과설계가 타이탄 로켓엔진의 신뢰도 및 개발비용에 미치는 영향

김경미(Kyungmee O. Kim),황준우(Junwoo Hwang) 한국항공우주학회 2015 韓國航空宇宙學會誌 Vol.43 No.4

로켓 엔진을 설계추력보다 낮은 추력으로 운용하면 신뢰도가 증가하는 것으로 알려져 있다. 따라서 엔진을 디레이팅하여 증가하는 신뢰도가 엔진을 과설계하기 위해 증가된 개발비를 상쇄할 수 있다면 개발비를 최소화하기 위해 엔진의 과설계를 고려할 수 있다. 본 연구의 목적은 엔진 과설계와 디레이팅이 신뢰도 및 비용에 미치는 영향을 설명하는 모형을 개발하고자 하는 것이다. 타이탄 로켓 엔진의 운용추력수준 및 연소시험횟수에 따른 신뢰도 자료에 로지스틱 회귀모형을 적합하여 신뢰도 성장을 모형화하고 Transcost 비용모형을 이용하여 엔진을 10% 과설계 하면 신뢰도 요구값에 따라 엔진 개발비를 9%에서 23% 감소시킬 수 있음을 보였다. 또한 이러한 엔진 개발비의 감소는 엔진이 사용하는 연료에 따라 달라짐을 지적하였다. Engine derating is often considered for reliability benefits because lower power operation reduces its failure probability. To be derated during operation, however, the engine must be initially overdesigned. The engine overdesign is cost effective only if reliability increased from derating is enough to offset the initial increase in the development cost caused from the overdesign. The purpose of this paper is to provide an analytical model to consider a trade-off between the engine overdesign and derating. We use a logistic regression model to explain reliability growth in the number of hot firing tests for a fixed power level. Using the Transcost model with the reliability growth model, we show that 10% overdesign of Titan rocket engine decreases its development cost by about 9% and 23% depending on the reliability requirement. We also point out that such a cost reduction depends on the fuel type a rocket uses.

순열검정을 이용한 품질의 집의 일관성 검정

김경미(Kyungmee O. Kim) 대한산업공학회 2008 대한산업공학회지 Vol.34 No.1

The house of quality (HOQ) involves subjective and ambiguous information typically through a likert scale. It is important to validate consistency of such input in the HOQ before rating the final importance of technical equirements. Previously, a methodology was developed to test the consistency of relationship strengths in the HOQ between roof matrix and relationship matrix. We described disadvantages of the previous method and propose a new approach based on the permutation test. Advantages of the proposed method are illustrated with an example.

비 직렬 시스템의 신뢰도 최적화를 위한 시스템 번인

김경미(Kyungmee O. Kim) 대한산업공학회 2007 대한산업공학회지 Vol.33 No.2

The decision of how long performing system burn-in must be answered with a probabilistic model of a system lifetime at which infant mortality failures created during assembly processes are quantified. In this paper, we propose such a model which is modified from previous results. Using the system model, we derived system reliability in terms of component and system burn-in times for the two cases of minimal repair at system failure and of component replacement and connection repair at their failure times. The procedure is illustrated with a bridge system and the optimal system burn-in times are obtained for maximizing system reliability. The result suggests that an assumption of minimal repair at system failure may underestimate the optimal burn-in time in practice.

추진제 및 연소 사이클을 고려한 액체로켓 엔진의 신뢰도 예측

김경미(Kyungmee O. Kim) 한국항공우주학회 2016 韓國航空宇宙學會誌 Vol.44 No.2

액체로켓 엔진의 신뢰도는 설계 추력, 추진제, 연소 사이클, 및 연소시험 시간의 영향을 받는다. 기존 연구에 따르면 신규 개발하는 엔진과 같은 추진제 및 연소 사이클을 가지는 참조 엔진들의 연소시험 자료가 알려져 있다면 참조 엔진들의 설계 추력과 연소시험 시간을 보정하여 신규 엔진의 신뢰도를 예측할 수 있다. 본 연구에서는 신규 개발하는 엔진과 같은 추진제 및 연소 사이클을 가지는 참조 엔진의 자료가 존재하지 않은 경우를 고려하여 두 엔진 사이의 유사성 분석을 통하여 고장률을 보정한 후 신뢰도를 예측하는 방법을 제시하였다. 또한 액체산소/케로신 추진제와 가스 발생기 사이클을 사용하는 한국형 발사체의 1단 엔진을 이용하여 제안된 방법을 예시하였다. It is known that reliability of liquid rocket engines depends on the design thrust, propellant, engine cycle, and hot firing test time. Previously, a method was developed for estimating reliability of a new engine by adjusting the design thrust and hot firing test time of reference engines where reference engines have the same propellant and engine cycle with the new engine. In this paper, we provide a procedure to predict the engine reliability when the new engine and the reference engine have different propellant and engine cycles. The proposed method is illustrated to estimate the engine reliability of the first stage of Korea Space Launch Vehicle II.

