Title

Semi-active control of air-suspended tuned mass dampers

Date of Award

2012

Degree Name

Ph.D. in Mechanical Engineering

Department

Department of Mechanical and Aerospace Engineering

Advisor/Chair

Advisor: Reza Kashani

Abstract

Extensive studies have been carried out, in recent years, to find methods to mitigate the unwanted structure vibration caused by human excitation, machinery, and winds. Modern structures such as floors and bridges using high strength materials, and extending across long spans are very flexible with negligible damping. Vibration control devices and strategies are constantly being developed to eliminate/dissipate the unwanted vibration and to increase the serviceability level of such structures. One such method for abating the vibration is tuned mass damping. In this dissertation, semi-active control of air-suspended tuned mass dampers with pendulum configuration was explored. A novel semi-active Air Sprung PTMD was designed, built, and evaluated, analytically and experimentally. The dynamics and control of such PTMD were evaluated, and its effectiveness was compared with that of the conventional passive PTMD. The main reason for introducing semi-active control to a TMD is to enable the TMD to adapt itself, robustly, to the primary structure's parameters (mainly mass and stiffness) changes and maintain its tuning. Following extensive analytical work, simulation, and experimentation it was found that the velocity feedback can modify the stiffness of the semi-active air-suspended tuned mass damper. Positive velocity feedback increases the stiffness while negative velocity feedback decreases it. Moreover, pressure and the acceleration feedback adjust the damping of the semi-active TMD. The air spring used in this work is of convoluted type. This type of air springs, because of their particular geometry, experiences a rather severe change in their cross-sectional area, as they contract and expand. It was found that to properly account for the impact of this important parameter on the inner-working of the air spring, one needs to consider two areas for the air spring, namely, the effective area and the geometric area. The effective area of the air spring is the area used to calculate the exerted force by the air spring while the geometric area is the cross-sectional area used to calculate the rate of change of the volume of the air enclosed in the air spring. The use of these two areas resulted in an accurate model of the air spring. The model of the semi-active PTMD was verified using the experimental setup. Both the simulation and experimental demonstrate the effectiveness of the semi-actively controlled air-suspended PTMD in adjusting its tuning frequency as well as damping.

Keywords

Tuned mass dampers, Damping (Mechanics), Structural stability, Mechanical engineering; semi-active control; TMD; air spring; vibration; air-suspended; stiffness; damping

Rights Statement

Copyright 2012, author

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