Discrete Dynamics in Nature and Society

Volume 2018, Article ID 9256192, 14 pages

https://doi.org/10.1155/2018/9256192

## Infinitely Many Solutions for a Class of Fractional Impulsive Coupled Systems with -Laplacian

^{1}School of Geosciences and Info-Physics, Central South University, Changsha, Hunan 410083, China^{2}Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, Central South University, Ministry of Education, Changsha, China^{3}Faculty of Science, Kunming University of Science and Technology, Kunming, Yunnan 650500, China^{4}School of Mathematics and Statistics, Central South University, Changsha, Hunan 410083, China

Correspondence should be addressed to Xingyong Zhang; moc.361@1gnoygnixgnahz

Received 23 January 2018; Accepted 28 March 2018; Published 8 May 2018

Academic Editor: Antonio Iannizzotto

Copyright © 2018 Junping Xie and Xingyong Zhang. 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

By using the symmetric mountain pass lemma, we investigate the problem of existence of infinitely many solutions for a class of fractional impulsive coupled systems with -Laplacian, which possesses mixed type nonlinearities, and the nonlinearities do not need to satisfy the well-known Ambrosetti-Rabinowitz condition.

#### 1. Introduction and Main Results

In this paper, we are concerned with existence of infinitely many solutions for the following fractional impulsive differential system with -Laplacian:

where , with , with , and , and (or ) denotes the right Riemann-Liouville fractional derivative of order (or ), (or ) is the left Caputo fractional derivative of order (or ), , are continuously differentiable, , , and where , , and satisfies and the following assumptions.

is measurable in for each , continuously differentiable in for a.e. , and there exist and such thatfor all and a.e. *.*

It is well known that critical point theory is a very important and effective tool to investigate the existence and multiplicity of various solutions for partial differential equations, ordinary differential equations, Hamiltonian systems, difference equations, and so on. Lots of important and interesting results have been established (see, e.g., [1–11] and reference therein). In 2011, Jiao and Zhou [12] first used critical point theory to investigate the existence of solutions for a class of fractional boundary value problems. Since then, critical point theory has also become an effective tool to obtain the existence and multiplicity results of solutions for various fractional differential equations (see, e.g., [13–17] and reference therein). Particularly, in [14], Zhao et al. considered existence of solutions for the following fractional coupled differential system with a parameter:where is a parameter, , and . By using a critical point theorem in [18], they obtained system (5) which has at least three weak solutions. In [13], Li et al. investigated a class of fractional coupled differential systems with a parameter:where is a parameter, , and . By using the least action principle and symmetric mountain pass theorem, they obtained system (6) which has at least one solution under asymptotically quadratic case and has infinitely many solutions under superquadratic case. For the superquadratic case, they assumed the following well-known Ambrosetti-Rabinowitz (AR) condition.

There are constants *, * such that for all and *.*

Over the past ten years, integer order impulsive differential equations with different boundary value conditions have been investigated deeply via variational methods (e.g., see [19–26] and reference therein). Recently, Bonanno et al. [27] and Rodrìguez-López and Tersian [28] were concerned with the following second-order impulsive fractional differential equation:where , and are two parameters, , , and . By using variational methods, they obtained some existence results about one or three solutions of (8). Subsequently, in [29], Nyamoradi and Rodríguez-López investigated the existence and multiplicity of solutions for (8) with . They obtained some existence results about one or infinitely many solutions of (8) by using the least action principle, the mountain pass theorem, and the symmetric mountain pass theorem. In [30],Y. Zhao and Y. Zhao investigated the existence and multiplicity of solutions for a class of perturbed fractional differential system with impulsive effects and one parameter, and they obtained system that has at least one or two nontrivial solutions by using two abstract critical point theorems due to [31]. In [32], Heidarkhani et al. investigated the multiplicity of solutions for a class of perturbed fractional differential system with impulsive effects and two parameters, and they obtained that system has infinitely many solutions by using the smooth version of an abstract critical point theorem due to [33]. In [34], Zhao et al. investigated the existence of solution for (8) with . By using the Morse theory and local linking argument, they obtained that equation has at least one nontrivial solution.

In [35], Zhao and Tang investigated the following impulsive fractional differential equations with -Laplacian:where and . By using the mountain pass theorem, a critical point theorem in [36], and symmetric mountain pass theorem, they obtained two multiplicity results of solutions for (9). In detail, they obtained the following theorems.

Theorem A (see [35]). *Suppose the following conditions hold.** There exists a constant such that for any , , where is defined in Section 2.** There exists a constant such that for all and , where .** There exist constants such that and , where ** There exist constants such that for all , .**Then (9) has at least two weak solutions.*

Theorem B (see [35]). *Suppose – hold and and are odd about , where . Then (9) has infinitely many weak solutions.*

Motivated by [12–14, 35], in this paper, we investigate the existence of infinitely many solutions for system (1). Obviously, system (1) is more general and complex than system (5), system (6), and (9). We present some techniques in [35], which were applied to fractional -Laplacian impulsive differential equation and can also be applied to fractional -Laplacian impulsive differential system, and present some more relaxed superquadratic conditions for nonlinearities than those in [35]. It is remarkable that the fractional coupled -Laplacian differential systems are different from the fractional -Laplacian differential equations. One stark difference is that the solutions of system (1) are the combination of and but not of (5), which causes the fact that system (1) number is possibly more than that of (9) and, hence, it is impossible that system (1) reduces to system (9). Moreover, since, in general, and we present more relaxed superquadratic conditions, it is difficult to prove the boundness of Cerami sequence (see the definition in Section 2 below) and we have to develop some techniques on inequalities. When , system (1) becomes the following integer order -Laplacian impulsive differential system:There have been some results on existence and multiplicity of solutions for integer order -Laplacian impulsive differential systems with different boundary value conditions (see, e.g., [4, 37, 38]). However, system (11) which has Dirichlet boundary value is different from those systems in [4, 37, 38] and our assumptions on are more relaxed than the well-known (AR) condition. Hence, our results are still new for integer order -Laplacian impulsive differential systems. Next, we state our results.

