• Nuclear Engineering and Technology
• /
• 제53권12호
• /
• pp.4042-4051
• /
• 2021

In this work, we applied a multilevel modeling technique to estimate the diametral creep in the pressure tubes of Korean Canada Deuterium Uranium (CANDU) units. Data accumulated from in-service inspections were used to develop the model. To confirm the strength of the multilevel models, a 2-level multilevel model considering the relationship between channels for a CANDU unit was compared with existing linear models. The multilevel model exhibited a very robust prediction accuracy compared to the linear models with different data pooling methods. A 3-level multilevel model, which considered individual bundles, channels, and units, was also implemented. The influence of the channel installation direction was incorporated into the three-stage multilevel model. For channels that were previously measured, the developed 3-level multilevel model exhibited a very good predictive power, and the prediction interval was very narrow. However, for channels that had never been measured before, the prediction interval widened considerably. This model can be sufficiently improved by the accumulation of more data and can be applied to other CANDU units.

• Nuclear Engineering and Technology
• /
• 제50권4호
• /
• pp.532-541
• /
• 2018

Decision support systems are a key focus of research on developing control rooms to aid operators in making reliable decisions and reducing incidents caused by human errors. For this purpose, models of complex systems can be developed to diagnose causes or consequences for specific alarms. Models applied in safety systems of complex and safety-critical systems require rigorous and reliable model building and testing. Multilevel flow modeling is a qualitative and discrete method for diagnosing faults and has previously only been validated by subjective and qualitative means. To ensure reliability during operation, this work aims to synthesize a procedure to measure model performance according to diagnostic requirements. A simple procedure is proposed for validating and evaluating the concept of multilevel flow modeling. For this purpose, expert statements, dynamic process simulations, and pilot plant experiments are used for validation of simple multilevel flow modeling models of a hydrocyclone unit for oil removal from produced water.

• 감성과학
• /
• 제19권4호
• /
• pp.95-110
• /
• 2016

본 연구의 목적은 다층자료 매개효과의 분석 방법을 제안하는 것이다. 연구내용은 다층자료 매개효과의 통계방법 탐색, 분석절차 제안, 그리고 분석의 실례 제시 등 세 가지다. 첫째, MLM (multilevel modeling)과 MSEM (multilevel structural equation modeling) 중에서 어떤 방법이 다층자료의 매개효과 분석에 유용한지 탐색하였다. MSEM은 MLM의 약점을 극복한 것으로서 유용한 다층 매개효과 분석방법이었다. 둘째, 다층자료 매개효과의 분석절차를 연구모형설정, 전제조건 검토, 모형검증, 계수검증의 4단계로 전개하였다. 셋째, 매개효과 분석의 실례에 사용된 자료는 2,695명의 초중등 학생과 88명의 학급교사로 구성되었다. 분석 실례로 2층${\rightarrow}$2층${\rightarrow}$1층과 1층${\rightarrow}$1층${\rightarrow}$2층 두 가지를 제시하였다. 2층${\rightarrow}$2층${\rightarrow}$1층과 1층${\rightarrow}$1층${\rightarrow}$2층 모형은 완전매개모형이 지지되었지만, 2층${\rightarrow}$2층${\rightarrow}$1층 모형의 매개효과 계수만 95% 신뢰구간에서 유의하였다. 분석 실례에 사용된 Mplus 프로그램은 부록에 제시하였다. 연구결과를 기초로 본 연구의 의의와 제한점, 그리고 후속연구의 방향이 논의되었다.

• Nuclear Engineering and Technology
• /
• 제50권4호
• /
• pp.553-561
• /
• 2018

To easily understand and systematically express the behaviors of the industrial systems, various system modeling techniques have been developed. Particularly, the importance of system modeling has been greatly emphasized in recent years since modern industrial systems have become larger and more complex. Multilevel flow modeling (MFM) is one of the qualitative modeling techniques, applied for the representation and reasoning of target system characteristics and phenomena. MFM can be applied to industrial systems without additional domain-specific assumptions or detailed knowledge, and qualitative reasoning regarding event causes and consequences can be conducted with high speed and fidelity. However, current MFM techniques have a limitation, i.e., the dynamic features of a target system are not considered because time-related concepts are not involved. The applicability of MFM has been restricted since time-related information is essential for the modeling of dynamic systems. Specifically, the results from the reasoning processes include relatively less information because they did not utilize time-related data. In this article, the concepts of time-to-detect and time-to-effect were adopted from the system failure model to incorporate time-related issues into MFM, and a methodology for enhancing MFM-based reasoning with time-series data was suggested.

