• Journal of Applied Reliability
• /
• v.16 no.4
• /
• pp.313-322
• /
• 2016

Purpose: We introduce ways to employ Markov chain model to evaluate the effect of preventive maintenance process. While the preventive maintenance process decreases the failure rate of each subsystems, it increases the downtime of the system because the system can not work during the maintenance process. The goal of this paper is to introduce ways to analyze this trade-off. Methods: Markov chain models are employed. We derive the availability of the system consisting of N repairable subsystems by the methods under various maintenance policies. Results: To validate our methods, we apply our models to the real maintenance data reports of military truck. The error between the model and the data was about 1%. Conclusion: The models developed in this paper fit real data well. These techniques can be applied to calculate the availability under various preventive maintenance policies.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.21 no.47
• /
• pp.47-55
• /
• 1998

This paper proposes a maintenance model considering the Inherent availability of certain requirement and two types of failures, repairable or irrepairable. In this model, the system is replaced in time when it doesn't meet the inherent availability requirement despite of all repairable failures; Otherwise it is replaced by the first irrepairable failure. Assuming that the j-th failure is repairable with probability ${\alpha}_j$, minimal repairs are performed for repairable failures between replacements. We drive the expected cost rate through the application of NHPP(Non-Homogeneous Poisson Process) in order to determine the optimal number $n^*$. The model includes some previous studies as special cases.

• International Journal of Knowledge Content Development & Technology
• /
• v.12 no.1
• /
• pp.35-47
• /
• 2022

This study adopted the descriptive survey research method. The population of this study comprised of the hearing impaired students in selected government secondary schools in Rivers state. The population of hearing impaired students in Rivers State is 257. A simple random sampling technique was used to select a sample size of 159. A self-developed instrument titled "Availability and Utilization of Library Information Resources Questionnaire (AULIRQ)" was utilized for data collection. 153 responses were collated, indicating a 96.2% response rate. The data collected was arranged and analyzed using frequency count, percentages, and mean and standard deviation. Finding reveals that information resources in the libraries understudied were inadequate and under-utilized. Also, it was established that among other barriers, under-funding is a major barrier to making information resources available for the physically challenged. It was recommended that schools offering special education for the hearing impaired should pace up in their developmental gap by providing such resources and ensure adequate funding by all stakeholders.

• Asian-Australasian Journal of Animal Sciences
• /
• v.15 no.6
• /
• pp.793-799
• /
• 2002

Four feeds, three concentrates (rice bran, soybean meal and flaked corn) and one forage (corn silage) were incubated in four ruminally fistulated Holstein steers over three one week periods in a 3${\times}$4 incomplete latin square design where steers served as blocks and feeds as treatment. The objectives of the study were to investigate in situ DM, N and P degradability characteristics of feeds in order to assess availability of these nutrients by ruminants. In each period, all feeds were incubated in quadruplets (corn silage in triplicates) in the rumen of each steer in a reverse order for 3, 6, 9, 12, 18, 24 and 48 h. The DM 'a' fraction was higher and lower (p<0.001) in corn silage and rice bran respectively. Although corn silage contained the lowest (p<0.01) DM 'b' fraction, flaked corn contained the highest. Rate of DM degradation of flaked corn and corn silage were half (p<0.05) of the rate of DM degradation of either rice bran or soybean meal. Potential or effective DM degradability (p<0.05 to 0.001) at various passage rates were the lowest for rice bran and the highest for soybean meal. Corn silage N 'a' and 'b' was the highest and lowest, respectively (p<0.01). N 'c' of corn silage and rice bran was higher (p<0.001) than other feeds. Potential N degradability was the lowest in flaked corn (p<0.05). P 'a' was high (p<0.01) for corn silage and rice bran. P 'b' fraction was very high (p<0.001) in soybean meal but was absent in corn silage. Availability of DM (p<0.01 or 0.001), N (p<0.001) and P (p<0.05) differed between feeds at various passage rates except P availability at k=0.02 per h (p>0.05). The results demonstrate that the availability of DM, N and P by ruminants depends on feed as well as categories of animal.

• ETRI Journal
• /
• v.42 no.1
• /
• pp.118-128
• /
• 2020

A semitransparent photovoltaic-thermal (PV/T) air collector can produce electricity and heat simultaneously. To maximize the thermal and overall efficiency of the semitransparent PV/T air collector, its availability should be maximum; this can be determined through a Markov analysis. In this paper, a Markov model is developed to select an optimized number of semitransparent PV modules in service with five states and two states by considering two parameters, namely failure rate (λ) and repair rate (μ). Three artificial neural network (ANN) models are developed to obtain the minimum cost, minimum temperature, and maximum thermal efficiency of the semitransparent PV/T air collector by setting its type appropriately and optimizing the number of photovoltaic modules and cost. An attempt is also made to achieve maximum thermal and overall efficiency for the semitransparent PV/T air collector by using ANN after obtaining its minimum temperature and available solar radiation.

