• 한국융합학회논문지
• /
• 제13권3호
• /
• pp.33-41
• /
• 2022

본 논문에서는 다중 요인을 고려한 천연 가스 누출 정도 예측을 위해 관련 요인을 포함하는 기상청 자료와 천연가스 누출 자료를 통합하고, 요인 분석을 기반으로 중요 특성을 선택하는 머신러닝 기법을 제안한다. 제안된 기법은 3단계 절차로 구성되어 있다. 먼저, 통합 데이터 셋에 대해 선형 보간법을 수행하여 결측 데이터를 보완하는 전처리를 수행한다. 머신러닝 모델 학습 최적화를 위해 OrdinalEncoder(OE) 기반 정규화와 함께 요인 분석을 사용하여 필수 특징을 선택하며, 데이터 셋은 k-평균 클러스터링으로 레이블을 지정한다. 최종적으로 K-최근접 이웃, DT(Decision Tree), RF(Random Forest), NB(Naive Bayes)의 네 가지 알고리즘을 사용하여 가스 누출 수준을 예측한다. 제안된 방법은 정확도, AUC, 평균 표준 오차(MSE)로 평가되었으며, 테스트 결과 OE-F 전처리를 수행한 경우 기존 기법에 비해 성공적으로 개선되었음을 보였다. 또한 OE-F 기반 KNN(OE-F-KNN)은 95.20%의 정확도, 96.13%의 AUC, 0.031의 MSE로 비교 알고리즘 중 최고 성능을 보였다.

• 한국유체기계학회 논문집
• /
• 제16권3호
• /
• pp.26-31
• /
• 2013

In present 3D CFD study, the method for determining leakage and rotordynamic coefficients of a plain-gas seal is suggested by using the relative coordinate system for steady-state simulation. In order to find the effect of pre-swirl speed at seal inlet, pre-swirl velocity is included as a parameter. Present analysis is verified by comparison with results acquired from Bulk-flow analysis code and published experimental results. The results of 3D CFD rotordynamic coefficients of direct stiffness(K) and cross-coupled stiffness(k) show improvements in prediction. As pre-swirl speed at seal inlet increases, k also increases to destabilize system. However, pre-swirl speed at seal inlet does not show sensitivity to the leakage and rotordynamic coefficients of K and damping(C).

• 한국소음진동공학회:학술대회논문집
• /
• 한국소음진동공학회 2002년도 추계학술대회논문집
• /
• pp.799-804
• /
• 2002

In this paper the leakage prediction and rotordynamic analysis of an annular seal with a smooth rotor and spiral-grooved stator are performed. For developing a theoretical model, the three-control-volume analysis of the circumferentially-grooved seal is expanded by considering pressure reduction due to the pumping effect of spiral groove and pressure flow through the spiral groove. Results by the present analysis are compared with available experimental data. For leakage the analysis results generally show a reasonable agreement to the experimental results. For rotordynamic coefficients the analysis results show the same trend as the experimental results for rotor speed with spiral angles, but their magnitudes show somewhat large deviations.

• 한국전산유체공학회:학술대회논문집
• /
• 한국전산유체공학회 2003년도 추계 학술대회논문집
• /
• pp.171-175
• /
• 2003

Numerical analysis of three-dimensional viscous flow-fields in the turbine rotor passages is carried out to investigate flow physics including the interaction between secondary vortices, tip leakage vortex, and the rotor wake. The blade tip geometry is accurately modeled adopting the embedded H grid topology. An explicit four-stage Runge-Kutta scheme is used for the time integration of both the mean flow and turbulence equations. The computational results for the entire turbine rotor flows, particularly the tip clearance flow and the secondary flows, are interpreted and compared with the experimental data from the Penn State turbine stage. Good agreement between the experimental data and the numerical prediction was achieved in the sense of the major features of the flow fields.

• 대한환경공학회지
• /
• 제27권10호
• /
• pp.1065-1071
• /
• 2005

유체의 파속과 파형을 이용한 많은 누수탐지 기술들이 연구되고 있다. 본 연구에서는 파속을 계산하기 위해 천이류 방법을 이용하였고 누수지점의 탐지를 위해 주파수 분석방법을 개발하였다. 가압관망의 자료획득 시스템을 개발하였으며, 이를 통해 고주파 수압자료를 획득하였다. 이들 방법론은 측정과 모의 과정에서 발생되는 오차로 인한 불화실성을 적절히 처리할 수 있으며, 수압자료의 측정간을 근거로 누수의 예측지점을 추정할 수 있다. 본 연구에서 개발된 방법은 수압자료로부터 확보되는 정보를 기반으로, 누수가 동반된 천이현상에서 누수예측능력을 보여주고 있다.

