Showing papers by "Thomas K. Caughey published in 1991"
TL;DR: In this article, the authors explored the potential of a time-domain identification procedure to detect structural changes on the basis of noise-polluted measurements, using the use of excitation and acceleration response records to develop an equivalent multi-degree-of-freedom mathematical model whose order is compatible with the number of sensors used.
Abstract: This paper explores the potential of a time-domain identification procedure to detect structural changes on the basis of noise-polluted measurements. The method of approach requires the use of excitation and acceleration response records, to develop an equivalent multi-degree-of-freedom (MDOF) mathematical model whose order is compatible with the number of sensors used. Application of the identification procedure under discussion yields the optimum value of the elements of equivalent linear system matrices. By performing the identification task before and after potential structural changes (damage) in the physical system have occurred, quantifiable changes in the identified mathematical model can be detected. The usefulness of the identification procedure under discussion for damage detection is demonstrated by means of an example of three-degree-of-freedom (DOF) linear system. This system is used to conduct synthetic experiments to generate noise-polluted “data” sets that are subsequently analyzed to determine the mean, variance, and probability density function corresponding to each element of the identified system matrices. Different versions of the model are investigated in which the location as well as the magnitude of the “damage” is varied. On the basis of this exploratory study, it appears that determining the probability density functions of the identified system matrices may furnish useful indices that can be conveniently extracted during an experimental test, to quantify changes in the characteristics of physical systems.
167 citations
TL;DR: This article applies discrete dynamical systems theory to the dynamic analysis of a simplified vertical hopping robot model that is analogous to Raibert's hopping machines, and finds that the strange attractor can be controlled and eliminated by tuning an appropriate parameter corresponding to the duration of applied hop ping thrust.
Abstract: This article applies discrete dynamical systems theory to the dynamic analysis of a simplified vertical hopping robot model that is analogous to Raibert's hopping machines. A Poincare return map is developed to capture the dynamic behavior, and two basic nondimensional parameters that influence the systems dynamics are iden tified. The hopping behavior of the system is investigated by constructing the bifurcation diagrams of the Poincare return map. The bifurcation diagrams show a period-dou bling cascade leading to a regime of chaotic behavior, where a "strange attractor" is developed. An interesting feature of the dynamics is that the strange attractor can be controlled and eliminated by tuning an appropriate parameter corresponding to the duration of applied hop ping thrust. Physically, the collapse of the strange attrac tor leads to a globally stable period-1 orbit, which guar antees a stable uniform hopping motion.
83 citations
TL;DR: In this paper, a carefully controlled experimental study is presented in which the frictional forces and dynamic response of a shaft oscillating within a pair of sleeve bearings were monitored and analyzed in order to gain further insight into the basic phenomenological features of bearing friction forces.
27 citations
TL;DR: In this paper, an analytical method for computing the exact steady state motions of forced, undamped, discrete systems with strong non-linearities is presented, where the forcing problem is transformed to an equivalent free oscillation and subsequently a matching procedure is followed which results in the uncoupling of the differential equations of motion at the steady state.
Abstract: An analytical method is presented for computing the exact steady state motions of forced, undamped, discrete systems with strong non-linearities. By expressing the forcing as a function of the steady state displacements, the forced problem is transformed to an equivalent free oscillation and subsequently a matching procedure is followed which results in the uncoupling of the differential equations of motion at the steady state. General conclusions are made concerning the topological portrait of the steady state response curves and applications of the method are given for systems with two degrees of freedom and cubic non-linearities.
27 citations
TL;DR: In this paper, the authors examined the distorted Nyquist plots of the frequency response functions of two interfering modes and developed a refined modal identification algorithm that takes into account mode interference and leads to improved modal estimates compared with those obtained by existing methods.
3 citations