10:15am - 10:45amUse of a hysteretic device in vibration mitigation (Keynote Lecture)
F. Vestroni, P. Casini
Sapienza University of Rome, Italy
Nonlinearities produce notable modifications of the dynamic response of mechanical systems. Nonlinearity is usually experienced as a source of unease, not to mention undesirable effects. However, recent advances make it possible to recognize that nonlinearity can also play a critical role and can even give advantageous effects [1].
Nonlinear coupling is an important phenomenon. In the case of strong nonlinearities, which characterize most of proposed nonlinear absorbers, the involvement of modes not directly excited is greater and novel phenomena occur. Here, focus is on the occurrence of novel periodic motions, that is the nonlinear system exhibits a number of resonances greater than the number of degrees-of-freedom, favouring the spreading of energy among the modes.
A standard technique to lower structural vibration of increasingly lean structures is to use elements capable of dissipating energy. The proposal to add a hysteretic element makes it possible to combine the twofold aim of increasing the structure dissipation and of introducing a strong nonlinearity. Hysteresis characterizes the mechanical behaviour of various materials and elements. With respect to viscoelastic tuned mass damper (TMD), introduced by the pioneering work by Den Hartog [2], the restoring force of a hysteretic vibration absorber combines the elastic and dissipation characteristics without the need of a damper. The modification of resonance frequencies, due to the notable dependence of stiffness and damping properties on the oscillation amplitude, easily leads to condition of internal resonance, with an increase of nonlinear modal coupling [3].
The hysteretic device, referred to is based on the restoring force of cables in flexure and it is described by the Bouc-Wen model, whose parameters are identified by experimental results. First, the case of internal resonance 1:1 which resembles the Den Hartog proposal is dealt with. In a definite excitation range, its effectiveness is similar to that of viscoelastic TMD, but in this case no typical phenomena of nonlinear dynamics are activated. Then, is the case of internal resonance conditions n:1, with 𝑛𝑛 > 1 which promotes a rich variety of nonlinear phenomena. In particular, the occurrence of a novel mode around the first resonance through a bifurcation mechanism involves the second mode in the response, with a beneficial effect on the vibration amplitude of the directly excited first mode. The analysis performed demonstrated the efficiency of adding a hysteretic element to a structure, suitably tuned, for the passive control of structural vibrations.
[1] A.F. Vakakis, O.V. Gendelman, L.A. Bergman, D.M. McFarland, G. Kerschen, Y.S. Lee, Nonlinear Targeted Energy Transfer in Mechanical and Structural Systems, vol. 156, Springer, Dordrecht (2008) [2] J.P. Den Hartog, Mechanical Vibrations; McGraw-Hill: New York, NY, USA, 1934. [3] P. Casini, F. Vestroni, The role of the hysteretic restoring force on modal interactions in nonlinear dynamics. Int. J. Non-Linear Mech., 143, 104029, 2022.
10:45am - 11:15amA theoretical and experimental study on the optimal design of Sliding Tuned Liquid Column Dampers for structural vibration control (Keynote Lecture)
C. Masnata1, C. Adam2, A. Pirrotta1
1University of Palermo, Italy; 2Universität Innsbruck, Austria
This study proposes a passive structural vibration control strategy based on the use of a sliding variant of the well-known Tuned Liquid Column Damper device (referred to as STLCD) and examines both theoretical and experimental perspectives. The STLCD configuration consists of a U-tube container filled with liquid that can slide along a linear guide rail and is connected to the structure by a spring-dashpot system. This setup, unlike conventional fixed TLCDs, offers the flexibility of tuning for short-period systems since the spring can be used for tuning and the dashpot for added damping. However, similar to TLCDs, the STLCD also shows slightly nonlinear behavior, hence, an equivalent linear mechanical model is employed to streamline the analyses necessary for the optimal design of the device. In particular, the selection process of the optimal design parameters of the STLCD is discussed, assuming a Gaussian white noise process as base excitation, with the aim of minimizing the total acceleration variance of the structural system. To validate the introduced mathematical formulation, experimental tests are conducted at the Laboratory of Experimental Dynamics at the University of Palermo, Italy, examining both time and frequency domains. Finally, the control performance of a scaled model of an STLCD-controlled structure is evaluated against its uncontrolled counterpart and commonly used devices such as the TLCD and the Tuned Mass Damper (TMD), under harmonic excitations, providing a comparative analysis.
11:15am - 11:35amImplementation of tuned mass damper control concept for integrated seismic and energetic retrofit of existing buildings
M. Basili1, M. De Angelis2, F. Busato1
1Universitas Mercatorum, Rome, Italy; 2Sapienza University, Rome, Italy
Structural rehabilitation of existing building heritage often built without modern seismic design considerations is a critical issue in seismic prone regions of the European community, where the 40% of them is affected by moderate earthquake activity. At the same time, energy rehabilitation to enhance existing buildings energy efficiency is a key issue, since the 75% is considered energy inefficient due to aging. While seismic and energy rehabilitation have been always considered two separate problems, in recent years the scientific community is making efforts to explore integrated seismic and energy retrofitting techniques, combining into a single assessment, aiming at simultaneous benefits also pointing to a more sustainable design [1].
