• 한국경영과학회:학술대회논문집
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• 한국경영과학회 2003년도 추계학술대회 및 정기총회
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• pp.187-190
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• 2003

Since the early 1980s, the concept of relationship management in marketing area has gained its importance. Acquiring and retaining the most profitable customers are serious concerns of a company to perform more targeted marketing campaigns. For effective CRM (Customer Relationship Management), it is important to gather information on customer value. Many researches have been performed to calculate customer value based on CLV (Customer Lifetime Value). It, however, has some limitations. It is difficult to consider the churn of customers, because the previous prediction models have focused mainly on expected future cash flow derived from customers'past profit contribution. In this paper we suggest a CLV model considering past profit contribution, potential benefit, and churn probability of a customer. We also cover a framework for analyzing customer value and segmenting customers based on their value. Customer value is classified into three categories: current value, potential value and customer loyalty. Customers are segmented according to the three categories of customer value. A case study on calculating customer value of a wireless communication company will be illustrated.

• 한국지능시스템학회논문지
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• 제26권5호
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• pp.343-350
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• 2016

Remaining lifetime prediction of the underground gas pipeline plays a key role in maintenance planning and public safety. One of main causes in the pipeline failure is metal corrosion. This paper deals with estimating the pipeline reliability in the presence of corrosion defects. Because a pipeline has uncertainty and variability in its operation, probabilistic approximation approaches such as first order second moment (FOSM), first order reliability method (FORM), second order reliability method (SORM), and Monte Carlo simulation (MCS) are widely employed for pipeline reliability predictions. This paper presents a fuzzy inference based reliability method (FIRM). Compared with existing methods, a distinction of our method is to incorporate a fuzzy inference into quantifying degrees of variability in corrosion defects. As metal corrosion depends on the service environment, this feature makes it easier to obtain practical predictions. Numerical experiments are conducted by using a field dataset. The result indicates that the proposed method works well and, in particular, it provides more advisory estimations of the remaining lifetime of the gas pipeline.

• International Journal of Automotive Technology
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• 제2권1호
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• pp.9-16
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• 2001

The lifetime of power train components can be improved dramatically by finding crack initiation points with suitable software tools and optimization of the critical areas. With increasing capacities of computers the prediction of the lifetime for components by numerical methods gets more and more important. This paper discusses some applications of the outstanding fatigue simulation program FEMFAT supporting the assessment of uniaxially and multiaxially loaded components (as well as welding seams and spot joints). The theory applied in FEMFAT differs in some aspects from classical approaches like the nominal stress concept or the local one and can be characterized by the term "influence parameter method". The specimen S/N-curve is locally modified by different influence parameters as stress-gradient to take into account notch effects, mean-stress influence which is quantified by means of a Haigh-diagram, surface roughness and treatments, temperature, technological size, etc. It is possible to consider plastic deformations resulting in mean-stress rearrangements. The dynamic loading of power train components is very often multiaxial, e.g. the stress state at each time is not proportional to one single stress state. Hence, the directions of the principal axes vary with time. We will present the way how such complex load situations can be handled with FEMFAT by the examples of a crank case and a gear box.

• Nuclear Engineering and Technology
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• 제50권1호
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• pp.107-115
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• 2018

To ensure the structural integrity of nuclear power plants, it is essential to predict the lifetime of Alloy 182 weld, which is used for welding in nuclear reactors. The lifetime of Alloy 182 weld is directly related to the crack initiation time. Owing to the large time scatter in most crack initiation tests, a probabilistic model, such as the Weibull distribution, has mainly been adopted for prediction. However, since statistically more advanced methods than current typical methods may be applied, we suggest a statistical procedure for parameter estimation of the crack initiation time of Alloy 182 weld, considering right-censored data and the covariate effect. Furthermore, we suggest a procedure for uncertainty evaluation of the estimators based on the bootstrap method. The suggested statistical procedure can be applied not only to Alloy 182 weld but also to any material degradation data set including right-censored data with covariate effect.

• 한국안전학회지
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• 제29권1호
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• pp.7-14
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• 2014

Inverter module, which feeds the converted power to the traction motor for EMU. Consists of the power semiconductors with their gate drive unit(GDU)s and the control computer for driving, voltage, current and speed controls. Electrolytic condenser, connected to the gate drive unit and a core component to drive the power semiconductor, has problems such as reduction in lifetime and malfunction caused by electrical and mechanical characteristic changes from heat generation during high speed switching for generation of stable power. In this study, To check the service life of electrolytic condenser, the test was carried out in two ways. First, In the case of accelerated life testing of condenser, the Arrhenius model is a way of life testing. Another way is to analyze the reliability of the failure data by the method of parametric data analysis. Eventually, life time by accelerated life test than a method of failure data analysis(Weibull distribution) was found to be slightly larger output.

