Thesis (M.S.)--West Virginia University, 2006. / Title from document title page. Document formatted into pages; contains x, 89 p. : ill. (some col.). Includes abstract. Includes bibliographical references (p. 87-89).

Thesis (M.S.)--Rochester Institute of Technology, 2006. / Typescript. Includes bibliographical references (leaves 132-137).

A method in which the transport and evolution of the bubble population in a surface ship wake is numerically simulated is presented. The simulation is accomplished by constructing an advective-diffusive transport model for the scalar bubble field and solving this model for late times after ship passage. The bubble population model requires convection velocities and turbulent diffusion information that is supplied by solving the Reynolds-averaged parabolized Navier-Stokes equations with a <i>k</i> - ∊ turbulence model. The mean flow equations are solved by approximating the differential equations with a second order accurate finite difference scheme. The resulting large, sparse, banded matrix is solved by applying a version of the conjugate gradient method. The method has proven to be efficient and robust for the free shear flow problems of interest here. The simulation is initiated with given information in a plane at some point downstream of the ship from which the solution is propagated. The model is executed for a single and a twin propeller ship at 15 knots. The simulation shows that the development of the hydrodynamic and bubble near wake is dominated by ship geometry via strong advective transport. The far wake is dominated by diffusion and bubble rise and dissolution. Thus relatively large changes in geometry have a limited influence on the far wake. / Ph. D.

The methodology used in analyzing the feasibility of installing direct and indirect intercooling systems on naval gas turbines is presented. The indirect system is comprised of two types of heat exchangers; an air to ethylene glycol, plate fin heat exchanger, and an ethylene glycol to seawater shell and tube heat exchanger. The direct system utilizes an air to seawater shell and tube heat exchanger. The analysis requires, as input, air mass flow rates, compressor efficiencies and pressure ratios. The output, based on given environmental constraints and an assumed overall intercooler effectiveness, provides mass flow rates of seawater and ethylene glycol, heat exchanger effectiveness and size, intermediate fluid temperatures, and air and seawater outlet temperatures. The output provides preliminary data for specific heat exchanger design and pump and piping selections. / Master of Science

A theoretical model and associated computer program are developed to compute hydrodynamic interaction forces and moments on passing ships in a shallow asymmetric canal, by applying generalized Lagally's theorem. Steady lift force on the ships are estimated following standard slenderbody approach. Passing ships are assumed to travel at constant speeds, parallel to the canal walls. Ships are assumed to be slender, the fluid is ideal and wave making effects are ignored. Numerical calculations for several passing cases show good agreement with existing model test results. / M.S.

This thesis presents an identification scheme for the dynamic model of a ship at sea. We determine the form of the governing differential equations for a ship which is free to pitch and roll, but constrained in all other degrees of freedom, using a perturbation-energy technique. This technique approximates energy expressions and applies Lagrange's equations for quazi-coordinates to develop the equations of motion. When formulating the energies, we take advantage of the ship's symmetry to reduce the number of terms. The equations of motions are approximated such that they contain quadratic and cubic nonlinear terms. Having the form of the governing equations, we set up the parametric identification procedure. Using the method of multiple scales, we exploit resonances and obtain expressions containing subsets of the parameters to be identified. Then we outline a scheme which uses these expressions in conjunction with experimental data to identify the ship parameters. / M.S.

In this dissertation, we present the theory and application of polyspectral signal analysis techniques for interharmonics in shipboard power systems. Interharmonics are generated from various kinds of adjustable speed drives (ASD) in such power systems. ASDs are highly nonlinear devices due to the use of rectifiers and inverters. Since interharmonics can seriously hamper the normal operation of electric ships in many different ways (e.g., excitation of undesirable electrical and/or mechanical resonances, misoperation of control devices, and light flicker), the detection and analysis of interharmonic-related events is a critical issue in assessing power quality in an all-electric ship. Standard signal analysis techniques for regular harmonics are not immediately applicable to interharmonics due to their small amplitude and uncertain frequency of occurrence. Hence, we propose the use of alternative polyspectral analysis techniques such as higher-order spectra (the cross bispectrum/bicoherence) for the detection and analysis of the ASD-generated interharmonics. First, we develop the interharmonic application specific definitions of the cross bispectrum and the cross bicoherence. The statistical characteristics and frequency domain symmetries are also investigated. We apply the modified cross bispectrum to interharmonic detection problems. Due to their small amplitudes, the detection of interharmonics is sensitive to many undesirable factors such as spectral leakage and measurement error. Our analysis results demonstrate that the detection performance of the conventional DFT-based method is seriously degraded in the presence of noise. Hence, we develop a constant false alarm rate (CFAR) interharmonic detector based on the modified cross bispectrum. Our analysis and experimental results show that our method can provide more robust detection performance than conventional methods in the presence of noise. We also develop an ASD condition monitoring method based on the cross bicoherence. The key idea is to diagnose the status of the load side of an ASD from observations made at the source side. In this dissertation, we apply our method to detection and analysis of phase imbalance at the load side of the ASD. Our experimental results demonstrate that the proposed method provides a unique interharmonic signature for detection and classification of asymmetric impedance associated with the phase imbalance. Furthermore, the proposed method shows a more sensitive detection performance compared to the conventional imbalance measurement method, which enables prognosis of potential faults. A novel quadratic phase coupling detector for a single data record with coherent interharmonics is developed. The traditional bicoherence definition fails when its ’phase randomization’ assumption is not satisfied. This assumption is not appropriate for certain applications such as continuous monitoring of rotating machines. Therefore, we propose a novel quadratic phase coupling detector and compare it with previous techniques. It is shown that our detector is superior to previous detectors at high SNRs, and can also address partially coherent cases which previous approaches could not properly address. Flicker issues related to interharmonics are also discussed. We present a newly found limitation of the current IEC flickermeter regarding detecting flicker caused by low frequency interharmonics. We also present observation results of flicker responses of various lamps including light-emitting-diode (LED) lamps. Our observation results confirm that compact fluorescent and LED lamps are sensitive to high frequency interharmonics, although the IEC flickmeter can not detect flicker caused by such interharmonics. Hence, we develop an alternative flicker detection method based on down-up sampling. Our experiment results show that our method can detect flicker regardless of the value of the interharmonic frequencies. Independent of interharmonic topics, we also present our additional achievement involving application of wavelet denoising techniques to network congestion monitoring problems. This was a collaboration with researchers at the Department of Computer Sciences in the University of Texas at Austin, and mainly completed before becoming engaged in the electric ship project. By applying wavelet techniques, we could drastically enhance shared congestion detection performance over previously proposed methods. / text

Thesis (Ph. D.)--University of Texas at Austin, 2008. / Vita. Includes bibliographical references.

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