# Controllability of the impulsive semilinear beam equation with memory and delay

Controllability of the impulsive semilinear beam equation with memory and delay Abstract The semilinear beam equation with impulses, memory and delay is considered and its approximate controllability obtained. This is done by employing a technique that avoids fixed point theorems and pulling back the control solution to a fixed curve in a short time interval. Demonstrating, once again, that the controllability of a system is robust under the influence of impulses and delays. 1. Introduction Beams have been used since ancient times to reinforce structures such as bridges, buildings, and others. Through the millennia, understanding the dynamics and controllability of beams, including bending and vibration has been of great importance. Pioneering studies goes back to 1493, Leonardo da Vinci’s manucript that identified properly the stresses and strains in a beam subject to bending (Da Vinci & Ladislao, 1943) and Galileo Galilei’s writings that identified the principle of virtual work as a general law but made incorrect assumptions (Timoshenko, 1921). It was not until the late 17th century with the elasticity theory evolution that Leonhard Euler and Daniel Bernoulli provided a second-order spatial derivatives mathematical model that later, in 1921, Stephen Timoshenko improved by including a shear deformation and rotational inertia effects, obtaining fourth order mathematical model (see Timoshenko, 1921, 1922, 1953 for details). Nowadays, adjustments of the Timoshenko beam model, in mechanical engineering and nanotechnology design (Wang et al., 2006a, b), yield to the impulsive semilinear beam equations of the form (1.1) where the memory and delay provide information of the viscoelasticity property and response of the materials. In this article, we are exploring the approximate controllability on a bounded domain |${\it{\Omega}} \subseteq \mathbb{R}^{N} (N\geq1)$| of $$w_{tt} - 2\beta{\it{\Delta}} w_t + {\it{\Delta}}^{2}w = u(t,x) + f(t,w(t-r),w_{t}(t-r),u)+\displaystyle \int_{0}^{t}M(t-s)g(w(s-r,x)){\rm d}s,$$ (1.1) subjected to the initial-boundary conditions and impulses $$\left\{\begin{array}{ll} w(t,x)={\it{\Delta}} w (t,x)=0, &\mbox{in}\; (0, \tau) \times \partial {\it{\Omega}},\\ \begin{split} &w(s,x)=\phi_1(s,x),\\ &w_{t}(s,x)=\phi_2(s,x), \end{split} & \mbox{in} \; [-r,0] \times {\it{\Omega}},\\ w_{t}(t_{k}^{+},x) = w_{t}(t_{k}^{-},x)+I_{k}(t_k,w(t_{k},x),w_{t}(t_{k},x),u(t_{k},x)), &t \neq t_k, \; k=1, \dots, p, \end{array} \right.$$ (1.2) where |${\it{\Delta}} w=\sum_{j=1}^{N}\frac{\partial^2w}{\partial x_j^2}$| and |${\it{\Delta}}^2 w=\sum_{j=1}^{N}\frac{\partial^4w}{\partial x_j^4}$|⁠. Additionally, the damping coefficient |$\beta > 1$| and the real-valued functions |$w = w(t,x)$| in |$(0, \tau] \times {\it{\Omega}}$| represents the beam deflection, |$u$| in |$(0, \tau] \times {\it{\Omega}}$| is the distributed control, |$M$| acts as convolution kernel with respect to the time variable, the impulses |$I_k$| are defined on |$[0, \tau] \times \mathbb{R}^3$| and the nonlinearities |$g$| on |$\mathbb{R}$|⁠, |$f$| on |$[0, \tau] \times \mathbb{R}^3$|⁠. Under the assumptions: H|$_1$||$M\in L^{\infty}((0,\tau)\times {\it{\Omega}})$|⁠, and |$g, f, I_{k}$| are smooth enough, in order that, for all |$\phi, \psi\in \mathcal{C}([-r,0],L^{2}({\it{\Omega}}))$| and |$u\in L^{2}([0,\tau]; L^{2}({\it{\Omega}}))$| the equation (1.1) admits only one mild solution on |$[-r,\tau]$|⁠. H|$_2$||$t\!\in\! [0,\tau],$||$a, b \geq \!0$| and |$u, v, y \in \mathbb{R}$|⁠, the nonlinearity |$f$| satisfies $$\begin{array}{ll} |f(t,y,v,u)| & \leq a\sqrt{|y |^2+ |v |^2} +b. \end{array}$$ (1.3) Abada et al. (2010) and Jain & Dhakne (2013) works showed the existence of solutions for impulsive evolution equations with delays. Balachandran et al. (2011) supplied existence results for the fractional impulsive integrodifferential equations and finally for the Beam equation with variable coefficients. Límaco et al. (2005) showed the existence and uniqueness of nonlocal strong solutions and the existence of a unique global weak solution with decay rate energy. Inspired in a series of papers from Carrasco et al. (2013, 2014, 2016) and the works on the approximate controllability for the semilinear heat and strongly damped wave equations with memory and delays by Guevara & Leiva (2016, 2017). We prove the approximate controllability of the beam equation (1.1) under the initial-boundary condition (1.2) with memory, impulses and delay terms by applying Bashirov & Ghahramanlou (2014, 2015, 2013); Bashirov et al. (2010), and avoiding the Rothe’s fixed point theorem used in Carrasco et al. (2013, 2016) and the Schauder fixed point theorem applied in Carrasco et al. (2014). The structure of this article is as follow: In section 2, we present the abstract formulation of the beam equation (1.1). Section 3, recalls the linear controllability characterization of the problem. In section 4, the approximated controllability of the beam equation with memory, delay and impulses is proved. 2. Abstract formulation of the problem In this section, we choose the appropriate Hilbert space where the Cauchy problem (1.1)–(1.2) can be written as an abstract differential equation. First of all, notice that the term |$-2\beta{\it{\Delta}} w_t$| in the equation (1.1) acts as a damping force, thus the energy space used to set up the wave equation is not suitable here. Even so, in de Oliveira (1998) shows that the uncontrolled linear equation can be transformed into a system of parabolic equations of the form |$w_{t} = D {\it{\Delta}} w$|⁠, obtaining that corresponding space for the abstract formulation of the problem is |$\mathcal{Z}^{1}=\left[H^{2}({\it{\Omega}}) \bigcap H^{1}_{0}({\it{\Omega}}) \right] \times L^{2}({\it{\Omega}})$| and proving that the linear part of this system generates a strongly continuous analytic semigroup in this space. Consider the Hilbert space |$\mathcal{X} = L^{2}({\it{\Omega}})$|⁠, and denote |$\mathcal{A}=-{\it{\Delta}}$| with eigenvalues |$0 < \lambda_{1}<\lambda_{2}< \cdots <\lambda_{j}\to \infty,$| with multiplicity |$\gamma_{j}<\infty$| equal to its corresponding eigenspace dimension. Recall, |$\mathcal{A}$| satisfies the following properties: (i) There exists a complete orthonormal set |$\left\{ \phi_{j_k} \right\}$| of eigenvectors of |$\mathcal{A}$|⁠. (ii) For all |$x \in D(\mathcal{A})$|⁠, \begin{equation*} \mathcal{A} x = \sum_{j = 1}^{\infty} \lambda_{j} \sum_{k = 1}^{\gamma_j} {\langle{\xi, \phi_{j_k}}\rangle} \phi_{j_k} =\sum_{j = 1}^{\infty} \lambda_{j}E_{j}x, \end{equation*} where |${\langle{\cdot, \cdot}\rangle}$| denotes the inner product in |$\mathcal{X}$|⁠, |$E_{n}x = \sum_{k = 1}^{\gamma_j} {\langle{z, \phi_{j_k}}\rangle} \phi_{j_k},$| and |$\{ E_j \}$| is a family of complete orthogonal projections in |$\mathcal{X}$|⁠. (iii) |$-\mathcal{A}$| generates an analytic semigroup |$\{ S(t) \}_{t \geq 0}$| given by $$S(t)x = \sum_{j = 1}^{\infty} e^{-\lambda_j t}E_{j}x \quad \mbox{and} \quad {\left\|{S(t)}\right\|} \leq e^{-\lambda_{1}t}.