Research Publications
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Publication Embargo Size-dependent nonlinear vibration problem of piezoelectric graphene origami auxetic metamaterial sandwich microplates under coupled thermo-fluid-viscoelastic multi-physics(Taylor and Francis Ltd., 2026-07-04) Saffari, P.R; Senjuntichai, T; Rajapakse, NThis paper investigates the nonlinear dynamic behavior of a microplate combining functionally graded graphene origami-enabled auxetic metamaterials (FG-GOEAM) in sandwich architecture with piezoelectric layers on a viscoelastic substrate under fluid-structure interaction and thermal loading. Accordingly, the primary objective is to develop a unified analytical framework to model and predict the intricate, size-dependent nonlinear dynamics of this multi-physics system. Graded graphene origami (GOri) elements are dispersed through the plate thickness to achieve negative Poisson’s ratio and improved thermal conductivity. First-order shear deformation theory (FSDT) with von Kármán geometric nonlinearity models large-amplitude deflections, while modified couple stress theory (MCST) captures size dependency. Thermal effects include uniform, linear, and nonlinear temperature distributions, and fluid-plate interaction is modeled via Navier-Stokes equations. Hamilton’s principle derives the governing equations, discretized using the Galerkin method into nonlinear time-dependent ordinary differential equations. The harmonic balance technique solves these equations to obtain nonlinear frequency-amplitude relationships for forced vibration. Effects of strain-gradient length-scale parameter, thermal field properties, piezoelectric actuation voltage, fluid layer depth, viscoelastic foundation stiffness and damping, GOri content, folding, and distribution patterns are parametrically examined using nonlinear frequency response curves.Publication Embargo Nonlocal strain gradient modeling of vibration energy harvesting in fluid-immersed bimorph sandwich nanoplates under thermal environment(American Institute of Physics, 2025-02-07) Roodgar Saffari, P; Senjuntichai, T; Rajapakse, NThis research details a method for mathematically simulating and assessing thermal vibration energy harvesting in laminated bimorph nanoplates in fluid contact. The model uses the piezoelectric characteristics of the outer layers and the functionally graded (FG) core material to transform thermal stresses into electrical energy efficiently. Nanostructures' size effects and nonclassical behavior are captured by the nonlocal strain gradient theory (NSGT). Combining the Navier-Stokes equations with the electromechanical equations obtained from Hamilton's principle, first-order shear deformation theory (FSDT), and Gauss's law yields an advanced multi-physics model. The FG core exhibits variations by the power law principle and is composed of both ceramic and metal components. Analytical solutions are obtained for the frequency response functions that relate the electrical power output to the external circuit load resistance by solving the coupled electromechanical-fluid equations. A thorough investigation is conducted to analyze how different elements impact energy harvesting performance using parametric studies. These factors include the configuration of the harvester (either parallel or series piezoelectric connections), nonlocal and strain gradient effects, temperature gradients, fluid depth, electrical load, geometric dimensions, and the material properties of the piezoelectric layers, and functionally graded core.