R E S E A R C H
Open Access
The existence of positive solution for
singular Kirchhoff equation with two
parameters
Ke Di
1and Baoqiang Yan
1**Correspondence:
1School of Mathematical Sciences, Shandong Normal University, Jinan, P.R. China
Abstract
In this paper, we consider the singular Kirchhoff equation with two parameters ⎧
⎪ ⎨ ⎪ ⎩
–a(Ω|∇u(x)|2dx)u(x) +K(x)g(u) =
λ
f(x,u) +μ
h(x) inΩ
, u> 0 inΩ
,u= 0 on
∂Ω
.By using the sub-supersolution method together with the comparison principle for elliptic equations, we obtain several existence and nonexistence theorems. Our works improve the results in the previous literature.
Keywords: Elliptic problems of Kirchhoff type; Positive solution; Subsolution; Supersolution
1 Introduction
In this paper, we study the existence and nonexistence of solutions to the following singular nonlocal elliptic problem with two parameters:
⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩
–a(Ω|∇u(x)|2dx)u(x) +K(x)g(u) =λf(x,u) +μh(x) inΩ,
u> 0 inΩ,
u= 0 on∂Ω,
(1.1)
whereΩis a smooth bounded domain inRN (N≥2),a: [0, +∞)→(0, +∞) is a continu-ous and nondecreasing function with
inf
t∈[0,+∞)a(t) =a(0) =a0> 0,
K,h∈C0,γ(Ω¯) withK> 0 andh> 0 onΩ, andλandμare positive real numbers.
This problem is related to the general form of the stationary counterpart of the hyper-bolic Kirchhoff equation
ρ∂
2u
∂t2 –
P0
h + E 2L
L
0
∂u
∂x 2dx
∂2u
∂t2 =g(x,u)
for free vibrations of elastic strings [7]. Kirchhoff ’s model takes into account the changes in length of the string produced by transverse vibrations, in whichLis the length of the string,
ρ is the mass density, andP0 is the initial tension. Many researchers began an extensive
research in equations of this type after Lions [10] put forward a basic framework. For example, Perera and Zhang [17,30] considered the following Kirchhof-type problems with 4-sublinear case, asymptotically 4-linear case, and 4-superlinear case terms:
⎧ ⎨ ⎩
–(a+bΩ|∇u(x)|2dx)u(x) =f(x,u) inΩ,
u= 0 on∂Ω. (1.2)
They obtained nontrivial solutions via the Yang index and the invariant sets of descent flow. Sun and Tang [22] obtained the existence and multiplicity of weak solutions of (1.2) by using the mountain pass theorem, the local linking theorem, the fountain theorem, and the symmetric mountain pass lemma in critical point theory. Utilizing the local link-ing theory, Yang and Zhang [29] obtained the nontrivial solutions of (1.2) with quasilinear terms. Yang and Han [28] obtained infinitely many solutions whenf(x,u) is odd by using the fountain theorem. In recent years, many researchers studied the fractional Kirchhoff equation. In [9] and [24] the authors deal with fractional Schrödinger–Kirchhoff equa-tions. In [23] the authors obtained the multiplicity of solutions of a fractionalp-Laplacian Kirchhoff system. In [16] authors deal with nonlocal fractional problems. In addition, in [25] the authors obtained the local existence and blowup of solutions of nonlocal Kirch-hoff diffusion problems. Some other results can be found in [3–5,11–15,20,26], and their references.
Since the method of sub-supersolutions is an important tool to solve the existence of so-lutions for boundary value problems, naturally, some authors hope to use the theorem of sub-supersolutions to discuss the elliptic problems of Kirchhoff type. However, the nonlo-cal term brings some difficulties. To overcome the difficulty from the nonlononlo-cal term, Alves and Corrêa [1] considered following problem:
⎧ ⎨ ⎩
–a(Ω|∇u(x)|2dx)u(x) =f(x,u) inΩ,
u= 0 on∂Ω, (1.3)
and obtained the existence of positive solutions by using the sub-supersolution method under the condition thatf :Ω×R→Ris an increasing function. Moreover, Alves and Corrêa [2] dealed with the quasilinear stationary Kirchhoff equation
⎧ ⎨ ⎩
–a(Ω|∇u(x)|2dx)u(x) =f(x,u,∇u) inΩ,
u= 0 on∂Ω, (1.4)
and using the pseudomonotone operator theory, they established the existence of weak solutions by constructing a supersolution and a family of subsolutions. Recently, Yan, O’Regan, and Agarwal [27] discussed the following problem:
⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩
–a(Ω|∇u(x)|2dx)u(x) =F(x,u) inΩ,
u> 0 inΩ,
u= 0 on∂Ω.
