Nonlinear energy harvesting analysis of sandwich cylindrical microshells with GPLRC piezoelectric face sheets and FG-TPMS core conveying fluid under hygrothermal environment

A comprehensive theoretical framework is established to examine the nonlinear electromechanical behavior and energy harvesting characteristics of a sandwich cylindrical microshell conveying internal fluid at a prescribed flow velocity. The proposed configuration consists of functionally graded piezoelectric (FGP) face layers enclosing a core constructed from graphene platelet-reinforced composite (GPLRC) with functionally graded triply periodic minimal surface (FG-TPMS) architecture, all embedded within a Pasternak elastic foundation. The interior fluid flow is represented using a velocity-potential formulation, capturing fluid-structure interaction effects under steady flow conditions. The modified couple stress theory (MCST) is integrated with first-order shear deformation theory (FSDT) to address the size dependency at the microscale, while von Kármán-type kinematic assumptions are employed to introduce geometrically nonlinear strains. The governing electromechanical equations, accounting for concurrent thermal and moisture variations, are derived using Hamilton’s variational principle alongside Gauss’s law of electrostatics. The resultant nonlinear equations of motion are analytically solved through a combination of the Galerkin discretization technique and the harmonic balance method, producing closed-form expressions for frequency–amplitude and voltage–frequency response curves bypassing numerical time integration. A series of parametric investigations reveals how TPMS surface topology, graphene platelet distribution pattern, internal fluid velocity, porosity level, and hygrothermal loading collectively govern the harvested power output and dynamic stability of the system. Stiffer TPMS topologies, surface-biased GPL distributions, higher fluid velocities, and uniform porosity profiles elevate both the resonance frequency and peak harvested voltage, while increased hygrothermal loading softens the structure, reduces dynamic stability, and shifts the operating frequency toward lower values.