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노광우(Kwangwoo No),황세윤(Seyun Hwang),이권영(Kwonyeong Lee) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12
Orifice is a device to generate pressure drop when the fluid passes through the narrow channel. In a kind of steam generator, helical coils are used as a heat transfer tubes. In this system, there will be a pressure deviation among helical coils. It will be difficult to generate high quality steam with this kind of unstable system with high deviation of pressure differences. To minimize the deviation, a multi-stage orifice with high pressure drop is suggested, and the characteristics of multi-stage orifice are investigated in this study. We performed not only single-phase flow pressure drop experiments with water, but also two-phase flow experiments with nitrogen/water for the multi-stage orifice. Also, the experimental data are compared with previous empirical correlations. Also, we study flow patterns about bubbly and slug in horizontal tube through visualizing the orifice.
비정상 신호를 가진 연료 펌프의 상태 진단에서 Conv1D 모델의 시간 간격 별 예측 정확성 비교
김형진(Hyungjin Kim),황세윤(Seyun Hwang),김교순(Gyosoon Kim),김경미(Kyungmi Kim),이장현(Jang Hyun Lee) (사)한국CDE학회 2022 한국CDE학회 논문집 Vol.27 No.4
This study deals with the condition detection of centrifugal pump supplying liquid to marine engines. The purpose is to detect the anomaly and the failure modes of the pump by applying the vibration signals from the simulated failures on the experimental bed. Since the pump rarely experiences faults as well as used to degradation experiments, the vibration signal was gathered from an experimental bed simulating the bearings and lubricant failures. Considering the non-stationarity of variable speed, the convolution is applied to extract the feature of time series rather than the frequency feature. The advantage of CNN implicitly extracting features from a non-stationary signal is used to extract the features applied to Conv1D. After learning the features, a multi-layer perceptron (MLP) was connected to failure classification to identify the operation state. Finally, it is suggested that the time series-based feature extraction can be applied to the condition monitoring of a centrifugal pump with variable speed and non-stationarity.
베어링 간극에 따른 회전기계의 위험 회전속도 회피를 위한 주파수 분석
홍규택(KyuTack Hong),황세윤(Seyun Hwang),이장현(JangHyun Lee) (사)한국CDE학회 2017 한국CDE학회 논문집 Vol.22 No.4
This study is concerned with the abnormality monitoring of the rotor unbalance that is one of the most common causes of severe vibration of rotating machinery. This study analyze the relationship between the eccentricity and vibration characteristics for the purpose of abnormal monitoring of rotating machinery with unbalance rotor. Based on the Jeffcott rotor model, the rubbing of a rotating system composed of a rotor and a bearing was formulated to predict the displacement of the rotor in terms of the eccentricity of the rotor, the clearance between the bearing and the rotor, and the rotational speed. The coupled differential equations of Jeffcott rotor is used to analyze the nonlinear dynamic behavior of rotor caused by rub-forces between rotor and bearing. The mathematical model including the eccentricity of the rotor, the clearance between the bearing and the rotor, and the rotational speed is used to derive the motion of rotor in time domain. The motion of the rotor is analyzed both in the frequency domain and the timefrequency domain using Fast Fourier Transform and Hilbert-Huang Transform, respectively, to predict the critical speed.
확률밀도함수(PDF)를 이용한 함정 피격성 분석 기법 연구
김광식(KwangSik Kim),이장현(JangHyun Lee),황세윤(SeYun Hwang),반일환(IlHwan Ban) (사)한국CDE학회 2014 한국 CAD/CAM 학회 학술발표회 논문집 Vol.2014 No.2
The survivability of the warship is defined as the capability of a warship to avoid or withstand a man-made hostile environment. The survivability of the warship consists of three categories (Susceptibility, Vulnerability and Recoverability). A warship performance in susceptibility terms is measured by the probability of detection, and probability of hit. So, the level of susceptibility of a warship in encounter with threat is dependent upon attributes for detection equipment and weapon system. This paper has described the theoretical procedure for the susceptibility assessment. And, the theoretical background which is suggested to assess the susceptibility of a warship is based on the simplified probabilistic theory. The main emphasis of this paper would be on simplified calculation model based on the probability density function for probability of hit. It implements assessment of the probability of hit given a both singlehit and multiple-hit. The susceptibility is accessed for a RCS (Radar Cross Section) and the hit probability for a rectangular target is applied for a given threat.
선박해양 시스템의 확률론적 위험도 평가 기법에 관한 연구
김광식(KwangSik KIM),이장현(JangSyun LEE),Burak Ozturk,황세윤(SeYun HWANG) (사)한국CDE학회 2013 한국 CAD/CAM 학회 학술발표회 논문집 Vol.2013 No.1
해양에서 선박해양 구조물의 사고(Accident)는 예기치 못한 상황에서 작업자의 오류 또는 장비의 고장, 외부의 환경적 영향에 의해 일어난다. 이러한 사고를 예방하기 위해서는 사고 후 나타나는 증상에 대하여 해결책을 제시하는 것보다 근본적으로 내재되어 있는 발생 가능한 문제를 제시하고 이를 해결할 수 있는 방법론을 정립해야 한다. 또한 최근의 고부가가치 선박해양 구조물의 경우 복잡하고 다양한 시스템의 탑재로 인해 단순한 내부 부품의 고장으로 해당 구성품 또는 시스템에 막대한 여파를 미치게 될 수 있다. 따라서 이러한 위험(Risk)을 사고 발생 이전에 미리 예측하고 이에 대한 대책을 세우기 위해 위험도(Risk Assessment)평가 기법이 필요하게 된다. 본 연구에서는 기존의 위험도 평가기법에 확률론적인 방법론을 추가하여 각 시스템을 구성하는 구성품들에 대한 확률론적(Probabilistic) 위험도 평가 기법에 대하여 정의하고, 이를 통해 잠재된 위협을 예측(Risk Prediction)하고 예방하기 위한 방법론을 제시하고자 한다.