ASA 125th Meeting Ottawa 1993 May

4pSA4. A simple test of the modal strain energy method.

J. Gregory McDaniel

BBN Systems and Technol. Corp., 10 Moulton St., Cambridge, MA 02138

Jerry H. Ginsberg

Georgia Inst. of Technol., Atlanta, GA 30332

Nashif et al. [Vibration Damping (Wiley, New York, 1985)] present a ``modal strain energy method'' (MSEM) that has seen increased use in the finite element community to estimate modal loss factors in elastic--viscoelastic structures. The method enables one to predict dynamic response without explicitly accounting for hysteretic damping in the free vibration analysis. Despite its wide usage, there does not seem to have been prior formal analyses of its validity. The presentation will report such a test of MSEM predictions for a two-degree-of-freedom system in which the two masses are connected by dissipative and elastic elements. The evaluations explore the dependence of MSEM on basic parameters characterizing stiffness, inertia, and damping. The main conclusion is that MSEM is very accurate if dissipation within the viscoelastic substructure is sufficiently low. Raising either the inertia or stiffness of this part of the system seems to enhance the accuracy of MSEM for a fixed value of its damping factor.