1. Statement of the initial-boundary value problem and formulation of the main result
Modeling the motion of multicomponent media, and hence the solution of the resulting mathematical problems, is an interesting and relatively little-studied problem of both physics and mathematics. Until now, a unified approach to this problem has not been developed, and there is no advanced mathematical theory about the existence, uniqueness, and properties of solutions to initial-boundary value problems that arise in this modeling. The purpose of this article does not include a detailed review of this problem as a whole; to a certain extent, an idea of it can be obtained from monographs [
1,
2], as well as from the reviews given in the articles [
3,
4]. The aim of the article is a mathematical study of the asymptotic behavior of the solution at
of the following initial-boundary value problem for one-dimensional isothermal equations of viscous compressible multicomponent media:
Here
,
,
are respectively the density and velocity of the medium components, which are sought functions of time
,
, and of the point
x of the flow domain
,
is and average velocity of the medium,
is the number of components,
, and constant viscosity coefficients
,
from a symmetric matrix
.
As can be seen, equations (
1), (
2) are a generalization of the one-dimensional isothermal Navier—Stokes equations for the multicomponent case. Equations (
2) contain higher order derivatives of the velocities of all components, since, unlike the Navier—Stokes equations, in which viscosity is a scalar, in the multicomponent case, due to the composite structure of viscous stress tensors, the viscosities form a matrix whose entries are responsible for viscous friction. Diagonal elements are responsible for viscous friction within each component, while off-diagonal elements are responsible for friction between components. This does not allow us to automatically extend the known results for the Navier—Stokes equations to the multicomponent case. In the case of a diagonal viscosity matrix, the equations are connected possibly via the lower order terms only. In this paper, we consider a more complex case of an off-diagonal viscosity matrix. Stabilization of solutions to one-dimensional Navier—Stokes equations is studied in [
5,
6,
7,
8,
9]. Unique solvability and asymptotic behavior (as
) of the solution to the considered one-dimensional equations of viscous compressible multicomponent media in the polytropic case is studied in [
10,
11,
12]. Similar questions for related one-dimensional models of multicomponent media are discussed in [
13,
14,
15,
16,
17,
18,
19,
20].
It will be useful to use mass Lagrangian coordinates in the study of the equations (
1), (
2). Let us consider
t and
as new independent variables. Then the system (
1), (
2) takes the form
After that, the flow domain
transforms to the domain
, where
, and the initial and boundary conditions arrive at the form
The main result of the article is the following assertion.
Theorem 1. Assume that , , , . Then , , , as , in the norm of the space .
Proof. Let us obtain a priori estimates for the solution to the problem (
1)–(
4), which would be uniform in
t, and from which the stabilization of the solution follows.
2. A priori estimates
Let us multiply the equations (
2) by
, summarize in
i and integrate in
y, thus, using (
1), we obtain
Since
, the second summand in the left-hand side of (9) satisfies the inequality
1 Multiplying (
1) by
and integrating in
x, we obtain for the right-hand side of (
9)
Thus, using (
10) and (
11), from (
9) we derive
In the Lagrangian coordinates
the formula (
12) looks like
From (
13), after integration in
t, we obtain the estimate
where
. Note that all terms in the left-hand side of (
14) are nonnegative.
Let us rewrite the equations (
6) as
where
,
are the entries of the matrix
. Summarizing (
15) in
i, we obtain
where
. The equations (
5) imply that
Substituting
from (17) into the equality (
16), we arrive at the relation
Let us multiply (
18) by
and integrate in
y, then we obtain the equality
The right-hand side of (
19) can be converted via integration by parts and using (
8), (
17):
Hence from (
19) it follows that
Let us integrate (
21) in
t:
The last equality and (
14) lead to the estimate
where
.
Let note that the equation (
5) implies, for every
, the existence of a point
such that
Since
then by the Hölder inequality, taking into account (
22) and (
23), we deduce that
and we immediately conclude that
Hence, from (
14), (
22) and (
24) we obtain the estimate
In order to derive the next group of estimates, we multiply (
6) by
and integrate in
y, thus we obtain
Let us summarize the equation (
26) over
i and integrate over
t, then we obtain
The left-hand side of (
27) satisfies the estimate
Due to (
25) and the inequalities (
)
the second summand in the right-hand side of (
27) satisfies the estimate
where
. The third summand in the right-hand side of (
27) can be estimated as follows:
Thus, from (
27), due to (
28), (
30) and (
31), the estimate
follows. Finally, integrating (
26) in
t, we arrive at the inequalities
3. Stabilization of the solution with an unlimited increase in time
From (
25) and (
33), the following convergence follow
as
. Differentiating (
5) with respect to
y and multiplying by
, using (
29), we arrive at the estimate
Hence, as
, we have
Thus, it is proved that (see (
23)) in the norm of
as
. It is easy to verify now that the same convergence takes place in the Euler variables in the norm of the space
. The theorem is proved. □
4. Conclusions
For the system of differential equations of isothermal viscous compressible multicomponent media with an non-diagonal, symmetric, and positive-definite viscosity matrix, an analysis is made of the asymptotic behavior (as ) of the solution to the initial-boundary value problem in the case of one spatial variable. The main difficulty was to obtain a priori estimates. To overcome it, the mass Lagrangian coordinates have been used. As a result, new a priori estimates are obtained and stabilization of the solution of the initial-boundary value problem is proved.
Funding
The research was supported by Russian Science Foundation (project 23–21–00381).
Conflicts of Interest
The author report no conflict of interest.
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Notes
1 |
Everywhere, , stand for various positive constants depending on the values given in brackets, but independent of t. |
|
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