818 research outputs found
Characteristics of smart composite wing with SMA actuators and optical fiber sensors
No full textRecently, morphing concepts for UAV or MAV have been significant issues in aerospace engineering. Morphing wing concept, a biomimetic technology in aerospace engineering, has been realized by various methods including changes of wing's cross-section, plan form, and spar position. This paper investigates a morphing wing with variable camber using SMA actuators. The test model is a symmetric wing structure composed of two tapered graphite/epoxy composite plates and a steel body. Shape memory alloy (SMA) is attracting much attention as actuators for controlling the shape of structures because of high recovery force and large deformation. Four pairs of the SMA wire actuators are attached on the bottom surfaces of the wings in the chord-wise direction. SMA actuators produce enough deformation to cause significant improvement the static and dynamic characteristics of the wing model. Lift and drag forces, most important static aerodynamic characteristics, were measured at various angles of attack. Lift of the wing was increased without increasing drag forces when electric current was applied to the SMA actuators. Dynamic vibration signals were measured by FBG sensor at the root of the wing. The FBG sensor was successfully applied to the monitoring of the aeroelastic unstable phenomena at various angles of attack. At flutter speed, limit cycle oscillation with constant frequency occurred. It was also observed that the vibration energy is concentrated on the flutter mode and increased with the increase of the airflow speed. The effects of the angle of attack on aeroelastic characteristics of the wing were investigated. The amplitude of the limit cycle oscillation was significantly reduced at the flutter velocity when SMA actuators were activated.This research was performed for the Smart UAV Development program, one of the 21st Century
Frontier R&D Programs funded by the Ministry of Science and Technology of Korea. The authors also
acknowledge the support from the National Research Laboratory (NRL) Program
Vibration Characteristics of Pre and Post Buckled Laminated Composite Spherical Shells
No full textThis work was supported by Defense Acquisition Program Administration and Agency for the
Defense Development under the contract UD060009AD. The first author thanks the support of
the second stage of the Brain Korea 21 project in 2007
Configuration Control of Aerospace Structures with Smart Materials
No full textThis article introduces some analytical and experimental researches on the application of smart materials, especially shape memory alloys (SMAs)and FBG optical fibers to control the shape and vibration of aerospace structures such as the inflated cylindrical beam and wing. In the first section, the methodology for adjusting the configuration of inflated cylindrical using SMA thin is presented. The second one is about the aeroelastic characteristic of Smart Composite Wing fabricated using SMA actuators and a FBG optical fiber sensor
Adaptive Thermal Post-buckling Responses of Shape Memory Hybrid Composite Shell Panel
No full textThis research was performed for the Smart UAV Development program, one of the 21st Century Frontier R&D Programs funded by the Ministry of Science and Technology of Korea
Study of a reduced and internally biased oxide wafer PZT actuator and its integration with shape memory alloy
No full textLarge displacement piezoelectric actuators of a new kind-RAINBOW (reduced and internally biased oxide wafer) actuators, which are composed of reduced and unreduced layers-were prepared from PZT (Pb(ZrxTi1-x)O-3) by chemical reduction. The distribution of stress inside the RAINBOW structure and its actuating properties were both studied. It is found that the optimal ratio of reduced layer thickness for the RAINBOW structure is 0.3; reduced RAINBOW PZT has a lower resonance frequency and a three-times-larger displacement than traditional PZT; furthermore, the possibility of integration of PZT and SMA (shape memory alloy) was also explored. The PVD (physical vapor deposition) method was applied to deposit SMA coatings on the reduced layers of RAINBOW PZT patches. Results of mechanical and actuating experiments show that this is a reasonable idea for manufacturing actuators with better performance.This work was financially supported by the Chinese
Aeronautics Foundation (04G52042). In addition, the author was also supported by the Brain Korea 21 program in
KAIST
Improved Aerodynamic Model for Efficient Analysis of Flapping-Wing Flight
No full textThis work was supported by a Korea Research Foundation Grant
funded by the Korean Government (MOEHRD) (KRF-2007-313-
D00122). The second author would like to thank the Brain Korea 21
Project in 2010. The authors would like to thank James D. DeLaurier
of the University of Toronto and M. Okamoto of the Akita National
College of Technology for their gracious support for this study. The
authors also thank anonymous reviewers and the Editor for their
valuable comments and suggestions
Correlated insulator collapse due to quantum avalanche via in-gap ladder states
No full textThe significant discrepancy observed between the predicted and experimental switching fields in correlated insulators under a DC electric field far-from-equilibrium necessitates a reevaluation of current microscopic understanding. Here we show that an electron avalanche can occur in the bulk limit of such insulators at arbitrarily small electric field by introducing a generic model of electrons coupled to an inelastic medium of phonons. The quantum avalanche arises by the generation of a ladder of in-gap states, created by a multi-phonon emission process. Hot-phonons in the avalanche trigger a premature and partial collapse of the correlated gap. The phonon spectrum dictates the existence of two-stage versus single-stage switching events which we associate with charge-density-wave and Mott resistive phase transitions, respectively. The behavior of electron and phonon temperatures, as well as the temperature dependence of the threshold fields, demonstrates how a crossover between the thermal and quantum switching scenarios emerges within a unified framework of the quantum avalanche. © 2023, The Author(s).11Nsciescopu
Bio-inspired Flapping UAV Design: A University Perspective
No full textThis work was supported by KAIST Institute for Design of Complex Systems. The second author would like to thank the
Brain Korea 21 Project of 2009
Zoology of domain walls in quasi-2D correlated charge density wave of 1T-TaS2
No full text© 2021, The Author(s).Domain walls in correlated charge density wave compounds such as 1T-TaS2 can have distinct localized states which govern physical properties and functionalities of emerging quantum phases. However, detailed atomic and electronic structures of domain walls have largely been elusive. We identify using scanning tunneling microscope and density functional theory calculations the atomic and electronic structures for a plethora of discommensuration domain walls in 1T-TaS2 quenched metastably with nanoscale domain wall networks. The domain walls exhibit various in-gap states within the Mott gap but metallic states appear in only particular types of domain walls. A systematic understanding of the domain-wall electronic property requests not only the electron counting but also including various intertwined interactions such as structural relaxation, electron correlation, and charge transfer. This work guides the domain wall engineering of the functionality in correlated van der Waals materials.11Nsciescopu
Programmable photonic arrays based on microelectromechanical elements with femtowatt-level standby power consumption
No full textProgrammable photonic integrated circuits offer exciting opportunities for optoelectronic signal processing, computing and communications in a number of emerging applications in classical and quantum photonics. In this work, we show the array-level demonstration of tunable couplers and phase shifters with capacitive electrostatic microelectromechanical actuators in a recirculating mesh network. The overall fabrication process is compatible with the conventional wafer-level passive silicon photonics platform. Extremely low unit-level standby power consumption of <10 femtowatts and reconfiguration energy of <40 picojoules with <11 V programming voltages offer well-balanced, scalable routes for efficient phase and amplitude modulation of the guided lightwaves with sub-decibel optical losses. The extinction ratios of the continuously tunable directional coupler exceed 30 dB. Full 2π-phase shifting can be achieved with a modulation efficiency of less than 0.075 V cm and a phase-dependent insertion-loss variation of 0.01 dB. © 2023, The Author(s), under exclusive licence to Springer Nature Limited.FALSEsciescopu
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