# A Transmission Problem for Euler-Bernoulli beam with Kelvin-Voigt. Damping

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1 Applied Mathematics & Information Sciences 5(1) (211), An International Journal c 211 NSP A Transmission Problem for Euler-Bernoulli beam with Kelvin-Voigt Damping C. A Raposo 1, W. D. Bastos 2 and J. A. J. Avila 3 1 Departament of Mathematics, Federal University of S. J. del-rei - UFSJ, MG, Brazil Address: 2 Departament of Mathematics, São Paulo State University - UNESP, SP, Brazil Address: 3 Departament of Mathematics, Federal University of S. J. del-rei - UFSJ, MG, Brazil Address: Received June 22, 2x; Revised March 21, 2x In this work we consider a transmission problem for the longitudinal displacement of a Euler-Bernoulli beam, where one small part of the beam is made of a viscoelastic material with Kelvin-Voigt constitutive relation. We use semigroup theory to prove existence and uniqueness of solutions. We apply a general results due to L. Gearhart [5] and J. Pruss [1] in the study of asymptotic behavior of solutions and prove that the semigroup associated to the system is exponentially stable. A numerical scheme is presented. Keywords: Transmission problem, Exponencial stability, Euler-Bernoulli beam, Kelvin-Voigt damping, Semigroup, Numerical scheme. 1 Introduction Consider a clamped elastic beam of length L. Let the interval [, L] be the reference configuration of a beam and x [, L] to denote its material points. We denote u(x, t) the longitudinal displacement of the beam. Suppose that the stress σ is of rate type, i. e., σ = αu x + γu xt with γ >. Then, the equation governing such a motion is given by u tt αu xx γu txx = in (, L) (, ). (1.1) Partially supported by CNPq. Grant /28-8 INCTMat.

2 18 C. A. Raposo, W. D. Bastos and J. A. J. Avila Assuming that the beam is held fixed at both ends, x = and x = L we have the following boundary conditions u(, t) =, u(l, t) =. Now we observe that in the equation (1.1) the viscosity is distributed uniformly in the whole beam. However, it is desirable in practice to consider a situation where viscosity is active only in a piece of the beam. In this case, it is important to know if the dissipation is transmitted and if it is strong enough to stabilize the whole system. In order to work out this question we consider the following model where one small part of the beam is made of a viscoelastic material with Kelvin-Voigt constitutive relation, with boundary conditions initial data transmission conditions and compatibility condition u tt αu xx γu txx = in (, L ) (, ), (1.2) v tt βv xx = in (L, L) (, ), (1.3) u(, t) = v(l, t) =, t >, (1.4) u(x, ) = u (x), u t (x, ) = u 1 (x), x (, L ), (1.5) v(x, ) = v (x), v t (x, ) = v 1 (x), x (L, L), (1.6) u(l, t) = v(l, t), t >, (1.7) αu x (L, t) = βv x (L, t), t >, (1.8) This kind of problem is known as a transmission problem. u tx (L, t) =, t >, (1.9) A relevant question raised about the transmission problems and problems with locally distributed damping, is the asymptotic behavior of the solutions. Does the solution goes to zero uniformly? If this is the case, what is the rate of decay? In [7] longitudinal and transversal vibrations of a clamped elastic beam where studied as problems with locally distributed damping. It was shown that when viscoelastic damping is distributed only on a subinterval in the interior of the domain, the exponential

3 A Transmission Problem for Euler-Bernoulli beam with Kelvin-Voigt Damping 19 stability holds for the transversal but not for for the longitudinal motion. At this point it is crucial to notice the difference between the formulation of transmission problems and problems with locally distributed damping. While in the former, the transmission conditions play decisive role establishing the way the parts of the body mingle with each other, in the latter it is expressed only by discontinuities in the coefficients of the equation. For further information on general transmission problems we refer to [4]. A exponential stability of transmission problem for waves with frictional damping was treated in [2], for the Timoshenko system it was treated in [12], the General Decay of solution for the transmission problem of viscoelastic waves with memory was treated in [13] and in [8] uniform stability is proved for the wave equation with smooth viscoelastic damping applied just around the boundary. In this work we address the questions above to the system (1.1)-(1.8). that the solution this system decay exponentially, i.e., the estimate, We prove E(t) CE()e wt, C >, w >, t > (1.1) holds for the total energy E(t) of the system. This is equivalent [15] to establish the exponential stability for the semigroup S(t) generated by the system, i. e., S(t) Ce wt, C >, w >, t >. The central idea is to explore the dissipative character of the infinitesimal generator of the semigroup and make use of a Theorem due to Gearhart [5] and Pruss [1]. It is in this point that transmission conditions makes the difference between the formulations of problems with locally distributed damping and transmission problems. Therefore, our result does not contradicts that in [7]. These type of questions for viscoelastic waves with memory are studied in [14], for frictional and viscoelastic damping for a semi-linear wave equation are studied in [3] and for Timoshenko s beams with viscoelastic damping and memory are studied in [12]. The paper is organized as follows, in the section 2 we introduce the notation and the functional spaces, in the section 3 we prove the existence and uniqueness of solutions, in the section 4 we prove exponential stability of the semigroup generated by the system and finally, in the section 5 a numerical scheme is presented.

