlinear effects. The HOSE method is applied to investigate dynamics of nonlinear waves and their interactions with obstacles. We first implement it to calculate the hydrodynamic forces and moments on a fixed underwater spheroid, with uniform current, different angles of attack and finite water depth included in the study. Extending this study to wave interaction with tethered bodies, we create an efficient simulation capability of moored buoys. Coupling the HOSE method with a robust implicit finite-difference solver of highly-extensible cables, our results show chaotic buoy motions and the ability for short wave generation. We then focus our attention on the free-surface patterns caused by nonlinear wave-wave and wave-body interactions. Starting with a two-dimensional canonical problem about the wave diffraction and radiation of a submerged circular cylinder, numerical evidences are obtained to corroborate that, for a fixed cylinder, a cylinder undergoing forced circular motion, or free to respond to incident waves, the progressive disturbances are in one direction only. The three-dimensional wave-wave interactions are studied. It is proved both analytically and numerically that new propagating waves could be generated by the resonant interactions between Kelvin ship waves and ambient waves. Another consequence of resonant wave-wave interactions is the instability of free-surface waves. In this dissertation, the three-dimensional unstable modes of plane standing waves and standing waves in a circular basin are identified numerically and then confirmed analytically. These investigations cover a large variety of nonlinear-wave problems and prove that the HOSE method is an efficient tool in studying scientific or practical problems.<br>by Qiang Zhu.<br>Ph.D.
2
Ferdousi, Mariya. "Nonlinear Wave-Wave Interactions in the Brain." Thesis, The University of Sydney, 2019. https://hdl.handle.net/2123/21410.
Full textAbstract:
Neural field theory of the corticothalamic system is used to analyze nonlinear wave-wave interactions in sleep and wake states and steady state visual evoked potential responses. The nonlinear power spectrum is analytically calculated by convolving the linear power spectrum with itself and other factors. Analysis shows that strong spectral peaks generate a harmonic at twice the original frequency with peak power proportional to the square of that of the original peak. Periodic sine and square wave stimuli are used to generate steady state visual evoked potential responses and to study stimulus-driven nonlinear corticothalamic dynamic interactions. Dual sine drives are then used to analyze the driven dynamics more clearly, without the complicating effects of a background spectrum. Numerical analysis shows that the nonlinear power spectrum embodies key nonlinear features, including harmonic and subharmonic generation, entrainment of alpha rhythm to periodic stimuli at the drive frequency, sum and difference frequencies due to wave-wave coalescence and decay. Further, the scaling properties of the key phenomena observed in nonlinear interactions are studied, verifying some of the theoretical predictions for these being generated by three-wave processes.
3
Sun, Haili. "Ray-tracing internal wave/wave interactions and spectral energy transfer /." Thesis, Connect to this title online; UW restricted, 1997. http://hdl.handle.net/1773/10973.
Full text
4
Kalkavage, Jean Hogan. "Nonlinear wave-wave interactions in ionospheric plasmas caused by injected VLF and HF waves." Thesis, Boston University, 2014. https://hdl.handle.net/2144/21184.
Full textAbstract:
Thesis (M.Sc.Eng.) PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you.<br>The study of wave-wave interactions in the ionosphere is important for designing communication systems, satellite systems, and spacecraft. Ionospheric research also informs laser and magnetic fusion plasma physics. This thesis focuses on two nonlinear wave-wave interactions in the ionosphere. The first interaction is a nonlinear mode conversion. Very Low Frequency (VLF) waves transmitted from the ground travel through the ionosphere as injected whistler waves. The whistler waves interact with naturally-occurring density fluctuations in the ionosphere and are mode converted into lower hybrid waves. The lower hybrid waves accelerate electrons along the geomagnetic field and the resulting beam mode Langmuir waves are detectable by radar. This type of mode conversion may combine additively with a four wave interaction with the same VLF wave as its source. Data collected at the Arecibo Observatory in Puerto Rico during the occurrence of spread F and sporadic E was analyzed. Plasma line enhancements may indicate the nonlinear mode conversion both separately from and in conjunction with the four wave interaction. The second nonlinear wave-wave interaction is the parametric decay instability (PDI) excited by High Frequency (HF) heater waves at the High Frequency Active Auroral Research Program facility in Gakona, Alaska. Resonant PDI cascades downwards, resulting in up-shifted ion line enhancements as detected by radar. This process has been detected in the presence of down-shifted ion line enhancements which may be caused by beating between PDI-produced Langmuir waves, or by naturally occurring ionospheric currents.<br>2031-01-01
5
Gibson, Richard Stewart. "Wave interactions and wave statistics in directional seas." Thesis, Imperial College London, 2005. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.413426.
Full text
6
Naciri, Mamoun. "On wave-wave interactions on the ocean surface." Thesis, Massachusetts Institute of Technology, 1992. http://hdl.handle.net/1721.1/47312.
Full text
7
Bird, Charlotte C. "Nonlinear interactions of water waves, wave groups and beaches." Thesis, University of Bristol, 1999. http://hdl.handle.net/1983/c8fedc4e-9c73-4791-b1d8-b4ff14646025.
Full text
8
Bourne, Neil Kenneth. "Shock wave interactions with cavities." Thesis, University of Cambridge, 1990. https://www.repository.cam.ac.uk/handle/1810/250963.
Full text
9
Andreae, Sigrid Barbara Margrid. "Wave interactions with material interfaces /." Aachen : Shaker, 2008. http://bvbr.bib-bvb.de:8991/F?func=service&doc_library=BVB01&doc_number=016487715&line_number=0001&func_code=DB_RECORDS&service_type=MEDIA.
Full text
10
Jones, David Caradoc. "Wave interactions in photorefractive materials." Thesis, University of Oxford, 1989. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.257934.
Full text
11
Smith, Sean Paul. "Laboratory Experiments on Colliding Nonresonant Internal Wave Beams." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3300.
Full textAbstract:
Internal waves are prominent fluid phenomena in both the atmosphere and ocean. Because internal waves have the ability to transfer a large amount of energy, they contribute to the global distribution of energy. This causes internal waves to influence global climate patterns and critical ocean mixing. Therefore, studying internal waves provides additional insight in how to model geophysical phenomena that directly impact our lives. There is a myriad of fluid phenomena with which internal waves can interact, including other internal waves. Equipment and processes are developed to perform laboratory experiments analyzing the interaction of two colliding nonresonant internal waves. Nonresonant interactions have not been a major focus in previous research. The goal of this study is to visualize the flow field, compare qualitative results to Tabaei et al., and determine the energy partition to the second-harmonic for eight unique interaction configurations. When two non-resonant internal waves collide, harmonics are formed at the sum and difference of multiples of the colliding waves' frequencies. In order to create the wave-wave interaction, two identical wave generators were designed and manufactured. The interaction flow field is visualized using synthetic schlieren and the energy entering and leaving the interaction region is analyzed. It is found that the energy partitioned to the harmonics is much more dependent on the general direction the colliding waves approach each other than on the angle. Depending on the configurations, between 0.5 and 7 percent of the energy within the colliding waves is partitioned to the second-harmonics. Interactions in which the colliding waves have opposite signed vertical wavenumber partition much more energy to the harmonics. Most of the energy entering the interaction is dissipated by viscous forces or leaves the interaction within the colliding waves. For all eight configurations studied, 5 to 8 percent of the energy entering the interaction has an unknown fate.
12
Longley, Kaitlyn E. "WAVE CURRENT INTERACTIONS AND WAVE-BLOCKING PREDICTIONS USING NHWAVE MODEL." Monterey, California. Naval Postgraduate School, 2013. http://hdl.handle.net/10945/32857.
