• 대한기계학회논문집
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• 제17권6호
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• pp.1640-1647
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• 1993

본 연구에서는 속도-압력 연계방법으로는 SIMPLE기법을 적용하고, 비균일 격자계에서도 사용할 수 있는 QUICKER방법과 함께 HYBRID방법을 이용하여 이와 같은 물음에 대한 대답을 구하고자 하였다. 이를 위하여 수치적 실험을 위한 흐름으로 본 연구에서 선택한 정사각형 공동 흐름 (square cavity flow)은 재순환 유동의 수치 적 해법을 위한 표준유동으로 많이 사용되어 왔으며, 대한기계학회 전산유체분과에서 도 여러 수치기법을 비교평가 하기 위한 흐름으로 채택된 적이 있는 흐름이다.

• 대한기계학회논문집
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• 제16권6호
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• pp.1179-1194
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• 1992

본 연구에서는 이 기존의 방법들을 개선하여 비균일격자계에서도 사용할 수 있는 비선형 함수관계를 제시하며, 이 방법과 기존의 해법들을 비교할 때 실제 유동장 에서의 해의 정확도 차이, 전산비용의 경제성등은 어느정도 인지를 밝히고, 또 개선된 해법이 앞서 제시한 좀 더 복잡한 유동장에서도 성공적으로 적용 가능한지의 여부를 판단하는 것을 그 목적으로 한다.

• 한국통계학회:학술대회논문집
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• 한국통계학회 2005년도 춘계 학술발표회 논문집
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• pp.191-196
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• 2005

Knowing the time of the process change could lead to quicker identification of the responsible special cause and less process down time, and it could help to reduce the probability of incorrectly identifying the special cause. In this paper, we propose a MLE of the process change point when control charts with the fixed sampling rate (FSR) scheme or the variable sampling rate (VSR) scheme monitor a process to detect changes in the process mean and/or variance of a normal quality variable.

• 한국품질경영학회:학술대회논문집
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• 한국품질경영학회 2004년도 품질경영모델을 통한 가치 창출
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• pp.436-441
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• 2004

Knowing the time of the process change could lead to quicker identification of the responsible special cause and less process down time, and it could help to reduce the probability of incorrectly identifying the special cause. In this paper, we propose a generalized maximum likelihood estimate. (MLE) of the process change point when a control chart with variable sample size (VSS) scheme signals a change in the process mean, and evaluate the performance of this estimator when it mi used with a VSS EWMA chart.

• Communications for Statistical Applications and Methods
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• 제10권3호
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• pp.825-833
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• 2003

Knowing the time of the process change could lead to quicker identification of the responsible special cause and less process down time, and it could help to reduce the probability of incorrectly identifying the special cause. In this paper, we propose a maximum likelihood estimator of the process change point when a Shewhart $\bar{X}$ chart with variable sample size (VSS) scheme signals a change in the process mean. Also we build a confidence interval for the process change point by using the likelihood function.

• ETRI Journal
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• 제44권6호
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• pp.903-914
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• 2022

Mobile and telecommunication networking uses temporary and random identifiers (IDs) to protect user privacy. For greater intelligence and security o the communications between the core network and the mobile user, we design and build a dynamic randomization scheme for the temporary IDs for mobile networking, including 5G and 6G. Our work for ID randomization (ID-RZ) advances the existing state-of-the-art ID re-allocation approach in 5G in the following ways. First, ID-RZ for ID updates is based on computing, as opposed to incurring networking for the re-allocation-based updates, and is designed for lightweight and low-latency mobile systems. Second, ID-RZ changes IDs proactively (as opposed to updating based on explicit networking event triggers) and provides stronger security (by increasing the randomness and frequency of ID updates). We build on the standard cryptographic primitives for security (e.g., hash) and implement our dynamic randomization scheme in the 5G networking protocol to validate its design purposes, which include time efficiency (two to four orders of magnitude quicker than the re-allocation approach) and appropriateness for mobile applications.

• 대한전기학회:학술대회논문집
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• 대한전기학회 1996년도 하계학술대회 논문집 A
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• pp.15-17
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• 1996

In this paper, a modified microstep drive of PM step motor is presented. The open-loop drive of a step motor is attractive and widely accepted in applications of speed and position controls. However, the performance of the step motor is limited under the open-loop drive. The closed-loop control is advantages over the open-loop control not only in that step failure never occurs but that the motion is much quicker and smoother. However, a high resolution sensor is needed for detecting position and speed. The modified microstep drive is constructed as a microstep drive with speed feedback. The advantages of the proposed method is that the controller can be designed by a low resolution sensor and is simpler than other closed-loop controller. A concept of vector control is used for verifying the proposed scheme. Simulations show the performance of the proposed method and a comparison with a classic drive method.

