Forced Response Analysis. Having carried out a normal modes analysis to determine resonant frequencies in a structure, a forced response analysis can be carried out to determine the stresses, strains and displacements due to dynamic inputs. For example, if a structure has a resonance at 50Hz, then a dynamic input at a point on the structure will only cause an energetic response when its frequency coincides with the 50Hz resonance. The magnitude of the response will be dependant on the damping in the structure.