This investigation communicates with an initial value problem (IVP) of Hilfer-generalized proportional fractional (GPF) differential equations in the fuzzy framework is deliberated. By means of the Hilfer-GPF operator, we employ the methodology of successive approximation under the generalized Lipschitz condition. Based on the proposed derivative, the fractional Volterra-Fredholm integrodifferential equations (FVFIEs) via generalized fuzzy Hilfer-GPF Hukuhara differentiability (HD) having fuzzy initial conditions are investigated. Moreover, the existence of the solution is proposed by employing the fixed-point formulation. The uniqueness of the solution is verified. Furthermore, we derived the equivalent form of fuzzy FVFIEs which is supposed to demonstrate the convergence of this group of equations. Two appropriate examples are presented for illustrative purposes.
Citation: Saima Rashid, Fahd Jarad, Khadijah M. Abualnaja. On fuzzy Volterra-Fredholm integrodifferential equation associated with Hilfer-generalized proportional fractional derivative[J]. AIMS Mathematics, 2021, 6(10): 10920-10946. doi: 10.3934/math.2021635
[1] | Yang Liu . Long-time behavior of a class of viscoelastic plate equations. Electronic Research Archive, 2020, 28(1): 311-326. doi: 10.3934/era.2020018 |
[2] | Mohammad M. Al-Gharabli, Adel M. Al-Mahdi . Existence and stability results of a plate equation with nonlinear damping and source term. Electronic Research Archive, 2022, 30(11): 4038-4065. doi: 10.3934/era.2022205 |
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[4] | Mingqi Xiang, Binlin Zhang, Die Hu . Kirchhoff-type differential inclusion problems involving the fractional Laplacian and strong damping. Electronic Research Archive, 2020, 28(2): 651-669. doi: 10.3934/era.2020034 |
[5] | Lingzheng Kong, Haibo Chen . Normalized solutions for nonlinear Kirchhoff type equations in high dimensions. Electronic Research Archive, 2022, 30(4): 1282-1295. doi: 10.3934/era.2022067 |
[6] | Jinheng Liu, Kemei Zhang, Xue-Jun Xie . The existence of solutions of Hadamard fractional differential equations with integral and discrete boundary conditions on infinite interval. Electronic Research Archive, 2024, 32(4): 2286-2309. doi: 10.3934/era.2024104 |
[7] | Wei Shi, Xinguang Yang, Xingjie Yan . Determination of the 3D Navier-Stokes equations with damping. Electronic Research Archive, 2022, 30(10): 3872-3886. doi: 10.3934/era.2022197 |
[8] | Fei Jiang . Stabilizing effect of elasticity on the motion of viscoelastic/elastic fluids. Electronic Research Archive, 2021, 29(6): 4051-4074. doi: 10.3934/era.2021071 |
[9] | Xu Liu, Jun Zhou . Initial-boundary value problem for a fourth-order plate equation with Hardy-Hénon potential and polynomial nonlinearity. Electronic Research Archive, 2020, 28(2): 599-625. doi: 10.3934/era.2020032 |
[10] | Xiaoxia Wang, Jinping Jiang . The uniform asymptotic behavior of solutions for 2D g-Navier-Stokes equations with nonlinear dampness and its dimensions. Electronic Research Archive, 2023, 31(7): 3963-3979. doi: 10.3934/era.2023201 |
This investigation communicates with an initial value problem (IVP) of Hilfer-generalized proportional fractional (GPF) differential equations in the fuzzy framework is deliberated. By means of the Hilfer-GPF operator, we employ the methodology of successive approximation under the generalized Lipschitz condition. Based on the proposed derivative, the fractional Volterra-Fredholm integrodifferential equations (FVFIEs) via generalized fuzzy Hilfer-GPF Hukuhara differentiability (HD) having fuzzy initial conditions are investigated. Moreover, the existence of the solution is proposed by employing the fixed-point formulation. The uniqueness of the solution is verified. Furthermore, we derived the equivalent form of fuzzy FVFIEs which is supposed to demonstrate the convergence of this group of equations. Two appropriate examples are presented for illustrative purposes.
A coupled system of two Kirchhoff plate equations is considered:
{|yt|ρytt−Δytt+Δ2y−∫t0h1(t−s)Δ2y(s)ds+f1(y,z)=0inΩ×(0,∞),|zt|ρztt−Δztt+Δ2z−∫t0h2(t−s)Δ2z(s)ds+f2(y,z)=0inΩ×(0,∞),y=∂νy=z=∂νz=0onΓ0×(0,∞),B1y−∫t0h1(t−s)B1y(s)ds=B1z−∫t0h2(t−s)B1z(s)ds=0onΓ1×(0,∞),B2y−∂νytt−∫t0h1(t−s)B2y(s)ds=0onΓ1×(0,∞),B2z−∂νztt−∫t0h2(t−s)B2z(s)ds=0onΓ1×(0,∞),y(x,0)=y0(x), yt(x,0)=y1(x), z(x,0)=z0(x), zt(x,0)=z1(x)inΩ, | (1.1) |
where Ω is a bounded domain of R2 with a smooth boundary Γ=∂Ω=Γ0∪Γ1, such that ¯Γ0∩¯Γ1=∅, the initial data y0, y1, z0 and z1 lie in appropriate Hilbert space.
The symbols yt and ytt refer, respectively, to first order and second order derivatives (with respect to t) of y, while Δ and Δ2 are the Laplacian and Bilaplacian operators. The functions hi and fi (for i=1,2) verify some assumptions that will be given in the next section. ρ is a positive constant, x=(x1,x2) is the space variable, and the operators B1 and B2 are defined by
B1y=Δy+(1−μ)(2ν1ν2yx1x2−ν21yx2x2−ν22yx1x1), |
and
B2y=∂νΔy+(1−μ)∂τ((ν21−ν22)yx1x2+ν1ν2(yx2x2−yx1x1)), |
where the constant 0<μ<12 is the Poisson coefficient. Here, ∂ν stands for normal derivative, ν=(ν1,ν2) is the unit outer normal vector to Γ and τ=(−ν2,ν1) is a unit tangent vector.
Model (1.1) describes the interaction of two viscoelastic Kirchhoff plates with rotational forces, which possess a rigid surface and whose interiors are somehow permissive to slight deformations, such that the material densities vary according to the velocity [1]. Each one of these two plates is clamped along Γ0, and without bending and twisting moments on Γ1. The analysis of stability issues for plate models is more challenging due to free boundary conditions and the presence of rotational forces, etc. [2]. Moreover, in our case the source term competes with the dissipation induced by the viscoelastic term only. Therefore, it will be interesting to study this interaction [3].
