Dynamics and control of truss structures with extendable members

Rong Tyai Wang, Purdue University

Abstract

The object of the research is to investigate the effectiveness of using extendable truss members to tailor the vibrational characteristics of large truss structures. In contrast to the conventional control of structures using actuators mounted externally on the structure, the use of extendable truss members allows one to vary the control force internally, and, thus, achieve a change in natural frequencies and damping factors. If the actuator in the extendable member reacts to the member force instantaneously, then a negative gain will give rise to a stiffening effect and damping effect is also magnified. Explicit relations between the apparent structural stiffness and damping factor are derived in this study. If there is a delayed response in the actuator, then the gain must be chosen positive in order to achieve dynamic stability of the system. Further, the value of the gain must be less than unity. It is found that delay-time can be used most effectively to provide significant damping effect. Power transmission through a cell with extendable members is also studied. The power loss of a wave passing through this cell is found to depend highly on the modes of wave and on its wavelength. The potential use of the extendable members in the cells at the boundary of the structure is also investigated. For a wave with given frequency, it is possible to design the internal control force to completely absorb the energy of the incident wave. For large truss structures consisting of repeating identical cells, the dynamic characteristics can be found from the typical cell. A simple procedure is presented to derive natural frequencies of large structures from a single cell characteristics. This procedure greatly reduces the amount of computation needed in vibration analysis of large truss structures.

Degree

Ph.D.

Advisors

Sun, Purdue University.

Subject Area

Aerospace materials

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