On linearly convex domains with smooth boundaries

We establish that an arbitrary locally linearly convex domain with a smooth boundary is strongly linearly convex. Chernigov Pedagogic Institute, Chernigov. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 49, No. 11, pp. 1553–1556, November, 1997.     

The evolution compressible Navier-Stokes system on polygonal domains

The evolution compressible Navier-Stokes system is considered on polygonal domains. It is shown that the lowest order of the corner singularity of the system is the same as that of the heat equation. In a suitable Banach space the velocity is split into singular and regular parts and the coefficient of the singularity is expressed by convolution of some two functions in the time variable. By a formula of the pressure we observe propagation of the corner singularity along the characteristic lines emanating from the corners and also unboundedness of derivatives of pressure there. An increased regularity for the remainder part is established.     

Solvability of boundary and initial-boundary value problems for the Navier-Stokes equations in domains with noncompact boundaries

One considers boundary and Initial-boundary value problems for Navier-Stokes equations in domains with several “outlets” at infinity. It is shown that if one prescribes the limiting values of the pressure at infinity in those “outlets” which expand sufficiently fast, then these problems are solvable in the class of vectors with a finite Dirichlet integral.     

Complete asymptotic decomposition of the sojourn probability of a diffusion process in thin domains with moving boundaries

We investigate a diffusion process ξ(t) with absorption defined in a thin domainD _ε ={(x,t)∶εG ₁ (t)<x<εG ₂ (t), t≥0}. We obtain the complete decomposition of the sojourn probability of ξ(t) inD _ε with respect to ε→0. Institute of Mathematics, Ukrainian Academy of Sciences, Kiev. Translated from Ukrainskii Matematicheskii Zhurnal, Vol. 51, No. 9, pp. 1155–1164, September, 1999.     

On isoperimetric problems for domains with partly known boundaries

In the present paper, we discuss the isoperimetric problems for domains with partly known boundaries, i.e., the problem of determining a domain that minimizes the capacity functional in the class of plain double-connected domains having the same fixed area and outer boundary. The formulas for capacity variations obtained in this paper allows us to formulate necessary conditions.It is proved that the convexity of the fixed outer boundary implies the convexity of the inner boundary corresponding to an optimal domain. Then, we discuss the case where the fixed part of the boundary is a square.Further, we consider similar problems with more complicated functionals. We introduce the concept of a minimal function in the class of equimeasurable functions. This concept allows us to unify the approach to all of these problems. At the end, we produce a hypothesis that, if proved, would enable us to characterize the shape of the optimal domains in the isoperimetric problems mentioned above.The author wishes to express his appreciation to Dr. K. A. Lurie for his help and unceasing attention.     

The effective boundary conditions for vector fields on domains with rough boundaries: Applications to fluid mechanics

The Navier-Stokes system is studied on a family of domains with rough boundaries formed by oscillating riblets. Assuming the complete slip boundary conditions we identify the limit system, in particular, we show that the limit velocity field satisfies boundary conditions of a mixed type depending on the characteristic direction of the riblets.     

Vanishing viscosity limit for a coupled Navier-Stokes/Allen-Cahn system

In this paper, we study the vanishing viscosity limit for a coupled Navier-Stokes/Allen-Cahn system in a bounded domain. We first show the local existence of smooth solutions of the Euler/Allen-Cahn equations by modified Galerkin method. Then using the boundary layer function to deal with the mismatch of the boundary conditions between Navier-Stokes and Euler equations, and assuming that the energy dissipation for Navier-Stokes equation in the boundary layer goes to zero as the viscosity tends to zero, we prove that the solutions of the Navier-Stokes/Allen-Cahn system converge to that of the Euler/Allen-Cahn system in a proper small time interval. In addition, for strong solutions of the Navier-Stokes/Allen-Cahn system in 2D, the convergence rate is cν1/2.