Semi-active Control of Base-isolated Structures

Abstract

A numerical and experimental analysis of semi-active (SA) control strategies for controlling seismic-excited structures is presented. A physical model consisting of a two degree-of-freedom (2DOF) mechanical system with a magneto-rheological (MR) damper was developed to evaluate this concept at LNEC's shaking table. Linear elastic and viscous models were used to describe the mechanical behavior of the 2DOF mechanical system. A Modified Bouc-Wen model was used to describe the behavior of the MR damper. Four distinct control strategies were implemented for numerical and experimental evaluation. The associated controllers were tuned using the system model and the ground motions information. The strategies were the integral control law, two linear quadratic regulator strategies and a predictive controller, in conjunction with a clipped on-off algorithm. In both the numerical and experimental tests the results reveal that the response of the structure is effectively mitigated by all of the analyzed control methods. It is shown that SA systems can outperform the original structure as well as one using the best passive solution for most of the strategies. The integral control law exhibits the best performance when collocated control was considered. If more responses are available for control, the linear quadratic regulator technique exhibits even better performance.

Effect of Particle Shape Anisotropy on the Performance and Stability of Magnetorheological Fluids

“…Thus, an MR fluid is a smart material. , The rheological properties of MR fluids can be easily controlled by regulating the strength of the external magnetic field and the volume fraction of magnetic particles. This unique feature has made MR fluids a core component in numerous industrial applications such as hydraulic valves, dampers, brakes, shock absorbers, actuators, medical systems, haptic devices, and polishing systems. − …”

Synergistic Effects of Nonmagnetic Carbon Nanotubes on the Performance and Stability of Magnetorheological Fluids Containing Carbon Nanotube-Co0.4Fe0.4Ni0.2 Nanocomposite Particles

“…A magnetorheological (MR) fluid is a suspension of magnetic particles in a nonmagnetic carrier medium and is classified as a smart material because of its unique response to an external magnetic field. − In an MR fluid under an external magnetic field, the magnetic particles aligned with the field direction because of magnetic dipole–dipole interaction, forming chainlike structures. , These structures inhibit the flow of the MR fluid and increase the viscosity by several orders of magnitude within a short time, resulting in a transition from a liquidlike state to a solidlike state. − This transition is reversible, and the rheological properties of an MR fluid can be easily controlled through manipulation of the magnetic field strength. , Such unique responsiveness and modifiability of rheological properties make MR fluids applicable to various devices, such as haptic devices, rotor dampers, and power steering pumps, where the flow of fluids needs to be controlled, and to devices such as shock absorbers in motorcycles and large damping systems in building and bridges to protect the systems from external impacts. − …”

Core–shell-structured Fe3O4 nanocomposite particles for high-performance/stable magnetorheological fluids: preparation and characteristics

“…Even though the saturation values of magnetization of Fe 3 O 4 nanocomposite particles are lower than other magnetic particles, still they have niche applications [10][11][12][13][14] which demand higher yield stress than the ER fluids and no electric field. Also, they have the edge in suspension stability which merits for the long-term application.…”

“…MR finishing for an optical system and an aspherical lens was introduced as a newer, and a high precision finishing method which includes MR fluids mainly by consisting of magnetic carbonyl iron (CI) particles and a carrier fluid such as silicone oil, hydrocarbon, or deionized water [10]. They are also found in large-scale damper systems such as seismic reduction for buildings and under bridges to mitigate vibrations caused by gusts [11][12][13]. In the application of crude oil, MR fluid could reduce the shear viscosity of crude oil production containing paraffin or asphaltene particles by changing their aggregation under the applied magnetic field [14].…”