• Advances in aircraft and spacecraft science
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• v.1 no.1
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• pp.69-91
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• 2014

Numerical investigations are presented, which show that a back-flow flap can improve the dynamic stall characteristics of oscillating airfoils. The flap was able to weaken the stall vortex and therefore to reduce the peak in the pitching moment. This paper gives a brief insight into the method of function of a back-flow flap. Initial wind tunnel experiments were performed to define the structural requirements for a detailed experimental wind tunnel characterization. A structural integration concept and two different actuation mechanisms of a back-flow flap for a helicopter rotor blade are presented. First a piezoelectric actuation system was investigated, but the analytical model to estimate the performance showed that the displacement generated is too low to enable reliable operation. The seond actuation mechanism is based on magnetic forces to generate an impulse that initiates the opening of the flap. A concept based on two permanent magnets is further detailed and characterized, and this mechanism is shown to generate sufficient impulse for reliable operation in the wind tunnel.

• Journal of Advanced Marine Engineering and Technology
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• v.33 no.7
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• pp.1017-1025
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• 2009

This study intends to study about the blade performance loss occurred due to the variation in the shape of airfoil from the attachment/non-attachment of blade erosion shield for hovercraft. This study model has used NACA 4412, has designed NACA 4412 by using Auto CAD and designed the shape that has attached an erosion shield to this model according to the thickness and length. By using these models, we have generated a grid by using GAMBIT and calculated the lift coefficient (Cl) and drag coefficient (Cd) by using the FLUENT code for flow analysis. Through this, we have calculated and compared the lift-to-drag ratio that is an indicator of airfoil performance according to the shape and attachment/non-attachment of erosion shield.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.20 no.10
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• pp.72-79
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• 2021

A circular saw is an effective tool for cutting glass and carbon-fiber hybrid composites. This study investigated tool wear and cut quality when reusing saw blades. The carbide saws wear four times faster than the new ones, and polycrystalline diamond (PCD) is very resistant to tool wear, except at the end of its lifespan. The cut cross-section quality is affected by the blade type, tool wear, and spindle speed. Alternate top bevel (ATB)-type blades are suitable for cutting fiber-reinforced plastics, but triple-chip grind (TCG)-type blades are unsuitable because they cause fiber-pullout defects. Tool wear and low spindle speeds increase the occurrence of arc scratches, due to the rear saw blade. A microscopic examination showed that the burr, which is a mixture of fiber chips and epoxy matrix, was bonded on top, and glass-fiber delamination occurred on the bottom glass-fiber-reinforced polymer (GFRP) surface.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.501-504
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• 2011

In this study, structural design of the propeller blade for turboprop aircraft was performed. The propeller shall have high strength to get the thrust to fly at high speed. The high stiffness and strength carbon/epoxy composite material was used for the major structure and skin-spar-foam sandwich structural type was adopted for improvement of lightness. As a design procedure for the present study, firstly the structural design load was estimated through investigation on aerodynamic load and then flanges of spars from major bending loads and the skin from shear loads were preliminarily sized using the netting rule. In order to investigate the structural safety and stability, stress analysis was performed by finite element analysis code MSC. NASTRAN. Finally, it is investigated that designed blade have high efficiency and structural safety to analyze of aerodynamic and structural design results.

• Journal of Ocean Engineering and Technology
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• v.28 no.4
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• pp.351-355
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• 2014

Today, carbon fibers are used as heating elements. Carbon fibers are generally used to reinforce composite materials because they are lightweight and have a high strength and modulus. Carbon fiber reinforced composite materials are used for aerospace, automobile, and wind turbine blade applications. This work explored the possibility of using carbon fiber reinforced composite materials as self heating materials. The temperatures of the carbon fiber reinforced composites were measured. These results verified that the carbon fiber reinforced composite materials could be used as heating elements. A glass fiber was laminated using various methods. The thermal characteristics of the composites were evaluated. This confirmed that the generation of heat varied according to the lamination thicknesses of the carbon fiber and glass fiber. As the number of carbon fiber laminations increased, the heat-generating temperature increased. In contrast, as the number of glass fiber laminations increased, the amount of heat decreased. The generation of heat and ability to remain warm could be controlled by controlling the carbon fiber and glass fiber laminations.