Theorem 1. *Suppose that the following conditions hold.**, .** is even in and for a.e. .** There exist constants , , such that for a.e. and all with .** There exists a positive constant such that for a.e. and all with .** There exists positive constants such that for a.e. and all with .** There exist , , such that for a.e. and all with .** There exist constants and such that for a.e. and all with .** There exist constants such that for all with , .** There exist constants such that for all with , .** There exist constants such that for all with , .** There exist constants such that for all with , .**, is even in , .**, is even in , .**Then system (1) has an unbounded sequence of weak solutions.*

Theorem 2. *Suppose that , , , –, –, , , , , and the following conditions hold.** There exist positive constants withand such that for all with , , and such that for all with , , where Then system (1) has an unbounded sequence of weak solutions.*

It is easy to prove that the following condition implies that and hold.

there are constants , such that for a.e. and all with .

Indeed, obviously, (AR)′ implies that holds with and . Moreover, by the proof of Theorem 1.2 in [4], (AR)′ and imply that there exist positive constants such that for all and a.e. , and so it is easy to see that holds. Then by Theorems 1 and 2, we have the following corollaries.

Corollary 3. *Suppose that , , , –, , –, , and hold. Then system (1) has an unbounded sequence of weak solutions.*

Corollary 4. *Assume that , , , –, , , , , , , and hold. Then system (1) has an unbounded sequence of weak solutions.*

*Remark 5. *There exist examples satisfying Theorems 1 and 2. For example, let , , , , , , and for all and a.e. , where and .

With similar proofs of Theorems 1 and 2, we can obtain the corresponding theorems for the following -Laplacian system:where for all and a.e. .

Theorem 6. *Suppose that the following conditions hold.** is measurable in for each , continuously differential in for a.e. , and there exist and such that for all and a.e. .**.** is even in and for a.e. .** There exist , , such that for a.e. and all with .** There exists a positive constant such that for a.e. and all with .** There exist positive constants such that for a.e. and all with .** There exist , such that for a.e. and all with .** There exist constants and such that for a.e. and all with .** There exist constants such that for all with , .** There exist constants such that for all with , .**, is even in , .**Then system (29) has an unbounded sequence of weak solutions.*

Theorem 7. *Suppose that , , , –, –, , , and the following condition holds.** There exist positive constants with and such that for all with , .**Then system (29) has an unbounded sequence of weak solutions.*

Corollary 8. *Suppose that , , , –, , and – and the following condition holds.** There are constants , such that for a.e. and all with .**Then system (29) has an unbounded sequence of weak solutions.*

Corollary 9. *Assume that , , , –, , , , , and hold. Then system (29) has an unbounded sequence of weak solutions.*

*Remark 10. *Corollaries 8 and 9 are still different from Theorem B. Indeed, if , , and for a.e. and all , system (29) reduces to (9). However, it is easy to see that and (or ) are different from . There exist examples satisfying and but not satisfying and . For example, let and for all , . Then . It is easy to see that , satisfy and . Set , . Obviously, , do not satisfy . Moreover, there exist examples satisfying – but not satisfying . For example, let for a.e. . Finally, one can also establish some results which are similar to Theorem A for system (1) and system (29) by combining those assumptions and arguments of Theorems 1 and 2 with those ideas proving Theorem A.

#### 2. Preliminaries

In this section, we recall some known definitions and lemmas about fractional derivatives. For more details, the readers can see [12, 39–42].

Let and

*Definition 11 (see [40, 42]). *Let and . and denote the left and right Riemann-Liouville fractional derivatives of order for function , respectively, which are defined by

*Definition 12 (see [40, 42]). *Let and . and denote the left and right Caputo fractional derivatives of order for function , respectively, which are defined by

*Remark 13 (see [40, 42]). *When , and .

Let with the norm , and, for , with the norm .

For and , we define as the closure of , with respect to the norm: Then by Proposition 3.1 in [12], is separable and reflexive Banach space, and if , then , and . Moreover, by Remark 3.1 in [12], , .

Proposition 14 (see [12]). *Assume that and . For all , where . Moreover, if , then where and .*

By Proposition 14, it is easy to obtain that

Proposition 15 (see [12]). *Assume that and , and the sequence converges weakly to in . Then in .*

Assume that . Let . On , define the norm: for all .

Similar to Definitions 2.4 and 2.5 in [35], we also present the following two definitions.

*Definition 16. *Let If satisfies the first equation of (1) for a.e. and the second equation of (1) for a.e. , , , , and exist and satisfy the impulsive conditions of (1), and boundary conditions and , then we call a classical solution of (1).

*Definition 17. *For any , if the following two equalities hold then the vector function is called a weak solution of (1).

For , we define the functional bywhere