Londoño Monsalve, Julián Mauricio (2009) Stability of delayed systems in structural control applications. [Tesi di dottorato] (Unpublished)

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This analyses the applicability of a quite novel methodology of experimental testing socalled Real-Time Dynamic Substructuring Test (RTDST) in the assessment of protection systems for natural hazards mitigation. RTDST allows testing critical components of structures at full-scale under realistic extreme loading conditions. Only those components where the nonlinearity behavior is concentrated are physically tested, whilst the remainder of the structure is simulated numerically. The main drawback of this technique lies in the unavoidable delays associated to the loop feeding back some experimental measurements to the numerical model. Such delays may cause instability during the test. This work is focused on testing passive control systems based on large-scale non linear fluid viscous dampers. Throughout a careful explicit stability analysis, we present a complete set of closed-form expressions to describe the dynamics of the main complex delay-induced phenomena exhibited for the delayed system. This analysis is addressed in the context of both classic stability theory for non-linear systems and the qualitative theory of Piecewise Smooth Dynamical Systems. The results obtained are also useful for other kind of mechanical systems where the response of some components is arriving with delay and may cause harmful effects on system behaviour. Semi-active control by MR dampers are examples of such systems. The theoretical results obtained were confirmed experimentally. When carrying out the experimental campaign, in fact, unexpected selfsustained oscillations were detected. This was caused by delays in the feedback loop, even when they are very small, unavoidably lead the system to self-sustained oscillations at high frequency.

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