  We explore the dynamics of a nanoscale doubly-clamped beam that is under high
tension, immersed in a viscous fluid, and driven externally by a spatially
varying drive force. We develop a theoretical description that is valid for all
possible values of tension, includes the motion of the higher modes of the
beam, and accounts for a harmonic force that is applied over a limited spatial
region of the beam near its ends. We compare our theoretical predictions with
experimental measurements for a nanoscale beam that is driven electrothermally
and immersed in air and water. The theoretical predictions show good agreement
with experiment and the validity of a simplified string approximation is
demonstrated.
