• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.7
• /
• pp.1808-1817
• /
• 1994

Unsteady aerodynamic analysis of an aircraft is done using a frequency domian 3-D panel method. The method is based on an unsteady linear compressible lifting surface theory. The lifting surface is placed in a flight patch, and angle of attack and camber effects are implemented in upwash. Fuselage effects are not considered. The unsteady solutions of the code are validated by comparing with the solutions of a hybrid doublet lattice-doublet point method and a doublet point method for various wing configurations at subsonic and supersonic flow conditions. The calculated results of dynamic stability derivatives for aircraft are shown without comparision due to lack of available measured data or calculated results.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.32 no.4
• /
• pp.1-11
• /
• 2004

Numerical analyses on the aerodynamic characteristics of a counter rotating axial flow fan were conducted for the development of an axial type in-line duct fan. The counter rotating fan has a front rotor and a rear rotor which are counter rotating each other. Blade design of the counter rotating fan was done by extension of design method for axial flow fan which consists of rotor and stator blades. Through flow analysis was performed using matrix method which is applied for flow fields prediction of compressors or turbines. Aerodynamic characteristics and characteristic curves of the counter rotating fan were analyzed by expansion of the frequency domain panel method with duct modeling. Pressure losses were higher at leading edge and hub region of rotor blades. Characteristic curve of the counter rotating fan was overpredicted without consideration of viscous effect.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.10
• /
• pp.955-965
• /
• 2010

The MH-75 propeller for the MAV propulsion is designed using a free vortex design method which considers design parameters such as the hub-tip ratio, the twist angle distribution, the maximum camber location and the chord length of the propeller blade. Aerodynamic characteristics of the MH-75 propeller are predicted by changing the flight speed using the frequency domain panel method. And, the thrust characteristics of the MH-75 propeller are measured using the balance system of the subsonic wind tunnel for the validation of numerical results. The performance characteristics of the MH-75 propeller satisfied with design requirements. Numerical results of the MH-75, which are predicted by the frequency domain panel method, are more agree with experimental results compare with XFOIL.

• Journal of the Korean Society for Precision Engineering
• /
• v.16 no.2 s.95
• /
• pp.153-163
• /
• 1999

본 연구에서는 격자패널을 통한 소음전달을 감소시키기 위하여 외부 구조적 가진으로부터 유발된 경량 패널의 진동을 능동 제어하는 기법을 기술한다. 최적 되먹임제어기와 적응 앞먹임제어기가 결합된 혼합형 제어기가 진동제어기로 사용된다. 되먹임제어기는 주파수 영역의 모델규명법에 의해 추출된 다중 입/출력 패널진동계 모델에 대하여 LQG 최적기법을 이용하여 감쇠능을 향상시키도록 설계된다. 앞먹임제어기는 되먹임 궤환의 결합효과를 자동적으로 보정할 수 있는 제안된 학습법칙에 기초하여 패널의 잔류진동이 최소가 되도록 적응된다. 45.7${\times}$45.7${\times}$2.54 ${cm^3}$ 벌집형상의 고강도 패널, 4개의 관성형 구동기 및 이산신호처리장치에 의해 구현된 패널 진동계에 대한 능동제어 실험을 수행해 본 결과 600Hz 주파수대역에 대한 12dB 진동저감이 이루어 질 수 있었다.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.35 no.5
• /
• pp.375-380
• /
• 2007

The nonlinear aerodynamic analysis of wing with control surface is performed using the frequency-domain panel method. To take into consideration the nonlinear aerodynamic characteristics of wing an iterative decambering approach is introduced. The iterative decambering approach uses the known aerodynamic characteristics of airfoil to calculate the aerodynamic characteristics of wing. The multi-dimensional Newton iteration is used to account for the coupling between the different sections of wing. The present method is verified by showing that it produces results that are in good agreement with experiments. The present method will be useful for the analysis of aircraft in the conceptual design because the present method can calculate promptly the nonlinear aerodynamic characteristics of wing with a few computing resources.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.28 no.1
• /
• pp.27-33
• /
• 2016

A numerical analysis on deck wetness is carried out for a large caisson directly wet-towed by tugs in irregular waves. A constant panel method is used for linear analysis in frequency domain and a statistical post-processing for the deck wetness is presented. Hydrodynamic coefficients obtained from the frequency domain computation are imported for time domain analysis which enables complete modeling for towing equipment, environment, etc. Both frequency and time domain computations over two sea states are performed and comparison is made. In the time domain analysis, towing systems of various arrangements of tugs are investigated from short-term prediction for the largest deck wetness and the number of occurrences of deck wetness.