$$ (iv) For |$\alpha\geq0$| the fractional powered spaces |$\mathcal{X}^{\alpha}$| are given by \begin{equation*} \mathcal{X}^{\alpha} =D(\mathcal{A}^{\alpha}) = \left\{x \in \mathcal{X} : \sum_{j = 1}^{\infty} \lambda_{j} ^{2 \alpha} {\left\|{ E_{j}x}\right\|}^2 < \infty \right\} \end{equation*} equipped with the norm |${\left\|{x}\right\|}_{\alpha}^2 = {\left\|{\mathcal{A}^{\alpha}x}\right\|}^2= \sum_{j = 1}^{\infty} \lambda_{j}^{2 \alpha} {\left\|{ E_{j}x}\right\|}^2$|⁠, where |$\mathcal{A}^{\alpha}x = \sum_{j = 1}^{\infty} \lambda_{j}^{ \alpha} E_{j}x$|⁠. In particular, |$\alpha=2$| yields |$\mathcal{A}^{2}x = \sum_{j = 1}^{\infty} \lambda_{j}^{ 2} E_{j}x=(-{\it{\Delta}})^2x={\it{\Delta}}^2x$|⁠. And for |$\alpha=1,$| the Hilbert space |$\mathcal{Z}^{1}=\mathcal{X}^{1}\times \mathcal{X}$| has the norm $$\displaystyle {\left\| {\left( \begin{array}{c} w \\ v \\ \end{array} \right)}\right\|}^{2}_{\mathcal{Z}^{1}}=\|w\|^{2}_{1}+\|v\|^{2}.$$ Using the above notation, we rewrite the system (1.1)–(1.2) as the second-order ordinary differential equations in the Hilbert space |$\mathcal{X}$| $$\left\{ \begin{array}{ll} \begin{split} w''(t) = &-\mathcal{A}^{2}w(t) - 2\beta \mathcal{A} w'(t) + u(t)+ \displaystyle \int_{0}^{t}M(t,s)g^{e}(w(s-r)){\rm d}s \\ &\ \ + f^{e}(t,w(t-r),w'(t-r),u(t)), \end{split} & t>0,t \neq t_k,\\ \begin{split} w(s) &= \phi_1(s), \\ w'(s)&=\phi_2(s), \end{split} &s \in [-r,0],\\ w' (t_{k}^{+}) = w' (t_{k}^{-})+I^{e}_{k}(t_k,w(t_{k}),w' (t_{k}),u(t_{k},)), & k=1, \dots, p, \end{array} \right.$$ (2.4) where |$\mathcal{U}=\mathcal{X}=L^{2}({\it{\Omega}})$|⁠, and \begin{eqnarray*} I_{k}^{e}:&[0, \tau]\times \mathcal{Z}^{1} \times \mathcal{U} &\longrightarrow \qquad \mathcal{X} \\ &(t,w,v,u)(\cdot)&\longmapsto \quad I_{k}(t,w(\cdot),v(\cdot),u(\cdot)),\\[-32pt] \end{eqnarray*} \begin{eqnarray*} f^{e}:&[0, \tau]\times \mathcal{C} (-r,0; \mathcal{Z}^{1} ) \times \mathcal{U} & \longrightarrow \qquad \mathcal{X}\\ &(t,{\it{\Phi}},u)(\cdot)&\longmapsto \quad f(t,\phi_1(-r, \cdot),\phi_2(-r, \cdot),u(\cdot)), \end{eqnarray*} and \begin{eqnarray*} g^{e}:&\mathcal{C}(-r,0; \mathcal{Z}^{1} ) &\longrightarrow \mathcal{Z}^{1} \\ &{\it{\Phi}}=\left(\begin{array}{c} \phi_1\\ \phi_2 \end{array}\right)&\longmapsto g(\phi_1(\cdot-r)). \end{eqnarray*} Changing variables, |$v=w',$| the systems (2.4) can be written as an abstract first order functional differential equations with memory, impulses and delay in |$\mathcal{Z}^{1}$| $$\left\{ \begin{array}{lr} z' = -\mathbb{A} z+ \mathbb{B} u + \displaystyle \int_{0}^{t}\mathbb{M}_g(t,s ,z_{s}(-r))ds + \mathbb{F}(t,z_{t}(-r),u(s)) ,& z\in Z^{1},\; t\geq 0, \\ z(s) = {\it{\Phi}}(s), & s \in [-r,0],\\ z(t_{k}^{+}) = z(t_{k}^{-})+\mathbb{I}_{k}(t_k, z(t_{k}),u(t_{k})), & k=1,2,3, \dots, p, \end{array} \right.$$ (2.5) where |$z = \left( {\matrix{w \cr v \cr} } \right)$|⁠, |${\it{\Phi}} = \left( {\matrix{{{\phi _1}} \cr{{\phi _2}} \cr} } \right) \in {\cal C}\left( { - r,0;{{\cal Z}^1}} \right),$||$u\in L^{2}(0,\tau;\mathcal{U})$|⁠, $$\mathbb{A} = \left( \begin{array}{rr} 0 & I_{\mathcal{X}} \\ - \mathcal{A}^2 & -2\beta \mathcal{A} \end{array}\right)$$ is a unbounded linear operator with domain $$D(\mathbb{A})=\{w\in H^{4}({\it{\Omega}}):\:w={\it{\Delta}} w=0\}\times D(\mathcal{A}),$$ and |$I_{\mathcal{X}}$| being the identity in |$\mathcal{X}$|⁠. |$\mathbb{B}: \mathcal{U} \longrightarrow \mathcal{Z}^{1}$| is the bounded linear operator defined by |$u = \left( {\matrix{ 0 \cr u \cr} } \right),$| and the functions \begin{eqnarray*} \mathbb{I}_{k}:&[0, \tau]\times \mathcal{Z}^{1} \times \mathcal{U}& \longrightarrow \qquad \mathcal{Z}^{1} \\ &(t, z,u)&\longmapsto \quad \left(\begin{array}{c} 0\\ I_{k}^{e}(t,w,v,u) \end{array}\right)\\[-28pt] \end{eqnarray*} \begin{eqnarray} \mathbb{F}:& [0, \tau] \times \mathcal{C}(-r,0; \mathcal{Z}^{1} ) \times \mathcal{U} & \longrightarrow \qquad \mathcal{Z}^{1}\\ &(t, {\it{\Phi}},u)&\longmapsto \quad \left( \begin{array}{c} 0 \\f^{e}(t,\phi_1(-r),\phi_2(-r),u) \end{array} \right),\notag \end{eqnarray} (2.6) and \begin{eqnarray*} \mathbb{M}_g:&[0,\tau]\times [0,\tau]\times \mathcal{C}(-r,0; \mathcal{Z}^{1} ) &\longrightarrow \mathcal{Z}^{1} \\ &(t,s,{\it{\Phi}})&\longmapsto \left( \begin{array}{c} 0 \\M(t,s) g^{e}({\it{\Phi}}) \end{array} \right). \end{eqnarray*} Moreover, this abstract formulation together with condition (1.3) and the continuous embedding |$\mathcal{X}^1 \subset \mathcal{X}$| yields Proposition 2.1 There exist constants |$\tilde{a},\tilde{b}>0$| such that, for all |$(t, {\it{\Phi}},u) \in [0, \tau] \times \mathcal{C}(-r,0; \mathcal{Z}^{1} ) \times \mathcal{U}$| the following inequality holds $${\left\|{\mathbb{F}(t,{\it{\Phi}},u)}\right\|}_{\mathcal{Z}^{1}} \leq \tilde{a}\| {\it{\Phi}}(-r) \|_{\mathcal{Z}^1}+\tilde{b}.$$ (2.7) Carrasco et al. (2013, Theorem 2.1) proved that the linear unbounded operator |$\mathbb{A}$| generates a strongly continuous compact semigroup in the space |$\mathcal{Z}^1$| which decays exponentially to zero, precisely: Proposition 2.2 The operator |$\mathcal{A}$| is the infinitesimal generator of a strongly continuous compact semigroup |$\{T(t)\}_{t\geq0}$| represented by $$T(t)z=\displaystyle\sum_{j=1}^{\infty}e^{\mathbb{A}_{j}t}P_{j}z,\qquad z\in \mathcal{Z}^{1},\;t\geq 0,$$ (2.8) where |$\{P_{j}\}_{j\geq0}$| is a complete family of orthogonal projections in the Hilbert space |$\mathcal{Z}^{1}$| given by $$P_{j} = diag(E_{j},E_{j}),$$ (2.9) and $$\mathbb{A}_{j}=K_{j}P_{j},\qquad K_{j}=\left( \begin{array}{cc} 0 & 1 \\ -\lambda_{j}^{2} & -2\beta\lambda_{j} \\ \end{array} \right)\!,\qquad j\geq 1,$$ and there exists |$M \geq 1$| and |$\mu >0$| such that $$\parallel T(t)\parallel\leq Me^{-\mu t},\qquad t\geq0.$$ 3. Approximate controllability of the linear system This section is devoted to characterize the approximate controllability of the linear system. Thus, for all |$z_{0}\in \mathcal{Z}^{1}$| and |$u\in L^{2}([0,\tau];\mathcal{U})$| consider the initial value problem $$\left\{ \begin{array}{lll} z'(t) = \mathbb{A} z(t) + \mathbb{B} u(t),\\ z(t_{0}) = z_{0}, \end{array} \right.$$ (3.10) obtained from (2.5). It admits only one mild solution on |$0\leq t_{0}\leq t\leq \tau$| given by $$z(t)=T(t-t_{0})z_{0} + \displaystyle\int_{t_{0}}^{t}T(t-s)\mathbb{B} u(s){\rm d}s.$$ (3.11) Definition 3.1. (Approximate controllability of (3.10)) The system (3.10) is said to be approximately controllable on |$[t_{0},\tau]$| if for every |$z_0$|⁠, |$z_1\in \mathcal{Z}$|⁠, |$\varepsilon>0$| there exists |$u\in L^{2}(t_{0},\tau;\mathcal{U})$| such that the solution |$z(t)$| of (3.11) corresponding to |$u$| verifies: $$\|z(\tau)-z_1\|<\varepsilon.