The variational principle[Formula: see text]involving the independent thermodynamic fluxes Ji and forces Xi and subject to the non-holonomic constraint, Xi = constant, gives an expression for the integral behavior of an unconstrained heterogeneous conduction–diffusion–reaction–viscous flow process. The validity of this expression can be checked by performing the variation with respect to the forces to obtain as Euler–Lagrange equations the phenomenological equations,[Formula: see text]This principle allows the unique mathematical specification of certain non-stationary systems which are not easily amenable to differential analysis.As an example, it is demonstrated that the principle generates an approximate expression for the steady growth velocity, v, of an isothermal segregation reaction in terms of the degree of advancement of the reaction, [Formula: see text], and its derivative with respect to v,[Formula: see text]
BDS PPP/INS Tight Coupling Method Based on Non-Holonomic Constraint and Zero Velocity Update