Abstract:The nonlinear dynamic response of thin plates made of linear viscoelastic material of fractional derivative type is investigated. The resulting governing equations are three coupled nonlinear fractional partial differential equations in terms of displacements. The solution is achieved using the AEM. According to this method the original equations are converted into three uncoupled linear equations, namely a biharmonic (linear thin plate) equation for the transverse deflection and two Poisson's (linear membrane) equations for the inplane deformation under time dependent fictitious loads. The resulting thus initial value problems for the fictitious loads is a system of nonlinear fractional ordinary differential equations, which is solved using the numerical method developed recently by Katsikadelis for multi-term fractional differential equations. Several plates subjected to various loads and boundary conditions are analyzed and the influence of the viscoelastic character of the material is investigated. Without excluding other viscoelastic models, the viscoelastic material employed herein is described by the generalized Voigt model of fractional order derivative. The numerical results demonstrate the efficiency and validate the accuracy of the solution procedure. Emphasis is given to the resonance response of viscoelastic plates under harmonic excitation, where complicated phenomena, similar to those of Duffing equation occur.

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We investigate the nonlinear flutter instability of thin elastic plates of arbitrary geometry subjected to a combined action of conservative and nonconservative loads in the presence of both internal and external damping and for any type of boundary conditions. The response of the plate is described in terms of the displacement field by three coupled nonlinear partial differential equations (PDEs) derived from Hamilton's principle. Solution of these PDEs is achieved by the analog equation method (AEM), which uncouples the original equations into linear, quasistatic PDEs. Specifically, these are a biharmonic equation for the transverse deflection of the plate, that is, the bending action, plus two linear Poisson's equations for the accompanying in-plane deformation, that is, the membrane action, under time-dependent fictitious loads. The fictitious loads themselves are established using the domain boundary element method (D/BEM). The resulting system for the semidiscretized nonlinear equations of motion is first transformed into a reduced problem using the aeroelastic modes as Ritz vectors and then solved by a new AEM employing a time-integration algorithm. A series of numerical examples is subsequently presented so as to demonstrate the efficiency of the proposed methodology and to validate the accuracy of the results. In sum, the AEM developed herein provides an efficient computational tool for realistic analysis of the admittedly complex phenomenon of flutter instability of thin plates, leading to better understanding of the underlying physical problem.

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The combined flutter and divergence instability of plates of arbitrary geometry subjected to any type of boundary conditions under interior and edge conservative and nonconservative loads are solved in presence of external and internal damping. In contrast to previous investigations, the membrane stress resultants are not in general uniform, since they result from plane stress problem under the given body forces (conservative and nonconservative) and the prescribed inplane boundary conditions. The differential equations of the problem are derived using Hamilton's principle. The resulted initial boundary value problem is solved using the analog equation method (AEM), which is a BEM-based domain meshless method. The combined action of conservative and nonconservative forces is also investigated. Several plates have been studied and useful conclusions on the effect of boundary conditions and damping on flutter load have been drawn. The obtained numerical results demonstrate the accuracy of the developed method and its capability to solve realistic engineering problems.