1. Introduction
Let us first introduce two parabolic-hyperbolic systems related with two particular cases of the abstract framework and are the motivation of our analysis. We begin with a Cauchy problem of a one-dimensional thermoelastic model obeying the Fourier’s law of heat flux and the theory due to Gurtin-Pipkin with short memory.
where
is the vertical displacement of a rod of length
L,
is the difference temperature,
is the temporal variable,
are positive numbers,
are nonnegative constants,
, is the convolution and
h is a relaxation function. This problem has been studied in [
1,
2,
3,
4,
5] without source term in the parabolic equation
. Here, we shall study this problem with
and an autonomous source term
f.
The second problem models the dynamics of a extensible plate equation with long thermal memory modeled by a heat flux theory due to Coleman-Gurtin with parameter
. This theory has the limit cases: the Fourier’s law when
and the theory due to Gurtin-Pipkin if
where
is a bounded domain, with smooth boundary
and corresponding normal vector
,
k is the long memory relaxation kernel,
are like before and
Similar problems have been studied in [
6,
7,
8], and in [
9,
10] where a rotational term is considered.
In the systems introduced above we have two types of memory terms, a short one and a long or infinite memory. We also observe that the coupling terms in these systems, those with the coefficient , are of two kinds. In , the corresponding operator has opposite signs in the equations of the system, is symmetric and positive. Meanwhile that in , the coupling operator is antisymmetric and the sign in both equations is the same. In order to handle these examples and some more, we shall work with two abstract systems. The first one is a system with short memory and an antisymmetric coupling operator. The second one is a system with long memory and a coupling positive and symmetric operator. Although more combinations of memory and coupling terms can be studied, their analysis can be performed in a similar way.
Let us consider the following semilinear problems associated with abstract parabolic-hyperbolic systems with short and long memory terms, respectively. The first one models problems with short memory. For every initial data
, find functions
, such that the following system holds, for every
,
In the second problem, we consider infinite memory as follows. For every initial data
, find functions
, such that the following system holds, for every
,
Here,
,
and
, are constants. The functions
and
are short and long memory relaxation kernels, respectively. The functions
and
are nonlinear source terms. The following operators, defined on Banach spaces, are linear and continuous
We assume that
are linear subspaces of a Hilbert space
H with inner product
, norm
, and
are the corresponding dual spaces. We identify
, then
In terms of the corresponding duality pairs, we have the following bilinear forms
We assume that
P and
, j = 1,2, are positive and symmetric, then we have the corresponding norms for
The following hypotheses are assumed to hold along the paper.
(i) There are constants
, such that
For the problem
, we assume that the operator
B is antisymmetric
in particular
For the problem
, we assume that the operator
B is symmetric and positive, then we define a norm for
B
(ii) The nonlinear source term
is a potential operator with potential
, that is,
. We assume that
, and there exists a constant
, such that
and
(iii) The relaxation kernel
, satisfies the following conditions
and
h is a positive definitive kernel, that is
for every
and some constant
, where
is the convolution of
h and
w.
(iv) The long memory relaxation kernel
, satisfies the following hypotheses
The phase space, where we study the dynamics of
, is
with corresponding square norm
For the problem
, we introduce the following new memory function
for every
, and hence
with
With respect to this new function, we define the following space
with norm
We notice that, by an integration by parts
Then, the problem is equivalent to the following.
For every initial data
, find functions
, such that the following system holds, for every
,
The phase space, where we study the dynamics of
, is
with corresponding square norm
The concavity argument, introduced by Professor Howard Levine [
11,
12] is one of the methods to study nonexistence of global solutions of evolution equations due to blow-up and has been generalized by means of the analysis of differential inequalities. See the book [
13] and references therein, for an account of several methods to study blow-up in equations of mathematical physics. Here, we shall apply the differential inequality recently studied in [
14].
Some authors have considered other mathematical models of thermoelasticity. For instance, in [
15,
16] chemical potentials are included. Time fractional parabolic-hyperbolic and time fractional hyperbolic thermo-elasticity equations are studied in [
17]. Other nonlinearities like p-Laplacian and fractional powers of operators are worked in [
18,
19,
20,
21,
22]. Equations with delay terms are studied in [
23,
24]. Similar parabolic-hyperbolic systems to the ones presented in the introduction have been analyzed in [
25,
26]. Thermoelasticity system in n dimensions with short memory are studied in [
27,
28] and are commented in last section.
The analysis of problem will be done for weak solutions in the following sense,
Definition . For every initial data
the map, for
,
is a weak local solution of problem
, if there exists some
, such that
with
and
a. e.
, for every
We shall consider that the solution in this sense is unique and satisfies the following energy equation for
,
where
Due to
and
,
Furthermore, if the maximal time of existence
, then
consequently,
The analysis of problem will be done for weak solutions in the following sense,
Definition . For every initial data
the map, for
,
where
, is a weak local solution of problem
, if there exists some
, such that
with
and
a. e.
, for every
We shall consider that the solution in this sense is unique and satisfies the following energy equation for
,
where
Indeed, from last definition
Due to
and
,
Furthermore, if the maximal time of existence
, then
consequently,
2. Main result
In this section we shall analyze the nonexistence of global solutions for both problems introduced in the introduction and any positive value of the initial energy. To this end, we define the following constants
Also, we define the functions
for
,
, and
Theorem .
