• 대한기계학회논문집B
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• 제26권10호
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• pp.1341-1347
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• 2002

In order to improve efficiency of a system with three-dimensional flow characteristics, this paper presents a new method that overcomes three-dimensional effects by using two-dimensional CFD and neural network. The method was applied to shape optimization of cut-off in a multi-blade fan/scroll system. As the entrance conditions of two-dimensional CFD, the experimental values at the positions out of the inactive zone were used. The distributions of velocity and pressure obtained by two-dimensional CFD were compared with those of three-dimensional CFD and experimental results. It was found that the distributions of velocity and pressure have qualitative similarity. The results of two-dimensional CFD were used for teaming as target values of neural network. The optimal angle and radius of cut-off were determined as 71$^{\circ}$and 0.092 times the outer diameter of impeller, respectively. It is quantified in the previous report that the optimal angle and radius of cut-off are approximately 72$^{\circ}$and 0.08 times the outer diameter of impeller, respectively.

• 한국자동차공학회논문집
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• 제11권1호
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• pp.225-231
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• 2003

In order to improve efficiency of a system with three-dimensional flow characteristics, this paper presents a new method that overcomes three-dimensional effects by using two-dimensional CFD and response surface method. The method was applied to shape optimization of cut-off in a multi-blade fan/scroll system. As the entrance conditions of two-dimensional CFD, the experimental values at the positions out of the inactive zone were used. In order to examine the validity of the two-dimensional CFD the distributions of velocity and pressure obtained by two-dimensional CFD were compared with those of three-dimensional CFD and experimental results. It was found that the distributions of velocity and pressure show qualitatively similarity. The results of two-dimensional CFD were used for constructing the objective function with design variables using response surface method. The optimal angle and radius of cut-off were determined as $72.4^{\circ}$ and 0.092 times the outer diameter of impeller, respectively. It is quantified the previous report that the optimal angle and radius of cut-off are approximately $72^{\circ}$ and 0.08 times the outer diameter of impeller, respectively.

• 방송공학회논문지
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• 제15권6호
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• pp.845-852
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• 2010

클라이언트로부터의 요구메시지의 통계를 바탕으로 하여 방송 서버는 데이터 아이템에 대하여 최적의 컷오프 포인트를 이용하여 핫 아이템과 콜드 아이템으로 나눈다. 핫 아이템은 주기적으로 방송되는데 이 때, 방송 주기는 아이템들의 인기도, 즉 요구확률에 따라 정해진다. 핫 아이템이 방송되지 않은 빈 슬롯에는 적절한 콜드 아이템을 골라 방송하게 되는데, 이 때 대기시간과 대기 중인 요구 메시지의 수 등을 고려하여 콜드 아이템을 정한다. 최적의 컷오프 포인트를 해석적으로 구하기 위하여 평균 응답시간을 컷오프 포인트의 함수로 나타나도록 계산하였다. 요청 도착율과 아이템의 인기도를 변화하면서 수행한 시뮬레이션을 통하여 본 논문에서 제안한 방법이 기존의 방법들보다 더욱 우수한 성능을 나타냄을 보였다.

• 한국소음진동공학회논문집
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• 제21권5호
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• pp.447-454
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• 2011

This paper reports a filtered velocity feedback(FVF) controller, which is an alternative to direct velocity feedback(DVFB) controller. The instability problems due to high frequency response under DVFB can be alleviated by the suggested FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The FVF controller and the dynamics of clamped beams under forces and moments are first formulated. The effects of the design parameters(cut-off frequency, gain, and damping ratio) on the stability and the performance are then investigated. The cut-off frequency should be selected not to affect the system stability. The magnitude of the open loop transfer function(OLTF) at the cut-off frequency should be small. As increasing the gain of the FVF controller, the magnitude of the OLTF is increased, so that the closed loop response can be reduced more. The enhancement of the OLTF at the cut-off frequency is reduced but the phase behavior around the cut-off frequency is distorted, as the damping ratio is increased. The control performance is finally estimated for the clamped beam. More than 10 dB reductions in velocity response can be achieved at the modal frequencies from the first to eighth modes.

• 대한산업공학회지
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• 제33권2호
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• pp.282-289
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• 2007

While demands for express couriers service are rapidly increasing due to recent progress of electronic commerce, express courier service companies are struggling to take a larger market share through ongoing improvement in their service processes. Cut-off time is the time limit that all orders delivered before the limit are guaranteed for the delivery within the very next day. Extending cut-off time for express service centers can provide the express company with increase of total sales, but it may also cause increasing the possibility not to satisfy customer needs due to work delay in the consolidation terminal. We develop a design model for express courier service network based on a recursive optimization/simulation procedure. With the optimization model, we seek key design parameters such as the cut-off time for express service centers and the capacity of the consolidation terminal maximizing total sales profit while satisfying the desired level of performances. With the simulation model, we consider the dynamic nature of the network and obtain relationships between the design parameters and the performance measures with the multiple linear regression. The validity of the model is examined with an example.

