• Composites Research
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• v.20 no.1
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• pp.8-14
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• 2007

Nonlinear aeroelastic analyses of composite wing with flap are performed considering free-play and dynamic stiffness of actuator. Doublet-Hybrid method is used for the calculation of subsonic unsteady aerodynamic forces. Free-play is modeled as a bilinear spring and is linearized by using the describing function method. Dynamic stiffness is obtained from governing equation of gear system and the aeroelastic analyses were performed according to ply-angle of laminate and material. The linear and nonlinear flutter analysis results show that the flutter characteristics are significantly dependent on the free-play and dynamic stiffness. from the nonlinear flutter analysis, various types of limit cycle oscillations are observed in a range of air speeds below or above the linear divergent flutter boundary.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.299-304
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• 2013

초음속 조건에서 Busemann biplane은 충격파의 중첩에 의해 항력 감소가 일어난다. 그러나 받음각이 증가 할 경우, 앞전에서 궁형 충격파가 발생하여 항력이 급격하게 증가한다. 이에 본 연구에서는 busemann biplane에 플랩을 주어 궁형 충격파를 감소시킬 수 있는 flap biplane의 플랩 길이와 각도의 변화에 따른 공력 성능의 변화를 분석하였다. Flap biplane의 공력성능을 기본 biplane형상 및 diamond airfoil과 비교한 결과, 동일한 양력 조건에서 항력은 diamond airfoil에 비해 약 75%정도 감소함을 확인하였다. 그리고 플랩의 길이와 양항비는 선형의 관계가 있음을 확인하였고, 특정한 플랩의 각도에서 최대 양항비가 도출된다는 사실을 확인하였다. 마지막으로 전압력의 감소를 충격파의 강도로 정의하고, 이를 비교한 결과 flap biplane의 전압력 감소가 diamond airfoil에 비해 약 25%정도가 더 작게 나타난 사실로 부터 flap biplane의 소음 감소 효과를 유추할 수 있었다. flap biplane은 초음속 영역에서 항력과 소음의 감소에 효율적인 익형임을 확인하였다.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.10
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• pp.891-898
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• 2007

Optimal aerodynamic design for the pitch-controlled horizontal axis wind turbine and its aerodynamic performance for various pitch angles are performed numerically by using the blade element momentum theory. The numerical calculation includes effects such as Prandtl‘s tip loss, airfoil distribution, and wake rotation. Six different airfoils are distributed along the blade span, and the special airfoil i.e. airfoil of 40% thickness ratio is adopted at the hub side to have structural integrity. The nonlinear chord obtained from the optimal design procedure is linearized to decrease the weight and to increase the productivity with very little change of the aerodynamic performance. From the comparisons of the power, thrust, and torque coefficients with corresponding values of different pitch angles, the aerodynamic performance shows delicate changes for just $3^{\circ}$ increase or decrease of the pitch angle. For precisive pitch control, it requires the pitch control algorithm and its drive mechanism below $3^{\circ}$ increment of pitch angle. The maximum torque is generated when the speed ratio is smaller than the designed one.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 2018.11a
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• pp.59-60
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• 2018

The oscillating-water-column wave energy converter represents the complex physical characteristics associated with the water column, turbines, generator, and power converter. This study focuses on the derivation of the physical relationship between the water column and turbine based on the 1/ 4 scale model test. The aerodynamic characteristics of the OWC ducted turbine were simulated using an orifice. The turbine effect, a key element in the OWC-chamber performance evaluation, can be represented by the flow rate and pressure drop through the orifice. The turbine effect of OWC-WEC was confirmed to have a non-linear relationship from the measured flow rate and pressure drop in the model test.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.11
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• pp.1039-1048
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• 2008

new computational procedure for the Non-Linear Vortex Lattice Method (NLVLM) is suggested in this work. Conventional procedures suggested so far usually involves inner iteration loop to update free vortex shape and an under-relaxation based iteration loop to determine the free vortex shape. In this present work, we suggest a new formula based on quasi-steady concept to fix free vortex shape which eliminates the need for inner iteration loop. Further, the ensemble averaging of the induced velocities for a given free vortex segment evaluated at each iteration significantly improves the convergence property of the algorithm without resorting to the under-relaxation technique. Numerical experiments over several low aspect ratio wings are carried out to obtain optimal empirical parameters such as the length of the free vortex segment, the vortex core radius, and the rolled-up wake length.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.33 no.2
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• pp.54-59
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• 2005