Full textAbstract:
Wave blocking in river inlets is examined using the NHWAVE (Non-Hydrostatic Wave) model under development. Blocking flows at river inlets are a significant hazard to navigation. Refractive and shoaling effects contribute to the enhancement of wave field energy, causing instabilities and breaking, resulting in energy dissipation and transfer at the blocking point. The non-linearity of wave-current interactions and wave breaking makes the dynamics of blocking flows difficult to model. Current efforts to use wave-averaged models are insufficient to describe the complex dynamics that occur within one or two wavelengths of a blocking point. NHWAVE uses the non-hydrostatic, incompressible Navier-Stokes equations to model fully dispersive wave processes in the time domain. Monochromatic wave cases are explored and compared with lab experiments of energy dissipation due to wave breaking under conditions of strong opposing current, conducted in 2002 at the University of Delaware by A. Chawla and T. J. Kirby. The model was initially unable to resolve the boundary conditions necessary to model wave blocking in a tank domain. However, developments to the numerical scheme in NHWAVE have advanced its capability in this regard. Due to the difficulties of modeling the dynamics of wave blocking and the boundary conditions in a wave tank, only preliminary results were obtained. NHWAVE needs further development; it shows promise, however, to be able to predict wave reflection, blocking, and dissipation on a strong opposing current.
13
Semedo, Alvaro. "Atmosphere-ocean Interactions in Swell Dominated Wave Fields." Doctoral thesis, Uppsala universitet, Geovetenskapliga sektionen, 2010. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-130650.
Full textAbstract:
Ocean wind waves represent the atmosphere-ocean boundary, playing a central role in the air-sea exchanging processes. Heat, mass and momentum are transferred across this boundary, with waves mediating the exchange of principally the momentum between the winds and the ocean surface. During the generation process waves are called wind sea. When they leave their generation area or outrun their generating wind they are called swell. The wave field can be said to be dominated either by wind sea or swell. Depending on the wave regime the momentum and energy exchanging processes and the degree of coupling between the waves and the wind is different. During the growing process, waves act as a drag on the surface wind and the momentum flux is directed downward. When swell dominates the wave field a reverse momentum flux mechanism occurs triggered by swell waves traveling considerably faster than the surface winds. The momentum transfer is now directed from the waves to the atmosphere, and takes place because swell waves perform work on the atmosphere as part of their attenuation process. This upward momentum transfer has an impact on the lower atmosphere dynamics, and on the overall turbulence structure of the boundary layer. A detailed qualitative climatology of the global wind sea and swell fields from wave reanalysis data, is presented, revealing a very strong swell dominance of the World Ocean. The areas of larger potential impact of swell on the atmosphere, from a climatological point of view, are also studied. A model that reproduces the swell impact on the lower atmosphere dynamics, conceptually based on the energy transfer from the waves to the atmosphere, is presented – a new parameterization for the wave-induced stress is also proposed. The model results are compared with field observations. A modeling simulation, using a coupled wave-atmosphere model system, is used to study the impact of swell in a regional climate model, by using different formulations on how to introduce the wave state effect in the modeling system.<br>Gränsen mellan hav och atmosfär beskrivs av vågor, dessa spelar en central roll i utbytesprocesser mellan hav och atmosfär. Värme, massa och rörelsemängd överförs vid ytan och utbytet av rörelsemängd mellan vind och havsyta styrs i stor utsträckning av vågorna. Då vågor skapas kallas de för vinddrivna vågor. När vågorna sedan lämnar området där de genererats eller rör sig fortare än den vind som genererat dem kallas de dyning. Ett vågfält kan sägas vara dominerat av antingen vinddrivna vågor eller dyningsvågor. Beroende på vilken vågregim som råder så är kopplingen mellan vågor och vind olika och därmed också utbytesprocesserna för rörelsemängd och energi. Då vågorna genereras fungerar de som en bromsande kraft för vinden och impulsutbytet är nedåtriktat. När dyning dominerar vågfältet inträffar en mekanism för omvänt impulsutbyte som sätts igång av dyningsvågor som färdas avsevärt snabbare än vinden. Rörelsemängd överförs då från vågorna till atmosfären, eftersom dyningsvågorna utför arbete på atmosfären då de dämpas. Den uppåtriktade transporten av rörelsemängd har en stor effekt på dynamiken och turbulensstrukturen i lägre delen av atmosfären. En detaljerad kvalitativ klimatologi av globala vågfält (vinddrivna och dyning) från återanalysdata presenteras och visar att dyning dominerar vågfältet på världshaven. Områden där man kan förvänta sig störst effekt av dyning på atmosfären har identifierats. En konceptuellt baserad modell som reproducerar effekten av dyning på dynamiken i lägre delen av atmosfären presenteras. Modellen styrs av överföring av energi från vågor till atmosfären. I modellen föreslås även en ny parameterisering för våginducerad kraft på havsytan. Modellresultaten är utvärderade mot fältmätningar. En regional klimatmodell, med ett kopplat våg-atmosfärssystem, har använts för att studera den långtida effekten av dyning vid klimatsimulering. Olika formuleringar för beskrivningen av vågornas effekt på atmosfären har använts, beroende på om vinddrivna vågor eller dyning dominerar vågfältet.
14
Xue, Ming 1967. "Three-dimensional fully-nonlinear simulations of waves and wave body interactions." Thesis, Massachusetts Institute of Technology, 1997. http://hdl.handle.net/1721.1/10216.
Full text
15
Chapman, John Richard. "Ultrasonic wave interactions with magnetic colloids." Thesis, University of Nottingham, 2001. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.366409.
Full text
16
Weaver, P. M. "Shock wave interactions with aqueous foams." Thesis, University of Southampton, 1991. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.292434.
Full text
17
Frank, Donya P. "Wave-Current Bottom Boundary Layer Interactions." The Ohio State University, 2008. http://rave.ohiolink.edu/etdc/view?acc_num=osu1229087949.
Full text
18
Ooi, Eng Seng. "Rayleigh wave interactions with tribological contacts." Thesis, University of Sheffield, 2015. http://etheses.whiterose.ac.uk/9963/.
Full textAbstract:
The use of ultrasonic reflectometry is a proven method of condition monitoring machine systems. The working principles are simple. A burst of ultrasonic signal is sent to the interface of interest where reflection of the signal takes place. The manner in which reflection takes place depends on the properties of the interface. As such, the reflected signal carries information regarding the interface that can be extracted with proper techniques. However, the use of ultrasonic reflectometry in condition monitoring is not without its limitations. Conventional ultrasound techniques make use of ultrasonic bulk waves that travel through the body of a given material. Problems arise when the medium through which the wave travels is attenuative. This prevents any passage of ultrasonic signals as most of the energy will be absorbed by the material. In addition, most components have complex designs, requiring that the signal pass through multiple interfaces before reaching the interface of interest. Reflections occur at these intermediate interfaces, reducing the overall energy content of the signal. In order to overcome these issues, the use of Rayleigh wave as an alternative is researched in the work carried out here. Instead of having to travel through the bulk of the material, Rayleigh waves function by propagating along the free surface of the said material, thereby circumventing the existing issues with the use of conventional bulk waves. The research here was carried out to seek an understanding of how Rayleigh waves interact with a contact interface. This was performed on three separate fronts. First, a novel analytical model was developed by modelling the contact interface as a series of springs. It is discovered that the stiffness of the springs are directly proportional to the reflection coefficient of the Rayleigh wave incident upon the interface. The implication of this finding is that rough interfaces will have a lesser reflection coefficient (due to decreased stiffness), with a perfectly smooth interface giving the maximum reflection coefficient obtainable from a particular interface. This was then followed by studies performed using both finite element simulations as well as experimental work. Data from all three studies (analytical model, finite element simulations and experimental work) were compared against each other and it was shown that a good agreement exists between all three methods. Exploratory work on lip seals were performed in order to research the potential of using Rayleigh wave as a condition monitoring tool. By measuring the delay in the time of arrival of a Rayleigh wave pulse reflected from the sealing zone, it is possible to measure the extent of misalignment that is present in a lip seal. Axial misalignments of the lip between 6mm to 8mm were successfully measured. Additional work in measuring the degradation of a lubricating film via evaporation was qualitative in nature, with the amplitude of the reflected pulse slowly decreasing as the layer of fluid at the sealing zone diminishes via evaporation.
19
Wu, Cheng Y. (Cheng Yi) 1938. "Wave-wave interactions and the infrasonic pressure field in the ocean." Thesis, University of Auckland, 1988. http://hdl.handle.net/2292/2469.
