Gen. Math. Notes, Vol. 28, No. 1, May 2015, pp. 59-71 c ISSN 2219-7184; Copyright ICSRS Publication, 2015 www.i-csrs.org Available free online at http://www.geman.in Dependency of the Solution of a Class of Quartic Partial Differential Quasilinear Equation With Periodic Boundary Condition on ε Hüseyin Halilov1 , Bahadır Özgür Güler2 and Kadir Kutlu3 1 Recep Tayyip Erdogan University Faculty of Arts and Science, Department of Mathematics E-mail: huseyin.halilov@erdogan.edu.tr 2 Karadeniz Technical University Faculty of Science, Department of Mathematics E-mail: boguler@ktu.edu.tr 3 Recep Tayyip Erdogan University Faculty of Arts and Science, Department of Mathematics E-mail: kadir.kutlu@erdogan.edu.tr (Received: 14-1-15 / Accepted: 27-4-15) Abstract In this paper, we study the multidimensional mixed problem with periodic 4u 2 boundary condition for quasilinear Euler-Bernoulli equation ∂∂t2u − εb2 ∂t∂2 ∂x 2 + ∂2u 2 ∂4u 2 ∂4v a ∂x4 = f (t, x, u). We also consider the mixed problem ∂t2 +a ∂x4 = f (t, x, v). Finally we prove that the solution function u(t, x, ε) of the quasilinear EulerBernoulli equation is convergent to the solution function v(t, x) of the quasilinear quartic equation, as ε → 0. Keywords: Mixed problem, Periodic boundary condition, Quasi-linear quartic partial differential equation. 1 Introduction In recent years, mathematical modeling of sound wave distribution problems and also the vibration, buckling and dynamic behavior of various building 60 Hüseyin Halilov et al. elements widely used in nano-technology are formulated with following EulerBernoulli equations 4 4 ∂ 2u 2 ∂ u 2∂ u − εb + a = f (t, x, u) (1) ∂t2 ∂t2 ∂x2 ∂x4 Due to the new and exceptionally its electronic and mechanical properties, carbon nanotubes are considered to be one of the most useful material in future. Nowadays, nanotubes are used as atomic force microscopy, nanofillers for composite materials, nanoscale electronic devices and even frictionless nanoactuators, nanomotors, nanobearings and nanosprings [4,9,13,16,17]. These elements are tackled by different boundary conditions depending on different loading conditions. Therefore, investigation of existence and uniqueness of the solution of Euler-Bernoulli equations with different boundary conditions used in the mathematical modeling of the structural components of nano-materials continues to be a focus of interest amongst mathematicians.The reader is refereed to [2,6,7,8] for some relevant previous work on linear and quasi-linear equations. The textbooks [3,11,12,14,15] also contain important results. In mathematics, the classical statement of Euler-Bernoulli equation 4 ∂ 2v 2∂ u +a =0 ∂t2 ∂x4 (2) which is taken ε = 0 from (1) is used for beam vibration equation. As well as the homogeneous equation, quasilinear and non-linear equations can be handled in this case. Various problems for equations of this type were investigated