• 한국군사과학기술학회지
• /
• 제14권5호
• /
• pp.859-870
• /
• 2011

The purpose of this paper is to develop reliability analysis procedures for repairable systems with interval failure time data and apply the procedures for assessing the storage reliability of a subsystem of a certain type of guided missile. In the procedures, the interval failure time data are converted to pseudo failure times using the uniform random generation method, mid-point method or equispaced intervals method. Then, such analytic trend tests as Laplace, Lewis-Robinson, Pair-wise Comparison Nonparametric tests are used to determine whether the failure process follows a renewal or non-renewal process. Monte Carlo simulation experiments are conducted to compare the three conversion methods in terms of the statistical performance for each trend test when the underlying process is homogeneous Poisson, renewal, or non-homogeneous Poisson. The simulation results show that the uniform random generation method is best among the three. These results are applied to actual field data collected for a subsystem of a certain type of guided missile to identify its failure process and to estimate its mean time to failure and annual mean repair cost.

• 한국기계가공학회지
• /
• 제12권4호
• /
• pp.22-28
• /
• 2013

It is important to begin left ventricular assist device (LVAD) treatment at appropriate time for heart failure patients who expect cardiac recovery after the therapy. In order to predict the optimal timing of LVAD implantation, we predicted pumping efficacy of LVAD according to the severity of heart failure theoretically. We used LVAD-implanted cardiovascular system model which consist of 8 Windkessel compartments for the simulation study. The time-varying compliance theory was used to simulate ventricular pumping function in the model. The ventricular systolic dysfunction was implemented by increasing the end-systolic ventricular compliance. Using the mathematical model, we predicted cardiac responses such as left ventricular peak pressure, cardiac output, ejection fraction, and stroke work according to the severity of ventricular systolic dysfunction under the treatments of continuous and pulsatile LVAD. Left ventricular peak pressure, which indicates the ventricular loading condition, decreased maximally at the 1st level heart-failure under pulsatile LVAD therapy and 2nd level heart-failure under continuous LVAD therapy. We conclude that optimal timing for pulsatile LVAD treatment is 1st level heart-failure and for continuous LVAD treatment is 2nd level heart-failure when considering LVAD treatment as "bridge to recovery".

• Structural Engineering and Mechanics
• /
• 제86권6호
• /
• pp.779-791
• /
• 2023

Long-termly used in water supply, an underground concrete pipe is easily subjected to the coupled action of pressure loading and flowing water, which can cause the chemo-mechanical damage of the pipe, resulting in its premature failure and lifetime reduction. Based on the leaching characteristics and damage mechanism of concrete pipe, this paper proposes a coupled chemo-mechanical damage and failure model of underground concrete pipe for water supply, including a calcium leaching model, mechanical damage equation and a failure criterion. By using the model, a numerical simulation is performed to analyze the failure process of underground concrete pipe, such as the time-varying calcium concentration in concrete, the thickness variation of pipe wall, the evolution of chemo-mechanical damage, the distribution of concrete stress on the pipe and the lifetime of the pipe. Results show that, the failure of the pipe is a coupled chemo-mechanical damage process companied with calcium leaching. During its damage and failure, the concentrations of calcium phase in concrete decrease obviously with the time, and it can cause an increase in the chemo-mechanical damage of the pipe, while the leaching and abrasion induced by flowing water can lead to the boundary movement and wall thickness reduction of the pipe, and it results in the stress redistribution on the pipe section, a premature failure and lifetime reduction of the pipe.

• 산업공학
• /
• 제15권1호
• /
• pp.89-98
• /
• 2002

This paper considers the optimum replacement times of a steam generator in nuclear power plant with failure data. It is assumed that the failure pattern of units is given as a Weibull distribution and repair and periodic preventive maintenance are performed periodically. The maximum likelihood method is used to estimated the Weibull parameters of failure distribution from failure data. Relpacement, output-decresing and maintenance costs are considered to determine the optimal replacement times by simulation. Numerical examples are included with actual failure data and cost estimators.

• 한국시뮬레이션학회논문지
• /
• 제14권1호
• /
• pp.1-8
• /
• 2005

In the semiconductor manufacturing, yield enhancement is an urgent issue. It is ideal to prevent all the failures. However, when a failure occurs, it is important to quickly specify the cause stage and take countermeasure. Reviewing wafer level and composite lot level yield patterns has always been an effective way of identifying yield inhibitors and driving process improvement. This process is very time consuming and as such generally occurs only when the overall yield of a device has dropped significantly enough to warrant investigation. The automatic method of failure pattern extraction from fail bit map provides reduced time to analysis and facilitates yield enhancement. The automatic method of failure pattern extraction from fail bit map provides reduced time to analysis and facilitates yield enhancement. This paper describes the techniques to automatically classifies a failure pattern using a fail bit map.

