Review on mechanics of fluid-conveying nanotubes

Fluid-conveying nanotubes have become important components of nanoelectromechanical systems (NEMS) working in fluid environments, exciting extensive research on the dynamics of flow-conveying nanotubes. This paper systematically reviews the research progress of mechanics of fluid-conveying nanotubes from several aspects, including tube displacement field, non-classical continuum theory models, modeling, governing equations, boundary condition treatments, and dynamic behaviors. First, a refined displacement field for the tube structure considering curvature nonlinearity is presented. Based on the generalized continuum theory, a size-dependent constitutive model of nanotubes is established that fully considers surface effects, non-local stress and strain gradient effects, as well as the slip flow model for modeling the size-dependency of nanofluid is derived. Subsequently, three types of planar nonlinear vibration problems related to boundary conditions of flow-conveying nanotubes are reviewed. Based on the different nonlinear characteristics caused by different boundary conditions, including curvature nonlinearity, inertia nonlinearity, boundary tension hardening nonlinearity, etc., corresponding assumptions are made and size-dependent longitudinal internal force-displacement relationship is established. The dynamic governing equations and classical and non-classical boundary conditions of flow-conveying nanotubes are derived based on the Hamiltonian variational principle. The current main treatment methods for non-classical boundary conditions are illustrated. Finally, the research status of mechanical behaviors of fluid-conveying nanotubes is reviewed and future research prospects are summarized. This article provides theoretical guidance for linear/nonlinear design of NEMS of next-generation working in fluid environments.