• 대한전기학회:학술대회논문집
• /
• 대한전기학회 1992년도 하계학술대회 논문집 B
• /
• pp.1119-1122
• /
• 1992

This paper deals with a novel method of modeling and analyzing multilevel pulse width modulation(PWM) inverter/rectifier, which leads to extraction of equivalent circuit in fundamental frequency domain. By the technique, we can draw out the corresponding linear time invariant circuit even thuogh the actual circuit is switched. A static VAR compensator using five-level inverter is modeled and simulated for the verification of the modeling.

• 아동학회지
• /
• 제28권5호
• /
• pp.109-126
• /
• 2007

A sample of 322 18-month-old infants and their mothers were assessed longitudinally at 24 and 30 months. Maternal utterances and styles of linguistic interaction were measured during a 10 minute free play session. Mothers completed a vocabulary checklist for infants. Longitudinal data were analyzed by multilevel modeling. Results indicated that vocabulary increased with age of infants and the growth rate was highly predictable by the size of vocabulary at 18 months. The growth rate was strongly influenced by maternal questioning and feedback. The effect of the maternal linguistic input was constant with age. Gender differences in size of vocabulary did not vary systematically with age.

• 대한토목학회논문집
• /
• 제31권3D호
• /
• pp.469-476
• /
• 2011

본 연구는 다층모형(multilevel model)을 상수원관리지역 주민지원사업 정책평가에 활용하는데 있어 유효성 및 효과를 이해하는데 연구의 목적이 있다. 정책의 대상이 위계적인(hierarchical) 특성을 지니고 있는 경우 다층모형을 이용하여 정책평가를 하는 것이 정책의 효과를 평가하고 검증하는데 있어 적절하다. 또한 이 모형은 기존 평가결과의 재평가 등에 응용될 수 있다. 상수원관리지역의 주민지원사업을 대상으로 주민만족도와 경제적 도움정도를 정책효과변수로 하여 다층모형을 적용 하였다. 그 결과 정책효과변수에 기존 평가결과 및 중요한 사업으로 여겨지던 소득증대사업 등이 직접적인 영향을 미치지 못함을 통계적으로 확인할 수 있었다. 본 연구는 다음과 같은 세 가지의 정책적 함의를 지닌다. 첫째, 정책 및 사업평가에 있어 정책의 효과를 엄밀히 파악하기 위하여 위계적 구조를 고려할 수 있는 다층모형을 이용하여야 한다. 둘째, 기관평가의 순위 도출에 있어 다층모형을 이용하여 지표에 의한 성과지표와 보완적으로 이용해야 한다. 셋째, 위계적 구조의 하나로서 공간적 위계를 고려하여 정책평가를 시행하여야 한다.

• 전력전자학회:학술대회논문집
• /
• 전력전자학회 2002년도 전력전자학술대회 논문집
• /
• pp.618-621
• /
• 2002

This paper proposes a static vu compensator using hybrid cascade 5-level PWM inverter, Circuit DQ transformation is used for modeling and analysis of the system, and it reveals the important characteristics and related equations of the system. Also, a multilevel PWM technique suitable to hybrid structure Is proposed for less harmonics in the input currents of the system. Finally, the validity of tile characteristics analysis is shown through PSIM simulations.

• Nuclear Engineering and Technology
• /
• 제50권4호
• /
• pp.542-552
• /
• 2018

Operators face challenges to plan alternative countermeasures when no procedure exists to address the current plant state. A model-based approach is desired to aid operators in acquiring plant resources and deriving response plans. Multilevel flow modeling (MFM) is a functional modeling methodology that can represent intentional knowledge about systems, which is essential in response planning. This article investigates the capabilities of MFM to plan alternatives. It is concluded that MFM has a knowledge capability to represent alternative means that are designed for given ends and a reasoning capability to identify alternative functions that can causally influence the goal achievement. The second capability can be applied to find originally unassociated means to achieve a goal. This is vital in a situation where all designed means have failed. A technique of procedure synthesis can be used to express identified alternatives as a series of operations. A case of station blackout occurring at the boiling water reactor is described. An MFM model of a boiling water reactor is built according to the analysis of goals and functions. The accident situations are defined by the model, and several alternative countermeasures in terms of operating procedures are generated to achieve the goal of core cooling.

• Journal of Power Electronics
• /
• 제14권6호
• /
• pp.1130-1138
• /
• 2014

This study analyzes a ladder multilevel converter (double ladder topology) with the use of a new averaging modeling technique. This technique introduces an analytical method to compute for the switching losses and is used to conduct an in-depth analysis of the influence of the switching frequency and parasitic resistance of components on converter efficiency. The obtained results enable the selection of switches and switching frequency to minimize losses. Moreover, simulation results and experimental measurements validate the analytical calculations.