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Existence of Solutions for Hyperbolic System of Second Order Outside a Domain
Journal of Inequalities and Applications volume 2009, Article number: 489061 (2009)
Abstract
We study the mixed initial-boundary value problem for hyperbolic system of second order outside a closed domain. The existence of solutions to this problem is proved and the estimate for the regularity of solutions is given. The application of the existence theorem to elastrodynamics is discussed.
1. Introduction
This paper is concerned with the exterior problem for hyperbolic system of second order. Let be a closed domain with smooth boundary in and let the origin belong to . Consider the following exterior problem for the hyperbolic system of second order:
where and . We assume that satisfies
for all symmetric matrixes , where , .
Let . The system (1.1) can be written as an evolution system in the form
where
Ikawa considered in [1] the mixed problem of a hyperbolic equation of second-order. The existence theorem is known for the obstacle free problem in [2]. Dafermos and Hrusa proved in [3] the local existence of the Dirichlet problem for the hyperbolic system inside a domain by energy method.
In this paper, we deal with the exterior problem for the second order hyperbolic system. In Section 2, we show the existence of the exterior problem for the problem (1.1) by the semigroup theory. In Section 3, we prove the regularity for the solutions of the exterior problem (1.1) and give the estimate for the regularity of solutions. In Section 4, we discuss the application of the existence theorem to elastrodynamics.
2. Existence of the Exterior Problem for Hyperbolic System of Second Order
Note that with the inner product
By (1.2) and Korn inequality (cf. [4, 5]), we have
Lemma 2.1.
For some , we have
Then is a Hilbert space with the inner product defined as above. We define the operator (without loss of generality, we still write this operator as ) in by
where It is obvious that is a densely defined operator.
Lemma 2.2.
There exists a constant such that for any ,
holds.
Proof.
Let .
Corollary 2.3.
For all real such that , the estimate
holds for any .
Proof.
By (2.4),
The estimate of the resolvent operator is the following.
Lemma 2.4.
There exists a constant such that for all real and ,
is a bijective mapping. Moreover, we have
Proof.
Consider the system
namely,
where .
The substitution of the first relation
in the second of (2.11) gives
By the well-known variation method, there exists a solution of the elliptic system (2.13) for any . Defining by (2.12), we have a solution
of (2.10). Therefore, is a surjection.
From (2.6), it follows that the existence of and the estimate
Let , we have (2.9).
For , we define the following norm:
Suppose that , we have
Corollary 2.5.
For the real number ( fixed) and the integer , where is as in Lemma 2.4, there exists such that for any
Proof.
From Lemma 2.4,
is a bijective continuous mapping, then is a closed operator. It implies that is also a closed operator. By Banach's closed graph theorem, is continuous. So for any we have
Definition 2.6.
Let be a Banach space. A family of infinitesimal generators of semigroups on is called stable if there are constants and (called the stability constants) such that
for every finite sequence , .
Lemma 2.7.
For , let be the infinitesimal generators of semigroups on the . The family of generators is stable if and only if there are constants and such that
for any finite sequence ,
Lemma 2.8.
Let be a stable family of infinitesimal generators of semigroups on the space such that is independent of and for every , is continuously differentiable in . If , then
has a unique classical solution such that
The proofs of Lemmas 2.7 and 2.8 are in [6]. The straightforward application of the semigroup theory to the system (1.3) gives the following proposition.
Proposition 2.9.
Given and , then there exists one and only one solution of (1.3) such that .
Proof.
Let . For given , is an infinitesimal generator of semigroups on . For any , it is easy to know that
Then for any , we have
namely,
For any finite sequence and any , ,
where . From Lemma 2.4, for any , . Then by Lemma 2.7, is a stable family. Obviously, is continuously differentiable in . So Proposition 2.9 follows from Lemma 2.8.
From Proposition 2.9, we obtain the existence of solutions to the problem (1.1).
Theorem 2.10.
Given and , then there exists one and only one solution of (1.1) such that
Proof.
Let , . By Proposition 2.9, there exists a solution of problem (1.3) such that . Let denote the forgoing three components of , then is the solution of problem (1.1) and satisfies (2.27).
3. Regularity of Solutions for the Exterior Problem
First, we show the energy inequalities for our problem. These inequalities play an important role in the proof of the regularity of solutions.
Proposition 3.1.
Suppose that
is a solution of problem (1.1) and that , then for any given , we have
where is a constant which depends on .
Proof.
Put , then and satisfies
where , . Obviously,
By (2.4),
Thus
Applying Gronwall's inequality, we get
Without loss of generality, we assume that . Then we see
Applying (3.7) for , we get
By (2.17) and (2.2),
Obviously,
Also we have
and for all ,
Inserting these estimates to the above inequality, we get
An application of Gronwall's inequality implies
Namely,
This completes the proof of (3.2).
Theorem 3.2.
For , suppose that , , , and
If the compatibility conditions of order are satisfied, then problem (1.1) has a solution such that
Proof.
At first we prove
Let and . We define by
then ,
We consider the following problem:
where
here .
From (3.21),
By (3.2), we have
thus
This implies that converges to some in . Set
then tends to in . The passage to the limit of (3.21) shows
namely,
Taking account of the definition of , we see
Therefore is the solution of problem (1.1) and satisfies (3.19).
We now prove (3.18) by induction. When , (3.18) follows from (3.2). For , suppose that (3.18) holds for . We show that it still holds for .
Applying (3.2) to (3.27), we conclude from the inductive hypothesis that
In a similar way, we can obtain
Set , then is the solution of (1.3) and
Now
then by (2.17) (taking ), we see
Differentiation of (3.33) with respect to gives
and by the above result ,
from which it follows that
Repeating this process, we get
Using this, we see the right-hand side of (3.33) , then by (2.17) (taking )
This assures that the right-hand side of (3.35) , then
Repeating this process, we get
Step by step, finally, we get
and (3.18).
4. Application to Elastrodynamics
It is well known that the displacement of an isotropic, homogeneous, hyperelastic material without the action of external force satisfies the following hyperbolic system (cf. [4, 5]):
where , and , are given by the Lamé constants , :
We assume that ,
From [5], system (4.1) can be written as
where stands for the elastic tensor.
The system (4.3) is the special case of the system (1.1). So by the existence Theorem 3.2, we derive the existence of solutions for the initial-boundary problem to the elastrodynamic system (4.3) outside a domain.
References
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Dafermos CM, Hrusa WJ: Energy methods for quasilinear hyperbolic initial-boundary value problems. Applications to elastodynamics. Archive for Rational Mechanics and Analysis 1985,87(3):267–292.
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Acknowledgments
Projects 10626046 supported by NSFC and 20070410487 supported by China Postdoctoral Science Foundation. The authors would like to thank Professor Tatsien Li and Professor Tiehu Qin for helpful discussions and suggestions.
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Xin, J., Sha, X. Existence of Solutions for Hyperbolic System of Second Order Outside a Domain. J Inequal Appl 2009, 489061 (2009). https://doi.org/10.1155/2009/489061
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DOI: https://doi.org/10.1155/2009/489061