We start off by reviewing some works related to quasi-linear wave equation and plate equation. Cavalcanti et al. [1] considered the following equation
|ut|ρutt−Δu−Δutt+∫t0g(t−s)Δu(s)ds−γΔut=0, | (1.2) |
and proved the global existence of weak solutions and a uniform decay rates of the energy in the presence of a strong damping, of the form −γΔut acting in the domain and assuming that the relaxation function decays exponentially. Messaoudi and Tatar [3] studied (1.2) but without a strong damping (γ=0). They showed that the memory term is enough to stabilize the solution. The global existence and uniform decay for solutions of (1.2), provided that the initial data are in some stable set, are obtained in [4] with the presence of a source term and with γ=0. Later, in [5], for γ=0, the authors investigated the general decay result of the energy of (1.2) with nonlinear damping. In [6], the author investigated (1.2) with weakly nonlinear time-dependent dissipation and source terms, and he established an explicit and general energy decay rate results without imposing any restrictive growth assumption on the damping term at the origin. For other related results for quasi-linear wave equations, we refer the reader to [7,8,9,10]. For quasi-linear plate equations, we mention the work of Al-Gharabli et al. [11] where the authors studied the well-posedness and asymptotic stability for a quasi-linear viscoelastic plate equation with a logarithmic nonlinearity. Recently, Al-Mahdi [12] studied the same problem as in Al-Gharabli et al. [11], but with infinite memory. With the imposition of a minimal condition on the relaxation function, he obtained an explicit and general decay rate result for the energy. Very recently, in [13], the authors considered a plate equation with infinite memory, nonlinear damping, and logarithmic source. They proved explicit and general decay rate of the solution.
The stability of coupled quasi-linear systems has been discussed by many authors. Liu [14] considered two coupled quasi-linear viscoelastic wave equations. He showed that the viscoelastic terms' dissipations guarantee that the solutions decay exponentially and polynomially. Later on, with more general relaxation functions and specific initial data, He [15] extended the result of Liu [14]. Recently, Mustafa and Kafini [16] considered the same problem and improved earlier results for a wider class of relaxation functions. In [17], the authors studied the same problem, but with nonlinear damping, and showed a general decay rate estimates of energy of solutions. Very recently, Pişkin and Ekinci [18] generalized and improved earlier results by considering a degenerate damping. Finally, let's mention the recent works of Fang et al.[19] and Zhu et al.[20] that relate to our problem.
As I know, there is no work regarding quasi-linear plate equations. This paper seems to be the first that deals with this problem.
The structure of this paper is shown as follows: In Section 2, we present some presumptions that are necessary for the proof of essential results. The third section provides the proof of well-posedness of our system. The general energy decay result is stated and established in Section 4. The fifth section provides two examples that illustrate explicit formulas for the energy decay rates. A concluding section is given at the end.
This part is devoted to give some necessary materials and assumptions for the proof of our key results. We define
V={y∈H2(Ω):y=∂νy=0 on Γ0}, |
and
W={y∈H1(Ω):y=0 on Γ0}. |
Denoting dx=dx1dx2, we define the bilinear form b:V×V→R by:
b(y,z)=∫Ω {yx1x1zx1x1+yx2x2zx2x2+2(1−μ)yx1x2zx1x2+μ(yx1x1zx2x2+yx2x2zx1x1)}dx. |
Firstly, we must recall Green's formula (see [2]):
b(y,z)=∫ΩΔ2yzdx+∫Γ(B1y∂νz−B2yz)dΓ, ∀y∈H4(Ω),z∈H2(Ω), | (2.1) |
and a weaker version of it (see Theorem 5.6 in [21]) in the following form:
b(y,z)=∫ΩΔ2yzdx+⟨B1y,∂νz⟩H−12(Γ),H12(Γ)−⟨B2y,z⟩H−32(Γ),H32(Γ), ∀z∈H2(Ω). | (2.2) |
We need the following lemma.
Lemma 2.1. ([22]) For any y∈C1(0,T;H2(Ω)), we get
b(∫t0h1(t−s)y(s)ds,yt)=−12h1(t)b(y,y)−12ddt{(h1◻y)(t)−(∫t0h1(s)ds)b(y,y)}+12(h′1◻y)(t), | (2.3) |
where
(h1◻y)(t)=∫t0h1(t−s)b(y(t)−y(s),y(t)−y(s))ds. |
In this paper, we suppose that:
(A1): The two non-increasing C1 functions hi:[0,+∞)→(0,+∞) (for i=1,2) such that
1−∫∞0hi(s)ds=li>0. | (2.4) |
(A2): There are a positive C1 functions Gi:(0,+∞)→(0,+∞), that are linear or strictly increasing and strictly convex C2 on (0,r],(r<1), with Gi(0)=G′i(0)=0, satisfying for all t≥0
h′i(t)≤−ξi(t)Gi(hi(t)),fori=1,2, | (2.5) |
where ξ1 and ξ2 are positive non-increasing differentiable functions.
(A3): fi:R2→R (for i=1,2) are C1 functions and there exists a positive function F, such that
f1(x1,x2)=∂F∂x1,f2(x1,x2)=∂F∂x2,x1f1(x1,x2)+x2f2(x1,x2)−F(x1,x2)≥0, |
and
|∂fi∂x1(x1,x2)|+|∂fi∂x2(x1,x2)|≤d(1+|x1|βi1−1+|x2|βi2−1),∀(x1,x2)∈R2, | (2.6) |
for some constant d>0 and βij≥1 for i,j=1,2.
Remark 2.1. 1.The condition (A1) guarantees the hyperbolicity of the first two equations in the system (1.1).
2. By (2.6) and the mean value theorem, we have for some positive constant d1
|fi(x1,x2)|≤d1(|x1|+|x2|+|x1|βi1+|x2|βi2), | (2.7) |
and
|fi(x1,x2)−fi(u1,u2)|≤d1(1+|x1|βi1+|x2|βi2+|u1|βi1+|u2|βi2)(|x1−u1|+|x2−u2|), | (2.8) |
for all (x1,x2),(u1,u2)∈R2 and i=1,2.
The energy functional is defined by
E(t)=1ρ+2∫Ω|yt|ρ+2dx+12‖∇yt‖2⏟Ky(t)+12(1−∫t0h1(s)ds)b(y,y)+12(h1◻y)(t)⏟Py(t)+1ρ+2∫Ω|zt|ρ+2dx+12‖∇zt‖2⏟Kz(t)+12(1−∫t0h2(s)ds)b(z,z)+12(h2◻z)(t)⏟Pz(t)+∫ΩF(y,z)dx. | (2.9) |
Here,
K(t)=Ky(t)+Kz(t)andP(t)=Py(t)+Pz(t)+∫ΩF(y,z)dx |
represent, respectively, the kinetic and the elastic potential energy of the model.
We have the following dissipation identity:
Proposition 2.1.
E′(t)=12(h′1◻y)(t)−12h1(t)b(y,y)+12(h′2◻z)(t)−12h2(t)b(z,z)≤0. | (2.10) |
Proof. Multiplying (1.1)1 by yt and (1.1)2 by zt, summing the resultant equations and integrating over Ω to get
ddt{1ρ+2∫Ω|yt|ρ+2dx+12‖∇yt‖2+12b(y,y)+1ρ+2∫Ω|zt|ρ+2dx+12‖∇zt‖2+12b(z,z)+∫ΩF(y,z)dx}−∫t0h1(t−s)b(y(s),yt)ds−∫t0h2(t−s)b(z(s),zt)ds=0. | (2.11) |
Inserting (2.3) in (2.11), we get the desired result.