$$ For the system (3.10) and |$\tau>0$|⁠, we have the following notions: (1) |$G_{\tau\delta}$| is the controllability operator defined by \begin{eqnarray*} G_{\tau\delta}: L^2(\tau-\delta,\tau;\mathcal{U}) \longrightarrow& \mathcal{Z}^{1}\\ u\longmapsto&\displaystyle \int_{\tau-\delta}^{\tau}T(\tau-s)\mathbb{B} u(s){\rm d}s, \end{eqnarray*} (2.1) with corresponding adjoint |$G^*_{\tau\delta}$| given by \begin{eqnarray*} G^*_{\tau\delta}: \mathcal{Z}^{1} \longrightarrow& L^2(\tau-\delta,\tau;\mathcal{U})\\ z\longmapsto& \mathbb{B} ^{*}T^{*}(\tau-\cdot)z. \end{eqnarray*} (2) The Gramian controllability operator is \begin{equation*} Q_{\tau \delta*} = G_{\tau\delta}G_{\tau\delta}^{*}= \int_{\tau-\delta}^{\tau}T(\tau-t)\mathbb{B} \mathbb{B} ^{*}T^{*}(\tau-t){\rm d}t. \end{equation*} In general, for linear bounded operator |$G$| between Hilbert spaces |$\mathcal{W}$| and |$\mathcal{Z}$|⁠, the following lemma holds (see Bashirov & Kerimov, 1997, Bashirov & Mahmudov, 1999, Leiva et al., 2013). Lemma 3.1. The approximate controllability of the linear system (3.10) on |$[\tau-\delta,\tau]$| is equivalent to any of the following statements (a) |$\overline{Rang(G_{\tau\delta})}=\mathcal{Z}^{1}.$| (b) |$\ker(G_{\tau\delta}^{*})={0}.$| (c) For |$0\neq z \in\ Z^{1}, \ \ {\langle{ Q_{\tau\delta}z,z}\rangle}>0.$| The controllability of the linear system (3.10) on |$[0,\tau]$| was proved by Carrasco et al. (2013). Theorem 3.1 and Lemma 3.2 characterized the controllability of the system (3.10), their proofs and details can be found in Bashirov & Kerimov (1997), Bashirov & Mahmudov (1999), Curtain & Pritchard (1978), Curtain & Zwart (1995), Leiva et al. (2013). Theorem 3.1. The system (3.10) is approximately controllable on |$[0,\tau]$| if and only if any one of the following conditions hold: (1) |$\displaystyle\lim_{\alpha \to 0^+} \alpha(\alpha I +Q_{\tau\delta}^{*})^{-1}z =0$|⁠. (2) If |$z\in Z^{1}$|⁠, |$0<\alpha \leq 1$| and |$u_{\alpha}=G_{\tau\delta}^{*}(\alpha I + Q_{\tau\delta}^{*})^{-1}z$|⁠, then $$G_{\tau\delta}u_{\alpha}=z - \alpha(\alpha I+ Q_{\tau\delta})^{-1}z \quad \mbox{and} \quad \displaystyle\lim_{\alpha\to 0}G_{\tau\delta}u_{\alpha}=z.$$ Moreover, for each |$v\in L^{2}([\tau-\delta,\tau];\mathcal{U})$|⁠, the sequence of controls $$u_{\alpha}=G_{\tau\delta}^{*}(\alpha I + Q_{\tau\delta}^{*})^{-1}z + (v-G_{\tau\delta}^{*}(\alpha I + Q_{\tau\delta}^{*})^{-1}G_{\tau\delta}v),$$ satisfies $$G_{\tau\delta}u_{\alpha}=z-\alpha(\alpha I + Q_{\tau\delta}^{*})^{-1}(z-G_{\tau\delta}v) \quad \mbox{and} \quad \displaystyle\lim_{\alpha\to 0}G_{\tau\delta}u_{\alpha}=z,$$ with the error |$E_{\tau\delta}z=\alpha(\alpha I + Q_{\tau\delta})^{-1}(z+G_{\tau\delta}v),\;\alpha\in(0,1].$| Theorem 3.1 indicates that the family of linear operators |${\it{\Gamma}}_{\tau\delta}=G_{\tau\delta}^{*}(\alpha I + Q_{\tau\delta}^{*})^{-1}$| is an approximate right inverse for the |$G_{\tau\delta}$|⁠, in the sense that $$\displaystyle\lim_{\alpha\longrightarrow 0}G_{\tau\delta}{\it{\Gamma}}_{\tau\delta}=I,$$ in the strong topology. Lemma 3.2 |$Q_{\tau\delta}> 0$|⁠, if and only if, the linear system (3.10) is controllable on |$[\tau-\delta, \tau]$|⁠. Moreover, for given initial state |$y_0$| and final state |$z_{1}$|⁠, there exists a sequence of controls |$\{u_{\alpha}^{\delta}\}_{0 <\alpha \leq 1}$| in the space |$L^2(\tau-\delta,\tau;\mathcal{U})$|⁠, defined by $$u_{\alpha}=u_{\alpha}^{\delta}= G_{\tau\delta}^{*}(\alpha I+ G_{\tau\delta}G_{\tau\delta}^{*})^{-1}(z_{1} - T(\tau)y_0),$$ such that the solutions |$y(t)=y(t,\tau-\delta, y_0, u_{\alpha}^{\delta})$| of the initial value problem $$\left\{ \begin{array}{l} y'=\mathbb{A} y+\mathbb{B} u_{\alpha}(t), \ \ y \in \mathcal{Z}^{1}, \ \ t>0,\\ y(\tau-\delta) = y_0, \end{array} \right.$$ (3.12) satisfies $$\lim_{\alpha \to 0^{+}}y(\tau) = \lim_{\alpha \to 0^{+}}\left(T(\delta)y_0 + \int_{\tau-\delta}^{\tau}T(\tau-s)\mathbb{B} u_{\alpha}(s)ds \right)= z_{1}.$$ (3.13) 4. Controllability of the semilinear system This section is devoted to prove the main result of this paper, the approximate controllability of the beam equation (Theorem 4.1), which is it is equivalent to prove the controllability of the abstract system (2.5) under the condition (2.7). Recall, Definition 4.1. (Approximate controllability) The system (2.5) is said to be approximately controllable on |$[0,\tau]$| if for every |$\epsilon>0$|⁠, every |${\it{\Phi}}\in \mathcal{C}\left(-r,0; \mathcal{Z}^{1} \right)$| and a given initial state |$z_{1}\in \mathcal{Z}^{1}$| there exists |$u\in L^{2}(0,\tau;\mathcal{U})$|⁠, such that, the corresponding mild solution \begin{align} z^{u}(t) &= \displaystyle T(t){\it{\Phi}}(0)+\int_{0}^{t}T(t-s)\left[\mathbb{B} u(s)+\left(\int_{0}^{s}\mathbb{M}_g(s,l,z(l-r))dl\right)\right]{\rm d}s \\ & \quad{} + \displaystyle \int_{0}^{t}T(t-s)\mathbb{F}(s,z(s-r),u(s))ds + \sum_{0 < t_k < t} T(t-t_k )\mathbb{I}_{k}(t_k,z(t_k), u(t_k)), \nonumber \end{align} (4.14) satisfies |$z(0)={\it{\Phi}}(0)$| and $$\left\| {{ z^u(\tau) - z_{1}}} \right\|_{\mathcal{Z}^1}<\epsilon.$$ (4.15) The approach to obtain (4.15) consist in construct a sequence of controls conducting the system from the initial condition |${\it{\Phi}}$| to a small ball around |$z_1.$| This is achieved taking advantage of the delay, which allows us to pullback the corresponding family of solutions to a fixed trajectory in short time interval. Now, we are ready to present the proof of our main result. Theorem 4.1. Under the condition (1.3) the impulsive semilinear beam equation with memory and delay (1.1)–(1.2) is approximately controllable on |$[0,\tau]$|⁠. Let |$\epsilon>0$|⁠, and given |${\it{\Phi}}\in \mathcal{C}$| and a final state |$z_{1}$|⁠. By section 2, we have that the semilinear beam equation in consideration can be represented as the abstract system (2.5) under the condition (2.7). Thus, consider any |$u\in L^{2}([0,\tau];\mathcal{U})$| and the corresponding mild solution (4.14) of the initial value problem (3.12), denoted by |$z(t)=z(t,0,{\it{\Phi}},u)$|⁠. For |$0\leq\alpha \leq 1,$| define the control |$u_{\alpha}^{\delta}\in L^{2}([0,\tau];\mathcal{U})$| as follows, $$u_{\alpha}^{\delta}(t)=\left\{\begin{array}{ccl} u(t), &&0\leq t\leq \tau-\delta, \\ u_{\alpha}(t), &\quad& \tau-\delta\leq t\leq \tau, \end{array}\right.$$ with |$u_{\alpha}= \mathbb{B}^{*}T^{*}(\tau-t)(\alpha I+ G_{\tau\delta}G_{\tau\delta}^{*})^{-1}(z_{1} - T(\delta)z(\tau-\delta)).$| For, |$0<\delta<\tau-t_{p}$| its corresponding mild solution at time |$\tau$| can be written as follows: \begin{eqnarray*} \displaystyle z^{\delta,\alpha}(\tau) &=& \displaystyle T(\tau){\it{\Phi}}(0) +\int_{0}^{\tau}T(\tau-s) \left[ \mathbb{B} u_{\alpha}^{\delta} (s) + \int_0^s \mathbb{M}_g(z^{\delta,\alpha}(l-r))dl\right]{\rm d}s+ \\ &&+ \int_{0}^{\tau}T(\tau-s)\mathbb{F}(s,z^{\delta,\alpha}(s-r),u_{\alpha}^{\delta}(s))ds+ \sum_{0 < t_k < \tau} T(t-t_k )\mathbb{I}_{k}(t_k,z^{\delta,\alpha}(t_k), u_{\alpha}^{\delta}(t_k))\\ &=&T(\delta)\left\{T(\tau-\delta){\it{\Phi}}(0) +\int_{0}^{\tau-\delta}T(\tau-\delta-s) \left(\mathbb{B} u_{\alpha}^{\delta} (s)+\mathbb{F}(s,z^{\delta,\alpha}(s-r),u_{\alpha}^{\delta}(s))\right){\rm d}s\right.