1. S. G. Krein and N. N. Moiseev, ‘‘On oscillations of a vessel containing a liquid with a free surface,’’ Prikl. Mat. Mekh. 21, 169–174 (1957).
2. N. D. Kopachevsky, S. G. Krein, and Ngo Zuy Kan, Operator Methods in Linear Hydrodynamics: Evolutionary and Spectral Problems (Nauka, Moscow, 1989) [in Russian].
3. N. D. Kopachevsky and S. G. Krein, Operator Approach in Linear Problems of Hydrodynamics, Vol. 2: Nonself-Adjoint Problems for Viscous Fluid (Birkhäuser, Berlin, 2003).
4. K. V. Forduk and D. A. Zakora, ‘‘Problem on small motions of a system of bodies filled with ideal fluids under the action of an elastic damping device,’’ Lobachevskii J. Math. 42, 889–900 (2021).
5. K. V. Forduk and D. A. Zakora, ‘‘A problem of normal oscillations of a system of bodies partially filled with ideal fluids under the action of an elastic damping device,’’ Sib. Electron. Math. Rep. 18, 997–1014 (2021).