Electronic Journal of Differential Equations, Vol. 2022 (2022), No. 10, pp. 1–23. ISSN: 1072-6691. URL: http://ejde.math.txstate.edu or http://ejde.math.unt.edu DYNAMICS OF A NON-AUTONOMOUS STOCHASTIC WEAKLY DAMPED PLATE MODEL WITH CRITICAL EXPONENT LAN WEN, LU YANG Abstract. In this article, we study the long-time behavior of the non-autonomous stochastic weakly damped plate model with critical exponent. By decompos- ing the solutions of the system and estimating the bounds of solutions in a more regular space, we obtain random attractors, when the external term is time-dependent and the nonlinearity has a critical growth. 1. Introduction In this article, we consider the non-autonomous stochastic weakly damped plate equation with critical nonlinearity and additive white noise, utt + αut + ∆2u+ λu+ f(u, x) = g(x, t) + h(x) ˙W (t), x ∈ U, t > τ, τ ∈ R, u(x, t)|∂U = ∂ ∂ν u|∂U = 0, t ≥ τ, τ ∈ R, u(x, τ) = uτ (x), ut(x, τ) = u1τ (x), x ∈ U, τ ∈ R, (1.1) where U is an open bounded set of Rn with a smooth boundary ∂U , u(t) = u(x, t) is a real-valued function on U × [τ,∞), τ ∈ R, λ > 0, α > 0, the external term g(·, t) ∈ Cb(R, H2 0 (U)), Cb(R, H2 0 (U)) denotes the set of continuous bounded functions from R into H2 0 (U), h ∈ H2 0 (U). W is a two-sided real-valued Wiener process on a probability space (Ω,F ,P), where Ω = {ω ∈ C(R,R) : ω(0) = 0}, the Borel σ- algebra F on Ω is generated by the compact open topology, P is the corresponding Wiener measure on F . For any t ∈ R, we can define a mapping θt on Ω by θt(·) = ω(t+·)−ω(·) for ω ∈ Ω, then (Ω,F ,P, (θt)t∈R) is an ergodic metric dynamical system. The nonlinear term f satisfies the following assumptions: (A1) f(u, x) = f1(u, x)+f2(u, x) and there exist positive constants c0, c1, c2, c3, c4, c5, and functions βi ∈ L1(U), i = 1, 2, such that for x ∈ U , u ∈ R, 0 ≤ G1(u, x) ≤ c0uf1(u, x) ≤ c1G1(u, x), G1(u, x) = ∫ u 0 f1(r, x)dr, f1 ∈ C2(R,R), f ′1,u(0, x) = 0, |f ′′1,u(u, x)| ≤ c2|u|q−2, (1.2) 2020 Mathematics Subject Classification. 37L05, 35B40, 35B41. Key words and phrases. Weakly damped plate equation; pullback random attractor; time-dependent external term; critical exponent. ©2022. This work is licensed under a CC BY 4.0 license. Submitted October 11, 2021. Published February 7, 2022. 1 2 L. WEN, L. YANG EJDE-2022/10 where 2 < q <∞ if n ≤ 4, and 2 < q ≤ n n−4 if n ≥ 5; f2(·, x) ∈ C1(R,R), |f ′2,u(u, x)| ≤ c3 (1 + |u|p) , 0 ≤ p < q − 1, (1.3) c4|u|q+1 − β1(x) ≤ G(u, x) ≤ c5uf(u, x) + δ0u 2 + β2(x), G(u, x) = ∫ u 0 f(r, x)dr, for some 0 ≤ δ0 ≤ c5 8λ2 1 , where λ1 is the first eigenvalue of operator A = −4. The plate equation arises in the nonlinear theory of oscillations, and our problem (1.1) has strong background in mathematical physics, the main motivation of the study comes not only from applications, but also from the mathematics, here the time-dependent external forcing and critical nonlinearity require more complicated techniques to some extent. In recent years the asymptotic behavior of the plate equation has been considered extensively in many papers(see, e.g., [1, 4, 11, 12, 14, 25]). For the deterministic plate equation without noise (i.e., h ≡ 0), [11, 12] established the existence of global attractors for localized damping, in [1, 25], the authors dealt with the plate equation with nonlinear damping; Von Karman equation is also one of the most important plate models (see [5, 6, 13] for details). As for the autonomous stochastic system (where the external term g is indepen- dent of t), for the wave equation, if the nonlinearity f has a subcritical exponent, the existence of random attractors have been investigated in [10, 28]. When f has a critical exponent, the existence of random attractors have been considered in [16, 26]. For the autonomous stochastic plate system, the authors in [17] proved the existence of random attractors for plate model with strongly damping, [18] showed the random attractors for plate equation with linear memory. When the forcing term g is time-dependent, for the non-autonomous stochastic wave equation, if f has a subcritical growth, the existence of random attractors were studied in [15, 20, 22], and [29, 30] showed the upper bound of fractal dimension of random attractors. When n = 3 and f has a critical exponent, the existence and boundedness of fractal dimension of random attractors have been successfully obtained for both additive noise and multiplicative noise, see [23, 24]. However, to the best of our knowledge, the non-autonomous stochastic weakly damped plate equation is less discussed, especially for the non-autonomous external term. In this article, inspired by the ideas in [23, 24], we analyze the dynamical behav- ior of the non-autonomous stochastic weakly damped plate equation. Under the assumptions that the external term g is time-dependent, and the nonlinear team f has a critical growth, by