▎ 摘　　要

The present study researches the free vibration of single and multi-walled circular graphene sheets in a thermal environment. To this aim, the graphene sheet is assumed to be single-layer and two-layer. In order to reach the governing equation, the nonlocal strain gradient theory is used along with the theories of higher-order shear deformation of the plate. Further, the effect of the heat field on the vibration behavior of the graphene sheet is investigated. Also, it is assumed that the graphene sheet is set on the viscoelastic medium to consider the foundation effect. Hamilton's principle is utilized to obtain the governing equations and is solved analytically using the generalized differential quadrature method. Results of the current research indicate that in all boundary conditions and for any value of the nonlocal parameter, the dimensionless natural frequency decreases with increasing temperature.