• Journal of the Society of Naval Architects of Korea
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• v.46 no.2
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• pp.203-217
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• 2009

The researches on the development of composite material propeller with outstanding damping effects have been actively attempted for the reduction of radiation noise of underwater vehicle propeller. Composite material suitable for the flexible propeller has the following advantages, such as high specific strength and specific stiffness, low thermal expansion coefficient, high resistance against environmental deterioration, low possibility of corrosion due to cavitation, nonoccurrence of rapid fracture due to fatigue, easy molding of complicated shape, easy repair maintenance and low production costs, etc. For the confirmation of optimal fiber array structures of composite material for the production of the flexible propeller blades, in this study, mechanical characteristics of its specimens according to materials were obtained and structural characteristics of propeller blade were also examined according to materials and stacking fiber arrays.

• International Journal of Fluid Machinery and Systems
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• v.9 no.1
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• pp.47-55
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• 2016

The portable hydraulic turbine we previously developed for open channels comprises an axial flow runner with an appended collection device and a diffuser section. The output power of this hydraulic turbine was improved by catching and accelerating an open-channel water flow using the kinetic energy of the water. This study aimed to further improve the performance of the hydraulic turbine. Using numerical analysis, we examined the performances and flow fields of a single runner and a composite body consisting of the runner and collection device by varying the airfoil and number of blades. Consequently, the maximum values of input power coefficient of the Runner D composite body with two blades (which adopts the MEL031 airfoil and alters the blade angle) are equivalent to those of the composite body with two blades (MEL021 airfoil). We found that the Runner D composite body has the highest turbine efficiency and thus the largest power coefficient. Furthermore, the performance of the Runner D composite body calculated from the numerical analysis was verified experimentally in an open-channel water flow test.

• 한국신재생에너지학회:학술대회논문집
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• 2011.11a
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• pp.41.2-41.2
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• 2011

NREL NWTC Deside codes are analyzed and introduced to develop the system performance simulation program for wind turbine generator systems. In this paper, The AirfoilPrep generating the airfoil data, the IECWind generating hub-height wind data with extreme condition following IEC 61400-1, the TurbSim generating stochastic full-field turbulent wind data, the PreComp calculating structural and dynamic properties of composite blade and the BModes making mode shapes of blade and tower are explained respectively.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.6
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• pp.496-502
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• 2007

In the present paper, a new version of DYMORE, which is an analysis to solve a nonlinear multi-body dynamics problem, is used to simulate an Individual Blade Control (IBC) algorithm in order to reduce vibration in helicopter rotors. The Active Twist Rotor (ATR), in which Active Fiber Composites (AFC) are embedded, is utilized for IBC. The main purpose of the present investigation is to compare the analytical results with experiments and previous version of DYMORE. The experiments are performed at NASA Langley Transonic Dynamics Tunnel. According to the present result, it is observed that the correlation regarding the vibratory loads is improved.

• Journal of the Korea institute for structural maintenance and inspection
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• v.22 no.6
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• pp.157-163
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• 2018

This study is aimed at controlling the fiber orientation and improve the fiber distribution in fiber-reinforced cement composites using blades that can be placed inside the existing nozzles. To optimize the blade parameters, multi-physics finite element analysis was performed that could account for the flow of the cementitious matrix material, the movement of the entrained fibers, and the interactions with the nozzle. As a result, this study defined the blade distance, length, and position as a function of the fiber length to be used in the field. The blades with a distance from 1.2 to 2.4 times the fiber length and length from 4 to 8 times the fiber length, as well as located at below 14 times the fzfiber length from the nozzle exit maintained the fiber orientation angle less than $5^{\circ}$. In addition, the blade-type nozzle proposed in the study can be attachable and detachable to the conventional casting equipment, and thus it can provide the usability and convenience in practical applications.