They presented some new definitions of a sub-supersolution to problem (1.5) and obtained the existence of classical solution to problem (1.5) whenF(x,u) =λuq–up+1 (0 <q< 1,
p> 0).
Motivated by the ideas introduced in [6], we suppose thatf :Ω×[0,∞)→[0,∞) is a Hölder-continuous function that is positive onΩ×(0,∞). We also assume thatf is nondecreasing with respect to the second variable and is sublinear, that is,
(f1) the mapping(0,∞)s →f(xs,s)is nonincreasing for allx∈Ω; (f2) lims→0f(xs,s)= +∞andlims→+∞f(xs,s)= 0uniformly inx∈Ω;
(f3) there existsn0> 0such thatλn0f(x,s)≥f(x,λn0+1s)for allλ≥1.
We assume thatg∈C0,γ(0,∞) is a nonnegative and nonincreasing function satisfying:
(g1) lims→0g(s) = +∞;
(g2) there existC,δ0> 0andτ∈(0, 1)such thatg(s)≤Cs–τ for alls∈(0,δ0).
Example The functionf(s) =sα(0 <α< 1) fulfills (f1)–(f3), whereasg(s) = (sα+sβ)–1(0 <
α< 1,β> 1) satisfies assumptions (g1)–(g2).
DenoteD={u∈C2(Ω)∩C(Ω);g(u)∈L1(Ω)}.
We show in this paper that (1.1) has at least one solution inDforλbelonging to a certain range and anyμ> 0. We also prove that in some cases, (1.1) has no solutions inD, provided thatλandμare sufficiently small.
Remark1.1
(i) Ifu∈D,v∈C2(Ω)∩C(Ω), and0 <u<vinΩ, thenv∈D.
(ii) Letu∈C2(Ω)∩C(Ω)be a solution of (1.1). Thenu∈Dif and only ifu∈L1(Ω).
Our main results are the following.
Theorem 1.1 Assume that f satisfies(f1)–(f3)and g satisfies(g1)–(g2).
(1) Iflimλ→+∞a(λ2+2λn0)= +∞,then there existsλ¯such that(1.1)has at least one solution
inDfor allλ>λ¯ andμ> 0.
(2) There existλ∗andμ∗small enough such that(1.1)has no solution inDfor allλ<λ∗ andμ<μ∗.
Theorem 1.2 Assume that f satisfies(f1)–(f2).If01g(s)ds= +∞,then(1.1)has no solution in D for anyλ,μ> 0.
This paper is organized as follows. Some preliminary lemmas are given in Sect.2, and Sect.3is devoted to proofs of the results. Some ideas also come from [19] and [18].
2 Preliminaries
In this section, we consider the general problem ⎧
⎨ ⎩
–a(Ω|∇u(x)|2dx)u(x) =F1(x,u) +F2(x,u) inΩ,
u= 0 on∂Ω. (2.1)
Definition 2.1 The pair of functionsα,β∈C1(Ω)∩C2(Ω) are a subsolution and
super-solution of (2.1) ifα(x)≤β(x) forx∈Ωand ⎧
⎨ ⎩
–α(x)≤b1
0F1(x,α(x)) +
1
a0F2(x,α(x)), x∈Ω,
α|∂Ω≤0,
⎧ ⎨ ⎩
–β(x)≥a1
0F1(x,β(x)) +
1
b0F2(x,β(x)), x∈Ω,
β|∂Ω≥0,
wherea0=a(0) andb0=a(
ΩH(x)
2dx),E∈Lp(Ω) (p>N); here
E(x) = sup
u∈[α(x),β(x)]
F(x,u) , x∈Ω,
H(x) = 1 a0
Ω
Gx(x,y) E(y)dy, x∈Ω,
G(x,y) is the Green function for –u(x) =h, andu|∂Ω= 0.