and many results have been obtained in different ways. We first discuss the following mixed problem for the Euler-Bernoulli equation with the nonlinear source term f = f (t, x, u): 4 4 ∂ 2u 2 ∂ u 2∂ u − εb 2 2 + a = f (t, x, u), (t, x) ∈ D{0 < t < T, 0 < x < π} (3) ∂t2 ∂t ∂x ∂x4 u(0, x, ε) = ϕ(x), ut (0, x, ε) = ψ(x), (0 ≤ x ≤ π) (4) u(t, 0, ε) = u(t, π, ε), ux (t, 0, ε) = ux (t, π, ε), ux2 (t, 0, ε) = ux2 (t, π, ε), ux3 (t, 0, ε) = ux3 (t, π, ε), (0 ≤ t ≤ T ) (5) and also we consider the following mixed problem for a quasilinear quartic equation with the nonlinear source term f = f (t, x, v): 4 ∂ 2v 2∂ v + a = f (t, x, v), (t, x) ∈ D{0 < t < T, 0 < x < π} ∂t2 ∂x4 (6) v(0, x) = ϕ(x), vt (0, x) = ψ(x), (0 ≤ x ≤ π) (7) Dependency of the Solution of a Class of Quartic... v(t, 0) = v(t, π), vx (t, 0) = vx (t, π), vx2 (t, 0) = vx2 (t, π), vx3 (t, 0) = vx3 (t, π), (0 ≤ t ≤ T ) 61 (8) where ϕ(x), ψ(x) and f (t, x, u) are given functions defined on [0, π] and D̄{0 ≤ t ≤ T, 0 ≤ x ≤ π} × (−∞, ∞), respectively, and the functions u(t, x, ε) and v(t, x) are solutions of the problems(3)-(5) and (6)-(8). In [7], the authors have studied the solution of the problem (3)-(5) for ε > 0. The same authors have considered the solution of the problem (6)(8) for ε = 0 in [8]. In the present paper, we discuss the solution of the problem (3)-(5) and (6)-(8) and show that the solution function of u(t, x, ε) of the quasilinear Euler-Bernoulli equation is convergent to the solution function v(t, x) of the quasilinear quartic equation, as ε → 0 (i.e., limε→0 u(t, x, ε) = v(t, x), (t ∈ [0, t])). 2 Preliminaries Definition 2.1 [1, 10] The function w(t, x) ∈ C(D̄) is called test function if it has continuous partial derivatives of order contained in equation (1) and satisfies both following conditions w(T, x) = wt (T, x) = wx2 (T, x) = wtx2 (T, x) = 0 and the boundary condition; w(t, 0) = w(t, π), wx (t, 0) = wx (t, π), wx2 (t, 0) = wx2 (t, π), wx3 (t, 0) = wx3 (t, π) Definition 2.2 The function u(t, x, ε) ∈ C(D̄ × [0, ε0 ]) satisfying the integral identity Z T Z πn 2 o 4 4 ∂ w 2 ∂ w 2∂ w − εb 2 2 + a u − f (t, x, u)w dx dt+ ∂t2 ∂t ∂x ∂x4 0 0 Z π Z π 4 4 2 ∂ w 2 ∂ w ϕ(x) vt (0, x) − εb 2 2 dx − ψ(x) v(0, x) − εb 2 2 dx = 0 ∂t ∂x ∂t ∂x 0 0 (9) for an arbitrary test function w(t, x) is called weak generalized solution of problem (3)-(5). Definition 2.3 The function v(t, x) ∈ C(D̄) satisfying the integral identity Z T Z πn 2 o 4 ∂ w 2∂ w v + a − f (t, x, u)w dx dt+ ∂t2 ∂x4 0 0 (10) Z π Z π ϕ(x)vt (0, x) dx − ψ(x)v(0, x) dx = 0 0 0 for an arbitrary test function w(t, x) is called weak generalized solution of problem (6)-(8). 62 3 Hüseyin Halilov et al. Solution of Problem The set 1 ū(t, ε) = u0 (t, ε), uc1 (t, ε), us1 (t, ε), . . . , uck (t, ε), usk (t, ε), . . . 