• Journal of Mechanical Science and Technology
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• 제18권2호
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• pp.286-293
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• 2004

The air fuel ratios of current gasoline engines are almost controlled by several air flow meters. When CVVT (Continuous Variable Valve Timing) is applied to a gasoline engine for higher engine performance, the MAP (Manifold Absolute Pressure) sensor is difficult to follow the instantaneous air fuel ratio due to the valve timing effect. Therefore, a HFM (Hot Film Flow Meter) is widely used for measuring intake air flow in this case. However, the HFMs are incapable of indicating to reverse flow, the oscillation of intake air flow has an negative effect on the precision of the HFM. Consequently, the various duct configurations in front of the air flow sensor affect the precision of HFM sensitivity. This paper mainly focused on the analysis of the reverse flow, flow fluctuation in throttle upstream and the geometry of intake system which influence the HFM measurement.

• 대한전자공학회논문지
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• 제25권3호
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• pp.294-301
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• 1988

A study on the lattice damages and impurity depth profiles have been performed with BF2 ion implanted silicon materials. Electrical measurement, SIMS and TEM analysis techniques were used in order to identify the reverse annealing phenomena, impurity depth profiles and lattice damages. A typical reverse annealing phenomena were shown at the dose of 1x10**15/cm\ulcorner and non-reverse annealing at the dose of 5x10**15/cm\ulcorner This was explained with the formation of the amorphous region at BF2+ ion implantation with high dose. That is, the amorphous reigons were recrystallized centrated at certain regions were measured by SIMS technique. The dislocation loops-like crystalline defects were observed with TEM cross sections, which were formed at the lattice damaged region during annealing process.

• 공업화학
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• 제8권2호
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• pp.276-285
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• 1997

역삼투복합막의 박막으로 사용되고 있는 polyamide의 성능을 용질투과방식과 연관하여 이론적으로 고려하고 단량체 및 제조 조건을 변화시켜 계면중합을 통해 제조하여 봄으로써 이의 검증을 시도하였다. 제조된 고분자는 중합조건에 따라 물질 구성의 변화를 보여 주었으며, 이는 이론적으로 제시한 값의 범주에 속하였다. 또한 이에 따라 막성능에서도 큰 영향을 발휘한 바, 용매의 변화, 수용상 및 유기상 단량체의 농도 비율에 따라 고분자의 함유성분의 변화를 가져왔다.

• 멤브레인
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• 제13권3호
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• pp.131-142
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• 2003

원통형 회전 역삼투법은 높은 전단력과 유체의 불안정성을 결합시켜 막오염을 감소시키는 동적 여과방법이다. 이 논문은, 회전여과의 물리적 특성, 물질전달과 농도분극 현상, 이론적 및 실험적 해석, 사례연구 등 회전역삼투법에 대한 최근의 연구를 요약해서 보여준다.

• Membrane and Water Treatment
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• 제9권2호
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• pp.129-136
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• 2018

In this contribution, the control of multivariable reverse osmosis (RO) desalination plant using proportional-integral-derivative (PID) controllers is presented. First, feed-forward compensators are designed using simplified decoupling method and then the PID controllers are tuned for flux (flow-rate) and conductivity (salinity). The tuning of PID controllers is accomplished by minimization of the integral of squared error (ISE). The ISEs are minimized using a recently proposed algorithm named as teacher-learner-based-optimization (TLBO). TLBO algorithm is used due to being simple and being free from algorithm-specific parameters. A comparative analysis is carried out to prove the supremacy of TLBO algorithm over other state-of-art algorithms like particle swarm optimization (PSO), artificial bee colony (ABC) and differential evolution (DE). The simulation results and comparisons show that the purposed method performs better in terms of performance and can successfully be applied for tuning of PID controllers for RO desalination plants.

• 대한공간정보학회지
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• 제18권4호
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• pp.79-86
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• 2010

본 연구는 태양광 에너지 발전 시설의 효율 증대와 입지 선정을 위한 태양광 역추적에 관한 연구이다. 기후 및 지형요소들을 가지고 소규모 지역의 태양광을 역추적 하는데 목적을 두고 있다. 6가지 기후요소들에 대해 상관 분석을 수행, 상관계수 및 유의확률을 확인하여 상관관계가 없다고 판단된 풍속과 구름의 양은 제외하였다. 나머지 기후요소 및 지형요소를 가지고 각각 회귀분석을 수행해본 결과, 일사량에 가장 큰 영향을 끼치는 요소로는 일조량과 지형의 고도였다. 이 결과를 바탕으로 정확한 일사량 모델링을 위해 기후 및 지형요소를 가지고 일사량 모델링을 수행한 결과, 기후요소가 지형요소에 비해 더 큰 계수 값을 가졌다. 이는 기후요소가 지형요소에 비해 더 큰 영향력을 가진다는 것을 의미한다.