Full textAbstract:
Building on Kibblewhite's long term investigations of the nonlinear wave-wave interactions and the infrasonic ocean noise and the microseisms these induce, this thesis further explores the physical nature of these processes. The classical description of this interaction, which takes into account only the homogeneous component of the induced field, has been extended to include the inhomogeneous component. A complete expression for the wave induced noise spectrum is established following a geometrical analysis of the dispersion relations among interacting waves. The relative importance of these two components and their directivity properties are also calculated and discussed. It is shown that while at observation points deeper than 500 meters the effects of the inhomogeneous component can be regarded as negligible, it can cause an increase of noise level of up to 40 dB in the region near the surface of the sea. Furthermore, in contrast to the nearly omni-directional distribution of the homogeneous component of the induced acoustic field, there is a tendency for the energy associated with the inhomogeneous component to focus in the wind direction. Based upon a multilayer analysis of a visco-elastic geoacoustic model, Green's functions and the spectral transfer functions relating the surface source pressure field to the underwater noise and microseism fields are derived for both near and far field cases. A 3-dimensional presentation defined on the dispersion plane (frequency and horizontal wave number) is introduced to describe the sea bottom reflection-loss and, Green's functions, and is extended to include the inhomogeneous region for the first time. The characteristics of this 3-D presentation are explained in terms of the geoacoustic parameters. The influence of the interaction of multiple seas (and swell) on the induced acoustic field are also discussed in this thesis. All these effects are considered in the calculation of the synthetic spectra of both the noise and microseism field. When compared with measured data excellent agreement is found between the theoretical and experimental results, which provides further confirmation that the nonlinear interaction is the most important source of the infrasonic ocean noise, as well as confirming the basic validity of the procedure introduced by Kibblewhite and Ewans to derive the ocean noise spectra from microseism records.
20
Blackhurst, Tyler D. "Numerical Investigation of Internal Wave-Vortex Dipole Interactions." BYU ScholarsArchive, 2012. https://scholarsarchive.byu.edu/etd/3133.
Full textAbstract:
Three-dimensional linear ray theory is used to investigate internal waves interacting with a Lamb-Chaplygin pancake vortex dipole. These interactions involve waves propagating in the same (co-propagating) and opposite (counter-propagating) horizontal directions as the dipole translation. Co-propagating internal waves in the vertical symmetry plane between the vortices of the dipole can approach critical levels where the wave energy is absorbed by the dipole or where the waves are overturned and possibly break. As wave breaking cannot be simulated with this linear model, changes in wave steepness are calculated to aid in estimating the onset of breaking. Counter-propagating internal waves in the vertical symmetry plane can experience horizontal and vertical reflections, including turning points similar to waves in two-dimensional steady shear. Wave capture is also a possible effect of either type of interaction, depending on initial wave properties and positioning relative to the vortex dipole. Away from the vertical symmetry plane, a spanwise converging (focusing) and diverging (defocusing) of wave energy is observed in co- and counter-propagating interactions as symmetric off-center rays interact with the dipole's individual vortices. Some off-center rays experience multiple horizontal refractions similar to wave trapping.
21
Barker, Adrian John. "Tidal interactions between planets and stars." Thesis, University of Cambridge, 2011. https://www.repository.cam.ac.uk/handle/1810/240581.
Full textAbstract:
Since the first discovery of an extrasolar planet around a solar-type star, observers have detected over 500 planets outside the solar system. Many of these planets have Jovian masses and orbit their host stars in orbits of only a few days, the so-called 'Hot Jupiters'. At such close proximity to their parent stars, strong tidal interactions between the two bodies are expected to cause significant secular spin-orbit evolution. This thesis tackles two problems regarding the tidal evolution of short-period extrasolar planets. In the first part, we adopt a simple model of the orbit-averaged effects of tidal friction, to study the tidal evolution of planets on inclined orbits. We also analyse the effects of stellar magnetic braking. We then discuss the implications of our results for the importance of Rossiter-Mclaughlin effect observations. In the second part, we study the mechanisms of tidal dissipation in solar-type stars. In particular, internal gravity waves are launched at the interface of the convection and radiation zones of such a star, by the tidal forcing of a short-period planet. The fate of these waves as they approach the centre of the star is studied, primarily using numerical simulations, in both two and three dimensions. We find that the waves undergo instability and break above a critical amplitude. A model for the tidal dissipation that results from this process is presented, and its validity is verified by numerical integrations of the linear tidal response, in an extensive set of stellar models. The dissipation is efficient, and varies by less than an order of magnitude between all solar-type stars, throughout their main-sequence lifetimes, for a given planetary orbit. The implications of this mechanism for the survival of short-period extrasolar planets is discussed, and we propose a possible explanation for the survival of all of the extrasolar planets currently observed in short-period orbits around F, G and K stars. We then perform a stability analysis of a standing internal gravity wave near the centre of a solar-type star, to understand the early stages of the wave breaking process in more detail, and to determine whether the waves are subject to weaker parametric instabilities, below the critical amplitude required for wave breaking. We discuss the relevance of our results to our explanation for the survival of short-period planets presented in the second part of this thesis. Finally, we propose an alternative mechanism of tidal dissipation, involving the gradual radiative damping of the waves. Based on a simple estimate, it appears that this occurs even for low mass planets. However, it is in conflict with current observations since it would threaten the survival of all planets in orbits shorter than 2 days. We discuss some hydrodynamic instabilities and magnetic stresses which may prevent this process.
22
Ellin, Hannah Catherine. "Aspects of wave interactions in photorefractive materials." Thesis, University of Oxford, 1994. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.296992.
Full text
23
Fashanu, Udofe Peter Taiwo. "Simulation and analysis of wave-structure interactions." Thesis, University of Newcastle Upon Tyne, 2011. http://hdl.handle.net/10443/1310.
Full textAbstract:
Today, it is widely recognized that Computational Fluid Dynamics (CFD) methodologies should be used for the analysis of Engineering systems and that design and method of simulation must be practical and realistic to provide cost effective solutions. The recent development in CFD of Engineering Structures has led to the adoption of the Eulerian and Lagrangian concepts of numerical analysis. Although the importance of these concepts cannot be overemphasised in offshore structures hydrodynamics, thus the choice of a concept to define the flow field surrounding a structure is one of the fundamental problems identifiable with marine hydrodynamics, especially where non linear effects become paramount. A narrow focus and use of a concept not adaptable to the ship hydrodynamic problem cannot guarantee the development of a good CFD code. Traditional approaches using the Eulerian and Lagrangian concepts have progressed relatively in the last three decades with the continuous rise in computer development. Smooth Particle Hydrodynamics (SPH), Volume of Fluid Method (VOF), Boundary Integral Method are but a few methods that have been widely used in recent applications. However when a detailed description, evaluation and analysis of the flow field is required in a ship hydrodynamics problem, some of these methods fall short of expectation when they have to strictly adhere to some given assumptions to make the computational analysis stable and provide results. In the use of Eulerian and Lagrangian concepts in fluid dynamics, mathematical skill is an essential requirement for solving flow problems. Modeling methods require discretization of the flow field equations which can be linear and non linear, depending on the parameters for simulation. The understanding of mathematical principles such as Partial differential equations, Fourier transforms and integrals, Integral calculus, Complex Analysis, Matrices, Vectors, Greens Function, Bessel Function, etc are necessary for solving the various equations of fluid motion when calculating the properties of the flow field associated with the hydrodynamic problem. Solution techniques which have the attributes of providing stability, consistency, convergence and accuracy are part of the mathematical requirements for a valid algorithm. Moving Particle Semi - Implicit Method is a computational method for incompressible fluid flow problems. MPS is a lagrangian particle method with robust capability for numerical representation. Particle interaction models representing differential operators in the Navier Stokes equation are proposed for divergence, gradient and laplacian. Boundary interfaces are transformed to interactions between particles. Computational difficulties associated with Eulerian methods such as numerical diffusion and regriding due to fragmentation and large deformations can be overcome with MPS method. This study addresses in detail the MPS method as a computational tool for wave - structure interactions. Investigation of both laboratory and numerical experiments associated with Wave - Structure Interactions were the primary focus of this study with the Development of a 2-dimensional MPS Simulation and Analysis of Wedge Water entries code, and Green Water flow simulation and effects on FPSO deck structure. Computational codes were developed for the prediction of deck flow and wave loads on the deck structure using the Navier Stokes equations. An experimental study was carried out at the Newcastle University Marine Laboratory in order to understand the detailed nature of green sea physics. Green Sea effects were measured on a model FPSO. Empirical relations and data obtained from the experiment were used in the numerical prediction code to obtain the deck flow pattern and validate the wave loads on the deck structure using the MPS method. The experiment on merit was necessary to test the capability of the hydrodynamics facility and provide understanding of the underlying principles surrounding the green water phenomena.