Throughout this paper, c denotes a generic positive constant, and not necessarily the same at different occurrences.
We begin this part by defining a weak solution of the system (1.1).
Definition 3.1. A couple of functions (y,z) defined on [0,T] is a weak solution of the problem (1.1) if y∈C([0,T],V)∩C1([0,T],W),z∈C([0,T],V)∩C1([0,T],W), and satisfies
∫Ω|yt|ρyttudx+∫Ω∇ytt∇udx+b(y,u)−∫t0h1(t−s)b(y(s),u)ds+∫Ωf1(y,z)udx=0,y(x,0)=y0(x),yt(x,0)=y1(x), |
and
∫Ω|zt|ρzttvdx+∫Ω∇ztt∇vdx+b(z,v)−∫t0h2(t−s)b(z(s),v)ds+∫Ωf2(y,z)vdx=0,z(x,0)=z0(x),zt(x,0)=z1(x), |
for a.e. t∈[0,T] and all test functions u,v∈V.
Theorem 3.1. Let (y0,y1),(z0,z1)∈V×W. Assume that assumptions (A1)–(A3) are true. Then, the system (1.1) has at least a local weak solution. Moreover, this solution is global and bounded.
Proof. With the help of the Faedo-Galerkin approach, the existence is demonstrated. In order to achieve this, let {wj}∞j=1 be a basis of V. Define Em=span{w1,w2,...,wm}. On the finite dimensional subspaces Em, the initial data are projected as follows:
ym0(x)=m∑k=1akwk,ym1(x)=m∑k=1bkwk,zm0(x)=m∑k=1ckwk,zm1(x)=m∑k=1dkwk, |
such that
(ym0,zm0)→(y0,z0)inV2,and(ym1,z1m)→(y1,z1)inW2. | (3.1) |
Considering the following solution
ym(x,t)=m∑k=1pk(t)wk(x),zm(x,t)=m∑k=1qk(t)wk(x), |
which satisfies the following approximate problem in Em:
∫Ω|ymt|ρymttwdx+∫Ω∇ymtt∇wdx+b(ym,w)−∫t0h1(t−s)b(ym(s),w)ds+∫Ωf1(ym,zm)wdx=0,∫Ω|zmt|ρzmttwdx+∫Ω∇zmtt∇wdx+b(zm,w)−∫t0h2(t−s)b(zm(s),w)ds+∫Ωf2(ym,zm)wdx=0,ym(0)=ym0,ymt(0)=ym1,zm(0)=zm0,zmt(0)=zm1. | (3.2) |
This leads to a system of ordinary differential equations (ODEs) for unknown functions pk and qk. Hence, from the standard theory of system of ODEs, a solution (ym,zm) of (3.2) exists, for all m≥1, on [0,tm), with 0<tm≤T,∀m≥1.
A priori estimate 1: Let w=ymt in (3.2)1 and w=zmt in (3.2)2. Combining the resultant equations and integrating on Ω to obtain
ddtEm(t)=12{(h1′◻ym)(t)−h1(t)b(ym,ym)+(h2′◻zm)(t)−h2(t)b(zm,zm)}, | (3.3) |
where
Em(t)=1ρ+2∫Ω|ymt|ρ+2dx+12(1−∫t0h1(s)ds)b(ym,ym)+12‖∇ymt‖2+12(h1◻ym)(t)+1ρ+2∫Ω|zmt|ρ+2dx+12(1−∫t0h2(s)ds)b(zm,zm)+12‖∇zmt‖2+12(h2◻zm)(t)+∫ΩF(ym,zm)dx. |
Noting, by (3.1), that
‖(ym0,z0m)‖V2,‖(ym1,zm1)‖W2≤c. |
Then, by integrating (3.3) over (0,t),0<t<tm, we get a constant M1>0 that doesn't depend on t and m, satisfying
Em(t)≤Em(0)≤M1. | (3.4) |
Hence, tm can be replaced by some T>0, for all m≥1.
A priori estimate 2: Let w=ymtt in (3.2)1 and w=zmtt in (3.2)2, adding the resultant equations, integrating on Ω, and using Young's inequality to obtain for all η>0
∫Ω|ymt|ρ|ymtt|2dx+∫Ω|zmt|ρ|zmtt|2dx+∫Ω|∇ymtt|2dx+∫Ω|∇zmtt|2dx=−b(ym,ymtt)+∫t0h1(t−s)b(ym(s),ymtt)ds−b(zm,zmtt)+∫t0h2(t−s)b(zm(s),zmtt)ds−∫Ωf1(ym,zm)ymttdx−∫Ωf2(ym,zm)zmttdx≤2η(b(ymtt,ymtt)+b(zmtt,zmtt))+14η(b(ym,ym)+b(zm,zm))+(1−l1)h1(0)+(1−l2)h2(0)4η∫t0(b(ym(s),ym(s))+b(zm(s),zm(s)))ds−∫Ωf1(ym,zm)ymttdx−∫Ωf2(ym,zm)zmttdx. | (3.5) |
Using Hölder's inequality, Sobolev's embedding, (2.7) and (3.4), one has for some M2>0,
|∫Ωf1(ym,zm)ymttdx|≤d∫Ω(|ym|+|zm|+|ym|β11+|zm|β12)|ymtt|dx≤c(‖ym‖2+‖ym‖2+‖ym‖β112β11+‖zm‖β122β12)‖ymtt‖2≤c({b(ym,ym)}12+{b(zm,zm)}12+{b(ym,ym)}β112+{b(zm,zm)}β122){b(ymtt,ymtt)}12≤M2{b(ymtt,ymtt)}12. | (3.6) |
Similarly, we obtain that
|∫Ωf2(ym,zm)zmttdx|≤M2{b(zmtt,zmtt)}12. | (3.7) |
From (3.5)–(3.7), we infer that
∫Ω|ymt|ρ|ymtt|2dx+∫Ω|zmt|ρ|zmtt|2dx+(∫Ω|∇ymtt|2dx−2ηb(ymtt,ymtt))+(∫Ω|∇zmtt|2dx−2ηb(zmtt,zmtt))≤14η(b(ym,ym)+a(zm,zm))+M2({b(ymtt,ymtt)}12+{b(zmtt,zmtt)}12)+(1−l1)h1(0)+(1−l2)h2(0)4η∫t0(b(ym(s),ym(s))+b(zm(s),zm(s)))ds. | (3.8) |
Integrating (3.8) on (0,T), and using (3.4) gives us
∫T0∫Ω|ymt|ρ|ymtt|2dxdt+∫T0∫Ω|zmt|ρ|zmtt|2dxdt+∫T0(∫Ω|∇ymtt|2dx−3ηb(ymtt,ymtt))dt+∫T0(∫Ω|∇zmtt|2dx−3ηb(zmtt,zmtt))dt≤T4η{M1(1+T[(1−l1)h1(0)+(1−l2)h2(0)])+M22}. | (3.9) |
Choosing η small enough, such that
12‖∇u‖22−3ηb(u,u)>0,∀u∈V, |
and so that
‖∇u‖22−3ηb(u,u)>12‖∇u‖22,∀u∈V. |
Consequently, (3.9) becomes
∫T0∫Ω|ymt|ρ|ymtt|2dxdt+∫T0∫Ω|zmt|ρ|zmtt|2dxdt+12∫T0∫Ω(|∇ymtt|2+|∇zmtt|2)dxdt≤T4η{M1(1+T[(1−l1)h1(0)+(1−l2)h2(0)])+M22}. |
Then, we have
∫T0∫Ω(|∇ymtt|2+|∇zmtt|2)dxdt≤M3, | (3.10) |
for some constant M3>0.
