To determine the effect of body shape on the response of underwater vehicles to surface waves in shallow water, the wave radiation hydrodynamic forces are evaluated for a family of (i) prolate spheroidal hull forms and (ii) cylindrical bodies with hemispherical nose and conical tail sections by systematically varying the geometric parameters but keeping displacement constant. The added-mass and wave damping coefficients are determined using a frequency-domain, simple-source based boundary integral method. Results are obtained for a range of wave frequencies and depths of vehicle submergence all for a fixed water depth of 10 m. With the wave exciting force and moment determined using the Froude-Krylov theory, the response transfer functions for heave and pitch are then determined. The heave and pitch response spectra in actual littoral seas are then determined with the sea state modeled using TMA spectral relations. Results show that vehicle slenderness is a key factor affecting the hydrodynamic coefficients and response. The results show two characteristics that increase the radiation hydrodynamic forces corresponding to heave and pitch motions: namely, vehicle length and further-away from mid-vehicle location of the body shoulder. The opposite is true for the oscillatory surge motion. By utilizing these observed characteristics, one can design the lines for maximum radiation forces and consequently minimum hull response for the critical modes of rigid-body motion in given waters and vehicle missions. In the studies carried out in the thesis, a hull with a long parallel middle body with hemispherical nose and conical tail sections has better heave and pitch response characteristics compared prolate spheroid geometry of same volume. The methodology developed herein, which is computationally efficient, can be used to determine optimal hull geometry for minimal passive vehicle response in a given sea. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2014. / FAU Electronic Theses and Dissertations Collection

This study is performed in tandem with numerous experiments performed by the U.S. Navy to characterize the ocean environment in the South Florida region. The research performed in this study includes signal processing steps for isolating ocean phenomena, such as internal waves, in the magnetic field. Raw magnetometer signals, one on shore and one underwater, are processed and removed of common distortions. They are then run through a series of filtering techniques, including frequency domain cancellation (FDC). The results of the filtered magnetic residual are compared to similarly processed Acoustic Doppler Current Profiler (ADCP) data to correlate whether a magnetic signature is caused by ocean phenomena. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2017. / FAU Electronic Theses and Dissertations Collection

The design, implementation, and testing of an experimental setup intended to evaluate the dynamic maneuvering performance of the Wave Adaptive Modular Vessel (WAM-V) class USV12, a 3.7 meter unmanned surface vehicle (USV) is described. A comprehensive sensor package was designed, fabricated and assembled to record the vehicle's dynamic response to various control inputs. All subsystems were fabricated and installed on a test vehicle, GUSS, and full system, open-loop maneuvering tests were conducted to show validity of data collection technique. Simulations were performed using model parameters found in the literature to create a "simulated experimental" data set, upon which system identification techniques were used to rediscover a suitable model with similar parameterization. Combined, the sensor package and the method for creating this model support future work in the design of automatic control, navigation, and guidance systems for the WAM-V USV12. / by Janine L. Mask. / Thesis (M.S.C.S.)--Florida Atlantic University, 2011. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2011. Mode of access: World Wide Web.

The goal of this thesis is to develop a test platform for measuring surface effect ship (SES) response to wave loads. The platform is designed and built incorporating a self-propelled vehicle with data acquisition and navigation capabilities. Theoretical analysis is performed, various hardware and electronic parts are designed and built and software applications developed. Wave tank experiments are conducted for test platform evaluation and determination of vehicle response to a range of wave conditions. Furthermore, a three-dimensional model of the AIRCAT scale model SES is created. The theoretical analysis shows that the scale effects in some cases are great, so resonance phenomena cannot be observed. The experimental results clearly show that the heave, pitch and aircushion excess pressure fluctuations increase as the air-blower input level increases. The bow skirt arrangement needs improvements and further experimentation is necessary in order to draw conclusions about the wave loads applied on the skirt. / by Nicholas Kouvaras. / Thesis (M.S.C.S.)--Florida Atlantic University, 2010. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2010. Mode of access: World Wide Web.

The South China Sea is a marginal basin with a complex circulation influenced by the East Asian Monsoon, river discharge and intricate bathymetry. As a result, both the mesoscale eddy field and the near-inertial energy distribution display large spatial variability and they strongly influence the oceanic transport and mixing. With an ensemble of numerical integrations using a regional ocean model, this work investigates how the temporal resolution of the atmospheric forcing fields modifies the horizontal and vertical velocity patterns and impacts the transport properties in the basin. The response of the mesoscale circulation in the South China Sea is investigated under three different forcing conditions: monthly, daily and six-hourly momentum and heat fluxes. While the horizontal circulation does not display significant differences, the representation of the vertical velocity field displays high sensitivity to the frequency of the wind forcing. If the wind field contains energy at the inertial frequency or higher (daily and six-hourly cases), then Vortex Rossby waves and near inertial waves are excited as ageostrophic expression of the vigorous eddy field. Those waves dominate the vertical velocity field in the mixed layer (vortex Rossby waves) and below the first hundred meters (near inertial waves) and they are responsible for the differences in the vertical transport properties under the various forcing fields as quantified by frequency spectra, vertical velocity profiles and vertical dispersion of Lagrangian tracers.

