• Journal of the Korean Operations Research and Management Science Society
• /
• v.16 no.2
• /
• pp.164-176
• /
• 1991

This paper considers the model of a k-out-of-n :G system with non-identical components which are subject to both forced and planned outages. For the forced outages, it assumes that there are the independent and common-cause outage events causing component failures. Then, the objective is to derive the upper and lower bounds on the mean operating time between system failures in the ample-server model. In addtion, the mean system failure times are also considered.

• Journal of the Korean Data and Information Science Society
• /
• v.14 no.3
• /
• pp.553-559
• /
• 2003

The reliability modeling of distributed systems requires a good understanding the reliability of the components. For thousands of web users, competitiveness in web services means a successful presence on the web. Mean time between failures of a web site on SOAP12/HTTP is considered, where SOAP12 is a protocol intended for exchanging structured information in a decentralized, distrbuted environment. Data were collected from statlab.cam.ac.uk/webstat/stat.html via the internet.

• Journal of Biosystems Engineering
• /
• v.28 no.6
• /
• pp.537-544
• /
• 2003

The objectives of this study were to investigate the failure characteristics of a total of 90 parts of tractor driveline, and to predict their average annual demands required to perform the after-sales service. The failure characteristics such as failure mode, mean time between failures, characteristic life and reliability were analyzed using the data collected through the experienced mechanics at the part centers of the tractor manufacturers. The analysis was based on the assumption that the failure distribution follows the Weibull distribution. The average annual demands were also predicted for the replacement parts using the mean time between failures and the renewal theory based on the Weibull distribution. The results of the study revealed that the driveline parts failure was mostly from wearout and their average characteristic life is about 1.760 hours. The estimated mean time between failures was in a range of 670∼3,740 hours and reliability in a range of 40∼60％. The annual replacement demands were in a range of 4∼45 for a service of 100 tractors.

• Magazine of the Korean Society of Agricultural Engineers
• /
• v.17 no.1
• /
• pp.3702-3711
• /
• 1975

This study was originated to investigate the imparired parts of the mist and dust blowers and intended to analyze the causes of their failures by the use of the Weibull probability paper. By the use of the paper, the parts which were needed to change the design, the force of the urgency, the mean time between failures of the parts and the basic causes of the troubles could be predicted. The survey showed that the following parts got out of order: (A) flexible rubber hose, (B) blowing fan, (C) lead valve, (D) piston ring. (E) crank main bearing, (F) coil in magneto and (G) needle valve in carburettor. The analysis of the survey indicated that the parts G, C, E and D were belonged to "wear-out failure", and that the mean time between failures became shorter in order as indicated above. To insure longer lives of those parts, it would be necessary to change the design and the material and to upgrade operators mechanical technique of the mist and dust blower. The failure of the parts A, B and F was classified as "randomfailure", and they did not seem to be the "wear-out" at that time. The parts B and F was evaluated as "initial failure". Quality controls and operating tests by the producer. and the operational training for users should be strengthened so as to eliminate these failures. Were the failures only in the parts A, C, D, E, F and G, it could be said that the "reliability" of the mist and dust blower would fall to 10 percent in the second year, and 50 percent of the mist and dust blowers would fail in all parts A, C, D, E, F and G before the blower would have control insect and disease in 58.2 hectares. The use of the Weibull probability paper for analyzing failures of the mist and dust blowers was effective in that it analyzed failure in the relationship between strength of the parts and users actual circumstanoes.

• Journal of Korea Society of Industrial Information Systems
• /
• v.12 no.1
• /
• pp.80-86
• /
• 2007

The concept of the coverage has been played an important role in the area of reliability evaluation of a system. The widely used measures of reliability include the m time between failures, the availability and so on. In this paper, we propose an estimator of the coverage probability in a redundant system with a control unit and investigate some moments of the proposed estimator. And assuming exponential distribution of all units, we conduct a simulation study for calculating the estimates of the coverage probability and its confidence bounds. An example of evaluating the availability of an optical transportation system is illustrated.

• The Korean Journal of Applied Statistics
• /
• v.11 no.1
• /
• pp.53-64
• /
• 1998

Recently, it is of great interest among engineers and reliability scientists to consider a statistical model to describe the failure times of various types of repairable systems. The main subject we deal with in this paper is the power law process which is proved to be a useful model to describe the reliability growth of the repairable system. In particular, we derive the bootstrap confidence intervals of the mean time between two successive failures of a repairable system using the time truncated data. We also compare our bootstrap confindence intervals with Crow's (1982) confidence interval.

• Journal of the Korean Society for Precision Engineering
• /
• v.31 no.1
• /
• pp.67-73
• /
• 2014

A reliability evaluation or prediction can be defined as MTBF which stands for mean time between failures (Exclusively for repairable failures). Spindle system has huge effect on performance of machine tools and working quality as well as is required of high reliability. Especially, it takes great importance in producing automobiles which includes a large number of working processes. However, it is unusually difficult to predict reliability because there are lack of data and research about reliability of spindle system. Standards and methods of examinations for reliability evaluation of machine tools are scarce at local and abroad as well. Therefore, this research is meant to improve the reliability of spindle system before mass produced with developing standards of reliability and methods of examinations through FMEA to assess reliability of spindle system in prototype stages of developing high speed spindle system of machining center.

• The Journal of the Korea institute of electronic communication sciences
• /
• v.9 no.10
• /
• pp.1117-1123
• /
• 2014

Nuclear industries have faced unfavorable circumstances such as an obsolescence of the instrumentation and control system, and therefore nuclear society is striving to resolve this trouble fundamentally. FPGAs are currently highlighted as an alternative means for obsolete control systems. Because of the obsolescence-unaffected characteristics, FPGA should be highly reliable in order to be a replacement for PLC (Programmable Logic Controller). Therefore, it is necessary to establish a software development aspect strategy that enhances the reliability of an FPGA-based controller. The reliability analysis including the MTBF (Mean Time Between Failures) is carried out based on the MIL-HDBK-217F. MTBFs are compared with the FPGA-based controller COMMON-Q PLC. As an analysis result, it shows that the reliability of the FPGA-based controller is better than or equal to that of PLC.

• Journal of the Korean Society for Industrial and Applied Mathematics
• /
• v.10 no.2
• /
• pp.41-47
• /
• 2006

The Renewal process and the Non-homogeneous Poisson process (NHPP) process are probably the most popular models for describing the failure pattern of repairable systems. But both these models are based on too restrictive assumptions on the effect of the repair action. For these reasons, several authors have recently proposed point process models which incorporate both renewal type behavior and time trend. One of these models is the Modulated Power Law Process (MPLP). The Modulated Power Law Process is a suitable model for describing the failure pattern of repairable systems when both renewal-type behavior and time trend are present. In this paper we propose Bayes estimation of the next failure time after the system has experienced some failures, that is, Mean Time Between Failure for the MPLP model. Numerical examples illustrate the estimation procedure.

• IE interfaces
• /
• v.1 no.2
• /
• pp.67-74
• /
• 1988

MTBF (Mean Time Between Failures) is one of the measures to express the reliability for a repairable system, especially for a military weapon system. But MTBF is meaningless without a clear definition of the system failures. In this paper we discuss two failure definitions, one is defined by US Army Training and Doctrine Command jointly with US Army Materiel Command and the other one is used to M1 Tank.