24
Ye, Jianhong. "Numerical analysis of Wave-Seabed-Breakwater interactions." Thesis, University of Dundee, 2012. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.604579.
Full text
25
King, Daniel Martin. "Wind/wave interactions in the surf zone." Thesis, University of Nottingham, 1994. http://eprints.nottingham.ac.uk/12802/.
Full textAbstract:
Wind/wave interactions in the surf zone are studied using a wave tank and environmental wind tunnel. The wind simulation is achieved over a relatively short fetch using accelerated growth techniques at a scale of roughly 1:100. Waves are scaled at approximately 1:50, and consequently there is some scaling mis-match between the wind and wave simulations. Results show that wind has a significant effect on the breaking of the waves. Both breaker location and breaker type are shown to be affected by the wind. Results are in agreement with those of Douglass (1989 & 1990), who used a wind/wave flume to simulate the prototype conditions, but made no attempt to correctly simulate the turbulence in the air flow. The main findings, are that onshore winds promote spilling waves and increase the surf zone width, whereas offshore winds promote plunging waves, decreasing surf zone width. Hot-film measurements of the air flow over the waves show that there exists significant differences between the air flow structure of offshore and onshore winds over the surf zone. Under offshore winds, the surf zone exerts a large drag on the air flow, dramatically increasing turbulence intensities aerodynamic roughness z0, and friction velocity, u*, near the point of wave breaking. Under onshore winds the air flow is less affected and at the point of wave breaking, z0 for onshore winds is an order of magnitude lower than the value under offshore winds. Phase-averaging techniques indicate large wave-induced perturbations to the mean velocity over the waves, and these are present to heights of up to 5 or 6 times the breaker height over the point of wave breaking. Spectra indicate that for onshore winds large wave-frequency fluctuations are present at the shore. Additionally, studies of particle motion offshore of the surf zone indicate wind effects on the drift velocities of suspended particles, although the precise nature of the wind effect was not clear.
26
Baddeley, Lisa. "Wave-particle interactions in the terrestrial magnetosphere." Thesis, University of Leicester, 2003. http://hdl.handle.net/2381/30668.
Full textAbstract:
This thesis examines small scale poloidal mode magnetohydrodynamic waves which have an energy generation mechanism internal to the magnetosphere in the form of unstable particle populations. The energy from these particles is fed into a resonant wave mode and, ultimately, dissipated in the terrestrial ionosphere. By analysing Ion Distribution Functions (IDFs) the statistical occurrence of the driving magnetospheric particle populations is presented. Results indicate that the dominant driving particle populations are those of ~10 - 40 keV protons. The free energy of the particles has been quantified, revealing the dominance of the lower energy particle populations. The majority of unstable low energy protons contain > 1010 J of free energy in comparison to the higher energy protons which contain < 109 J. Using this method, one event, using conjugate ionospheric - magnetospheric data is examined and compared to a similar conjugate event of a rare subset of small scale waves called Giant Pulsations (Pgs). The available free energy is compared to the energy dissipated into the conjugate ionospheres. Estimates of the energy at the source and sink reveal that ~ 1010 J is transferred for the first event. Pgs are shown to transfer ten times this energy. The statistical study reveals that 1010 J is frequently available from unstable IDFs but 1011 J is not, thus providing an exploration for both the rarity of Pgs and the ubiquity of other small scale waves. Observations also suggest that drawn sector waves are driven by the drift-bounce resonance mechanism, while in the dark sector waves are driven by both drift and drift-bounce resonance mechanisms. Additionally, ionospheric observations indicate that the occurrence of small scale pulsations could be more abundant than previously thought. This implies that the quantity of energy being transported round the magnetospheric cavity and into the ionosphere via wave-particle interactions has previously been underestimated.
27
Touber, Emile. "Unsteadiness in shock-wave/boundary layer interactions." Thesis, University of Southampton, 2010. https://eprints.soton.ac.uk/161073/.
Full textAbstract:
The need for better understanding of the low-frequency unsteadiness observed in shock wave/turbulent boundary layer interactions has been driving research in this area for several decades. This work investigates the interaction between an impinging oblique shock and a supersonic turbulent boundary layer via large-eddy simulations. Special care is taken at the inlet in order to avoid introducing artificial low-frequency modes that could affect the interaction. All simulations cover extensive integration times to allow for a spectral analysis at the low frequencies of interest. The simulations bring clear evidence of the existence of broadband and energetically-significant low-frequency oscillations in the vicinity of the reflected shock, thus confirming earlier experimental findings. Furthermore, these oscillations are found to persist even if the upstream boundary layer is deprived of long coherent structures. Starting from an exact form of the momentum integral equation and guided by data from large-eddy simulations, a stochastic ordinary differential equation for the reflectedshock foot low-frequency motions is derived. This model is applied to a wide range of input parameters. It is found that while the mean boundary-layer properties are important in controlling the interaction size, they do not contribute significantly to the dynamics. Moreover, the frequency of the most energetic fluctuations is shown to be a robust feature, in agreement with earlier experimental observations. Under some assumptions, the coupling between the shock and the boundary layer is mathematically equivalent to a first-order low-pass filter. Therefore, it is argued that the observed lowfrequency unsteadiness is not necessarily a property of the forcing, either from upstream or downstream of the shock, but simply an intrinsic property of the coupled dynamical system.
28
Nové-Josserand, Clotilde. "Converting wave energy from fluid-elasticity interactions." Thesis, Sorbonne Paris Cité, 2018. http://www.theses.fr/2018USPCC124/document.
Full textAbstract:
Le développement des systèmes houlomoteurs ainsi que la gestion du littoral reposent sur une bonne compréhension des mécanismes liés aux interactions houle-structure. Dans cette thèse, nous nous intéressons à l'étude d'un champ de structures flexibles soumises à des ondes de surface, en vue de développer un système qui puisse à la fois atténuer les vagues et absorber l'énergie qui leur est associée de manière efficace. Les résultats présentés se basent autour d'expériences réalisées dans des installations de petite échelle, dans lesquelles la disposition spatiale des objets flexibles est le principal paramètre étudié. Dans un premier temps, nous caractérisons notre champ modèle afin d'évaluer l'influence de divers paramètres (configuration, flexibilité, fréquences des vagues) sur la distribution de l'énergie dans le système. Sur la base de ces résultats, nous développons ensuite un modèle d'interférences permettant de décrire les observations globales du système à partir de paramètres locaux connus, associés à une portion unitaire du champ. Ce modèle nous sert ensuite d'outil pour l'exploration d'une multitude de configurations spatiales, afin de déterminer le choix optimal vis-à-vis de l'atténuation et de l'absorption des vagues incidentes. Enfin, une campagne de mesures supplémentaire est utilisée afin d'expliquer les résultats obtenus avec le modèle et d'identifier les principes sous-jacents à cette optimisation<br>Understanding the mechanisms involved in wave-structure interactions is of high interest for the development of efficient wave energy harvesters as well as for coastal management. In this thesis, we study the interactions of surface waves with a model array of slender flexible structures, in view of developing an efficient system for both attenuating and harvesting wave energy. The presented results are based around experimental investigations, by means of small scale facilities, in which the spatial arrangement of the flexible objects is the key parameter of study. The model array is first characterised by evaluating the role played by various parameters (configuration, flexibility, wave frequency) on the energy distribution in our system. Following these first observations, an interference model is then developed in order to describe the observed global effects of the array on both the wave field and the blade dynamics, based on known local parameters of a unit item of the array. This model then serves as a tool for exploring many possible array configurations, in order to determine the optimal choice regarding both the attenuation and the absorption of the imposed waves. A final experimental study is presented, in which the key results from the interference model are evaluated and the underlying principles of array optimisation are identified
29
Koo, Weoncheol. "Fully nonlinear wave-body interactions by a 2D potential numerical wave tank." Diss., Texas A&M University, 2003. http://hdl.handle.net/1969.1/1118.