decomposing the solutions of system through two different modes, we estimate the bounds of solutions in a higher regular space, and then es- tablish the existence of random attractors. For the existence of random attractors, some kind of compactness of the process is a key ingredient, when verifying the pullback compactness, it is important to deal with the critical nonlinearity. This article is organized as follows. In section 2, we give some preparations for our consideration. In section 3, we estimate the bounds of solutions. In section 4, we decompose the solutions of the equation into two parts: one part decays exponentially, another part is bounded in a higher regular space. In section 5, we obtain the existence of random attractors of the system (1.1). EJDE-2022/10 DYNAMICS OF A PLATE MODEL WITH CRITICAL EXPONENT 3 2. Preliminaries In this section, we recall some basic concepts of pullback random attractors [2, 7, 8]. We know that self-adjoint positive linear sectorial operator A = −4 has eigen- values {λi}i∈N such that 0 < λ1 ≤ λ2 ≤ · · · ≤ λm ≤ . . . , λm → +∞ as m → +∞. For r ∈ R, the r-th powers Ar of A can be defined. Denote V2r = D(Ar), and it is a Hilbert space with inner product (u, v)2r = (Aru,Arv). The injection Vr1 ↪→ Vr2 is compact for any r1 > r2 and V0 = L2(U), V2 = H2 0 (U). Write Er = D(Ar+1)×D(Ar) for r ∈ R, and let E = H2 0 (U)× L2(U). Denote the inner products and norms of L2(U), H2 0 (U) and E by (u, v) = ∫ U uv dx, ‖u‖2 = (u, u), ∀u, v ∈ L2(U), (u, v)2 = ∫ U ∆u∆v dx, ‖u‖22 = (u, u)2, ∀u, v ∈ H2 0 (U), (y1, y2)E = (u1, u2)2 + (v1, v2), ∀yi = (ui, vi) T ∈ E, i = 1, 2, ‖y‖2E = ‖u‖22 + ‖v‖2, ∀y = (u, v)T ∈ E. First of all, we transfer the stochastic differential equation (1.1) into a random system without noise term. Write z(θtω) := −α ∫ 0 −∞ eαs(θtω)(s)ds (t ∈ R) as an Ornstein-Uhlenbeck stationary process which can solve the equation dz + αzdt = dW (t). From [2, 3, 9, 30], we know that t 7→ z(θtω) is continuous in t for almost every ω ∈ Ω and lim t→+∞ e−γt|z(θ−tω)| = 0, ∀γ > 0; E[|z(θtω)|r] = Γ( 1+r 2 ) √ παr , (2.1) for all r > 0 and t ∈ R, where Γ is Gamma function. Actually, as z(θtω) is Gauss stationary process with expectation 0 and square variance 1 2α [2, 9, 20]. Then for any r > 0 and t ∈ R, by [23], E[|z(θtω)|r] = 1√ παr ∫ +∞ 0 ξ 1+r 2 −1e−ξdξ = Γ( 1+r 2 ) √ παr . For simplicity, in this paper, we write a.e. ω ∈ Ω as ω ∈ Ω; all the numbers ci (i ∈ N) below are independent of (ω, τ, t). Let v = ut + εu− h(x)z(θtω), ε = λ2 1α α2 + 3λ2 1 , t ≥ τ, τ ∈ R. Then (1.1) can be changed into the stochastic system in the Hilbert space E, ϕ̇+ Λϕ = F (ϕ, θtω, t), t ≥ τ, ϕ(τ, ω) = ϕτ (ω) = (uτ , u1,τ + εuτ − h(x)z(θτω))T, (2.2) τ ∈ R, where ϕ = ( u v ) , Λ = ( εI −I A2 − ε(α− ε)I (α− ε)I ) F (ϕ, θtω, t) = ( h(x)z(θtω) −f(u, x)− λu+ g(x, t) + εh(x)z(θtω) ) . Following the arguments in [16, 17, 18, 20, 26], it can be proved that for any ϕτ = ϕ(τ, ω) ∈ E, problem (2.2) is well-posed in E; that is, the (weak) solution 4 L. WEN, L. YANG EJDE-2022/10 ϕ(·, τ, ω, ϕτ ) of (2.2) exists uniquely and globally for t ∈ [τ,∞), and ϕ(·, τ, ω, ϕτ ) ∈ C([τ,∞);E) can define a continuous cocycle on E, Φ : R+ × R × Ω × E → E, (t, τ, ω, ϕτ ) 7→ Φ(t, τ, ω)ϕτ (ω) by Φ(t, τ, ω)ϕτ (ω) = ϕ(t+ τ, τ, θ−τω, ϕτ (θ−τω)) = ( u(t+ τ, τ, θ−τω, ϕτ (θ−τω)) ut(t+ τ, τ, θ−τω, ϕτ ) + εu(t+ τ, τ, θ−τω, ϕτ )− h(x)z(θtω) ) over R and (Ω,F ,P, (θt)t∈R), where Φ(0, τ, ω)ϕτ (ω) = ϕτ (θ−τω) and Φ(t, τ − t, θ−tω)ϕτ−t(θ−tω) = ϕ(τ, τ − t, θ−τω, ϕτ−t(θ−τω)). We notice that the initial data uτ (x), u1τ (x) of (1.1) is independent of ω, con- versely, u(t, τ, ω, x) and ut(t, τ, ω, x) depend on ω for t > τ . Next, we recall the definition of random attractor and the existence criterion of random attractor for cocycle Φ. Definition 2.1. A family K = {K(τ, ω) : τ ∈ R, ω ∈ Ω} ∈ D(E) of nonempty subsets of E is called a measurable D(E)-pullback attracting set for Φ if (i) K is a measurable with respect to F in Ω; (ii) for all τ ∈ R, ω ∈ Ω, and for every B ∈ D(E), lim t→+∞ dH (Φ(t, τ − t, θ−tω,B(τ − t, θ−tω)),K(τ, ω)) = 0, where dH(·, ·) denotes the Hausdorff semi-distance between two subsets of E. Definition 2.2. A family A = {A(τ, ω) : τ ∈ R, ω ∈ Ω} ∈ D(E) of nonempty subsets of E is called a measurable D(E)-pullback random attractor for Φ if (i) A is a measurable in ω and compact in E for any τ ∈ R, ω ∈ Ω; (ii) A is invariant, i.e., for any τ ∈ R, ω ∈ Ω, t ≥ 0, Φ(t, τ, ω,A(τ, ω)) = A(τ + t, θtω); (iii) A is an attracting set in D(E). Lemma 2.3. [2, 3] If Φ has a compact measurable (with respect to F) D(E)- pullback attracting set K in D(E), then Φ has a unique D(E)-pullback attractor A in D(E) given by: for each τ ∈ R and ω ∈ Ω, A(τ, ω) = ∩r≥0∪t≥rΦ(t, τ − t, θ−tω,K(τ − t, θ−tω)). 