• International Journal of Fluid Machinery and Systems
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• 제3권4호
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• pp.315-323
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• 2010

This work investigates the influence of water compressibility on pressure pulsations induced by rotor-stator interaction (RSI) in hydraulic machinery, using the commercial CFD solver ANSYS-CFX. A pipe flow example with harmonic velocity excitation at the inlet plane is simulated using different grid densities and time step sizes. Results are compared with a validated code for hydraulic networks (SIMSEN). Subsequently, the solution procedure is applied to a simplified 2.5-dimensional pump-turbine configuration in prototype with different speeds of sound as well as in model scale with an adapted speed of sound. Pressure fluctuations are compared with numerical and experimental data based on prototype scale. The good agreement indicates that the scaling of acoustic effects with an adapted speed of sound works well. With respect to pressure fluctuation amplitudes along the centerline of runner channels, incompressible solutions exhibit a linear decrease while compressible solutions exhibit sinusoidal distributions with maximum values at half the channel length, coinciding with analytical solutions of one-dimensional acoustics. Furthermore, in compressible simulation the amplification of pressure fluctuations is observed from the inlet of stay vane channels to the spiral case wall. Finally, the procedure is applied to a three-dimensional pump configuration in model scale with adapted speed of sound. Normalized Pressure fluctuations are compared with results from prototype measurements. Compared to incompressible computations, compressible simulations provide similar pressure fluctuations in vaneless space, but pressure fluctuations in spiral case and penstock may be much higher.

• 한국자동차공학회논문집
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• 제17권3호
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• pp.45-53
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• 2009

Die casting process of Mg alloys for high temperature applications was studied to produce an engine oil pan. The aim of this paper is to evaluate die casting processes of the Aluminium oil pan and in parallel to apply new Mg alloy for die casting the oil pan. Temperature distributions of the die and flow pattern of the alloys in cavity were simulated to diecast a new Mg alloy by the flow simulation software. Dies have to be modified according to material characteristics because melting temperature and heat capacity are different. We changed the shape and position of runner, gate, vent hole and overflow by the simulation results. After several trial and error, oil pans of AE44 and MRI153M Mg alloys are produced successfully without defect. Sleeve filling ratio, cavity filling time and shot speed of die casting machine are important parameter to minimize the defect for die casting Magnesium alloy.

• 한국자동차공학회논문집
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• 제5권6호
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• pp.175-182
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• 1997

The purpose of this study is to investigate the effects of intake manifold shapes to improve the engine performance in a 3-cylinder LPG engine with a closed loop fuel supply system. To know the flow resistance of intake manifolds with shape, the intake negative pressure of each runner in intake manifolds were measured by using the digital pressure meter at each driving condition. And, the engine torque and power have been measured with an engine dynamometer while adjusting the optimal fuel consumption ratio with a solenoid driver. As 속 results form this experiment, the torque characteris- tics were more improved with the plenum chamber(B type intake manifold) than with the banana type(A type intake manifold). The torque characteristics were improved at mid-engine speed(rpm) range as the inner diameter of the intake manifold became smaller. And also the optimum volume among the examined plenum chamber volume was 0.74 times(590cc) the displacement of the test engine.

• 한국공작기계학회:학술대회논문집
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• 한국공작기계학회 2005년도 춘계학술대회 논문집
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• pp.174-179
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• 2005

In the super slow speed die casting process, the casting defects due to melt flow should be controlled in order to obtain sound casting products. The casting defects that are caused by molten metal were cold shut formation, entrapment of air, gas, and inclusion. But the control of casting defects has been based on the experience of the foundry engineers. The calculation of simulation can produce very useful and important results. The calculation data of die casting process condition from the computer simulation by the Z-CAST is made to insure that the liquid metal is injected at the right velocity range and that the filling time is small enough to prevent premature solidification. The parameters of runner shape that affected on the optimized conditions that was calculated with simple equation were investigated. These die casting process control techniques of automobile valve body mid-plate have achieved good agreement with the experimental data of tensile strength, hardness test, and material structure photographies satisfactory results.

• 대한기계학회논문집B
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• 제20권1호
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• pp.237-243
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• 1996

Current low head and small scale hydroturbines have limitations in the minimum required head and flow rate for efficient operation. This study attempts to develop a new concept hydroturbine which is expected to run efficiently even in very low head and small flow rate, so that the limitations on the conventional small scale hydropower could be alleviated and competition with other alternative energy sources in the economic respect could be attained. A small scale catapillar track- hydroturbine was fabricated and the performance test was carried out in a water tunnel over the head range of H = 0.8 m ~ 1.26 m. The peak turbine efficiency was 41.3% at the speed ratio of 0.6, and the turbine loss was mostly due to the friction at the chain drive used for power transmission from the runner to the shafts. This type of turbine is expected to become competitive when some improvement in the power transmission mechanism is made.

