/ / Article
Special Issue

## Complex Boundary Value Problems of Nonlinear Differential Equations 2014

View this Special Issue

Research Article | Open Access

Volume 2014 |Article ID 728760 | 6 pages | https://doi.org/10.1155/2014/728760

# Boundary Stabilization of a Semilinear Wave Equation with Variable Coefficients under the Time-Varying and Nonlinear Feedback

Accepted04 Mar 2014
Published10 Apr 2014

#### Abstract

We study the boundary stabilization of a semilinear wave equation with variable coefficients under the time-varying and nonlinear feedback. By the Riemannian geometry methods, we obtain the stability results of the system under suitable assumptions of the bound of the time-varying term and the nonlinearity of the nonlinear term.

#### 1. Introduction

Many results concerning the boundary stabilization of classical wave equations are available in literatures. See  for linear cases and  for nonlinear ones. The stability of a nondissipative system described by partial differential equations (PDEs) has attracted much attention. Reference  developed the exponential stability for an abstract nondissipative linear system, and in , the Riesz basis property was developed for a beam equation with nondissipativity.

In , the following semilinear wave equation was considered: and the well-posedness and uniform decay of the energy of the system (1) was also established with linearly bounded in .

Based on , we study the system (1) with time-varying and nonlinear feedback: The decay rate of the energy (when goes to infinity) of the wave equation with time-varying feedback was established under the assumption is decreasing  or has an upper bound .

In this paper, we consider the decay rate of the energy under suitable assumptions of the bound of the time-varying term and the nonlinearity of the nonlinear term .

#### 2. Some Notation

Let be a bounded domain in    with smooth boundary . It is assumed that consists of two parts and with , .

Let be symmetric, positively definite matrices for each , and are smooth functions on . As in , we define as a Riemannian metric on and consider the couple as a Riemannian manifold with an inner product:

Denote by , , , and the Levi-Civita connection, the gradient operator, the divergence operator, and the Beltrami-Laplace operator in terms of the Riemannian metric , respectively. It can be easily shown that, under the Euclidean coordinate, where is the gradient of in the standard metric and .

Let be a vector field on . Then for each , the covariant differential of determines a bilinear form on : where stands for the covariant derivative of the vector field with respect to .

#### 3. The Main Results

We consider the semilinear wave equation with variable coefficients under the time-varying and nonlinear boundary feedback: where are continuous nonlinear functions and is the outside unit normal vector of the Riemannian manifold for each . Different from , in this paper, we consider a general ; that is, satisfies where is a positive and nondecreasing function satisfying

Let be a positive and nondecreasing function with 0 as the limit. Then satisfies (9). There are many examples of such as and .

The main assumptions are listed as follows.

Assumption A. derives from a potential : and satisfies where are positive constants, and the parameter satisfies
Being different from , we assume the nonlinear term has no growth restriction near zero as in [23, 24].

Assumption B. is a nondecreasing function satisfying

Assumption C. There exists a vector field on such that where and where is a constant. Moreover we assume that

Condition (14) as a checkable assumption is very useful to study the control and stabilization of the wave equation with variable coefficients and the quasilinear wave equation [22, 25]. For the examples of the condition, see [22, 26].

Based on condition (14), Assumption C was given by  to study the stabilization of the wave equation with variable coefficients and nonlinear boundary condition. Being different from , the lower bound of was relaxed on from a positive constant to zero.

To facilitate the writing, we denote the volume element of by and denote the volume element of by . Define the energy of the system (7) by

As in [23, 24], we let be a concave increasing function such that With (18), the stabilization of the wave equation with variable coefficients and time dependent delay was studied by .

The main result of this paper is as follows.

Theorem 1. Let Assumptions A–C hold true. Assume that where is defined in (15).
(a) If the function in (7) satisfies then there exist constants such that
(b) If the functions in (7) satisfy where is a positive constant, then there exist constants such that
(c) If the function in (8) is a constant function; that is, then there exist constants such that

#### 4. Well Posedness of the System

Define By a similar proof as Lemma  7.1 in , we have the following result.

Theorem 2. Let Assumptions A-B hold true. For any initial data , system (7) admits a unique weak solution u such that .

To prove Theorem 1, we still need several lemmas further. Define Then, we have

The following lemma shows the energy of the system (7) is decreasing.

Lemma 3. Suppose that Assumptions A-B hold true. Let be the solution of the system (7). Then The assertion (29) implies that is decreasing.