A technique that allows for nonparallel interfaces and lateral inhomogeneities in an irregular layered medium is described. The formulation combines a semidiscrete finite-element technique with a perturbation method, providing an approximate treatment of wave propagation in irregular layered media. The procedure treats the irregularities as perturbations with respect to a reference, horizontally-layered, laterally-homogeneous medium and produces approximations of the perturbed wave motion with little additional computation effort. Within the framework of the method, consistent transmitting boundaries and other semidiscrete hyperelements as well as Green’s functions, already available for regular layered media, can be reformulated. The method is relevant in problems of foundation dynamics, ground response to seismic waves and site characterization. Example problems are presented toward evaluation of the effectiveness of the method. / text

We are concerned with forward wave motion simulations in two-dimensional elastic, heterogeneous, semi-infinite media. We use Perfectly Matched Layers (PMLs) to truncate the semi-infinite extent of the physical domain to arrive at a finite computational domain. We use a recently developed hybrid formulation, where the Navier equations for the interior domain are coupled with a mixed formulation for an unsplit-field PML. Here, we implement the hybrid formulation using spectral elements, and report on its performance. The motivation stems from the following considerations: Of concern is the long-time instability that has been reported even in homogeneous and isotropic cases, when the standard complex-stretching function is used in the PML. The onset of the instability is always within the PML zone, and it manifests as error growth in time. It has been suggested that the instability arises when waves impinge at grazing angle on the PML-interior domain interface. Yet, the instability does not always appear. Furthermore, different values of the various PML parameters (mesh density, attenuation strength, order of attenuation function, etc) can either hinder or delay the onset of the instability. It is thus conjectured that the instability is associated with the spectral properties of the discrete operators. In this thesis, we report numerical results based on both Lagrange interpolants, and results based on spectral elements. Spectral elements are explored since they lead to diagonal mass matrices, have improved dispersion error, and, more importantly, have different spectral properties than Lagrangian-based finite elements. Spectral elements are thus used in an attempt to explore whether the reported instability issues could be alleviated. We design numerical experiments involving explosive sources situated at varying depths from the surface, capable of inducing grazing-angle waves. We use the energy decay as the primary metric for reporting the results of comparisons between various spectral element orders and classical Lagrange interpolants. We also report the results of parametric studies. Overall, it is shown that the spectral elements alone are not capable of removing the instability, though, on occasion, they can. Careful parameterization of the PML could also either remove it or alleviate it. The issue remains open. / text

Thesis (Ph. D.)--University of Texas at Austin, 2007. / Vita. Includes bibliographical references.

Techn. Univ., Habil.-Schr.--Braunschweig, 2001. / Literaturverz.S. [159] - 168.

Accretion discs efficiently transport angular momentum by a wide variety of as yet imperfectly understood mechanisms, with profound implications for the disc lifetime and planet formation. We discuss two different methods of angular momentum transport: first, generation of acoustic waves by mixing of inertial waves, and second, the generation of a self-sustaining magnetic field via the magnetorotational instability (MRI) which would be a source of dissipative turbulence. Previous local simulations of the MRI have shown that the dynamo changes character on addition of vertical stratification. We investigate numerically 3D hydrodynamic shearing waves with a conserved Hermitian form in an isothermal disc with vertical gravity, and describe the associated symplectic structure. We continue with a numerical investigation into the linear evolution of the MRI and the undular magnetic buoyancy instability in isolated flux regions and characterise the resultant quasi-linear EMFs as a function of height above the midplane. We combine this with an analytic description of the linear modes under an assumption of a poloidal-toroidal scale separation. Finally, we use RAMSES to perform full MHD simulations in a zero net flux shearing box, followed by spatial and a novel temporal averaging to reveal the essential structure of the dynamo. We find that inertial modes may be efficiently converted into acoustic modes for "bending waves", despite a fundamental ambiguity in the inertial mode structure. With our linear MRI and the undular magnetic buoyancy modes we find the localisation of the instability high in the atmosphere becomes determined by magnetic buoyancy rather than field strength for small enough azimuthal wavenumber, and that the critical Alfven speed below which the dynamo can operate increases with increasing distance from the midplane. We calculate analytically quasi-linear EMFs which predict both a vertical propagation of toroidal field and a method for creation of radial field. From our fully nonlinear calculations we find an electromotive force in phase with the toroidal field, which is itself 3π/2 out of phase with the radial (sheared) field at the midplane, and good agreement with our quasi-linear analytics. We have identified an efficient mechanism for generating acoustic waves in a disc. In our investigation of the accretion disc dynamo, we have reproduced analytically the EMFs calculated in our simulations, given arguments based on the phase of relevant quantities, several correlation integrals and the scalings suggested by our analytic work. Our analysis contributes significantly to an explanation for the dynamo in an accretion disc.