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首页零扩散极限下的非线性动力系统边界层分析
零扩散极限下的非线性动力系统边界层分析
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更新于2024-07-16
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本文探讨的是非线性发展方程中的一个重要问题,即带阻尼和扩散作用的边界层现象,特别是在扩散参数β趋向于零的极限情况下。作者彭红云、阮立志和朱长江,来自华中师范大学数学与统计学学院,重点关注了这种特殊条件下边界层效应的深入研究。他们的研究对象是具有非线性特性的偏微分方程,这类方程在物理、工程等领域有着广泛的应用。 研究的核心内容是分析当扩散参数β趋近于零时,系统的动态行为如何受到影响,以及相应的收敛速度。他们发现,边界层的厚度在这一极限过程中表现出特定的阶数,即O(β^γ),其中0 < γ < 3/4。这一发现相比于之前文献[L.Z.Ruan和C.J.Zhu, Discrete Contin. Dyn. Syst. Ser. A, 32(2012), 331-352]有所突破,因为他们没有假设参数ν和β之间的线性关系,从而扩展了理论的适用范围。此外,他们在W1,∞模下的收敛率也得到了改进,这表明了他们研究方法的严谨性和有效性。 该工作的创新之处在于对传统边界层理论的一次拓展,它不仅深化了我们对非线性发展方程在扩散消失时行为的理解,还为实际问题提供了更精确的理论预测工具。对于偏微分方程的研究者而言,这篇论文提供了一个重要的参考点,尤其是在处理具有类似特征的物理系统时,可以参考其边界层分析和收敛性结果。 关键词包括偏微分方程、非线性发展方程、零扩散极限、边界层和边界层厚度,这些都直接反映了研究的核心内容。通过阅读这篇论文,读者将能够了解到如何在非线性动力系统中处理扩散与边界交互作用的问题,以及如何估计在极限情况下边界层的动态行为。这篇文章为学术界贡献了一项重要的理论成果,有助于推动相关领域的进一步研究和发展。
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˖ڍመڙጲ
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the boundary layer requires some special treatment in making estimates, cf. [27, 28]. In our
model (1), due to the presence of the second order derivative terms αψ
β
xx
and βθ
β
xx
, it seems
that we cannot directly use the standard energy method to deduce such some desired estimates
on ∥ψ
β
xx
(t)∥
H
1
and ∥θ
β
xx
(t)∥. However we found that if we can establish another some estimates
on ∥ψ
β
t
(t)∥
H
1
and ∥θ
β
t
(t)∥
H
1
instead, we can also obtain the desired estimates mentioned above.
Based on these observations, we can indeed show such some desired estimates by combining the
equations (1) with estimates on ∥ψ
β
t
(t)∥
H
1
and ∥θ
β
t
(t)∥
H
1
. In terms of the model (10), based on
the similar method, we establish further regularity estimates on ∥∂
xx
ψ
0
(t)∥
H
2
and ∥∂
xx
θ
0
(t)∥
H
2
by combining the equations (10) with estimates on ∥ψ
0
t
(t)∥
H
1
, ∥ψ
0
tt
(t)∥ and ∥θ
0
t
(t)∥
H
1
, where the
implicit boundary conditions (13) play an important role. It is noticed that, in contrast with
[13], the important point in this paper is that the restriction on the linear relation between the
parameters ν and β is removed. In addition, the convergence rates in W
1,∞
norm are improved
since the regularity on both solutions
ψ
β
, θ
β
and (ψ
0
, θ
0
) is improved.
The rest of this paper is arranged as follows. In Sections 2-4, we give the proof of Theorems
1.1-1.3 respectively. Precisely speaking, in Section 2, we establish a series of a priori estimates
on the solutions to (1)-(3) and obtain the global existence results. In Section 3, we devote
ourselves to the a priori estimates of the solution (ψ
0
(x, t), θ
0
(x, t)) of (10)-(12), obtain the
global existence and improve the regularity. Finally the convergence rates and the BL-thickness
are given in Section 4 as the diffusion parameter β → 0
+
.
1 Proof of Theorem 1.1
In this section, we devote ourselves to the a priori estimates of the solution
ψ
β
(x, t), θ
β
(x, t)
of (1)-(3) under the a priori assumption
N
1
(T ) = sup
0<t<T
ψ
β
, θ
β
(t)
2
2
6 ε
2
1
, (1)
where ε
1
is a positive constant satisfying 0 < ε
1
≪ 1, independent of β.
By Sobolev inequality, we have
ψ
β
, θ
β
(t)
W
1,∞
6 Cε
1
, (2)
which will be used later.
What follows will be a series of lemmas contributing to our desired estimates.
Lemma 2.1. Suppose that the assumptions in Theorem 1.1 hold. Then there exists a positive
constant C, independent of β, such that
1
0
ψ
β
2
+
θ
β
2
dx +
t
0
1
0
ψ
β
2
+
θ
β
2
+
ψ
β
x
2
+ β
θ
β
x
2
dxdτ ≤ C (3)
- 6 -
˖ڍመڙጲ
http://www.paper.edu.cn
and
1
0
ψ
β
x
2
+
θ
β
x
2
dx
+
t
0
1
0
ψ
β
x
2
+
θ
β
x
2
+
ψ
β
xx
2
+ β
θ
β
xx
2
dxdτ ≤ C. (4)
Proof. Multiplying the first and second equations of (1) by ψ
β
and θ
β
, then integrating the
resulting equations over (0, 1), using integration-by-parts and the boundary conditions (3), we
arrive at
1
2
d
dt
1
0
ψ
β
2
+
θ
β
2
dx +
1
0
(σ − α)
ψ
β
2
+ (1 − β)
θ
β
2
dx
+α
1
0
ψ
β
x
2
dx + β
1
0
θ
β
x
2
dx
= (σ + ν)
1
0
ψ
β
x
θ
β
dx −
1
0
ψ
β
x
θ
β
2
dx. (5)
Integrating (5) over (0, t), using Cauchy-Schwarz inequality and (2), we obtain for any λ > 0
1
2
1
0
ψ
β
2
+
θ
β
2
dx +
t
0
1
0
(σ − α)
ψ
β
2
+ (1 − β)
θ
β
2
dxdτ
+α
t
0
1
0
ψ
β
x
2
dxdτ + β
t
0
1
0
θ
β
x
2
dxdτ
≤
1
2
1
0
ψ
2
0
+ θ
2
0
dx +
t
0
σ + ν +
θ
β
(t)
L
∞
1
0
ψ
β
x
θ
β
dxdτ
≤
1
2
1
0
ψ
2
0
+ θ
2
0
dx + λ
t
0
1
0
ψ
β
x
2
dxdτ +
(σ + ν + Cε
1
)
2
4λ
t
0
1
0
θ
β
2
dxdτ. (6)
As in [13], we can choose λ > 0 such that
α > λ, 1 − β >
(σ + ν + Cε
1
)
2
4λ
, (7)
then we will deduce
1
0
ψ
β
2
+
θ
β
2
dx
+
t
0
1
0
ψ
β
2
+
θ
β
2
+
ψ
β
x
2
+ β
θ
β
x
2
dxdτ ≤ C ∥(ψ
0
, θ
0
)∥
2
, (8)
which shows that (3) holds.
Next, we turn to prove (4). To this end, multiplying the first and second equations of (1)
by −ψ
β
xx
and −θ
β
xx
, then integrating the resulting equations over (0, t)×(0, 1), using integration-
- 7 -
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