The Experimental and Finite Element Investigation of Added Mass Effects on Ship Structures comprised three phases : 1) investigation of the fluid modelling capabilities of the Finite Element Program VAST, 2) experimental investigation to determine the effect of the fluid on the lowest natural frequencies and mode shapes of a ship model, and 3) comparison of these experimental results with numerical results obtained from VAST. The fluid modelling capabilities of VAST were compared with experimental results for submerged vibrating plates, and the effect of fluid element type and mesh discretization was considered. In general, VAST was able to accurately predict the frequency changes caused by the presence of the fluid. Experimental work both in air and water was performed on a ship model. The lowest four modes of vertical, horizontal, and torsional vibration were identified, and the effect of draught on the frequencies and mode shapes was recorded. When the experimentally obtained frequencies and mode shapes for the ship model were compared with the numerical predictions of VAST, good agreement was found in both air and water tests for the vertical vibration modes. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Airwakes are shed behind the ship’s superstructure and represent a highly turbulent and rapidly distorting flow field. This flow field severely affects pilot’s workload and such helicopter shipboard operations. It requires both the one-point statistics of autospectrum and the two-point statistics of coherence (normalized cross-spectrum) for a relatively complete description. Recent advances primarily refer to generating databases of flow velocity points through experimental and computational fluid dynamics (CFD) investigations, numerically computing autospectra along with a few cases of cross-spectra and coherences, and developing a framework for extracting interpretive models of autospectra in closed form from a database along with an application of this framework to study the downwash effects. By comparison, relatively little is known about coherences. In fact, even the basic expressions of cross-spectra and coherences for three components of homogeneous isotropic turbulence (HIT) vary from one study to the other, and the related literature is scattered and piecemeal. Accordingly, this dissertation begins with a unified account of all the cross-spectra and coherences of HIT from first principles. Then, it presents a framework for constructing interpretive coherence models of airwake from a database on the basis of perturbation theory. For each velocity component, the coherence is represented by a separate perturbation series in which the basis function or the first term on the right-hand side of the series is represented by the corresponding coherence for HIT. The perturbation series coefficients are evaluated by satisfying the theoretical constraints and fitting a curve in a least squares sense on a set of numerically generated coherence points from a database. Although not tested against a specific database, the framework has a mathematical basis. Moreover, for assumed values of perturbation series constants, coherence results are presented to demonstrate how coherences of airwakes and such flow fields compare to those of HIT. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

This thesis presents two-dimensional hydrodynamic analysis of flapping foils for the propulsion of underwater vehicles using a source-vortex panel. Using a simulation program developed in MatLab, the hydrodynamic forces (such as the lift and the drag) as well as the propulsion thrust and efficiency are computed with this method. The assumptions made in the analysis are that the flow around a hydrofoil is two-dimensional, incompressible and inviscid. The analysis is first considered for the case of a deeply submerged hydrofoil followed by the case where it is located in shallow water depth or near the free surface. In the second case, the presence of the free surface and wave effects are taken into account, specifically at high and low frequencies and small and large amplitudes of flapping. The objective is to determine the thrust and efficiency of the flapping –foils under the influence of added effects of the free surface. Results show that the free-surface can significantly affect the foil performance by increasing the efficiency particularly at high Frequencies. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2015. / FAU Electronic Theses and Dissertations Collection

A parametrically forced, single-degree-of-freedom equation modelling ship roll is investigated through the numerical study of invariant manifolds, Me1nikov's method, and transient basins. The calculation of the manifolds is facilitated through the development of a sophisticated algorithm for approximating the locations of the saddle points of the Poincaré map. For selected fixed values of the restoring-moment and damping parameters (the "base case"), the manifolds of the saddles of the Poincaré map are repeatedly computed for increasingly higher excitation amplitudes until homo clinic , heteroclinic, and mixed manifold intersections are observed. The critical amplitudes at which these tangles first occur are accurately predicted by Melnikov's method, verifying its viability as a tool for analyzing ship roll. Corresponding transient basins indicate that fractally mixed regions of stable and unstable initial conditions appear with the onset of transverse manifold intersections. For parametric forcing, the fractal areas are symmetric about the origin and do not significantly affect the integrity of the safe region near the origin. Test cases involving external or combined external-plus-parametric excitation result in asymmetric transient basins and, following the appearance of manifold tangling, a catastrophic reduction of the safe area. Lastly, Melnikov's method is used to perform a parameter study that indicates the effects of varying the restoring-moment and damping coefficients on the critical excitation level.</P. / Master of Science