Lemma 2.2(see [27]) LetΩ⊆RN(N≥1)be a smooth bounded domain.Let F:Ω×R→
Rbe a continuous function. Letα andβ be the subsolution and supersolution of (2.1), respectively.If
F1(x,u)≥0, F2(x,u)≤0, ∀x∈Ω,α(x)≤u≤β(x),
then problem(2.1)has at least one solution u such that
α(x)≤u(x)≤β(x) for all x∈Ω.
Letϕ1be the normalized positive eigenfunction corresponding to the first eigenvalueλ1
of the problem ⎧ ⎨ ⎩
–u(x) =λu inΩ,
u= 0 on∂Ω.
(2.2)
Lemma 2.3(see [8]) Ωϕ–1s<∞if and only if s< 1.
Lemma 2.4(see [21]) Let F:Ω¯ ×(0,∞)→Rbe a Hölder-continuous function with
ex-ponentγ∈(0, 1)on each compact subset ofΩ×(0,∞)satisfying: (F1) lims→∞sup(s–1maxx∈ ¯ΩF(x,s)) <λ1;
(F2) for eacht> 0,there exists a constantD(t) > 0such that
F(x,r) –F(x,s)≥–D(t)(r–s) forx∈Ωandr≥s≥t;
(F3) there existη0> 0and an open subsetΩ0⊂Ωsuch that
min
x∈ ¯Ω
and
lim
s→0
F(x,s)
s = +∞ uniformly inx∈Ω0.
Then for any nonnegative functionϕ0∈C2,γ(∂Ω),the problem
⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩
–u(x) =F(x,u) inΩ,
u> 0 inΩ,
u=ϕ0 on∂Ω
(2.3)
has at least one positive solution u∈C2,γ(G)∩C(Ω)for any compact set G⊂Ω∪ {x∈ ∂Ω;ϕ0(x) > 0}.
Lemma 2.5(see [21]) Let F:Ω×(0,∞)→Rbe a continuous function such that the
mapping(0,∞)s → F(xs,s) is strictly decreasing at each x∈Ω.Assume that there exists
ν,ω∈C2(Ω)∩C(Ω)such that:
(a) ω+F(x,ω)≤0≤ ν+F(x,ν)inΩ; (b) ν,ω> 0inΩandν≤ωon∂Ω;
(c) ν∈L1(Ω).
Thenν≤ωinΩ.
We observe that the hypotheses of Lemmas2.4and2.5are fulfilled for
Φλ(x,s) =
1 a0
λf(x,s) +h(x).
Lemma 2.6 Let f satisfy(f1)–(f2).Then for anyλ,μ> 0,according to Lemmas2.4and2.5,
the boundary value problem
⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩
–U(x) =λf(x,U) +μh(x) inΩ,
U> 0 inΩ,
U= 0 on∂Ω
(2.4)
has a unique solution Uλ,μ∈C2,γ(Ω)∩C(Ω).
3 Proofs of main theorems
DenoteK∗=maxx∈ΩK(x),K∗=minx∈ΩK(x).
Proof of Theorem1.1 According to Lemma2.6, the boundary value problem
⎧ ⎪ ⎪ ⎨ ⎪ ⎪ ⎩
–U(x) =a1
0(f(x,U) +h(x)) inΩ, U> 0 inΩ,
U= 0 on∂Ω
has a unique solutionU∈C2,γ(Ω)∩C(Ω). LetH: [0,∞)→[0,∞) be such that
⎧ ⎨ ⎩
H(t) =g(H(t)) for allt> 0,
H(0) =H(0) = 0. (3.2)
Obviously,H∈C2(0, +∞)∩C1[0, +∞) exists by our assumption (g2). From (3.2) it fol-lows that His nonincreasing, whereasH andH are nondecreasing on (0,∞). Using this fact and applying the mean value theorem, we deduce that, for allt> 0, there exist
ξ1
t,ξt2∈(0,t) such that
H(t) t =
H(t) –H(0) t– 0 =H
ξ1
t
≤H(t)
and
H(t) t =
H(t) –H(0) t– 0 =H
ξ2
t
≥H(t).