• Proceedings of the Acoustical Society of Korea Conference
• /
• autumn
• /
• pp.323-326
• /
• 2004

에어컨 실외기의 구조 방사 소음을 줄이기 위해 제진재를 적용함에 있어 구조 인텐서티(structural intensity)법을 사용할 수 있다. 에어컨 실외기 각 패널의 법선 방향의 속도는 레이져 스케닝 바이브로미터(laser scanning vibrometer)에 의해 측정되며, 측정된 데이터는 공간 주파수 영역(k-domain)으로 변환하여 구조 인텐서티 계산에 필요한 공간 미분값이 구해진다. 이러한 과정을 통하여 계산된 구조 인텐서티 중 반동 전단 구조인텐서티(reactive shearing structural intensity)값이 가장 높은 부분에 사각형 형상의 제진재를 적용한다. 본 논문은 패널에 비해 그 크기가 작은 제진재의 적용으로 에어컨 실외기의 구조 방사 소음을 줄일 수 있음을 보여준다.

• Journal of the Society of Naval Architects of Korea
• /
• v.38 no.3
• /
• pp.47-53
• /
• 2001

When a ship advancing in waves is subjected to impact forces or irregular forces, the motion analyses for ship are convenient for being calculated in the time domain. The added mass, wave damping coefficients, wave exciting forces and mean drift forces are calculated by 3-Dimensional panel method used the translating pulsating Green function in the frequency domain and the motion equations which are considered by the memory effect due to waves are numerically solved by using the Newmark-$\beta$ method in the time domain. The motion analyses are carried out for a Series 60($C_B=0.7$) moving in irregular waves. The items of calculation are 6-degree motions, accelerations at the fore and after position, numbers of deck wetness and numbers of exposure at ship-bottom, etc. Moreover, the thrust addition in waves is examined by considering the time mean drift forces in the motion equations of time domain.

• Proceedings of the KSME Conference
• /
• 2001.11b
• /
• pp.604-609
• /
• 2001

This numerical analysis uses the lifting surface method and frequency-domain panel method based on the linear compressible aerodynamic theory. Increased knowledge of flow conditions within mixed-flow fan should indicates means of improving performance of these turbomachines. Thus, only an approximate solution is obtained whose prime intent is to recognize the most significant characteristics of the "ideal" geometry. For a given set of operating condition, the flow conditions within mixed-flow fan depend on the geometry of the machine (three-dimensional flow effects) and on the properties of the fluid. But most treatments of the problem have been concerned with the two-dimensional flow effects for incompressible, non-viscous fluids. Interest in the field of mixed-flow fan resulted in the undertaking of a program to develop reliable design procedures that would avoid the need for lengthy development work.

• Transactions of the Korean Society of Mechanical Engineers B
• /
• v.24 no.3
• /
• pp.325-337
• /
• 2000

A study was done on the numerical and experimental analyses of the aerodynamic characteristics of a counter rotating axial fan. The numerical analysis uses the frequency domain panel method developed for the aerodynamic analysis of interacting rotating systems, which is based on the unsteady lifting surface panel method. Each stage of interaction involves the solution of an isolated rotor, the interaction being done through the Fourier transform of the induced velocity field. Numerical results showed good agreements with other experimental data for single and counter rotating propeller systems. And they were compared with the experimental results of the counter rotating axial fan studied in the present paper. The performance test was carried out based on the Korean Standard (KS B 6311). It was focused on the relative efficiency increase of a counter rotating system for a single rotating one, and effects of the axial distance between the front and rear rotors on overall fan performances were investigated. As a result, it was shown that the counter rotating axial fan has the efficiency 14% higher than the single rotating one at peak efficiency points.