• 한국작물학회지
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• 제32권2호
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• pp.215-223
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• 1987

본 연구는 벼의 주요생육단별로 저온하에서 질소시비량과 시비시기를 달리해서 수도품종의 내냉성과 도체내 질소함량 및 ethylene 생성량과의 관계를 명백히 함으로서, 내냉성 품종육성과 냉해경감을 위한 재배기술확립의 기초자료를 얻고자 실시한바, 그 결과는 다음과 같다. 1. 분얼기의 저온처리는 초장과 분얼을 크게 억제시켰으며, 질소시비량의 증가는 저온하에서도 초장, 분얼수는 다소 증가되나, 저온에 약한 태백벼가 현저히 적었다. 그러나 저온처리 종료후 회복력은 내냉성이 약한 태백 벼가 현저했다. 2. 분얼기, 감수분열기, 등숙기 저온처리는 엽신의 질소함양은 증가시키나 탄수화물함양은 감소하는 영향이었다. 3. 감수분열기는 질소시비량의 증가에 따라 저온에 의한 임실비율이 감소하며, 그 경향은 내냉성이 약한 품종에서 현저했으며, 엽신의 질소함양과 임실비율간에는 부의 유의 상관관계가 인정되었다. 4. 출수기의 실비의 증비는 저온하에서 등숙률을 저하시켰으며, 그 경향 내냉성이 약한 품종에서 뚜렷했다. 5. 엽신의 ethylene 생성량은 품종간 큰 차이를 나타냈고, 질소시비량 증가에 따라 ethylene 생성량이 감소하는데. 이 같은 결과는 품종의 내비성 또는 내냉성과 관계가 있는 것으로 사료된다. 6. 엽신의 ethylene 생성량의 저온처리기간 또는 처리후의 추이를 보면, 저온처리와 함께 급격히 감소하고, 저온처리 종료후는 다시 증가하나, 그 경향은 시비하에서는 현저한 증가를 보이나 질소증비에 따라 생성량은 현저히 감소하였다. 또한 품종간 차이가 큼을 인정할 수 있었다.

• 한국해양환경ㆍ에너지학회지
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• 제13권4호
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• pp.241-248
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• 2010

본 논문은 조류발전을 위하여 가장 보편적으로 사용되는 수직축 조류발전 터빈의 하나인 다리우스 터빈의 효율에 미치는 다양한 설계변수의 영향을 살펴보기 위하여 수행하였다. 날개 수, 코드 길이, 피치 및 캠버를 설계변수로 채택하였으며, 2차원 및 3차원 비정상 난류유동해석을 위하여 FLUENT의 RANS방정식과 k-e 난류모델을, 격자계 모델링을 위하여 GAMBIT을 이용하였다. 기본적인 수치해석방법은 정현주 등(2009)을 참조하였다. 설계변수 변경에 따른 방대한 계산 량을 감안하여 수치해석의 신뢰도가 허락하는 범위에서 대부분 2차원 해석으로 결과를 도출하였다. 본 연구에서 제시한 설계변수의 최적화를 통하여 기준모형보다 월등한 성능을 보이는 고효율 수직축 터빈 모델을 제시할 수 있었다.

• 한국해양환경ㆍ에너지학회지
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• 제12권1호
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• pp.9-14
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• 2009

2차원 비정상의 RANS 방정식을 이용하여 피치가 고정된 3개 혹은 4개의 날개(hydrofoil)를 가지는 조류발전용 수직축 터빈주위의 비정상 유동장 해석을 수행하였다. 상용수치해석코드인 Fluent를 이용하여, 균일류에 놓인 $NACA65_3$-018날개에 대하여 받음각(angle of attack)의 변화를 주며 계산되는 유체력을 실험값과 비교하였고, 이를 바탕으로 대표적인 수직축 조류발전 터빈의 특성을 2차원적으로 고찰하였다. 사용된 수치해법은 대상 유동을 효과적으로 모사할 수 있음을 확인 하였고, 터빈의 최적 효율은 날개수 및 유속 대비 회전수 등의 적절한 조합으로 실현 될 수 있음을 파악하였다.

• 대한조선학회논문집
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• 제42권6호
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• pp.619-630
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• 2005

A two-frame PIV (Particle Image Velocimetry) technique is used to investigate the wake characteristics behind a marine propeller with 4 blades at high Reynolds number. For each of 9 different blade phases from $ 0^{\circ} $ to $ 80^{\circ} $, one hundred and fifty instantaneous velocity fields are measured. They are ensemble averaged to study the spatial evolution of the propeller wake in the region ranging from the trailing edge to one propeller diameter (D) downstream location. The phase-averaged mean velocity shows that the trailing vorticity is related to radial velocity jump, and the viscous wake is affected by boundary layers developed on the blade surfaces and centrifugal force. Both Galilean decomposition method and vortex identification method using swirling strength calculation are very useful for the study of vortex behaviors En the propeller wake legion. The slipstream contraction occurs in the near-wake region up to about X/D : 0.53 downstream. Thereafter, unstable oscillation occurs because of the reduction of interaction between the tip vortex and the wake sheet behind the maximum contraction point.