2 of functions satisfying the condition ∞ X 1 max |u0 (t, ε)| + max |uck (t, ε)| + max |usk (t)| < ∞. t∈[0,T ] t∈[0,T ] 2 t∈[0,T ] k=1 for all ε ∈ [0, ε0 ] is denoted by BT . Let ku(t, ε)kBT ∞ X 1 = max |u0 (t, ε)| + max |uck (t, ε)| + max |usk (t, ε)| t∈[0,T ] t∈[0,T ] 2 t∈[0,T ] k=1 be the norm in BT . It can be shown that BT is Banach space. Looking for the weak solutions of (3)-(5) and (6)-(8) of which existence and uniqueness are proven under certain conditions as following respectively; ∞ X 1 u(t, x, ε) = u0 (t, ε) + [uck (t, ε) cos 2kx + usk (t, ε) sin 2kx] 2 k=1 (11) ∞ X 1 v(t, x) = u0 (t) + [uck (t) cos 2kx + usk (t) sin 2kx] , 2 k=1 (12) and we get the following infinite system of integral equations for the unknown functions u0 (t, ε), uck (t, ε), usk (t, ε) and v0 (t), vck (t), vsk (t), (k = 1, ∞) Dependency of the Solution of a Class of Quartic... 63 Z Z 2 t π 1 v0 (t) = ϕ0 + ψ0 t + (t − τ )f τ, ξ, u0 (τ, ε)+ π 0 0 2 ∞ X [ucn (τ, ε) cos 2nξ + usn (τ, ε) sin 2nξ] dξ dτ, n=1 uck (t, ε) = ϕck cos αk t + 2 παk Z tZ 0 0 π ψck sin αk t+ αk ∞ X 1 [ucn (τ, ε) cos 2nξ + usn (τ, ε) sin 2nξ] × f τ, ξ, u0 (τ, ε) + 2 n=1 cos 2kξ sin αk (t − τ ) dξ dτ, ψsk usk (t, ε) = ϕsk cos αk t + sin αk t+ αk Z tZ π ∞ X 2 1 [ucn (τ, ε) cos 2nξ + usn (τ, ε) sin 2nξ] × f τ, ξ, u0 (τ, ε) + παk 0 0 2 n=1 sin 2kξ sin αk (t − τ ) dξ dτ, a(2k)2 αk = , k = 1, ∞. (13) 1 + ε(2k)2 and Z Z 2 t π 1 v0 (t) = ϕ0 + ψ0 t + (t − τ )f τ, ξ, v0 (τ )+ π 0 0 2 ∞ X [vcn (τ ) cos 2nξ + vsn (τ ) sin 2nξ] dξ dτ, n=1 vck (t) = ϕck cos α fk t + 2 πf αk Z tZ 0 0 π ψck sin α fk t+ α fk ∞ X 1 f τ, ξ, v0 (τ ) + [vcn (τ ) cos 2nξ + vsn (τ ) sin 2nξ] × 2 n=1 cos 2kξ sin α fk (t − τ ) dξ dτ, ψsk vsk (t) = ϕsk cos α fk t + sin α fk t+ α fk Z tZ π ∞ X 2 1 f τ, ξ, v0 (τ ) + [vcn (τ ) cos 2nξ + vsn (τ ) sin 2nξ] × πf αk 0 0 2 n=1 sin 2kξ sin α fk (t − τ ) dξ dτ, α fk = a(2k)2 , k = 1, ∞. (14) 64 Hüseyin Halilov et al. For simplicity, let ∞ X 1 Au(τ, ξ, ε) = u0 (t, ε) + [ucn (τ, ε) cos 2kx + usn (τ, ε) sin 2nx] 2 k=1 and ∞ X 1 Av(τ, ξ) = u0 (t) + [ucn (τ ) cos 2kx + usn (τ ) sin 2nx] . 2 k=1 To examine the difference of the systems (13) and (14), we write as following; 2 u0 (t, ε)−v0 (t) = π Z tZ 0 π (t−τ ) f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) dξ dτ, 0 fk t sin αk t sin α − αk α ek sin αk t sin α fk t − αk α ek uck (t, ε) − vck (t) = ϕck (cos αk t − cos α fk t) + ψck Z tZ π 2 f {τ, ξ, Au(τ, ξ, ε)} cos 2kξ sin αk (t − τ ) dξ dτ − παk 0 0 Z tZ π 2 f {τ, ξ, Av(τ, ξ)} cos 2kξ sin α fk (t − τ ) dξ dτ πf αk 0 0 usk (t, ε) − vsk (t) = ϕsk (cos αk t − cos α fk t) + ψsk + + Z tZ π 2 f {τ, ξ, Au(τ, ξ, ε)} sin 2kξ sin αk (t − τ ) dξ dτ − παk 0 0 Z tZ π 2 f {τ, ξ, Av(τ, ξ)} sin 2kξ sin α fk (t − τ ) dξ dτ πf αk 0 0 then we have 2 u0 (t, ε)−v0 (t) = π Z tZ 0 π (t−τ ) f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) dξ dτ, 0 fk t sin αk t sin α − αk α ek uck (t, ε) − vck (t) = ϕck (cos αk t − cos α fk t) + ψck + Z Z 1 1 1 t π − f {τ, ξ, Au(τ, ξ, ε)} cos 2kξ sin αk (t − τ ) dξ dτ + αk α fk π 0 0 Z tZ π 2 f {τ, ξ, Av(τ, ξ)} cos 2kξ[sin αk (t − τ ) − sinf αk (t − τ )] dξ dτ + πf αk 0 0 65 Dependency of the Solution of a Class of Quartic... 