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Frequency downshifting in surface wa...

University of California, Santa Barbara.

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Frequency downshifting in surface waves and free surface flows without waves.

紀錄類型:	書目-語言資料,印刷品 : Monograph/item
正題名/作者:	Frequency downshifting in surface waves and free surface flows without waves./
作者:	Oshri, Ofer.
面頁冊數:	237 p.
附註:	Chair: Marshall P. Tulin.
Contained By:	Dissertation Abstracts International58-03B.
標題:	Applied Mechanics. -
電子資源:	http://pqdd.sinica.edu.tw/twdaoapp/servlet/advanced?query=9724590
ISBN:	9780591334364

Frequency downshifting in surface waves and free surface flows without waves.
Oshri, Ofer.

Frequency downshifting in surface waves and free surface flows without waves. - 237 p.

Chair: Marshall P. Tulin.

Thesis (Ph.D.)--University of California, Santa Barbara, 1996.

This dissertation is composed of two independent parts. The first part is about frequency downshifting in ocean spectra. This was the last research subject in my PhD program. It deals with, qualitatively and quantitatively, a description of a well known feature in the development of wind wave spectrum--the shift of energy to lower frequencies with the wind fetch or duration. We show analytically, and numerically, that ideas Tulin suggested (see Chapter 3) are very successful in describing the phenomenon. The second part describes modifications of a twenty five year old theory on hydrodynamic shapes with less wave resistance. The modified theory is used to demonstrate the construction of 2D and 3D bodies with zero or substantially reduced wave resistance.

ISBN: 9780591334364Subjects--Topical Terms:

1018410
Applied Mechanics.

Frequency downshifting in surface waves and free surface flows without waves.
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245 1 0 $a Frequency downshifting in surface waves and free surface flows without waves.
300 $a 237 p.
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500 $a Source: Dissertation Abstracts International, Volume: 58-03, Section: B, page: 1492.
502 $a Thesis (Ph.D.)--University of California, Santa Barbara, 1996.
520 $a This dissertation is composed of two independent parts. The first part is about frequency downshifting in ocean spectra. This was the last research subject in my PhD program. It deals with, qualitatively and quantitatively, a description of a well known feature in the development of wind wave spectrum--the shift of energy to lower frequencies with the wind fetch or duration. We show analytically, and numerically, that ideas Tulin suggested (see Chapter 3) are very successful in describing the phenomenon. The second part describes modifications of a twenty five year old theory on hydrodynamic shapes with less wave resistance. The modified theory is used to demonstrate the construction of 2D and 3D bodies with zero or substantially reduced wave resistance.
520 $a In part I, a physical description of frequency downshifting, observed in the ocean and also in wave tank experiments, is presented by employing a narrow-banded wave system approximation, Hamiltonian formulation, and spectral methods. The general picture is based on Tulin's heuristic theory. It is shown that the heuristic description can be derived, almost perfectly, rigorously for cases of single and multi-wave systems under the narrow-banded assumption. Equations for the evolution of the energy and the wave celerity are derived in the presence of non-conservative effects such as the wind input and wave breaking. The importance of the imbalance between the energy dissipation and momentum loss for frequency downshifting, which is described, mathematically, by the celerity evolution equation, is shown.
520 $a A general scheme for numerical simulation of a discrete set of wave modes is presented. The scheme is based on set of equations which are derived in the process of getting the celebrated Zakharov equation. A numerical scheme, modified to incorporate non-conservative influences, based on these equations is presented here for the first time. Conservative and non-conservative systems are simulated. In cases of conservative systems, we show the conservation of energy, within computational accuracy, during the whole evolution process. The effect of bound waves on the general evolution process (instability and recurrence) is also studied. To simulate non-conservative effects we apply pressure distributions on the free surface which simulate the wind input and wave breaking. Permanent frequency downshifting is observed. The importance of the energy-momentum imbalance is shown.
520 $a In part II, old ideas and theory on the combination of vertical force distribution (vertical dipole), and cross section squashing (transverse quadrupole) are utilized to construct bodies with substantially reduced wave resistance. In 2D flows, a vertical dipole distribution is added to a source (a volume forming singularity) distribution to generate wave-free bodies, even at high speeds, with shapes that are rather remarkable. In 3D flows, the basic tool is a 3D compound singularity composed of a source, a vertical dipole, and a transverse quadrupole all at the same position. Their strength relation is optimized at each non-dimensional depth. The lifting capabilities of the hulls, built by using the optimized compound singularity, is hardly changed by the dipole distribution because the total lift generated is essentially zero. In this case, applications are made to submerged near surface hulls and modified Wigley hulls. In both cases the resistance is substantially reduced over the speed range.
590 $a School code: 0035.
650 4 $a Applied Mechanics. $3 1018410
650 4 $a Engineering, Mechanical. $3 783786
650 4 $a Physics, Fluid and Plasma. $3 1018402
690 $a 0346
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710 2 $a University of California, Santa Barbara. $3 1017586
773 0 $t Dissertation Abstracts International $g 58-03B.
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790 1 0 $a Tulin, Marshall P., $e advisor
791 $a Ph.D.
792 $a 1996
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