## Fractional Delay Differential Equations and their Numerical Solutions

View this Special IssueResearch Article | Open Access

Abdelbaki Choucha, Salah Mahmoud Boulaaras, Djamel Ouchenane, Ali Allahem, "Global Existence for Two Singular One-Dimensional Nonlinear Viscoelastic Equations with respect to Distributed Delay Term", *Journal of Function Spaces*, vol. 2021, Article ID 6683465, 18 pages, 2021. https://doi.org/10.1155/2021/6683465

# Global Existence for Two Singular One-Dimensional Nonlinear Viscoelastic Equations with respect to Distributed Delay Term

**Academic Editor:**Mahmoud A. Zaky

#### Abstract

In this current work, we are interested in a system of two singular one-dimensional nonlinear equations with a viscoelastic, general source and distributed delay terms. The existence of a global solution is established by the theory of potential well, and by using the energy method with the function of Lyapunov, we prove the general decay result of our system.

#### 1. Introduction

We are interested in the following system: with where , , , , , , the second integral represents the distributed delay and are bounded functions, where are two real numbers satisfying , and , are defined functions later.

Three decades ago, these problems that arise in one-dimensional elasticity have been studied and developed with regard to viscosity with long-term memory. And it has been studied in many fields of science, engineering, medical sciences, and chemistry, as well as population and other matters; see, for example, [1â€“24]. Recently, in the absence of delay (), problem (1) was studied in [25], and also later in [26], the authors considered problem (1) with localized frictional damping term. We also know that delay, especially distributed delay, is a phenomenon in our life and is almost found in various fields, and its inclusion in any problem makes it more important. The distributed delay in many works has been studied and many authors have taken care of it, for example, [5, 9, 27, 28]. Based on all this and the results of the research papers [14, 15, 17, 28â€“30, 31], the introduction of the term distributed delay as a damping mechanism in problem (1) makes it a new problem from what has been previously studied.

And we have divided this paper into the following. We present in the second section the definitions, basics, and theories of function spaces that are required throughout the rest of the paper. In Section 3, we present the energy function while proving to be decreasing. And in the final section, the general decay is obtained by applying the energy method and the function of Lyapunov.

#### 2. Preliminaries

Let be the weighted Banach space equipped with the norm

be the Hilbert space of square integral functions having the finite norm and be the Hilbert space equipped with the norm

is the Hilbert space equipped with the norm

Theorem 1 [27]. *For and in , we have
where is a constant depending on and only.*

As in [18], introducing the new variables yields

Problem (1) arrives at where

With the initial data and boundary conditions

We have the following assumptions:

(G1) are , nonincreasing functions satisfying

(G2) a differentiable function, such that and satisfies for some

And also, where , fixed, , such that

(G3) we take where and .

We have where

(G4) satisfying

Theorem 2. *Assume (14) and . Then, , and problem (1) has a unique local solution
for small enough.*

Lemma 3. *For , such that , we have
*

*Proof. *It is clear that by using the Minkowski inequality we get
Also, Hlderâ€™s and Youngâ€™s inequalities give us
By applying the embedding and (25), (27) gives (15).

Lemma 4. * such that
*

*Proof. *We prove inequality for and the same result also holds for .

It is clear that
By Youngâ€™s inequality, with
we get
Therefore,
Hence, by PoincarĂ©â€™s inequality and (11), we obtain
The proof of lemma is complete.

The energy function (see, e.g., [8, 19] and reference therein) is defined by where

Lemma 5. *Let be the solution of system (11); then, is a nonincreasing function, that is, where
*

*Proof. *Multiplying equation (11)_{1,2} by , and integrating over , we find
Using integration by parts, we get
Now, multiplying equation (11)_{3} by and integrating over , we get
Similarly, by multiplying equation (11)_{4} by and integrating over , we get
Using Youngâ€™s and Cauchy-Schwartz inequalities, we have
Similarly, we get
By combining (39), (40), (41), (42), (43), (45), (46), (47), (48), (49), and (50) in (38), we get (34) and (36).

#### 3. Global Existence

In this section, we showed the global existence of the solutions of the system (11).

First, introducing the following notation note that

Lemma 6. *Assume that (24), (14), (15), (16), (17), and (22) hold, and , and satisfying
*

Then, such that where

*Proof. *As , then by continuity of , such that , ; this implies that we have a maximum time value noting such that
This, with (51), (52), and (14), we have
Hence,
By (24) and (54), we get
Hence,
This proves that . By repeating the procedure, is extended to .

Theorem 7. *Let (14), (15), (16), (17), (22), and (24) hold. Then, , , and satisfying (54) the solution of system (11) is bounded and global.*

*Proof. *To prove that is bounded independently of , using (36) yields
Using (52), we find
By using (62) in (63), we get
and using (14), (15), and (54) in (64), we get
So
where
Hence, the solution of system (11) is bounded and global.

#### 4. Decay of Solutions

In this section, the decay result is showed by using several lemmas.

As, we let where , and

Lemma 8. *There exist , such that
**for , , and small enough.*

*Proof. *Using the inequality of Young and the PoincarĂ©-type inequality and , we find
where .

A combination of (73), (74), (75), (76), and (77) in (68) gives
Then, , for , , and small enough, such that
Similarly, thanks to the inequalities of Young and PoincarĂ©-type and using gives