Global Existence and Blow-Up of Solutions to a Parabolic Nonlocal Equation Arising in a Theory of Thermal Explosion
Abstract
Focusing on the physical context of the thermal explosion model, this paper investigates a semilinear parabolic equation with nonlocal sources under nonlinear heat-loss boundary conditions, where a, p > 0 is constant, QT = Ω × (0, T], ST = ∂Ω × (0, T], and Ω is a bounded region in RN, N ≥ 1 with a smooth boundary ∂Ω. First, we prove a comparison principle for some kinds of semilinear parabolic equations under nonlinear boundary conditions; using it, we show a new theorem of subsupersolutions. Secondly, based on the new method of subsupersolutions, the existence of global solutions and blow-up solutions is presented for different values of p. Finally, the blow-up rate for solutions is estimated also.
1. Introduction
Moreover, some Fujita type results for parabolic inequalities are also studied. In [11], authors studied the quasilinear parabolic inequalities with weights and showed the existence of Fujita type exponents. And in [12], it investigated the nonexistence of nonnegative solutions of a class of quasilinear parabolic inequalities featuring nonlocal terms.
There are also some interesting results on the behaviour and stability for perturbed nonlinear impulsive differential systems (see [13–19]). And the stability of stochastic differential equations with impluses is studied in [20, 21].
In this paper, we will show the existence of global solution and the blow-up property of problem (1).
Now some assumptions are listed below.
(H1)
(H2) g > 0 and satisfies the local Lipschitz condition
In our paper, we use the method of subsupersolutions (see [22–25]). Since the there exist nonlinear boundary conditions and nonlocal term, we list the definitions of super- and subsolutions for our problem as follows.
Definition 1. is called a a supersolution to equation (1) if it satisfies that
is called a subsolution to equation (1) if it satisfies that
Blow-up and global existence solutions are defined as follows.
Definition 2. The solution u of the problem (1) blows up in finite time if there exists a positive real number T∗ < ∞, such that
And the solution u of the problem (1) exists globally if for any t ∈ (0, +∞),
Theorem 3 states the problem of local existence of the solution to equation (1) and is the main conclusion of this paper.
Theorem 3. Suppose are the sub- and supersolutions to equation (1), respectively, and . If u0(x) satisfies assumption (H1) and the function g satisfies assumption (H2), then there exists , which is the solution to equation (1).
The following two theorems show that whether the solution to equation (1) exists globally or blows up in finite time is related to constant p.
Theorem 4. Suppose assumptions (H1) and (H2) hold, and the equation (1) satisfies one of the following conditions.
- (i)
0 < p ≤ 1
- (ii)
p > 1, and the initial value u0(x) is sufficiently small
Then, the solution of this equation exists globally.
Theorem 5. Assume (H1) and (H2). If p > 1 and the initial value u0(x) is sufficiently large, then the solution to equation (1) blows up in finite time.
And the blow-up rate of the equation is given by Theorem 6.
Theorem 6. Assume (H1)–(H3) (see below). Then, there exists a solution u(x, t) blowing up at T∗ < ∞. Specifically, there exist constants C1, C2 such that
Remark 7. See Definition 2 for the description of global existence and blow-up solutions.
This paper is organized as follows. In Section 2, the local existence theory of solutions to equation (1) is established and Theorem 3 is proved. In Section 3, the conditions for the global existence of the solution are discussed and Theorem 4 is proved. In Section 4, the conclusions related to the blow-up solution are obtained and Theorem 5 is proved. In Section 5, the blow-up rate of the blow-up solution to equation (1) is further discussed and Theorem 6 is proved.
2. Proof of Theorem 3
In this section, the local existence of the solution to equation (1) is proved by using the fixed-point theorem and monotone iterative technique (see [26–29]).
First, the following lemma is present, which is proved according to [2].
Lemma 8. Suppose that assumptions (H1) and (H2) hold. Let and satisfy
Proof 1. Let and v = e−λtw, where . Then, the first equation in equation (13) can be deduced to
Hence,
- (i)
If x0 ∈ ∂Ω, then
At this point, we have n · ∇v0 ≥ −g(v0)v0 > 0, which is contradictory to n · ∇v0 < 0.
It yields , contradicting .
Combining (i) and (ii), there is no negative minimum value of v; thus, v is nonnegative. So v = e−λtw ≥ 0, i.e., w ≥ 0. Lemma 8 is proved.
Let Gk(u) = G(u) + Ku. Then, the function Gk(u) is increasing under this definition.
3. Proof of Theorem 4
In this section, the proof of the global results of solution to equation (1) is given.
Case 1. Combining assumptions (H1) and (H2) and Definition 1, u(x, t) = 0 satisfies
Therefore, u(x, t) = 0 is a subsolution to equation (1). According to Theorem 3, we need to determine a globally existing supersolution. Set φ as the unique solution of the ellipse problem
Let ϕ = Mφ where M > 0 is a constant. Obviously, on the boundary, we have
And the initial value ϕ0 = ϕ ≥ 0 is
- (1)
In case of 0 < p < 1, equation (31) can be transformed into
(32)
- (2)
In case of p > 1, equation (31) can be transformed into
(33)
Without loss of generality, we can take M = a1/(1 − p)μ1/(1 − p) such that u0(x) ≤ Mφ = a1/(1 − p)μ1/(1 − p)φ, that is, when u0(x) is sufficiently small, the solution u to equation (1) exists globally.
Case 2. In case of p = 1, the form of equation (1) is as follows:
Let b > a|Ω|, , and z(t) be the solution to the following Cauchy problem
This means that when p = 1, for any given a, z(t) is a supersolution to equation (1), and z(t) exists globally. Thus, the solution to equation (1) exists globally.
4. Proof of Theorem 5
The above theorem states that the classic solution of equation (1) exists globally when 0 < p ≤ 1. In this section, we will get the blow-up results of solutions to equation (1) when p > 1 and prove Theorem 5.
5. Proof of Theorem 6
In this section, we show the blow-up rate of the blow-up solution to equation (1) near its blow-up time.
Suppose that the solution u of equation (1) blows up in finite time T∗ and the assumptions (H1) and (H2) hold. We need the following assumption on the boundary condition:
(H3) There exists a constant γ > 0 such that infg(u) ≥ γ
Let function , where u(x, t) is a blow-up solution to equation (1). The following lemma is given according to [8, 30, 31].
Lemma 9. Suppose equation (1) satisfies the assumptions (H1) and (H2), and there exists a positive real number C1 such that
Conflicts of Interest
No conflicts of interest exist.
Acknowledgments
The authors thank the National Natural Science Foundation of China (62073203), the Fund of Natural Science of Shandong Province (ZR2018MA022), the National University Student Innovation Training Project (202110445095), and the Shandong University Students Innovation Training Project (S202110445194).
Open Research
Data Availability
No data were used to support the study.