These inequalities imply
H(t)≤tH(t)≤2H(t) for allt> 0.
Hence
1≤tH (t)
H(t) ≤2 for allt> 0. (3.3)
On the other hand, by (g2) and (3.2) there existsη> 0 such that
⎧ ⎨ ⎩
H(t)≤δ0 for allt∈(0,η),
H(t)≤CH–τ(t) for allt∈(0,η), (3.4)
which yields
H(t)≤ct1+2τ for allt∈(0,η), (3.5)
wherec> 0 is a constant. Set
αλ,μ=MH(ϕ1),
whereMis a positive constant. Then we can get
–αλ,μ+
1 a0
K(x)g(αλ,μ)
=λ1MH(ϕ1)ϕ1+
1 a0
K(x)gMH(ϕ1)
–MgH(ϕ1)
FixM≥1. The monotonicity ofgleads to
gMH(ϕ1)
≤gH(ϕ1)
inΩ,
and by (3.6)
–αλ,μ+
1 a0
K(x)g(αλ,μ)
≤λ1MH(ϕ1)ϕ1+
1 a0
K∗gH(ϕ1)
–MgH(ϕ1)
|∇ϕ1|2 inΩ. (3.7)
By Hopf ’s maximum principle there existδ0andΣ⊂Ωsuch that
|∇ϕ1| ≥δ0 inΩ\Σ, |ϕ1| ≥δ0 inΣ.
OnΩ\Σ, we chooseM≥M1=max{1, K ∗
a0δ2}. Then we have
1 a0
K∗gH(ϕ1)
≤MgH(ϕ1)
|∇ϕ1|2 inΩ\Σ. (3.8)
ChoosingM≥max{M1, K ∗g(H(δ
0))
a0λ1H(δ0)δ0}, we have
1 a0
K∗gH(ϕ1)
≤λ1MH(ϕ1)ϕ1 inΣ. (3.9)
It follows from (3.7)–(3.9) that
–αλ,μ+
1 a0
K(x)g(αλ,μ)≤2λ1MH(ϕ1)ϕ1 inΩ. (3.10)
Sinceϕ1> 0 inΩ, from (3.3) we have
1≤H (ϕ
1)ϕ1
H(ϕ1) ≤
2 inΩ. (3.11)
Then (3.10) and (3.11) yield
–αλ,μ+
1 a0
K(x)g(αλ,μ)≤4λ1MH(ϕ1) = 4λ1αλ,μ inΩ. (3.12)
TakeA0= 4a0λ1c–1|α(x)|∞, wherec=infx∈ ¯Ωf(x,|αλ,μ|∞) > 0. Ifλ>A0, then assumption
(f1) produces
λf(x,αλ,μ)
a0αλ,μ
≥A0f(x,|αλ,μ|∞)
a0|α(x)|∞ ≥4λ1 for allx∈Ω.
Combined with (3.12), this gives
–αλ,μ+
1 a0
K(x)g(αλ,μ)≤
1 a0
DenoteΩ0={x∈Ω;ϕ1(x) <η}. By (3.4) and (3.5) it follows that
g(αλ,μ) =g
MH(ϕ1)
≤gH(ϕ1)
≤CH–τ(ϕ1)≤C0ϕ
–2τ
1+τ
1 inΩ0,
g(αλ,μ)≤g
MH(η) inΩ\Ω0.
These estimates combined with Lemma2.3yieldg(αλ,μ)∈L1(Ω), and soαλ,μ∈L1(Ω).
Set
βλ,μ=λn0+1U,
whereλ≥max{1,μ}.
We now prove that there existsA0such thatαλ,μ≤βλ,μfor allλ>A0.