The study explores new possible schemes where the structural control strategy based on the tuned mass damper concept is effectively combined with suitable energy retrofitting strategies in a single intervention. In fact, while tuned mass damper ant its variations, is considered effective for mitigating the seismic risk, it is not explored in conjunction with interventions to improve buildings energy efficiency. The integrated interventions proposed are implemented on the building roof, which can be disconnected and isolated from the substructure, or rebuilt and isolated from the substructure, adding improved energy performances. Various structural solutions are investigated based on different control approaches: non-conventional TMD, large mass TMD [2], TMD with inerter [3]. The framework where the methodology for the implementation of the integrated intervention, comprising its optimal design and the structural and energy assessment, is described. Numerical simulations on a typical example of the Italian building stock are presented where the different integrated strategies are compared and a procedure to select the best integrated intervention is highlighted.
References
[1] Pohoryles D.A. et al. J.Build.Eng. 2022,61,105274.
[2] Reggio A. et al. Earth.Eng.Struct.Dyn., 2015,44,1623–1642.
[3] Pietrosanti D. et al. Earth.Eng.Struct.Dyn., 2017,46,1367–1388.
11:35am - 11:55amA fundamental study on active vibration control of cross-laminated timber members
N. Hirschfeldt, T. Furtmüller, C. Adam
Universität Innsbruck, Austria
Cross-laminated timber (CLT) is a structural member composed of layers of wood glued together perpendicular. When compared to common concrete or steel structures, CLT structures are considered lightweight, which makes them more prone to vibrations that can cause discomfort to people inside buildings made of CLT. It is therefore desirable to reduce the vulnerability of CLT components to vibration by implementing smart measures, such as passive or active control mechanisms, without changing the design of the CLT structure. This paper presents a study on the feasibility of active vibration control of CLT panels based on laboratory tests and mathematical modelling. In the laboratory tests, external excitation is applied by electrodynamic shakers. The resulting CLT-shakers assembly is an electromechanical system, i.e., a system composed of a mechanical and an electromagnetic subsystem, which interact through coupling elements. First, system identification is performed to obtain the parameters composing the CLT-shakers system, which are both mechanical (such as mass, damping and stiffness elements) and electromagnetic (such as inductance and resistance) in origin, where a mathematical model of the whole electromechanical system is compared with experimental data of the multi-input multi-output system excited by both shakers with independent white noise inputs. Active vibration control depends on an external power supply and requires a set of actuators and sensors. In this study, active vibration control of the CLT panel is performed by using one of the shakers for excitation and the other one for control. A setup where the target point of vibration mitigation and actuator are not positioned in the same location in the CLT panel is used, known as non-collocated control. This non-collocated configuration poses additional challenges in the control process and will be examined in more detail. Both Velocity Feedback and Optimal Control are conducted, presenting two different approaches to non-collocated vibration control.
11:55am - 12:15pmNanoscale modeling for structural vibration control
R. Barretta1, R. Luciano2, F. Marotti de Sciarra1, M. S. Vaccaro1
1University of Naples Federico II, Italy; 2University of Naples Parthenope, Italy
Smart ultrasmall devices offer fascinating opportunities for structural control since they enable extremely accurate and efficient real-time monitoring of parameters such as strain, stress, vibration and temperature [1-2]. Due to their reduced size, small-scale sensors allow for placement in hard-to-reach areas of structures while nanoactuators can conveniently operate according to the sensor feedback. Nanoscale energy harvesters can convert structural vibrations into electrical energy, supporting self-powered structural monitoring without external power sources. Additionally, NEMS-enabled structures can be integrated into Internet of Things networks for remote monitoring. To properly model these nanodevices, accurate assessment of size effects is needed. The work investigates dynamics of nano-systems, exploiting non-conventional approaches of nonlocal continuum mechanics [3-4]. Modelling of size effects is achieved adopting an integral approach based on a stress-driven convolution [5]. The relevant problem is reverted into an equivalent differential formulation. Fundamental natural frequencies are numerically assessed for selected case studies of current nanomechanical interest, providing benchmark results for modelling and design of small-scale devices.
[1] Han D., Hosamo H., Ying C., Nie R. A Comprehensive review and analysis of nanosensors for structural health monitoring in bridge maintenance: Innovations, challenges, and future perspectives. Appl. Sci. 13(20), 11149 (2023). [2] Javaid M., Haleem A., Singh R. P., Shanay Rab S., Suman R. Exploring the potential of nanosensors: A brief overview. Sensors International 2, 100130 (2021). [3] Di Matteo A., Pavone M., Pirrotta A. Exact and approximate analytical solutions for nonlocal nanoplates of arbitrary shapes in bending using the line element-less method. Meccanica 57, 923–941 (2022). [4] Barretta R., Čanađija M., Feo L., Luciano R., Marotti de Sciarra F., Penna R. Exact solutions of inflected functionally graded nano-beams in integral elasticity. Compos. B Eng. 142, 273-286 (2018). [5] Romano G., Barretta R. Nonlocal elasticity in nanobeams: the stress-driven integral model. Int. J. Eng. Sci. 115, 14–27 (2017).
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