소형 위그선의 복합재 주익의 강제진동 거동에 관한 연구

Abstract

Recently, various kinds of high speed maritime transportation systems using WIG(Wing In Ground Effect) have been developed in the world[1]. The WIG flight craft has a specific behavior that its wing can enhance the lift by Wing-In-Ground-Effect between the wing and the surface if it may fly near by land or sea water surface. So the wing of WIG craft structure is relatively larger than the conventional aircraft wing to obtain the WIG effect. The WIG crafts have been mostly developed by Russia. Also several research works have been performed in Rep. of Korea. structural design and analysis of the main wing for a small scale WIG craft was previously performed by C. Kong. et al.[1] The skin-spar structure with a urethane foam sandwich was adopted for improvement of lightness and structural stability, and the carbon/epoxy composite was selected as the major structure materials because of high strength and stiffness. Structural design loads were estimated through critical flight load case study. In this study, the forced vibration analysis was performed on the composite main wing structure of the twenty-seat class WIG craft with two-stroke pusher type reciprocating engine. The vibration analysis based on the finite element method was performed using a commercial FEM code, MSC/NASTRAN. Excitations for the frequency response analysis were assumed as the X-mode(longitudinal mode), the Y-mode(lateral mode), the Z-mode(vertical mode) and three twisted modes which are typical main vibration modes of engine. The engine was assumed as a rigid body which can generate the thrust of 1000hp(horse power) at maximum rpm of 7000. The unit harmonic load was applied at each mode to excite the engine. And excitations for the transient response analysis were assumed as the X-mode with the oscillating propeller thrust which occurs in operation. When an aircraft is maneuvered in the air, propeller cyclic loading can be presented as the sine pulse load due to the gyroscopic effect and the side slip motion. Thus, the sine pulse thrust may excited the wing with the direction of the center of propeller hub having propeller rotational frequency, and 2% propeller thrust rate of change was applied to the excitation thrust for considering the flight conditions. According to the analysis results, structural design was modified to avoid resonance possibilities and reduce vibration.