From (3.4) and (3.10), we conclude that
ym,zm are uniformly bounded inL∞(0,T;V), | (3.11) |
ymt,zmt are uniformly bounded inL∞(0,T;W), | (3.12) |
and
ymtt,zmtt are uniformly bounded inL2(0,T;W). | (3.13) |
Hence, we can extract subsequence of (ym) and (zm), still denoted by (ym) and (zm) respectively, such that
ym∗⇀y,zm∗⇀z in L∞(0,T;V)and ym⇀y,zm⇀zinL2(0,T;V), | (3.14) |
ymt∗⇀yt,zmt∗⇀ztinL∞(0,T;W) and ymt⇀yt,zmt⇀ztinL2(0,T;W), | (3.15) |
and
ymtt⇀ytt,zmtt⇀ztt weakly inL2(0,T;W). | (3.16) |
Analysis of the non-linear terms:
1. Term fi(ym,zm): We have that (ym) and (zm) are bounded in L∞(0,T;V). This shows, by the use of the embedding of V⊂L∞(Ω)(Ω⊂R2), the boundedness of (ym) and (zm) in L2(Ω×(0,T)). Likewise, (ymt) and (zmt) are bounded in L2(Ω×(0,T)). Hence, by the use of the Aubin-Lions Theorem, we get, up to a subsequence, that
ym→yandzm→zstrongly inL2(Ω×(0,T)). |
Then,
ym→yandzm→za.e inΩ×(0,T), |
and, therefore, from (A3),
fi(ym,zm)→fi(y,z)a.e inΩ×(0,T),fori=1,2. | (3.17) |
On the other hand, we have (ym) and (zm) that are bounded in L∞(0,T;L2(Ω)), then, by using (2.7) and (3.4), we get that fi(ym,zm) is bounded in L∞(0,T;L2(Ω)). This fact and (3.17) leads to
fi(ym,zm)⇀fi(y,z)inL2(0,T;L2(Ω)),fori=1,2. |
2. Terms |ymt|ρymt and |zmt|ρzmt: We recall that (ymt) and (zmt) are bounded in L∞(0,T;W), which gives that (ymt) and (zmt) are bounded in L∞(Ω×(0,T)), and so in L2(Ω×(0,T)). By the same, we deduce that (ymtt) and (zmtt) are bounded in L2(Ω×(0,T)). Now, using Aubin-Lions theorem, we conclude, up to a subsequence, that
ymt→ytandzmt→ztstrongly inL2(Ω×(0,T)), |
and
|ymt|ρymt→|yt|ρytand|zmt|ρzmt→|zt|ρzta.e inΩ×(0,T). | (3.18) |
Using (3.4), we see that
‖|ymt|ρymt‖2L2(0,T;L2(Ω))≤C2(ρ+1)∗∫T0‖∇ymt‖2(ρ+1)2dt≤C2(ρ+1)∗Mρ+11T, | (3.19) |
and similarly
‖|zmt|ρzmt‖2L2(0,T;L2(Ω))≤C2(ρ+1)∗Mρ+11T, | (3.20) |
where C∗ is a positive constant satisfying ‖u‖2≤C∗‖∇u‖2, for all u∈W.
Then, the sequences (|ymt|ρymt) and (|zmt|ρzmt) are bounded in L2(Ω×(0,T)). Combining (3.18), (3.19) and (3.20) and using Lion's lemma [23], one derives
|ymt|ρymt⇀|yt|ρytand|zmt|ρzmt⇀|zt|ρztinL2(0,T;L2(Ω)). | (3.21) |
Next, by integrating (3.2) on (0,t), one obtains
1ρ+1∫Ω|ymt|ρymtwdx+∫Ω∇ymt∇wdx+∫t0b(ym,w)ds−∫t0∫s0h1(s−ζ)b(ym(ζ),w)dζds+∫t0∫Ωf1(ym,zm)wdxds=1ρ+1∫Ω|ym1|ρym1wdx+∫Ω∇ym1∇wdx,1ρ+1∫Ω|zmt|ρzmtwdx+∫Ω∇zmt∇wdx+∫t0b(zm,w)ds−∫t0∫s0h2(s−ζ)b(zm(ζ),w)dζds+∫t0∫Ωf2(ym,zm)wdxds=1ρ+1∫Ω|zm1|ρzm1wdx+∫Ω∇zm1∇wdx. | (3.22) |
Letting m→+∞, the aforementioned convergence results give that
1ρ+1∫Ω|yt|ρytwdx+∫Ω∇yt∇wdx−1ρ+1∫Ω|y1|ρy1wdx−∫Ω∇y1∇wdx=−∫t0b(y,w)ds+∫t0∫s0h1(s−ζ)b(y(ζ),w)dζds−∫t0∫Ωf1(y,z)wdxds,1ρ+1∫Ω|zt|ρztwdx+∫Ω∇zt∇wdx−1ρ+1∫Ω|z1|ρz1wdx−∫Ω∇z1∇wdx=−∫t0b(z,w)ds+∫t0∫s0h2(s−ζ)b(z(ζ),w)dζds−∫t0∫Ωf2(y,z)wdxds, | (3.23) |
for all w∈V.