4 2 C. A. Raposo, W. D. Bastos and J. A. J. Avila 2 Notation and Functional Spaces For the Sobolev spaces we use the standard notation as in [1]. We define I 1 = (, L ) and I 2 = (L, L). We also define V 1 = {u H 1 (I 1 ) : u() = }, V 2 = {v H 1 (I 2 ) : v(l) = }, and H = u 1 v 1 u 2 v 2 : ui V i, v i L 2 (I i ). In H we consider the following inner product U 1, U 2 = L L αu 1 xu 2 x + v 1 v 2 dx + βzxz 1 x 2 + w 1 w 2 dx, L (2.1) where U = u i v i z i w i H i = 1, 2. Following [9] we define the linear operator A : D(A) H H with and D(A) = u 1 v 1 u 2 v 2 H : ui V i H 2 (I i ), v i V i, αu 1 x + γvx 1 H 1 (I 1 ) A = I γ 2 x 2 I α 2 x 2 The problem (1.2)-(1.3) can be written as β 2 x 2. U t A U = (2.2) U() = U (2.3)

5 A Transmission Problem for Euler-Bernoulli beam with Kelvin-Voigt Damping 21 where U(t) = u u t v v t, U() = u u 1 v v 1, AU = u t αu xx + γu txx v t βv xx. 3 Existence of Solutions From the construction of the functional spaces and from the theory of Sobolev Spaces, it follows that D(A) is dense in H. Now we will to show that the full system is dissipative. energy of the system by First we define the total E(t) = 1 2 L and denote the energy in each part as u t 2 + u x 2 dx E 1 (t) = 1 2 E 2 (t) = 1 2 L L L u t 2 + u x 2 dx, L v t 2 + v x 2 dx. L v t 2 + v x 2 dx, Multiplying equation (1.2) by u t and performing integration by part on (, L ) we obtain, d L dt E 1(t) = γ u tx 2 dx + αu x (L )u t (L ) αu x ()u t () + βu tx (L )u t (L ).(3.1) Multiplying equation (1.3) by v t and performing integration by part on (L, L) we obtain, d dt E 2(t) = βv x (L)v t (L) βv x (L )v t (L ). (3.2) Now adding (3.1)-(3.2), using boundary condition, transmissions conditions and compatibility condition, we get the dissipative character as we intend, that is, d L E(t) = γ u tx 2 dx. dt In this direction, the operator A has an important property which will be used in the sequel.

6 22 C. A. Raposo, W. D. Bastos and J. A. J. Avila Lemma 3.1. The operator A : H H is dissipative. Proof. Using the definition of the inner product (2.1), we have AU, U = L αu tx u x + (αu xx + γu txx )u t dx + L L βv tx v x + βv xx v t dx. Performing integration by parts and using the boundary conditions, the transmission conditions and the compatibility condition, we get AU, U = γ which proves the dissipativeness of A. L u tx 2 dx (3.3) Theorem 3.1. The operator A generates a C -Semigroup of contractions S(t) = e At. Proof. For any consider the equation AU = F, i.e., F = f 1 f 2 f 3 f 4 H, u t = f 1 H 1 (I 1 ) (3.4) αu xx + γu txx = f 2 L 2 (I 1 ) (3.5) v t = f 3 H 1 (I 2 ) (3.6) βv xx = f 4 L 2 (I 2 ). (3.7) Using (3.4), (3.5) and observing the regularity of the stress, as settled in the definition of D(A), we get αu xx = f 2 γf 1 xx L 2 (I 1 ). Thus, by the standard results of the theory of elliptic equations we conclude that u H 2 (I 1 ). Then we obtain a unique solution u u t U = v H, v t such that U D(A), U k F for k > and satisfies (3.4)-(3.7). Thus ρ(a) the resolvent set of A, and then, A is invertible and A 1 is bounded linear operator. By the contraction mapping theorem, the operator λ I A = A(λ A 1 I) is invertible for < λ < A 1 1. Therefore, it follows from the Lummer-Phillips Theorem that A is the infinitesimal generator of a C -semigroup of contractions S(t) = e At.

