Mechanics of particles for fluid dynamics: derivation of dissipative equations of motion using the principle of least action and fractional derivatives
Abstract:
Equations of motion for systems with forces proportional to velocity are
derived from the principle of least action using classical Euler-Lagrange
equation and Lagrangian that contains terms responsible for energy
dissipation. These terms are expressed through fractional derivatives of the
coordinate of order $0 < \alpha < 1$.
This approach naturally leads to the introduction of non-uniform flow of
time in dissipative processes. It incorporates inhomogeneous velocity without unphysical
approximations. The fractional term in the Lagrangian provides correct
Euler-Lagrange and, ultimately, Hamilton equations with energy
dissipation rate defined by $\alpha$.
Smooth, gradual transition from classical mechanics (for example, Molecular
Dynamics of point masses) to fluid dynamics (Navier-Stokes) can be
realised using this approach.