Since
βλ,μ+
1 a0
λf(x,βλ,μ) +h(x)
=λn0+1U+ 1 a0
λfx,λn0+1U+h(x)
≤λn0+1
U+ 1 a0
f(x,U) +h(x)= 0,
we can get
βλ,μ+Φλ(x,βλ,μ)≤0≤ αλ,μ+Φλ(x,αλ,μ) inΩ,
αλ,μ,βλ,μ> 0 inΩ,
αλ,μ=βλ,μ on∂Ω,
αλ,μ∈L1(Ω).
By Lemma2.5it follows thatαλ,μ≤βλ,μonΩfor allλ>A0.
Define
E1(x) =λf(x,βλ,μ) +μh(x) +K(x)g(αλ,μ), x∈Ω,
H1(x) =
1 a0
Ω
Gx(x,y) E1(y)dy, x∈Ω,
b1=a
Ω
H1(x)2dx
,
that is,
E(x) = sup
u∈[αλ,μ(x),βλ,μ(x)]
F(x,u) ≤E1(x), x∈Ω,
H(x) = 1 a0
Ω
Gx(x,y) E(y)dy≤H1(x), x∈Ω,
b0=a
Ω
H(x)2dx
≤b1=a
Ω
H1(x)2dx
We have
b1=a
Ω
H1(x)2dx
=a Ω 1 a0 Ω
Gx(x,y) λf
y,λn0+1U+μh(y) +K(y)gMH(ϕ
1) dy 2 dx ≤a Ω 1 a0 Ω
Gx(x,y) λf
y,λn0+1U+λh(y) +K∗gH(ϕ
1) dy 2 dx ≤a λ a0 2 Ω Ω
Gx(x,y) f
y,λn0+1U+h(y) +K∗gH(ϕ
1) dy 2 dx ≤a
λ2+2n0 a2 0 Ω Ω
Gx(x,y) f(y,U) +h(y) +K∗g
H(ϕ1)
dy 2 dx . Let C= 1 a0 2 Ω Ω
Gx(x,y) f(y,U) +h(y) +K∗g
H(ϕ1)
dy
2
dx,
that is,
b1≤a
Cλ2+2n0,
whereCis a positive constant. Sincelimλ→+∞a(λ2+2λn0)= +∞, there existsB0such that
λ
a(Cλ2+2n0)≥4λ1c
–1|α|
∞ for allλ≥B0.
Choosingλ¯=max{1,μ,A0,B0}, we easily to see that
–αλ,μ≤
1 b0
λf(x,αλ,μ) +μh(x)
– 1
a0
K(x)g(αλ,μ) inΩfor allλ>λ¯.
Since
–λn0U= 1 a0
λn0f(x,U) +h(x)≥ 1 a0
fx,λn0+1U+h(x) inΩ,
we get
–λn0+1U≥ λ a0
fx,λn0+1U+h(x) inΩ.
Hence
–βλ,μ≥
1 a0
λf(x,βλ,μ) +μh(x)
– 1
b0
K(x)g(βλ,μ) inΩfor allλ>λ¯.
By Lemma2.2(1.1) has at least one solutionuλ,μsuch thatαλ,μ≤uλ,μ≤βλ,μinΩ. Since
Nonexistence forλ,μsmall. Letλ,μ> 0. Set
Θλ,μ(x.s) =
1 a0
λf(x,s) +μh(x) –K(x)g(s) inΩ.
SinceK∗> 0, assumption (g1) implieslims→0Θλ,μ(x.s) = –∞uniformly inx∈Ω. Then
there existsc> 0 such that
Θλ,μ(x.s) < 0 for all (x,s)∈Ω×(0,c). (3.13)
Lets≥c. From (f1) we deduce
Θλ,μ(x.s)
s ≤
1 a0
λf(x,s)
s +μ h(x)
s
≤ 1
a0
λf(x,c)
c +μ
|h|∞ s
for allx∈ ¯Ω. Fixμ≤cλ1a0
2|h|∞ and letM=supx∈Ω
f(x,c)
a0c > 0. From the above inequality we have
Θλ,μ(x.s)
s ≤λM+
λ1
2 for all (x,s)∈Ω×(c, +∞). (3.14)
SetA(λ) =λM. Inequalities (3.13) and (3.14) yield
Θλ,μ(x.s)≤A(λ)s+ λ1
2s for all (x,s)∈Ω×(0, +∞). (3.15)
Moreover,A(λ)→0 asλ→0. If (1.1) has a solutionuλ,u, then
λ1
Ω
u2λ,μ(x)dx≤
Ω
∇uλ,μ(x) 2
dx
= –
Ω
uλ,μ(x)uλ,μ(x)dx,
and using (3.15), we get
λ1
Ω
u2λ,μ(x)dx≤
A(λ) +λ1
2 Ω
u2λ,μ(x)dx.
