• 동력기계공학회지
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• 제11권3호
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• pp.47-52
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• 2007

Punching, blanking, trimming and slitting are widely used in shearing processes in sheet metal forming of automotive parts. In this paper the effects of clearance, cutting angle and tool sharpness on the formation of burr were investigated by experimental method in shearing processes of steel sheets, SPCEN and SPRC35E. The amount of burr and the shapes of burr were different between two kinds of steel sheets. It has been shown that the cutting angle of the shearing blade had no effects on the height of burr when the clearance was below the 10% of the steel sheet thickness, and also that the height and shape of burr were not affected by the cutting angle when the wear of shearing blade was below the 10% of the steel sheet thickness. It was known that there had been existing the critical clearance of 10 to 15% for the tested steel sheet, SPCEN and SPRC35E.

• 신재생에너지
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• 제5권2호
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• pp.3-8
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• 2009

Tidal current power system is one of ocean renewable energies that can minimize the environmental impact with many advantages compared to other energy sources. Not like others, the produced energy can be precisely predicted without weather conditions and also the operation rate is very high. To convert the current into power, the first device encountered to the incoming flow is the rotor that can transform into rotational energy. The performance of rotor can be determined by various design parameters including numbers of blade, sectional shape, diameter, and etc. The stream lines near the rotating rotor is very complex and the interference effects around the system is also difficult to predict. The paper introduces the experiment of rotor performance and also the fundamental study on the characteristics of three different rotors and flow near the rotor by CFD.

• 한국추진공학회:학술대회논문집
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• 한국추진공학회 2007년도 제29회 추계학술대회논문집
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• pp.297-301
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• 2007

초음속 충동형 터빈과 같이 종횡비가 작은 경우 로터 익형은 반경방향으로 동일한 단면을 갖는 형태로 구현된다. 이 경우 터빈 로터는 터빈 동익의 프로파일 직경에 따라 설계에서 의도하지 않은 유로면적분포와 터빈 성능의 차이를 보인다. 본 연구에서는 터빈 동익 프로파일을 정의하는 직경이 터빈 성능에 미치는 영향을 고찰하기 위하여 3개의 다른 위치에서 정의된 터빈 로터에 대한 유동해석을 수행하고 결과를 고찰하였다. 계산 결과 팁에서 단면이 정의된 경우 설계에서 의도한 유로면적 변화를 보이며 다른 프로파일 직경에서 정의된 터빈에 비해 우수한 성능을 보임을 확인하였다.

• 대한기계학회논문집B
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• 제25권2호
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• pp.164-170
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• 2001

The influence of unsteady wake on the flow and heat transfer characteristics in a four-vane linear cascade was experimentally investigated. The unsteady wake was generated with four rotating rectangular plates located upstream of the cascade. Tested inlet Reynolds number based on chord length was set to 66,000 by controlling free-stream velocity. A hot-wire anemometer system was employed to measure turbulent velocity components. For the convective heat transfer coefficients measurement on turbine blade surface, thermochromic liquid crystal and gold film Intrex were used. It was found that the unsteady wake enhances the turbulent motion in the cascade passage and accordingly promotes the development and transition of boundary layer. It was found that the heat transfer coefficients on the blade surface increase as the plate rotating speed increases. However, the increasing of heat transfer coefficients is not significant in the case that Strouhal number is higher than 0.503.

• International Journal of Fluid Machinery and Systems
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• 제7권3호
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• pp.86-93
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• 2014

This paper describes performance enhancement of a regenerative blower used for a 20 kW fuel cell system. Two design variables, bending angle of an impeller and blade thickness of an impeller tip, which are used to define an impeller shape, are introduced to enhance the blower performance. Internal flow of the regenerative blower has been analyzed with three-dimensional Navier-Stokes equations to obtain the blower performance. General analysis code, CFX, is introduced in the present work. SST turbulence model is employed to estimate the eddy viscosity. Throughout the numerical analysis, it is found that the thickness of impeller tip is effective to increase the blower efficiency in the present blower. Pressure is successfully increased up to 2.8% compared to the reference blower at the design flow condition. And efficiency is also enhanced up to 2.98 % compared to the reference one. It is noted that low velocity region disturbs to make strong recirculation flow inside the blade passages, thus increases local pressure loss. Detailed flow field inside the regenerative blower is also analyzed and compared.