• 대한기계학회:학술대회논문집
• /
• 대한기계학회 2004년도 춘계학술대회
• /
• pp.508-512
• /
• 2004

An aerospace vehicle in flight can be exposed to random gust which may cause critical structural failure. In this paper, the failure analysis is conducted for composite wing subjected to random gust. For this, the profile of random gust is idealized as a stationary Gaussian random process and the power spectral density (PSD) of wing bending moment induced by gust is obtained. The PSD function is converted to probabilistic distributions and the failure probability during total flight time is calculated by Monte Carlo simulation.

• 한국시뮬레이션학회논문지
• /
• 제8권3호
• /
• pp.49-66
• /
• 1999

Semiconductor wafer fabrication is known to be one of the most complex manufacturing processes due to process intricacy, random yields, product diversity, and rapid changing technologies. In this study we are concerned with the impact of lot release and dispatching policies on the performance of semiconductor wafer fabrication facilities. We consider several semiconductor wafer fabrication environments according to the machine failure types such as no failure, normal MTBF, bottleneck with low MTBF, high randomness, and high MTBF cases. Lot release rules to be considered are Deterministic, Poisson process, WR(Workload Regulation), SA(Starvation Avoidance), and Multi-SA. These rules are combined with several dispatching rules such as FIFO (First In First Out), SRPT (Shortest Remaining Processing Time), and NING/M(smallest Number In Next Queue per Machine). We applied the combined policies to each of semiconductor wafer fabrication environments. These policies are assessed in terms of throughput and flow time. Basically Weins fabrication setup was used to make the simulation models. The simulation parameters were obtained through the preliminary simulation experiments. The key results throughout the simulation experiments is that Multi-SA and SA are the most robust rules, which give mostly good performance for any wafer fabrication environments when used with any dispatching rules. The more important result is that for each of wafer fabrication environments there exist the best and worst choices of lot release and dispatching policies. For example, the Poisson release rule results in the least throughput and largest flow time without regard to failure types and dispatching rules.

• 터널과지하공간
• /
• 제12권3호
• /
• pp.189-197
• /
• 2002

최근 들어 확률론적 해석 방법이 암반사면공학에서 많이 사용되고 있으며 이는 불연속면과 암반의 지질학적 및 지반공학적 특성에 불확실성이 포함되며 이러한 불확실성에 의해 해석결과에 영향을 미치고 있기 때문이다. 암반사면의 안정성 해석에서 주로 사용되고 있는 전통적인 결정론적인 해석에서는 이러한 불확실성을 해석에 고려하기 어려운 반면 확률론적 해석에서는 불확실성을 수량화하여 해석에 고려할 수 있다는 장점을 가지고 있다. 이러한 확률론적 해석방법으로는 몬테카를로 방법이 주로 사용되고 있으나 방법은 파괴확률을 획득하기 위하여 많은 반복된 계산이 요구되며 따라서 많은 시간과 노력이 필요하다는 단점을 가지고 이다. 반면 본 연구에서 제안된 점추정법은 확률변수의 통계적 파라미터, 즉, 평균과 표준편차만을 이용하여 단순한 계산을 통해 파괴확률을 구할 수 있는 장점을 가지고 있다. 따라서 본 연구에서는 점추정법을 이용하여 평면파괴의 파괴확률을 산정하였으며 이를 몬테카를로 방법과 비교해 보았다.

• 한국지진공학회:학술대회논문집
• /
• 한국지진공학회 2002년도 추계 학술발표회 논문집
• /
• pp.300-307
• /
• 2002

Bridge foundation failure considering the effect of local scour around pier foundations under hi-directional seismic excitations is examined in probabilistic perspectives. The seismic responses of bridges with deep foundations are evaluated with a simplified mechanical model, which can consider the local scour effect around the deep foundation in addition to many other components. The probabilistic characteristics of local scour depths are estimated by using the Monte Carlo simulation. The probabilistic characteristics of basic random variables used in the Monte Carlo simulation are determined from the actual hydraulic data collected in middle size streams in Korea. The failure condition of deep foundation is assumed as bearing capacity failure of the ground below the foundation base. The probability of foundation failure of a simply supported bridge with various scour conditions and hi-directional seismic excitations are examined. It is found that the local scour and the recovery duration are critical factors in evaluating the probability of foundation failure. Moreover, the probability of foundation failure under hi-directional seismic excitations is much higher than under uni-directional seismic excitations. Therefore, it is reasonable to consider hi-directional seismic excitations in evaluating the seismic safety of bridge systems scoured by a flood.

• 한국시뮬레이션학회논문지
• /
• 제13권2호
• /
• pp.65-73
• /
• 2004

The capability to provide the network service must survive even if a significant network system element is disrupted. To sustain the network service under the system failure, network survivability mechanisms minimizing the impact of failures are needed. Also, since the mobile network has its unique characteristic, the survivability scheme for the vulnerability of the mobile network is required. This paper proposes a survivability scheme to support the reliable service of the wireless access point level (BS-base station system). By the survivability scheme, the mobile network can use an overlap BS of the cellular network architecture after a BS system failure. We analyze the performance of the proposed scheme using Markov model. Also, a computer simulation is used for the scheme analysis. The proposed scheme shows that the service of the mobile network can be provided under the BS system failure.