Full textAbstract:
A 2D fully nonlinear Numerical Wave Tank (NWT) is developed based on the potential theory, mixed Eulerian-Lagrangian (MEL) time marching scheme, and boundary element method (BEM). Nonlinear Wave deformation and wave forces on stationary and freely floating bodies are calculated using the NWT. For verification, the computed mean, 1st, 2nd, and 3rd order wave forces on a single submerged cylinder are compared with those of Chaplin's experiment, Ogilvie's 2nd-order theory, and other nonlinear computation called high-order spectral method. Similar calculations for dual submerged cylinders are also conducted. The developed fully nonlinear NWT is also applied to the calculations of the nonlinear pressure and force of surface piercing barge type structures and these obtained results agree with experimental and theoretical results. Nonlinear waves generated by prescribed body motions, such as wedge type wave maker or land sliding in the coastal slope area, can also be simulated by the developed NWT. The generated waves are in agreement with published experimental and numerical results. Added mass and damping coefficients can also be calculated from the simulation in time domain. For the simulation of freely floating barge-type structure, only fully nonlinear time-stepping scheme can accurately produce nonlinear body motions with large floating body simulations. The acceleration potential method, which was developed by Tanizawa (1996), is known to be the most accurate, consistent and stable. Using acceleration potential method, in the present study, the series of motions and drift forces were calculated over a wide range of incident wave frequencies including resonance region. To guarantitatively compare the nonlinear contribution of free-surface and body-boundary conditions, the body-nonlinear-only case with linearized free-surface condition is separately simulated. All the floating body motions and forces are in agreement with experimental results. Finally, the NWT is extended to fully nonlinear wave-body-current interactions of freely floating bodies, which has not been published in the open literature until now.
30
McLandress, Charles. "A study of wave-wave interactions in a steady-state stratospheric model /." Thesis, McGill University, 1988. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=75839.
Full textAbstract:
Interactions among stationary planetary waves in the winter stratosphere are studied using steady-state quasi-geostrophic models from both a theoretical and numerical point of view.<br>A triad of small amplitude waves is examined analytically using a constant zonal wind $ beta$-plane model in which dissipation is required for the waves to interact. The nature of the modifications to the linear solutions is found to depend both on the propagation characteristics and the zonal wavenumber of the modes.<br>Numerical solutions are determined using a climatological basic state and boundary forcing. The changes to the linear structure are relatively weak. Zonal wavenumber 1 is the most affected, experiencing primarily an increase in amplitude in the vicinity of 65$ sp circ$N, 26 km. As a direct consequence of the almost linear relationship found to exist between the zonal streamfunction and the zonal potential vorticity in middle and northerly latitudes, the wave-wave interactions are, to a first approximation, dissipation-induced. The presence of weak dissipation in this region implies only weak interactions, which explains the quasi-linear structure of the solutions.
31
Xie, Jinhan. "Wave-mean flow interactions : from nanometre to megametre scales." Thesis, University of Edinburgh, 2015. http://hdl.handle.net/1842/10475.
Full textAbstract:
Waves, which arise when restoring forces act on small perturbations, are ubiquitous in fluids. Their counterpart, mean flows, capture the remainder of the motion and are often characterised by a slower evolution and larger scale patterns. Waves and mean flows, which are typically separated by time- or space-averaging, interact, and this interaction is central to many fluid-dynamical phenomena. Wave-mean flow interactions can be classified into dissipative interactions and non-dissipative interactions. The former is important for small-scale flows, the latter for large-scale flows. In this thesis these two kinds of interactions are studied in the context of microfluidics and geophysical applications. Viscous wave-mean flow interactions are studied in two microfluidic problems. Both are motivated by the rapidly increasing number of microfluidic devices that rely on the mean-flow generated by dissipating acoustic waves - acoustic streaming - to drive small-scale flows. The first problem concerns the effect of boundary slip on steady acoustic streaming, which we argue is important because of the high frequencies employed. By applying matched asympototics, we obtain the form of the mean flow as a function of a new non-dimensional parameter measuring the importance of the boundary slip. The second problem examined is the development of a theory applicable to experiments and devices in which rigid particles are manipulated or used as passive tracers in an acoustic wave field. Previous work obtained dynamical equations governing the mean motion of such particles in a largely heuristic way. To obtain a reliable mean dynamical equation for particles, we apply a systematic multiscale approach that captures a broad range of parameter space. Our results clarify the limits of validity of previous work and identify a new parameter regime where the motion of particles and of the surrounding fluid are coupled nonlinearly. Non-dissipative wave-mean flow interactions are studied in two geophysical fluid problems. (i) Motivated by the open question of mesoscale energy transfer in the ocean, we study the interaction between a mesoscale mean flow and near-inertial waves. By applying generalized Lagrangian mean theory, Whitham averaging and variational calculus, we obtain a Hamiltonian wave-mean flow model which combines the familiar quasi-geostrophic model with the Young & Ben Jelloul model of near-inertial waves. This research unveils a new mechanism of mesoscale energy dissipation: near-inertial waves extract energy from the mesoscale ow as their horizontal scale is reduced by differential advection and refraction so that their potential energy increases. (ii) We study the interaction between topographic waves and an unidirectional mean flow at an inertial level, that is, at the altitude where the Doppler-shifted frequency of the waves match the Coriolis parameter. This interaction can be described using linear theory, using a combination of WKB and saddle-point methods, leading to explicit expressions for the mean-flow response. These demonstrate, in particular, that this response is switched on asymptotically far downstream from the topography, in contrast to what is often assumed in parameterisation.
32
Wheadon, Andrew John. "Wave-turbulence interaction in shallow water numerical models : asymptotic limits, and subgrid interactions." Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34333.
Full textAbstract:
The ability to directly simulate all atmospheric motion is currently well beyond the limits of the computers available to us. As such techniques must be developed that accurately model important processes in an affordable manner. Large-scale balanced motion is well understood, but as affordable resolution increases, models are able to resolve scales where large-scale turbulence and small-scale waves are important. This requires a new set of techniques that respect the interactions between these different kinds of motion. In this thesis we look at two ways of assessing the accuracy of models capable of representing the scales at which these interactions occur. The first approach uses asymptotic limit solutions to derive a set of terms whose scale is known. These terms can then be evaluated as the model approaches a relevant asymptotic regime, and a `good' model should reproduce the expected rate of scaling. We apply this method of asymptotic limit solutions to an Eulerian and a Lagrangian shallow water model. The former is based upon ENDGame, the model currently in use at the Met Office, and the latter is based upon a candidate model from GungHo which is seeking a replacement for ENDGame. In addition, the Eulerian model is evaluated with both small and large timesteps and the results confirm the ability of the semi-implicit scheme to retain accuracy at large timesteps. Errors in the higher-order diagnostics used in this section highlight the need to make these analytic diagnostics consistent with the discretisations of the model in question. The second method involves looking at the exchanges of energy in a spectral shallow water model in order to inform the design of subgrid models. By running a high-resolution simulation and truncating the energy at a certain wavenumber, comparing the result to a run without truncation shows the contribution of the scales below the truncation limit. We extend this by separating the total energy into separate components that may be truncated and evaluated individually in order to give a more complete picture of energy exchanges at the subgrid scale.
33
Threadgill, James. "Unsteadiness of shock wave boundary layer interactions across multiple interaction configurations and strengths." Thesis, Imperial College London, 2016. http://hdl.handle.net/10044/1/48475.