• 한국산림과학회지
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• 제76권1호
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• pp.27-32
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• 1987

강원도(江原道) 원주시(原州市) 우산동(牛山洞)에 소재(所在)한 상지대학(尙志大學) 구내(構內)에 생육중(生育中)인 8종(種)의 조경수목(造景樹木)을 대상(對象)으로 기공형질(氣孔形質)(기공형(氣孔型), 밀도(密度) 및 기공장(氣孔長))을 조사(調査)하였다. 개나리, 수수꽃다리, 느티나무 및 모과나무의 기공(氣孔)은 irregular-celled type(anomocytic)이며, 백당나무, 튜울립나무 및 목련의 기공(氣孔)은 parallel-celled type(paracytic)이었다. 개나리의 경우, 엽신장(葉伸長)에 따른 기공장(氣孔長)의 변화(變化)는 거의 없었고, 단위엽면적당(單位葉面積當) 기공수(氣孔數)는 크게 감소(減少)했으며, 개체엽당(個體葉當) 기공수(氣孔數)는 증가(增加)하였다. 주목의 경우, 침엽신장(針葉伸長)에 따라 기공장(氣孔長)은 계속 증가(增加)했으며, 단위엽면적당(單位葉面積當) 기공수(氣孔數)는 감소(減少)하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.1726-1731
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• 2004

This paper presents the response surface optimization method using three-dimensional Navier-Stokes analysis to optimize the shape of a forward-curved blades centrifugal fan. For numerical analysis, Reynolds-averaged Navier-Stokes equations with $k-{\varepsilon}$ turbulence model are discretized with finite volume approximations. In order to reduce huge computing time due to a large number of blades in forward-curved blades centrifugal fan, the flow inside of the fan is regarded as steady flow by introducing the impeller force models. Three geometric variables, i.e., location of cut off, radius of cut off, and width of impeller, and one operating variable, i.e., flow rate, were selected as design variables. As a main result of the optimization, the efficiency was successfully improved. And, optimum design flow rate was found by using flow rate as one of design variables. It was found that the optimization process provides reliable design of this kind of fans with reasonable computing time.

• 대한기계학회논문집B
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• 제23권7호
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• pp.864-870
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• 1999

An experimental study Is conducted in a four-vane linear cascade in order to examine the influence of the wake behind rectangular bars on the flow and heat transfer characteristics. Flow and heat transfer measurements are made for the inlet Reynolds number of 66000(based on chord length and free-stream velocity). Turbulent intensity and stress are measured using a hot-wire anemometer, and to measure the convective heat transfer coefficients on the blade surface liquid crystal/gold film Intrex technique is used. Each of experimental cases is characterized by the unsteadiness measured at the entrance of the cascade. The wake behind the rectangular bars enhances the turbulent motion of the flow in the cascade passage. It also promotes the boundary layer development and transition. The results show that heat transfer coefficients on the blade surface increase with increasing unsteadiness.

• Journal of Plant Biology
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• 제37권1호
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• pp.53-67
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• 1994

대표적인 규소축적 식물 중에 하나인 벼(Orzy sativa)의 규소체를 기관별로 광학현미경과 주사전자현미경 하에서 조사하였다. 또한 규소체의 명칭에 대하여 가능한 기원조직에 근거하여 정리하였다. 벼의 조사된 주요 기관 7개 부위, 즉 엽신, 엽초, 줄기, 뿌리, 포영, 호영, 그리고 내영에서 특징적인 규소체가 확인되었다. 각 기관에 형성된 규소체 중 특히 장세포 기원의 규소체, 단세포 기원의 규소체 그리고 표피부속체 기원의 규소체 등은 기관별로 그 형태가 다양하게 나타났다. 또한 엽신에서는 벼의 다른 기관에서 형성되는 대부분의 규소체가 형성되는 것으로 밝혀졌다.

• 한국주조공학회지
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• 제19권5호
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• pp.427-432
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• 1999

Most investment castings contain some porosities and microcavities. In this study, we investigated the elimination trends of various internal defects in IN738LC investment castings for industrial gas turbine blade by hot isostatic pressing. The results showed that cylindrical defects which are under $0.6mm{\Phi}{\times}7mm$ size are mostly eliminated and aspect ratio of defects is more sensitive factor than their cross section shape in removing these defects. Increasing hot isostatic pressure and holding time doesn't affect the elimination trend of cylindrical defects over $0.6mm{\Phi}{\times}7mm$ size because first step(plastic deformation) of HIP densification doesn't occur under these HIPping conditions.