1,721,023 research outputs found
Limit cycle oscillation of missile control fin with structural non-linearity
No full textNon-linear aeroelastic characteristics of a deployable missile control fin with structural non-linearity are investigated. A deployable missile control fin is modelled as a two-dimensional typical section model. Doublet-point method is used for the calculation of supersonic unsteady aerodynamic forces, and aerodynamic forces are approximated by using the minimum-state approximation. For non-linear flutter analysis structural non-linearity is represented by an asymmetric bilinear spring and is linearized by using the describing function method. The linear and non-linear flutter analyses indicate that the flutter characteristics are significantly dependent on the frequency ratio. From the non-linear flutter analysis, various types of limit cycle oscillations are observed in a wide range of air speeds below or above the linear divergent flutter boundary. The non-linear flutter characteristics and the non-linear aeroelastic responses are investigated. (C) 2003 Elsevier Ltd. All rights reserved.This research was supported by Agency for Defense Development (ADD) and the Ministry of
Science and Technology (National Research Laboratory Program) in the Republic of Korea. This
support is gratefully acknowledged
Flutter analysis of a wraparound fin projectile considering rolling motion
No full textThe aeroelastic stabilities of curved fins (or wraparound fins) in rolling motion are investigated in the supersonic flow region. Because of their inherent roll, wraparound fins are subjected to both aerodynamic and centrifugal forces. The aerodynamic force is computed by solving Euler equations in a body-fixed rotating coordinate frame. The normal mode analyses of the spinning structure are performed by using a multipurpose finite element code. For the consistent analysis a nondimensionalized aeroelastic equation considering the rolling motion is derived and aeroelastic parameters, such as velocity index and mass ratio, are devised. From the flutter analyses for wraparound fins, it is observed that the flutter characteristics with roll are very different from those without roll. It indicates that the consideration of the rolling motion must be made to predict the flutter stability accurately. Because of the geometric asymmetry of the wraparound fin, the flutter characteristics in each roll directions are different from each other. Flutter analyses indicate that there exists a more stable roll direction for flutter.This researchwas supportedby Agencyfor DefenseDevelopment
in the Republic of Korea. This support is gratefully acknowledged
Effects of structural nonlinearity on subsonic aeroelastic characteristics of an aircraft wing with control surface
No full textThe nonlinear aeroelastic characteristics of an aircraft wing with a control surface are investigated. A doublet-hybrid method is used for the calculation of subsonic unsteady aerodynamic forces and the minimum-state approximation is used for the approximation of aerodynamic forces. A free vibration analysis is performed using the finite element and the fictitious mass methods. The structural nonlinearity in the control surface hinge is represented by both free-play and a bilinear nonlinearity. These nonlinearities are linearized using the describing function method. From the nonlinear flutter analysis, various types of limit cycle oscillations and periodic motions are observed in a wide range of air speeds below the linear flutter boundary. The effects of structural nonlinearities on aeroelastic characteristics are investigated. (C) 2004 Elsevier Ltd. All rights reserved.This research was supported by Agency for Defense Development (ADD) and the Ministry of Science and
Technology (National Research Laboratory Program) in the Republic of Korea. This support is gratefully
acknowledged. And also, the authors appreciate the review and comments of Mr Christopher O. Johnston of Virginia
Tech about this paper and express special thanks to the associate Editor Dr Earl H. Dowell and reviewers for many
valuable comments and suggestions
A known-signal detector based on ranks in weakly dependent noise
No full textLocally optimum rank detection of known signals under a weakly dependent noise model is considered in this paper. The weakly dependent noise model is known to be useful for modeling inter-user interference, which is important in the synthesis and analysis of mobile communication systems. For good weak-signal detection performance under any specified noise probability density function, the locally optimum detector is derived based on signs and ranks of the observation. It is also shown that the locally optimum rank detector has the same asymptotic performance as the locally optimum rank detector which uses the actual values of the observations.Ministry of Information and Communication (MIC) under grant from the University Basic Research Fun
Linear and nonlinear aeroelastic analysis of fighter-type wing with control surface