Full textAbstract:
Shock Wave Boundary Layer Interactions (SWBLIs) represent complex flow phenomena that remain poorly understood despite their prevalence on high-speed vehicles, in part due to their complicated underlying physics. In particular, the mechanisms that drive the high-amplitude, low-frequency unsteadiness within the interaction have perplexed researchers for many years while remaining a limitation to vehicle performance and a potential danger to airframe integrity. This investigation has specifically examined the influence of interaction strength and configuration type on the characteristic unsteady behaviour that describes the flow environment. Until now, researchers have typically focused on testing a specific configuration in a given test facility. This approach can obscure meaningful conclusions that may be drawn due to the interference of the test environment. The present research effort therefore tackles this flaw by assessing flow behaviours across a range of SWBLIs, all tested within a common environment. Four strengths of oblique shock reflection interactions and two strengths of compression ramp interactions have been assessed and compared. Experiments have been conducted in the Imperial College Supersonic Wind Tunnel with a Mach 2 turbulent incoming boundary layer with momentum thickness Reynolds number of 8000. Using a combined approach of synchronised PIV and fast-response wall-pressure measurements the unsteady elements to the interactions have been investigated. The spectral evolutions of unsteady wall-pressure disturbances are assessed throughout each of the interactions. Results confirm that the high-frequency component of the separation shock spectral content is common across all interactions. Meanwhile, low-frequency amplitudes scale with the interaction length, acting to decrease the characteristic frequency used to describe such motion when the interaction strength is increased. Instantaneous shock structures have also been identified which confirm the presence of two unsteady mechanisms governing the dynamics of the separation shock: rotation and translation. Quasi-steady modelling of these mechanisms indicates how their relative dominance varies with interaction strength and configuration type. This body of work represents a unique assessment of valuable data that is crucial to the development of unsteady SWBLI understanding.
34
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.
Full textAbstract:
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.
35
Gately, Bernard M. Colson William B. "A theory for whistler wave amplification and wave particle interactions in the magnetosphere /." Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from the National Technical Information Service, 1992. http://handle.dtic.mil/100.2/ADA257782.
Full text
36
Gately, Bernard M. "A theory for whistler wave amplification and wave particle interactions in the magnetosphere." Thesis, Monterey, California. Naval Postgraduate School, 1992. http://hdl.handle.net/10945/38526.
Full textAbstract:
Approved for public release; distribution is unlimited.<br>Whistler waves are a type of very low frequency (VLF) radiation which propagate through the earth's magnetosphere. This phenomenon can occur as a result of a lightning discharge and can be produced using ground-based VLF transmitters. It is theorized that these signals travel through ducts centered on geomagnetic field lines. While passing through these ducts the waves are amplified through resonant interaction with electrons in the radiation belts which are following helical paths around magnetic field lines. A description of whistlers and the related topic of VLF emissions is presented in Chapter II, along with a description of how these effects change the properties of the ionosphere. Starting with the Lorentz force equation, the equations of motion for electrons in the magnetosphere are developed in Chapter III. These equations are numerically integrated along with a wave equation developed in Chapter IV. The results of the simulation are presented in Chapter V for the idealized case of a monoenergetic beam of electrons. High and low gains in the wave amplitude are observed for both strong and weak initial VLF fields. The simulation is also run using distributions to represent the initial energies of the electrons in the radiation belts. Chapter VI presents some possible ways to make the simulation more realistic along with a summary of the similarities between the theory presented and Free Electron Laser theory.
37
Li, Zhaobin. "Two-phase spectral wave explicit Navier-Stokes equations method for wave-structure interactions." Thesis, Ecole centrale de Nantes, 2018. http://www.theses.fr/2018ECDN0041/document.
Full textAbstract:
Cette thèse propose un algorithme efficace pour la simulation numérique des interactions houle-structure avec des solveurs CFD bi-phasiques. L'algorithme est basé sur le couplage de la théorie potentielle et des équations bi-phasiques de Navier-Stokes. C'est une extension de la méthode Spectral Wave Explicit Navier-Stokes Equations (SWENSE) pour les solveurs CFD bi-phasiques avec une technique de capture d'interface. Dans cet algorithme, la solution totale est décomposée en une composante incidente et une composante complémentaire. La partie incidente est explicitement obtenue avec des méthodes spectrales basées sur la théorie des écoulements potentiels ; seule la partie complémentaire est résolue avec des solveurs CFD, représentant l'influence de la structure sur les houles incidentes. La décomposition assure la précision de la cinématique des houles incidentes quel que soit le maillage utilisé parles solveurs CFD. Une réduction significative de la taille du maillage est attendue dans les problèmes typiques des interactions houle structure. Les équations sont présentées sous trois formes : la forme conservative, la forme non conservative et la forme Ghost of Fluid Method. Les trois versions d'équations sont implémentées dans OpenFOAM et validées par une série de cas de test. Une technique d'interpolation efficace pour reconstruire la solution des houles irrégulières donnée par la méthode Higher-Order Spectral (HOS) sur le maillage CFD est également proposée<br>This thesis proposes an efficient algorithm for simulating wave-structure interaction with two-phase Computational Fluid Dynamics (CFD) solvers. The algorithm is based on the coupling of potential wave theory and two phase Navier-Stokes equations. It is an extension of the Spectral Wave Explicit Navier-Stokes Equations (SWENSE) method for generalized two-phase CFD solvers with interface capturing techniques. In this algorithm, the total solution isdecomposed into an incident and acomplementary component. The incident solution is explicitly obtained with spectral wave models based on potential flow theory; only the complementary solution is solved with CFD solvers, representing the influence of the structure on the incident waves. The decomposition ensures the accuracy of the incident wave’s kinematics regardless of the mesh in CFD solvers. A significant reduction of the mesh size is expected in typical wave structure interaction problems. The governing equations are given in three forms: the conservative form, the non conservative form, and the Ghost of Fluid Method (GFM) form. The three sets of governing equations are implemented in OpenFOAM and validated by a series of wave-structure interaction cases. An efficient interpolation technique to map the irregular wave solution from a Higher-Order Spectral (HOS) Method onto the CFD grid is also proposed
38
Tan, Loh Teng Young. "Assessments of wave-structure interactions for an oscillating wave surge converter using CFD." Thesis, University of Plymouth, 2018. http://hdl.handle.net/10026.1/12230.
Full textAbstract:
This thesis is concerned with the use of the open source computational fluid dynamics (CFD) software package, OpenFOAM® for predicting and analysing the behaviour of a near-shore oscillating wave surge converter (OWSC), when subject to various types of ocean wave conditions in a numerical wave tank (NWT). OpenFOAM® which utilises a Finite Volume Method (FVM) is used to solve the incompressible, Reynolds Averaged Navier-Stokes (RANS) equations for a two-phase fluid, based on a Volume of Fluid (VOF) phase-fraction approach to capture the interface between the air and water phases. Preliminary studies on classic wave-structure interaction benchmark cases, involving a fixed and a vertically oscillating semi-immersed horizontal cylinder are carried out. The gradual transition of the linear to non-linear behaviour of the horizontal and vertical forces induced on a fixed cylinder when subject to various regular waves, and the amplitude ratios of the surface waves elevations generated by the prescribed oscillatory motion of the cylinder, are shown to provide good overall agreement within the limitations of the relevant theory and the experimental data in the literature. The OWSC is modelled with the inclusion of a Power Take-Off (PTO) system, using a linear damping restraint, and simulated in two-dimensional (2D) and three-dimensional (3D) setups. The 2D and 3D numerical results, such as the surface wave elevations, flap angular velocity, PTO torque and flap angular displacement, compare well with one another and with the experimental data for operational regular head-on and oblique wave conditions. Small discrepancies between numerical results and experimental data are likely to be caused by non-linear behaviour of the PTO system. Pressure distributions on the flap surfaces and forces induced on the flap and hinge of the OWSC for various wave conditions are also presented. The effects between 2D and 3D wave-structure interactions become more significant when subject to large waves that break during impact. Comparison between the full scale and 1:24 scale numerical results of the OWSC shows no significant evidence of viscous and scaling effects. The validated 2D OWSC model is also subject to embedded focused waves, to predict the worse possible scenario of wave loading in extreme wave conditions. The delay of the focus event breaking is shown to affect the slamming behaviour for the larger focus event wave heights. Incorporation of a focused wave at different phase positions within a background of regular waves reveals that the focus event wave height has little effect on the peak tangential force on the flap during the slamming event, when a PTO cut-off mechanism is implemented to prevent excessive torque surges. In contrast, the peak radial force on the flap and the maximum resultant force on the hinge appear to respond more sensitively to the focus event wave height. It has been demonstrated that OpenFOAM® is able to provide a comprehensive understanding of the complex hydrodynamic analysis and prediction of highly non-linear wave-structure interactions for an OWSC, which give useful guidance and confidence to WEC developers on the design considerations relevant to the OWSC systems.
