BK -- How to Determine the Modal Parameters of Simple Struct

http://www.cadfamily.com/a/CAE_FEA_CFD/BK/BK----How-to-Determine-the-Modal-Parameters-of-Simple-Struct_6549.html

The modal parameters can be determined from a set of frequency response measurements between a reference point and a number of measurement points. Such a measurement point, as introduced here, is usually called a Degree-of-Freedom (DOF). The

modal frequencies and dampings can be found from all frequency response measurements on the structure (except those for which the excitation or response measurement

is in a nodal position, that is, where the displacement is zero). These two parameters

are therefore called “Global Parameters”. However, to accurately model the associated

mode shape, frequency response measurements must be made over a number of Degrees-of-Freedom, to ensure a sufficiently detailed covering of the structure under test.