Since the terms in the right hand side of (3.23)1 and (3.23)2 are absolutely continuous, then (3.23) is differentiable for a.e. t≥0, and, therefore, one has for all w∈V
∫Ω|yt|ρyttwdx+b(y,w)+∫Ω∇ytt∇wdx−∫t0h1(t−s)b(y(s),w)ds+∫Ωf1(y,z)wdx=0,∫Ω|zt|ρzttwdx+b(z,w)+∫Ω∇ztt∇wdx−∫t0h2(t−s)b(z(s),w)ds+∫Ωf2(y,z)wdx=0. |
Regarding the initial conditions, we recall that
{ym⇀y,zm⇀z inL2(0,T;V)ymt⇀yt,zmt⇀zt inL2(0,T;W). | (3.24) |
Consequently, the use of Lion's Lemma [23] leads to
ym→y,zm→zinC([0,T),L2(Ω)). | (3.25) |
Hence, ym(x,0) and zm(x,0) make sense and ym(x,0)→y(x,0), zm(x,0)→z(x,0) in L2(Ω). Recalling that
ym(x,0)=ym0(x)→y0(x),zm(x,0)=zm0(x)→z0(x)inV, |
we obtain that
y(x,0)=y0(x)andz(x,0)=z0(x). | (3.26) |
Besides, multiplying (3.2) by ϕ∈C∞0(0,T) [24] and integrating on (0,T), to get
−1ρ+1∫T0(|ymt|ρymt,w)L2(Ω)ϕ′(t)dt=−∫T0∫Ω∇ymtt∇wϕ(t)dxdt−∫T0b(ym,w)ϕ(t)dt+∫T0∫t0h1(t−s)b(ym(s),w)ϕ(t)dsdt−∫T0∫Ωf1(ym,zm)wϕ(t)dxdt, |
and
−1ρ+1∫T0(|zmt|ρzmt,w)L2(Ω)ϕ′(t)dt=−∫T0∫Ω∇zmtt∇wϕ(t)dxdt−∫T0b(zm,w)ϕ(t)dt+∫T0∫t0h2(t−s)b(zm(s),w)ϕ(t)dsdt−∫T0∫Ωf2(ym,zm)wϕ(t)dxdt. |
As m→+∞, we have for any w∈V and any ϕ∈C∞0(0,T)
−1ρ+1∫T0(|yt|ρyt,w)L2(Ω)ϕ′(t)dt=−∫T0∫Ω∇ytt∇wϕ(t)dxdt−∫T0b(y,w)ϕ(t)dt+∫T0∫t0h1(t−s)b(y(s),w)ϕ(t)dsdt−∫T0∫Ωf1(y,z)wϕ(t)dxdt, |
and
−1ρ+1∫T0(|zt|ρzt,w)L2(Ω)ϕ′(t)dt=−∫T0∫Ω∇ztt∇wϕ(t)dxdt−∫T0b(z,w)ϕ(t)dt+∫T0∫t0h2(t−s)b(z(s),w)ϕ(t)dsdt−∫T0∫Ωf2(y,z)wϕ(t)dxdt. |
This means that (see [24])
yttandztt∈L2(0,T;V). |
Since yt and zt∈L2(0,T;L2(Ω)), we deduce that yt and zt∈C(0,T;V).
So, ymt(x,0) and zmt(x,0) make sense and
ymt(x,0)→yt(x,0),zmt(x,0)→zt(x,0)inV. |
But
ymt(x,0)=ym1(x)→y1(x),zmt(x,0)=zm1(x)→z1(x)inW. |
Hence,
yt(x,0)=y1(x)andzt(x,0)=z1(x). |
Consequently, the proof of local existence of weak solutions is complete. Besides, it is easy to see that
l1b(y,y)+‖∇yt‖2+l2b(z,z)+‖∇zt‖2≤2E(t)≤2E(0), | (3.27) |
which gives the globalness and boundedness of the solution of problem (1.1).
We denote by ξ(t)=min{ξ1(t),ξ2(t)},h(t)=max{h1(t),h2(t)} and G(t)=min{G1(t),G2(t)}.
Theorem 4.1. Let (u0,u1),(v0,v1)∈V×W. Suppose that (A1)–(A3) hold. Thus, the energy E(t) satisfies
E(t)≤β2G−10(β1∫th−1(r)ξ(s)ds),∀t>h−1(r),withG0(t)=∫rt1sG′(s)ds, | (4.1) |
for some positive constants β1 and β2.
Remark 4.1. ([16])
1. We recall the Jensen's inequality: Assume F is a concave function on [a,b],f:Ω→[a,b] and g are in L1(Ω), with g(x)≥0 and ∫Ωg(x)dx=m>0, then
1m∫ΩF[f(x)]g(x)dx≤F[1m∫Ωf(x)g(x)dx]. |
2. From (A2), one has limt→+∞hi(t)=0. Hence, ∃t1≥0 is large enough, verifying
hi(t1)=r⇒hi(t)≤r, ∀ t≥t1. | (4.2) |
One can easily check, for i=1,2, that
ai≤ξi(t)Gi(hi(t))≤bi, |
for some constants ai>0 and bi>0. This implies that
h′i(t)≤−ξi(t)Gi(hi(t))≤−aihi(0)hi(0)≤−aihi(0)hi(t), ∀t∈[0,t1]. | (4.3) |
Proof of Theorem (4.1): The proof is divided into three steps.
Step 1: In this step, we give estimates for the derivatives (with respect to t) of the functionals φ(t) and ψ(t) defined below by:
φ(t)=φ1(t)+φ2(t), | (4.4) |
with
φ1(t)=1ρ+1∫Ωy|yt|ρytdx+∫Ω∇yt∇ydx, |
φ2(t)=1ρ+1∫Ωz|zt|ρztdx+∫Ω∇zt∇zdx, |
and
ψ(t)=ψ1(t)+ψ2(t), | (4.5) |
with
ψ1(t)=−1ρ+1∫Ω|yt|ρyt∫t0h1(t−s)(y(t)−y(s))dsdx−∫Ω∇yt∫t0h1(t−s)∇(y(t)−y(s))dsdx, | (4.6) |
ψ2(t)=−1ρ+1∫Ω|zt|ρzt∫t0h2(t−s)(z(t)−z(s))dsdx−∫Ω∇zt∫t0h2(t−s)∇(z(t)−z(s))dsdx. |
Lemma 4.1. If (A1)–(A3) hold. The functional φ(t) defined in (4.4) verifies, along the solution of (1.1),
φ′(t)≤−l12b(y,y)+∫Ω|∇yt|2dx+1ρ+1∫Ω|yt|ρ+2dx+c(h1◻y)(t)−l22b(z,z)+∫Ω|∇zt|2dx+1ρ+1∫Ω|zt|ρ+2dx+c(h2◻z)(t)−∫ΩF(y,z)dx. | (4.7) |
Proof. We have φ′(t)=φ′1(t)+φ′2(t). By using (1.1), we obtain
φ′1(t)=∫Ω|yt|ρyttydx+1ρ+1∫Ω|yt|ρ+2dx+∫Ω|∇yt|2dx+∫Ω∇y∇yttdx=−b(y,y)+∫t0h1(t−s)b(y(s),y(t))ds+∫Ω|∇yt|2dx+1ρ+1∫Ω|yt|ρ+2dx−∫Ωf1(y,z)ydx. | (4.8) |
Since ∫t0h1(s)ds≤∫+∞0h1(s)ds=1−l1, then, by the use of Cauchy-Schwarz's inequality and Young's inequality, we derive
∫t0h1(t−s)b(y(t),y(s))ds=∫t0h1(t−s)b(y(s)−y(t),y(t))ds+∫t0h1(t−s)b(y(t),y(t))ds≤∫t0h1(t−s){b(y(s)−y(t),y(s)−y(t))}12{b(y(t),y(t))}12ds+(∫t0h1(s)ds)b(y(t),y(t))≤l12b(y(t),y(t))+12l1(∫t0√h1(t−s){h1(t−s)b(y(s)−y(t),y(s)−y(t))}12ds)2+(1−l1)b(y(t),y(t))≤(1−l12)b(y(t),y(t))+c(h1◻y)(t). | (4.9) |
Inserting (4.9) in (4.8), we get that
φ′1(t)≤−l12b(y,y)+∫Ω|∇yt|2dx+1ρ+1∫Ω|yt|ρ+2dx+1−l12l1(h1◻y)(t)−∫Ωf1(y,z)ydx. |
Similarly, we infer that
φ′2(t)≤−l22b(z,z)+∫Ω|∇zt|2dx+1ρ+1∫Ω|zt|ρ+2dx+1−l22l2(h2◻z)(t)−∫Ωf2(y,z)zdx. |
Summing the last two inequalities, we get the desired inequality (4.7).