• 한국항행학회논문지
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• 제18권4호
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• pp.381-386
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• 2014

전기 커넥터에 영향을 주는 프레팅 부식 요인 중 하나인 접촉 부하의 영향을 조사하기 위하여, 프레팅 부식 표본 쌍을 두께 $3{\mu}m$의 두께를 갖는 주석으로 도금된 황동 표본을 사용하여 제조하였다. 접점의 전기저항은 프레팅 부식 시험 기간 동안 측정되었다. 프레팅 주기에서 저항은 증가하였다. 저항의 변화는 3단계로 나눌 수 있다. 첫 번째 단계는 미미하고 안정적인 저항을 나타내었다. 두 번째 단계는 저항이 꾸준한 증가를 보여 주었다. 그리고 세 번째 단계는 매우 높고 간헐적인 저항을 보여주었다. 실패주기(Nf)와 접촉력(P) 사이의 관계는 다음과 같이 표현될 수 있다. 각각의 하중, 변위, 온도 등 다양한 조건에서 프레팅 테스트를 통해 다양한 환경 조건 하에서 매우 높고 간헐적인 저항에 대응 전기 커넥터의 실패주기 예측공식의 표현이 가능할 것이다.

• 한국정보통신학회논문지
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• 제21권2호
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• pp.333-338
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• 2017

최근 모바일 기기의 보편화로 인하여 모바일 데이터베이스를 필요로 하는 많은 새로운 모바일 응용들이 나타나고 있다. 대표적인 모바일 데이터베이스로는 SQLite, Realm 등이 있는데, 이들은 리소스 제약이 큰 소형기기에 적합한 데이터베이스 엔진들이며 리눅스 기반 모바일 기기에 많이 사용되고 있다. 이 엔진들은 대부분 오픈소스 프로그램들이며 범용 데이터베이스에 비해 가볍고 속도가 빠른 장점을 지닌다. 이 논문에서는 모바일 데이터베이스의 선두 주자인 SQLite의 성능 실험과 분석에 초점을 맞춘다. 대상인 모바일 환경을 고려하여 리눅스 기반 환경에서 실험한다. 그리고, SQLite 데이터베이스의 검색 성능을 파악하기 위한 테스트 프로그램을 구현하고 성능 실험을 실시한다. 실험은 같은 환경에서 실행되는 Oracle 데이터베이스와 비교하여 진행한다.

• 한국운동역학회지
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• 제18권3호
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• pp.93-105
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• 2008

본 연구는 스타팅 블록 유형에 따른 운동학적 변인을 분석하기 위하여 남자 단거리 선수 8명을 대상으로 스타팅 블록간의 거리를 세 가지(25cm, 40cm, 35cm)유형으로 구분하여 분석하였다. 본 연구에 참여한 평균 신장 180cm의 선수들에게는 출발선과 앞 블록의 거리 45cm, 블록간의 거리 40cm의 출발 유형이 100m 기록 단축을 위해서 유리한 스타팅 블록의 유형이라 할 수 있다. 이상의 결론을 종합해보면 100m 출발은 정지 상태에서 짧은 시간에 가능한 큰 추진력을 얻는 데 있으며, 중요한 기술적 요점은 출발 신호에 재빠르게 반응하고, 강한 킥에 의해 큰 추진력을 얻어 전경각과 중력을 잘 이용하여 빠른 시간 내에 최고의 속도에 도달하는데 있다. 본 연구에서는 B유형의 출발법이 기록 향상을 위해 효과적인 분석 결과를 보여주고 있다.

• 복식문화연구
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• 제29권2호
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• pp.185-203
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• 2021

The aim of this study was to reveal the modern succession and reinterpretation of brand identity through the case of Balenciaga design presented by Demna Gvasalia through a review of the literature, design collection, and design review analysis. The design collection analysis was conducted from 2016 F/W to 2020 F/W, when Demna Gvasalia commenced responsibility for the Balenciaga collection. A total of 12 articles from overseas fashion magazines and newspapers were analyzed. A modern reinterpretation of Demna Gvasalia's Balenciaga design is as follows. First, he introduced luxury mode to reflect a sense of the times and introduced luxury street looks based on street and sports sensibilities, showing various styles without specific concepts. Second, by sharing universal sensibilities based on pragmatism, he proposed an easy-to-wear outfit for daily life to demonstrate the everydayness of fashion. Third, as a new exploration of traditional structural beauty, the design of Cristobal Balenciaga was reinterpreted through the conversion of items, overlapping outfits, and the introduction of high-tech technologies. Fourth, by taking a conceptual approach to fashion, he has renewed the spirit of experimentation and modernity shown by Cristobal Balenciaga. Fifth, with the presentation of a new icon, new styles of sneakers such as Triple S and Speed Runner are presented as new icons. He inherited the original mindset and creative approach of the house's founder, Cristobal Balenciaga, and reinterpreted it from a contemporary street sensibility and pragmatic perspective.

• 한국기계가공학회지
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• 제20권2호
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• pp.107-119
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• 2021

The cross-flow turbine is one of the most famous and widely used hydraulic power systems for a long time. The cross-flow turbine is especially popular in many countries and remote regions where off-grided because of its many benefits such as low cost, high efficiency at low head, simple structure, and easy maintenance. However, most modern turbines, including the cross-flow turbine, are unsuitable for the ultra-low head situation, known as less than 3m water head or zero head with over 0.5m/s flow velocity. In this study, we demonstrated a 20kW class inverted-type cross-flow turbine's performance. First, we reevaluated our previous studies and introduced how to design the inverted-type cross-flow turbine. Secondly, we fabricated the 20kW class inverted-type cross-flow turbine for the performance test. And then, we designed a testbed and installed the turbine system in the demonstration facility. In the end, we compare the demonstration with its previous CFD results. The comparing result shows that both CFD and real model fitted on guide vane angle at 10 degrees. At the demonstration, we achieved 42% turbine efficiency at runner speed 125 RPM.