\\ &&+\int_{0}^{\tau-\delta}T(\tau-\delta-s) \int_0^s \mathbb{M}_g(s,l, z^{\delta,\alpha}(l-r)){\rm d}l{\rm d}s\\ &&\left.+ \sum_{0 < t_k < \tau-\delta} T(t-\delta-t_k )\mathbb{I}_{k}(t_k,z^{\delta,\alpha}(t_k), u_{\alpha}^{\delta}(t_k))\right\}+\\ && + \int_{\tau-\delta}^{\tau}T(\tau-s)\left(\mathbb{B} u_{\alpha}(s)+ \mathbb{F}(s,z^{\delta,\alpha}(s-r),u_{\alpha}^{\delta}(s))+\int_0^s\mathbb{M}_g(s,l,z^{\delta,\alpha}(l-r))dl\right){\rm d}s. \end{eqnarray*} (4.16) Therefore, \begin{align*} z^{\delta,\alpha}(\tau) & = T(\delta)z(\tau-\delta)+ \int_{\tau-\delta}^{\tau}T(\tau-s)\left(\mathbb{B} u_{\alpha}(s)+ \mathbb{F}(s,z^{\delta,\alpha}(s-r),u_{\alpha}^{\delta}(s))\right){\rm d}s \\ &\quad{} + \int_{\tau-\delta}^{\tau}T(\tau-s)\int_0^s\mathbb{M}_g(s,l,z^{\delta,\alpha}(l-r)){\rm d}l{\rm d}s. \end{align*} Observing that the corresponding solution |$y^{\delta,\alpha}(t)=y(t,\tau-\delta,z(\tau-\delta),u_{\alpha})$| of the initial value problem (2.5) at time |$\tau$| is: $$y^{\delta,\alpha}(\tau)=T(\delta)z(\tau-\delta)+ \int_{\tau-\delta}^{\tau}T(\tau-s)\mathbb{B}_{\varpi} u_{\alpha}(s){\rm d}s,$$ yields, $$z^{\delta,\alpha}(\tau)-y^{\delta,\alpha}(\tau)= \int_{\tau-\delta}^{\tau}T(\tau-s)\left(\int_{0}^{s}\mathbb{F}(s,z^{\delta,\alpha}(s-r),u_{\alpha}^{\delta}(s))+\mathbb{M}_g(s,l,z^{\delta,\alpha}(l-r))dl)\right){\rm d}s,$$ and together with condition (2.7), we obtain \begin{align*} \left\| {{ z^{\delta,\alpha}(\tau)-y^{\delta,\alpha}(\tau)}} \right\| & \leq \int_{\tau-\delta}^{\tau} \left\| {{ T(\tau-s)}} \right\|\left( \tilde{a}\left\| {{{\it{\Phi}}(s-r)}} \right\|+\tilde{b}\right){\rm d}s \\ &\quad{} + \int_{\tau-\delta}^{\tau}\left\| {{ T(\tau-s)}} \right\|\int_{0}^{s}\left\| {{\mathbb{M}_g(s,l,z^{\delta,\alpha}(l-r))}} \right\|{\rm d}l{\rm d}s. \end{align*} Observe that |$0< \delta< r$| and |$\tau-\delta \leq s\leq \tau$|⁠, thus $$l-r \leq s-r \leq \tau-r< \tau-\delta.$$ Therefore, |$z^{\delta,\alpha}(l-r)=z(l-r)$| and |$z^{\delta,\alpha}(s-r)=z(s-r),$| implying that for |$\epsilon>0,$| there exists |$\delta>0$| such that \begin{align*} \left\| {{z^{\delta,\alpha}(\tau)-y^{\delta,\alpha}(\tau)}} \right\| & \leq \int_{\tau-\delta}^{\tau}\left\| {{ T(\tau-s)}} \right\|\left( \tilde{a}{\left\|{z(s-r)}\right\|}+\tilde{b}\right){\rm d}s \\ &\quad + \int_{\tau-\delta}^{\tau}{\left\|{T(\tau-s)}\right\|}\int_{0}^{s}{\left\|{ \mathbb{M}_g(s,l,z(l-r))}\right\|} {\rm d}l{\rm d}s \\ & < \displaystyle\frac{\epsilon}{2}. \end{align*} Additionally, for |$0<\alpha <1$|⁠, Lemma 3.2 (3.13) yields $${\left\|{ y^{\delta,\alpha}(\tau)-z_{1}}\right\|} < \frac{\epsilon}{2}.$$ Thus, $$\begin{array}{lll} {\left\|{ z^{\delta,\alpha}(\tau)-z_{1}}\right\|} & \leq & \left\| {{ z^{\delta,\alpha}(\tau)-y^{\delta,\alpha}(\tau)}} \right\| + {\left\|{ y^{\delta,\alpha}(\tau)-z_{1}}\right\|} < \frac{\epsilon}{2}+ \frac{\epsilon}{2}=\epsilon, \end{array}$$ which completes our proof. 5. Final remarks We believe this technique can be applied for controlling diffusion processes systems involving compact semigroups. In particular, our result can be formulated in a more general setting for the semilinear evolution equation with impulses, delay and memory in a Hilbert space |$\mathcal{Z}$| \begin{equation*} \left\{ \begin{array}{lr} z' = -\mathbb{A} z+ \mathbb{B} u + \displaystyle \int_{0}^{t}\mathbb{M}_g(t,s ,z(s-r))ds + \mathbb{F}(t,z_{t}(-r),u(s)) ,& z\in Z^{1},\; t\geq 0, \\ z(s) = {\it{\Phi}}(s), & s \in [-r,0],\\ z(t_{k}^{+}) = z(t_{k}^{-})+\mathbb{I}_{k}(t_k, z(t_{k}),u(t_{k})), & k=1,2, \dots, p, \end{array} \right. \end{equation*} where |$u\in L^{2}(0,\tau;\mathcal{U})$|⁠, |$\mathcal{U}$| is another Hilbert space, |$\mathbb{B} :\mathcal{U} \longrightarrow \mathcal{Z}$| is a bounded linear operator, |$\mathbb{I}_{k}, \mathbb{F}:[0, \tau]\times \mathcal{C}(-r,0; \mathcal{Z}) \times \mathcal{U} \rightarrow \mathcal{Z}$|⁠, |$\mathbb{A} :D(\mathbb{A}) \subset \mathcal{Z} \rightarrow \mathcal{Z}$| is an unbounded linear operator in |$\mathcal{Z}$| that generates a strongly continuous semigroup (Leiva, 2003, Lemma 2.1) \begin{equation*} T(t)z =\sum_{nj=1}^{\infty}e^{\mathbb{A}_{j}t}P_jz \mbox{, } \ \ z\in \mathcal{Z} \mbox{, } \ \ t \geq 0, \end{equation*} where |$\left\{ P_j\right\} _{j \geq 0}$| is a complete family of orthogonal projections in the Hilbert space |$\mathcal{Z}$| and \begin{equation*} \|\mathbb{F}(t,{\it{\Phi}},u) \|_{\mathcal{Z}} \leq \tilde{a} \|{\it{\Phi}}(-r)\|_{\mathcal{Z}} +\tilde{b}, \end{equation*} for all |$(t, {\it{\Phi}}, u) \in [0, \tau]\times \mathcal{C}(-r,0; \mathcal{Z} ) \times \mathcal{U}.$| Acknowledgements The authors are thankful to the anonymous referees for valuable comments that help improve the quality of the article. This work has been supported by Louisiana State University, Universidad YachayTech and Universidad Centroccidental Lisandro Alvarado. References Abada N. , Benchohra M. & Hammouche H. ( 2010 ) Existence results for semilinear differential evolution equations with impulses and delay . Cubo , 12 , 1 – 17 . Google Scholar Crossref Search ADS Balachandran K. , Kiruthika S. & Trujillo J. ( 2011 ) Existence results for fractional impulsive integrodifferential equations in banach spaces . Commun. Nonlinear Sci. Numer. Simul. , 16 , 1970 – 1977 . Google Scholar Crossref Search ADS Bashirov A. E. & Ghahramanlou N. ( 2014 ) On partial approximate controllability of semilinear systems . Cogent Eng. , 1 , 965947 . Google Scholar Crossref Search ADS Bashirov A. E. & Ghahramanlou N. ( 2015 ) On partial S-controllability of semilinear partially observable systems . Int. J. Control , 88 , 969 – 982 , 2015 . Google Scholar Crossref Search ADS Bashirov A. E. & Jneid M. ( 2013 ) On partial complete controllability of semilinear systems. Abstract and Applied Analysis , Vol. 2013 . Hindawi Publishing Corporation . doi:10.1155/2013/521052 . Bashirov A. E. & Kerimov K. R. ( 1997 ) On controllability conception for stochastic systems . SIAM SIAM J. Control Optim. , 35 , 384 – 398 . Google Scholar Crossref Search ADS Bashirov A. E. & Mahmudov N. I. ( 1999 ) On concepts of controllability for deterministic and stochastic systems . SIAM J. Control Optim. , 37 , 1808 – 1821 . Google Scholar Crossref Search ADS Bashirov A. E. , Etikan H. & Șemi N. ( 2010 ) Partial controllability of stochastic linear systems . Int. J. Control , 83 , 2564 – 2572 . Google Scholar Crossref Search ADS Carrasco A. , Leiva H. & Merentes N. ( 2016 ) Controllability of the perturbed beam equation . IMA J. Math. Control Inform. , 33 , 603 – 615 . Google Scholar Crossref Search ADS Carrasco A. , Leiva H. & Sanchez J. ( 2013 ) Controllability of the semilinear beam equation . J. Dyn. 