Proof. Differentiating (17), we obtain Then the inequality (29) follows directly from (30) integrating from to .

#### 5. Proofs of Theorem 1

Lemma 4. Let be the solution of the equation and that is a vector field defined on . Then for
Moreover, assume that . Then

Proof. Note that The equality (31) and the equality (32) follow from Proposition  2.1 in .

Lemma 5. Suppose that all assumptions in Theorem 1 hold true. Let solve the system (7). Then there exist positive constants for which where .

Proof. From (15), we choose a positive constant satisfying Set We substitute the formula (32) into the formula (31), and we have where
Decompose as where stands by the value of the terms on the right side of (38) integrating on .
Similar to [5, 22], we deal with as follows.
Since , we have ; that is, Similarly, we obtain Using the equality (40) and (41) in the equality (38) on the portion , with (16) we obtain
Let be a vector field on such that Set ; it follows from (31) that Then we obtain that With (16) and (45), we have
Note that Substituting the formulas (42) and (46) into the formula (37), with (19) and (35), we obtain
Since from (48), we have
Since is decreasing, we deduce that Substituting the formulas (51) into the formula (50), for sufficiently large , we have The inequality (34) holds.

Proof of Theorem 1. (a) From (8), (13), (20), (29), and (34), for we deduce that Note that is decreasing, and the estimate (21) holds.
(b) From (8), (13), (22), (29), and (34), for we deduce that Note that is decreasing, and the estimate (23) holds.
(c) From (8), (13), (24), (29), and (34), for we deduce that Note that is decreasing, and the estimate (25) holds.

#### Conflict of Interests

The authors declare that there is no conflict of interests regarding the publication of this paper.

#### Acknowledgments

The authors would like to express their deep thanks to Zhen-Hu Ning for bringing conditions (8) and (16) to us as the requirements for the stability results in Theorem 1. The research is supported by the Open Fund of Trust Computing Laboratory of Beijing University of Technology Start-up Fund of Beijing University of Technology under Grants (007000543113522).

1. J. E. Lagnese, “Note on boundary stabilization of wave equations,” SIAM Journal on Control and Optimization, vol. 26, no. 5, pp. 1250–1256, 1988.
2. D. L. Russell, “Controllability and stabilizability theory for linear partial differential equations: recent progress and open questions,” SIAM Review, vol. 20, pp. 639–739, 1978.
3. R. Triggiani, “Wave equation on a bounded domain with boundary dissipation: an operator approach,” Journal of Mathematical Analysis and Applications, vol. 137, no. 2, pp. 438–461, 1989.
4. Y. You, “Energy decay and exact controllability for the Petrovsky equation in a bounded domain,” Advances in Applied Mathematics, vol. 11, no. 3, pp. 372–388, 1990.
5. Z.-H. Ning and Q.-X. Yan, “Stabilization of the wave equation with variable coefficients and a delay in dissipative boundary feedback,” Journal of Mathematical Analysis and Applications, vol. 367, no. 1, pp. 167–173, 2010.
6. Z. H. Ning, C. X. Shen, and X. P. Zhao, “Stabilization of the wave equation with variable coeffcients and a delay in dissipative internal feedback,” Journal of Mathematical Analysis and Applications, vol. 405, no. 1, pp. 148–155, 2013. View at: Publisher Site | Google Scholar
7. M. Aassila, M. M. Cavalcanti, and V. N. Domingos Cavalcanti, “Existence and uniform decay of the wave equation with nonlinear boundary damping and boundary memory source term,” Calculus of Variations and Partial Differential Equations, vol. 15, no. 2, pp. 155–180, 2002.
8. M. M. Cavalcanti, V. N. Domingos Cavalcanti, and P. Martinez, “Existence and decay rate estimates for the wave equation with nonlinear boundary damping and source term,” Journal of Differential Equations, vol. 203, no. 1, pp. 119–158, 2004.
9. F. Conrad and B. Rao, “Decay of solutions of the wave equation in a star-shaped domain with nonlinear boundary feedback,” Asymptotic Analysis, vol. 7, no. 3, pp. 159–177, 1993.
10. V. Komornik, “On the nonlinear boundary stabilization of the wave equation,” Chinese Annals of Mathematics B, vol. 14, no. 2, pp. 153–164, 1993.
11. V. Komornik, Exact Controllability and Stabilization: The Multiplier Method, John Wiley and Sons. Ltd, Chichester, UK, 1994.
12. V. Komornik and E. Zuazua, “A direct method for the boundary stabilization of wave equation,” Journal de Mathématiques Pures et Appliquées, vol. 69, pp. 33–54, 1990. View at: Google Scholar | Zentralblatt MATH
13. I. Lasiecka and D. Tataru, “Uniform boundary stabilization of semilinear wave equation with nonlinear boundary condition,” Differential Integral Equations, vol. 6, pp. 507–533, 1993. View at: Google Scholar
14. E. Zuazua, “Uniform stabilization of the wave equation by nonlinear boundary feedback,” SIAM Journal on Control and Optimization, vol. 28, no. 2, pp. 466–477, 1990.
15. K. S. Liu, Z. Y. Liu, and B. Rao, “Exponential stability of an abstract nondissipative linear system,” SIAM Journal on Control and Optimization, vol. 40, no. 1, pp. 149–165, 2002. View at: Publisher Site | Google Scholar | MathSciNet
16. B. Z. Guo, J. M. Wang, and S. P. Yung, “On the C0-semigroup generation and exponential stability resulting from a shear force feedback on a rotating beam,” Systems & Control Letters, vol. 18, no. 6, pp. 1013–1038, 2005. View at: Publisher Site | Google Scholar
17. B.-Z. Guo and Z.-C. Shao, “Exponential stability of a semilinear wave equation with variable coeffcients under the nonlinear boundary feedback,” Nonlinear Analysis, vol. 71, pp. 5961–5978, 2009. View at: Publisher Site | Google Scholar
18. M. Bellassoued, “Decay of solutions of the wave equation with arbitrary localized nonlinear damping,” Journal of Differential Equations, vol. 211, no. 2, pp. 303–332, 2005.
19. A. Benaissa and A. Guesmia, “Energy decay for wave equations of φ-Laplacian type with weakly nonlinear dissipation,” Electronic Journal of Differential Equations, vol. 109, pp. 1–22, 2008. View at: Google Scholar
20. A. Benaissa, A. Benaissa, and S. A. Messaoudi, “Global existence and energy decay of solutions for the wave equation with a time varying delay term in the weakly nonlinear internal feedbacks,” Journal of Mathematical Physics, vol. 53, no. 12, Article ID 123514, 2012. View at: Google Scholar | Zentralblatt MATH
21. H. Li, C. S. Lin, S. P. Wang, and Y. M. Zhang, “Stabilization of the wave equation with boundary time-varying delay,” Advances in Mathematical Physics, vol. 2014, Article ID 735341, 6 pages, 2014. View at: Publisher Site | Google Scholar
22. P.-F. Yao, “On the observability inequalities for exact controllability of wave equations with variable coefficients,” SIAM Journal on Control and Optimization, vol. 37, no. 5, pp. 1568–1599, 1999.
23. I. Lasiecka and D. Tataru, “Uniform boundary stabilization of semilinear wave equation with nonlinear boundary dissipation,” Differential Integral Equations, vol. 6, pp. 507–533, 1993. View at: Google Scholar
24. M. M. Cavalcanti, V. N. Domingos Cavalcanti, and I. Lasiecka, “Well-posedness and optimal decay rates for the wave equation with nonlinear boundary damping-source interaction,” Journal of Differential Equations, vol. 236, no. 2, pp. 407–459, 2007.
25. P. F. Yao, “Boundary controllability for the quasilinear wave equation,” Applied Mathematics and Optimization, vol. 61, no. 2, pp. 191–233, 2010.
26. P. F. Yao, Modeling and Control in Vibrational and Structural Dynamics. A Differential Geometric Approach, Applied Mathematics and Nonlinear Science Series, Chapman and Hall/CRC CRC Press, Boca Raton, Fla, USA, 2011.
27. Z. H. Ning, C. X. Shen, X. P. Zhao, H. Li, C. S. Lin, and Y. M. Zhang, “Nonlinear Boundary Stabilization of the Wave Equations with Variable coeffcients and time dependent delay,” Applied Mathematics and Computation, vol. 232, pp. 511–520, 2014. View at: Publisher Site | Google Scholar

#### More related articles

We are committed to sharing findings related to COVID-19 as quickly and safely as possible. Any author submitting a COVID-19 paper should notify us at help@hindawi.com to ensure their research is fast-tracked and made available on a preprint server as soon as possible. We will be providing unlimited waivers of publication charges for accepted articles related to COVID-19. Sign up here as a reviewer to help fast-track new submissions.