Abstract
This paper deals with the existence and uniqueness of solutions of a new class of Moore-Gibson-Thompson equation with respect to the nonlocal mixed boundary value problem, source term, and nonnegative memory kernel. Galerkin’s method was the main used tool for proving our result. This work is a generalization of recent homogenous work.
1. Introduction
In this contribution, we are interested to study the existence and uniqueness of solutions of the following problem
Here, and are physical parameters, and is the speed of sound. The convolution term reflects the memory effect of materials due to vicoelasticity, is a given function, and is the relaxation function satisfying
(H1) is a nonincreasing function satisfying where , , and .
(H2) satisfying
(H3)
The phenomena resulting from sound waves (diffraction, interference, reflection) in terms of modeling are very important. As the existence of the third derivative is very important, especially in the field of thermodynamics (EIT), the study of these models is considered the beginning of an in-depth understanding of both convergent and good behavior. From the results extracted, the equation of MGT resulted in nonlinear acoustics, for much depth, see ([1–7]) and especially [8] where equation of MGT appeared for the first time. Also, nonlinear problems of great importance can be considered [9], where Galerkin’s method was applied in solving them, for more depth ([2, 3, 10–13]). Recently, in [14], the authors studied the equation of MGT with memory. Likewise, in [1], the authors used Galerkin’s method to demonstrate the ability to solve a mixed problem of MGT equation in the absence of viscous elasticity and memory. Based on work [9] and the works we mentioned earlier, we want to prove the existence and uniqueness of a weak solution to the problem (1).
We divide this paper into the following: in the second part, we put some definitions and appropriate spaces. Then, we apply Galerkin’s method to prove the existence, and in the fourth part, we demonstrate the uniqueness.
2. Preliminaries
We will define the spaces: and by where
Consider the equation where and stands for the inner product in , is supposed to be a solution of (1) and . Evaluation of the inner product in [9] gives
We give two useful inequalities: (i)Gronwall inequality. Let the nonnegative integrable functions on the interval with the nondecreasing function . If , we have where , hence, (ii)Trace inequality (see [15]). If where Ω is a bounded domain in with smooth boundary , then for any , where .
Definition 1. We call a generalized solution to the problem (1) for each function that fulfills the equation (9) for each .
3. Solvability of the Problem
In this section, we use Galerkin’s method to prove the existence of a generalized solution of our problem.
Theorem 2. If , , , and , then there is at least one generalized solution in to problem (1).
Proof. Let be a fundamental system in , such that .
First, we will give an approximate solution of the problem (1) in the form
where are constants given by the conditions, for and can be determined from the relations
substitution of (13) into (15), and we find for .
From (15) it follows that
Let
Then, (17) can be written as
By differentiating (two times) with respect to , it gives
We find a system of differential equations of fifth order with respect to , constant coefficients, and the initial conditions (21). Hence, we obtain a Cauchy problem of linear differential equations with smooth coefficients that is uniquely solvable. Thus, ∀n, ∃uN (x) satisfying (15).
Now, we prove that uN is sequence bounded. To do this, we multiply each equation of (15) by the appropriate summing over from 1 to . Hence, by integration the result equality with respect to from 0 to , and , it gives
Evaluation of the terms on the LHS of (22) gives
So,
Thus,
Taking into account the equalities (23)–(30) in (22), we end up with
Now, multiplying the equations of (15) by , collect them from 1 to and integrating the result with respect to from 0 to , and , we find
With the same reasoning in (22), we find
A substitution of equalities (33)–(40) in (22) gives
Multiplying (32) by and using (41), we get
where
With the help of Cauchy and the trace inequalities, we can estimate all the terms in the RHS of (42) that gives
Combining inequalities (45)-(60) and equality (44) and make use of the following inequality
where
and we have
where
Choosing and sufficiently large
By using (2)-(4), the relation (64) reduces to
where
Using the inequality of Gronwall to (67) and integrating the result from 0 to τ that gives
where
We deduce from (69) that
Hence, is sequence bounded in , and we can extract from it a subsequence for which we use the same notation which converges weakly in to a limit function , and we have to show that is a generalized solution of (1). Since in and in , then .
Now to prove that (15) holds, we multiply each of the relations (15) by a function , . Hence, collect them the obtained equalities ranging from to and integrating the result over on . If we let , then we have
for all of the form and
Since
Thus, the limit function satisfies (15) for every .
We define the totality of all functions of the form by , with , .
But is dense in , hence the relation (15) holds . Then, we have shown that the limit function is a generalized solution of problem (1) in .
4. Uniqueness of the Problem
Theorem 3. The problem (1) cannot have more than one generalized solution in .
Proof. Suppose that two different generalized solutions for the problem (1). Hence, the difference solves
and (9) gives
where
Let the function
It is obvious that and for all . By integration by parts in the LHS of (75) that yields
Plugging (78)–(82) into (75), we obtain
Now since
then
Applying the inequality of the trace, the RHS of (83) gives
Combining the relations (86)–(83) and (87)–(88), we get
Next, multiplying (74) by and integrating the result over , we find
An integration by parts in (91) yields
Substitution (91)–(95) into (90), we get the equality
The RHS of (96) can be bounded as follows
So, combining inequalities (97)–(102), we obtain
Adding side to side (89) and (103) that gives
where
Now, the last term on the RHS of (104), we give the function θ (x,t) by
Hence, we use (77), and we get
And using the inequalities
Let
and we choose and sufficiently large
As τ is arbitrary, and we get
Thus, inequality (104) takes the form
where
We get
where
Hence, applying Gronwall’s lemma to (114) gives
for all .
For the intervals, we use the same method
to cover the whole interval and thus proving that , in Hence, the uniqueness is proved.
5. Conclusion
The objective of this work is the study of solvability of the Moore-Gibson-Thompson equation with viscoelastic memory term and integral condition by using the Galerkin method. The MGT equation is a nonlinear partial differential equation that arises in hydrodynamics and some physical applications. Recent developments in numerical schemes for solving MGT have placed immense interest in nonlinear dispersive wave models. In the next work, we will try to use the same method with Boussinesque and Hall-MHD equations which are nonlinear partial differential equation that arises in hydrodynamics and some physical applications. It was subsequently applied to problems in the percolation of water in porous subsurface strata (see [6, 15–24], for example, [10, 11, 25, 26]) by using some famous algorithms (see [27–29]).
Data Availability
No data were used to support the study.
Conflicts of Interest
The authors declare that they have no conflicts of interest.
Acknowledgments
The fifth author extends his appreciation to the Deanship of Scientific Research at King Khalid University for funding this work through research groups program under grant (R.G.P-2/1/42).