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( 2013 ) On mild solutions of nonlocal semilinear impulsive functional integro-differential equations . Appl. Math. E-Notes , 13 , 109 – 119 . Leiva H. ( 2003 ) A lemma on |$C_0$|-semigroups and applications . Quaest. Math. , 26 , 247 – 265 . Google Scholar Crossref Search ADS Leiva H. , Merentes N. & Sanchez J. ( 2013 ) A characterization of semilinear dense range operators and applications. Abstract and Applied Analysis , Vol. 2013 . Hindawi Publishing Corporation. doi:10.1155/2013/729093 . Límaco J. , Clark H. & Feitosa A. ( 2005 ) Beam evolution equation with variable coefficients . Math. Methods Appl. Sci. , 28 , 457 – 478 . Google Scholar Crossref Search ADS De Oliveira L. A. F. ( 1998 ) On reaction-diffusion systems . Electron. J. Dier. Equ. , 1 – 10 . Timoshenko S. P. ( 1921 ) On the correction for shear of the differential equation for transverse vibrations of prismatic bars . Lond. Edinb. Dubl. Phil. Mag. J. Sci. , 41 , 744 – 746 . Google Scholar Crossref Search ADS Timoshenko S. P. ( 1922 ) On the transverse vibrations of bars of uniform cross-section . Lond. Edinb. Dubl. Phil. Mag. J. Sci. , 43 , 125 – 131 . Google Scholar Crossref Search ADS Timoshenko S. ( 1953 ) History of strength of materials: with a brief account of the history of theory of elasticity and theory of structures . New York : Courier Corporation & Dover Publications, INC . Wang C. , Tan V. & Zhang Y. ( 2006a ) Timoshenko beam model for vibration analysis of multi-walled carbon nanotubes. J. Sound Vib., 294 , 1060 – 1072 . Wang C. , Zhang Y. , Ramesh S. S. & Kitipornchai S. ( 2006b ) Buckling analysis of micro-and nano-rods/tubes based on nonlocal timoshenko beam theory . J. Phys. D , 39 , 3904 . Google Scholar Crossref Search ADS © The authors 2017. Published by Oxford University Press on behalf of the Institute of Mathematics and its Applications. All rights reserved. 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# Controllability of the impulsive semilinear beam equation with memory and delay

IMA Journal of Mathematical Control and Information, Volume 36 (1) – Mar 22, 2019
11 pages

/lp/ou_press/controllability-of-the-impulsive-semilinear-beam-equation-with-memory-ytahcX8KBZ
Publisher
Oxford University Press
ISSN
0265-0754
eISSN
1471-6887
DOI
10.1093/imamci/dnx042
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### Abstract

Abstract The semilinear beam equation with impulses, memory and delay is considered and its approximate controllability obtained. This is done by employing a technique that avoids fixed point theorems and pulling back the control solution to a fixed curve in a short time interval. Demonstrating, once again, that the controllability of a system is robust under the influence of impulses and delays. 1. Introduction Beams have been used since ancient times to reinforce structures such as bridges, buildings, and others. Through the millennia, understanding the dynamics and controllability of beams, including bending and vibration has been of great importance. Pioneering studies goes back to 1493, Leonardo da Vinci’s manucript that identified properly the stresses and strains in a beam subject to bending (Da Vinci & Ladislao, 1943) and Galileo Galilei’s writings that identified the principle of virtual work as a general law but made incorrect assumptions (Timoshenko, 1921). It was not until the late 17th century with the elasticity theory evolution that Leonhard Euler and Daniel Bernoulli provided a second-order spatial derivatives mathematical model that later, in 1921, Stephen Timoshenko improved by including a shear deformation and rotational inertia effects, obtaining fourth order mathematical model (see Timoshenko, 1921, 1922, 1953 for details). Nowadays, adjustments of the Timoshenko beam model, in mechanical engineering and nanotechnology design (Wang et al., 2006a, b), yield to the impulsive semilinear beam equations of the form (1.1) where the memory and delay provide information of the viscoelasticity property and response of the materials. In this article, we are exploring the approximate controllability on a bounded domain |${\it{\Omega}} \subseteq \mathbb{R}^{N} (N\geq1)$| of $$w_{tt} - 2\beta{\it{\Delta}} w_t + {\it{\Delta}}^{2}w = u(t,x) + f(t,w(t-r),w_{t}(t-r),u)+\displaystyle \int_{0}^{t}M(t-s)g(w(s-r,x)){\rm d}s,$$ (1.1) subjected to the initial-boundary conditions and impulses $$\left\{\begin{array}{ll} w(t,x)={\it{\Delta}} w (t,x)=0, &\mbox{in}\; (0, \tau) \times \partial {\it{\Omega}},\\ \begin{split} &w(s,x)=\phi_1(s,x),\\ &w_{t}(s,x)=\phi_2(s,x), \end{split} & \mbox{in} \; [-r,0] \times {\it{\Omega}},\\ w_{t}(t_{k}^{+},x) = w_{t}(t_{k}^{-},x)+I_{k}(t_k,w(t_{k},x),w_{t}(t_{k},x),u(t_{k},x)), &t \neq t_k, \; k=1, \dots, p, \end{array} \right.$$ (1.2) where |${\it{\Delta}} w=\sum_{j=1}^{N}\frac{\partial^2w}{\partial x_j^2}$| and |${\it{\Delta}}^2 w=\sum_{j=1}^{N}\frac{\partial^4w}{\partial x_j^4}$|⁠. Additionally, the damping coefficient |$\beta > 1$| and the real-valued functions |$w = w(t,x)$| in |$(0, \tau] \times {\it{\Omega}}$| represents the beam deflection, |$u$| in |$(0, \tau] \times {\it{\Omega}}$| is the distributed control, |$M$| acts as convolution kernel with respect to the time variable, the impulses |$I_k$| are defined on |$[0, \tau] \times \mathbb{R}^3$| and the nonlinearities |$g$| on |$\mathbb{R}$|⁠, |$f$| on |$[0, \tau] \times \mathbb{R}^3$|⁠. Under the assumptions: H|$_1$||$M\in L^{\infty}((0,\tau)\times {\it{\Omega}})$|⁠, and |$g, f, I_{k}$| are smooth enough, in order that, for all |$\phi, \psi\in \mathcal{C}([-r,0],L^{2}({\it{\Omega}}))$| and |$u\in L^{2}([0,\tau]; L^{2}({\it{\Omega}}))$| the equation (1.1) admits only one mild solution on |$[-r,\tau]$|⁠. H|$_2$||$t\!\in\! [0,\tau],$||$a, b \geq \!0$| and |$u, v, y \in \mathbb{R}$|⁠, the nonlinearity |$f$| satisfies $$\begin{array}{ll} |f(t,y,v,u)| & \leq a\sqrt{|y |^2+ |v |^2} +b. \end{array}$$ (1.3) Abada et al. (2010) and Jain & Dhakne (2013) works showed the existence of solutions for impulsive evolution equations with delays. Balachandran et al. (2011) supplied existence results for the fractional impulsive integrodifferential equations and finally for the Beam equation with variable coefficients. Límaco et al. (2005) showed the existence and uniqueness of nonlocal strong solutions and the existence of a unique global weak solution with decay rate energy. Inspired in a series of papers from Carrasco et al. (2013, 2014, 2016) and the works on the approximate controllability for the semilinear heat and strongly damped wave equations with memory and delays by Guevara & Leiva (2016, 2017). We prove the approximate controllability of the beam equation (1.1) under the initial-boundary condition (1.2) with memory, impulses and delay terms by applying Bashirov & Ghahramanlou (2014, 2015, 2013); Bashirov et al. (2010), and avoiding the Rothe’s fixed point theorem used in Carrasco et al. (2013, 2016) and the Schauder fixed point theorem applied in Carrasco et al. (2014). The structure of this article is as follow: In section 2, we present the abstract formulation of the beam equation (1.1). Section 3, recalls the linear controllability characterization of the problem. In section 4, the approximated controllability of the beam equation with memory, delay and impulses is proved. 