Comment on 'Vibration analysis of fluid-conveying double-walled carbon nanotubes based on nonlocal elastic theory'.

Most recently, Lee and Chang (2009 J. Phys.: Condens. Matter 21 115302) combined nonlocal theory and Euler-Bernoulli beam theory in the study of the vibration of the fluid-conveying double-walled carbon nanotube. In this recent published work, the importance of using nonlocal stress tensors consistently has been overlooked, and some ensuring relations were still presented based on the local stress components. Therefore, the governing equations and applied forces obtained in this manner are either inconsistent or incomplete. In this comment, the consistent governing equations for modelling free transverse vibration of the fluid-conveying double-walled carbon nanotube using the nonlocal Euler-Bernoulli beam model are derived.