A Family of Global Attractors for a Class of Generalized Kirchhoff-Beam Equations ()
1. Introduction
In order to study the global stability of a wide norm model for vertical beam vibration, the initial boundary value problems of the following Kirchhoff-Beam equations are studied:
(1)
(2)
(3)
where
is a positive integer,
is the bounded region in
with smooth boundary
.
is the external force term.
is the strongly damped term,
are positive constants,
,
are the general non-negative real-valued functions,
, and the relevant assumptions will be given later. In this
paper, we study the existence and uniqueness of global solutions for problems (1) - (3), prove the existence of a family global attractor and estimate its Hausdorff dimension and Fractal dimension.
In 1883, Kirchhoff [1] proposed the following model when studying the free vibration of elastic strings:
This model more accurately describes the motion of the elastic rod and reveals the physical significance of elastic vibration, from which the Kirchhoff equation model becomes a kind of classical problems in infinite-dimensional dynamic systems. Many scholars have also achieved some good results in their research on the global attractor of Kirchhoff equation and the estimation of Hausdorff dimension. For details, please refer to references [1] [2] [3].
Igor Chueshov [4]: the long time behavior of the following Kirchhoff wave equations with strong nonlinear damping is studied
Tokio Matsuyama and Ryo Ikehata [5]: the attenuation of global solution of Kirchhoff type wave equation with nonlinear damping is proved:
where
are constants.
Guoguang Lin, Yunlong Gao [6]: the initial boundary value problem of Kirchhoff type equation with strongly damped term is studied
The existence and uniqueness of knowledge are proved by prior estimation and Galerkin’s method, and then the existence of global attractor is obtained. The Hausdorff dimension and Fractal dimension of global attractor are estimated.
Lin Chen, Guoguang Lin [7]: study the well-posedness and long-time behavior of solutions for a class of nonlinear higher-order Kirchhoff equations:
The existence and uniqueness of global solutions are proved by prior estimation and Galerkin’s method, and the Hausdorff dimension and Fractal dimension of global attractors are estimated. More studies of wave equations can be found in reference [8] - [19].
For the convenience of statement, the following Spaces and notations are defined:
,
,
,
.
are the different positive constants.
,
,
.
Defines
and
represents H the inner product and norm respectively:
,
,
.
is
-global attractors,
is the bounded absorption set in
,
.
Kirchhoff stress
meet the conditions:
1)
,
,
are the positive constants;
2)
,
,
are the positive constants;
3)
,
,
2. The Existence of the Family of Globals
For the initial boundary value problem (1) - (3), the existence of global solutions is proved by prior estimation and Galerkin’s finite element method, and then the uniqueness of global solutions is proved. Finally, the operator semigroup theory is used to prove that the solution semigroup of this problem has a family of global attractors.
Lemma 1. Assumes that (a), (b), (c) are held,
,
, then the initial boundary value problem (1) - (3) has global smooth solutions
,
(4)
(5)
where
,
,
, a non-negative real number
and
.
Proof. Take the inner product of
and Equation (1) both sides,
(6)
By using Holder’s Inequality, Young’s Inequality, and Poincare’s Inequality, The items in (6) can be obtained by successive processing:
(7)
(8)
(9)
(10)
(11)
(12)
(13)
where
be the first eigenvalue of
with a homogeneous Dirichlet boundary.
Substitute Formulas (7) - (13) into Equation (6) to obtain
(14)
According to the hypothesis (a), (c),
(15)
(16)
Thus
(17)
Using Gronwall’s inequation,
(18)
(19)
So there’s a positive constant
,
, such that
(20)
Lemma 1 is proved.
Lemma 2. Assumes that (a), (b), (c) are held,
,
, then the initial boundary value problem (1) - (3) has global smooth solutions
,
(21)
(22)
where
,
,
,
.
Proof. Take the inner product of
and Equation (1) both sides,
(23)
By using Holder’s Inequality, Young’s Inequality, and Poincare’s Inequality, The items in (23) can be obtained by successive processing:
(24)
(25)
with
.
(26)
(27)
The following two cases are used for prior estimation of Equation (25):
1) As
, By assuming (b),
(28)
let
,
(29)
2) As
, By assuming (b),
(30)
let
,
(31)
Similarly discussion (27) can be obtained
(32)
(33)
(34)
The comprehensive Equations (24) - (34) and (23) can be written as
(35)
According to the hypothesis (c),
(36)
Let
,
(37)
By Gronwall’s inequality, we can get
(38)
where
.
(39)
(40)
So there’s a positive constant
,
, such that
(41)
Lemma 2 is proved.
Theorem 1. (existence and uniqueness of solutions) Under the hypothesis of Lemma 1 and Lemma 2,
,
. Then there exists a unique global solution to the initial boundary value problem (1) - (3),
.
Proof. Existence: The existence of global solution is proved by Galerkin’s finite element method.
The first step: To construct approximate solutions
Let
, where
is the eigenvalues of
with homogeneous Dirichlet boundary on
,
is the eigenfunctions determined by the corresponding eigenvalues and
are the orthonormal basis formed by the eigenvalue theory.
Let the approximate solution of problems (1) - (3) be
, and
is determined by the following nonlinear ordinary differential equations
(42)
It satisfies the initial conditions
. As
, In
,
in
. It is known from the basic theory of ordinary differential that approximate solutions exist on
.
The second step: A prior estimation
Because we want to prove the existence of weak solutions in space
.
So we multiply both sides of Equation (42) with
, and the sum of j, let
.