3. Boundedness of solutions In this section, we obtain bounds for solutions. Define D(E) as the collection of all tempered families of nonempty subsets of E with respect to (θt)t∈R [21], which means, for every B = {B(τ, ω) ⊂ E : τ ∈ R, ω ∈ Ω} ∈ D(E), it holds that for any γ > 0, ω ∈ Ω, limt→∞ e−γ|t|‖B(τ + t, θtω)‖E = 0, where ‖B(τ, ω)‖E = supx∈B(τ,ω) ‖x‖. Lemma 3.1. For any τ ∈ R, ω ∈ Ω, there exists a tempered variable M0(ω)( independent of τ) such that for any set B ∈ D(E), there exists T (τ, ω,B) ≥ 0 such that the solution ϕ(τ, τ − t, θ−τω, ϕτ−t(θ−τω)) of (2.2) with ϕτ−t(θ−τω) ∈ B(τ − t, θ−tω) satisfies ‖ϕ(τ, τ − t, θ−τω, ϕτ−t(θ−τω))‖E ≤M0(ω), ∀t ≥ T (τ, ω,B), EJDE-2022/10 DYNAMICS OF A PLATE MODEL WITH CRITICAL EXPONENT 5 that is, the closed tempered measurable ball B0(ω) = {ϕ ∈ E : ‖ϕ‖E ≤ M0(ω)} of E satisfies Φ(t, τ − t, θ−tω,B(τ − t, θ−tω)) ⊆ B0(ω), ∀t ≥ T (τ, ω,B). (3.1) Proof. For any τ ∈ R, ω ∈ Ω, t ≥ 0, let ϕ(r) = ϕ(r, τ − t, θ−τω, ϕτ−t(θ−τω)) = (u(r), v(r))T ∈ E (r ≥ τ − t) is a solution of (2.2) with ϕ(τ − t) = ϕτ−t(θ−τω) = (uτ−t, u1,τ−t + εuτ−t − h(x)z(θ−tω))T ∈ E. From (A1) we obtain (f(u, x), u) ≥ 1 c5 Ḡ(r)− 1 8 ‖u‖22 − β̄2 c5 ,∫ U |u|q+1dx ≤ 1 c4 [Ḡ(r) + β̄1], |f(u, x)| ≤ c6(1 + |u|)q, (3.2) here Ḡ(r) = ∫ U G(u(r, x), x)dx, β̄i(x) = ∫ U βi(x)dx, i = 1, 2. Taking the inner product of (2.2) in E with ϕ(r), for r ≥ τ − t, we have 1 2 d dt [ ‖ϕ(r)‖2E + 2Ḡ(r) + 2β̄1 + λ‖u‖2 ] + (Λϕ,ϕ)E + ε(f(u, x) + λu, u) = (f(u, x) + λu, h(x)z(θr−τω)) + (h(x)z(θr−τω), u)2 + (g(x, r) + εh(x)z(θr−τω), v) . (3.3) From [9, 30] we obtain (Λϕ,ϕ)E ≥ ε 2 (‖u‖22 + ‖v‖2) + α 2 ‖v‖2. (3.4) So we can deduce that (f(u, x) + λu, h(x)z(θr−τω)) ≤ c7|z(θr−τω)| ( ‖h‖+ ( ∫ U |u|q+1dx) q q+1 ‖h‖Lq+1 + λ( ∫ U |u|q+1dx) 1 q+1 ‖h‖ L q+1 q ) ≤ c7|z(θr−τω)| ( ‖h‖+ ( 1 c4 [Ḡ(r) + β̄1] ) q q+1 ‖h‖Lq+1 + λ ( 1 c4 [Ḡ(r) + β̄1] ) 1 q+1 ‖h‖ L q+1 q ) ≤ c7‖h‖|z(θr−τω)|+ c8 ( 1 c4 [Ḡ(r) + β̄1] ) q q+1 ‖h‖Lq+1 |z(θr−τω)| + c8λ ( 1 c4 [Ḡ(r) + β̄1] ) 1 q+1 ‖h‖ L q+1 q |z(θr−τω)| ≤ c7‖h‖|z(θr−τω)|+ ε 2c5 Ḡ(r) + c9β̄1 + c10‖h‖q+1 2 |z(θr−τω)|q+1 + c11‖h‖ q+1 q 2 |z(θr−τω)| q+1 q , (3.5) where c11 depends on λ, (h(x)z(θr−τω), u)2 ≤ 2 ε z2(θr−τω)‖h‖22 + ε 8 ‖u‖22, (3.6) and (g(x, r) + εh(x)z(θr−τω), v) ≤ 1 α [ ‖g‖2 + ε2z2(θr−τω)‖h‖2 ] + α 2 ‖v‖2, (3.7) 6 L. WEN, L. YANG EJDE-2022/10 where ‖g‖2 = supr∈R ‖g(·, r)‖2 <∞. From (3.3)-(3.7), we obtain that d dt y(r) + ρy(r) ≤ q(θr−τω), ∀r ≥ τ − t, (3.8) where ρ = min{ ε2 , ε 2c5 } and y(r) = ‖ϕ(r)‖2E + 2Ḡ(u) + 2β̄1 + λ‖u‖2 ≥ ‖ϕ(r)‖2E , q(θr−τω) = 4 ε z2(θr−τω)‖h‖22 + 2 α [ ‖g‖2 + ε2z2(θr−τω)‖h‖2 ] + c7‖h‖|z(θr−τω)|+ 2c9β̄1 + c10‖h‖q+1 2 |z(θr−τω)|q+1 + c11‖h‖ q+1 q 2 |z(θr−τω)| q+1 q + 4ε c5 β̄2 + 2ρβ̄1 ≤ c12 + c13|z(θr−τω)|q+1, where c13 depends on λ. By (3.2), we have −β̄1 ≤ Ḡ(r) + λ 2 ‖u‖2 ≤ c14 ( 1 + ∫ U |u|q+1dx ) + λ‖u‖2 ≤ c15 ( 1 + ‖u‖q+1 2 ) , where c15 depends on λ. Using the Gronwall’s inequality to (3.8) on [τ − t, r] (r ≥ τ − t), we can deduce that for r ≥ τ − t, y (r, τ − t, θ−τω, ϕτ−t(θ−τω)) ≤ y (τ − t, τ − t, θ−τω, ϕτ−t(θ−τω)) e−ρ(r+t−τ) + ∫ r τ−t q(θs−τω)e−ρ(r−s)ds, (3.9) where y(τ − t, τ − t, θ−τω, ϕτ−t(θ−τω)) ≤ ‖ϕτ−t(θ−τω)‖2E + 2c15(1 + ‖uτ−t‖q+1 2 ) + 2β̄1, and ∫ r τ−t q(θs−τω)e−ρ(r−s)ds ≤ c12 ρ + c13 ∫ r τ−t |z(θs−τω)|q+1e−ρ(r−s)ds. From (3.9) we obtain ‖ϕ(r, τ − t, θ−τω, ϕτ−t(θ−τω))‖2E ≤ ( ‖ϕτ−t(θ−τω)‖2E + 2c15(1 + ‖uτ−t‖q+1 2 ) ) e−ρ(r+t−τ) + c16 + c13 ∫ r τ−t |z(θs−τω)|q+1e−ρ(r−s)ds, ∀r ≥ τ − t. So we have ‖ϕ(τ, τ − t, θ−τω, ϕτ−t(θ−τω))‖2E ≤ ( ‖ϕτ−t(θ−τω)‖2E + 2c15(1 + ‖uτ−t‖q+1 2 ) ) e−ρt + c16 + c13 ∫ 0 −∞ |z(θsω)|q+1eρsds. (3.10) For any set B(τ, ω) ∈ B ∈ D(E), ϕτ−t(θ−τω) = (uτ−t, u1,τ−t + εuτ−t − h(x)z(θ−tω))T ∈ B(τ − t, θ−tω) ∈ D(E), EJDE-2022/10 DYNAMICS OF A PLATE MODEL WITH CRITICAL EXPONENT 7 we obtain lim sup t→+∞ ( ‖ϕτ−t(θ−τω)‖2E + 2c15(1 + ‖uτ−t‖q+1 2 ) ) e−ρt = 0. (3.11) Writing M2 0 (ω) = 2 ( c16 + c13 ∫ 0 −∞ |z(θsω)|q+1eρsds ) <∞, (3.12) this is a tempered random variable, then from (3.10) and (3.11), there exists T (τ, ω,B) ≥ 0 such that ϕ(τ, τ−t, θ−τω, ϕτ−t(θ−τω)) ∈ B0(ω) for all t ≥ T (τ, ω,B), i.e., (3.1) holds. � By (3.1), then there exists T (τ, ω,B0) ≥ 0 such that ϕ(r, τ − t, θ−τω,B0(θ−tω)) ∈ B0(θr−τω), ∀t ≥ T (τ, ω,B0), τ − t ≤ r ≤ τ. (3.13) From (2.1) and (3.12), for any τ ∈ R, we have E ( M2 0 (θτω) ) = 2 ( c16 + c13 1 ρ Γ( q+2 2 )√ παq+1 ) and for k > 1, E(M2k 0 (θτω)) ≤ 22k [ ck16 + ck13 (∫ 0 −∞ e k 2(k−1) ρsds )k−1 E (∫ 0 −∞ e k 2 ρs|z(θs+τω)|(q+1)kds )] = 22k [ ck16 + ck13 (2(k − 1) kρ )k−1 2 kρ Γ( 1+(q+1)k 2 ) √ πα (q+1)k 2 ] <∞. (3.14) 4. Decomposition of solutions In this section, we decompose the solution of (2.2) into two parts, one of them decays exponentially and another one is ultimately pullback bounded in a more regular space. For this goal, we make two methods of decomposing the solutions of (2.2) with different initial data. For any τ ∈ R and ω ∈ Ω, let B1(τ, ω) = ∪t≥T (τ,ω,B0)ϕ(τ, τ − t, θ−τω,B0(θ−tω)) ⊆ B0(ω). Let ϕ(r) = ϕ(r, τ − t, θ−τω, ϕτ−t(θ−τω))(r ≥ τ − t, t ≥ 0) be a solution of (2.2) with ϕτ−t(θ−τω) ∈ B1(τ − t, θ−tω) ⊆ B0(θ−tω), then by (3.13) we know that ϕ(r) ∈ B0(θr−τω) for