• 한국유체기계학회 논문집
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• 제18권1호
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• pp.44-50
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• 2015

Labyrinth seals are commonly used in various kinds of turbomachinery to reduce leakage flow. In the present 3D CFD analysis of see-through-type labyrinth air seal, the methodology of determining leakage and rotordynamic coefficients is suggested with the relative coordinate system for steady-state simulation. The leakage flow and rotordynamic forces predicted by using different solvers and turbulent models of FLUENT are compared with the results of the existing bulk-flow analysis code LABYSEAL.FOR and experiment. The present CFD result of direct stiffness(K) shows only improvement in prediction. The results of leakage and rotordynamic coefficients as well as computing time are sensitive against the used solver and turbulent model.

• 설비공학논문집
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• 제25권10호
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• pp.562-567
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• 2013

1D-numerical analysis of the network algorithm with the orifice equation for the relationship between pressure difference and flowrate has been mostly used to analyse leakage flow at the gap. In this study, a 3D-numerical method applying momentum loss model to the gap region in the computational domain is represented to reflect effectively the effect of leakage flow by determining the proportion of pressure difference to air passage velocity. While the 3D-numerical method is verified through the computation of the two compartments model, the numerical analysis of the stack effect in a building stairway is performed. As the temperature of air outside drops, the pressure in the upper stairway and leakage flowrate through the gap in the door rise. The change of gap area does not have an effect on pressure in the stairway for the analysis conditions.

• 대한기계학회논문집B
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• 제21권10호
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• pp.1339-1349
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• 1997

A numerical method of calculating the performance of a scroll compressor for refrigerant R-22 and R-134a is presented in this paper. A series of involute curves are employed for the scroll wrap design and the compression volume is investigated geometrically. The radial leakage flow rate through tip clearance is calculated by the two-dimensional compressible flow. On the basis of the results, quasi one-dimensional leakage modeling can be applied to the performance analysis of a scroll compressor, more effectively. Furthermore, the heat transfer effect between scroll wrap and working fluid in compression chamber is considered for the performance analysis. As the results of this study, the effects of the radial and tangential leakage flow rate and heat transfer on the scroll compressor performance are derived precisely. These results may provide the guideline for the design and development of a real scroll compressor.

• 한국가스학회지
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• 제16권6호
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• pp.23-28
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• 2012

우리나라의 LPG자동차 기술은 2003년 LPG액상분사방식 차량의 양산을 계기로 크게 발전하기 시작하였으며, 지금까지 관련기술의 발전을 거치면서 SULEV 배출가스 규제를 만족하는 수준에 이르렀다. 우리나라의 LPG자동차 등록수는 240여만 대를 넘어서면서 세계 1위의 LPG자동차 보유수를 보이고 있다. 그러나 이러한 많은 대수를 보유하고 있음에도 불구하고, 지금까지 LPG자동차의 핵심 연료시스템은 외산기술을 이용하는 라이센스 제작, 조립 및 판매를 진행하고 있다. 특히 LPG액상분사식 자동차의 핵심부품인 LPG인젝터는 국제 부품공급사인 C사의 D 인젝터를 이용하여 왔다. 이에 본 연구에서는 국산 LPG인젝터의 개발을 이루고자 하며, 개발과정에서 가장 핵심적인 LPG 누설성능 개선에 영향을 미치는 코팅기술의 성능향상연구를 집중하였다. 본 연구에서 WCC 코팅 및 구조 최적화를 통하여 기존의 D 인젝터의 0.06cc/min 누설성능을 0.04cc/min 수준 이하로 낮출 수 있었다.

• 한국지반공학회논문집
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• 제32권2호
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• pp.19-30
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• 2016

도심지 지반함몰 현상의 대부분이 노후된 하수관에 의해 발생한다는 것은 이미 잘 알려진 사실이다. 따라서 관 파손의 위치와 주변 지반의 상대밀도가 지반의 거동에 미치는 영향을 알아보기 위해 실내모형시험을 수행하였다. 관 파손은 관 둘레에 대해 20% 파손된 것으로 가정하여 관 상부에 파손이 발생한 경우와 하부에 발생한 경우로 고려하였다. 느슨한 지반과 조밀한 지반을 상대밀도 30%, 70%로 조성하여 관 파손의 위치에 따른 지반 거동을 측정하였을 뿐만 아니라, 유한요소해석을 이용하여 실내모형시험 결과와 비교 분석하였다. 관 하부가 파손되어 누수가 발생되는 것이 상부가 파손되는 것보다 더 큰 지반 거동을 유발하는 것으로 나타났을 뿐만 아니라, 느슨한 지반에서 더 큰 지표침하량이 발생하는 것을 알 수 있었다.