Lemma 4.2. If (A1)–(A3) hold. The functional defined in (4.6) verifies, for any 0<δ<1 and for all t≥t1, along the solution of (1.1),
ψ′1(t)≤−h0ρ+1∫Ω|yt|ρ+2dx−h02‖∇yt‖2+cδ(b(y,y)+b(z,z))+cδ(h1◻y)(t)−c(h′1◻y)(t). | (4.10) |
Here h0=min{∫t0h1(s)ds,∫t0h2(s)ds}.
Proof. Differentiating ψ1(t) with respect to t and using (1.1)1, we get
ψ′1(t)=−∫Ω|yt|ρytt∫t0h1(t−s)(y(t)−y(s))dsdx−1ρ+1∫Ω|yt|ρyt∫t0h′1(t−s)(y(t)−y(s))dsdx−1ρ+1(∫t0h1(s)ds)∫Ω|yt|ρ+2dx−∫Ω∇ytt∫t0h1(t−s)∇(y(t)−y(s))dsdx−∫Ω∇yt∫t0h′1(t−s)∇(y(t)−y(s))dsdx−(∫t0h1(s)ds)∫Ω|∇yt|2dx=∫t0h1(t−s)b(y,y(t)−y(s))ds−∫t0h1(t−ζ)∫t0h1(t−s)b(y(s),y(t)−y(ζ))dsdζ+∫Ωf1(y,z)∫t0h1(t−s)(y(t)−y(s))dsdx−1ρ+1∫Ω|yt|ρyt∫t0h′1(t−s)(y(t)−y(s))dsdx−1ρ+1(∫t0h1(s)ds)∫Ω|yt|ρ+2dx−∫Ω∇yt∫t0h′1(t−s)∇(y(t)−y(s))dsdx−(∫t0h1(s)ds)∫Ω|∇yt|2dx. | (4.11) |
Now, we estimate the terms in the right-hand side of (4.11) as follows:
∙ Estimation of the term ∫t0h1(t−s)b(y,y(t)−y(s))ds.
Cauchy Schwarz's inequality and Young's inequality are used to get, for any δ>0,
∫t0h1(t−s)b(y,y(t)−y(s))ds≤∫t0h1(t−s)[b(y(t),y(t))]12[b(y(t)−y(s),y(t)−y(s))]12ds≤δb(y,y)+14δ{∫t0h1(t−s)[b(y(t)−y(s),y(t)−y(s))]12ds}2≤δb(y,y)+cδ(h1◻y)(t). | (4.12) |
∙ Estimation of the term −∫t0h1(t−ζ)∫t0h1(t−s)b(y(s),y(t)−y(ζ))dsdζ.
We have
−∫t0h1(t−ζ)∫t0h1(t−s)b(y(s),y(t)−y(ζ))dsdζ≤∫t0h1(t−ζ)∫t0h1(t−s)b(y(s)−y(t),y(t)−y(ζ))dsdζ+∫t0h1(t−ζ)∫t0h1(t−s)b(y(t),y(t)−y(ζ))dsdζ≤∫t0h1(t−ζ)∫t0h1(t−s)[δb(y(t)−y(s),y(t)−y(s))+14δb(y(t)−y(ζ),y(t)−y(ζ))]dsdζ+(∫t0h1(ζ)dζ)∫t0h1(t−ζ)b(y,y(t)−y(ζ))dζ≤cδb(y,y)+c(δ+1δ)(h1◻y)(t). | (4.13) |
∙ Estimation of the term −∫Ω∇yt∫t0h′1(t−s)(y(t)−y(s))dsdx.
One has
−∫Ω∇yt∫t0h′1(t−s)(y(t)−y(s))dsdx≤δ1∫Ω|∇yt|2+14δ1∫Ω(∫t0h′1(t−s)(y(t)−y(s))ds)2dx≤δ1∫Ω|∇yt|2−h1(0)4δ1∫t0h′1(t−s)∫Ω|y(t)−y(s)|2dxds≤δ1∫Ω|∇yt|2−cδ1(h′1◻y)(t). | (4.14) |
∙ Estimation of the term ∫Ωf1(y,z)∫t0h1(t−s)(y(t)−y(s))dsdx.
By using (2.7) and (3.27), we derive that
∫Ωf1(y,z)∫t0h1(t−s)(y(t)−y(s))dsdx≤cδ∫Ω(|y|2+|z|2+|y|2β11+|z|2β12)dx+cδ∫Ω(∫t0h1(t−s)(y(t)−y(s))ds)2dx≤cδ(b(y,y)+b(z,z)+(b(y,y))β11+(b(z,z))β12)+cδ(h1◻y)(t)=cδ(b(y,y)+b(z,z)+b(y,y)(b(y,y))β11−1+b(z,z)(b(z,z))β12−1)+cδ(h1◻y)(t)≤cδ(b(y,y)+b(z,z)+b(y,y)(2E(0)l1)β11−1+b(z,z)(2E(0)l2)β12−1)+cδ(h1◻y)(t)≤cδ(b(y,y)+b(z,z))+cδ(h1◻y)(t). | (4.15) |
∙ Estimation of the term −1ρ+1∫Ω|yt|ρyt∫t0h′1(t−s)(y(t)−y(s))dsdx.
Using (3.27) again, we infer that
−1ρ+1∫Ω|yt|ρyt∫t0h′1(t−s)(y(t)−y(s))dsdx≤cδ1∫Ω|yt|2(ρ+1)dx−cδ1(h′1◻y)(t)≤cδ1‖∇yt‖2(ρ+1)−cδ1(h′1◻y)(t)≤cδ1(2E(0))ρ‖∇yt‖2−cδ1(h′1◻y)(t). | (4.16) |
By combining (4.12)–(4.16), using the fact that −(∫t0h1(s)ds)≤−h0 for all t≥t1 and choosing δ1 small enough, we derive the estimate (4.10).