• International Journal of Reliability and Applications
• /
• v.8 no.1
• /
• pp.83-94
• /
• 2007

In this paper, we consider a standby redundant structure with a function of switchover processing which may not be not perfect. The switchover processing is governed by a control module whose failure may cause the failure of the whole system. The parameters measuring such an effect of failure of the control module is included in our reliability model. We compute several reliability measures such as reliability function, failure rate, MTBF, mean residual life function, and the steady state availability. We also compare a single unit structure and the redundant structure with regard to those reliability measures. An example is given to illustrate our results.

• Journal of Korean Society of Industrial and Systems Engineering
• /
• v.33 no.3
• /
• pp.199-207
• /
• 2010

In this paper considered is the provisioning quantity determination problem of consumable concurrent spare parts (CSP) of a new equipment system to minimize the procurement cost under the operational availability constraint. When a part fails, repair of the failed part is impossible and the part is replaced and cannibalization is allowed. The failure of a part is assumed to follow a Poisson process and the operational availability in CSP is defined. The solution procedure consists of two parts. Firstly, a heuristic algorithm is developed under the assumption that the failure rate is constant during the CSP period. Secondly, proposed is a simulation search procedure which improves the heuristic solution to the near optimal solution in a reasonable amount of time. An illustrative example is shown to explain the solution procedure.

• Journal of Environmental Science International
• /
• v.4 no.5
• /
• pp.427-435
• /
• 1995

In order to discuss the differences among the SMP(Surface Moisture Availability Parameter), by previous researchers on the basis of their own theoretical and empirical background, we assessed the SMP according to the soil types and volumetric soil water contents. The results are as follows. There are differences among all the five SMAPs. There's a tendency that the larger grain size, the higher value of parameters. And they divided into two groups for their value: one group has parameters with exponential function and the other with cosine and linear function. The maximum difference between the two groups appears when the volumetric soil water contents are 0.07m3m-3 for sand, 0.l1m3m-3 for loam, 0.12 for clay, and 0.13m3m-3 for silt loam. So, these differences must be considered when we estimate the surface evaporation rate. From field data, the paddy field soil around Junam reservoir is classified as a silt has high wetness, 0.56. So, the parameter obtained from the field measurement is much higher than that of Clapp and Hornberger(1978)'s Table. This study treated the SMP for a certain point of time in winter season. But if we measured the soil water contents continuously, we could obtain better time-dependent parameter. Key words : SMAP(Surface Moisture Availability Parameter), Paddy field, Volumetric soil water content, Evaporation, Capillary potential.

• Journal of Applied Reliability
• /
• v.7 no.1
• /
• pp.13-22
• /
• 2007

A preventive maintenance model, caller FNBM (${\alpha},{\delta},{\gamma}$) model, is proposed to decide an optimal repair number under achieved availability requirements (r) along with taking two types of failures (repairable or irrepairable) into account. In this model, the current system is replaced by a new one in case when it doesn't meet the achieved availability requirement, even though it is repairable failure; Othewise it is replaced in time of the first irrepairable failure. Assumed that the j-th failure is repairable with probability ${\alpha}_j$ minimal repairs are allowed for repairable failure between replacements. Expected cost rate for preventive maintenance model is developed using NHPP (Non - Homogeneous Poisson Process) in order to de term in the optimal number $n^*$, also numerical examples are shown in order to explain the proposed model. Since the proposed FNBM (${\alpha},{\delta},{\gamma}$) model includes Park FNBM model (1979) and Nakagawa FNBM (p) model (1983) m this proposed model is thought to be better than previous model, especially for weapon system which requires availability as primary parameter.

• Journal of the Korean Society of Systems Engineering
• /
• v.13 no.1
• /
• pp.79-88
• /
• 2017

For the PBL contract, it is necessary for the contracting parties to share information regarding the reasonable inventory-level and the cost of its repair parts for the estimated demand. There are various models which can be used for this purpose. Among them, V-METRIC model is considered to be the most efficient and is most frequently applied. However, this model is usually used for optimizing the inventory level of the repair parts of the system under operation. The model uses a time series forecast model to determine the demand rate, which is a mandatory input factor for the model, based on past field data. However, since the system at the deployment stage has no operational performance record, it is necessary to find another alternative to be used as the demand rate of the model application. This research applies the V-METRIC model to find the optimal inventory level and cost estimation for repairable items to meet the target operational availability, which is a key performance indicator, at the time of the PBL contract for the deployment system. This study uses the calculated value based on the allocated MTBF to the system as the demand rate, which is used as input data for the model. Also, we would like to examine changes in inventory level and cost according to the changes in target operational availability and MTBF allocation.