ABSTRACT
The important issue of projecting in dynamic problems, and, in particular, in hydrodynamics, is to establish individual modes as relations of specific perturbations of a medium. As with the first approximation, these links may be established as they follow from the linearized equations, that is, in the flow of infinitely-small magnitudes of perturbations. These links may be corrected with any desired accuracy by involving the nonlinear terms. Sound is usually determined as the isentropic or nearly isentropic mode. Hence, the links of perturbations in sound should support its adiabaticity with some accuracy. The modes propagate independently in a linear flow exclusively. The nonlinear coupling of modes may be described by the means of linear projecting.
