• 한국항공우주학회지
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• 제44권7호
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• pp.552-561
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• 2016

본 연구에서는 강제진동 기법을 이용하여 람다형상을 갖는 무미익 무인기의 동안정 미계수를 측정하였다. 강제진동 기법은 시험모델을 일정한 크기의 각 변위로 진동시키면서 항공기에 작용하는 공력의 시간이력(time history) 데이터를 측정하고, 입력진동 대비 공력데이터의 위상차와 진폭을 추출함으로써 비행체의 동안정 미계수를 계산하는 방법이다. 본 연구에서는 롤, 피치, 요 방향으로 각각 진동시킬 수 있는 실험 장치를 설계, 제작하여 국내 최초로 무미익 항공기의 동안정 미계수 측정 시험을 수행하였다. 롤 댐핑 동안정 미계수 측정 결과, 진동 주파수와 진동의 크기가 증가하여도 동안정 미계수의 경향성은 동일하게 나타나며, 전반적으로 측정 받음각 구간에서 안정한 특성을 보였다. 피치 댐핑 동안정 미계수의 경우 작은 진동 주파수에서 동적으로 더 안정해지며, 받음각 $15^{\circ}$ 이상에서는 동적으로 불안정해지는 경향성을 보였다. 각 시험데이터들은 반복성 시험을 통해 데이터의 신뢰성을 검증하였으며, 본 연구에 적용된 강제진동 기법이 무미익 항공기의 동안정 미계수를 성공적으로 측정할 수 있음을 확인하였다.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1990년도 하계학술대회 논문집
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• pp.135-138
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• 1990

For transient stability analysis of a power system, the new method using transition matrix is introduced in this paper. At the present the, Runge-Kutta, Modified-Euler and Trapezoidal methods have been very popular in most stability programs, Modified-Euler and Trapezoidal methods are inferior in accuracy and Runge-Kutta method has problems in computation time. The proposed algorithm requires transition matrix and its integrated values with derivatives of nonlinear parts in nonlinear differential equations for stability analysis. The method presented in this paper is between Modified-Euler and Runge-Kutta methods from the view point of computation time and is superior to the other methods in accuracy.

• 한국항공우주학회지
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• 제40권5호
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• pp.385-394
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• 2012

아음속-초음속 패널법(panel method)을 이용하여 항공기의 정적 안정성 미계수와 동적 안정성 미계수 및 조종미계수를 예측할 수 있는 프로그램을 개발하였다. 사용된 코드는 아음속-초음속 소스(source)와 말굽 와류(elementary horse shoe vortex)의 분포를 사용하고, 그 분포의 크기는 얇은 물체 근사(thin body approximation)을 적용하여 간략히 한 경계 조건을 이용하여 계산하였다. 항공기에 부착된 물체 좌표계에서 준정상(quasi-steady) 해석을 통해서 항공기 3축의 댐핑 계수를 예측하였다. 개발된 코드는 삼각날개(delta-wing)의 중립점(neutral point), 롤, 피치 댐핑 계수의 이론치와 비교하여 검증하였다. 마지막으로 F-18의 정적, 동적 안정성 미계수와 조종 미계수를 풍동 시험치와 계산치에 비교하여 개발한 코드의 정확성과 유용성을 확인하였다.

• Wind and Structures
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• 제9권2호
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• pp.159-178
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• 2006

For the slender and flexible cable supported bridges, identification of all the flutter derivatives for the vertical, lateral and torsional motions is essential for its stability investigation. In all, eighteen flutter derivatives may have to be considered, the identification of which using a three degree-of-freedom elastic suspension system has been a challenging task. In this paper, a system identification technique, known as covariance-driven stochastic subspace identification (COV-SSI) technique, has been utilized to extract the flutter derivatives for a typical bridge deck. This method identifies the stochastic state-space model from the covariances of the output-only (stochastic) data. All the eighteen flutter derivatives have been simultaneously extracted from the output response data obtained from wind tunnel test on a 3-DOF elastically suspended bridge deck section-model. Simplicity in model suspension and measurements of only output responses are additional motivating factors for adopting COV-SSI technique. The identified discrete values of flutter derivatives have been approximated by rational functions.

• 한국수학교육학회지시리즈B:순수및응용수학
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• 제21권1호
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• pp.61-75
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• 2014

The purpose of this paper is to obtain some integral inequalities with impulses by using the method of Stieltjes derivatives, and we use our results in the study of Lyapunov stability of solutions of a certain nonlinear impulsive integro-differential equation.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1992년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 19-21 Oct. 1992
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• pp.153-158
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• 1992

The purpose of this paper is to calculate the dynamic derivatives of single rotor Helicopter in forward flight. From trim condition, the equation of motion is derived, and we can calculate the dynamic dervatives. The results were compared with flight test data. The phase angle and stick displacement are obtained and compared at the trim condition.

