MS2.2 Advances in Control of Structural Vibrations

Liquid storage tanks are an integral part of any industry, including chemical, gas, or nuclear and are the fundamental civil engineering structure employed in public utility for various functions, including the delivery of drinking water and the suppression of fires. Storage tanks are more prone to sustain severe damage during seismic excitations due to their strong base shear response and large convective displacement. This study proposes a hybrid control strategy with a clutched inerter (CID) for the seismic protection of a base-isolated (BI) liquid storage tank. A bilinear lead rubber bearing (LRB) and a linear rubber bearing (RB) are used as isolation devices, whilst a CID connects the rubber bearings to the ground through an inerter. Seven actual earthquake ground motions are considered. Furthermore, a MATLAB code using the State-Space approach is developed to examine the broad and slender BI tank's seismic performance to determine the inerter system's efficiency. A parametric analysis has been performed to assess the impact of the CID's inertance mass ratio and aspect ratio of the tank on the peak bearing and sloshing displacement, peak sloshing acceleration, and peak normalized base shear responses. Based on the response of time history analysis performed under seven ground motion records, the proposed hybrid control strategy shows a reduction in the bearing displacement response and meets the required demands of sloshing displacement. The inertance mass ratio of the CID is optimum when the total base shear response is significantly reduced. The CID, however, adds to the sloshing acceleration response, which can be offset by the tank's improved total base shear response and reduced isolation displacement.

The subject of this paper is the control of flexural waves on an infinite beam using a vibration neutraliser located in the far field of a forcing input. The neutraliser analytical model consists of a beam carrying three concentrated masses that can be further simplified to a mass-spring-mass system given the system symmetry. Depending on the input frequency, position and value of the masses can be tuned either to maximize the power reflection or the power absorption. The bandwidth of attenuation is limited so the neutraliser may become ineffective when the forcing frequency changes. To overcome this limitation, shape memory alloy wires are used to design an adaptive beam neutraliser. The wires, made of a Nitinol alloy, exhibit a change with temperature in the elastic modulus of the material caused by a lattice structure reorganisation. This property allows adaptive tuning for different input frequencies via flexural rigidity variation. A preliminary design of the neutraliser is proposed. Analytical and experimental data are compared to assess the validity of the model.

Tuned vibration neutralisers are used to suppress the vibration of a host structure subjected to external harmonic forces. Although they are analogous to tuned vibration absorbers, the primary difference is that while absorbers are usually designed with optimum damping to attenuate vibration in a frequency range around a resonance, neutralisers are designed with relatively low damping to act as a mechanical notch-filter. The narrow band frequency in which the conventional neutralisers are effective, and the mistuning compromising their performance, are known problems. Thus, self-tuning vibration neutralisers were introduced to make them more robust. In many cases, however, these systems need an external power source to adapt. This paper concerns an investigation into a self-tuning vibration neutraliser for two distinct frequencies, that does not need an external power source. It consists of a rectangular beam with tip masses, which is held at its centre in a roller bearing that is fixed to a host structure. The rectangular cross section has two different stiffnesses in the local coordinates that can rotate with respect to the global reference. Results from some experimental tests compare very well with time domain numerical simulations. It is shown that the coupling between two orthogonal degrees-of-freedom enables the neutraliser to passively tune to one of two tuned frequencies, depending on the frequency of the external harmonic force.