Eric Ungar and vibration damping

This presentation honors Eric Ungar’s contributions to vibration damping. The classic paper titled “Loss Factors of Viscoelastic Systems in Terms of Energy Concepts,” which he co-authored with Edward Kerwin in 1962, takes center stage. Two significant contributions of the paper deserve detailed discussion. The first is the time dependence of total energy for viscoelastic systems with added mass, which results in ambiguous loss factor definitions off resonance. The second and most important contribution is an equation for the loss factor of a network of ideal viscoelastic springs. This equation reveals that the system loss factor is a weighted average of the loss factors of the viscoelastic springs, where the weights are the total energies in the viscoelastic springs. Next, the value of this work is illustrated by some recent work inspired by the 1962 paper. This recent work, which was published 60 years after the 1962 paper, involves the calculation of loss factors from finite element models of complex structures with viscoelastic elements. The presentation concludes with recollections that celebrate Eric Ungar’s talent in educating and inspiring generations of engineers and researchers. Work supported by ONR under Grant N00014-22-1-2785.