all r ≥ τ − t, ‖ϕ(r, τ − t, θ−τω, ϕτ−t(θ−τω))‖E ≤M0(θr−τω). (4.1) 4.1. Decomposition of solution I. First, we decompose ϕ(r) = ϕ1(r) + ϕ2(r). Here ϕ1(r) = (u1, v1)T and ϕ2(r) = (u2, v2)T satisfy ϕ̇1 + Λϕ1 + F1(ϕ1, x) = 0, r > τ − t, ϕ1(τ − t, τ − t, θ−τω, ϕτ−t(θ−τω)) = ϕτ−t(θ−τω), (4.2) and ϕ̇2 + Λϕ2 + F2(ϕ,ϕ1, x) = F3(θr−τω, r), r > τ − t, ϕ2(τ − t, τ − t, θ−τω, ϕτ−t(θ−τω)) = (0, 0)T, (4.3) where v1 = u1,t + εu1, v2 = u2,t + εu2 − h(x)z(ω), F1(ϕ1, x) = ( 0 f1(u1, x) + λu1 ) , F2(ϕ,ϕ1, x) = ( 0 f(u, x)− f1(u1, x) + λu2 ) , 8 L. WEN, L. YANG EJDE-2022/10 F3(ω, r) = ( h(x)z(ω) g(x, r) + εh(x)z(ω) ) . Next we appraise the part ϕ1. Lemma 4.1. For any τ ∈ R, ω ∈ Ω, t ≥ 0, there exist a constant σ1 > 0 and a tempered random variable M1(ω) > 0 (independent of t and τ) such that the solution ϕ1(r) = ϕ1(r, τ − t, θ−τω, ϕτ−t(θ−τω)) of (4.2) satisfies ‖ϕ1(r, τ − t, θ−τω, ϕτ−t(θ−τω))‖E ≤M1(θ−tω)e−σ1(t+r−τ), ∀ r ≥ τ − t. (4.4) Proof. As for (3.3), we take the inner product (·, ·)E of (4.2) with ϕ1 = (u1, v1)T. Then from (1.2) and (3.4), the following inequality holds for r ≥ τ − t, d dt [ ‖ϕ1(r)‖2E + 2Ḡ1(r) + λ‖u1‖2 ] + ε(‖u1‖22 + ‖v1‖2) + 2ε c0 (Ḡ1(r) + λ‖u1‖2) ≤ 0, here Ḡ1(r) = ∫ U G1(u1(r, x), x)dx ≥ 0. Therefore, d dt y1(r) + 2σ1y1(r) ≤ 0, ∀r ≥ τ − t, (4.5) where y1(r) = ‖ϕ1(r)‖2E + 2Ḡ1(u1) + λ‖u1‖2 ≥ ‖ϕ1(r)‖2E , σ1 = min{ε 2 , ε c0 }. Using the Gronwall’s inequality in (4.5), we obtain that ‖ϕ1(r)‖2E ≤ y1(r) ≤ y1(τ − t)e−2σ1(t+r−τ) ≤ ( c17‖ϕτ−t(θ−τω)‖2E + 2c15(1 + ‖uτ−t‖q+1 2 ) ) e−2σ1(t+r−τ) ≤ c18 ( 1 +Mq+1 0 (θ−tω) ) e−2σ1(t+r−τ) = M2 1 (θ−tω)e−2σ1(t+r−τ), ∀ r ≥ τ − t. (4.6) � For the part ϕ2, we have the following estimate. Lemma 4.2. For any τ ∈ R, ω ∈ Ω, t ≥ 0, there exists a positive-value random variable M2(t, ω) > 0 such that for r ≥ τ − t, the solution ϕ2(r) = (u2, v2)T of (4.3) satisfies ‖Aν+1u2(τ, τ − t, θ−τω, ϕτ−t)‖2 + ‖Aνv2(τ, τ − t, θ−τω, ϕτ−t)‖2 ≤M2(t, ω) (4.7) with a positive constant ν = min {1 2 , n− 4 4 , 4− (n− 4)p 4 } > 0. (4.8) EJDE-2022/10 DYNAMICS OF A PLATE MODEL WITH CRITICAL EXPONENT 9 Proof. Taking the inner product (·, ·)E with A2νϕ2 = (A2νu2, A 2νv2)T of (4.3), we obtain 1 2 d dt ( ‖Aν+1u2‖2 + ‖Aνv2‖2 + 2 ∫ U [f(u, x)− f1(u1, x) + λu2]A2νu2dx ) + (Λϕ2, A 2νϕ2) + ε ∫ U [f(u, x)− f1(u1, x) + λu2]A2νu2dx − ∫ U [( f ′1,u(u, x)− f ′1,u(u1, x) ) u1,t + f ′2,u(u, x)u1,t +f ′u(u, x)u2,t + λu2,t]A 2νu2dx = ( f(u, x)− f1(u1, x) + λu2, A 2νh(x)z(θr−τω) ) + ( h(x)z(θr−τω), A2νu2 ) 2 + ( g(x, r) + εh(x)z(θr−τω), A2νv2 ) , ∀r ≥ τ − t. (4.9) Similar to (3.4)-(3.7), we obtain that for r ≥ τ − t, (Λϕ2, A 2νϕ2) ≥ ε 2 ‖Aν+1u2‖2 + ε 2 ‖Aνv2‖2 + α 2 ‖Aνv2‖2,( f(u, x)− f1(u1, x) + λu2, A 2νh(x)z(θr−τω) ) ≤ c19 ( 1 +M2q 0 (θr−τω) +M2 0 (θr−τω) + z2(θr−τω) ) ,( h(x)z(θr−τω), A2νu2 ) 2 ≤ 4 ε z2(θr−τω)‖h‖22 + ε 16 ‖Aν+1u2‖2,( g(x, r) + εh(x)z(θr−τω), A2νv2 ) ≤ 2 α [‖g‖22 + ε2z2(θr−τω)‖h‖22] + α 4 ‖Aνv2‖2, where c19 depends on λ and ‖g‖22 = supr∈R ‖g(·, r)‖22 <∞. Using Hölder’s inequal- ity, (1.2), (1.3), (4.1), and (4.4), we have the following estimates for r ≥ τ − t,∫ U f ′u(u, x)u2,t ·A2νu2 dx ≤ c20 ∫ U ( 1 + |u|q−1 ) |u2,t||A2νu2|dx ≤ c21 (∫ U (1 + |u|q−1) n 2 dx )2/n(∫ U |A2νu2| 2n n−4+4ν dx )n−4+4ν 2n (∫ U |u2,t| 2n n−4ν dx )n−4ν 2n ≤ c22 ( 1 + ‖u‖q−1 2 ) ‖Aν+1u2‖ [ ‖Aνv2‖+ ‖εAνu2 + z(θr−τω)Aνh‖ ] ≤ 1 2 c22 ( 1 +Mq−1 0 (θr−τω) ) (‖Aν+1u2‖2 + ‖Aνv2‖2) + c23 ( 1 +M4q−4 0 (θr−τω) + z4(θr−τω) ) + ε 16 ‖Aν+1u2‖2,∫ U f ′2,u(u, x)u1,t ·A2νu2dx ≤ c3 ∫ U |u1,t|(1 + |u|p)|A2νu2|dx ≤ c3 (∫ U |u1,t|2dx )1/2(∫ U (1 + |u|p) 2n 4−4ν dx ) 4−4ν 2n (∫ U |A2νu2| 2n n+4ν−4 dx )n+4ν−4 2n ≤ c24 (‖v1‖+ ε‖u1‖) (1 + ‖u‖p2) ‖Aν+1u2‖ ≤ c25 [ 1 +M4p 0 (θr−τω) +M4 1 (θ−tω)e−4σ1(t+r−τ) ] + ε 16 ‖Aν+1u2‖2, 10 L. WEN, L. YANG EJDE-2022/10 and∫ U [f ′1,u(u, x)− f ′1,u(u1, x)]u1,tA 2νu2dx ≤ c26 ∫ U |u1,t| ( |u1|q−2 + |u|q−2 ) |u2||A2νu2|dx ≤ c26 (∫ U |u1,t| 2n 4q−nq+2n dx ) 4q−nq+2n 2n (∫ U (|u1|q−2 + |u|q−2) 2n (n−4)(q−2) dx ) (n−4)(q−2) 2n × (∫ U |u2| 2n n−4−4ν dx )n−4−4ν 2n (∫ U |A2νu2| 2n n−4+4ν dx )n−4+4ν 2n ≤ c27(1 + ε√ λ1 )M1(θ−tω)e−σ1(t+r−τ) × ( Mq−2 1 (θ−tω)e−(q−2)σ1(t+r−τ) +Mq−2 0 (θr−τω) ) ‖Aν+1u2‖2 ≤ c28 [ Mq−1 0 (θr−τω) +Mq−1 1 (θ−tω)e−(q−1)σ1(t+r−τ) ] ‖Aν+1u2‖2. Also we have∫ U λu2tA 2νu2dx ≤ λc29 ( ‖Aν+1u2‖2 + ‖Aνv2‖2 + z2(θr−τω) ) . By the above inequalities and (4.9), we obtain d dt y2(r) ≤ m1(θr−τω)y2(r) + q1(θr−τω), ∀r ≥ τ − t, (4.10) where y2 = ‖Aν+1u2‖2 + ‖Aνv2‖2 + 2 ∫ U [f(u, x)− f1(u1, x) + λu2]A2νu2dx, (4.11) m1(θr−τω) = c30[1 +Mq−1 0 (θr−τω) +Mq−1 1 (θ−tω)e− 4 n−4σ1(t+r−τ)]− ε 4 , (4.12) q1(θr−τω) = c31[1 +M4q−4 0 (θr−τω) + z4(θr−τω) +M2q 1 (θ−tω)e−2qσ1(t+r−τ)], y2 (τ − t, τ − t, θ−τω, ϕτ−t(θ−τω)) = (0, 0)T, where c30, c31 depend on λ. By using the Gronwall’s inequality to (4.10) on [τ−t, r] (r ≥ τ − t), we have y2(r, τ − t, θ−τω, ϕτ−t(θ−τω)) ≤ ∫ r τ−t q1(θξ−τω)e ∫ r ξ m1(r,ω)drdξ, (4.13) for all r ≥ τ − t. Note that∣∣ ∫ U f2(u, x) ·A2νu2dx ∣∣ ≤ c32 ∫ U ( 1 + |u|p+1 ) |A2νu2|dx ≤ c32 (∫ U ( 1 + |u|p+1 )2 dx )1/2(∫ U |A2νu2|2dx )1/2 ≤ c32 [ 1 +M2p+2 0 (θr−τω) +M2 1 (θ−tω)e−2σ1(t+r−τ) ] , and ∫ U ∣∣[f1(u, x)− f1(u1, x) + λu2]A2νu2 ∣∣ dx ≤ c33 ∫ U (1 + |u2|q + |u1|q + λ|u2|) |A2νu2|dx EJDE-2022/10 DYNAMICS OF A PLATE MODEL WITH CRITICAL EXPONENT 11 ≤ c33 (∫ U ( 1 + |u2|q + |u1|q + λ|u2| )2 dx )1/2(∫ U |A2νu2|2dx )1/2 ≤ c34 [ 1 +M2q 0 (θr−τω) +M2q 1 (θ−tω)e−2qσ1(t+r−τ) ] . Therefore,∫ U [f(u, x)− f1(u1, x) + λu2]A2νu2dx = ∫ U [f2(u, x) + f1(u, x)− f1(u1, x) + λu2]A2νu2dx ≤ c35[1 +M2q 0 (θr−τω) +M2q 1 (θ−tω)e−2qσ1(t+r−τ)], ∀r ≥ τ − t, (4.14) where c34, c35 depend on λ. Thus, according to (4.11), (4.13) and (4.14), we obtain that for r ≥ τ − t, ‖Aν+1u2(r, τ − t, θ−τω, ϕτ−t(θ−τω))‖2 + ‖Aνv2(r, τ − t, θ−τω, ϕτ−t(θ−τω))‖2 ≤ 2y2 (r, τ − t, θ−τω, ϕτ−t(θ−τω)) + 2c35[1 +M2q 0 (θr−τω) +M2q 1 (θ−tω)e−2qσ1(t+r−τ)] ≤ 2c35[1 +M2q 0 (θr−τω) +M2q 1 (θ−tω)e−2qσ1(t+r−τ)] + 2c31 ∫ r τ−t [1 +M4q−4 0 (θξ−τω) + z4(θξ−τω) +M2q 1 (θ−tω)e−2qσ1(t+ξ−τ)]e ∫ r ξ m1(θs−τω)drdξ. (4.15) Denoting M2(t, ω) = 2c35[1 +M2q 0 (ω) +M2q 1 (θ−tω)e−2qσ1t] + 2c31 ∫ 0 −t [1 +M4q−4 0 (θξω) + z4(θξω) +M2q 1 (θ−tω)e−2qσ1(t+ξ)]e ∫ 0 ξ m1(θrω)drdξ, (4.16) then we can obtain (4.7) from (4.15) and (4.16). � Motivated by [27, Proposition 1.4], Lemmas 4.1 and 4.2, we obtain the following decomposition of solutions for (2.2). Lemma 4.3. Let τ ∈ R, ω ∈ Ω and t ≥ 0. Then for any T > 0, the following statements are valid. (i) There exist two positive constants K̄, K1 and the solution ϕ(r) of (2.2) has a decomposition: ϕ(r) = φ1(r) + φ2(r), where φ1(r), φ2(r) satisfy∫ τ r ‖φ1 (ξ, τ − t, θ−τω, ϕτ−t(θ−τω))‖q−1 E dξ ≤ K0 σ1T (τ − r) + K̄, ‖φ2(r, τ − t, θ−τω, ϕτ−t(θ−τω))‖q−1 E ≤ K1M2(T, ω), ∀r ≥ τ − t. (4.17) (ii) The first component u(r) of solution ϕ(r) of (2.2) has a decomposition that u(r) = w1(r) + w2(r), where w1(r), w2(r) satisfy∫ τ r ‖w1(ξ, τ − t, θ−τω, ϕτ−t(θ−τω))‖q−1 2 dξ ≤ K0 σ1T (τ − r) + K̄, ‖Aν+1w2(r, τ − t, θ−τω, ϕτ−t(θ−τω))‖q−1 ≤ K1M2(T, ω), ∀r ≥ τ − t, (4.18) where ν is as in (4.8), K0 = E[Mq−1 1 (ω)]. 12 L. WEN, L. YANG EJDE-2022/10 Proof. From (4.6), we know M2 1 (ω) = c18 ( 1 +Mq+1 0 (ω) ) , then we can find a pos- itive constant c36 that Mq−1 1 (ω) = c36 ( 1 +M q2−1 2 0 (ω) ) . As (θt)t∈R is measure-preserving and ergodic on (Ω,F ,P), from the Birkhoff ergodic Theorem [19], we obtain E[Mq−1 1 (θsω)] = E[Mq−1 1 (ω)] = c36 ( 1 + E [ M q2−1 2 0 (ω) ]) = c36 ( 1 + 2 q2−1 2 [ c q2−1 4 16 + c q2−1 4 13 ( 2q2 − 10 (q2 − 1)ρ ) q2−5 4 8 (q2 − 1)ρ Γ( 4+(q+1)(q2−1) 8 ) √ πα (q+1)(q2−1) 8 ]) = K0 <∞, ∀s ∈ R, and for any fixed T > 0, s ∈ R and ω ∈ Ω (in fact for a.e.ω ∈ Ω), 1 k k∑ l=1 Mq−1 1 (θs+lTω)→ E[Mq−1 1 (θsω)] = K0, k →∞. Therefore, for ω ∈ Ω, there exists a large integer k0(ω) <∞ satisfying K0 2 ≤ 1 k k∑ l=1 Mq−1 1 (θs+lTω) ≤ 3K0 2 , ∀k ≥ k0(ω), ∀s ∈ R, and K0 2 k0(ω) ≤ k0(ω)∑ l=1 Mq−1 1 (θs+lTω) ≤ 3K0 2 k0(ω), ∀s ∈ R. (4.19) Taking the expectation on (4.19), we obtain 1 2 E[k0] ≤ k0(ω) ≤ 3 2 E[k0], k0(ω) <∞, so, we have E[k0] <∞. (i) We construct functions φ1(r) and φ2(r). When T > 0 and k ∈ N, consider equations (4.2) and (4.3) at the interval [τ − t+ (k − 1)T, τ − t+ kT ]. Note φ1 = (w1, w̃1)T = ϕ1, φ1(τ − t+ (k − 1)T ) = ϕ(τ − t+ (k − 1)T ), φ2 = (w2, w̃2)T = ϕ2, φ2(τ − t+ (k − 1)T ) = (0, 0)T. By (4.4), as s ≥ 0, r ∈ [τ − t+ s+ (k − 1)T, τ − t+ s+ kT ], we obtain ‖φ1(r)‖q−1 E = ‖w1‖q−1 2 + ‖w̃1‖q−1 ≤Mq−1 1 (θ−t+s+(k−1)Tω)e−(q−1)σ1(t−s−(k−1)T+r−τ), (4.20) and ∫ τ−t+s+kT τ−t+s+(k−1)T ‖φ1(ξ)‖q−1 E dξ ≤ ∫ τ−t+s+kT τ−t+s+(k−1)T Mq−1 1 (θ−t+s+(k−1)Tω)e−(q−1)σ1(t−s−(k−1)T+ξ−τ)dξ EJDE-2022/10 DYNAMICS OF A PLATE MODEL WITH CRITICAL EXPONENT 13 ≤ Mq−1 1 (θ−t+s+(k−1)Tω) (q − 1)σ1 . By (4.20), as k ≥ k0(ω) and s ≥ 0,∫ τ−t+s+kT τ−t+s ‖φ1(ξ)‖q−1 E dξ ≤ (∫ τ−t+s+T τ−t+s + ∫ τ−t+s+2T τ−t+s+T + · · ·+ ∫ τ−t+s+kT τ−t+s+(k−1)T ) ‖φ1(ξ)‖q−1 E dξ ≤ 1 (q − 1)σ1 [ Mq−1 1 (θ−t+sω) +Mq−1 1 (θ−t+s+Tω) + · · ·+Mq−1 1 (θ−t+s+(k−1)Tω) ] ≤ K0 σ1 k. Thus, when τ − t ≤ r ≤ τ and τ − r = mT + r̄, m ∈ Z+, r̄ ∈ [0, T ), we obtain: (a) If m ≥ k0(ω), then∫ τ r ‖φ1(ξ)‖q−1 E dξ ≤ ( ∫ r+T r + ∫ r+2T r+T + · · ·+ ∫ r+(m+1)T r+mT )‖φ1(ξ)‖q−1 E dξ ≤ K0 σ1T (τ − r) + K0 σ1 . (b) If 0 < m < k0(ω), then∫ τ r ‖φ1(ξ)‖q−1 E dξ ≤ (∫ τ−(k0−1)T τ−k0T + ∫ τ−(k0−2)T τ−(k0−1)T + · · ·+ ∫ τ τ−t ) ‖φ1(ξ)‖q−1 E dξ ≤ K0 σ1 k0(ω). Thus ∫ τ r ‖φ1(ξ)‖q−1 E dξ ≤ K0 σ1T (τ − r) + K̄, where K̄ = 3K0 2σ1 E[k0] + K0 σ1 . For t ≥ T , ϕ2(r) is the solution of (4.3) on the interval [r−T, r] with ϕ2(r−T ) = (0, 0)T, by (4.7), we obtain ‖ϕ2(r, r − T, θ−τω, ϕr−T )‖q−1 Eν ≤ c37‖ϕ2(r, r − T, θ−τω, ϕr−T )‖2Eν ≤ K1M2(T, ω), ∀r ≥ τ − t. (4.21) Thus, combining (4.7) and (4.21), for any t ≥ 0 and r ≥ τ − t, we can choose φ2 like this, then (4.17) holds. (ii) can be obtained directly from (i). � 4.2. Decomposition of solutions II. Let ϕ(r) be the solution of (2.2), and write ϕ(r) = ϕL(r) + ϕN (r). Here ϕL(r) = (uL, vL)T and ϕN (r) = (uN , vN )T satisfy ϕ̇L + ΛϕL + F1(ϕL, x) = 0, r > τ − t, ϕL(τ − t, τ − t, θ−τω, ϕτ−t(θ−τω)) = ϕL,τ−t = (uτ−t, u1,τ−t + εuτ−t) T, (4.22) and ϕ̇N + ΛϕN + F2(ϕ,ϕL, x) = F̃2(θr−τω, r), r > τ − t, ϕN (τ − t, τ − t, θ−τω, ϕτ−t(θ−τω)) = (0,−h(x)z(θ−tω))T, t ≥ 0, (4.23) 14 L. WEN, L. YANG EJDE-2022/10 where uτ−t and u1,τ−t are independent of ω, and vL = uL,t + εuL, vN = uN,t + εuN − h(x)z(ω). Next, we estimate the component ϕL. Lemma 4.4. For any τ ∈ R and ω ∈ Ω, t ≥ 0, there exists a constant ML > 0 (independent of ω, t and τ) such that the solution ϕL(r) = ϕL(r, τ − t, ϕL,τ−t) of (4.22) satisfies ‖ϕL(r, τ − t, ϕL,τ−t)‖E = ( ‖uL(r)‖22 + ‖vL(r)‖2 )1/2 ≤MLe −σ1(t+r−τ), ∀r ≥ τ − t. (4.24) Proof. Note that ϕL,τ−t = ϕτ−t(θ−τω)+(0, h(x)z(θ−tω))T ∈ B0(θ−tω) and ϕL,τ−t is independent of ω, we replace θtω by ω, so we have ‖ϕL,τ−t‖2E ≤ 2M2 0 (ω) + 2‖h(x)‖2|z(ω)|2, ∀τ ∈ R, ω ∈ Ω, t ≥ 0. Taking the expectation with respect to ω ∈ Ω, we obtain that ‖ϕL,τ−t‖2E = ‖uτ−t‖22 + ‖u1,τ−t + εuτ−t‖2 ≤ 2 E[M2 0 (ω)] + 2‖h(x)‖2 · E[|z(ω)|2] ≤ 4 ( c16 + c13 1 ρ Γ( q+2 2 ) √ παq+1 ) + 2‖h(x)‖2 Γ( 1+2 2 ) √ πα = 4 ( c16 + c13 1 ρ Γ( q+2 2 ) √ παq+1 ) + 1 α ‖h(x)‖2. As in (4.6) for r ≥ τ − t, we obtain ‖ϕL(r)‖2E ≤ [‖ϕL,τ−t‖2E + 2c15(1 + ‖uτ−t‖q+1 2 )]e−2σ1(t+r−τ) = M2 Le −2σ1(t+r−τ), where M2 L = 4c16 + 4c13 1 ρ Γ( q+2 2 ) √ παq+1 + 1 α ‖h(x)‖2 + c15 + c15 ( 4c16 + 4c13 1 ρ Γ( q+2 2 ) √ παq+1 + 1 α ‖h(x)‖2 ) q+1 2 . � The following estimate is same as in Lemma 4.2. Lemma 4.5. For any τ ∈ R, ω ∈ Ω, there exist a random variable tν(ω) ≥ 0 and a tempered random variable Mν(ω) > 0 (independent of t and τ) such that the solution ϕN (τ, τ − t, θ−τω, ϕτ−t(θ−τω)) of (4.23) satisfies: for t ≥ tν(ω), ‖Aν+1uN (τ, τ − t, θ−τω, ϕτ−t)‖2 +‖AνvN (τ, τ − t, θ−τω, ϕτ−t)‖2 ≤M2 ν (ω), (4.25) where ν is as in (4.8). EJDE-2022/10 DYNAMICS OF A PLATE MODEL WITH CRITICAL EXPONENT 15 Proof. Similar to (4.9), we take the inner product ((4.23), A2νϕN )E , then 1 2 d dt ( ‖Aν+1uN‖2 + ‖AνvN‖2 + 2 ∫ U [f(u, x)− f1(uL, x) + λuN ]A2νuNdx ) + (ΛϕN , A 2νϕN ) + ε ∫ U [f(u, x)− f1(uL, x) + λuN ]A2νuNdx − ∫ U [(f ′1(u, x)− f ′1(uL, x))uL,t + f ′2(u, x)uL,t + f ′(u, x)uN,t + λuN,t]A 2νuNdx = ( f(u, x)− f1(uL, x) + λuN , A 2νh(x)z(θr−τω) ) + ( h(x)z(θr−τω), A2νuN ) 2 + (g(x, r) + εh(x)z(θr−τω), A2νvN ), ∀r ≥ τ − t. (4.26) From ϕN (r) = ϕ(r)− ϕL(r) and (4.1), (4.24), ‖ϕN (r)‖E ≤ML +M0(θr−τω), ∀r ≥ τ − t. Using Hölder’s inequality, (A1) and Lemma 4.3, we obtain that: for r ≥ τ − t,∫ U [f ′1(u, x)− f ′1(uL, x)]uL,tA 2νuNdx ≤ c2 ∫ U |uL,t| ( |uL|q−2 + |u|q−2 ) |uN ||A2νuN |dx ≤ c2 (∫ U |uL,t| 2n 4q−nq+2n dx ) 4q−nq+2n 2n (∫ U ( |uL|q−2 ) 2n (n−4)(p−2) dx ) (n−4)(p−2) 2n × (∫ U |uN | 2n n−4−4ν dx )n−4−4ν 2n (∫ U |A2νuN | 2n n−4+4ν dx )n−4+4ν 2n + c2 (∫ U |uL,t| 2n 4q−nq+2n dx ) 4q−nq+2n 2n (∫ U ( |w1|q−2 ) 2n (n−4)(p−2) dx ) (n−4)(p−2) 2n × (∫ U |uN | 2n n−4−4ν dx )n−4−4ν 2n (∫ U |A2νuN | 2n n−4+4ν dx )n−4+4ν 2n + c2 (∫ U |uL,t| 2n 4q−nq+2n dx ) 4q−nq+2n 2n (∫ U |uN | 2n (n−4)(p−2) dx ) (n−4)(p−2) 2n × (∫ U ( |w2|q−2 ) 2n n−4−4ν dx )n−4−4ν 2n (∫ U |A2νuN | 2n n−4+4ν dx )n−4+4ν 2n ≤ c38 ( ‖uL‖q−2 2 + ‖w1‖q−2 2 ) ‖Aν+1uN‖2 + c39 [ 1 +M4 0 (θr−τω) + ‖Aν+1w2‖4q−8 ] + ε 16 ‖Aν+1uN‖2, and∫ U [f ′(u, x)uN,t + λuN,t]A 2νuNdx ≤ c20 ∫ U [( 1 + |u|q−1 ) |uN,t|+ λuN,t ] |A2νuN |dx ≤ c20 (∫ U |uN,t|2dx )1/2(∫ U |A2νuN |2dx )1/2 + c20 (∫ U |w1| n(q−1) 2 dx )2/n(∫ U |A2νuN | 2n n−4+4ν dx )n−4+4ν 2n (∫ U |uN,t| 2n n−4ν dx )n−4ν 2n 16 L. WEN, L. YANG EJDE-2022/10 + c20 (∫ U |uN,t|2dx )1/2(∫ U ( |w2|q−1 ) 2n 4−4ν dx ) 4−4ν 2n × (∫ U |A2νuN | 2n n+4ν−4 dx )n+4ν−4 2n + c20 (∫ U |λ|n2 )2/n(∫ U |uN,t| 2n n−4ν dx )n−4ν 2n (∫ U |A2νuN | 2n n+4ν−4 dx )n+4ν−4 2n ≤ c40‖w1‖q−1 2 ( ‖Aν+1uN‖2 + ‖AνvN‖2 ) + ε 16 ‖Aν+1uN‖2 + c41 [ M4 0 (θr−τω) + z4(θr−τω) + ‖w1‖4q−4 2 + ‖Aν+1w2‖4q−4 ] , where c40 is dependent of λ;∫ U f ′2(u, x)uL,t ·A2νuNdx ≤ c42 ∫ U |uL,t| (1 + |u|p) |A2νuN |dx ≤ c43 (∫ U |uL,t|2dx )1/2(∫ U (1 + |u|pdx) 2n 4−4ν dx ) 4−4ν 2n (∫ U |A2νuN | 2n n+4ν−4 dx )n+4ν−4 2n ≤ c44 [ 1 +M2p 0 (θr−τω) ] + ε 16 ‖Aν+1uN‖2. From (4.26) and similar to (4.10), we have d dt yN (r) +m2(r)yN (r) ≤ q2(θr−τω), ∀r ≥ τ − t, (4.27) where yN = ‖Aν+1uN‖2 + ‖AνvN‖2 + 2 ∫ U [f(u, x)− f1(uL, x) + λu2]A2νuNdx, (4.28) m2(r) = ε 2 − c45‖w1(r)‖q−1 2 − c45‖uL(r)‖q−2 2 , q2(θr−τω) = c46[1 +M2q 0 (θr−τω) + z4(θr−τω) + ‖w1‖4q−4 2 + ‖Aν+1w2‖4q−4], yN (τ − t, τ − t, θ−τω, ϕτ−t(θ−τω)) ≤ ‖h‖22 · z2(θ−tω), 2 ∫ U [f(u, x)− f1(uL, x) + λuN ]A2νuNdx ≤ c47[1 +Mq+1 0 (θr−τω)], where c45, c46, and c47 are dependent of λ. Using the Gronwall’s inequality in (4.27), on [τ − t, r] (r ≥ τ − t), we have yN (r) ≤ yN (τ − t)e− ∫ r τ−tm2(s)ds + ∫ r τ−t q2(θξ−τω)e− ∫ r ξ m2(s)dsdξ. (4.29) Let T = T1 = 4c45K0 σ1ε in (4.18), for τ − t ≤ r ≤ τ , we have∫ τ r ‖w1(s)‖q−1 2 ds ≤ ε 4c45 (τ − r) + K̄, ‖Aν+1w2(r)‖q−1 ≤ K1M2(T1, ω). (4.30) EJDE-2022/10 DYNAMICS OF A PLATE MODEL WITH CRITICAL EXPONENT 17 For r ≥ ξ ≥ τ − t, from (4.30) and (4.32), we obtain that∫ τ ξ m2(s)ds = ∫ τ ξ ε 2 − c45‖w1(s)‖q−1 2 − c45‖uL(s)‖q−2 2 ds, ≥ ε 4 (τ − ξ)− c48, (4.31) where c48 = c45K̄ + c45 σ1(q−2)M q−2 L . So we have yN (τ − t)e− ∫ r τ−tm2(s)ds ≤ ‖h‖22z2(θ−tω)e− ε 4 t+c48 t→+∞−→ 0. (4.32) From (4.20), we obtain∫ −(m−1)T1 −mT1 ‖w1(r)‖4q−4 2 e ε 4 rdr ≤ ∫ −(m−1)T1 −mT1 M4q−4 1 (θ−mT1ω)e−(4q−4)σ1(r+mT1)e ε 4 rdr ≤ 4 ε e ε 4T1M4q−4 1 (θ−mT1 ω)e− ε 4mT1 , ∀m ≥ 1, and ∫ 0 −∞ ‖w1(r)‖4q−4 2 e ε 4 rdr = ( · · ·+ ∫ −(m−1)T1 −mT1 + · · ·+ ∫ −T1 −2T1 + ∫ 0 −T1 ) ‖w1‖4q−4 2 e ε 4 rdr ≤ 4 ε e ε 4T1 +∞∑ m=1 M4q−4 1 (θ−mT1 ω)e−εmT1/4. From [2], we know that M4q−4 1 (ω) is tempered and M4q−4 1 (θtω) is continuous in t, so we can find a tempered random variable ς(ω) (> 0) such that M4q−4 1 (θ−mT1ω) ≤ ς(ω)e ε 4q−4mT1 , ∀m ≥ 1, then we obtain∫ 0 −∞ ‖w1(r)‖4q−4 2 e ε 4 rdr ≤ ς(ω) 4 ε e ε 4T1 +∞∑ m=1 e ε(2−q) 4q−4 mT1 = 4 ε e ε 4q−4T1 1− e ε(2−q) 4q−4 T1 ς(ω) <∞. Hence∫ τ τ−t q2(θξ−τω)e− ∫ τ ξ m2(s)dsdξ ≤ c49 ∫ τ τ−t [ 1 +M2q 0 (θr−τω) + z4(θr−τω) + ‖w1‖4q−4 2 +M4 2 (T1, ω) ] e− ε 4 (τ−ξ)dξ ≤ c50 ( 1 +M4 2 (T1, ω) + ∫ 0 −∞ ( M2q 0 (θrω) + z4(θrω) + ‖w1(r)‖4q−4 2 ) e ε 4 rdr ) <∞, where c49 and c50 depend on λ. 18 L. WEN, L. YANG EJDE-2022/10 From (4.28), (4.29) and (4.32), for t ≥ 0, we can deduce that ‖Aν+1uN (τ, τ − t, θ−τω, ϕτ−t)‖2 + ‖AνvN (τ, τ − t, θ−τω, ϕτ−t)‖2 ≤ 2yN (τ, τ − t, θ−τω, ϕτ−t(θ−τω)) + 2c47[1 +Mq+1 0 (ω)] ≤ 2‖h‖22 · z2(θ−tω)e− ε 4 t+c48 + 2c51 [ 1 +Mq+1 0 (ω) ] + c52(1 +M4 2 (T1, ω). + ∫ 0 −∞ ( M2q 0 (θrω) + z4(θrω) + ‖w1(r)‖4q−4 2 ) e ε 4 rdr). (4.33) By (4.32), there exists a random variable tν(ω) ≥ 0 such that 0 ≤ 2‖h‖22 · z2(θ−tω)e− ε 4 t+c48 ≤ 1, ∀t ≥ tν(ω). (4.34) We denote M2 ν (ω) = c52 ( 1 +M4 2 (T1, ω) + ∫ 0 −∞ ( M2q 0 (θrω) + z4(θrω) + ‖w1(r)‖4q−4 2 ) e ε 4 rdr ) + 1 + 2c51 [ 1 +Mq+1 0 (ω) ] , (4.35) which is tempered, then we have (4.25) from (4.33) and (4.34). � Lemma 4.6. For any τ ∈ R, ω ∈ Ω, t ≥ 0, assume that Bν(τ, ω) ⊆ B1(τ, ω) ⊆ B0(ω) and Bν(τ, ω) ∈ D(Eν) where ν is same as in (4.8). Then there exist a random variable t̃ν(ω) > 0 and a tempered random variable M̃ν(ω) > 0 (indepen- dent of t and τ) such that the solution ϕ(τ, τ − t, θ−τω, ϕτ−t(θ−τω)) of (2.2) with ϕτ−t(θ−τω) ∈ Bν(τ − t, θ−tω) ⊆ B0(θ−tω) ∩ D(Eν) satisfies ‖ϕ(τ, τ − t, θ−τω, ϕτ−t(θ−τω))‖2Eν = ‖Aν+1u(τ, τ − t, θ−τω, ϕτ−t)‖2 + ‖Aνv(τ, τ − t, θ−τω, ϕτ−t)‖2 ≤ M̃2 ν (ω), ∀t ≥ t̃ν(ω). (4.36) Proof. We take the inner product ((2.2), A2νϕ)E with A2νϕ = (A2νu,A2νv)T, we obtain 1 2 d dt ( ‖Aν+1u‖2 + ‖Aνv‖2 + 2 ∫ U [f(u, x) + λu]A2νudx ) + (Λϕ,A2νϕ) + ε ∫ U [f(u, x) + λu]A2νudx− ∫ U [f ′u(u, x)ut + λut]A 2νudx = ( f(u, x) + λu,A2νh(x)z(θr−τω) ) + ( h(x)z(θr−τω), A2νu ) 2 + ( g(x, r) + εh(x)z(θr−τω), A2νv ) , ∀r ≥ τ − t. (4.37) Then, for r ≥ τ − t,∫ U [f ′(u, x)ut + λut]A 2νudx ≤ c43‖w1‖q−1 2 ( ‖Aν+1u‖2 + ‖Aνv‖2 ) + ε 16 ‖Aν+1u‖2 + c45 [ M4 0 (θr−τω) + z4(θr−τω) + ‖w1‖4q−4 2 + ‖Aν+1w2‖4q−4 ] ,∫ U [f(u, x) + λu]A2νudx ≤ c53 [ 1 +Mq+1 0 (θr−τω) ] , EJDE-2022/10 DYNAMICS OF A PLATE MODEL WITH CRITICAL EXPONENT 19 where c53 depends on λ. Similar to (4.27) by using (4.37), we obtain d dt ỹ1(r) + m̃1(r)ỹ1(r) ≤ q̃1(θr−τω), ∀r ≥ τ − t, (4.38) where ỹ1(r) = ‖Aν+1u‖2 + ‖Aνv‖2 + 2 ∫ U [f(u, x) + λu]A2νu dx, q̃1(θr−τω) = c54 [ 1 +M4 0 (θr−τω) + z4(θr−τω) + ‖w1‖4q−4 2 +M4 2 (T1, ω) ] , m̃1(r) = ε 2 − c47‖w1(r)‖q−1 2 . Using the Gronwall’s inequality in (4.38) on [τ − t, r] (r ≥ τ − t), we have ỹ1(r) ≤ ỹ1(τ − t)e− ∫ r τ−t m̃1(s)ds + ∫ r τ−t q̃1(θξ−τω)e− ∫ r ξ m̃1(s)dsdξ. (4.39) Same as (4.31), for τ ≥ ξ ≥ τ − t, we obtain that∫ τ ξ m̃1(s)ds ≥ ε 4 (τ − ξ)− c50, so ∫ τ τ−t q̃1(θξ−τω)e− ∫ τ ξ m̃1(s)dsdξ ≤ c55 ( 1 +M4 2 (T1, ω) + ∫ 0 −∞ ( M4 0 (θrω) + z4(θrω) + ‖w1(r)‖4q−4 2 ) e ε 4 rdr ) . From ϕτ−t(θ−τω) ∈ B0(θ−tω) ∩ D(Eν), we obtain ỹ1(τ − t)e− ∫ r τ−t m̃1(s)ds ≤ ( ‖Aν+1uτ−t‖2 + ‖Aνvτ−t‖2 + 2c53 [ 1 +Mq+1 0 (θr−τω) ]) e− ε 4 t+c50 t→+∞−→ 0. Hence, there exists a random variable t̃ν(ω) ≥ 0 satisfying 0 ≤ ỹ1(τ − t)e− ∫ τ τ−t m̃1(s)ds ≤ 1, ∀t ≥ t̃ν(ω). Based on (4.39), we obtain ‖Aν+1u(τ, τ − t, θ−τω, ϕτ−t)‖2 + ‖Aνv(τ, τ − t, θ−τω, ϕτ−t)‖2 ≤ 2ỹ1(τ, τ − t, θ−τω, ϕτ−t(θ−τω)) + 2c53[1 +Mq+1 0 (ω)] ≤ c55 ( 1 +M4 2 (T1, ω) + ∫ 0 −∞ ( M4 0 (θrω) + z4(θrω) + ‖w1(r)‖4q−4 2 ) e ε 4 rdr ) + 1 + 2c53 [ 1 +Mq+1 0 (ω) ] = M̃2 ν (ω), ∀t ≥ t̃ν(ω). (4.40) � Using Lemmas 4.1-4.6, by recursion we obtain the following result. Lemma 4.7. For any τ ∈ R, ω ∈ Ω, t ≥ 0, let Bκ(τ, ω) ⊆ B1(τ, ω), Bκ(τ, ω) ∈ D(Eκ) and ϕτ−t(θ−τω) ∈ Bκ(τ−t, θ−tω). Then there exist Tκ(ω) ≥ 0 and tempered random variables M̃κ(ω) > 0, Mκ(ω) > 0 (independent of t and τ) such that for t ≥ Tκ(ω), the solution ϕ(τ, τ − t, θ−τω, ϕτ−t(θ−τω)) of (2.2) satisfies 20 L. WEN, L. YANG EJDE-2022/10 (i) for ν ≤ κ ≤ 1, ‖ϕ(τ, τ − t, θ−τω, ϕτ−t(θ−τω))‖2Eκ = ‖Aκ+1u(τ, τ − t, θ−τω, ϕτ−t(θ−τω))‖2 + ‖Aκv(τ, τ − t, θ−τω, ϕτ−t(θ−τω))‖2 ≤ M̃2 κ(ω); (ii) for ν ≤ κ ≤ 1− ν, ‖ϕN (τ, τ − t, θ−τω, ϕτ−t(θ−τω))‖2Eκ+ν = ‖Aκ+ν+1uN (τ, τ − t, θ−τω, ϕτ−t)‖2 + ‖Aκ+νvN (τ, τ − t, θ−τω, ϕτ−t)‖2 ≤M2 κ(ω), (4.41) where ν is same as in (4.8). 