Discrete Dynamics in Nature and Society

Volume 2014 (2014), Article ID 821503, 4 pages

http://dx.doi.org/10.1155/2014/821503

## Blow-Up and Global Existence for a Quasilinear Parabolic System

Zhicheng College, Fuzhou University, Fuzhou, Fujian 350002, China

Received 22 October 2013; Accepted 5 January 2014; Published 12 February 2014

Academic Editor: Elena Braverman

Copyright © 2014 Chunchen Wu. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### Abstract

The problem of solutions to a class of quasilinear coupling parabolic system was studied. By constructing weak upper-solutions and weak lower-solutions, we obtain the global existence and blow-up of solutions under appropriate conditions.

#### 1. Introduction and Main Result

In this paper, we consider global existence of nonnegative solutions for a class of nonlocal degenerate quasilinear parabolic system as follows: where is bounded region; has smooth boundary ; the parameters , , , , and , ; the initial functions , , and are nonnegative and bounded, and .

Quasilinear parabolic system is the model for many problems in the scientific field, for example, gas flow model in some seepage medium, some biological population growth model. In recent years, there are many papers to investigate the nonlinear parabolic equation and many excellent results are obtained (see [1–10] and the references cited therein). In this paper, we expand the equation of [10] into 3 and discuss the global existence and blow-up of the solutions for problem (1), and the main results of this paper are the following.

Theorem 1. *If one of the following conditions holds, system (1) has global solutions:*(1)*, , , and ;*(2)*, , , and , and the magnitude of the region is sufficiently small;*(3)*If , , or , or if , , and , and the initial data , , and are sufficiently small.*

*Theorem 2. If one of the following conditions holds, the solution of system (1) blows up in finite time:(1), , , and , and the initial data , , and are sufficiently large;(2), , or , and the initial data , , and are sufficiently large.*

*2. Proof of Global Existence*

*2. Proof of Global Existence*

*As we know, nonlocal degenerate quasilinear parabolic system may not have classical solutions. Similar to the proof in [10] (see page 388-389), we can obtain that system (1) has nonnegative weak upper-solutions and nonnegative weak lower-solutions, and the following comparison principle holds.*

*Lemma 3 (comparison principle). Suppose , are the nonnegative weak upper-solutions and nonnegative weak lower-solutions of system (1), if
one has for every .*

*Therefore, in order to prove Theorem 1, we only show that, for all , there exists a positive bounded weak upper-solutions. Let be the unique positive solution of linear elliptic equation as follows:
*

*Denote , then . Define as follows:
where and satisfy . is a positive constant to be determined suitably. For all , , , and are bounded, and , and . By deducing, we have
Similarly
*

*Denote
(1) If , , , and , there exist positive constants , such that
and . And there exists positive constant such that
Thus,
From (11), we can choose sufficiently large, such that and
By (4)–(12) we obtain that is the weak upper-solutions of system (1).*

*(2) If , , , and , there exist positive constants , such that
And there exists positive constant such that
Therefore,
*

*Without loss of generality, we assume that the domain we discuss is contained in a sufficiently large ball ; denote is the unique positive solution of the following linear elliptic equation:
Let ; hence . Suppose that is sufficiently small such that
In addition, we choose large enough, such that satisfies (12); then from (5), (6), and (12)–(17) we obtain that is the weak upper-solutions of system (1).*

*(3) At last, if , , or , or if , , , and , there exist positive constants , , and such that
Therefore, from (18), we can choose small enough,such that . Furthermore, if , , and are sufficiently small to satisfy (12), then by (5), (6), (12), and (18) we obtain that is the weak upper-solutions of system (1).*

*This completes the proof of Theorem 1.*

*3. Proof of Blow-Up*

*3. Proof of Blow-Up*

*In this section we will prove Theorem 2, so we construct blow-up positive weak lower-solutions of system (1). Let , be the first eigenvalue and corresponding eigenfunction of the eigenvalue problem as follows:
Then . Standardized , such that and , then , where is the outer normal direction of , suppose is a compact subset of , if any solution blows up in , also blows up in .*

*Define functions
where , , and satisfy , and is the solution of the initial value problem as follows:
Here , is to be determined suitably. It is clear that and are unbounded in finite time, and
where ; by computing we obtain that
Similarly
where
(1) If , , , and , there exist positive constants , , and satisfying and
Choose
From (26)-(27) and , we have , , and . Suppose that , , and are sufficiently large to satisfy
From (20)–(28),we obtain that () is positive weak lower-solutions of system (1) in .*

*(2) If , , or , (26) still holds, the results are obtained by the same methods.*

*Thus completes the proof of Theorem 2.*

*Conflict of Interests*

*Conflict of Interests*

*The author declares that there is no conflict of interests regarding the publication of this paper.*

*Acknowledgments*

*Acknowledgments*

*The author would like to thank the referees for their helpful comments and suggestions which greatly improve the presentation of the paper. This work was supported by the Program for Science and Technology Development Foundation of Fujian Education Bureau (JA12374).*

*References*

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