“…Under these assumptions, problem (1), (2) has a unique solution u ∈ C [0, T ]; H 1 0 (Ω) , ∂ t u ∈ C [0, T ]; L 2 (Ω) for any T > 0 (see [4][5][6]). Hence, this problem generates a continuous semigroup {S(t)}, t 0, acting on the phase space H = H 1 0 (Ω) × L 2 (Ω) by the formula S(t)(u 0 (x), p 0 (x)) = y(t) ≡ (u(t, x), p(t, x)) ∈ H, This work was financially supported by the Russian Foundation for Basic Research (grant no.…”