Nonlinear aeroelastic analyses of a missile control fin are performed considering backlash and dynamic stiffness of actuator. Doublet-Hybrid method is used for the calculation of subsonic unsteady aerodynamic forces, and aerodynamic forces are approximated by the minimum-state approximation. For nonlinear flutter analysis backlash is represented by a free-play and is linearized by using the describing function method. Also, dynamic stiffness is function of frequency and is calculated by solving equation of motion for actuator. The linear and nonlinear flutter analyses show that the aeroelastic characteristics are significantly dependent on the backlash and dynamic stiffness. From the nonlinear flutter analysis, various types of limit cycle oscillations are observed in a range of air speeds below the linear divergent flutter boundary. The nonlinear flutter characteristics and the nonlinear aeroelastic responses are also investigated in the time domain.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.4
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• pp.295-301
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• 2007

The aeroelastic characteristics of a wing with control surface freeplay are investigated. The transonic small disturbance equation is used for unsteady aerodynamic forces in subsonic/transonic region. The fictitious mass method is introduced to apply a modal approach to nonlinear structural models. Nonlinear aeroelastic time responses are calculated by the coupled time integration method. Using these methods, an efficient aeroelastic analysis is achieved for aerodynamic and structural nonlinearities simultaneously. The effects of the aerodynamic nonlinearity, initial flap amplitude, and freeplay magnitude in aeroelastic characteristics are investigated in this study.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2009.11a
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• pp.387-391
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• 2009

The experimental study on the ducted fan for the propulsion system of a small UAV has been performed. In this paper, to investigate the three-dimensional unsteady flow field characteristics of the ducted fan, it was measured by using a $45^{\circ}$ inclined hot-wire from hub to tip at inlet, behind the rotor and outlet of the ducted fan. The hot-wire signal data was acquired at fixed yaw angle. The data was averaged by using the PLEAT (Phase Locked Ensemble Averaging Technique), and then three of non-linear equations were solved simultaneously by using the Newton-Rhapson numerical method. Flow characteristics such as tip vortex, secondary flow and tip leakage flow were confirmed through axial, radial and tangential contour plot.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.6
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• pp.503-508
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• 2007

In this study, the aeroelastic response and stability of bearingless rotors are investigated using a large deflection beam theory. The outboard main blade, flexbeam, and torque tube are all assumed to be an elastic beam undergoing arbitrary large displacements and rotations. The finite element equations of motion obtained from Hamilton's principle. Two-dimensional quasi-steady strip theory is used to evaluate aerodynamic forces. In hover, the modal approach method based on coupled rotating natural modes is used for the stability analysis. In forward flight, the nonlinear periodic blade steady response is obtained by integrating the full finite element equation in time through a coupled trim procedure with a vehicle trim. The results of the full finite element analysis using the large deflection beam theory are compared with those of a previously published modal analysis using the moderate deflection-type beam theory.

• Journal of Aerospace System Engineering
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• v.17 no.6
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• pp.82-93
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• 2023

In this paper, nonlinear transonic flutter analyses of a composite missile fin considering the effect of delamination are conducted. An effective modal analysis methodology is adopted and verified with the experimental modal test data for laminated composite plates with delamination. Extended version of the in-house computational aeroelastic analysis program with the transonic small-disturbance (TSD) code is used in order to predict the flutter dynamic pressure of the delaminated composite fin models. In the subsonic, transonic, and supersonic flow regions, nonlinear time-domain flutter analyses are performed for various delamination conditions, and aeroelastic characteristics due to the delamination phenomena are examined in detail.