7 A Transmission Problem for Euler-Bernoulli beam with Kelvin-Voigt Damping 23 From the theory of semigroup it follows that U(t) = e At U is the unique solution of (1.1)- (1.8) in the class U C ([, ) : D(A)) C 1 ([, ) : H). 4 Exponential Stability In order to prove the exponential decay we are going to use the following result. Theorem 4.1. Let S(t) = e At be a C -Semigroup of contractions in a Hilbert space. Then S(t) is exponentially stable if and only if, and i R = {i β : β R} ρ(a) (λ I A) 1 C, λ i R. Proof. This result is due to L. Gearhart and its proof can be found in [5] or in Huang [6] and Prüss [1]. Now, by using the stability criterium due to Gearhart we prove the main result of this paper. Theorem 4.2. The C -Semigroup of contractions S(t) = e At generated by A is exponentially stable. Proof. Since ρ(a) then, for every β with β < A 1 1 the operator i β A = A(i βa 1 I) is invertible and (i β A) 1 is a continuous function of β ( A 1 1, A 1 1 ). At this point we are going to use an argument of contradiction. First we suppose that the condition {i β : β R} ρ(a) is not satisfied. Then, there exists w R with A 1 1 w < such that {i β : β < w } ρ(a) and the Sup { (i β A) 1 : β < w } =. Hence, there exists (β n ) R with β n w, β n < w and a sequence of complex vector functions U n D(A) such that U n = 1 in H and (i β n A)U n. Taking the inner product of (i β n A)U n with U n we obtain i β n U n 2 AU n, U n.

8 24 C. A. Raposo, W. D. Bastos and J. A. J. Avila Now, using (3.3) arrive at Taking the real part we get Using (4.2) in (4.1) we can say that L i β n U n 2 + γ vn,x 1 2 dx. (4.1) L γ vn,x 1 2 dx. (4.2) i β n U n 2. (4.3) Observing that β n U n = 1. w, β n < w we conclude that U n which contradicts In order to finish the proof it remains to prove that (λ I A) 1 C, λ i R. Suppose that it is not true. Then there exist a sequence of vector function (V n ) such that (i β n A) 1 V n > n V n. (4.4) As (V n ) H and i β n ρ(a), there exists a unique sequence U n D(A) such that i β n U n AU n = V n with U n = 1. Introducing g n = (i β n A)U n and using (4.4) we obtain g n 1 n and hence g n. By taking the inner product of g n with U n and using (3.3) we get L i β n U n 2 + γ vn,x 1 2 dx = g n, U n. Now, taking the real part and observing that (U n ) is bounded and that g n we deduce L γ vn,x 1 2 dx. Proceeding as in the previous case we prove U n which is a contradiction. This completes de proof.

9 A Transmission Problem for Euler-Bernoulli beam with Kelvin-Voigt Damping 25 5 Numerical Results In this section we implement a numerical scheme using the method of finite difference without any additional technic of numerical dissipation. In order to verify our computational code we construct an analytic solution which produces source terms in the equation (1.2) and (1.3). These solutions are defined by, where a i = cos u(x, t) = ( ) [ 1 a t 4 i= a i a (4 i) ] in (, L ) (, ) (5.1) v(x, t) = u(x, t) in (L, L) (, ) (5.2) [ ] (i+1)(x π) 2, i =,..., 4. Observe that u(x, t), t. We considered a spacial domain of length L = 2π with a grid with 128 nodes uniformly distributed. The convergence of the solution, or permanent regime, is attained after 29. iterations in time, with error of 1 7 to u and 1 4 to v, with t x =, 22. We made four tests. In the first one the viscosity was distributed uniformly in the whole string L while in the others viscosity was localized in the piece of length L. If L = L we have exponential stabilization for the solutions of equation (1.2) well illustrated in the figure 5.1. In the figures the lengths for L were: { π, π 2, } π 4, respectively. The parameters used in all the tests were α = 1, γ =, 2 and β = 1. We could have used other sets of parameters since our code accepts any. In the sequence of the tests we observed that, as L decreases, the solutions oscillate with larger amplitude, and, bigger values for γ could be considered. We finally observe that exponential decay occurs no matter what is the size of the interval (, L ). This indicates that the presence of any quantity of viscous material in the mixture will cause exponential stability for the problem considered here.