Repeating the calculations above with ψ2(t) yields
ψ′2(t)≤−h0ρ+1∫Ω|zt|ρ+2dx−h02‖∇zt‖2+cδ(b(y,y)+b(z,z))+cδ(h2◻y)(t)−c(h′2◻z)(t). | (4.17) |
Combining (4.10) and (4.17), we obtain the following result.
Corollary 4.1. Assume that (A1)–(A3) hold. Then, the functional ψ satisfies, along the solution, the estimate
ψ′(t)≤−h0ρ+1∫Ω|yt|ρ+2dx−h02‖∇yt‖2+cδb(y,y)+cδ(h1◻y)(t)−c(h′1◻y)(t)−h0ρ+1∫Ω|zt|ρ+2dx−h02‖∇zt‖2+cδb(z,z)+cδ(h2◻z)(t)−c(h′2◻z)(t),∀t≥t1, | (4.18) |
for any 0<δ<1.
Step 2: The aim of this step is to establish the inequality (4.26).
Let's define the functional
F(t)=NE(t)+φ(t)+4h0ψ(t), | (4.19) |
where N>0. For N sufficiently large, one has that F∼E, i. e.
c1E(t)≤F(t)≤c2E(t), | (4.20) |
for some c1,c2>0.
Let l=min{l1,l2}. By using (2.10), (4.7), (4.18), and taking δ=lh016c, we get for any t≥t1
F′(t)≤−l4(b(y,y)+b(z,z))−3ρ+1∫Ω(|yt|ρ+2+|zt|ρ+2)dx−‖∇yt‖2−‖∇zt‖2−∫ΩF(y,z)dx+(c+64c2lh20)((h1◻y)(t)+(h2◻z)(t))+(N2−4ch0)((h′1◻y)(t)+(h′2◻z)(t)). |
Taking N, such that
N2−4ch0>0, |
to obtain that
F′(t)≤−l4(b(y,y)+b(z,z))−3ρ+1∫Ω(|yt|ρ+2+|zt|ρ+2)dx−‖∇yt‖2−‖∇zt‖2−∫ΩF(y,z)dx+c((h1◻y)(t)+(h2◻z)(t)),∀t≥t1. | (4.21) |
By the virtue of (2.10) and (4.3), we infer that for any t≥t1,
∫t10h1(s)b(y(t)−y(t−s),y(t)−y(t−s))ds≤−h1(0)a1∫t10h′1(s)b(y(t)−y(t−s),y(t)−y(t−s))ds≤−cE′(t), |
and similarly
∫t10h2(s)b(z(t)−z(t−s),z(t)−z(t−s))ds≤−cE′(t). |
Hence, (4.21) becomes
F′(t)≤−αE(t)+c(h1◻y)(t)+c(h2◻z)(t)≤−αE(t)−cE′(t)+c∫tt1h1(s)b(y(t)−y(t−s),y(t)−y(t−s))ds+c∫tt1h2(s)b(z(t)−z(t−s),z(t)−z(t−s))ds,∀t≥t1, | (4.22) |
where α>0. Define H(t)=F(t)+cE(t). It is easy to see that H(t)∼E(t). Using (4.22), we get
H′(t)≤−αE(t)+c∫tt1h1(s)b(y(t)−y(t−s),y(t)−y(t−s))ds+c∫tt1h2(s)b(z(t)−z(t−s),z(t)−z(t−s))ds. | (4.23) |
The following two situations are then distinguished.
First Case: G1(t) and G2(t) are linear.
By multiplying (4.23) by ξ(t) and using (A2) and (2.10) to obtain
ξ(t)H′(t)≤−αξ(t)E(t)+cξ(t)∫tt1h1(s)b(y(t)−y(t−s),y(t)−y(t−s))ds+cξ(t)∫tt1h2(s)b(z(t)−z(t−s),z(t)−z(t−s))ds≤−αξ(t)E(t)+c∫tt1ξ1(s)h1(s)b(y(t)−y(t−s),y(t)−y(t−s))ds+c∫tt1ξ2(s)h2(s)b(z(t)−z(t−s),z(t)−z(t−s))ds≤−αξ(t)E(t)−c∫tt1h′1(s)b(y(t)−y(t−s),y(t)−y(t−s))ds−c∫tt1h′2(s)b(z(t)−z(t−s),z(t)−z(t−s))ds≤−αξ(t)E(t)−cE′(t). | (4.24) |
Since ξ is non-increasing, then by using (4.24), the functional F(t)=ξ(t)H(t)+cE(t) satisfies for any t≥t1,
F′(t)≤−αξ(t)E(t). |
It is obvious that F∼E, and then we get the existence of some positive constant m1, such that
F′(t)≤−m1ξ(t)F(t). |
By applying Gronwall's Lemma, there exists a constant m2>0, such that
F(t)≤m2e−m1∫tt1ξ(s)ds, |
and then we have
E(t)≤m3e−m1∫tt1ξ(s)ds, |
where m3>0.
Second Case: G1(t) or G2(t) is nonlinear. Defining J1 and J2 by
J1(t)=λt∫t0b(y(t)−y(t−s),y(t)−y(t−s))ds,t>0, |
and
J2(t)=λt∫t0b(z(t)−z(t−s),z(t)−z(t−s))ds,t>0. |
Since b(y(t),y(t))+b(y(t−s),y(t−s))≤2l(E(t)+E(t−s))≤4lE(0), for all 0<s<t, we infer that
J1(t)≤8λlt∫t0E(0)ds=8λlE(0)<+∞, |
and similarly
J2(t)≤8λlE(0)<+∞. |
By taking 0<λ<1 sufficiently small, we get, for all t>0,
J1(t)<1andJ2(t)<1. | (4.25) |
Now, defining K1(t) and K2(t) by
K1(t)=−∫t0h′1(s)b(y(t)−y(t−s),y(t)−y(t−s))ds, |
and
K2(t)=−∫t0h′2(s)b(z(t)−z(t−s),z(t)−z(t−s))ds. |
One can easily check that Ki(t)≤−cE′(t), for i=1,2.
Given that G1(0)=0 and the strict convexity of G1 on (0,r], one has then G1(κx)≤κG1(x),∀0≤κ≤1 and x∈(0,r]. Now, using (A1), (4.25) and Jensen's inequality, we obtain
K1(t)=1λJ1(t)∫t0J1(t)(−h′1(s))λb(y(t)−y(t−s),y(t)−y(t−s))ds≥1λJ1(t)∫t0J1(t)ξ1(s)G1(h1(s))λb(y(t)−y(t−s),y(t)−y(t−s))ds≥ξ1(t)λJ1(t)∫t0G1(J1(t)h1(s))λb(y(t)−y(t−s),y(t)−y(t−s))ds≥ξ1(t)λG1(1J1(t)∫t0J1(t)h1(s)λb(y(t)−y(t−s),y(t)−y(t−s))ds)=ξ1(t)λG1(λ∫t0h1(s)b(y(t)−y(t−s),y(t)−y(t−s))ds)=ξ1(t)λ¯G1(λ∫t0h1(s)b(y(t)−y(t−s),y(t)−y(t−s))ds). |
Note that ¯G1 is an extension of G1, satisfying ¯G1 as strictly convex and strictly increasing on (0,+∞). Thus, we have
∫t0h1(s)b(y(t)−y(t−s),y(t)−y(t−s))ds≤1λ¯G−11(λK1(t)ξ1(t)). |
Similarly, we have
∫t0h2(s)b(z(t)−z(t−s),z(t)−z(t−s))ds≤1λ¯G−12(λK2(t)ξ2(t)), |
where ¯G2 is an extension of G2.
