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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 269 for “"Helmholtz"”.
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Mesospheric Kelvin-Helmholtz instability
This work examines the Kelvin-Helmholtz instability, comparing features extracted from a numerical fully nonlinear model to radar and rocket measurements of free electron density and neutral motions in the mesosphere. Previous models of shear instability are reviewed, and relevant mesospheric …
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Kelvin-Helmholtz Instability in Magnetized Plasma
… systems in the universe, are generally Kelvin-Helmholtz unstable. If the medium is ionized, the presence of a magnetic field can influence the evolution of this instability; depending on its strength and orientation, the field has either a stabilizing or destabilizing effect. We performed …
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Kelvin-Helmholtz instability in aluminium reduction cells
… between the layers, which gives rise to a Kelvin-Helmholtz instability, and the study of this effect is the subject of the thesis. The role of the basic steady flow is focused in this analysis, while most previous MHD analyses neglect it and emphasise on the interaction between the interface wave …
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Acoustic metamaterials : microperforated shell and Helmholtz resonator
… in designing efficient noise control. Helmholtz has been used to design a high-performance and broadband acoustic silencer. Specifically, five slit-type Helmholtz resonators, which possess a massive viscous area, are packed together to create a single-layer silencer. In turn, two …
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Compressed absorbing boundary conditions for the Helmholtz equation
… of an absorbing boundary condition for the Helmholtz equation in a heterogeneous medium. It is always possible to reduce an absorbing layer to an operator at the boundary by layer-stripping elimination of the exterior unknowns, but the linear algebra involved is costly. We propose to bypass …
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Fast and scalable solvers for the Helmholtz equation
… algorithms to solve the 2D high-frequency Helmholtz equation in heterogeneous medium. The algorithms rely on a layered domain decomposition and a coupling between subdomains using the Green's representation formula, which reduces the problem to a boundary integral system at the interfaces …
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Multifluid Kelvin-Helmholtz instability in weakly ionised astrophysical plasmas
… on fluid instabilities, in particular the Kelvin-Helmholtz (KH) instability. The KH instability could, for example, play a role in the momentum transfer between the bowshock of a protostellar jet and its surrounding molecular cloud. In particular, changes to the development of the KH instability …
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Damping acoustic pressure pulsations in pipelines using Helmholtz resonators
… thesis, an acoustic damping device known as the Helmholtz resonator (HR) is experimentally studied. The effects of HR cavity volume, pipeline diameter, HR location, the use of multiple HRs, and mean flow velocity are investigated to determine their effects on the acoustic attenuation achieved …
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Applications of a fast helmholtz solver in exploration seismology
… the subsurface. In this thesis, I combine a fast Helmholtz solver, the field expansion method, with a reduced velocity model parameterization to address the impact of an uncertain or inaccurate velocity model. I modify the field expansion framework to accurately simulate the acoustic field for …
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Shape optimization for thermoacoustic instability with an adjoint Helmholtz solver
… system in the linear regime. We derive a Helmholtz equation with an unsteady heat release source and acoustic impedance boundary conditions. We apply the finite element method with P2 elements to discretize the weak formulation of the Helmholtz equation. We obtain a nonlinear eigenvalue …
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Numerical analysis and visualization of the ionospheric Kelvin-Helmholtz instability
… namely the evolution of the Kelvin-Helmholtz instability (KHI) is studied. The simulation model consists of two-dimensional, electrostatic, nonlinear, and time dependent fluid equations that describe the KHI evolution. Spectral and pseudospectral methods are used to solve the spatial …
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Helmholtz Equation Least Squares Based Near-Field Acoustic Holography With Laser
<p>This dissertation presents the HELS based NAH with laser and use normal surface velocity as input in near-field acoustic holography. The conventional HELS based NAH uses acoustic pressure as input to reconstruct sound field quantities, while this modified HELS based NAH with laser utilizes the …
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Reconstruction Resolution Of Coherent Point Sources With Helmholtz Equation Least Squares
… reconstruction of coherent point sources using Helmholtz Equation Least Squares (HELS) method based on measurements in violation of Nearfield Acoustical Holography (NAH) resolution guidelines. In HELS, the Helmholtz equation is solved by matching a series of localized spherical expansion …
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Periodic orbit analysis of the Helmholtz equation in two-dimensional enclosures
… used in acoustics to understand solutions of the Helmholtz equation. A review of the links between ray and wave mechanics is given including WKBJ (Wentzel, Kramers, Brillouin and Jeffreys) and EBK (Einstein, Brillouin, Keller) methods. It is also noted that some mode shapes in chaotic enclosures …
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Calibration and Characterization of Cubesat Magnetic Sensors Using a Helmholtz Cage
… generation of Cal Poly CubeSates, utilizing a Helmholtz cage to simulate any desired orbital magnetic field that would be experienced by a spacecraft around Earth, as well as investigation of magnetic interference as a result of on-board electrical activity.</p>
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A Coarse Mesh Nodal Method for Solving the MultiDimensional Helmholtz Equation
Made available in DSpace on 2017-07-06T18:42:29Z (GMT). No. of bitstreams: 3 Bosnic_Don_P_MS.pdf: 33492823 bytes, checksum: 82a1bfe934175084c06ed6af875ec7cc (MD5) Bosnic_Don_P_MS_ABS.pdf: 496288 bytes, checksum: 0c4e1361066079bfebbfc8f7e75a0808 (MD5) license.txt: 4813 bytes, checksum: …
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Design and construction of a Helmholtz coil apparatus for nanoparticle heating
… the effects of magnetic heating. By using a Helmholtz coil pair, I have successfully created a coil set-up that can manipulate a sample of biomolecules within a fluorometer.
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Identifying Signatures of Plasma Waves and Reconnection Associated with Kelvin-Helmholtz Activity
… work has shown that reconnection in Kelvin-Helmholtz vortices can transport plasma into the magnetosphere. Previous studies have also shown that mode conversion at the magnetopause can generate kinetic Alfvén wave (KAW) activity. Both magnetic reconnection and plasma wave activity can heat …
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MMS Observations of the Kelvin-Helmholtz Instability and Associated Ion Scale Waves
… be at work. One potential process is the Kelvin-Helmholtz instability (KHI). The KHI is a convective instability which operates at the fluid scale in plasmas, but is capable of driving secondary process at smaller scales. Previous work has shown evidence of magnetic reconnection, various ion …
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Métodos de elementos finitos e diferenças finitas para a equação de Helmholtz
… finitas, quando aplicados à equação de Helmholtz, apresentam o que é chamado de efeito de poluição do erro, comprometendo seriamente a qualidade da solução aproximada. Em virtude de numérico, foram desenvolvidos, nas últimas décadas, uma série de métodos que são capazes de contornar esse …
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