2. Abstract formulation of the problem In this section, we choose the appropriate Hilbert space where the Cauchy problem (1.1)–(1.2) can be written as an abstract differential equation. First of all, notice that the term |$-2\beta{\it{\Delta}} w_t$| in the equation (1.1) acts as a damping force, thus the energy space used to set up the wave equation is not suitable here. Even so, in de Oliveira (1998) shows that the uncontrolled linear equation can be transformed into a system of parabolic equations of the form |$w_{t} = D {\it{\Delta}} w$|⁠, obtaining that corresponding space for the abstract formulation of the problem is |$\mathcal{Z}^{1}=\left[H^{2}({\it{\Omega}}) \bigcap H^{1}_{0}({\it{\Omega}}) \right] \times L^{2}({\it{\Omega}})$| and proving that the linear part of this system generates a strongly continuous analytic semigroup in this space. Consider the Hilbert space |$\mathcal{X} = L^{2}({\it{\Omega}})$|⁠, and denote |$\mathcal{A}=-{\it{\Delta}}$| with eigenvalues |$0 < \lambda_{1}<\lambda_{2}< \cdots <\lambda_{j}\to \infty,$| with multiplicity |$\gamma_{j}<\infty$| equal to its corresponding eigenspace dimension. Recall, |$\mathcal{A}$| satisfies the following properties: (i) There exists a complete orthonormal set |$\left\{ \phi_{j_k} \right\}$| of eigenvectors of |$\mathcal{A}$|⁠. (ii) For all |$x \in D(\mathcal{A})$|⁠, \begin{equation*} \mathcal{A} x = \sum_{j = 1}^{\infty} \lambda_{j} \sum_{k = 1}^{\gamma_j} {\langle{\xi, \phi_{j_k}}\rangle} \phi_{j_k} =\sum_{j = 1}^{\infty} \lambda_{j}E_{j}x, \end{equation*} where |${\langle{\cdot, \cdot}\rangle}$| denotes the inner product in |$\mathcal{X}$|⁠, |$E_{n}x = \sum_{k = 1}^{\gamma_j} {\langle{z, \phi_{j_k}}\rangle} \phi_{j_k},$| and |$\{ E_j \}$| is a family of complete orthogonal projections in |$\mathcal{X}$|⁠. (iii) |$-\mathcal{A}$| generates an analytic semigroup |$\{ S(t) \}_{t \geq 0}$| given by $$S(t)x = \sum_{j = 1}^{\infty} e^{-\lambda_j t}E_{j}x \quad \mbox{and} \quad {\left\|{S(t)}\right\|} \leq e^{-\lambda_{1}t}.$$ (iv) For |$\alpha\geq0$| the fractional powered spaces |$\mathcal{X}^{\alpha}$| are given by \begin{equation*} \mathcal{X}^{\alpha} =D(\mathcal{A}^{\alpha}) = \left\{x \in \mathcal{X} : \sum_{j = 1}^{\infty} \lambda_{j} ^{2 \alpha} {\left\|{ E_{j}x}\right\|}^2 < \infty \right\} \end{equation*} equipped with the norm |${\left\|{x}\right\|}_{\alpha}^2 = {\left\|{\mathcal{A}^{\alpha}x}\right\|}^2= \sum_{j = 1}^{\infty} \lambda_{j}^{2 \alpha} {\left\|{ E_{j}x}\right\|}^2$|⁠, where |$\mathcal{A}^{\alpha}x = \sum_{j = 1}^{\infty} \lambda_{j}^{ \alpha} E_{j}x$|⁠. In particular, |$\alpha=2$| yields |$\mathcal{A}^{2}x = \sum_{j = 1}^{\infty} \lambda_{j}^{ 2} E_{j}x=(-{\it{\Delta}})^2x={\it{\Delta}}^2x$|⁠. And for |$\alpha=1,$| the Hilbert space |$\mathcal{Z}^{1}=\mathcal{X}^{1}\times \mathcal{X}$| has the norm $$\displaystyle {\left\| {\left( \begin{array}{c} w \\ v \\ \end{array} \right)}\right\|}^{2}_{\mathcal{Z}^{1}}=\|w\|^{2}_{1}+\|v\|^{2}.$$ Using the above notation, we rewrite the system (1.1)–(1.2) as the second-order ordinary differential equations in the Hilbert space |$\mathcal{X}$| $$\left\{ \begin{array}{ll} \begin{split} w''(t) = &-\mathcal{A}^{2}w(t) - 2\beta \mathcal{A} w'(t) + u(t)+ \displaystyle \int_{0}^{t}M(t,s)g^{e}(w(s-r)){\rm d}s \\ &\ \ + f^{e}(t,w(t-r),w'(t-r),u(t)), \end{split} & t>0,t \neq t_k,\\ \begin{split} w(s) &= \phi_1(s), \\ w'(s)&=\phi_2(s), \end{split} &s \in [-r,0],\\ w' (t_{k}^{+}) = w' (t_{k}^{-})+I^{e}_{k}(t_k,w(t_{k}),w' (t_{k}),u(t_{k},)), & k=1, \dots, p, \end{array} \right.$$ (2.4) where |$\mathcal{U}=\mathcal{X}=L^{2}({\it{\Omega}})$|⁠, and \begin{eqnarray*} I_{k}^{e}:&[0, \tau]\times \mathcal{Z}^{1} \times \mathcal{U} &\longrightarrow \qquad \mathcal{X} \\ &(t,w,v,u)(\cdot)&\longmapsto \quad I_{k}(t,w(\cdot),v(\cdot),u(\cdot)),\\[-32pt] \end{eqnarray*} \begin{eqnarray*} f^{e}:&[0, \tau]\times \mathcal{C} (-r,0; \mathcal{Z}^{1} ) \times \mathcal{U} & \longrightarrow \qquad \mathcal{X}\\ &(t,{\it{\Phi}},u)(\cdot)&\longmapsto \quad f(t,\phi_1(-r, \cdot),\phi_2(-r, \cdot),u(\cdot)), \end{eqnarray*} and \begin{eqnarray*} g^{e}:&\mathcal{C}(-r,0; \mathcal{Z}^{1} ) &\longrightarrow \mathcal{Z}^{1} \\ &{\it{\Phi}}=\left(\begin{array}{c} \phi_1\\ \phi_2 \end{array}\right)&\longmapsto g(\phi_1(\cdot-r)). \end{eqnarray*} Changing variables, |$v=w',$| the systems (2.4) can be written as an abstract first order functional differential equations with memory, impulses and delay in |$\mathcal{Z}^{1}$| $$\left\{ \begin{array}{lr} z' = -\mathbb{A} z+ \mathbb{B} u + \displaystyle \int_{0}^{t}\mathbb{M}_g(t,s ,z_{s}(-r))ds + \mathbb{F}(t,z_{t}(-r),u(s)) ,& z\in Z^{1},\; t\geq 0, \\ z(s) = {\it{\Phi}}(s), & s \in [-r,0],\\ z(t_{k}^{+}) = z(t_{k}^{-})+\mathbb{I}_{k}(t_k, z(t_{k}),u(t_{k})), & k=1,2,3, \dots, p, \end{array} \right.$$ (2.5) where |$z = \left( {\matrix{w \cr v \cr} } \right)$|⁠, |${\it{\Phi}} = \left( {\matrix{{{\phi _1}} \cr{{\phi _2}} \cr} } \right) \in {\cal C}\left( { - r,0;{{\cal Z}^1}} \right),$||$u\in L^{2}(0,\tau;\mathcal{U})$|⁠, $$\mathbb{A} = \left( \begin{array}{rr} 0 & I_{\mathcal{X}} \\ - \mathcal{A}^2 & -2\beta \mathcal{A} \end{array}\right)$$ is a unbounded linear operator with domain $$D(\mathbb{A})=\{w\in H^{4}({\it{\Omega}}):\:w={\it{\Delta}} w=0\}\times D(\mathcal{A}),$$ and |$I_{\mathcal{X}}$| being the identity in |$\mathcal{X}$|⁠. |$\mathbb{B}: \mathcal{U} \longrightarrow \mathcal{Z}^{1}$| is the bounded linear operator defined by |$u = \left( {\matrix{ 0 \cr u \cr} } \right),$| and the functions \begin{eqnarray*} \mathbb{I}_{k}:&[0, \tau]\times \mathcal{Z}^{1} \times \mathcal{U}& \longrightarrow \qquad \mathcal{Z}^{1} \\ &(t, z,u)&\longmapsto \quad \left(\begin{array}{c} 0\\ I_{k}^{e}(t,w,v,u) \end{array}\right)\\[-28pt] \end{eqnarray*} \begin{eqnarray} \mathbb{F}:& [0, \tau] \times \mathcal{C}(-r,0; \mathcal{Z}^{1} ) \times \mathcal{U} & \longrightarrow \qquad \mathcal{Z}^{1}\\ &(t, {\it{\Phi}},u)&\longmapsto \quad \left( \begin{array}{c} 0 \\f^{e}(t,\phi_1(-r),\phi_2(-r),u) \end{array} \right),\notag \end{eqnarray} (2.6) and \begin{eqnarray*} \mathbb{M}_g:&[0,\tau]\times [0,\tau]\times \mathcal{C}(-r,0; \mathcal{Z}^{1} ) &\longrightarrow \mathcal{Z}^{1} \\ &(t,s,{\it{\Phi}})&\longmapsto \left( \begin{array}{c} 0 \\M(t,s) g^{e}({\it{\Phi}}) \end{array} \right). \end{eqnarray*} Moreover, this abstract formulation together with condition (1.3) and the continuous embedding |$\mathcal{X}^1 \subset \mathcal{X}$| yields Proposition 2.1 There exist constants |$\tilde{a},\tilde{b}>0$| such that, for all |$(t, {\it{\Phi}},u) \in [0, \tau] \times \mathcal{C}(-r,0; \mathcal{Z}^{1} ) \times \mathcal{U}$| the following inequality holds $${\left\|{\mathbb{F}(t,{\it{\Phi}},u)}\right\|}_{\mathcal{Z}^{1}} \leq \tilde{a}\| {\it{\Phi}}(-r) \|_{\mathcal{Z}^1}+\tilde{b}.