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The Lecture Notes in Physics Part 9

Một số nhà vật lý cho rằng thuyết cơ học cổ điển vẫn có nhiều điểm hạn chế như khi được đặt ở một phạm vi khác, như thế giới vi mô hay thế giới vĩ mô, thì cơ học cổ điển không còn mô tả chính xác nữa. Cơ học cổ điển vấn rất gần gũi với chúng ta, bởi vì nó mô tả đúng những gì trong thế giới mà chúng ta đang sống. | 158 O. Buhler Fig. 5.3 Plunging wave breaker. The wave is moving left to right and the rolling motion after breaking implies an organized bundle of vorticity pointing into the picture along the wave crest spinning clockwise overturning irrotational water mass into a rolling water mass with an appreciable amount of solid-body rotation in the y-direction i.e. clockwise in the xz-plane. Now in the strict two-dimensional version of this problem which is physically impossible of course because of the three-dimensional turbulence this organized vorticity points strictly into the y-direction. However we can imagine that the breaking wave is confined in the y-direction such that wave breaking is possible only in y e 0 D with some lateral breaking width D. This would be appropriate for the localized wave breaking on a beach with a point break for instance. In this case the vorticity must be confined to this lateral interval and because vorticity lines cannot end in the fluid that means the clockwise vorticity in the core of the breaker must burrow out and connect to the boundaries of the fluid. If the water is deep enough it stands to reason that the only possible boundary is the water-air boundary. This leads to the image of a banana-shaped region of organized vorticity with the core of the banana lying in y e 0 D and the upwards-bending ends of the banana connecting to the free surface. A modicum of doodling then shows that viewed from above i.e. looking down onto the xy-plane the vertical vorticity components are such that there is positive vorticity to the left of the propagation direction of the breaking wave and negative vorticity to the right 37 38 .9 Consequently the impulse associated with this vertical vorticity points in the x-direction i.e. it points in the same direction as the phase velocity of the wave. This is consistent with a breaking-induced conversion of horizontal pseudomomentum which is parallel to the intrinsic phase speed into mean flow impulse. 9 To