Professor Caughey was a leading international ÿgure in the ÿeld of dynamics and vibrations, particularly in the responses of non-linear systems and randomly excited systems. He took an active leadership role in the area of stochastic non-linear systems; his work on parametrically excited random systems laid the foundation of this important ÿeld. He was the ÿrst investigator to develop exact solutions of the Fokker Planck equation applied to non-linear dynamic systems. His work on piecewise linear systems, which predates the discovery of strange attractors and chaos in engineering systems, was fundamental in guiding later investigators in their studies of chaotic behavior of impact oscillators. His early work on the response of simple linear and non-linear oscillators to random excitation was key in the applications of stochastic methods to problems in earthquake engineering. Of special signiÿcance in my own work was his 1961 paper, 'Transient Response of a Dynamic System Under Random Excitation,' co-authored with H. J. Stumpf, which appeared in the Journal of Applied Mechanics. This work underlay not only the generation of artiÿcial earthquakes, but gave the insights needed to determine the magnitudes of earthquakes from the response of seismoscopes and similar historic instruments.
His relatively recent work in the identiÿcation and control of non-linear systems, smart materials, active damping of large structures, and the dynamics of systems with large nonlinearities continues to guide the scientiÿc community. This work ÿnds application in the monitoring and active control of large structures, such as buildings and bridges, when subjected to earthquakes or strong winds. Additionally, he did important work with Caltech colleagues on uid-induced forces in turbomachinery, in particular, problems of rotor dynamics in centrifugal pumps.
His research contributions in applied mechanics have been widely recognized.