$$ (2.7) Carrasco et al. (2013, Theorem 2.1) proved that the linear unbounded operator |$\mathbb{A}$| generates a strongly continuous compact semigroup in the space |$\mathcal{Z}^1$| which decays exponentially to zero, precisely: Proposition 2.2 The operator |$\mathcal{A}$| is the infinitesimal generator of a strongly continuous compact semigroup |$\{T(t)\}_{t\geq0}$| represented by $$T(t)z=\displaystyle\sum_{j=1}^{\infty}e^{\mathbb{A}_{j}t}P_{j}z,\qquad z\in \mathcal{Z}^{1},\;t\geq 0,$$ (2.8) where |$\{P_{j}\}_{j\geq0}$| is a complete family of orthogonal projections in the Hilbert space |$\mathcal{Z}^{1}$| given by $$P_{j} = diag(E_{j},E_{j}),$$ (2.9) and $$\mathbb{A}_{j}=K_{j}P_{j},\qquad K_{j}=\left( \begin{array}{cc} 0 & 1 \\ -\lambda_{j}^{2} & -2\beta\lambda_{j} \\ \end{array} \right)\!,\qquad j\geq 1,$$ and there exists |$M \geq 1$| and |$\mu >0$| such that $$\parallel T(t)\parallel\leq Me^{-\mu t},\qquad t\geq0.$$ 3. Approximate controllability of the linear system This section is devoted to characterize the approximate controllability of the linear system. Thus, for all |$z_{0}\in \mathcal{Z}^{1}$| and |$u\in L^{2}([0,\tau];\mathcal{U})$| consider the initial value problem $$\left\{ \begin{array}{lll} z'(t) = \mathbb{A} z(t) + \mathbb{B} u(t),\\ z(t_{0}) = z_{0}, \end{array} \right.$$ (3.10) obtained from (2.5). It admits only one mild solution on |$0\leq t_{0}\leq t\leq \tau$| given by $$z(t)=T(t-t_{0})z_{0} + \displaystyle\int_{t_{0}}^{t}T(t-s)\mathbb{B} u(s){\rm d}s.$$ (3.11) Definition 3.1. (Approximate controllability of (3.10)) The system (3.10) is said to be approximately controllable on |$[t_{0},\tau]$| if for every |$z_0$|⁠, |$z_1\in \mathcal{Z}$|⁠, |$\varepsilon>0$| there exists |$u\in L^{2}(t_{0},\tau;\mathcal{U})$| such that the solution |$z(t)$| of (3.11) corresponding to |$u$| verifies: $$\|z(\tau)-z_1\|<\varepsilon.$$ For the system (3.10) and |$\tau>0$|⁠, we have the following notions: (1) |$G_{\tau\delta}$| is the controllability operator defined by \begin{eqnarray*} G_{\tau\delta}: L^2(\tau-\delta,\tau;\mathcal{U}) \longrightarrow& \mathcal{Z}^{1}\\ u\longmapsto&\displaystyle \int_{\tau-\delta}^{\tau}T(\tau-s)\mathbb{B} u(s){\rm d}s, \end{eqnarray*} (2.1) with corresponding adjoint |$G^*_{\tau\delta}$| given by \begin{eqnarray*} G^*_{\tau\delta}: \mathcal{Z}^{1} \longrightarrow& L^2(\tau-\delta,\tau;\mathcal{U})\\ z\longmapsto& \mathbb{B} ^{*}T^{*}(\tau-\cdot)z. \end{eqnarray*} (2) The Gramian controllability operator is \begin{equation*} Q_{\tau \delta*} = G_{\tau\delta}G_{\tau\delta}^{*}= \int_{\tau-\delta}^{\tau}T(\tau-t)\mathbb{B} \mathbb{B} ^{*}T^{*}(\tau-t){\rm d}t. \end{equation*} In general, for linear bounded operator |$G$| between Hilbert spaces |$\mathcal{W}$| and |$\mathcal{Z}$|⁠, the following lemma holds (see Bashirov & Kerimov, 1997, Bashirov & Mahmudov, 1999, Leiva et al., 2013). Lemma 3.1. The approximate controllability of the linear system (3.10) on |$[\tau-\delta,\tau]$| is equivalent to any of the following statements (a) |$\overline{Rang(G_{\tau\delta})}=\mathcal{Z}^{1}.$| (b) |$\ker(G_{\tau\delta}^{*})={0}.$| (c) For |$0\neq z \in\ Z^{1}, \ \ {\langle{ Q_{\tau\delta}z,z}\rangle}>0.$| The controllability of the linear system (3.10) on |$[0,\tau]$| was proved by Carrasco et al. (2013). Theorem 3.1 and Lemma 3.2 characterized the controllability of the system (3.10), their proofs and details can be found in Bashirov & Kerimov (1997), Bashirov & Mahmudov (1999), Curtain & Pritchard (1978), Curtain & Zwart (1995), Leiva et al. (2013). Theorem 3.1. The system (3.10) is approximately controllable on |$[0,\tau]$| if and only if any one of the following conditions hold: (1) |$\displaystyle\lim_{\alpha \to 0^+} \alpha(\alpha I +Q_{\tau\delta}^{*})^{-1}z =0$|⁠. (2) If |$z\in Z^{1}$|⁠, |$0<\alpha \leq 1$| and |$u_{\alpha}=G_{\tau\delta}^{*}(\alpha I + Q_{\tau\delta}^{*})^{-1}z$|⁠, then $$G_{\tau\delta}u_{\alpha}=z - \alpha(\alpha I+ Q_{\tau\delta})^{-1}z \quad \mbox{and} \quad \displaystyle\lim_{\alpha\to 0}G_{\tau\delta}u_{\alpha}=z.$$ Moreover, for each |$v\in L^{2}([\tau-\delta,\tau];\mathcal{U})$|⁠, the sequence of controls $$u_{\alpha}=G_{\tau\delta}^{*}(\alpha I + Q_{\tau\delta}^{*})^{-1}z + (v-G_{\tau\delta}^{*}(\alpha I + Q_{\tau\delta}^{*})^{-1}G_{\tau\delta}v),$$ satisfies $$G_{\tau\delta}u_{\alpha}=z-\alpha(\alpha I + Q_{\tau\delta}^{*})^{-1}(z-G_{\tau\delta}v) \quad \mbox{and} \quad \displaystyle\lim_{\alpha\to 0}G_{\tau\delta}u_{\alpha}=z,$$ with the error |$E_{\tau\delta}z=\alpha(\alpha I + Q_{\tau\delta})^{-1}(z+G_{\tau\delta}v),\;\alpha\in(0,1].$| Theorem 3.1 indicates that the family of linear operators |${\it{\Gamma}}_{\tau\delta}=G_{\tau\delta}^{*}(\alpha I + Q_{\tau\delta}^{*})^{-1}$| is an approximate right inverse for the |$G_{\tau\delta}$|⁠, in the sense that $$\displaystyle\lim_{\alpha\longrightarrow 0}G_{\tau\delta}{\it{\Gamma}}_{\tau\delta}=I,$$ in the strong topology. Lemma 3.2 |$Q_{\tau\delta}> 0$|⁠, if and only if, the linear system (3.10) is controllable on |$[\tau-\delta, \tau]$|⁠. Moreover, for given initial state |$y_0$| and final state |$z_{1}$|⁠, there exists a sequence of controls |$\{u_{\alpha}^{\delta}\}_{0 <\alpha \leq 1}$| in the space |$L^2(\tau-\delta,\tau;\mathcal{U})$|⁠, defined by $$u_{\alpha}=u_{\alpha}^{\delta}= G_{\tau\delta}^{*}(\alpha I+ G_{\tau\delta}G_{\tau\delta}^{*})^{-1}(z_{1} - T(\tau)y_0),$$ such that the solutions |$y(t)=y(t,\tau-\delta, y_0, u_{\alpha}^{\delta})$| of the initial value problem $$\left\{ \begin{array}{l} y'=\mathbb{A} y+\mathbb{B} u_{\alpha}(t), \ \ y \in \mathcal{Z}^{1}, \ \ t>0,\\ y(\tau-\delta) = y_0, \end{array} \right.$$ (3.12) satisfies $$\lim_{\alpha \to 0^{+}}y(\tau) = \lim_{\alpha \to 0^{+}}\left(T(\delta)y_0 + \int_{\tau-\delta}^{\tau}T(\tau-s)\mathbb{B} u_{\alpha}(s)ds \right)= z_{1}.$$ (3.13) 4. Controllability of the semilinear system This section is devoted to prove the main result of this paper, the approximate controllability of the beam equation (Theorem 4.1), which is it is equivalent to prove the controllability of the abstract system (2.5) under the condition (2.7). Recall, Definition 4.1. (Approximate controllability) The system (2.5) is said to be approximately controllable on |$[0,\tau]$| if for every |$\epsilon>0$|⁠, every |${\it{\Phi}}\in \mathcal{C}\left(-r,0; \mathcal{Z}^{1} \right)$| and a given initial state |$z_{1}\in \mathcal{Z}^{1}$| there exists |$u\in L^{2}(0,\tau;\mathcal{U})$|⁠, such that, the corresponding mild solution \begin{align} z^{u}(t) &= \displaystyle T(t){\it{\Phi}}(0)+\int_{0}^{t}T(t-s)\left[\mathbb{B} u(s)+\left(\int_{0}^{s}\mathbb{M}_g(s,l,z(l-r))dl\right)\right]{\rm d}s \\ & \quad{} + \displaystyle \int_{0}^{t}T(t-s)\mathbb{F}(s,z(s-r),u(s))ds + \sum_{0 < t_k < t} T(t-t_k )\mathbb{I}_{k}(t_k,z(t_k), u(t_k)), \nonumber \end{align} (4.14) satisfies |$z(0)={\it{\Phi}}(0)$| and $$\left\| {{ z^u(\tau) - z_{1}}} \right\|_{\mathcal{Z}^1}<\epsilon.$$ (4.15) The approach to obtain (4.15) consist in construct a sequence of controls conducting the system from the initial condition |${\it{\Phi}}$| to a small ball around |$z_1.