액체로켓엔진의 신뢰도 및 개발비용 추정 방법

김경미(Kyungmee O. Kim),황준우(Junwoo Hwang) 한국항공우주학회 2014 韓國航空宇宙學會誌 Vol.42 No.5

엔진은 로켓의 임무성공에 가장 중요한 부품이다. 본 연구에서는 신규 개발하는 액체로켓 엔진의 신뢰도 및 개발비용을 추정하는 방법을 제시한다. 신뢰도에 영향을 미치는 요인들 중 모형화가 어려운 인자들을 고려하여 베이스라인 엔진을 선택하고 신뢰도에 미치는 영향을 양적으로 파악할 수 있는 인자들을 반영하여 베이스라인 엔진의 신뢰도를 수정하였다. 또한 엔진개발비용을 건조 질량과 연소시험횟수로 나타낸 Transcost 엔진 개발비용 모형을 신규 개발하는 엔진의 요구추력과 신뢰도의 함수로 표현하였다. 마지막으로 액체산소와 액체수소를 추진제로 사용하는 다단연소 사이클 엔진에 대해 제안된 방법을 예시하였다. Engine is one of the most important parts in a rocket for completing its mission successfully. In this paper, we provide a methodology for estimating reliability and development cost of a liquid rocket engine newly developed. To estimate reliability, a baseline engine is selected considering factors whose effects on reliability are unquantifiable. Then reliability of a baseline engine is adjusted to reflect the effect of factors that can be modeled quantitatively. Using the previous Transcost engine cost expressed in terms of mass and the number of hot firing tests, the engine development cost is reexpressed in reliability and thrust requirements. Finally, a numerical example is given to illustrate the application of the methodology to a turbopump rocket engine using staged combustion cycle with LOX/LH2 propellant.

Risk Assessment in the Failure Mode, Effect and Criticality Analysis(FMECA)

Kyungmee O. Kim(김경미),Ming J. Zuo 대한산업공학회 2014 대한산업공학회 춘계학술대회논문집 Vol.2014 No.5

Risk Assessment in the Failure Mode, Effect and Criticality Analysis(FMECA)

Kyungmee O. Kim(김경미),Ming J. Zuo 한국경영과학회 2014 한국경영과학회 학술대회논문집 Vol.2014 No.5

가속수명모형을 이용한 부하분담시스템의 신뢰성 설계

김경미(Kyungmee O. Kim) 한국신뢰성학회 2021 신뢰성응용연구 Vol.21 No.4

Purpose: A reliability model is presented that can be used to predict the reliability of a load sharing system in the development stage. Methods: Previous research has focused on estimating the reliability of a given load sharing system during operation, under the assumption that the design load of each component is fixed in advance. Then, an accelerated life model is incorporated to consider the effect of the increased workload on the component reliability after taking the reliability of a component operating at the lowest workload as the baseline. In this case, the baseline reliability changes if the number of components in the system changes. We modify the previous model to differentiate the design load from the workload of each component as well as take the reliability of a component operating at the design load as the baseline. Results: The proposed model is effective in determining the number of components for maximizing system reliability. Conclusion: The number of components in a load sharing system must be determined depending on the reliability decrease resulting from developing large components, and the reliability increase achieved from operating large components at a load lower than the design load.

영어 협동 수업이 초등학생의 정의적 영역에 미치는 영향과 효율적인 협동 수업의 방향

김경미(Kim Kyungme),이충현(Lee Chung-Hyun) 한국초등영어교육학회 2005 초등영어교육 Vol.11 No.2

The purposes of this study are to investigate the effects of team teaching with native speakers of English on elementary school students' affective domains and to suggest directions for effective team teaching models or EPIK(English Program in Korea). Quantitative and qualitative research methods were adopted. That is, questionnaire, interview and classroom observations were used to collect the data required for this study. The subjects consisted of 443 students who were working at J Elementary School in Kyunggi-do in Korea. The results of the study showed that: 1) Team teaching with a native speaker of English generally has a positive effect on the development of students' four language skills and understanding non-verbal communication and the target culture regardless of grade, gender or level 2) Team teaching generally has a positive effect on students' affective domains in English learning; 3) 5th graders are generally more positive towards affective domains than 6th graders; 4) The higher level students in each grade are more positive towards affective domains than the lower level students; and 5) The students want to have more team teaching lessons regardless of grade, gender or level. Finally, based on the findings, some suggestions were made for directions for team teaching models or EPIK(English Program in Korea).

하중변화에 따른 리던던트 시스템의 신뢰도 비교

김찬용(Chan Yong Kim),김경미(Kyungmee O.Kim) 대한기계학회 2019 대한기계학회 춘추학술대회 Vol.2019 No.2