We infer from (4.23) that
H′(t)≤−αE(t)+c¯G−11(λK1(t)ξ1(t))+c¯G−12(λK2(t)ξ2(t)),∀t≥t1. | (4.26) |
Step 3: Here, we shall prove the desired inequality (4.1).
We set G=min{¯G1,¯G2}. For ε0<r, using (4.26) and since E′≤0, ¯G′i>0, ¯G″i>0, i=1,2, we claim that the functional G, defined by
G(t)=G′(ε0E(t)E(0))H(t)+E(t), |
is equivalent to E(t) and satisfies
G′(t)=E′(t)+ε0E′(t)E(0)G″(ε0E(t)E(0))H(t)+G′(ε0E(t)E(0))H′(t)≤−αE(t)G′(ε0E(t)E(0))+cG′(ε0E(t)E(0))¯G−11(λK1(t)ξ1(t))+cG′(ε0E(t)E(0))¯G−12(λK2(t)ξ2(t)). | (4.27) |
The convex conjugate of G in the Young's sense (see [25]) is denoted by G∗ and satisfies
G∗(t)=t(G′)−1(t)−G((G′)−1(t)). | (4.28) |
The following inequality holds true:
ABi≤G∗(A)+G(Bi),i=1,2, | (4.29) |
with A=G′(ε0E(t)E(0)) and Bi=¯G−1i(λKi(t)ξi(t)),i=1,2.
Using (4.27), (4.28) and (4.29), we obtain
G′(t)≤−αE(t)G′(ε0E(t)E(0))+cε0E(t)E(0)G′(ε0E(t)E(0))+cλ(K1(t)ξ1(t)+K2(t)ξ2(t)). |
Since Ki(t)≤−cE′(t) (for i=1,2), we infer that
ξ(t)G′(t)≤−αE(t)ξ(t)G′(ε0E(t)E(0))+cε0E(t)E(0)ξ(t)G′(ε0E(t)E(0))−cE′(t). | (4.30) |
Consequently, letting G1=ξG+cE, we have: α1G1(t)≤E(t)≤α2G1(t), for some α1,α2>0.
Thus, we get
G′1(t)≤−β1ξ(t)E(t)E(0)G′(ε0E(t)E(0)):=−β1ξ(t)G2(E(t)E(0)),∀t≥t1, | (4.31) |
where β1>0 and G2(t)=tG′(ε0t). Since G′2(t)=G′(ε0t)+ε0tG″(ε0t), then using the strict convexity of Gi(i=1,2) on (0,r], we have G′2(t),G2(t)>0 on (0,1]. Since G1∼E and using (4.31), one derives that
R(t)∼E(t),whereR(t)=α1G1(t)E(0), | (4.32) |
and
R′(t)≤−β2ξ(t)G2(R(t)),∀t≥t1, |
with β2>0. Integrating the last inequality over (t1,t) yields
∫tt1−R′(s)G2(R(s))ds≥β2∫tt1ξ(s)ds⇒∫ε0R(t1)ε0R(t)1sG′(s)ds≥β2∫tt1ξ(s)ds. |
Now, the function G_0 defined by G_0(t) = \int^r_t\frac{1}{sG'(s)}ds, is strictly decreasing on (0, r] and satisfies \lim\limits_{t\rightarrow0}G_0(t) = +\infty . Thus, we deduce that
\mathcal{R}(t)\leq \frac{1}{\varepsilon_0}G^{-1}_0\left(\beta_1\int^t_{t_1}\xi(s)ds\right). |
This inequality together with (4.32) yields to (4.1). This ends the proof of Theorem (4.1).
In this section, we give two examples that illustrate explicit formulas for the decay rates of the energy.
1. Let h_1(t) = h_2(t) = pe^{-k(1+t)^q}, \; t\geq0 , where p > 0 , 0 < q\leq1 and p > 0 is chosen so that h_i satisfies (2.4). We can see, for i = 1, 2 , that
h^{'}_i(t) = -pqk(1+t)^{q-1} e^{-k(1+t)^q} = -\xi_i(t)G_i(h_i(t)), |
where \xi_i(t) = qk(1+t)^{q-1} and G_i(t) = t . From (4.1), it holds that
E(t)\leq \beta_2 e^{-\beta_1 k(1+t)^q},\;\forall\;t\geq0. |
2. Let h_i(t) = \frac{p_i}{(1+t)^{q_i}}, \; i = 1, 2 , where q_i > 0 and p_i > 0 is chosen such that, (2.4) holds true. One has, for i = 1, 2 ,
h^{'}_i(t) = \frac{-p_iq_i}{(1+t)^{q_i+1}} = -\frac{q_i}{p_i^{\frac{1}{q_i}}}\left( \frac{p_i}{(1+t)^{q_i}}\right)^{\frac{q_i+1}{q_i}} = -\xi_i(t)G_i(h_i(t)), |
where \xi_i(t) = \frac{q_i}{p_i^{\frac{1}{q_i}}} and G_i(t) = t^{\frac{q_i+1}{q_i}}.
Putting q_3 = \min\{q_1, q_2\} . Therefore, it follows from (4.1) that
E(t)\leq\frac{c}{(1+t)^{q_3}},\;\forall\;t\geq0. |
This paper focuses on the existence and the asymptotic stability of solutions for a system of two coupled quasi-linear Kirchhoff plate equations in a bounded domain of \mathbb{R}^2 , subject only to viscoelasticity dissipative terms and with the presence of rotational forces and source terms. Each one of these two equations describes the motion of a plate, which is clamped along one portion of its boundary and has free vibrations on the other portion of the boundary. This work is motivated by previous results concerning coupled quasi-linear wave equations [14,15,16] and single quasi-linear plate equation [12,13].
As future works, we can change the type of damping by considering, for example, weak damping (of the form y_t ), Balakrishnan-Taylor damping (of the form (\nabla y, \nabla y_t) \Delta y ) or strong damping (of the form \Delta^2 y_t) .
This work is supported by Researchers Supporting Project number (RSPD2023R736), King Saud University, Riyadh, Saudi Arabia.
The author declares that there are no conflicts of interest.
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1. | Adel M. Al-Mahdi, The coupling system of Kirchhoff and Euler-Bernoulli plates with logarithmic source terms: Strong damping versus weak damping of variable-exponent type, 2023, 8, 2473-6988, 27439, 10.3934/math.20231404 |