Browsing by Author "Na, Sungsoo"
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- Control of Dynamic Response of Thin-Walled Composite Beams Using Structural Tailoring and Piezoelectric ActuationNa, Sungsoo (Virginia Tech, 1997-09-28)A dual approach integrating structural tailoring and adaptive materials technology and designed to control the dynamic response of cantilever beams subjected to external excitations is addressed. The cantilevered structure is modeled as a thin-walled beam of arbitrary cross-section and incorporates a number of non-classical effects such as transverse shear, warping restraint, anisotropy of constituent materials and heterogeneity of the construction. Whereas structural tailoring uses the anisotropy properties of advanced composite materials, adaptive materials technology exploits the actuating/sensing capabilities of piezoelectric materials bonded or embedded into the host structure. Various control laws relating the piezoelectrically-induced bending moment with combined kinematical variables characterizing the response at given points of the structure are implemented and their effects on the closed-loop frequencies and dynamic response to external excitations are investigated. The combination of structural tailoring and control by means of adaptive materials proves very effective in damping out vibration. In addition, the influence of a number of non-classical effects characterizing the structural model on the open and closed-loop dynamic responses have been considered and their roles assessed.
- Dynamic Response of Cantilevered Thin-Walled Beams to Blast and Sonic-Boom LoadingsLibrescu, Liviu; Na, Sungsoo (Hindawi, 1998-01-01)
- Vibration and dynamic response control of cantilevers carrying externally mounted storesLibrescu, Liviu; Na, Sungsoo (Acoustical Society of America, 1997-12-01)The vibrational and dynamic response control of cantilevers carrying externally mounted stores is investigated, The cantilevered structure is modeled as a thin-walled beam of arbitrary cross section and incorporates a number of nonclassical effects such as transverse shear, secondary warping, anisotropy of constituent materials, and heterogeneity of the construction. The control is carried out via a dynamic bending moment applied al the rip of the structure. A feedback control law relating the boundary moment with one of the kinematical variables characterizing the response of the beam is implemented, and its results upon the closed-loop eigenfrequencies and dynamic response are highlighted. The obtained numerical results emphasize the efficiency of this control methodology to enhance, without weight penalties, vibrational and dynamic response behavior and inhibit and even suppress the occurrence of the resonance phenomenon. (C) 1997 Acoustical Society of American. [S0001-4966(97)01712-8].
- Vibration and Dynamic Response Control of Nonuniform Composite Rotating BladesNa, Sungsoo; Librescu, Liviu; Rim, Sung-Nam; Yoon, Gwon-Chan (Hindawi, 2006-05-08)This paper addresses the free vibration, dynamic response, and theactive control of composite rotating pretwisted blades modeled asnonuniform thin-walled beams, fixed at the hub at a settingangle, and incorporating piezoelectrically induced dampingcapabilities. In this sense, a distributed piezoelectric actuatorsystem activated through the application of an out-of-phaseelectrical current is used to suppress the dynamic response of therotating beam subjected to a Heaviside pulse. The blade modelincorporates nonclassical effects such as transverse shear,secondary warping, and rotary inertias, and includes thecentrifugal and Coriolis force fields. A velocity feedback controllaw relating the piezoelectrically induced bending moment at thebeam tip with appropriately selected kinematical responsequantities is used, and the beneficial effects of itsimplementation upon the closed loop eigenvibration and dynamiccharacteristics of the blade are highlighted.