• 한국멀티미디어학회논문지
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• 제21권7호
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• pp.772-778
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• 2018

We have previously proposed a preliminary cut-off indoor positioning scheme considering the reference point with the same signal similarity. This scheme estimates the position using the relative rank of the peak of received signal strength from the beacons around user. However, this scheme has a weak point with lower accuracy when there are more than one nearest reference points having the same signal similarity. In order to tackle this, we propose a weighted preliminary cut-off indoor positioning scheme. Firstly, if the above problem occurs, the similarity to the peak of signal strength is considered as well as the relative rank. Next, weights are assigned to the nearest reference points using the similarity to the peak of the received signal strength. Finally, the user's position is estimated by applying the weights. As a result, the weighted preliminary cut-off scheme improves the positioning accuracy by about 7.9% compared to the previous scheme.

• 전력전자학회논문지
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• 제3권4호
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• pp.273-279
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• 1998

본 논문에서는 제안하는 계단충전방식에서는 직렬로 연결된 전지에 있어서 각 전지의 $\Delta$V=0 시점이 서로 다름을 고려하여 각 전지별로 선택적으로 충전단계를 절환시킴으로써 과충전 또는 부족충전을 예방할 수 있도록 하였다. 또한, 각 단계의 초기에 전지간의 잔존용량의 불균등을 해소하기 위해 시분할 균등충전모드를 추가하였다. 기존의 계단충전방식에 비해 선택적 충전단계절환을 위한 간단한 회로가 추가되지만 과충전과 부족충전을 예방하므로 전지수명과 충전효율을 개선시킬 수 있다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 춘계학술대회 논문집
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• pp.264-270
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• 2011

This paper reports a filtered velocity feedback (FVF) controller, which is an alternative to direct velocity feedback (DVFB) controller. The instability problems due to high frequency response under DVFB can be alleviated by the suggested FVF controller. The FVF controller is designed to filter out the unstable high frequency response. The FVF controller and the dynamics of clamped beams under forces and moments are first formulated The effects of the design parameters (cut-off frequency, gain, and damping ratio) on the stability and the performance are then investigated. The cut-off frequency should be selected not to affect the system stability. The magnitude of the open loop transfer function (OLTF) at the cut-off frequency should be small. As increasing the gain of the FVF controller, the magnitude of the OLTF is increased, so that the closed loop response can be reduced more. The enhancement of the OLTF at the cut-off frequency is reduced but the phase behavior around the cut-off frequency is distorted, as the damping ratio is increased The control performance is finally estimated for the clamped beam. More than 10dB reductions in velocity response can be achieved at the modal frequencies from the first to eighth modes.

• 한국진공학회:학술대회논문집
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• 한국진공학회 2012년도 제42회 동계 정기 학술대회 초록집
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• pp.181-181
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• 2012

The microwave probe for measuring plasma density is widely used for its advantages: First, it is not affected by the reactive gas. Second, it can measure local plasma parameters such as plasma density, plasma potential and plasma temperature. Third, it is simple and robust. A cut-off probe is the one of the most promising microwave probe. Recently, Kim et al. reveals the physics of the cut-off probe but the effect of the sheath on the determination of the plasma density is not explained. In this presentation, for taking account of sheath effects on determination of plasma density from the cut-off peak, a simplified circuit modeling and an E/M simulation are conducted. The results show that occupation ratio of sheath volume between two tips of the cut-off probe and subsequence pressure condition mainly change position of the cut-off peak with respect to plasma frequency. Magnitude of relative voltage taken on the impedance of sheath and the impedance of bulk plasma can explain this effect. Furthermore, effects of gap size, tip radius, and tip length ware revealed based on above analysis.

• 한국자동차공학회논문집
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• 제22권7호
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• pp.23-30
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• 2014

"Cut off line" in automotive passing beam has very important safety function because it serves for headlamp aiming. Headlights that are aimed incorrectly will not only perform poorly but also offend oncoming traffic. In addition, an objective definition of cut off line in low beam is necessary, since a requirement for correct aiming of the beams is specified within all the existing regulations. Accordingly, headlight regulations are requirements that automobiles must satisfy in order to be sold in a particular country. In this study, a more advanced recognition method for the cut off lines of the various headlamps commonly used in Europe, North America, and domestic is suggested and a headlamp testing system is developed to adjust the beam to the country-specific regulation. This system uses image processing technology to detect the cut off lines in the beam patterns of halogen headlamps, high-intensity discharge headlamps, and light-emitting diode headlamps as well.