Global ETD Search
Search theses and dissertations gathered from participating repositories worldwide. Every result links back to the library that holds it. No account is needed.
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Showing 1 to 20 of 36 for “"Eigenmode"”.
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A numerical eigenmode analysis of the progressive buckling of thin-walled tubes
[page 76 missing]Structural impact is concerned with the behaviour of structures subject to static and dynamic loads which produce inelastic deformations. This field is of particular interest for the crash-worthiness design of aeroplanes, motor cars, buses, trains, ships and marine structures, …
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Statistical Properties of Transmission Spectra of Ergodic Wave Billiards: Random Hamiltonian Approach
… 'naive' model that takes both the RMT and eigenmode complexity into account, but is less technically involved than the supersymmetry method. Such a modification of the naive approach is likely to be useful in studies of power variance and transient decay in chaotic cavities.
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Frequency chirping of energetic particle driven modes in tokamaks; Self-consistent modelling and simulation
… have revealed that an isolated Alfven eigenmode can evolve into chirping signals if the mode is subject to intrinsic damping into the cold plasma. In 1997, Berk-Breizman and co-workers studied the nonlinear stage of an excited electrostatic plasma wave where chirping signals were …
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Frequency chirping of energetic particle driven modes in tokamaks; Self-consistent modelling and simulation
… have revealed that an isolated Alfven eigenmode can evolve into chirping signals if the mode is subject to intrinsic damping into the cold plasma. In 1997, Berk-Breizman and co-workers studied the nonlinear stage of an excited electrostatic plasma wave where chirping signals were …
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Optical properties of III-V semiconductors
… diffraction grating coupler. The resulting eigenmode distributions were used to obtain the refractive index of GaAs at a matrix of sub bandgap photon energies (1.40 eV $<$ h$\nu <$ 1.50 eV) and temperatures (40 K $<$ T $<$ 300 K). Values for the temperature dispersion (dn/dT) at each photon …
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Efficient perturbative framework for coupling of radiative and guided modes in nearly periodic surfaces
… perturbative modeling of guided waves using an eigenmode expansion. We derive our framework for both nearly uniform and nearly periodic surfaces, and we validate each case against brute-force finite-difference time-domain simulations, which show increasing agreement as the surface varies more …
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Receptivity to free stream acoustic disturbances due to a roughness element on a flat plate
… equal to that of the Tollmien-Schlichting (TS) eigenmode and a frequency equal to that of the free-stream acoustic disturbance. The basic (mean) flow is calculated using an interacting boundary layer (IBL) scheme that accounts for viscous/inviscid interactions. Then, the method of multiple …
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Biegeknicken und Biegedrillknicken von Stäben und Stabsystemen auf einheitlicher Grundlage
… effects are expressed in terms of series of Eigenmodes including the basic Eigenmode, which already has been used to define the initial equivalent imperfection. The convergence could be optimised in such a way, that a good approximation is given on the basis of the first Eigenmode only. For …
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Ventilation, stratification and flow instability driven by vertically distributed buoyancy sources
… the numerical difficulty of tracking the eigenmodes when evaluating a fully numerical dispersion relationship. Based on this numerical approach, the absolute/convective instability of the same annular plume as that in the second project is analysed. Following a discussion about the …
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Plasma stability in a dipole magnetic field
… stability condition and an integro-differential eigenmode equation for ballooning modes are derived, using the MHD energy principle. The existence of plasma equilibria which are both interchange and ballooning stable for arbitrarily large beta = plasma pressure / magnetic pressure, is …
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A study of reversed shear Alfvén eigenmodes in Alcator C-Mod with phase contrast imaging
… oscillation and may exist in tokamak plasmas as eigenmodes with a global structure and discrete frequencies. The inhomogeneity of the plasma profiles in conjunction with tokamak geometry tends to focus the Alfvén waves in regions of near uniformity defined by local extrema in the Alfvén …
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Methodologies and Algorithms for Finite Element Analysis of Electromagnetic Devices and Systems
… are presented for two-dimensional waveguide eigenmode analysis, which provides the foundation for the development of a waveguide-mode based port excitation model. This model is used in the multiple-input, multipleoutput finite element analysis of multiport electromagnetic devices and, in …
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Optical and optoelectronic fiber devices
… algorithm that can yield the complete vectorial eigenmode content of any general waveguiding structure and demonstrated its validity experimentally. In the third chapter an active material is introduced into the hollow-core to form a surface-emitting fiber laser. A unique azimuthally anisotropic …
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Three-Dimensional Unsteady Hydrodynamics of Tidal Turbines
… features in the incoming flow, this thesis uses eigenmode decomposition of the vortex lattice model, which finds the spatial shapes of the gusts that will cause the largest forces on a given aerofoil geometry. This is shown through the concept of "mode resonance": if a gust is similar in shape to …
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Photoexcited hypersonic surface acoustic waves propagating under periodic metal grating
… Further, we conduct finite element based eigenmode analysis on the Si-Al periodic composite which show a good agreement with the experimental data. Modal analysis further reveals that higher attenuation in the duty cycle regime 0.3 to 0.6 is due to radiation of the energy from the surface …
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Photonic Integrated Circuit Packaging Using Silicon Based Optical Interconnects
… 3D finite-difference time-domain (FDTD) and eigenmode expansion (EME) methods were utilized to determine quantitative performance metrics including coupling efficiency, packaging misalignment tolerance, and wavelength and polarization dependence. The comparison of these coupling designs to …
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Resource management of cognitive radio networks with optimization methods.
… secondary user is the power allocation along the eigenmode directions. When considering orthogonal access to the spectrum by secondary users, MIMO cognitive radio networks are further simplified, and a parallel sub-channel transmission method is proposed. NC-OFDM is a promising technique for …
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Ponderomotive Forces in Pilot-Wave Hydrodynamics
… histogram coincident with extrema of the cavity eigenmode. Stroboscopic models that idealize the drop’s bouncing dynamics as being perfectly resonant with their Faraday wave field have proven incapable of capturing the emergent statistics. In this thesis, we present new experimental and …
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Tidal Dissipation in Extrasolar Planets
… forcing happens to land on that of an internal eigenmode, this mode can be resonantly excited to a very large amplitude. The damping of such a mode inside the planet may explain the observed Q value. The only normal modes that fall in the frequency range of the tidal forcing (~ few days) are …
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Cosmic String Radiation with Adaptive Mesh Refinement
… quantitative diagnostic tools to determine their eigenmode decomposition. We find that the massless quadrupole is dominant and massive radiation is strongly suppressed with increasing mass, with a complex wavepacket structure that is sensitive to numerical resolution. String network configurations …
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