No full textLinear and nonlinear aeroelastic analyses of a fighter-type Wing with a control surface have been performed by using frequency-domain and time-domain analyses. Modes from free vibration analysis and a doublet-hybrid method are used for the computation of subsonic unsteady aerodynamic forces. The fictitious mass modal approach is used to reduce the problem size and the computation time in the linear and nonlinear flutter analyses. For the nonlinear flutter analysis, the control surface hinge is, represented by a free-play spring and is linearized by using the describing function method. The linear and nonlinear flutter analysers indicate that the flapping mode of the control surface and the hinge stiffness have significant effects on the flutter characteristics. From the nonlinear flutter analysis, limit-cycle oscillation and chaotic motion are observed in a wide range of air speed below the linear flutter boundary, and a jump of limit-cycle oscillation amplitude is observed.This research was supported by the Agency for Defense Development
and the Ministry of Science and Technology (National
Research Laboratory Program) in the Republic of Korea. This support
is gratefully acknowledged
Effect of different oxidation methods on microstructures and properties of AlOx in magnetic tunnel junction
No full textEffects of actuator nonlinearity on aeroelastic characteristics of a control fin
No full textThe influences of actuator nonlinearities on actuator dynamics and the aeroelastic characteristics of a control fin were investigated by using iterative V-g methods in subsonic flows; in addition, the doublet-hybrid method (DHM) was used to calculate unsteady aerodynamic forces. The changes of actuator dynamics induced by nonlinearities, such as backlash or freeplay, and the variations of flutter boundaries due to the changes of actuator dynamics were observed. Results show that the aeroelastic characteristics can be significantly dependent on actuator dynamics. Thus, the actuator nonlinearities may play an important role in the nonlinear aeroelastic characteristics of an aeroelastic system. The present results also indicate that it is necessary to seriously consider the influence of actuator dynamics on the flutter characteristics at the design stage of actuators to prevent aeroelastic instabilities of aircraft or missiles. (C) 2007 Elsevier Ltd. All rights reserved.This research was supported by the Agency for Defense Development (ADD) in the Republic of Korea. This support is gratefully acknowledged
Fe-Cr-Ni 오스테나이트계 스테인리스강의 미소편석과 잔류 δ-페라이트 양에 대한 계산
No full textIn equilibrium, 304 stainless steel has only γ-austenite phase below about 1170℃ and solutes are uniformly distributed in γ-austenite. Due to incomplete solid-state diffusion, it has retained δ-ferrite as well as γ-austenite and the solute distribution becomes inhomogeneous in each phase. To further understand the solidification behavior of 304 stainless steel, the variation of δ-ferrite amount with temperature and the solute concentration in each phase across the phase boundary are calculated in this study. The calculated solute contents at the interface are in good agreement with experimental data available. It is shown that the equilibrium calculation using 304 steel composition itself produces better results than using equivalent composition. The calculated amounts of retained δ-ferrite using 304 equivalent composition are somewhat higher than experimentally observed values. Much better agreement between calculation results and experimental data is expected if more reliable experimental data can be obtained
Study of the effect of natural oxidation and thermal annealing on microstructures of AlOx in the magnetic tunnel junction by high-resolution transmission electron microscopy
No full textIn a magnetic tunnel junction, the formation of an insulator is sensitive and critical to the stable performance and reproducibility of the junction. The oxidation path and the microstructural change with time of the insulator in natural oxidation have been studied by the high-resolution transmission electron microscopy. It has been observed that the oxidation path is primarily through the grain boundary at an early stage of oxidation and then through the grains at a later stage. The morphology of the oxide layer was rugged and modulated. There also occurred an isotropic volume expansion with increased oxidation. It was observed that the ferromagnetic Co layer below an insulator was partially oxidized because of the preferred grain boundary oxidation. When this multilayer was annealed, the locally oxidized Co layer was reduced and the metallic layer formed as a continuous film type, thereby improving the interface. (C) 2002 American Institute of Physics.This research was supported by the Ministry of Science
and Technology through the Nanostructure Technology
Project. Additional support from the Ministry of Education
through the BK21 Project is also acknowledged
Extension of flutter prediction parameter for multimode flutter systems
No full textThis research was supported by the Agency for Defense Development
and was partially supported Ministry of Science and Technology
(National Research Laboratory Program) in the Republic of
Korea. This support is gratefully acknowledged. Authors express
thanks to the associate editor Franklin Eastep, and to reviewers for
many valuable comments and suggestions. Also, the authors appreciate
the review and comment of Henry A. Sodano of Virginia
Polytechnic Institute and State University about this paper
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