• 대한기계학회논문집
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• 제18권2호
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• pp.414-423
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• 1994

The planar laminar impingement jet with a confinement plate has been studied numerically. Discretzing the convection term with the QUICKER scheme, the full Navier-Stokes equations for fluid flow were solved using the well known SIMPLER algorithm. The flow characteristics with Reynolds number and jet exit velocity profile effects on it were considered for H=3, Re=200 - 2000. Results show that vortical flow forms in turn along the confinement and impingement plates as the Reynolds number increases and such a complicated flow pattern has never been reported prior. The jet exit velocity profile is shown to do an important role in determining the position of vortex flow and its size as well as in stagnation and wall jet flow region. Parabolic jet exit profile results in peak of skin friction 1.4-1.6 times greater than that of uniform profile. The channel height effects are also studied and shown to have an effect on flow pattern similar to that of Reynolds number. Also shown is that effects of the jet exit velocity profile becomes less significant over a certain channel height.

• Tribology and Lubricants
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• 제35권1호
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• pp.77-86
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• 2019

The present study focuses on the effect of staggered integration factor (SIF) on Morton effect simulation results. The Morton effect is a synchronous rotordynamic instability problem caused by the temperature differential across the journal in fluid film bearings. Convection and conduction of heat in the thin film displaces the hot spot, which is the hottest circumferential position in the thin film, from -20 to 40 degrees ahead of the high spot, where the minimum film clearance is experienced. The temperature differential across the journal causes a bending moment and the corresponding thermal bow in the rotating frame acts like a distributed synchronous excitation in the fixed frame. This thermal bow may cause increased vibrations and continued growth of the synchronous orbit into a limit cycle. The SIF is developed assuming that the response of the rotor-lubricant-bearing dynamic system is much quicker than that of the bearing-journal thermal system, and it is defined as the ratio between the simulation time of the thermal system and the rotor-spinning period. The use of the SIF is unavoidable for efficient computing. The value of the SIF is chosen empirically by the software users as a value between 100 and 400. However, the effect of the SIF on Morton effect simulation results has not been investigated. This research produces simulation results with different values of SIF.

• 한국정보처리학회논문지
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• 제4권1호
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• pp.237-245
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• 1997

본 논문에서는 우선순위에 기초를 둔 새로운 흐름제어 방식을 제안한다. 이 방식 에 따르면 각 통신경로는 유지하고자 하는 적정 버퍼의 크기를 설정하고, 전송중 이 를 초과하지 않도록 해당 통신경로의 전송 우선순위를 조절한다. 대용량의 통신대역 폭을 요구하는 통신경로는 작은 크기의 적정 버퍼를 설정한다. 적정 버퍼의 크기와 전송 우선순위가 반비례하게 정의하면, 통신경로의 전송 우선순위는 높게 설정되므 로, 각 노드는 설정된 통신경로를 지나는 패킷에 높은 처리 기회를 제공하게 되고, 이를 통하여 버퍼의 크기를 적정 수준이하로 감소시키는 작용을 한다. 또한 대용량의 통신대역폭을 요구하는 통신경로에서는 경로상에 있는 노드에 적은 수의 패킷을 유지 하게 함으로 짧은 전송지연을 갖게 된다. 각 통신경로의 버퍼 크기는 통신경로가 연 결된 동안 일정한 시간 간격으로 재조정될 수 있다. 사용하고 있는 통신망 대역폭이 통신경로의 최종 목적지 응용 프로그램이 필요로 하는 데이타 흐름보다 적은 경우, 그 노드는 큐의 크기를 줄임으로써 대역폭을 보다 크게 확보할 수 있다. 통신망간 연 동 환경에서는 나은 통신망 대역폭을 근접한 노드로 확보할 수 있으며, 따라서 데이 타의 응답이 전통적인 end-to 흐름제어 기법보다 빨라진다. 고속의 통신망 환경에서 는 제안된 흐름제어 기법이 보다 효율적인 성능을 보인다.