39
Spentza, Eirini. "Nonlinear wave interactions with fixed and floating bodies leading to unexpected wave impacts." Thesis, Imperial College London, 2011. http://hdl.handle.net/10044/1/8987.
Full textAbstract:
This thesis deals with the nonlinear interaction of water waves with fixed and floating bodies. The case of a two-dimensional fixed surface body is first investigated using a newly developed linear and second-order boundary element model, the fully nonlinear model of Hague & Swan (2009) and new experimental observations. In this case, second-order freely propagating harmonics arising due to the wave-structure interaction are identified and quantified. Subsequently, a two- dimensional floating body is investigated, undergoing one or two motion modes, and comparisons with the fixed body case are made. These observations confirm that the wave-vessel interactions again lead to the generation of freely propagating nonlinear wave harmonics and that the magnitude of these components varies significantly for bodies with different hydrodynamic properties. Building on the physical understanding achieved from the two-dimensional study, the case of a three-dimensional floating body is considered. This concerns the interaction with both regular waves, propagating at varying angles of wave incidence, and directional wave groups. In both cases the effects of wave-vessel interactions on the surface profile are identified. Finally, it is shown that the nonlinear wave-vessel interactions identified previously can, after interacting with the incoming wave field, lead to unexpected wave impacts on the vessel. As a result, it is concluded that the occurrence of wave impacts, particularly on the side shell of a vessel, cannot be assessed on the basis of the incident waves alone.
40
Haase, Heiko. "Full-wave field interactions of nonuniform transmission lines." [S.l. : s.n.], 2005. http://deposit.ddb.de/cgi-bin/dokserv?idn=975448641.
Full text
41
Andreae, Sigrid B. [Verfasser]. "Wave Interactions with Material Interfaces / Sigrid B Andreae." Aachen : Shaker, 2008. http://d-nb.info/1164342029/34.
Full text
42
Hanasoge, Shravan M. "Theoretical studies of wave interactions in the sun /." May be available electronically:, 2007. http://proquest.umi.com/login?COPT=REJTPTU1MTUmSU5UPTAmVkVSPTI=&clientId=12498.
Full text
43
Renaud, Antoine. "On wave-mean flow interactions in stratified fluid." Thesis, Lyon, 2018. http://www.theses.fr/2018LYSEN059/document.
Full textAbstract:
La dynamique des écoulements géophysiques planétaires est fortement influencée par des processus physiques souvent non résolus par les modèles numériques de circulation générale. Il est essentiel de comprendre les mécanismes physiques sous-jacents pour paramétrer l’effet des petites échelles sur les grandes. Dans cette thèse, nous étudions un problème emblématique d’interactions entre ondes et écoulements moyens : la dynamique des écoulements zonaux forces par des ondes internes de gravite. Une manifestation remarquable de ces interactions est l’oscillation quasi-biennale (QBO) des vents équatoriaux dans l’atmosphère terrestre. Dans un premier temps, nous décrivons une transition vers le chaos dans un modèle quasi-linéaire classique du QBO. Nous montrons que ces bifurcations persistent dans des simulations numériques directes. A l’aune de ces résultats, nous proposons une interprétation de l’observation d’une rupture inattendue de la périodicité du QBO en 2016. Le mécanisme de génération d’écoulements moyens par les ondes dans les fluides stratifies nécessite la prise en compte d’effets dissipatifs. Il s’agit d’un phénomène analogue au "streaming" acoustique. Dans un second temps nous exploitons cette analogie en étudiant la génération d’écoulements moyens par les ondes internes proche d’une paroi, a l’aide d’approches asymptotiques multi échelles. Finalement, nous proposons une approche inertielle pour décrire l’émergence spontanée d’écoulements vorticaux en présence d’ondes : nous appliquons les outils de mécanique statistique pour calculer la partition d’énergie entre petites et grandes échelles dans le modèle d’eau peu profonde<br>The dynamics of planetary-scale geophysical flows is strongly influenced by physicalprocesses, mostly unresolved by general circulation numerical models. To parametrisethe coupling between small and large scales, it is essential to understand the underlying physical mechanisms. In this thesis, we study an emblematic problem of interactions between waves and mean flows: the dynamics of zonal flows forced by internal gravity waves. A striking manifestation of these interactions is the quasi-biennial oscillation (QBO) of equatorial winds in the Earth’s atmosphere. First, we describe a transition to chaos in a classical quasilinear model of the QBO and show that these bifurcations persist in direct numerical simulations. Based on these results, we suggest an interpretation for the observation of the unexpected periodicity disruption of the QBO in 2016. The mechanism by which mean flows are generated by waves in stratified fluids requires the consideration of dissipative effects. This phenomenon is analogous to acoustic "streaming". In a second time, we exploit this analogy to study the generation of mean flows by internal gravity waves close to a wall, using multi-scale asymptotic approaches. Finally, we propose an inertial approach to describe the spontaneous emergence of vortical flows in the presence of waves: we apply the tools of statistical mechanics to calculate the partition of energy between small and large scales in the shallow-water model
44
Weller, Samuel David. "Wave energy extraction from device arrays : experimental investigation in a large wave facility." Thesis, University of Manchester, 2011. https://www.research.manchester.ac.uk/portal/en/theses/wave-energy-extraction-from-device-arrays-experimental-investigation-in-a-large-wave-facility(5e43e3e5-4776-42c1-9d4e-22160de8abbe).html.
Full textAbstract:
Multiple wave energy devices supported by a common structure represent one possible method of efficiently converting ocean wave energy into electricity. In this study, experimental measurements of multiple small-scale wave energy devices are reported to assist the development and validation of numerical models. Through observation and measurement, the response of two float geometries subjected to a range of wave conditions and device settings were determined. A range of regular wave conditions were identified that caused a linear relationship to occur between the heave displacement amplitude of the float and the incident wave amplitude. These test cases will enable comparisons to be made with linear simulations of response. Tests conducted in various wave conditions have highlighted the capability of altering the device response by changing the equilibrium draft of one float geometry. Additional damping on the upper surface of the float, due to wave overtopping, could be exploited as a method of limiting the heave response of the device in large amplitude waves. The influence of hydrodynamic interactions on arrays of closely spaced devices has been experimentally investigated for devices subjected to regular and irregular wave conditions. The magnitude and occurrence of interactions and their affect on the individual device response is demonstrably dependent on the incident wave frequency and device separation distance. Compared to an isolated device, positive interactions result in higher average power outputs for an array of devices at certain wave frequencies. Positive interactions occuring at particular wave frequencies are balanced by negative interactions at other wave frequencies, in agreement with published numerical studies of array performance. Varying the level of mechanical damping applied to the float through the power take-off system results in a frequency shift of the calculated power transfer function and alters the motion path of the float. This finding implies that the level of generator torque could be used as an alternative method to tune the response of the device based on the measured incident wave-field. Several time-averaged and time-varying approaches to simulating the response of a wave energy device subjected to wave-field forcing and undergoing free response have been studied. By comparing the simulated and measured responses, the feasibility of using linear and non-linear force terms in a time-varying model has been assessed. In general, single degree-of-freedom simulations based on linear hydrodynamic parameters tend to over-predict device response amplitudes, requiring the application of additional damping. The simulation approach which resulted in the closest agreement with measured responses required the combination of linear diffraction force and radiation added mass terms with non-linear drag and buoyancy force terms, as well as body inertia and gravity forces. This approach goes part way to simulating the complex time-varying hydrodynamics associated with a wave energy device subjected to wave-field forcing.
45
Gras, Slawomir M. "Opto-acoustic interactions in high power interferometric gravitational wave detectors." University of Western Australia. School of Physics, 2009. http://theses.library.uwa.edu.au/adt-WU2010.0093.