2 f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) cos 2kξ sin αk (t − τ ) dξ dτ, πf αk usk (t, ε) − vsk (t) = ϕck (cos αk t − cos α fk t) + ψck sin αk t sin α fk t − αk α ek + Z Z 1 1 1 t π f {τ, ξ, Au(τ, ξ, ε)} sin 2kξ sin αk (t − τ ) dξ dτ + − αk α fk π 0 0 Z tZ π 2 f {τ, ξ, Av(τ, ξ)} sin 2kξ[sin αk (t − τ ) − sinf αk (t − τ )] dξ dτ + πf αk 0 0 Z tZ π 2 f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) sin 2kξ sin α fk (t−τ ) dξ dτ. πf αk 0 0 Take the absolute values of differences and after making the necessary grouping, we form a sum as following; 1 |u(t, ε) − v(t)| = |u0 (t, ε) − v 0 (t)|+ 2 ∞ X [|uck (t, ε) − vck (t)| + |usk (t, ε) − vsk (t)|] ≤ T π k=1 π Z tZ 0 |f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) | dξ dτ + 0 ∞ ∞ X X (|ψck | + |ψsk |) sinααk k t − (|ϕck | + |ϕsk |)| cos αk t − cos α fk t| + k=1 k=1 ∞ X sin α fk t α ek + Z Z t 2 π 1 1 − αfk f τ, ξ, Au(τ, ξ, ε) cos 2kξdξ| + | αk π 0 0 k=1 Z 2 π | f τ, ξ, Au(τ, ξ, ε) sin 2kξdξ| dτ + π 0 Z t Z π ∞ X 2 1 f τ, ξ, Au(τ, ξ, ε) cos 2kξdξ| + | α fk 0 π 0 k=1 Z π 2 | f τ, ξ, Au(τ, ξ, ε) sin 2kξdξ| | sin αk (t − τ ) − sinf αk (t − τ )|dτ + π 0 Z t Z π ∞ X 1 2 | f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) cos 2kξdξ| + α fk 0 π 0 k=1 Z π 2 | f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) sin 2kξdξ| dτ. (15) π 0 66 Hüseyin Halilov et al. 1 kt 1 − Each of the statements | cos αk t−cos α fk t|, sinααk k t − sinαeαf , | sin αk (t− , α α f k k k τ ) − sinf αk (t − τ )| of the right side of in the equality (15) are bounded for k, τ and t (0 ≤ τ ≤ t ≤ T ), as ε → 0. Let us denote these statements by δ1 (ε), δ2 (ε), δ3 (ε), δ4 (ε), respectively, and then write last inequality as following; T |u(t, ε) − v(t)| ≤ π Z tZ 0 δ1 (ε) π |f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) |+ 0 ∞ X k=1 (|ϕck | + |ϕsk |) + δ2 (ε) ∞ X (|ψck | + |ψsk |)+ k=1 Z ∞ Z t X 2 π f τ, ξ, Au(τ, ξ, ε) cos 2kξdξ| + δ3 (ε) | π 0 k=1 0 Z 2 π | f τ, ξ, Au(τ, ξ, ε) sin 2kξdξ| dτ + π 0 Z t Z π ∞ X 1 2 δ4 (ε) f τ, ξ, Au(τ, ξ, ε) cos 2kξdξ| + | α fk 0 π 0 k=1 Z π 2 | f τ, ξ, Au(τ, ξ, ε) sin 2kξdξ| dτ + π 0 Z t Z π ∞ X 2 1 f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) cos 2kξdξ| + | α fk 0 π 0 k=1 Z π 2 | f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) sin 2kξdξ| dτ. π 0 (16) Under the assumptions of the theorem given below, we can take δ(ε) as the sum of the 2nd, 3rd, 4th, 5th sums in the right side of the inequality (14), then we have |u(t, ε) − v(t)| ≤ δ(ε)+ Z Z T t 2 π | f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) dξ|dτ + 2 0 π 0 ∞ X 1 Z t 2 Z π | f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) cos 2kξdξ| + α fk 0 π 0 k=1 Z 2 π f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) sin 2kξdξ| dτ. π 0 Dependency of the Solution of a Class of Quartic... 