## Fractional Delay Differential Equations and their Numerical Solutions

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Abdelbaki Choucha, Salah Mahmoud Boulaaras, Djamel Ouchenane, Bahri Belkacem Cherif, Mohamed Abdalla, "Exponential Stability of Swelling Porous Elastic with a Viscoelastic Damping and Distributed Delay Term", *Journal of Function Spaces*, vol. 2021, Article ID 5581634, 8 pages, 2021. https://doi.org/10.1155/2021/5581634

# Exponential Stability of Swelling Porous Elastic with a Viscoelastic Damping and Distributed Delay Term

**Academic Editor:**Qifeng Zhang

#### Abstract

In this paper, we consider a swelling porous elastic system with a viscoelastic damping and distributed delay terms in the second equation. The coupling gives new contributions to the theory associated with asymptotic behaviors of swelling porous elastic soils. The general decay result is established by the multiplier method.

#### 1. Introduction and Preliminaries

In the late 19th century, Eringen [1] proposed a theory in which he presented a mixture of viscous liquids and elastic solids in addition to gas. And he also studied the equilibrium laws for all components of this mixture, and finally, you get the field equations for a heat conductive mixture (for more details, see [2]). In [3], the author has classified expansive (swelling) soils under the classification of porous media theory.

On the other hand, it contains clay minerals that attract and absorb water, which leads to an increase in pressure [4], and this is considered a harmful and dangerous problem in architecture and civil engineering in most countries of the world, especially in foundations, which leads to cracks in buildings and ripples in sidewalks and roads (see [5–8]). From there, studies began to eliminate or reduce the damage, as in ([9–13]), where the basic field equations of the linear theory of swelling porous elastic soils were presented by where are the displacement of the fluid and the elastic solid material. And are the densities of each constituent. The functions () represent the partial tension, internal body forces, and eternal forces acting on the displacement, respectively. Similarly (), it works on the elastic solid. In addition, the constitutive equations of partial tensions are given by where and is a real number. is a matrix positive definite in the sense that .

Quintanilla [10] investigated (1) by taking where ; they obtained that the stability is exponential. Similarly, in [14], the authors considered (1) with different conditions where is an internal viscous damping function with a positive mean. They established the exponential stability result (see ([10–20]) for some other interesting results on the swelling porous system).

Time delays arise in many applications because most phenomena naturally depend not only on the present state but also on some past occurrences.

In recent years, the control of PDEs with time delay effects has become an active area of research (see, for example, [15, 20–27]). In many cases, it was shown that delay is a source of instability unless additional condition or control terms are used; the stability issue of systems with delay is of theoretical and practical great importance.

A complement to these works, and by introducing the terms of memory and distributed delay, forms a new problem different from previous studies. Under appropriate assumptions and by using the energy method, we prove the stability results.

In this paper, we are interested in problem (1) with null internal body forces, but the eternal force acting only on the elastic solid is in the form of viscoelastic damping and distributed delay terms, that is,

*Remark 1. *Regarding the problems of swelling porous elastic, we believe that there are no studies of viscoelasticity (the memory) and the distributed delay conditions that act as a simultaneous dissipation mechanism, and hence, our coupling constitutes a new contribution.

Thus, we are interested in the following problem:
where
under the initial and boundary conditions
First, as in [27], taking the following new variable
then we obtain
Consequently, the problem is equivalent to
where
with the initial data
and the boundary conditions
Here, are positive constants and is a real number, with satisfying . The integrals represent the memory and the distributed delay terms with are a time delay, is an function, and the kernel is the relaxation function, under the following assumptions.

(H1) is a nonincreasing function satisfying
where .

(H2) There exists a positive nonincreasing differentiable function, such that
(H3) is a bounded function satisfying

*Remark 2. *The results that we obtained in this work are also correct with other conditions, including
Of course, there can be some difficulties with regard to the following boundary conditions:
unless we assume
respectively.

In this paper, we consider to be a solution of system (12)–(15) with the regularity needed to justify the calculations. In Section 2, we proved our decay result. And we symbolize that is a positive constant.

#### 2. Main Result

In this section, we prove our stability result for the energy of system (12)–(15).

We need the following lemmas.

Lemma 3. *The energy functional , defined by
satisfies
where and
*

*Proof. *Multiplying (12)_{1,2} by and , then integration by parts over , with (15), gives
The estimate of the last term in the LHS of (25) is as follows:
Now, multiplying ((12))_{3} by , and by integration over Now, by substituting (26) into (25), and using Young’s inequality, we have
then, by (18), there exists so that
then we obtain (22) and (23) ( is a nonincreasing function).

Lemma 4. *The functional
satisfies
*

*Proof. *Direct computation using integration by parts and Young’s inequality, for , yields
The estimate of the two last terms in the RHS of (32) is as follows:
where we have used Cauchy-Schwartz, Young’s, and Poincaré’s inequalities, for , and (18).

By substituting (33) and (34) into (32), we find
Bearing in mind that and using (16), we get
let , and letting , , gives (31).

Lemma 5. *Assume that (16) hold. Then, the functional
satisfies,
*

*Proof. *By differentiating , then using (12), integration by parts, and (15), we find
In what follows, we estimate the different terms in the RHS of (39); we use Young’s, Cauchy-Schwartz, and Poincaré’s inequalities. For , we have
By letting and substituting into (39), we get (38).

Lemma 6. *The functional
satisfies
*

*Proof. *Direct computations give
Estimate (42) easily follows by using Young’s inequality and .

Now, let us introduce the following functional used.

Lemma 7. *The functional
satisfies
where .*

*Proof. *By differentiating , with respect to and using the last equation in (12), we have
By using , and , for all , we find

Because is an increasing function, we have , for all .

Finally, setting and recalling (18) give (45). We are now ready to prove the main result.

Theorem 8. *Assume (16)–(18) hold.**Then, there exist such that the energy functional given by (22) satisfies
*

*Proof. *We define the functional of Lyapunov
where to be selected later.

By differentiating (49) and using (22), (31), (38), (42), and (45), we have
By setting
we obtain
At this stage, we choose our different constants.

First, choosing large enough such that
then we pick large enough such that
then we select large enough such that
Thus, we arrive at
where .

On the other hand, if we let
then
Exploiting Young’s, Cauchy-Schwartz, and Poincaré inequalities, we obtain
On the other hand, from (22), we can write
where
Since and (16), we deduce that
Consequently, we find
that is,
At this point, we choose large enough such that
and exploiting (22), estimates (56) and (64), respectively, leads to
for some

By multiplying (67) by we get
Now, by using (17), we have the following estimate:
Thus, (68) becomes
which can be rewritten as
By using , we have
By exploiting (66), we notice that
Consequently, for , we get
Integrating (74) over gives
Consequently, (48) is established by virtue of (66) and (75).

*Remark 9. *The estimate (48) also remains valid for , thanks to the boundedness and continuity of and .

#### Data Availability

No data were used to support the study.

#### Conflicts of Interest

This work does not have any conflicts of interest.

#### Acknowledgments

The fifth author extends their appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through General Research Project under Grant No. (G.R.P-2/42).

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#### Copyright

Copyright © 2021 Abdelbaki Choucha et al. 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.