Report (M.S.)--Virginia Polytechnic Institute and State University. M.S. 1992. / Abstract. Includes bibliographical references (leaves 202-206). Also available via the Internet.

No description available.

In maritime vessels, it is desirable to minimise the structural and acoustic responses for several reasons, including passenger comfort, minimisation of crew fatigue, and in the case of military vessels, to avoid detection. The propeller-shafting system represents one of the most critical areas which must be addressed in order to reduce the low frequency acoustic signature. The propeller-shafting system is primarily excited by axial oscillations at the propeller. The force transmitted along the propeller-shafting system from these disturbances results in axial excitation of the hull and subsequent sound radiation. The aim of this thesis is to apply a combination of passive and active control techniques, in order to minimise the low frequency radiated noise signature of a pressure hull submerged in a fluid. Dynamic models of the propeller-shafting system, foundation and cylindrical hull including complicating factors such as fluid loading, bulkheads and onboard equipment are developed and described using the transmission matrix approach. This modular description enables greater flexibility for dynamic modelling of the propeller shafting system, and can be easily manipulated for future design modifications. The far-field radiated sound pressure from the submarine hull is evaluated and related to the force delivered to the hull by the propeller-shafting system. A passive optimisation scheme involving a genetic and general non-linear constrained algorithm is used to minimise fitness functions associated with the vibration of the propeller, vibration transmission to the hull and far-field radiated sound pressure over a low frequency range. This results in optimal resonance changer parameters for single and multiple resonance changers in a variety of configurations. A new quasi-adaptive resonance changer system is proposed and optimised to minimise the radiated sound pressure or propeller velocity. The optimal use of an adaptive resonance changer is investigated in both the frequency and time domains to reduce the hull velocity and subsequently the far-field radiated sound pressure. Fully active control is also evaluated by introducing a control force to the resonance changer with the aim of minimising either the propeller velocity or the radiated noise level. Finally, the concept of hybrid control is investigated by coupling passive, active and semi-active control techniques together to improve the overall performance.

In maritime vessels, it is desirable to minimise the structural and acoustic responses for several reasons, including passenger comfort, minimisation of crew fatigue, and in the case of military vessels, to avoid detection. The propeller-shafting system represents one of the most critical areas which must be addressed in order to reduce the low frequency acoustic signature. The propeller-shafting system is primarily excited by axial oscillations at the propeller. The force transmitted along the propeller-shafting system from these disturbances results in axial excitation of the hull and subsequent sound radiation. The aim of this thesis is to apply a combination of passive and active control techniques, in order to minimise the low frequency radiated noise signature of a pressure hull submerged in a fluid. Dynamic models of the propeller-shafting system, foundation and cylindrical hull including complicating factors such as fluid loading, bulkheads and onboard equipment are developed and described using the transmission matrix approach. This modular description enables greater flexibility for dynamic modelling of the propeller shafting system, and can be easily manipulated for future design modifications. The far-field radiated sound pressure from the submarine hull is evaluated and related to the force delivered to the hull by the propeller-shafting system. A passive optimisation scheme involving a genetic and general non-linear constrained algorithm is used to minimise fitness functions associated with the vibration of the propeller, vibration transmission to the hull and far-field radiated sound pressure over a low frequency range. This results in optimal resonance changer parameters for single and multiple resonance changers in a variety of configurations. A new quasi-adaptive resonance changer system is proposed and optimised to minimise the radiated sound pressure or propeller velocity. The optimal use of an adaptive resonance changer is investigated in both the frequency and time domains to reduce the hull velocity and subsequently the far-field radiated sound pressure. Fully active control is also evaluated by introducing a control force to the resonance changer with the aim of minimising either the propeller velocity or the radiated noise level. Finally, the concept of hybrid control is investigated by coupling passive, active and semi-active control techniques together to improve the overall performance.

Thesis (M.S. in Operations Research)--Naval Postgraduate School, Dec. 2004. / Thesis Advisor(s): Steven E. Pilnick. Includes bibliographical references (p. 73-74). Also available online.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 47-49). Also available via the Internet.

Thesis (M.A.) -- Central Connecticut State University, 2006. / Thesis advisor: M.B.B. Biskupski. "... in partial fulfillment of the requirements for the degree of Master of Arts in History." Includes bibliographical references (leaves 102-104). Also available via the World Wide Web.

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

No description available.

The last decade has been marked by a continuous growth in computational power, which has allowed for elaborate modelling techniques like LES and DES applied at engineering scales which generally imply a Reynolds number in excess of 1×106. One field that has seen a rapid growth in use of numerical methods in design and performance analysis is the naval sector, especially in the design of submarines where the free-surface boundary plays an important role. This thesis is devoted to the study of free-surface flow past submerged bodies, with the objective of numerically studying free-surface flow past a submarine fairwater at periscope depth near actual operating conditions. This work is motivated by DSTL, who have reported that near periscope depth submarines exhibit an increased drag (private communication). In this work both LES and DES modelling approaches are also utilized, while the submerged body is accounted through the use of an immersed boundary method and the free-surface is through the use of a part moving mesh. The thesis is split in two main parts. The first part of the thesis focuses on low and moderate Reynolds number flow about a submerged cube (bluff body) for various submergence depths. Two configurations are examined one being that of a single cube in a uniform flow, while the other is that of a matrix of equally spaced cubes. Results show that for both cases a reduction in submergence depth causes the forces, the fluctuation in the forces and shedding frequencies to alter, while the level of interaction between vortices and free-surface to increase. The second part of this thesis focuses on the main study of free-surface flow past a submerged fairwater at a high and near operating Reynolds number. It is found that for both Reynolds numbers the flow behaviour shows little change, while the effects of reducing submergence depth results in the forces, the force variation and shedding frequency to increase. Surface waves are found to disperse by an angle of up to 40° for all submergence depth and are of the Kelvin wave kind. No direct interaction between vortical structures shed from the fairwater and free-surface are found, whilst the increases in forces acting on the fairwater are directly attributed due to wave motion.