ABSTRACT
A problem may be analysed for a system of constant mass, or volume for an incompressible flow motion. The description of the flow motion is called a system approach and the basic equations are the integral forms of the continuity, momentum and energy principles. The technique yields global results without entering into the details of the flow field at the small scale. For example, the application of the integral form of the conservation of mass and conservation of momentum to the flow underneath a vertical sluice gives an expression of the pressure force applied to the gate (Fig. 1A), without the need to know the pressure distribution on the gate upstream face.