Full textAbstract:
[Truncated abstract] Advanced laser interferometer gravitational wave detectors require an extremely high optical power in order to improve the coupling between the gravitational wave signal and the optical field. This high power requirement leads to new physical phenomena arising from nonlinear interactions associated with radiation pressure. In particular, detectors with multi-kilometer-long arm cavities containing high density optical fields suffer the possibility of 3-mode opto-acoustic interactions. This involves the process where ultrasonic vibrations of the test mass cause the steady state optical modes to scatter. These 3-mode interactions induce transverse optical modes in the arm cavities, which then can provide positive feedback to the acoustic vibrations in the test masses. This may result in the exponential growth of many acoustic mode amplitudes, known as Parametric Instability (PI). This thesis describes research on 3-mode opto-acoustic interactions in advanced interferometric gravitational wave detectors through numerical investigations of these interactions for various interferometer configurations. Detailed analysis reveals the properties of opto-acoustic interactions, and their dependence on the interferometer configuration. This thesis is designed to provide a pathway towards a tool for the analysis of the parametric instabilities in the next generation interferometers. Possible techniques which could be helpful in the design of control schemes to mitigate this undesirable phenomenon are also discussed. The first predictions of parametric instability considered only single interactions involving one transverse mode and one acoustic mode in a simple optical cavity. ... In Chapter 6, I was able to make use of a new analytical model due to Strigin et al., which describes parametric instability in dual recycling interferometers. To make the solution tractable, it was necessary to consider two extreme cases. In the worst case, recycling cavities are assumed to be resonant for all transverse modes, whereas in the best cases, both recycling cavities are anti-resonant for the transverse modes. Results show that, for the worst case, parametric gain values as high as ~1000 can be expected, while in the best case the gain can be as low as ~ 3. The gain is shown to be very sensitive to the precise conditions of the interferometer, emphasising the importance of understanding the behaviour of the detectors when the cavity locking deviates from ideal conditions. Chapter 7 of this thesis contains work on the observation of 3-mode interactions in an optical cavity at Gingin, which confirms the analysis presented here, and also a paper which shows how the problem of 3-mode interactions can be harnessed to create new devices called opto-acoustic parametric amplifiers. In the conclusions in Chapter 8, I discuss the next important steps in understanding parametric interactions in real interferometers including the need for more automated codes relevant to the design requirements for recycling cavities. In particular, it is pointed out how the modal structure of power and signal recycling cavities must be understood in detail, including the Gouy phase for each transverse mode, to be able to obtain precise predictions of parametric gain. This thesis is organised as a series of papers which are published or have been submitted for publication. Such writing style fills the condition for Ph.D. thesis at the University of Western Australia.
46
Saputo, Roberto. "Two dimensional P-wave superconductors with long range interactions." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2018. http://amslaurea.unibo.it/16315/.
Full textAbstract:
L' interesse crescente che circonda lo studio delle proprietà topologiche della materia è
profondamente collegato all' effettiva possibilità di verifica in laboratorio. Negli ultimi decenni infatti la fisica sperimentale degli atomi ultrafreddi ha raggiunto livelli di precisione
prima inimmaginabili. Attraverso reticoli ottici si possono riprodurre sistemi multicorpo
fortemente interagenti di cui si possono controllare in maniera quasi esatta i parametri
fisici, come i potenziali. In questo contesto si inserisce il modello bidimensionale P-wave
con interazioni a lungo raggio. Le interazioni in questo modello avvengono tra tutte le
componenti, quindi in tutte le direzioni. Questo sistema fisico topologico inoltre è caratterizzato da una Hamiltoniana con potenziale di interazione che decade con la distanza
secondo una legge di potenza per cui, per quanto detto, la sua realizzazione sperimentale è possibile.
In questo lavoro abbiamo iniziato studiando lo spettro di questo sistema partendo da un approccio analitico. Dopo aver compreso il comportamento dei vari termini energetici abbiamo selezionato dei casi di studio per diversi range di interazione. In
questi casi successivamente abbiamo analizzato le varie fasi e transizioni di fase tramite simulazioni numeriche. All' aumentare del range di interazione abbiamo visto l' emergere
di nuovi fenomeni assenti nei modelli con interazione a corto raggio.
47
Levinsen, Jesper F. "Paired fermionic superfluids with s- and p-wave interactions." Connect to online resource, 2007. http://gateway.proquest.com/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:3284444.
Full text
48
Risch, Stephan Hermann. "Large-scale wave interactions in baroclinic flow with topography." Thesis, University of Oxford, 1999. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.312449.
Full text
49
Mahoney, Daniel J. (Daniel John). "On wave interactions--explosive resonant traids and critical layers." Thesis, Massachusetts Institute of Technology, 1994. http://hdl.handle.net/1721.1/12055.
Full text
50
Yan, Hongmei. "Computations of fully nonlinear three-dimensional wave-body interactions." Thesis, Massachusetts Institute of Technology, 2010. http://hdl.handle.net/1721.1/61616.
Full textAbstract:
Thesis (Ph. D. in Ocean Engineering)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2010.<br>Cataloged from PDF version of thesis.<br>Includes bibliographical references.<br>Nonlinear effects in hydrodynamics of wave-body interaction problems become critically important when large-amplitude body motions and/or extreme surface waves are involved. Accurate prediction and understanding of these fully nonlinear effects are still challenges in the design of surface ships and marine structures, owing to the complexity of the hydrodynamic problem itself and limited computational facilities. This research is focused on: (i) development of a highly efficient numerical scheme for the computation of fully-nonlinear three-dimensional wave-body interactions; and (ii) investigation of several highly nonlinear wave-body interaction problems for understanding associated key nonlinear effects. A highly efficient high-order boundary element method is developed based on the framework of the quadratic boundary element method (QBEM) for the boundary integral equation and using the pre-corrected fast Fourier transform (PFFT) algorithm to accelerate the evaluation of far-field influences of source and/or normal dipole distributions on boundary elements. The resulting numerical scheme reduces the computational effort of solving the boundary-value problem from O(N 2 ~3) (with the traditional boundary element methods) to O(N ln N) where N represents the total number of boundary unknowns. Combining with the mixed-Eulerian-Lagrangian (MEL) approach for nonlinear free surface tracking, we develop an efficient and accurate initial boundary value problem (IBVP) solver, PFFT-QBEM, which allows for practical simulations of fully nonlinear three-dimensional wave-body interaction problems. Three nonlinear wave-body interaction problems, which are of scientific interest and practical importance, are investigated in detail: water surface impact of threedimensional objects, cavity dynamics in water entries, and coupled unstable motions of floating structures in waves. For the water impact problem, with the development of an adaptive jet flow treatment and an effective approach for accurately tracking water-body separation point/line, we obtain a thorough understanding of the gravity effect on the characteristics of slamming pressure/load on the object and free-surface profiles. For the cavity problem, we investigate the formation and evolution of an air cavity behind an object dropped into water (from air) at relatively low Froude numbers where the inertia and gravity effects are comparable. A theoretical solution is newly derived based on a matched asymptotic approach and a fully nonlinear numerical simulation is carried out, for the description of the kinematics and dynamics of the air cavity. Satisfactory quantitative comparisons are obtained among the theoretical predictions, numerical simulations, and existing experimental measurements for the dependence of cavity shape and closure time/height on Froude number and body geometry. For floating structures in waves, our focus is on the understanding of the fundamental mechanism and basic characteristics for coupled unstable heave-pitch motions of floating platforms/vessels. Through stability analyses, we identify that the second-order difference-frequency interaction between surface waves and body motions is the key mechanism for the excitation of unstable resonant motions. Fully nonlinear simulations are conducted to study the development of large-amplitude body motions and investigate quantitatively the dependence of the instability on related physical parameters, such as incident wave amplitude and phase, frequency detuning, body geometry, and system damping. Theoretical analyses and numerical simulations are verified by comparison to available experiments for the coupled unstable motions of a deep draft caisson vessel (DDCV).<br>by Hongmei Yan.<br>Ph.D.in Ocean Engineering