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In this work, the applicability of a dynamic testing technique known as real-time dynamic substructuring (RTDS) for the assessment of passive vibration suppression systems in seismic protection of buildings is analysed. RTDS is an efficient method for the assessment of dynamic and rate-dependent behaviour of systems subjected to dynamic excitation at real scale and in real scenarios. The actuators used in RTDS test introduce additional undesirable dynamics into the system, which are often not fully compensated for in the actuator controller—these dynamics are commonly approximated as a feedback delay. To guarantee the validity and accuracy of an RTDS simulation, a stability analysis of the substructured system that includes the feedback delay should be carried out. In this paper, we present explicit analyses that provide a dynamic characterization of the delay-induced phenomena in RTDS simulations when considering passive vibration suppression systems with strong nonlinearities. We present a complete set of closed-form expressions to describe the main phenomena because of delay in terms of dynamic stability in an RTDS simulation. Through an experimental study, we confirm the existence of self-sustained oscillations caused by very small delay in the feedback loop. This lead the system to instability in the form of high-frequency oscillations. Copyright © 2011 John Wiley & Sons, Ltd.

This paper considers the hybrid simulation of under-damped dynamical systems using numerical–experimental real-time substructuring. Substructuring joins together a physical plant with a numerical model using real-time control techniques, such that the combined model emulates the behaviour of the entire system. Due to the low damping, the control of substructured systems can be highly sensitive to delay and uncertainty. We present a technique for calculating the critical delay of the substructured system using a phase margin approach. In addition, it is shown that robustness techniques, drawn from feedback control theory, can be used to reduce the destabilising effect of uncertainty. To demonstrate this, a comparison of three different robustness compensators is presented, using a well-known linear system. The level of uncertainty is deliberately increased to compare their performances and a discussion is made on when each may be most useful. Copyright © 2006 John Wiley & Sons, Ltd.

In this paper, we present results from real-time dynamic substructuring tests used to model the dynamics of a coupled pendulum–oscillator system. The substructuring technique is particularly suitable for systems where the nonlinear and linear parts of the system can be separated. The nonlinear part is built full size and tested physically (the substructure) while the linear part is simulated numerically. Then, in order to replicate the dynamics of the complete system the substructure and the numerical model must be coupled in real time. In this study, we demonstrate how real-time dynamic substructure testing can be used to model systems with strongly nonlinear behaviour using parametric variation. We show that the substructuring results give good qualitative and quantitative agreement with purely numerical simulations of the complete system for a range of parameters values. This includes single parameter bifurcation diagrams, some of which cannot be obtained from a full physical experiment. We also briefly discuss the effects of delay and noise on the stability of the substructured system, and how these effects can be mitigated. Copyright © 2006 John Wiley & Sons, Ltd.

Summary This paper investigates the use of a two-terminal vibration suppression device in a building. The use of inerter-spring-damper configurations for a multi-storey building structure is considered. The inerter has been used in Formula 1 racing cars and applications to various systems such as road vehicles have been identified. Several devices that incorporate inerter(s), as well as spring(s) and damper(s), have also been identified for vibration suppression of building structures. These include the tuned inerter damper and the tuned viscous mass damper. In this paper, a three-storey building model with a two-terminal absorber located at the bottom subjected to base excitation is studied. The brace stiffness is also taken into consideration. Four optimum absorber layouts, in terms of how spring, damper and inerter components should be arranged, for minimising the maximum relative displacements of the building are obtained with respect to the inerter's size and the brace stiffness. The corresponding parameter values for the optimum absorber layouts are also presented. Furthermore, a real-life earthquake data is used to show the advantage of proposed absorber configurations. Copyright © 2016 John Wiley & Sons, Ltd.

Summary In this paper, the use of a tuned inerter damper (TID) as a vibration absorber is studied numerically and experimentally, with civil engineering applications in mind. Inerters complete the analogy between mechanical and electrical networks, as the mechanical element equivalent to a capacitor and were developed in the 2000s. Initially, inerters were used for applications in automotive engineering, where they are known as J-dampers. Recently, research has suggested that inerter-based networks could be used for civil engineering applications, offering interesting advantages over traditional tuned mass dampers. In the civil engineering context, research has been mainly theoretical, considering ideal inerters. Because the dynamics of an inerter device include nonlinearities, especially at the low frequencies associated with civil engineering applications, the performance of the TID device using an off-the-shelf inerter has been experimentally tested in the work presented here. The chosen system, comprising a host structure with a TID attached to it, was tested using real-time dynamic substructuring (RTDS) or hybrid testing. The inerter was tested physically, while the remaining components of the TID device, the spring and damper, together with the host structure, were simulated numerically. Displacements and forces at the interface between numerical and physical components are updated in real time. This numerical–physical split allows the optimisation of the TID parameters, because the values of the spring and the damper can be changed without altering the experimental setup. In addition, this configuration takes into account the inerter's potentially complex dynamics by testing it experimentally, together with the characteristics of the host structure. Developing RTDS tests for physical inertial substructures, where part of the fed back interface forces are proportional to acceleration, is a challenging task because of delays arising at the interface between the experimental and the numerical substructures. Problems associated with stability issues caused by delay and causality arise, because we are dealing with neutral and advanced delayed differential equations. A new approach for the substructuring algorithm is proposed, consisting of feeding back the measured force deviation from the ideal inerter instead of the actual force at the interface. The experimental results show that with appropriate retuning of the components in the TID device, the performance in the TID incorporating the real inerter device is close to the ideal inerter device. © 2016 The Authors. Structural Control and Health Monitoring published by John Wiley & Sons, Ltd.