• Journal of the Korean Society for Aviation and Aeronautics
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• v.21 no.4
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• pp.41-46
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• 2013

This paper deals with an experimental technique for the measurement of dynamic stability derivatives in the roll motion of aircraft. Experimental aquisition method for aircraft's dynamic stability derivatives is conducted on the oscillation condition of aircraft model in the subsonic wind tunnel. The oscillation of aircraft model was forced by the oscillation apparatus. The forced oscillation technique is the method getting data from the internal balance inserted into the aircraft model during oscillating it. Dynamic stability derivatives of rolling motion were calculated by data reduction from the measurements of rolling moment, frequency and amplitude of aircraft model due to forced oscillation under wind conditions. Results of experiment is obtained similar one with those of roll dynamic stability derivatives measured in other institutes.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2011.04a
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• pp.332-335
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• 2011

바람에 의해 발생하는 장대교량의 진동현상은 버펫팅과 와류진동 그리고 플러터 등으로 구분할 수 있으며, 특히 설계풍속에 해당하는 강풍에 안전한 교량을 설계하는 것이 주된 관심사항이다. 이러한 장대교량의 공기역학적인 안정성 검토에 사용되는 플러터 계수를 풍동실험을 통하여 산정하였다. 본 논문에서는 일반적인 플레이트 거더교의 강풍에 대한 안정성을 검토하기 위하여 풍동실험을 수행하였으며, 자유진동 기법과 강제진동 기법을 사용하여 추출한 플러터 계수를 비교하였다. 자유진동 기법은 교량단면에 초기변위를 주어 상하 및 회전 진동을 하는 교량단면의 변위를 측정한 후 system identification 기법으로 플러터 계수를 구하게 된다. 그리고 강제진동 기법은 상하방향의 강제진동과 회전방향의 강제진동 실험을 독립적으로 수행하여 교량단면에 작용하는 풍하중과 단면의 진동을 분석함으로써 플러터 계수를 추정하게 된다. 그리고 플러터 계수의 비교를 통하여 강제진동 기법과 자유진동 기법의 장단점을 분석하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.44 no.7
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• pp.552-561
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• 2016

In this experimental study, the dynamic stability derivatives of a tailless lambda-shape UAV are estimated from time history data of aerodynamic moments measured from the internal balance while the test model is forced to oscillate at given frequencies and amplitudes. A 3-axis forced oscillation apparatus is designed to induce decoupled roll, yaw, pitch oscillations respectively. The results show that the roll damping derivatives remain stable at the entire range of angle of attack tested, whereas the pitch damping derivatives become unstable beyond $15^{\circ}$ angle of attack. The amplitude and frequency have little impact on roll damping derivatives while the smaller amplitude and frequency of oscillation improves the pitch stability. The yaw damping derivative values are fairly small as expected for a tailless configuration. The results indicate that the proposed methodology and test apparatus area valid for estimating the dynamic stability derivatives of a tailless UAV.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.6
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• pp.17-22
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• 2003

An airship is statically unstable, because it has no wing, relatively small tails and a large hull. Hence, an accurate prediction of dynamic stability is critical. In this study, dynamic stability data of the 50m Length Airship were acquired through forced oscillation wind tunnel tests. The tests were done in Birhle Applied Research Inc's Lange Amplitude Multi-Purpose(BAR LAMP) Facility located in Germany. The tests were composed with 16 static runs and 26 dynamic runs. As results, it is obtained that dynamic characteristics of the airship depend on the sideslip angle, the angular rate and its direction as well as the angle of attack. Generally, three directional moments have damping, but the normal force, the side force, and the cross-derivatives are unstable. The dynamic derivatives are not sensitive to the control surfaces, but nonlinear to the sideslip angle.

