Free oscillations hâve periods that are dépendent upon the horizontal
and vertical dimensions of the basin, the number of nodes of the standing
wave, that is, lines where déviation of the free surface from its undisturbed value is zéro, and friction. The period of a true forced-wave
oscillation is the same as the period of the causative force. Forced
oscillations, however, are usually generated by intermittent extemàl
forces, and the period of the oscillation is determined partly by the
period of the extemal force and partly by the dimensions of the water
basin and the mode of oscillation. Oscillations of this type hâve been
called forced seiches (Chrystal, 1905) to distinguish them from free
seiches in which the oscillations are free.
(B) CLOSED BASIN
(A) STANDING WAVES
(-0
_
( I ). Fundamental Mode
(First Harmonie)
(2). Second Mode
(Second Harmonie)
(3) Third Mode
(Third Harmonie)
(I). Fundamental Mode
(First Harmonie)
(C) OPEN-ENDED tfASIN
(2). Second Mode
(Third Harmonie)
(3).Third Mode
(Fifth Harmonie)
Surface profiles for oscillating waves
( after Corr ,1953 )
Figure 3-40. Long-Wave Surface Profiles
For the simplest form of a standing one-dimensional wave in a closed
rectangular basin with vertical sides and uniform depth (Fig. 3-40(B)),
wave antinodes, that is, lines where déviation of the free surface from
its undisturbed value is a relative maxima or minima, are situated at the
ends (longitudinal seiche) or sides (transverse seiche). The num er o
nodes and antinodes in a basin dépends on which mode or modes of oscillation are présent. If n = number of nodes along a given basin axis,
-
basin depth, and
= basin length along that axis, then Tn, the natural
free oscillating period is given by
T = 2(b
(3-42)
"
nx/gcT
3-79
and vertical dimensions of the basin, the number of nodes of the standing
wave, that is, lines where déviation of the free surface from its undisturbed value is zéro, and friction. The period of a true forced-wave
oscillation is the same as the period of the causative force. Forced
oscillations, however, are usually generated by intermittent extemàl
forces, and the period of the oscillation is determined partly by the
period of the extemal force and partly by the dimensions of the water
basin and the mode of oscillation. Oscillations of this type hâve been
called forced seiches (Chrystal, 1905) to distinguish them from free
seiches in which the oscillations are free.
(B) CLOSED BASIN
(A) STANDING WAVES
(-0
_
( I ). Fundamental Mode
(First Harmonie)
(2). Second Mode
(Second Harmonie)
(3) Third Mode
(Third Harmonie)
(I). Fundamental Mode
(First Harmonie)
(C) OPEN-ENDED tfASIN
(2). Second Mode
(Third Harmonie)
(3).Third Mode
(Fifth Harmonie)
Surface profiles for oscillating waves
( after Corr ,1953 )
Figure 3-40. Long-Wave Surface Profiles
For the simplest form of a standing one-dimensional wave in a closed
rectangular basin with vertical sides and uniform depth (Fig. 3-40(B)),
wave antinodes, that is, lines where déviation of the free surface from
its undisturbed value is a relative maxima or minima, are situated at the
ends (longitudinal seiche) or sides (transverse seiche). The num er o
nodes and antinodes in a basin dépends on which mode or modes of oscillation are présent. If n = number of nodes along a given basin axis,
-
basin depth, and
= basin length along that axis, then Tn, the natural
free oscillating period is given by
T = 2(b
(3-42)
"
nx/gcT
3-79