Addition of viscoelastic layers on flexible beam improves the behavior of flexible robots. However, the time domain simulation of such multilayer flexible beams is usually done through finite elements which makes it very time consuming. This paper proposes to build an equivalent homogenous flexible beam such that the flexible manipulator can be simulated using the variety of efficient methods developed in robotics. We propose a method to develop the equivalent Voigt-Kelvin model based on the frequency response obtained from the finite-element model. Then, we evaluate the performance of the model by simulating an experimental slewing beam covered with constrained viscoelastic material. The results are very satisfactory and the simulation is one hundred times faster than with the finite element method.