• Wind and Structures
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• 제32권3호
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• pp.205-217
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• 2021

Cold regions with high air density and wind speed attract wind energy producers across the globe exhibiting its potential for wind exploitation. However, exposure of wind turbine blades to such cold conditions bring about devastating impacts like aerodynamic degradation, production loss and blade failures etc. A series of wind tunnel tests were performed to investigate the effect of icing on the aerodynamic properties of wind turbine blades. A baseline clean wing configuration along with four different ice accretion geometries were considered in this study. Aerodynamic force coefficients were obtained from the surface pressure measurements made over the test model using MPS4264 Simultaneous pressure scanner. 3D printed Ice templates featuring different ice geometries based on Icing Research Tunnel data is utilized. Aerodynamic characteristics of both the clean wing configuration and Ice accreted geometries were analysed over a wide range of angles of attack (α) ranging from 0° to 24° with an increment of 3° for three different Reynolds number in the order of 105. Results show a decrease in aerodynamic characteristics of the iced aerofoil when compared against the baseline clean wing configuration. The key flow field features such as point of separation, reattachment and formation of Laminar Separation Bubble (LSB) for different icing geometries and its influence on the aerodynamic characteristics are addressed. Additionally, attempts were made to understand the influence of Reynolds number on the iced-aerofoil aerodynamics.

• 한국소음진동공학회논문집
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• 제15권6호
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• pp.687-696
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• 2005

Acoustic power spectrum of the upstream and downstream sound field due to an isotropic frozen turbulent gust impinging on a cascade of flat plate airfoils are computed by using a analytic formulation derived from Smith's method, and Whitehead's LINSUB codes. A parametric study of the effects on sound power of the number of blades and turbulence length scale is performed with an emphasis on analyzing the characteristics of sound power spectrum. Through the comparison of the computed results of sound power, it is found that acoustic power spectrum from the 2-D cascade subject to a ingested turbulence can be categorized into two distinct regions. one is lower frequency region where some spectral components of turbulence do not contribute to the cut-on acoustic modes and therefore the effect of the cascade geometry is more dominant ; the other is higher frequency region where all of spectral components of turbulence make contributions to cut-on acoustic modes and thus acoustic power is approximately proportional to the blade number.

• 한국표면공학회지
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• 제34권2호
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• pp.161-168
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• 2001

A Thermal Barrier Coating (TBC) can play an important role in protecting parts from harmful environments at high temperatures such as oxidation, corrosion, and wear in order to improve the efficiency of aircraft engines by lowering the surface temperature of the turbine blade. The TBC can increase the life span of the product and improve the operating properties. Therefore, in this study the mechanical and thermal properties of the TBC such as oxidation, fatigue and shock at high temperatures were evaluated. A samples of a bond coat (CoNiCrAlY) produced by the High Velocity Oxygen Fuel (HVOF) and Low Pressure Plasma Spray (LPPS) method were used. The thickness of the HVOF coating layer was approximately $450\mu\textrm{m}$ to 500$\mu\textrm{m}$ and the hardness number of the coating layer was between 350Hv and 400Hv. The thickness of the LPPS coating was about 350$\mu\textrm{m}$ to 400$\mu\textrm{m}$ and the hardness number of the coating was about 370Hv to 420Hv. The X-ray diffraction analysis showed that CoNiCrAlY coating layer of the HVOF and LPPS was composed of the $\beta$and ${\gamma}$phase. After the high temperature oxidation test, the oxide scale with about l0$\mu\textrm{m}$ to 20$\mu\textrm{m}$ thickness appeared at the coating surface on the Al-depleted zone was observed under the oxide scale layer.

• 신재생에너지
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• 제8권1호
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• pp.44-51
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• 2012

Due to a high tidal range of up to 10 m on the west coast of Korea, numerous tidal current projects are being planned and constructed. The turbine, which initially converts the tidal energy, is an important component because it affects the efficiency of the entire system. Its performance is determined by design variables such as the number of blades, the shape of foils, and the size of a hub. To design a turbine that can extract the maximum power on the site, the depth and duration of current velocity with respect to direction should be considered. Verifying the performance of a designed turbine is important, and requires a circulating water channel (CWC) facility. A physical model for the performance test of the turbine should be carefully designed and compared to results from computational fluid dynamics (CFD) analysis. In this study, a horizontal axis tidal current turbine is designed based on the blade element theory. The proposed turbine's performance is evaluated using both CFD and a CWC experiment. The sealing system, power train, measuring devices, and generator are arranged in a nacelle, and the complete TCP system is demonstrated in a laboratory scale.

• 한국해양공학회지
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• 제28권4호
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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.

• 한국소음진동공학회논문집
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• 제13권5호
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• pp.357-363
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• 2003

There have been lots of studies on noise transmission analysis and noise reduction In ducts. In order to reduce the noise transmission in ducts. active noise cancellation techniques have often been employed and a rotation shaft with blades has sometimes been suggested. These Ideas were not successfully commercialized because of the limitation of real life such as size or application difficulties. This study investigated how a rotational shaft with blades could reduce the noise transmission in a duct. To do so, an assembly of the shaft and the $haft housing was built In the middle of a duct. and the clearance between the blades and the housing was 0.2 mm. The noise reduction was experimentally evaluated with respect to the number of blades. the rotation speed, and the rotation or stop. This paper showed that the noise reduction resulted in about 14∼19 dBA regardless of the three test conditions only If the blades always blocked the duct. And. the noise reduction increased due to the higher number of blades and the lower speed of the shaft.