Digital image processing for system identification

Emerging digital image processing techniques(1.2) are utilized to demonstrate their potential applications in earthquake engineering, particularly in the area of system identification. In this respect, the objectives of this research are to demonstrate the underlying principle that permits nonlinear system identification, non-intrusively and remotely, with the aid of CCD camera and, for the purpose of the proof-of-concept, to apply the principle to an identification problem involving friction forces, a simple but not necessarily easy problem to solve, on the basis of the image captured by a CCD camera. On the one hand, intricate micromechanic(3) interpretation of friction phenomena is prevalent and necessary in the area of Tribology(4) and similarly detailed analysis of friction is performed as the extension of contact problem in continuum mechanics. On the other hand, the practice in the structural dynamics dealing with the friction issue is such that the Coulomb friction model(5) is widely used for its mathematical expedience and ease of application. In this study, the method of digital image processing is applied to the identification of friction behavior between two solids with the aid of the Coulomb friction model. For this purpose, a pendulum is used which has a metal weight hung by a metal wire from a fixed point on a slant solid board and sliding on the board. The algorithm developed for this problem can be extended to identify, simultaneously and in near realtime, the friction coefficient and the relative motion between the model structure and the base in a shaking table test of a structure base-isolated by a sliding system. The proof-of-concept experiment was successfully carried out to show that the proposed identification method based on digital image processing can be used with appropriate modifications to identify many other engineering-wise significant quantities remotely. For example, the system in principle can be used to identify the friction coefficient of friction base-isolators of model or actual buildings during strong earthquakes.