The Family of Global Attractors for a Generalized Kirchhoff Equations ()
1. Introduction
This paper will study the initial-boundary value problems of the following generalized Kirchhoff equations:
(1)
(2)
(3)
where
is a bounded domain with smooth boundary
,
is an external force term,
is the stress term of Kirchhoff equation,
,
is a strong dissipative term,
is a nonlinear source term.
Many scholars have studied the existence of global attractor of Kirchhoff equation with strong dissipative term, [1] - [7] can be referred.
In reference [8], scholars considered the following Kirchhoff type wave equation with nonlinear strong damping term
(4)
(5)
(6)
Here,
is a bounded domain with smooth boundary
in
,
are normal numbers.
TokioMatsuyama and RyoIkehata [9] proved the global solution and attenuation of the solution of Kirchhoff type wave equation with nonlinear damping:
(7)
With compact boundary conditions
(8)
FucaiLi discussed the higher-order Kirchhoff type equations with nonlinear terms in reference [10]:
(9)
(10)
(11)
In a bounded domain, where
is a positive integer,
is a normal number, if
, the existence of global solution will be obtained, if
, for any initial value with negative initial energy, the solution explodes in a finite time. For more related research results, please refer to references [11] [12] [13] [14].
In this paper, for the convenience of narration, the following spaces and marks are defined:
,
,
,
,
. Define
and
to represent the inner product and norm of H respectively,
namely
Let
be the family of global attractor from
to
,
be the bounded absorption set in
, where
.
represents a constant.
(H1) assume that Kirchhoff type stress term
satisfies:
where
is a constant.
(H2)
There exist constant
,
.
2. The Existence and Uniqueness of Global Solution
In this section, under the assumption of Kirchhoff stress term, the existence and uniqueness of global solution are obtained by prior estimation and Galerkin’s method.
Lemma 2.1 Suppose Kirchhoff stress term
satisfies the conditions (H1), Assume that (H2) holds,
,
,
,
, then the smooth solution of the initial-boundary value problem (1.1)-(1.3) satisfies
,
,
, and satisfy that following inequality
(1)
(2)
where
,
.
So there is a non-negative real number
and
, make
(3)
Proof. Set
, take the inner product of both sides of Equation (1.1) with v in H, we obtain
(4)
(5)
According to hypothesis (H1), we can get
(6)
By Young’s inequality and Poincaré’s inequality
(7)
where
is the first eigenvalue of
with homogeneous Dirichlet boundary condition on
.
we can get
(8)
According to Young’s inequality, we get
(9)
Substitute (2.5)-(2.9) into (2.4),
(10)
Make
.
Take
.
Then (2.10) can be converted into
(11)
By Gronwall’s inequality
(12)
(13)
where
.
So there is a non-negative real number
and
, such as
(14)
Lemma 2.1 is proved.
Lemma 2.2 Assume that (H1), (H2) holds, if
,
,
,
, Then the smooth solution
of the initial-boundary value problem (1.1)-(1.3) satisfies
,
and satisfy that following inequality
(15)
(16)
So there is a non-negative real number
and
, make
(17)
Proof. Take the inner product of
and the two sides of Equation (1.1), and get
(18)
By Young’s inequality, Poincaré’s inequality
(19)
According to hypothesis (H1)
(20)
By Young’s inequality, Poincaré’s inequality
(21)
where
is the first eigenvalue of
with homogeneous Dirichlet boundary condition on
.
we can get
By Young’s inequality, Poincaré’s inequality
(22)
By Schwarz’s inequality, Young’s inequality
(23)
Substitute (2.19)-(2.23) into (2.18) to get
(24)
Take
.
Let
.
Then (2.24) can be converted into
(25)
By Gronwall’s inequality
(26)
(27)
where
.
So there is a non-negative real number
and
, make
(28)
Lemma 2.2 is proved.
Theorem 2.1 Under the assumption of lemma 2.1 and lemma 2.2, and satisfy the hypothesis (H1), (H2), Then the initial-boundary value problem (1.1)-(1.3) has a unique smooth solution
,
,
.
Proof. Existence: Galerkin’s method is used to prove the existence of global smooth solution.
Step 1: construct an approximate solution.
Let
. where
is the eigenvalue of
with homogeneous Dirichlet boundary on
,
denotes the eigenfunction determined by the corresponding eigenvalue
,
constitute the orthonormal basis of H from the eigenvalue theory.
Let the approximate solution of the problem (1.1)-(1.3) be
, where
is determined by the following equations.
(29)
The formula (2.29) satisfies the initial condition
.
When
,
in
, according to the basic theory of ordinary differential equations, the approximate solution
exists on
.
Step 2: Prior estimation.
, multiplying by
and summing over j, we can get
1)
, by lemma 2.1, there is
(30)
(31)
2)
, by lemma 2.2, there is
(32)
(33)
From (2.30) and (2.32),
is bounded in
,
in
is bounded.
It can be seen that the formula (2.30)-(2.33) holds a priori estimates for lemma 2.1 and lemma 2.2 respectively.
Step 3: Limit process.
In
space, select the subsequence
from the sequence
,
Make
in
weak * convergence.
According to Rellich-Kondrachov compact embedding theorem,
compactly embeds
, Then
converges strongly almost everywhere in
.