• 설비공학논문집
• /
• 제13권6호
• /
• pp.497-504
• /
• 2001

A study to improve the accuracy of a map-based compressor model with experiment was performed. Corrections on the effects of suction gas superheat and heat leakage from a compressor shell are required to apply the compressor amp model based on the empirical performance data(map) of compressor manufacturers to the actual system. So experiments to assess the effects of superheat and hat leakage were performed and the corrected equations were made. Compressors and refrigerant used in the experiment were the high pressure type rotary compressor and R-22, experiments were performed by compressor calorimeter. From the experiment, a volumetric efficiency correction factor$(F_ν)$ showed the value of 0.77, slightly higher than 0.75 proposed by Dabiri and Rice for low pressure type reciprocating compressor, and the heat leakage from the compressor shell turned out to be a factor that influenced the discharged mass flow rate. The relation between heat leakage of compressor shell and the variation of discharged mass flow rate from compressor was considered in compressor map modeling as an empirical function. With this function, the prediction accuracy of compressor model in system conditions was improved.

• 한국생산제조학회지
• /
• 제18권6호
• /
• pp.652-657
• /
• 2009

MPW(Magnetic Pulse Welding) is a technologies for welding of metals by means of repulsive force on account of the interaction between electro-magnetic field of coil and current induced in outer pipe. These MPW is one of the most useful welding process of welding ability of the dissimilar metal in which cylindrical materials, such as pipe, tube. As the quality of a weld joint is strongly influenced by process parameters during the welding process and the success of the welding to evaluated according to the leakage pressure. Generally, the process parameters is magnetic pressure, the gap between outer pipe and inner pipe, and the ratio of thickness to diameter of pipe(D/T) in MPW. Therefore, the goal of this study was to explain the effect of parameters on the weld joint leakage pressure. For these purposes, FFD(Fractional Factorial Design) were used for the experiment. The measured data were analyzed by regression analysis and verification experiments with random condition were conducted to confirm the suggested experimental model.

• Journal of Magnetics
• /
• 제22권1호
• /
• pp.34-42
• /
• 2017

Material defects in the Steam Generator Tubes (SGT) of sodium cooled fast breeder reactor (PFBR) can lead to leakage of water into sodium. The water and sodium reaction will lead to major accidents. Therefore, the examination of steam generator tubes for the early detection of defects is an important requirement for safety and economic considerations. In this work, the Magnetic Flux Leakage (MFL) based Non Destructive Testing (NDT) technique is used to perform the defect detection process. The rectangular notch defects on the outer surface of steam generator tubes are modeled using COMSOL multiphysics 4.3a software. The obtained MFL images are de-noised to improve the integrity of flaw related information. Grey Level Co-occurrence Matrix (GLCM) features are extracted from MFL images and taken as input parameter to train the neural network. A comparative study on characterization have been carried out using feed-forward back propagation (FFBP) and cascade-forward back propagation (CFBP) algorithms. The results of both algorithms are evaluated with Mean Square Error (MSE) as a prediction performance measure. The average percentage error for length, depth and width are also computed. The result shows that the feed-forward back propagation network model performs better in characterizing the defects.

• Journal of Electrical Engineering and Technology
• /
• 제9권5호
• /
• pp.1677-1685
• /
• 2014

Major problem in the high voltage power transmission line is the flashover due to polluted ceramic insulators which leads to failure of equipments, catastrophic fires and power outages. This paper deals with the development of a better diagnostic tool to predict the flashover and pollution severity of power transmission line insulators based on the wavelet transform and fuzzy c-means clustering approach. In this work, laboratory experiments were carried out on power transmission line porcelain insulators under AC voltages at different pollution conditions and corresponding leakage current patterns were measured. Discrete wavelet transform technique is employed to extract important features of leakage current signals. Variation of leakage current magnitude and distortion ratio at different pollution levels were analyzed. Fuzzy c-means algorithm is used to cluster the extracted features of the leakage current data. Test results clearly show that the flashover and pollution severity of power transmission line insulators can be effectively realized through fuzzy clustering technique and it will be useful to carry out preventive maintenance work.

• Journal of Magnetics
• /
• 제21권4호
• /
• pp.644-651
• /
• 2016

A novel zero voltage switching (ZVS) phase shift full bridge (PSFB) converter used in geophysical exploration is proposed in this paper. To extend the ZVS ranges and increase power density of the converter, external inductor acting as leakage inductance is applied and integrated into the integrated magnetic (IM) transformer with separated secondary winding. Moreover, the loss of ZVS PSFB converter is also decreased. Besides, the analysis and accurate prediction methodology of the leakage inductance of the IM transformer are proposed, which are based on magnetic energy and Lebedev. Finally, to verify the accuracy of analysis and methodology, the experimental and finite element analysis (FEA) results of IM transformer and 40 kW converter prototypes are given.