碩士 / 國立臺灣大學 / 造船工程學系 / 86 / The ocean environment can be regarded as one time-varying,
dynamic structure. Therefore, one often analyzes the ocean
environment by transformation its characteristics into modal
domains. The modal analysis decomposes the acoustic field into
modal space, and obtains the energy distribution of each
individual mode (mode coupling coefficient) and the modal travel
time. The acoustics field is computed by the parabolic equation
method (PE method ). The mode functions and modal?&Uenumbers
are computed by solvi the local modal equation. The modal travel
time is a measure of the sound speed variations. For range-
independent environment (no horizontal variations in sound speed
and topography), the mode coupling coefficients equal to zero.
For range-dependent environment such as cold eddy, front and
bottom topographical changes, mode coupling will occur, hence
the mode coupling coefficient will be non-zero. Mode coupling
coefficients are a measure of complexity of the ocean
environment.The modal analysis in this woris based on the theory
of MOSPEF (Modal Spectrum of PE Field). The goal is to establish
the framework of 3D modal analysis (Modal Spectrum of 3D PE
Field , MOS3DPEF). The desired results are mode coupling
coefficients and the travel time. All results in this work are
calculated by the MOS3DPEF program. In the ridge case, when
excite by different mode starter, the modal amplitudes of
dominant modes decay at the apex line, which is due to energy is
being transfered to adjacent vertical plane, that is theta-
cpling effects on modes. However, the modal travel time remain
the same for the first three modes at the apex. Hence, the modal
coupling affects energy distribution, but not for modal travel
time. In the case for the front, the modal amplitude results
show having re-population phenomena in high frequency condition,
which is due to mode coupling, but nor from theta-coupling. At
high frequency, the change of modal amplitude and mode shape
decrease with increasing mode number.
| Identifer | oai:union.ndltd.org:TW/086NTU00345002 |
| Date | January 1998 |
| Creators | Chen, Ping-Shen, 陳屏先 |
| Contributors | Chen Chi-Fang, 陳琪芳 |
| Source Sets | National Digital Library of Theses and Dissertations in Taiwan |
| Language | zh-TW |
| Detected Language | English |
| Type | 學位論文 ; thesis |
| Format | 1 |
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