• 정보처리학회 논문지
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• 제13권2호
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• pp.41-47
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• 2024

시간 및 주파수 영역에서 각각 학습한 모델 간에 성능 차이가 발생할 경우, 앙상블을 수행하더라도 개별 모델 간의 성능 불균형으로 인하여 앙상블의 성능이 오히려 저하되는 현상을 확인할 수 있었다. 따라서, 본 논문은 시간 영역과 주파수 영역에서 특징을 추출하고, 이들을 융합한 단계적 학습 방법을 통해 파이프라인 누출 감지의 정확성을 높이기 위한 누출판별 기법을 제안한다. 이 방법은 두 단계의 학습 과정으로 이루어지며, 먼저, 단계 1에서는 시간 영역과 주파수 영역에서 독립적으로 모델 학습을 수행하여 도메인별로 주어진 데이터로부터 중요한 특징들을 효과적으로 추출하도록 하였다. 단계 2에서는 사전학습 완료된 각 모델로부터 해당 분류기를 제거한 후, 두 도메인의 특징들을 서로 융합하고 새로운 분류기를 추가하여 재학습을 수행하였다. 본 논문에서 제안하는 전이학습 기반 특징융합 기법은 시간 및 주파수 영역에서 추출된 특징들을 융합하여 모델 학습을 수행함으로써, 두 영역의 특징이 상호 보완적으로 작용하여 모델이 다양한 정보를 활용함으로 인해 99.88%의 높은 정확도를 달성하여 파이프 누수 감지에 있어 우수한 성능을 입증하였다.

• 한국재료학회지
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• 제13권1호
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• pp.11-17
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• 2003

DC characteristics of recessed gate 4H-SiC MESFET were investigated using the device/circuit simulation tool, PISCES. Results of theoretical calculation were compared with the experimental data for the extraction of modeling parameters which were implemented for the prediction of DC and gate leakage characteristics at high temperatures. The current-voltage analysis using a fixed mobility model revealed that the short channel effect is influenced by the defects in SiC. The incomplete ionization models are found out significant physical models for an accurate prediction of SiC device performance. Gate leakage is shown to increase with the device operation temperatures and to decrease with the Schottky barrier height of gate metal.

• 전력전자학회논문지
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• 제25권1호
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• pp.13-20
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• 2020

Accurate parameters based on equivalent circuit are required for high-performance field-oriented control in a three-phase induction motor. In a normal case, stator resistance can be accurately measured using a measuring equipment. Except for stator resistance, all machine parameters on the equivalent circuit should be estimated with particular algorithms. In the viewpoint of traditional regions, the parameters of an induction motor can be identified through the no-load and standstill test. This study proposes an identification method that uses the d-axis model of the induction motor in a stationary frame with the predefined information on stator resistance. Mutual inductance is estimated on the rotational dq coordination similar to that in the traditional no-load experiment test. The leakage inductance and rotor resistance can be estimated simply by applying different voltages and frequencies in the d-axis model of the induction motor. The proposed method is verified through simulation and experimental results.

• Structural Engineering and Mechanics
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• 제20권1호
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• pp.1-20
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• 2005

The present paper deals with the seismic response analysis and the evaluation of most likely failure modes for a water storage structure. For the stress analysis, a 3-D mathematical model has been adopted to represent the structure appropriately. The structure has been analyzed for both static and seismic loads. Seismic analysis has been carried out considering the hydrodynamic effects of the contained water. Based on the stress analyses results, the most likely failure modes viz. tensile cracking and compressive crushing of concrete for the various structural elements; caused by the seismic event have been investigated. Further an attempt has also been made to quantify the initial leakage rate and average emptying time for the structure during seismic event after evaluating the various crack parameters viz. crack-width and crack-spacing at the locations of interest. The results are presented with reference to peak ground acceleration (PGA) of the seismic event. It has been observed that, an increase in PGA would result in significant increase in stresses and crack width in the various structural members. Significant increase in initial leakage rate and decrease in average emptying time for the structure has also been observed with the increase in PGA.

• 드라이브 ㆍ 컨트롤
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• 제12권2호
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• pp.1-6
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• 2015

Recently, the Electro-Hydrostatic Actuator(EHA) has been developed as a result of research on energy saving. EHA is usually composed of a direct driven pump from an electric motor and is available to control cylinder displacement or velocity with high efficiency. In addition, it has the advantage of compactness, minimum leakage and availability of decentralized control. In this study, an EHA system was designed to decrease the path tracking error and manufactured for test. The linearization method provided in AMESim software was used to derive the model of EHA system. The derived model was applied to design the PI-D controller to effectively overcome the disturbance. The effectiveness of this controller was verified by further testing.