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キーワード:
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MPIPKS:
Time dependent processes
要旨:
Interfacial internal wave excitation in the wake of towed ships is studied experimentally in a quasi-two-layer fluid. At a critical
'resonant' towing velocity, whose value depends on the structure of the
vertical density profile, the amplitude of the internal wave train
following the ship reaches a maximum, in unison with the development of
a drag force acting on the vessel, known in the maritime literature as
'dead water'. The amplitudes and wavelengths of the emerging internal
waves are evaluated for various ship speeds, ship lengths and
stratification profiles. The results are compared to linear two- and
three-layer theories of freely propagating waves and lee waves. We find
that despite the fact that the observed internal waves can have
considerable amplitudes, linear theories can still provide a
surprisingly adequate description of subcritical-to-supercritical
transition and the associated amplification of internal waves. We argue
that the latter can be interpreted as a coalescence of frequencies of
two fundamental stable wave motions, namely lee waves and propagating
interfacial wave modes.
