The motions of a small spar buoy were measured in deep water. The measured variables were two buoy tilts, three accelerations, two wave slopes and the wave height. The variables were corrected for buoy motion and rotated to stationary coordinates, Fast Fourier Transformed, and analyzed spectrally. Analysis included power spectra, coherence, phase and transfer functions. It was found that the buoy was a surface follower at low frequencies up to the frequency of the peak of the wave spectrum. At higher sea wave frequencies, the buoy resists sea motion. The RMS tilts of the buoy are about 0.6 of the RMS sea slopes, and practically all of the buoy motion is concentrated in the frequency band from 0.1 to 0.3 Hertz. / Graduation date: 1972

The dynamics of a submarine detection system using neutrally buoyant inflated structural members is investigated with mathematical models representing increasing order of complexity. An appreciation of the flexural deflections of a single inflated viscoelastic cylindrical cantilever is first gained using the three parameter solid model. This is followed by its free vibration analysis in the presence of hydrodynamic forces and axial tension arising due to the internal pressure. The approximate solutions of the governing nonlinear, partial differential equation are substantiated through numerical and experimental data. An analysis of dynamical response to the surface wave excitations provides useful design information. Next, the coupled motion of an array consisting of three legs and a central head is studied. The inplane and out of plane motions, which essentially decouple for small oscillations, are considered separately. Effects of the inflation pressure and inertia parameters on the natural frequencies of the system are examined and the possibility of dynamic instability for certain parametric values established. The vertical motion of a buoy-cable-array assembly is considered subsequently. The cable is replaced by a spring of equivalent stiffness and the flexural displacements of the legs are superposed on the motion of the central head. The free vibration of the system is studied first and the influence of the important system parameters on the natural frequencies evaluated. The motion excited by a sinusoidal surface wave is also studied to explore the possibility of reducing the tip displacements. The dynamics of a buoy-cable-array assembly drifting with a uniform velocity is then investigated. As the motion is rather complex because of the large number of degrees of freedom involved, a relatively simple model is considered to obtain some appreciation of the problem. The oscillations of the buoy and flexibility of the legs are ignored and the cable is represented by two straight lines. The steady state configurations of this system and their dependence on various parameters are examined. The double pendulum type motion of the cable along with the rotational oscillations of the array around the equilibrium positions are studied to obtain preliminary information regarding the stability of the motion. Reduction in the length or diameter of the arms appears to improve the damping rates of the system. Finally, some of the restrictions inherent in the simplified model are removed. The flexibility of the legs and the tangential drag which were neglected earlier, are taken into account. A more accurate cable configuration is considered to make the model closer to the reality. However, the oscillations of the buoy are again ignored. With this, the steady state configurations of the system are determined around which a linearized perturbation analysis is carried out. Longitudinal and lateral motions essentially decouple for small amplitude motions. Natural frequencies of the system are found by analyzing the resulting eigenvalue problem and the influence of various parameters on the damping of the disturbances examined. As noticed in the rigid array analysis, shorter arm lengths improve the decaying characteristics of the system. But the minimum acceptable length being governed by the signal processing considerations, a compromise is indicated in the design. For given cable and arm lengths, there appears to be an optimum diameter from the stability considerations. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Originally presented as the author's thesis, (M.S.) in the M.I.T. Dept. of Aeronautics and Astronautics, 1976. / Research sponsored by the Office of Naval Research under Contract N00014-74-C-0163 and N00014-75-C-1065. Bibliography : p. 54.

Thesis (Ph. D.)--Florida State University, 1972. / Includes bibliographical references (leaves 87-89).