$| This is achieved taking advantage of the delay, which allows us to pullback the corresponding family of solutions to a fixed trajectory in short time interval. Now, we are ready to present the proof of our main result. Theorem 4.1. Under the condition (1.3) the impulsive semilinear beam equation with memory and delay (1.1)–(1.2) is approximately controllable on |$[0,\tau]$|⁠. Let |$\epsilon>0$|⁠, and given |${\it{\Phi}}\in \mathcal{C}$| and a final state |$z_{1}$|⁠. By section 2, we have that the semilinear beam equation in consideration can be represented as the abstract system (2.5) under the condition (2.7). Thus, consider any |$u\in L^{2}([0,\tau];\mathcal{U})$| and the corresponding mild solution (4.14) of the initial value problem (3.12), denoted by |$z(t)=z(t,0,{\it{\Phi}},u)$|⁠. For |$0\leq\alpha \leq 1,$| define the control |$u_{\alpha}^{\delta}\in L^{2}([0,\tau];\mathcal{U})$| as follows, $$u_{\alpha}^{\delta}(t)=\left\{\begin{array}{ccl} u(t), &&0\leq t\leq \tau-\delta, \\ u_{\alpha}(t), &\quad& \tau-\delta\leq t\leq \tau, \end{array}\right.$$ with |$u_{\alpha}= \mathbb{B}^{*}T^{*}(\tau-t)(\alpha I+ G_{\tau\delta}G_{\tau\delta}^{*})^{-1}(z_{1} - T(\delta)z(\tau-\delta)).$| For, |$0<\delta<\tau-t_{p}$| its corresponding mild solution at time |$\tau$| can be written as follows: \begin{eqnarray*} \displaystyle z^{\delta,\alpha}(\tau) &=& \displaystyle T(\tau){\it{\Phi}}(0) +\int_{0}^{\tau}T(\tau-s) \left[ \mathbb{B} u_{\alpha}^{\delta} (s) + \int_0^s \mathbb{M}_g(z^{\delta,\alpha}(l-r))dl\right]{\rm d}s+ \\ &&+ \int_{0}^{\tau}T(\tau-s)\mathbb{F}(s,z^{\delta,\alpha}(s-r),u_{\alpha}^{\delta}(s))ds+ \sum_{0 < t_k < \tau} T(t-t_k )\mathbb{I}_{k}(t_k,z^{\delta,\alpha}(t_k), u_{\alpha}^{\delta}(t_k))\\ &=&T(\delta)\left\{T(\tau-\delta){\it{\Phi}}(0) +\int_{0}^{\tau-\delta}T(\tau-\delta-s) \left(\mathbb{B} u_{\alpha}^{\delta} (s)+\mathbb{F}(s,z^{\delta,\alpha}(s-r),u_{\alpha}^{\delta}(s))\right){\rm d}s\right.\\ &&+\int_{0}^{\tau-\delta}T(\tau-\delta-s) \int_0^s \mathbb{M}_g(s,l, z^{\delta,\alpha}(l-r)){\rm d}l{\rm d}s\\ &&\left.+ \sum_{0 < t_k < \tau-\delta} T(t-\delta-t_k )\mathbb{I}_{k}(t_k,z^{\delta,\alpha}(t_k), u_{\alpha}^{\delta}(t_k))\right\}+\\ && + \int_{\tau-\delta}^{\tau}T(\tau-s)\left(\mathbb{B} u_{\alpha}(s)+ \mathbb{F}(s,z^{\delta,\alpha}(s-r),u_{\alpha}^{\delta}(s))+\int_0^s\mathbb{M}_g(s,l,z^{\delta,\alpha}(l-r))dl\right){\rm d}s. \end{eqnarray*} (4.16) Therefore, \begin{align*} z^{\delta,\alpha}(\tau) & = T(\delta)z(\tau-\delta)+ \int_{\tau-\delta}^{\tau}T(\tau-s)\left(\mathbb{B} u_{\alpha}(s)+ \mathbb{F}(s,z^{\delta,\alpha}(s-r),u_{\alpha}^{\delta}(s))\right){\rm d}s \\ &\quad{} + \int_{\tau-\delta}^{\tau}T(\tau-s)\int_0^s\mathbb{M}_g(s,l,z^{\delta,\alpha}(l-r)){\rm d}l{\rm d}s. \end{align*} Observing that the corresponding solution |$y^{\delta,\alpha}(t)=y(t,\tau-\delta,z(\tau-\delta),u_{\alpha})$| of the initial value problem (2.5) at time |$\tau$| is: $$y^{\delta,\alpha}(\tau)=T(\delta)z(\tau-\delta)+ \int_{\tau-\delta}^{\tau}T(\tau-s)\mathbb{B}_{\varpi} u_{\alpha}(s){\rm d}s,$$ yields, $$z^{\delta,\alpha}(\tau)-y^{\delta,\alpha}(\tau)= \int_{\tau-\delta}^{\tau}T(\tau-s)\left(\int_{0}^{s}\mathbb{F}(s,z^{\delta,\alpha}(s-r),u_{\alpha}^{\delta}(s))+\mathbb{M}_g(s,l,z^{\delta,\alpha}(l-r))dl)\right){\rm d}s,$$ and together with condition (2.7), we obtain \begin{align*} \left\| {{ z^{\delta,\alpha}(\tau)-y^{\delta,\alpha}(\tau)}} \right\| & \leq \int_{\tau-\delta}^{\tau} \left\| {{ T(\tau-s)}} \right\|\left( \tilde{a}\left\| {{{\it{\Phi}}(s-r)}} \right\|+\tilde{b}\right){\rm d}s \\ &\quad{} + \int_{\tau-\delta}^{\tau}\left\| {{ T(\tau-s)}} \right\|\int_{0}^{s}\left\| {{\mathbb{M}_g(s,l,z^{\delta,\alpha}(l-r))}} \right\|{\rm d}l{\rm d}s. \end{align*} Observe that |$0< \delta< r$| and |$\tau-\delta \leq s\leq \tau$|⁠, thus $$l-r \leq s-r \leq \tau-r< \tau-\delta.$$ Therefore, |$z^{\delta,\alpha}(l-r)=z(l-r)$| and |$z^{\delta,\alpha}(s-r)=z(s-r),$| implying that for |$\epsilon>0,$| there exists |$\delta>0$| such that \begin{align*} \left\| {{z^{\delta,\alpha}(\tau)-y^{\delta,\alpha}(\tau)}} \right\| & \leq \int_{\tau-\delta}^{\tau}\left\| {{ T(\tau-s)}} \right\|\left( \tilde{a}{\left\|{z(s-r)}\right\|}+\tilde{b}\right){\rm d}s \\ &\quad + \int_{\tau-\delta}^{\tau}{\left\|{T(\tau-s)}\right\|}\int_{0}^{s}{\left\|{ \mathbb{M}_g(s,l,z(l-r))}\right\|} {\rm d}l{\rm d}s \\ & < \displaystyle\frac{\epsilon}{2}. \end{align*} Additionally, for |$0<\alpha <1$|⁠, Lemma 3.2 (3.13) yields $${\left\|{ y^{\delta,\alpha}(\tau)-z_{1}}\right\|} < \frac{\epsilon}{2}.$$ Thus, $$\begin{array}{lll} {\left\|{ z^{\delta,\alpha}(\tau)-z_{1}}\right\|} & \leq & \left\| {{ z^{\delta,\alpha}(\tau)-y^{\delta,\alpha}(\tau)}} \right\| + {\left\|{ y^{\delta,\alpha}(\tau)-z_{1}}\right\|} < \frac{\epsilon}{2}+ \frac{\epsilon}{2}=\epsilon, \end{array}$$ which completes our proof. 5. Final remarks We believe this technique can be applied for controlling diffusion processes systems involving compact semigroups. In particular, our result can be formulated in a more general setting for the semilinear evolution equation with impulses, delay and memory in a Hilbert space |$\mathcal{Z}$| \begin{equation*} \left\{ \begin{array}{lr} z' = -\mathbb{A} z+ \mathbb{B} u + \displaystyle \int_{0}^{t}\mathbb{M}_g(t,s ,z(s-r))ds + \mathbb{F}(t,z_{t}(-r),u(s)) ,& z\in Z^{1},\; t\geq 0, \\ z(s) = {\it{\Phi}}(s), & s \in [-r,0],\\ z(t_{k}^{+}) = z(t_{k}^{-})+\mathbb{I}_{k}(t_k, z(t_{k}),u(t_{k})), & k=1,2, \dots, p, \end{array} \right. \end{equation*} where |$u\in L^{2}(0,\tau;\mathcal{U})$|⁠, |$\mathcal{U}$| is another Hilbert space, |$\mathbb{B} :\mathcal{U} \longrightarrow \mathcal{Z}$| is a bounded linear operator, |$\mathbb{I}_{k}, \mathbb{F}:[0, \tau]\times \mathcal{C}(-r,0; \mathcal{Z}) \times \mathcal{U} \rightarrow \mathcal{Z}$|⁠, |$\mathbb{A} :D(\mathbb{A}) \subset \mathcal{Z} \rightarrow \mathcal{Z}$| is an unbounded linear operator in |$\mathcal{Z}$| that generates a strongly continuous semigroup (Leiva, 2003, Lemma 2.1) \begin{equation*} T(t)z =\sum_{nj=1}^{\infty}e^{\mathbb{A}_{j}t}P_jz \mbox{, } \ \ z\in \mathcal{Z} \mbox{, } \ \ t \geq 0, \end{equation*} where |$\left\{ P_j\right\} _{j \geq 0}$| is a complete family of orthogonal projections in the Hilbert space |$\mathcal{Z}$| and \begin{equation*} \|\mathbb{F}(t,{\it{\Phi}},u) \|_{\mathcal{Z}} \leq \tilde{a} \|{\it{\Phi}}(-r)\|_{\mathcal{Z}} +\tilde{b}, \end{equation*} for all |$(t, {\it{\Phi}}, u) \in [0, \tau]\times \mathcal{C}(-r,0; \mathcal{Z} ) \times \mathcal{U}.$| Acknowledgements The authors are thankful to the anonymous referees for valuable comments that help improve the quality of the article. 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This article is published and distributed under the terms of the Oxford University Press, Standard Journals Publication Model (https://academic.oup.com/journals/pages/open_access/funder_policies/chorus/standard_publication_model)

### Journal

IMA Journal of Mathematical Control and InformationOxford University Press

Published: Mar 22, 2019

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