• Aerospace Engineering and Technology
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• v.2 no.2
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• pp.1-10
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• 2003

An airship is statically unstable, because it has no wing, comparatively small tail and large hull. Hence, an accurate prediction of dynamic stability is critical. In this study, dynamic stability data of the Mid-Size Airship is acquired through forced oscillation wind tests. The test was done in BAR LAMP which is Birhle Applied Research Inc's facility located in Germany. The test was composed with 16 static runs and 26 dynamic runs. As a result, dynamic characteristics of the airship depends on sideslip angle, angular rate and its direction as well as angle of attack. Generally, it is obtained that 3 directional moments have damping, but normal force, side force, and cross-derivatives are unstable. The dynamic derivatives are not sensitive to control surfaces, but have nonlinear dependency on sideslip angle.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.321-326
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• 2013

본 연구에서는 원형실린더의 강제 수평 및 수직진동에 따른 와흘림을 관찰하였다. EDISON_CFD의 가상경계법을 이용하여 원형실린더 주위 유동현상을 수치 모사하였다. 원형실린더의 강제 진동 특성에 따른 와흘림 진동수, 공력계수 등의 영향을 분석하였다. 특히, 진동방향에 따른 와흘림의 영향을 분석하여, 원형실린더의 강제 진동에 따른 유동의 선형성을 평가하였다.

• Journal of the Korea Institute of Military Science and Technology
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• v.3 no.2
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• pp.81-87
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• 2000

This paper presents an application of forced oscillation technique to measure pitch dynamic stability derivatives of a missile model in the low speed wind tunnel. The missile model is oscillated by D.C. electric servomotor with constant amplitudes and frequencies. Phase shift is determined as the difference of peak values between input and output signals from the dynamic stability balance installed at the center of gravity of the model. Stability derivatives were calculated by using phase shifts, amplitudes, forcing moments and input frequencies. Test results show the proper usage of the force oscillation technique with good damping effects.

• Proceedings of the KSME Conference
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• 2000.04a
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• pp.585-590
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• 2000

Problems involved in the numerical analysis on the forced oscillation of nonlinear oscillators such a microbubble oscillation under ultrasound and Duffing oscillator were discussed. One of the problems is proper choice of the time scale of the driving force. which is related to the numerical artifacts due to the mismatch between the natural frequency of an oscillator(or bubble) and the characteristic frequency of the applied force. Such problem may occur in a nonlinear oscillator whose behavior is crucially dependent on the frequency of the applied force. The artificial resonance problem during the numerical evaluation of such nonlinear systems was also discussed.

• Journal of Ocean Engineering and Technology
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• v.32 no.5
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• pp.341-350
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• 2018

A series of model tests was carried out to investigate the vortex-induced vibration (VIV) characteristics of a free hanging PVC pipe under forced oscillation conditions. The prescribed displacement with a period and amplitude was forced at the top of the riser. The motion of the riser along its length was measured with underwater cameras in three dimensions. The top-excited responses in the inline direction and vortex-induced vibration in the cross-flow direction were examined in the time and frequency domains. Multi-peak frequencies in the VIV were demonstrated to be strongly dependent upon the Keulegan-Carpenter number, corresponding with the results of Blevin. It was found that the Reynolds numbers (excitation period) was a critical parameter for the dominant VIV characteristics, even under the condition of using the same Keulegan-Carpenter number, under the top-excited condition. In the resonance at the nth natural frequency by the forced-motion induced VIV frequency, the riser responded with a large amplitude and forced frequency, dominantly in the VIV CF direction.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.40 no.11
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• pp.948-956
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• 2012

This paper presents the computations of the longitudinal and directional stability derivatives for the SDM(Standard Dynamic Model). The static and dynamic derivatives are evaluated at once using forced harmonic oscillations in the pitch and yaw directions. For the numerical simulations, a 3-D Euler solver that uses a dual time stepping method for unsteady time accurate simulations is applied. This work investigates the variation of the derivatives in terms of the Mach number and the several motion parameters. Good agreement of the pitch and yaw stability derivatives with previously published numerical results and experimental results are observed.