As
, Get a priori estimate of the solution in space
:
(43)
As
, Get a priori estimate of the solution in space
:
(44)
It can be known that the prior estimates of lemma 1 and lemma 2 of Equations (43) and (44) are valid respectively. According to Equations (43) and (44),
be bounded in
,
be bounded in
.
The third step: Limit process
In the space
, Selecting subcolumns
from the sequence
,
Weak*-convergence, in
(45)
By Rellich-Kohdrachov Compact embedding theorem,
compact embedded
,
Strong convergence almost everywhere in
. (46)
Let
, From (45),
Weak*-convergence in
.
Thus,
convergence in
, here
is
Conjugate space of infinitely differentiable space
.
Weak*-convergence in
.
Weak*-convergence in
.
Weak*-convergence in
.
.
Weak*-convergence in
.
In particular
weak convergence in
,
weak convergence in
. For all j and
, It follows that
(47)
Therefore, the existence of the weak solution of the problem (1) - (3) is obtained, and the existence is proved.
The uniqueness of the solution of the following proof.
Let
be two solutions of Equation (1), set
and take the inner product of
in H,
(48)
Similar to Lemma 1, can be obtained
(49)
(50)
(51)
(52)
(53)
where
.
Substitute (49) - (53) into Equation (48)
(54)
(55)
,
and (c),
Take
Then, according to Gronwall’s inequality, get
(56)
Then
, that is
, So the uniqueness is proved. Theorem 1 is proved.
Theorem 2. According to lemma 1 and theorem 1, then the initial boundary value problem (1) - (3) has a family of global attractors
,
where
is a bounded absorbing set in
and satisfies the following conditions:
1)
;
2)
is a bounded set;
Where
,
is the solution semigroup generated by the initial boundary value problem (1) - (3).
Proof. It is necessary to verify the conditions (I), (II) and (III) for the existence of attractors in reference [8]. Under the condition of Theorem 1, there exists a solution semigroup
of the initial boundary value problem (1) - (3).
From lemma 1, we can obtain that
is a bounded set that includes in the ball
.
(57)
where
,
, this shows that
is uniformly bounded in
.
Furthermore, for any
, when
, we have
, (58)
Therefore,
is a bounded absorbing set in semigroup
.
According to the rellich kondrachov’s compact embedding theorem, if
is compactly embedded in
, then the bounded set in
is the compact set in
. Therefore, the solution semigroup
is a completely continuous operator, thus the family of global attractors
of solution semigroup
is
obtained. Where
.
The proof is completed.
3. The Dimension Estimation for the Family of Global Attractors
In this part, we first linearize the equation into a first-order variational equation and prove that the solution semigroup
is Fréchet differentiable on
. furthermore, we prove the decay of the volume element of the linearization problem. Finally, we estimate the upper bound of the Hausdorff dimension and fractal dimension of
Linearize problems (1) - (3),
(59)
(60)
(61)
where
,
is the solution of problems (1) - (3) with
.
Given
,
, Verifiable to any
, Linearization of initial boundary value problems (59) - (61) has a unique solution:
(62)
Lemma 3. If
, the Frechet differential on
is a linear operator
, then
,
, the mapping
is Fréchet differentiable on
, where
is the solution of the linearized initial boundary value problem (59) - (61).
Proof. Set
,
and
,
the semigroup
is Lipschitz continuous on the bounded set of
, i.e.
(63)
Let
, then
(64)
(65)
Set
,
Then the three equations can be subtracted
(66)
then
,
(67)
(68)
(69)
(70)
(71)
(72)
(73)
we obtain from Equations (69) - (73),
with
.
Do the same thing,
(74)
Take inner product
with
, by usingYoung’s inequality, Poincare’s inequality,
(75)
where
(76)
(77)
(78)
From Equation (75) - (78), it follows
(79)
where
.
Equation (73) and Equation (79) deduce that,
(80)
According to the hypothesis (c),
,
(81)
with
,
Obtained by Gronwall inequality
.
(82)
From (82), as
,
(83)
Lemma 3 is proved.
Theorem 3. Under the assumptions and conditions of theorem 2, then a family of global attractors
of initial boundary value problem (1) - (3) has Hausdorff dimension and fractal dimension, and
.
Proof. Let
, then
is an isomorphic mapping. If
is the global attractor of
, then
is the global attractor of
, and they have the same dimension.
From Lemma 3, we can get that
is Fréchet differentiable, then the linearized first order variational Equation (59) can be rewritten as
, (84)
. (85)
(86)
where
.
For a fixed
, let
be n elements of
, and
be n solutions of linear Equation (84), whose initial value is
.
Therefore,
(87)
where
is the outer product,
is the trace,
is an orthogonal projection from space
to
.
For a given time
, let
be the standard orthogonal basis of spance
.
We define the inner product of
as
(88)
To sum up, it can be concluded that
(89)
where
(90)
(91)
According to the hypothesis (c),
From (84) and (85),
(92)
Owing to the
is the standard orthonormal basis of
, so
(93)
(94)
(95)
Therefore
(96)
(97)
And
(98)
Thus, the Lyapunov exponent
of
is uniformly bounded
(99)
then, there is a
, such that
(100)
where
is the eigenvalue of
,
.
(101)
(102)
Then
,
the Hausdorff dimension and Fractal dimension of the family of global attractors are finite. Theorem 3 is proved.
4. Conclusion
We have shown the existence and uniqueness of global solutions, the existence of the family of global attractors and the upper bound estimates of Hausdoff and Fractal dimensions for the wide norm model of vertical beam vibration. The global stability of the problem is obtained.