Purpose <p>This study aims to elucidate the vibration behavior of multilayer nanobeams immersed in a fluid environment, taking into account the combined effects of temperature and environmental damping, within the framework of a novel shear deformation theory.</p> Method <p>The governing formulations are established within the framework of nonlocal elasticity theory,and the equilibrium equations of the beam are derived based on the principle of virtual work.Subsequently, an analytical solution procedure is employed to obtain explicit solutions and to conduct detailed parametric investigations of the damped natural frequencies of the nanobeam.</p> Results <p>The computed results for the damped natural frequencies of the nanobeam,including both the real and imaginary components, have been systematically evaluated and thoroughly discussed. These findings provide meaningful references for the design and optimization of multilayer nanobeams operating in hot water environments.</p> Conclusion <p>The numerical analysis leads to several principal findings: + The predictions obtained from the classical beam theory and the refined shear deformation theory exhibit slight discrepancies; however, these differences are not substantial. + The incorporation of viscous damping associated with the hot water environment yields complex natural frequencies, comprising both real and imaginary components. + With increasing viscous damping intensity, the natural frequencies vary in a nonlinear manner, and the imaginary component bifurcates as the real component approaches zero. + A critical value of the viscous damping parameter Gvis can be identified, at which the natural frequency becomes insensitive to the volume fraction index k, and thus independent of the material gradation profile.</p>