The purpose of this study is to explore the feasibility of a recent development in oceanographic instrumentation known as an active drifter buoy. The active drifter is a self-propelled, solar-powered data buoy which has the capability of influencing its drift rate and direction with the use of a thruster/rudder system. This study examines the active drifters developed thus far, and discusses a series of experiments which provide sufficient information to predict the performance of a buoy offshore. The active drifter was conceived at the Institute of Ocean Sciences at Patricia Bay, B.C. Under the direction of Engineer G.R. Smith, a prototype was built and received limited testing in inshore waters. Seaboy Marine Services Ltd., a manufacturer of data buoys, began its own active drifter program in 1984, and in 1985 made its prototype available to the author for a series of experiments to define its capabilities and provide data for future development. The Seaboy active drifter was named Ranger 1, and had a shallow, spoon-shaped hull with a circular deck to maximize the area available for a photovoltaic array. The buoy was 2m in diameter and had a foil shaped keel 1m deep. A 12 V DC thruster combined with a 36 cm. model airplane propeller propelled the buoy at a speed of 0.50 m/s in calm water. The 210 peak watt solar array charged a bank of six 55 amp hour gelled electrolyte lead acid batteries and provided the power to operate the electronics payload and for propulsion. The Ranger testing program included a measurement of the effective power of the hull at the B.C. Research tow tank facilities. Experiments in the tow tank revealed that a design speed of 0.50 m/s required 4 watts of thrust, and that a static aft trim was required to prevent the buoy from submerging into its own wake. Extensive inshore tests were performed on the Ranger buoy in Elk Lake, near Victoria. These tests showed that the actual power required to propel the buoy at 0.50 m/s was 32 watts. Downwind drift tests showed the buoy travelled at a rate of 5% of the lm wind speed. Upwind, the combined effects of surface drift, waves and wind drag reduced the forward buoy speed by a factor equal to 5.4% of the wind speed, and the maximum speed in which the buoy could make forward headway was 10 m/s. A simulation based on the results of these experiments was performed to predict the performance of an active drifter deployed at Ocean Station Papa (50°N, 145°W). At this site, the average wind speeds are 10.5 m/s, with surface drift currents equal to 3.3% of the wind speed. With an average daily total insolation of 9.6 MJ/m² the buoy would be able to motor 12.7 hours a day. In these conditions, the active drifter could reduce the annual drift rate to 43% of a comparable unpropelled buoy. This is comparable to a deep-drogued spar buoy, indicating no significant improvement inperformance over the less sophisticated buoys commonly in use. The simulation shows that for an active drifter buoy to become a practical alternative to buoys now available, changes must be made in the hull shape to reduce drag and the effects of winds and waves on buoy mobility. / Science, Faculty of / Earth, Ocean and Atmospheric Sciences, Department of / Graduate

Thesis. 1976. M.S.--Massachusetts Institute of Technology. Dept. of Aeronautics and Astronautics. / Microfiche copy available in Archives and Aero. / Includes bibliographical references. / by Prafulla K. Padhi. / M.S.

Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, December 2009. / Thesis Advisor(s): Papoulias, Fotis ; Rice, Joseph. "December 2009." Author(s) subject terms: Acoustic modem, Cable, Steady state, Undersea sensors, Catenary, Mooring. Includes bibliographical references (p. 41). Also available in print.

Thesis (Ph. D.)--University of Hawaii at Manoa, 1995. / Includes bibliographical references (leaves 136-141). / Microfiche. / xi, 141 leaves, bound ill., maps 29 cm

Statics and dynamics of the neutrally buoyant inflated viscoelastic cantilevers constituting a submarine detection system is investigated. Two geometries of the thin-walled beams are considered: uniform circular cylindrical and circular tapered. The static flexural behaviour of the beam is studied using the three parameter viscoelastic solid model which yields material properties for the mylar-polyethylene-mylar plastic film used. Results of a detailed experimental program are also presented to substantiate validity of the analytical model. This is followed by free vibration analyses of the inflated cantilevers in the ocean environment accounting for the added inertia and nonlinear hydrodynamic drag. For the uniform cylindrical beam, thin-shell theories are employed to account for the inflation effects on the free vibration characteristics. A significant feature of the analysis is the reduction of the shell equations (the membrane, Fliigge's, and Herrmann-Armenakas') into a single equation which is similar in form to that for a vibrating beam with rotary inertia effects. The natural frequencies obtained are compared with the experimental results and those predicted by the Rayleigh-Ritz method in conjunction with the Washizu and membrane shell theories. The analyses show, and experimental program confirms, that Fliigge's shell equation in the reduced form is capable of predicting free vibration behaviour quite accurately. However, the reduction technique should be applied with care, since in several cases it leads to misleading results (e.g. in the case of Herrmann-Armenakas theory). For the tapered case the elementary beam theory is used to predict their natural frequencies. Next, the dynamical response of the uniform and tapered cantilevers to root excitation, at the fundamental wave frequency and its second harmonic, is studied. The governing nonlinear equations are analyzed by taking two terms of the assumed Fourier series solution. Results suggest that for the case of the simple harmonic excitation, the nonlinear hydrodynamic drag introduces no superharmonic components into the response. For low forcing frequencies typical of the ocean environment, an increase in taper ratio tends to reduce the tip amplitudes. However, for frequencies above the fundamental, the response characteristics are completely reversed. The analysis provides valuable information concerning the system parameters leading to critical response and hence should prove useful in the design of inflatable members employed in the submarine detection system. / Applied Science, Faculty of / Mechanical Engineering, Department of / Graduate

Thesis (M.S. in Meteorology and Physical Oceanography)--Naval Postgraduate School, December 1990. / Thesis Advisor(s): Bourke, Robert H. ; Morison, James. "December 1990." Description based on title screen as viewed on April 1, 2010. DTIC Identifier(s): Buoys, Sea Ice, Arctic Buoys, Ice Forecast, Arctic, Theses. Author(s) subject terms: PIPS, Sea Ice, Arctic Buoys, Ice Forecast, Arctic. Includes bibliographical references (p. 106-111). Also available in print.