• 대한기계학회논문집A
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• 제38권11호
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• pp.1221-1229
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• 2014

본 논문은 가속시험법을 이용하여 추진축의 피로 수명을 예측하는 것이다. 가속시험방법으로는 교정가속시험법을 적용하였으며, 이 시험법은 시험시료 수량이 적을 경우에 시험시간 단축과 신뢰성을 높이는 매우 효과적인 방법이다. 두 수준의 고부하 스트레스 수준에서 피로시험을 수행하고, 외삽법과 가용한 시험시간을 고려하여 저부하 스트레스 시험 수준을 결정하여 피로시험을 수행하였다. 본 논문에서는 가속지수와 형상모수 등의 신뢰성 파라미터를 시험을 수행하여 획득하였고, 실제 사용 환경의 로드 스펙트럼을 분석하고 시험 결과와 비교하여 추진축의 수명을 예측할 수 있었다.

• 한국안전학회지
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• 제18권1호
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• pp.108-115
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• 2003

교량은 강도설계법이나 허용응력 설계 법에 의해, 두 가지 단계에서 평가된다. 낮은 단계를 Inventory 높은 단계를 Operating이라 부른다. 교량을 효과적으로 유지관리 보수하기 위하여, 교량의 실제하중수용 능력을 평가하고 시스템 신뢰성으로부터 교량의 잔여 수명을 예측하는 것은 매우 시급하다. 생애함수가 시간 의존적 파괴확률을 예측하기 위하여 소개되고 설명된다. 이 논문에서 연구되는 교량은30년 전 농촌지역에 시공되었다. 이 교량에 대하여 하중시험과 보강이 이루어졌다. 시간 의존적 파괴확률이 보수보강 된 경우와 그렇지 않은 경우 대하여 예측되었다. 또 다른 연구로서 새로운 보수보강이 제시되고 이 보수보강에 대하여 내하력이 평가되었고 시간 의존적 파괴확률이 예측되었다. 유지관리 가격과 확장된 교량의 생애를 기본으로, 최적의 보수보강 기법이 제시되었다.

• 한국정밀공학회지
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• 제33권10호
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• pp.829-835
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• 2016

Electro-Mechanical Actuator installed on the aircraft plays a key role in an aircraft's flight control through flight control computer. Reliable prediction of the actuator is important for the aircraft. To estimate the lifetime of a product, it is necessary to test full target life. However, it is very difficult to perform it due to the long life time of actuator but short period of development time with increasing cost. Therefore, accelerated life test has been used to reduce the test time for various reasons such as reducing product's development cycle and cost. In this paper, to predict the lifetime of the actuator, we analyzed the flight profile of aircraft and adapted the method of accelerated life test in order to accelerate failure modes that might occur under user conditions. We also set up an endurance test equipment for validating the demanded lifetime of an actuator and performed accelerated life test.

• 산업경영시스템학회지
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• 제38권4호
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• pp.142-148
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• 2015

Due to advancements in technology and manufacturing capability, it is not uncommon that life tests yield no or few failures at low stress levels. In these situations it is difficult to analyse lifetime data and make meaningful inferences about product or system reliability. For some products or systems whose performance characteristics degrade over time, a failure is said to have occurred when a performance characteristic crosses a critical threshold. The measurements of the degradation characteristic contain much useful and credible information about product or system reliability. Degradation measurements of the performance characteristics of an unfailed unit at different times can directly relate reliability measures to physical characteristics. Reliability prediction based on physical performance measures can be an efficient and alternative method to estimate for some highly reliable parts or systems. If the degradation process and the distance between the last measurement and a specified threshold can be established, the remaining useful life is predicted in advance. In turn, this prediction leads to just in time maintenance decision to protect systems. In this paper, we describe techniques for mapping product or system which has degrading performance parameter to the associated classical reliability measures in the performance domain. This paper described a general modeling and analysis procedure for reliability prediction based on one dominant degradation performance characteristic considering pseudo degradation performance life trend model. This pseudo degradation trend model is based on probability modeling of a failure mechanism degradation trend and comparison of a projected distribution to pre-defined critical soft failure point in time or cycle.

• 분석과학
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• 제21권2호
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• pp.148-157
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• 2008

$1,000^{\circ}C$ 이상의 고온에서 수천~수만 rpm으로 작동하는 가스터빈 부품의 수명을 예측하기 위하여 크립파단 실험으로 얻어진 Larson-Miller 크립곡선을 활용하고 있다. 이 방법은 고온에서 시편에 하중을 주어 파단수명을 구하여 크립 파단수명을 온도와 하중의 함수로 나타낸 실험결과 곡선이다. 파손적 실험으로서 오차가 수십배를 상회하여 수명예측이 정확하지 않다. 반면에 본 연구에서는 비 파손적일 뿐 아니라 더 정확한 수명예측이 가능한 방법을 소개하고자 한다. 즉, $1,280^{\circ}C$에서 22,000시간(6,000 기동) 사용되어 폐기된 보령 가스터빈 제1단 단결정 블레이드(버켓)에 국부적으로 polishing한 후, 부식시킨 다음 replica를 떤다. 이 replica에 붙은 석출물들은 TEM과 SEM 사진으로 구하여 디지털 이미지하여 크기가 측정된다. 블레이드가 사용 전에 $0.45{\mu}m$ 크기에서 사용 후, $0.6{\mu}m$로 성장하였으나, 추가적으로 약 만여 시간 더 사용할 수 있으며 열처리를 추가하면 이만여 시간 더 사용할 수 있음을 알 수 있었다.