• 한국정보디스플레이학회:학술대회논문집
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• 한국정보디스플레이학회 2004년도 Asia Display / IMID 04
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• pp.873-876
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• 2004

New Oligothiophene derivatives having liquid crystalline property have been designed, synthesized and characterized. New oligothiophene derivatives were prepared by a palladium-catalyzed cross-coupling reaction via zinc-substituted thiophene. The structures of materials were characterized by various spectroscopies. The new obtained oligothiophene derivatives showed high thermal stability above 300 $^{\circ}C$ and exhibited several transition temperatures, evidence of mesophase. In field-effect transistors, a charge carrier mobility of 1.9 x $10^{-2}$ $cm^2$/Vs was observed.

• Bulletin of the Korean Chemical Society
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• 제33권2호
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• pp.564-570
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• 2012

s-Tetrazine is the essential candidate of many energetic compounds due to its high nitrogen content, enthalpy of formation and thermal stability. The present study explores the design of s-tetrazine derivatives in which different $-NO_2$, $-NH_2$ and $-N_3$ substituted azoles are attached to the tetrazine ring via C-N linkage. The density functional theory (DFT) is used to predict the geometries, heats of formation (HOFs) and other energetic properties. The predicted results show that azide group plays a very important role in increasing HOF values of the s-tetrazine derivatives. The densities for designed molecules were predicted by using the crystal packing calculations. The introduction of $-NO_2$ group improves the density as compared to $-N_3$, and $-NH_2$ groups and hence the detonation performance. Bond dissociation energy analysis and insensitivity correlations revealed that amino derivatives are better candidates considering insensitivity and stability.

• 한국소음진동공학회논문집
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• 제19권6호
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• pp.575-582
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• 2009

This study presents the vibration excitation system to extract the aerodynamic stability derivatives which is generally called as flutter derivatives in civil engineering. The system consists of the excitation part to give a forced harmonic motion to the model and the sensing part to measure the aerodynamic forces as well as inertia forces acting on a bridge model. A data processing algorithm for extracting the flutter derivatives from the measured forces is also presented. From the wind tunnel tests, verification of present system was done by comparing the measured and analytical results for rectangular shaped model. The effects of excitation frequencies and amplitudes on flutter derivatives are discussed. Five kinds of actual bridge model were presented from the wind tunnel.

• 한국환경보건학회지
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• 제31권6호
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• pp.498-503
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• 2005

Stability of soybean isoflavone isomers according to extraction conditions such as temperature, pH, and extracting solvents was investigated. Heating induced three chemical reactions to occur for malony1 derivatives of isoflavones, namely decarboxylation of malony1 groups into acety1 derivatives, deesterification of malony1 residues, and hydrolysis of $\beta$-glycosidic bonds. Among the twelve isoflavone isomers, change in concentrations of acety1glycosides were most pronounced: Acety1 derivatives were present only in trace amounts in unheated hypocotyls, but the content increased dramatically during heating. As for the glycosides, concentrations of daidzin and glycitin increased due to heat treatment, though that of genistin remained almost unchanged. Heat decomposition rates and the patterns differed among the three malony1 derivatives. After 120 min at $80^{circ}C$, the relative concentrations of daidzin, glycitin and genistin were increased from $9.2\%$, $12.4\%$ and $3.3\%$ to $19.3\%$, $21.9\%$ and $6.2\%$, respectively. When crude isoflavones were solubilized in glycine buffer (pH 10.0) and incubated at $80^{circ}C$, deesterification occurred faster than at pH 7.0. When the pH of isoflavone solution was increased, the malony1glycosides were hydrolyzed to their respective glycosides at increased rate. Both acetyl and aglycone forms were unchanged and only de-esterification reactions occurred. At the acidic pH, malonylglycosides were much stable both at 60 and $80^{circ}C$. However at pH 10, $80^{circ}C$ and 1 hr, $75-80\%$ of malonylglycosides were transformed to their deesterified glycosides. When isoflavones were extracted with $60\%$ aqueous ethanol at $60^{circ}C$, isoflavone isomers were stable and the deesterification reactions did not occur in these conditions. However, at $80^{circ}C$ deesterification of malonyiglycosides occurred significantly with $15-20\%$ of malonylglycosides being hydrolyzed into their respective glycosides. This experiment showed that malonylglycosides undergo decomposition when heated or exposed to alkaline conditions. Also, aqueous ethanol was preferred to aqueous methanol as solubilizing media for obtaining extract with minimum degradation of malonylglycosides.