67 Applying Hölder inequality to third sum in the right side of the inequality above, we obtain |u(t, ε) − v(t)| ≤ δ(ε)+ !1/2 Z Z ∞ X T t2 π 1 |f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) |dξdτ + 2 0 π 0 α f2 k=1 k ( ∞ Z Z t X 2 π | f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) cos 2kξdξ + π 0 0 k=1 2 )1/2 Z 2 π f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) sin 2kξdξ| dτ . (17) π 0 Applying Cauchy inequality to the integrals in the right side of (17), then applying following inequality (a1 + a2 + . . . + an )2 ≤ n(a21 + a22 + . . . + a2n ) (18) to third sum for n = 2, we obtain |u(t, ε) − v(t)| ≤ δ(ε)+ (Z Z 2 ) 21 t 2 π T 3/2 f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) dξ dτ + 2 π 0 0 !1/2 (∞ Z Z ∞ t X √ X 2 π 1 2 T f τ, ξ, Au(τ, ξ, ε) − π 0 α f2 0 k=1 k=1 k 2 f τ, ξ, Av(τ, ξ) cos 2kξdξ dτ + 2 )1/2 Z π Z t ∞ X 2 T f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) sin 2kξdξ dτ π 0 0 k=1 (19) and then, |u(t, ε) − v(t)| ≤ δ(ε)+ (Z Z 2 ) 21 t 2 π T 3/2 f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) dξ dτ + 2 π 0 0 !1/2 (Z " ∞ Z ∞ t X X √ 1 2 π 2T T f τ, ξ, Au(τ, ξ, ε) − 2 π 0 α f 0 k=1 k k=1 2 f τ, ξ, Av(τ, ξ) cos 2kξdξ + 68 Hüseyin Halilov et al. 2 π Z π f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) sin 2kξdξ )1/2 2 # dτ . (20) 0 Taking square and using the inequality (18) to the inequality above for n = 3, we have |u(t, ε) − v(t)|2 ≤ 3δ(ε)2 + 2 Z Z 3T 3 t 2 π f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) dξ dτ + 4 0 π 0 ( Z 2 Z tX ∞ ∞ X 2 π 1 6T f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) cos 2kξdξ + 2 π α f 0 0 k k=1 k=1 2 ) Z π 2 f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) sin 2kξdξ . (21) π 0 Supposing max ∞ X 3T 3 1 , 6T 2 α f2 k=1 k ! = µ0 , let us combine the integrals of the right side of (21) as follows, |u(t, ε) − v(t)|2 ≤ 3δ(ε)2 + 2 Z t ( Z π 2 µ0 f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) dξ dτ + π 0 0 " Z 2 ∞ X 2 π f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) cos 2kξdξ + π 0 k=1 2 #) Z 2 π f τ, ξ, Au(τ, ξ, ε) − f τ, ξ, Av(τ, ξ) sin 2kξdξ . (22) π 0 Applying Bessel inequality to the sum in (22), we obtain 2 |u(t, ε)−v(t)| ≤ 3δ +µ0 π 2 2 Z tZ 0 π 2 f τ, x, Au(τ, x, ε) − f τ, x, Av(τ, x) dx. 0 Using Lipshitzs inequality, we have 2 |u(t, ε) − v(t)| ≤ 3δ(ε) + µ0 π 2 2 Z tZ 0 0 π b2 (t, x) [Au(τ, x, ε) − Av(τ, x)]2 dxdτ 69 Dependency of the Solution of a Class of Quartic... or 2 |u(t, ε) − v(t)| ≤ 3δ(ε) + µ0 π 2 2 Z tZ 0 π b2 (t, x)|u(τ, ε) − v(τ )|2 dxdτ. (23) 0 Applying Gronwall inequality to (23), we obtain Z Z 2 t π 2 2 2 b (t, x)dxdτ, |u(t, ε) − v(t)| ≤ 3δ(ε) exp µ0 π 0 0 or √ µ0 |u(t, ε) − v(t)| ≤ 3δ(ε) exp exp k b(t, x) k2L2 dxdτ. π In the last inequality, taking into account δ(ε) → 0 for ε → 0, we see that lim u(t, ε) = v(t). ε→0 Hence, the following theorem is proved. 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