• 한국산업융합학회 논문집
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• 제24권6_2호
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• pp.773-779
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• 2021

CNG, which has recently been attracting attention as an alternative fuel in the transportation field to reduce emissions caused by global warming, is natural gas with abundant reserves and mainly composed of methane. Being in a gaseous state, natural gas requires the compression and liquefaction processes for transportation. Until now, general shut-off valves for liquid and gas piping have been developed in Korea, but there are few studies on shut-off valves for high pressures of about 200 bar. Currently, research on the flow analysis of valves is being actively conducted around the world. However, there are relatively many studies on large valves such as low-pressure valves or shipbuilding and marine, and the safety factor through structural analysis to check the structural integrity of the valve is checked at the design stage. Since it is necessary to have a fast response speed while minimizing pressure and speed loss due to flow change, basic research was conducted on the flow analysis of the valve to secure design data, and the numerical analysis was performed on high-pressure automatic shut-off valves applied to CNG refueling stations. After securing the basic valve shape through reverse engineering for advanced products, we compared the valve flow coefficient Cv coefficient with advanced products. As a result, it was found that the reverse engineering model was at the level of about 60%. However, we compared the Cv coefficient by modifying the reverse engineering model, and the result showed that it was improved to about 96%.

• Design & Manufacturing
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• 제9권1호
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• pp.18-22
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• 2015

Mold making and product manufacturing process was made by a die through a number of stages. Thereby, it takes a long period of time from the manufacture of mold until passed the products to consumers. However, it is not possible to meet the diverse desires purchasing of consumer. We made a 3D CAD Model aligned with product scan data using reverse engineering. Utilizing thereafter flow analysis to derive the optimal mold conditions, by applying the condition, and devised a mold fabrication process that is much shorter than the conventional process for fabricating a mold. In this study, the outlet cover to the product, it describes a process, as a result, it was confirmed that the number of steps can be shortened much more than the conventional process.

• 전기학회논문지
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• 제59권8호
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• pp.1394-1400
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• 2010

This paper introduces a newly improved Ultra-FRFET that has much better reverse recovery characteristic than that of the typical MOSFET and presents its effectiveness in the HV-BLU system of LCD TVs. The reverse recovery time, $T_{rr}$ of Ultra-FRFET is shorter than 40nsec and the peak value of reverse current, $i_{rr}$ is also much smaller compared to the typical MOSFET's, which are sufficient to prevent the MOSFET’s failures without additional FRDs and diodes in HV-BLU system with a half-bridge resonant inverter topology worked by PWM method. In order to verify the validity, the loss analysis and the implementation results in cases when both the conventional solution using typical MOSFETs with additional FRDs and a new solution using Ultra-FRFETs are applied to a HV-BLU of 40" LCD TV are presented. As a result, the effectiveness of Ultra-FRFET was verified and the results are presented in this paper.

• Industrial Engineering and Management Systems
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• 제16권1호
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• pp.1-21
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• 2017

This paper discusses a reverse supply chain (RSC) which consists of the process flows from procurement of used products collected from a market, through remanufacturing products from the used products, to sales of the products in a market. In general, it is conceivable for the RSC to face the uncertainty in quality of used products collected from a market. Inspection is one of efficient methods to deal with the problem regarding quality of used products. However, there is a trade-off between inspection cost and inspection accuracy. This paper focuses on the following five types of inspection: (1) 100% inspection, (2) sampling inspection, (3) sampling inspection with screening of rejected lots, (4) sampling inspection with screening of acceptable lots, and (5) no inspection, and determines the optimal operation consisting of the optimal number of procured used products and the optimal inspection policy. Numerical analysis clarifies not only how changes of conditions of the RSC affect the manufacturer's optimal operation but also features of each inspection type. In addition, from the results of numerical analysis, this paper shows the usability to add the proposed inspection in this paper, the sampling inspection with screening of acceptable lots, to choices of inspection type.