Khi coi chất lỏng là lý tưởng (không có tính nhớt) áp suất thủy động hướng theo pháp tuyến của mặt tác dụng, còn trong chất lỏng thực, áp suất thủy động cũng hướng vào mặt tiếp xúc nhưng xiên góc với phương pháp tuyến, vì nó là tổng hợp của ứng suất pháp tuyến và ứng suất tiếp tuyến do lực nhớt gây ra. | 116 Rotating Shallow-Water and Wave Dynamics Fig. . Oceanic internal gravity waves on the near-surface pycnocline as measured by a satellite s Synthetic Aperture Radar reflection from the associated disturbances of the sea surface. The waves are generated by tidal flow through the Straits of Gibraltar. NASA internal-gravity inertial and Rossby wave oscillations. In this chapter a more extensive examination is made for the latter three wave types plus some others. This is done using a dynamical system that is more general than 2D fluid dynamics because it includes a non-trivial influence of stable buoyancy stratification but it is less general than 3D fluid dynamics. The system is called the Shal low-Water Equations. In a strict sense the Shallow-Water Equations represent the flow in a fluid layer with uniform density Po when the horizontal velocity is constant with depth Fig. . This is most plausible for flow structures whose horizontal scale L is much greater than the mean layer depth H . H L c 1. Recall from Sec. that this relation is the same assumption that justifies the hydrostatic balance approximation which is one of the ingredients in deriving the Shallow-Water Equations. It is also correct to say that the Shallow-Water Equations are a form of the hydrostatic Primitive Equations Sec. limited to a single degree of freedom in the vertical flow structure. Rotating Shallow-Water Equations 117 The Shallow-Water Equations can therefore be interpreted literally as a model for barotropic motions in the ocean including effects of its free surface. It is also representative of barotropic motions in the atmospheric troposphere although less obviously so because its upper free surface the tropopause may more readily influence and in response be influenced by the flows above it whose density is closer to the troposphere s than is true for air above water. The Shallow-Water Equations mimic baroclinic motions in a restricted sense explained below