5. Existence of a random attractor In this section, by applying [29, Lemma 3.7] and Lemma 4.7, show the existence of a random attractor for (1.1). Firstly, we consider the Lipschitz property of cocycle Φ on B1(τ, ω). For any τ ∈ R, ω ∈ Ω and any ϕjτ (ω) = (ujτ (ω), vjτ (ω)) ∈ B1(τ, ω), j = 1, 2, let ϕj(r) = ϕj(r, τ, ω, ϕjτ (ω)) = (uj(r), vj(r)), r ≥ τ, be solutions of (2.2) with initial data ϕjτ (ω), j = 1, 2, respectively, and let ψ(r) = ϕ1(r)− ϕ2(r) = (u1(r)− u2(r), v1(r)− v2(r)) = (ξ(r), η(r)). So that ψ̇ + Λψ = F (ϕ1, θrω, r)− F (ϕ2, θrω, r), r ≥ τ, ψτ (ω) = (ξτ , ητ ) = (ξτ , u1,1,τ − u2,1,τ + εξτ ) = (u1τ − u2τ , v1τ − v2τ ). (5.1) Lemma 5.1. There exists a tempered random variable C1(ω) > 0 such that for any τ ∈ R, t ≥ 0, and ω ∈ Ω, it holds ‖ϕ(t+ τ, τ, θ−τω, ϕ1τ (θ−τω))− ϕ(t+ τ, τ, θ−τω, ϕ2τ (θ−τω))‖E ≤ e ∫ t 0 C1(θsω)ds‖ϕ1τ − ϕ2τ‖E . (5.2) Proof. From (4.1), for r ≥ τ , we obtain ‖ϕ1(r)‖E ≤M0(θrω), ‖ϕ2(r)‖E ≤M0(θrω). Based on (5.1), we have the following inequality by taking the inner product (·, ·)E with ψ(r), d dt ‖ψ(r)‖2E ≤ (c56 2α ( 1 +M2q−2 0 (θr−τω) ) − ε+ λ ) ‖ψ(r)‖2E , ∀r ≥ τ. (5.3) Using Gronwall’s inequality on (5.3), we obtain ‖ϕ1(r)− ϕ2(r)‖2E ≤ ‖ϕ1τ − ϕ2τ‖2Ee ∫ r−τ 0 ( c562α (1+M2q−2 0 (θτ+sω))−ε+λ)ds, ∀r ≥ τ. As ω → θ−τω and r → t+ τ , (5.2) holds with C1(ω) = c56 2α ( 1 +M2q−2 0 (ω) ) + λ, 0 < E(C1(ω)) = c56 2α ( 1 + E[M2q−2 0 (ω)] ) + λ ≤ c56 2αc18 K0 + λ <∞. � EJDE-2022/10 DYNAMICS OF A PLATE MODEL WITH CRITICAL EXPONENT 21 Lemma 5.2. For any τ ∈ R, ω ∈ Ω, there exist a Tν(ω) ≥ 0, a random bounded ball B̃1(ω) of E1 with radius b1(ω), a positive number σ̃ and a tempered random variable Q̃(ω) > 0 such that the solution ϕ(τ, τ− t, θ−τω, ϕτ−t(θ−τω)) of (2.2) with initial data ϕτ−t(θ−τω) ∈ B1(τ − t, θ−tω), it holds that dE ( ϕ(τ, τ − t, θ−τω,B1(τ − t, θ−tω)), B̃1(ω) ) ≤ Q̃(θ−tω)e−σ̃t, t ≥ Tν(ω). Proof. Now we assume ϕτ−t(θ−τω) ∈ B1(τ − t, θ−tω), and K̃ν(ω) ⊂ Eν ⊂ E is the random ball of Eν with radius Mν(ω) defined in (4.35), here ν is same as in (4.8). By Lemma 4.4, we can deduce that for any t ≥ 0, dE ( ϕ(τ, τ − t, θ−τω,B1(τ − t, θ−tω)), K̃ν(ω) ) ≤MLe −σ1t. (5.4) For ϕτ−t(θ−τω) ∈ K̃ν(θ−tω), according to Lemmas 4.4–4.7, there exist t1ν(ω) ≥ 0 and a random ball K̃2ν(ω) of E2ν with the radius M2ν(ω) and satisfies dE ( ϕ(τ, τ − t, θ−τω, K̃ν(θ−tω)), K̃2ν(ω) ) ≤ P1ν(θ−tω)e−σ1t, t ≥ t1ν(ω), (5.5) where P 2 1ν(θ−tω) = c̃1 [ 1 +M4 ν (θ−tω) ] + 2‖h‖2 · |z(θ−tω)|2. From [29, Lemma 3.7], Lemma 5.1 and (5.4) and (5.5), there exists T1ν(ω) ≥ t1ν(ω) ≥ 0 (independent of τ), such that for t ≥ T1ν(ω), dE ( ϕ(τ, τ − t, θ−τω,B1(τ − t, θ−tω)), K̃2ν(ω) ) ≤ P2ν(θ−tω)e− a1 2 σ1t, where P2ν(θ−tω) = ML + P1ν(θ−(1−a1)tω) is tempered and 0 < a1 ≤ σ1 3 E[C1(ω)] + 4σ1 . There exists an integer k̃ ≥ 1 such that 1 − ν ≤ (k̃ − 1)ν < 1 when ν > 0 is a fixed positive constant. Repeating k̃ (≤ [ 1 ν ] + 2) steps as above recursion, we can obtain that there exist Tk̃ν(ω) > 0 (independent of τ) and a random ball B̃1(ω) of E1 with radius b1(ω) (defined in (4.41)) such that for t ≥ Tk̃ν(ω), dE ( ϕ(τ, τ − t, θ−τω,B1(τ − t, θ−tω)), B̃1(ω) ) ≤ Pk̃ν(θ−tω)e− a k̃−1 2 σ1t, (5.6) where 0 < aj ≤ aj−1 2 σ1 3 E[C1(ω)] + aj−1 2 σ1 + 3σ1 <∞, j = 2, · · · , k̃ − 1, Pk̃ν(θ−tω) = ML + P(k̃−1)ν(θ−(1−ak̃−1)tω), is tempered. � Combining Lemmas 2.3 and 5.2, the existence of a random attractor for the RDS Φ can be proved. Theorem 5.3. The cocycle Φ associated with (2.2) possesses a D(E)-pullback ran- dom attractor A ∈ D(E) such that for any τ ∈ R, ω ∈ Ω, A(τ, ω) ⊆ B̃1(ω)∩B0(ω) and ‖A(τ, ω)‖E1 = sup ϕ∈A(τ,ω) ‖ϕ‖E1 ≤ b1(ω), where b1(ω) is the radius of the bounded ball B̃1(ω) ⊂ E1. 22 L. WEN, L. YANG EJDE-2022/10 Proof. Since E1 ↪→ E is a compact embedding, from (5.6) we know that B̃1(ω) in Lemma 5.2 is a compact measurable D(E)-pullback attracting ball in E for any τ ∈ R and ω ∈ Ω. According to Lemma 2.3, the RDS Φ possesses a D(E)- pullback random attractor A ∈ D(E), that is for any τ ∈ R, ω ∈ Ω, and A(τ, ω) ⊆ B̃1(ω)∩B0(ω). Based on (4.35), (4.40) and (4.41), the radius b1(ω) of B̃1(ω) ⊂ E1 is given by b21(ω) = c57 ( 1 +M4k̃ 2 (T1, ω) +M (q+1)k̃ 0 (ω) ) + c58 ∫ 0 −∞ ( M4k̃ 0 (θrω) + |z(θrω)|4k̃ + ‖w1(r)‖(4q−4)k̃ 2 ) eεr/4dr. (5.7) � Acknowledgments. The authors express their gratitude to the anonymous referee for the valuable comments and suggestions.This research was partially supported by the NSFC grant (12071192). References [1] M. Al-Gharabli, S. Messaoudi; Existence and a general decay result for a plate equation with nonlinear damping and a logarithmic source term, J. Evol. Equ., 18 (2018), 105–125. [2] L. Arnold; Random Dynamical Systems, Springer-Verlag, Berlin, 1998. [3] T. Caraballo, P. Kloeden, B. Schmalfuss; Exponentially stable stationary solutions for sto- chastic evolution equations and their perturbation, Appl. Math. Optim., 50 (2004), 183–207. 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Existence of a random attractor Acknowledgments References