Let
in (2.29), and take the limit, for fixed j,
,
Then from (2.29), make
in
weak * convergence.
Thus
in
weak * convergence.
in
weak * convergence.
So
in
convergence.
is a conjugate space of
infinite differentiable space.
in
weak * convergence.
in
weak * convergence.
in
strong convergence, almost everywhere convergence.
(34)
In
weak * convergence.
Take
. (2.34) almost everywhere
,
in
weak convergence.
Therefore
, so
in
weak * convergence. In particular,
weak convergence in the
,
weak convergence in
, From all j and
,it can be introduced
Because of the density of
.
Therefore, the existence is proved.
The uniqueness of the solution.
Set
is equations of two solutions, make
, w satisfies
(35)
Take inner product of (2.35) and
in H is as follows
(36)
Therefore
(37)
(38)
By differential mean value theorem, Young’s inequality
(39)
where
.
By Young’s inequality
by the interpolation inequality
in the same way with
where
.
By Poincaré’s inequality
(40)
By (2.37)-(2.40)
(41)
Take the
,
there are
(42)
where
.
By Gronwall’s inequality
(43)
Thus
, or
, therefore, the uniqueness is proved.
Theorem 2.2 [11] Let E be a Banach space and
semigroups satisfy the following conditions.
1) semigroup
is uniformly bounded in E, and
, there is a constant
, so that when
, there is
2) There is a bounded absorption set
in E.
3)
is a fully continuous operator
Then a semigroup
is said to have a compact global attractor
.
Theorem 2.2 in Banach space E change to the Hilbert space
, has the following the existence theorem of the family of global attractor.
Theorem 2.3 If the global smooth solution of the problem (1.1)-(1.3) satisfies the assumptions and conditions of lemma 2.1 and lemma 2.2, then the problem (1.1)-(1.3) have a family of global attractor
. That is, there is a compact set
, which makes:
1)
.
2)
.
where
,
is the solution semigroup of (1.1)-(1.3).
Proof. It is necessary to verify the hypothesis (1), (2), (3) of theorem 2.2. It is easy to know that the Equation (1.1) has a solution semigroup
under the hypothesis of theorem 2.3.
1) by lemma 2.1, lemma 2.2, bounded set for
and contained in
.
where
, this suggests that the
in
uniformly bounded.
2) by lemma 2.1, lemma 2.2, there are further
.
So
is the bounded absorbing set of semigroup
.
3) since
is embedded, then
bounded set of compact set of
, so the family of semigroup operators
is continuous, so the equation exists a family of global attractor
.
3. Estimation of the Dimension of the Family of Global Attractor
Firstly, we linearize the equation into a first-order variational equation and prove that the solution semigroup
is Fréchet differentiable on
, and further prove the attenuation of the volume element of the linearization problem. Finally, the upper bound of Hausdorff dimension and Fractal dimension of
is estimated.
The Equations (1.1)-(1.3) is linearized
(1)
(2)
(3)
where
is the solution of the problem (1.1)-(1.3) with
. Given
, it can be proved that for any
, there is a unique solution
to the linearized initial-boundary value problem.
Lemma 3.1 if
, Fréchet differential on
is a linear operator
, let
, and the mapping
is Fréchet differentiable on
, where
is the solution of linearized initial-boundary value problem.
Proof.set
,
, and
,
, make
,
, In which the semigroup
is Lipschitz continuous on the bounded set of
, that is,
, Make
. so you can get it.
(4)
(5)
Make
.
(6)
Subtract these three equations to get:
(7)
where
(8)
Make
.
(9)
By the differential mean value theorem
(10)
where
,
.
Take inner product of
and
, there is
(11)
where
.
(12)
(13)
(14)
The
.
Take inner product of
and
.
(15)
where
Combined with (3.11)-(3.15), there are
(16)
Through the Gronwall’s inequality, there is
(17)
When
(18)
So the lemma 3.1 is proved.
Lemma 3.2 Under the assumption and condition of lemma 3.1, the family of global attractor
of initial-boundary value problem (1.1)-(1.3) has Hausdoff dimension and Fractal dimension, and
,
.
Proof. Make
,
,
,
is an isomorphic mapping, let
be the global attractor of
, and
is the global attractor of
, and they have the same dimension, from lemma 3.1, we can know that
is Fréchet differentiable. The linearized first-order variational Equation (3.1) can be rewritten as
(19)
(20)
where
,
I is an identity operator.
,
. Make
,
,
is an isomorphic mapping. For a fixed
, let
be n element of
, let
be n solutions of the linear Equation (3.19), its initial value is
.
so
(21)
Further, by the same Gronwall’s inequality, available:
(22)
where
stands for outer product and tr stands for trace.
is an orthogonal projection from space
to
.
Given a certain moment
,
set
is
orthonormal basis.
We define the inner product in
is
(23)
To sum up, it is available
(24)
where
.
(25)
where
.
Above all there is
(26)
Because
is
orthonormal basis. Therefore
(27)
(28)
Almost all the t.
(29)
The
and
,
is
characteristic value, and
, so there is
(30)
Set
(31)
and
(32)
Therefore,
(33)
Therefore,
Lyapunov index
is uniformly bounded, and
(34)
make
(35)
(36)
Further,
(37)
From this we can get
, Then the Hausdorff dimension and Fractal dimension of the family of global attractor
are finite.