When a fluid is in motion, it must move in such a way that mass is conserved. To see how mass conservation places restrictions on the velocity field, consider the steady flow of fluid through a duct ...

1 I. Vekua Sokhumi Institute of Physics and Technilogy (SIPT), Tbilisi, Georgia. 2 Sokhumi State University, Tbilisi, Georgia. In the monography [1] , the expression for the square of phase speed of ...