Consider any solution either from problem or problem , in the sense of Definitions 1.1, 1.2, respectively. Assume that hypotheses hold. If
is satisfied, then there exists a nonempty interval
with the following consequences:
(i) If , then blows-up at a finite time , that is
Hence, the corresponding solution of anyone of the two problems is not global.
(ii) and , moreover
for some and , where is a function of .
(iii) For fixed ,
(iv) Furthermore, for fixed, we have the limit values as ,
Corollary . Consider any solution either from problem or problem , in the sense of Definitions 1.1, 1.2, respectively. Assume that hypotheses of Theorem 2.1 are met. Given any numbers , we can choose initial data with large enough, so that the conclusions of Theorem 2.1 are satisfied for initial energy with at a blow-up time
For the proof we will employ the following definitions and remarks.
First, we define the following orthogonal decomposition of the velocity
Second, since the conditions on the initial data that produce the nonexistence of global solution in both problems are only on
, we define the auxiliary space
then the phase spaces for the problems, in the sense of Definitions 1.1, 1.2 become, respectively
Third, we define the concept of a positive invariant set with respect to any solution either from problem
or problem
, in the sense of Definitions 1.1, 1.2, respectively. Indeed,
is a positive invariant set, along
, respectively
is a positive invariant set, along
, if
Fourth, from (2.2)-(2.3) and by introducing the function,
the inequality in (2.4) has the equivalent forms
Finally, we define the sets
Lemma 2.3.
Consider any solution either from problem or problem , in the sense of Definitions 1.1, 1.2, respectively. Assume that hypotheses hold and (2.4) is satisfied. If there exists a constant such that
where the function defined by
then, along the solution, the corresponding set is positive invariant. Furthermore,
Proof. (of Lemma 2.3.) Consider a solution either from problem
or problem
, such that the initial data are in the corresponding
. Then, in any case
. To show the invariance property, we proceed by contradiction. Assume that there exists some
such that
that is
We shall prove that the time
is never reached. To this end, we first construct a differential inequality for the function
We calculate the first and second derivatives of
, and we use Definitions 1.1 and 1.2. First, we only use the hyperbolic equation, which is the same in both problems. Then, we conclude the following for
,
We shall estimate the terms of the right hand side of the second derivative of
. First, we consider the problem
. By the corresponding energy equation and hypothesis
, we obtain the following
For the problem
, we estimate in a similar way the terms of the right hand side of the second derivative of
Consequently, from (2.7), hypothesis
, (2.5) and last inequalities, we get for both problems and for
,
That is, for
, the following inequality is satisfied
From
, we can simplify the notation by substituting the constants defined in (2.1). After multiplying the differential inequality (2.8) by
, we obtain
If we now introduce
, this inequality becomes
From the definition of
,
Hence, and from the differential inequality for
we obtain
Consequently, we arrive to
Multiplying (2.10) by
, we conclude the following integral
By hypotheses, there is a constant
such that
then, from (2.11)
By continuity, when
,
which contradicts the definition of
. Hence, as long as the solution exits,
and the corresponding
, is positive invariant.
□
Proof. (of Theorem 2.1.) If the solution is global, then
that is, it is well defined for any
. The conclusions of Theorem 2.1 are derived from the analysis of (2.9), as was made in [
5]. However, for completeness we shall sketch the proof. First, from Lemma 2.3,
And consequently,
Then
implies that
. That is,
blows-up at
.
The proof of (2.6) is as follows. First, we notice that
attains an absolute minimum at
, that is
where
We define
. Then, (2.6) holds if and only if
Furthermore,
where
. Hence, there exist two different roots, denoted by
and
, of
That is, there exists a nonempty interval
, such that
and
Then, (2.6) holds if and only if
. The strict monotonicity of
for
and
, implies that, for fixed
, the interval
grows as
grows. That is,
The rest of the conclusions follow as in [
5].
□
Proof. (of Corollary 2.3.) Since , and , then, for every there exists , such that Also, for every there exists , such that . Hence, any solution with blows-up at a finite time if □
Remark 2.1. Notice that , the assumption (2.4) in Theorem 2.1, is the condition that allows the existence of , and characterizes the condition that implies the positive invariance of and hence the blow up of in finite time and consequently the nonexistence of global solutions.
Remark 2.2. The blow-up of the solution it comes from two different sources of the system. (i) The physical properties of the model: . (ii) The initial data: . The blow-up property is reached for a larger set of values of r as long as decreases. If we decouple the system, , then the blow-up is reached as if the parabolic equation did not exist. The coupling with the parabolic equation stabilizes the system, as does the damping term in the hyperbolic equation. Indeed, the numbers and are closer one each other as the damping coefficient or the coupling factor grows. Hence, the length of the blow-up interval decreases as or increases. Therefore, as the damping coefficient or the coupling factor grows, then the set of initial energies where we can have global non existence becomes smaller. On the other hand, a notable property that should be highlighted is that the blow-up time approaches zero and the length of the blow-up interval becomes infinity as goes to infinity.