The aim of this work is to study the modal behavior of structures covered with a complex pattern of viscoelastic material in Free Layer Damping (FLD) configuration in terms of damping performances. Two original methods based on the Modal Strain Energy (MSE) method named New Modified MSE method and the Corrected MSE method have been developed and applied to some test cases. A comparison between the new methods and the classic one has been done. Different viscoelastic distributions have been analyzed in order to evaluate how the patch design may influence the damping performances of the coupled structure. The structure has been discretized by means of a hybrid Finite Element (FE) developed to simulate the structure with the FLD viscoelastic treatment. The hybrid FE element has been benchmarked against an analytical example with full FLD coverage.