## Recent Advances in Function Spaces and its Applications in Fractional Differential Equations 2021

View this Special IssueResearch Article | Open Access

Abdelbaki Choucha, Salah Mahmoud Boulaaras, Djamel Ouchenane, Salem Alkhalaf, Ibrahim Mekawy, Mohamed Abdalla, "On the System of Coupled Nondegenerate Kirchhoff Equations with Distributed Delay: Global Existence and Exponential Decay", *Journal of Function Spaces*, vol. 2021, Article ID 5577277, 13 pages, 2021. https://doi.org/10.1155/2021/5577277

# On the System of Coupled Nondegenerate Kirchhoff Equations with Distributed Delay: Global Existence and Exponential Decay

**Academic Editor:**Xinguang Zhang

#### Abstract

This paper studies the system of coupled nondegenerate viscoelastic Kirchhoff equations with a distributed delay. By using the energy method and Faedo-Galerkin method, we prove the global existence of solutions. Furthermore, we prove the exponential stability result.

#### 1. Introduction

Let , in this work, we consider where under the initial and boundary conditions where be a bounded domain in with smooth boundary , and is the Laplacian operator, and the functions are bounded, with , and the relaxation functions are denoted by . The function is given by with , and , and the functions will be defined later.

In 1976, Kirchhoff developed an equation describing the vibrations produced by a fixed series at its end, since it is considered a generalization of the dâ€™Alembert equation, and it belongs to the wave equation models. Over time, many researchers and authors addressed these issues and problems with their continuous and rapid development, for example, see [1â€“4].

As for viscoelasticity, it is possible to delve into the following works for further clarification [3â€“10].

Also, the time or delay recorded in many natural and physical phenomena, especially problems resulting from vibrations, is an important factor for stability in general. And it has been studied extensively by many authors, including [5â€“7, 11â€“21]. Recently, in the presence of the varying delay, Mezouar and Boularrass studied system (1); for more information, see [22]. Based on these works, we in this work expand the results in [22] by adding the term of distributed delay.

We, under appropriate conditions, obtained the global existence of solutions, and we proved the exponential stability result of the system.

And we divided the paper into the following: in the second part, we set out the necessary hypotheses and the main result; in the third part, we prove the global existence of solutions, while in the fourth part, we present our result for exponential stability.

#### 2. Preliminaries

In this section, we set the necessary hypotheses for proving the main result.

We need the following assumptions:

(A1) are functions satisfying

(A2) satisfying

(A3) The number satisfying and

(A4) where such that and are onjugate and satisfy

We set the notations

As in [17], we introduce the new variables We have

Consequently, problem (1) is equivalent to where with the initial and boundary conditions

We need the following lemma.

Lemma 1. *The energy functional , given by
satisfies
where ,**and .*

*Proof. *Multiplying equation (13)_{1,2} by , and we use (15), one gets
And multiplying equation (13)_{3} by , and integrating the result over , one gets
Similarly, multiplying equation (13)_{4} by , we find
by using the inequalities of Young and Cauchy-Schwartz for , we have
Similarly, we get
By summing (18)â€“(20) and using (21) and (22), and choosing such that , we find (16) and (17). This completes the proof.

#### 3. Global Existence

Theorem 2. *Suppose that (5)â€“(8) hold. Then, given , , and , there exists a weak solution of problem (13)â€“(15) such that
where
*

*Proof. *Let the Galerkin basis , for , we set
The sequences are defined for by
Then, taking by over and denoting
Given initial data , , and , we define the approximations
It investigates the following problem:
with initial conditions
which satisfies
Noting that , by using HÃ¶lderâ€™s inequality, we get
As (8) holds, using the embedding of Sobolev, the terms and in (29) make sense (see [22]).

First estimate.

As the sequences and converge and from (17) and Gronwallâ€™s lemma, we get independent of such that
where
using (33) and (8), one gets
The second estimate.

We multiply equation (29)_{1,2} by ; by summing from to , one gets
By differentiating (29)_{3,4}, we get
And we multiply (37)_{1} by and (37)_{2} by ; by summing from to , we have
Integrating the result (38) over with respect to , we obtain
Summing (36) and (39) and using , we get
At this point, we estimate the RHS of (40).

Integrating by parts, and using Youngâ€™s and Poincareâ€™ inequalities, one gets
Similarly, we get
And, by using the inequality of Young, we get
we have
Similarly, we get
substituting (41)â€“(45) into (40), and using (17), one gets
where depends on .

Integrating (41) over , we get
At this stage, choosing such that
we find
We have from (17) and (49) that there exist subsequences of and of