Motions and stability of a typical B.C. fishing vessel were experimentally and numerically investigated in a longitudinal seaway condition. The experimental model was self-propelled, radio-controlled and equipped with an on-board data acquisition system. Pitch, roll, yaw, surge, and heave responses to regular waves of predetermined frequencies and amplitudes generated along a 220-ft model basin were obtained. Different displacement conditions and GM configurations were tested. The numerical model for the dynamic analysis of the fishing vessel motions has been implemented using strip theory. A computer program was developed to study the nonlinear motions of the vessel. The velocity dependent coupling terms, responsible for a major part of the nonlinear behavior, were included. A time dependent component analysis of the roll damping has been performed. Regular linear and nonlinear waves were used. A parametric study of the fishing vessel stability has been carried out by considering its dynamic response in waves of varying characteristics. Unstable behaviour was found to be closely related to waves of length of similar magnitude to the ship length. The effects of wave amplitude and rudder usage were found to be of capital importance in the capsizing process. Experimental and numerical results showed good agreement. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

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

A procedure to generate an approximate bifurcation diagram for a single-degree-of-freedom system in a selected parameter space is developed. The procedure is based on the application of Floquet analysis to determine the stability of second-order perturbation approximations of the solutions of the system in the neighborhoods of specific resonances. As a control parameter is varied, a combination of elementary concepts of bifurcation theory and the proposed method are used to detect the first bifurcation from the periodic solutions and hence infer the qualitative changes that the system experiences. Codimension-one bifurcations are investigated in a two-dimensional parameter space composed of the amplitude and frequency of the excitation. The behavior of a softening Duffing oscillator is analyzed under external and parametric excitation. The dynamics of a ship rolling in waves is also considered and three types of excitations are treated: external, parametric, and a combination of both. Analog- and digital-computer simulations are used to verify the accuracy of the analytical predictions. It is found that the predictions based on the first bifurcation of the analytical solution give a good estimate of the actual behavior of the system. The stability regions of the solutions near each of the resonances display a self-similar structure in the parameter space. The physical implications of these bifurcation patterns are important for the prediction of the capsizing of ships. The dangerous regions of the parameter space where capsizing might occur are identified for a given system. Capsizing is found to occur via two distinct scenarios: one evolving from a large oscillation through a disappearance of a chaotic attractor (crises) and a second, potentially more dangerous, developing from a small oscillation through a sudden tangent instability. These scenarios agree with previous experimental studies. / Ph. D.

The relationship between cross-flow at a waterjet inlet and delivered thrust is not fully understood. A direct thrust measurement system was designed for a waterjet propelled, free running USV. To induce sway velocity at the waterjet inlet, which was considered equivalent to the cross flow, circles of varying radii were performed at Reynolds Numbers between 3.48 x 106 and 8.7 x 106 and radii from 2.7 to 6.3 boat lengths. Sway velocities were less than twenty percent of mean forward speed with slip angles that were less than 20°. Thrust Loading Coefficients were compared to sway as a percent of forward speed. In small radius turns, no relationship was seen, while in larger radius turns, peaks of sway velocity corresponded with drops in thrust, but this was determined to be caused by reduced vehicle yaw in these intervals . Decoupling of thrust and yaw rate is recommended for future research. / Thesis (M.S.)--Florida Atlantic University, 2013.

Scale model tests are conducted of a Surface Effect Ship in a near-shore developing sea. A beach is built and installed in a wave tank, and a wavemaker is built and installed in the same wave tank. This arrangement is used to simulate developing sea conditions and a 1:30 scale model SES is used for a series of experiments. Pitch and heave measurements are used to investigate the seakeaping response of the vessel in developing seas. The air-cushion pressure and the vessel speed are varied, and the seakeeping results are compared as functions of these two parameters. The experiment results show a distinct correlation between the air-cushion pressure and the response amplitude of both pitch and heave. The results of these experiments are compared against results of a computer model of a Surface Effect Ship (SES). / by Michael Kindel. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Electronic reproduction. Boca Raton, Fla., 2012. Mode of access: World Wide Web. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

Thesis (Nav.Arch)--Massachusetts Institute of Technology, Dept. of Ocean Engineering, 1975. / Bibliography: leaves 152-157. / Nav.Arch

Ship-shaped hulls have often been found to be subject to excessive roll motions, and therefore, inhibit their use as a stable production platform. To solve the problem, bilge keels have been widely adopted as an effective and economic way to mitigate roll motions, and their effectiveness lies in their ability to damp out roll motions over a range of frequencies. In light of this, the present research focuses on roll motions of shipshaped hulls. A finite volume method based two-dimensional Navier-Stokes solver is developed and further extended into three dimensions. The present numerical scheme is implemented for modeling the flow around ship-shaped hulls in roll motions and for predicting the corresponding hydrodynamic loads. Also conducted are studies on the hydrodynamic performance of ship-shaped hull sections in prescribed roll motions and in transient decay motions. Systematic studies of the grid resolutions and the effects of free surface, hull geometries and amplitude of roll angle are performed. Predictions from the present method compare well to those of other methods, as well as to measurements from experiments. Non-linear effects, due to flow viscosity, were observed in small as well as in large roll amplitudes, particularly in the cases of hulls with sharp corners. The study also shows that it is inadequate to use a linear combination of added-mass and damping coefficients to represent the corresponding hydrodynamic loads. As a result, it also makes the calculation of the hull response in time domain inevitable. Finally, the capability of the present numerical scheme to apply to fully three-dimensional ship motion simulations is demonstrated. / text

Thesis (M.S.)--Mississippi State University. Department of Computational Engineering. / Title from title screen. Includes bibliographical references.

This thesis presents the results of an experimental investigation of the hydrodynamic characteristics of the Monoform hull in calm water. The forces acting on a 1.7 meter model were measured as the model was held captive and towed in calm water. The model was tested at speeds up to three meters per second. The rudders were held straight during one part of the study and were deflected during another to test both their ability to correct for pitching moment and to create yaw moments. The draft of the model was also varied during this study and included drafts of 1.90, 2.21, and 2.42 hull diameters. All three forces and all three moments were measured. The model was tested in a 31 meter towing basin located at Virginia Polytechnic Institute and State University. The results are presented in Figure form in the thesis body and in numerical form in an appendix. Recommendations for future work and improvements to the instrumentation are presented along with conclusions at the end of the thesis. / M.S.

The effect of fin and jet vortex generators on the crossflow separation of a 688 class submarine in a turning maneuver was studied. The vortex generators are located on the top and bottom centerline of the submarine. The intent of the vortex generators is to improve turning performance by changing the hydrodynamic forces incurred from crossflow separation. Performance of the jets and the fins are compared. Oil flow visualization and force and moment measurements were used as the primary diagnostics in determining the effectiveness of various vortex generator configurations. The fins were found to be very effective in delaying cross flow separation, while the jets were less effective. In addition, the oil flows revealed the importance of locating vortex generators near the bow and the critical role the sail plays in the fluid dynamics near the submarine. Overall, the fins were found to be viable as a concept for flow control, while the jets were less attractive. / Master of Science