MS16.2 - Recent advances in vibration control of structures with isolation and/or energy dissipation devices

In this research paper, the KDamper concept is extended and applied to multiple floors of exist-ing low-rise, mid-rise, and high-rise building structures. Inspired by the concept of MTMDs, multiple EKDs (d-EKDs) are installed and distributed along the height of the structure, aiming to achieve seismic protection of the building in terms of accelerations, displacements, and base shear, without the need of introducing significant additional masses. The design and spatial al-location of the EKDs is based on a Harmony Search (HS) algorithm that provides optimal pa-rameters of the device based on constraints and limitations imposed by the structure, as well as constructability of the system. In addition, static and dynamic stability conditions are imposed in the optimization procedure, to ensure the stability of the examined structure, as the d-EKD concept introduces negative stiffness elements. A number of Eurocode 8 compatible accelero-grams are generated and introduced as input to the optimization process in order to obtain op-timal EKD parameters for the benchmark structure. Furthermore, the performance of the con-trolled buildings is assessed on a set of performance criteria for the dynamic responses, evalu-ated for a set of real earthquake records. Based on the numerical results obtained, the d-EKD concept, as compared to an optimally designed d-TMD concept, outperforms the d-TMD in re-ducing the structural dynamic responses, introducing one order of magnitude smaller added oscillating masses.

The contribution presents recent progress in development of predictive control methods for optimal mitigation of impact excitations. The attention is focused on a control of semi-active system subjected to an impact of a rigid object moving with initial velocity. Objective of the solved control problem is dissipation of the entire impact energy with minimal value of generated force and minimal corresponding value of impacting object’s deceleration. Challenges in problem solution result from unknown parameters of the impact as well as occurrence of unknown process disturbances and uncertainties. The proposed novel solution method effectively utilizes the paradigm of model predictive control combined with techniques of system parameters identification. As a result, adaptive system operation ensuring efficient impact mitigation is provided. As an illustrative example, we discuss control of the semi-active fluid-based damper equipped with fast-operating piezoelectric valve. The system is subjected to an impact of a rigid object of unknown mass moving with initial unknown velocity and unknown external force. The considered disturbances include unknown friction forces and leakages of the fluid through the valve. The corresponding control problem is formulated as state-dependent kinematic path-tracking aimed at minimization of the difference between actual and currently optimal value of object’s deceleration. The main unknown of this problem is time-dependent voltage signal which controls operation of the valve and resulting fluid flow. The proposed solution approach is based on repetitive solution of the control problems defined at subsequent time intervals of arbitrary lengths. Solution of each control problem is preceded by identification of the actual values of friction force and fluid leakage which are required for prediction of object deceleration as well as computation of the currently optimal deceleration value using the condition of kinematic optimality of the process. The proposed solution methods utilize specific parametrisations of the control function with a special focus on those providing analytical solution of equations governing system dynamics. The entirely novel aspects covered by the contribution include: i) application of the realistic model of piezoelectric valve and investigation of the influence of its operating time on impact mitigation process, ii) comparison of the effectiveness of semi-active and active control systems with and without leakage identification, iii) investigation of the influence of control cost on the applied control strategy.

Damping enhancement of slender beam-like structures continues be an underlying motive behind current interests of many engineering disciplines, including aerospace structures. In particular, with the increased focus surrounding High Aspect Ratio Wings (HARWs) owing to their potential in reducing induced drag, the suppression of related aeroelastic instabilities and detrimental responses continues to receive increasing attention. Such systems can potentially benefit from vibration control devices thoroughly studied since the early 20th century with the introduction of the classical tuned vibration absorber. However, the implementation of such discrete devices on lifting surfaces are often restricted by the continuum nature and geometrical constraints of these structures. The present study aims to introduce and investigate an enabling mechanism that allows such devices to be integrated with slender continuum structures such as HARWs. The hosting system in question consists of a tendon that is guided across a series of methodically located points placed eccentrically along the span of the continuum. The working principle of the mechanism relies of the induced axial activity of the tendon triggered as a result of the movement of the primary structure, where a localised device (Tuned Mass Dampers, Nonlinear energy sinks, Inerter-Dampers, etc) can be integrated with the tendon at a point where an aggregate of the movement is observed. The scope of the presented study revolves around the mechanics behind the idealisation of the guiding elements and the tendon. For instance, with guides comprising of pulleys, the combination of their rotational inertia and the finite axial stiffness of the tendon gives rise to a secondary system that exhibits its own (coupled) dynamics. Moreover, the influence of impeding effects at the guides, not limited to the imposed inertia, is likely to influence the effectiveness of the motion aggregation capability of the mechanism. The present study aims to assess the suitability of an inerto-viscous idealisation of the guiding elements, along with the finite stiffness of the tendon. In addition to this, evidence of interactional behaviour between the introduced tendon-guide system and the primary structure are explored, as a mean of comparing the interlinked modal characteristics between experiment and the idealised interpretation of a guide.

An Acoustic Black Hole (ABH) is a scatterer, embedded in a panel, allowing passive vibration control without adding mass. In practice, it is achieved by means of a local reduction in thickness (axisymmetric disc with a parabolic profile) and the addition of a thin viscoelastic coating in a central region of uniform thickness. The vibration absorption induced by the ABH, allows the design of stiff, light and non-resonant panels. In this paper, we propose to study this effect for a three-layer sandwich panel (glass fiber skin/honeycomb core/glass fiber skin), which gives rise to both bending and shear effects. The equations of motion of the thick, symmetrical sandwich panel with variable characteristics is obtained within the framework of the zig-zag theory by applying Hamilton's principle. These equations lead to a sixth-order analytical model, allowing the dispersion curves to be obtained, and then an analytical model of the scatterer inserted in an infinite panel. The analysis of the local modes of the scatterer allows the evaluation of its absorption; the interpretation of the TNA effect is carried out using its scattering matrix, calculated in the complex frequency plane. The model allows in particular the analysis of the effect of shear on the TNA effect. Experimental tests, based on vibrational maps obtained by vibrometry, are used to discuss and validate the predictions.