10 26 C. A. Raposo, W. D. Bastos and J. A. J. Avila 6 u (x) 6 u (x) v (x) u 2 u x -1 x L Figure 5.1: Test 1, with L = L. Figure 5.2: Test 2, with L = L u 3 2 u 2 1 u (x) v (x) u (x) v (x) x L x L Figure 5.3: Test 3, with L = L 4. Figure 5.4: Test 4, with L = L 8. References [1] R. A. Adams, Sobolev Spaces, Academic Press, New York, [2] W. D. Bastos, C. A. Raposo. Transmission problem for waves with frictional damping. Electronic Journal of Differential Equations, 27 (27), 1-1. [3] M. M. Cavalcanti and H. P. Oquendo, Frictional versus viscoelastic damping in a

11 A Transmission Problem for Euler-Bernoulli beam with Kelvin-Voigt Damping 27 semilinear wave equation. SIAM J. Control Optim. 42 (23), [4] R. Dautray, J.L. Lions, Mathematical Analysis and Numerical Methods for Sciences and Technology. Vol. 1, Springer-Verlag, Berlin - Heidelberg, 199. [5] L. Gearhart, Spectral Theory for the Contractions Semigroups on Hilbert Spaces. Trans. of the American Mathematical Society. 236 (1978), [6] F. Huang, Characteristic Conditions for Exponential Stability of the Linear Dynamical Systems in Hilbert Spaces. Annals of Differential Equations. 1 (1985), [7] K. Liu, Z. Liu, Exponential decay of the energy of the Euler-Bernoulli beam with locally distributed Kelvin-Voigt damping, SIAM J. Control Optim. 36(3) (1998), [8] K. Liu, B. Rao, Exponential stability for the wave equations with local Kelvin-Voight damping. Z. angew. Math. Phys. 57 (26), [9] Z. Liu, & S. Zheng; Semigroups Associated with Dissipative Systems, CRC Research Notes Mathematics, Chapmam & Hall, [1] J. Prüss, On the Spectrumm of C -semigroups. Trans. of the American Mathematical Society 284 (1984) [11] C. A. Raposo,W. D. Bastos, M. L. Santos. A Transmission Problem for Timoshenko System. Computational and Applied Mathematics, 26 (27), [12] C. A. Raposo, The transmission problem for Timoshenkos system of memory type. International Journal of Modern Mathematics. 3(3) (28), [13] C. A. Raposo. General Decay of Solution for the Transmission Problem of Viscoelastic Waves with Memory. Advances in Differential Equations and Control Processes, 3 (29), [14] J. E. M. Rivera, H. P. Oquendo, The transmission problem of viscoelastic waves. Acta Applicandae Mathematicae. 62 (2), [15] S. Zheng, Nonlinear parabolic Equation and Hyperbolic-Parabolic Coupled Systems, Pitman series Monographs and Survey in Pure and Applied Mathematics, Longman, 1995.

12 28 C. A. Raposo, W. D. Bastos and J. A. J. Avila Waldemar Donizete Bastos, PhD in Mathematics from University of Minnesota Associate Professor at State University of Sao Paulo State in Sao Jos do Rio Preto. Has experience in Mathematics with emphasis in Partial Differential Equations. The areas of interest are controllability for pdes, asymptotic behavior of solutions and transmission problems. Jorge Andrs Julca Avila, PhD in Mechanical Engineering from USP - University of S?o Paulo. Assistant Professor at the Department of Mathematics of UFRJ- Federal University of Sao Joao del Rei. Has experience in Applied Mathematics emphasizing Numerical Analysis, Functional Analysis and PDEs. For the moment, the major interests are in the Navier-Stokes Equations, Non Newtonian Fluids and Finite Elements. Is also experienced in Mechanical Engineering with emphasis in Fluid Mechanics and Fluid Dynamics and Hyperbolic Conservation Laws. Is member of the Scientific Committee of UFSJ. Carlos Alberto Raposo da Cunha, PhD in Mathematics from UFRJ - Federal University of Rio de Janeiro. Full Professor at the Department of Mathematics of UFSJ - Federal University of Sao Joao del Rei. Has experience in Mathematics with emphasis in Partial Differential Equations. The interests are mainly in decay of energy for dissipative systems, transmission problems, problems in viscoelasticity with memory, termoelasticity and asymptotic behavior of solutions of pdes. Is the local representative of SBMAC - Sociedade Brasileira de Matem?tica Aplica e Computacional and Reviewer for the Mathematical Reviews / AMS - American Mathematical Society. Has served as referee for several international mathematical journals. Recently has occupied, in the UFSJ, the positions of Head of Department of Mathematics and Director of Graduate Studies. For the moment is the Director of the INCTMat-Instituto Nacional de Cincia e Tecnologia de Matemtica /28-8/CNPq.

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