SinceA(λ)→0 asλ→0, this relation leads to a contradiction forλ,μ> 0 sufficiently
small. The proof of Theorem1.1is now complete.
Proof of Theorem 1.2 Suppose to the contrary that existλandμ such that (1.1) has a solutionuλ,μ∈D, and by Lemma2.6the boundary value problem
⎧ ⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎩
–V(x) =a( 1
Ω|∇uλ,μ|2dx)(λf(x,V) +μh(x)) inΩ,
V> 0 inΩ,
V= 0 on∂Ω
(3.16)
Set
Ψλ,μ(x,s) =
1 a(Ω|∇uλ,μ|2dx)
λf(x,s) +μh(x).
Since
Vλ,μ+Ψλ,μ(x,Vλ,μ)≤0≤ uλ,μ+Ψλ,μ(x,uλ,μ) inΩ,
by Lemma2.5we getuλ,μ≤Vλ,μinΩ.
Consider the perturbed problem ⎧
⎪ ⎪ ⎪ ⎨ ⎪ ⎪ ⎪ ⎩
–u+K∗g(u+) =a( 1
Ω|∇uλ,μ|2dx)(λf(x,u) +μh(x)) inΩ,
u> 0 inΩ,
u= 0 on∂Ω.
(3.17)
SinceK∗> 0, it follows thatuλ,μandVλ,μare subsolution and supersolution for (3.17),
respectively. Then there exists a solutionu∈C2,γ(Ω) of (3.17) such that
uλ,μ≤u≤Vλ,μ.
Integrating in (3.17), we deduce
–
Ω
udx+K∗
Ω
g(u+)dx=
1 a(Ω|∇uλ,μ|2dx)
Ω
λf(x,u) +μh(x)
dx.
Hence
–
∂Ω ∂u
∂n +K∗
Ω
g(u+)dx≤M, (3.18)
whereM> 0 is a constant. Since∂u
∂n ≤0 on∂Ω, relation (3.18) yieldsK∗
Ωg(u+)dx≤
M, and soK∗Ωg(Vλ,μ+)dx≤M. Thus, for any compact subsetω⊂Ω, we have
K∗
ω
g(Vλ,μ+)dx≤M.
Letting→0, this relation leads toK∗ωg(Vλ,μ)dx≤M. Therefore
K∗
Ω
g(Vλ,μ)dx≤M. (3.19)
Chooseδ> 0 sufficiently small and defineΩδ :={x∈Ω;dist(x,∂Ω)≤δ}. Taking into
ac-count the regularity of the domain, we get that there existsk> 0 such that
Vλ,μ≤kdist(x,∂Ω) for allx∈Ωδ.
Then
Ω
g(Vλ,μ)dx≥
Ωδ
g(Vλ,μ)dx≥
Ωδ
which contradicts (3.19). It follows that problem (1.1) has no solution inD, and the proof
of Theorem1.2is now complete.
Acknowledgements
The authors thank the referees for their comments.
Funding
This work is supported by the National Natural Science Foundation of China (61603226) and the Fund of Natural Science of Shandong Province (ZR2018MA022).
Availability of data and materials Not applicable.
Competing interests
The authors declare that they have no competing interests.
Authors’ contributions
Both authors contributed equally to the writing of this paper. Both authors read and approved the final manuscript.
Authors’ information Not applicable.
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Received: 6 November 2018 Accepted: 11 February 2019 References
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