• Journal of Applied Reliability
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• v.9 no.2
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• pp.121-130
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• 2009

The power law process model the Rate of occurrence of failures(ROCOF) with monotonic trend during the operating time. However, the power law process is inappropriate when a non-monotonic trend in the failure data is observed. In this paper we deals with the reliability modeling of the failure process of large and complex repairable system whose rate of occurrence of failures shows the non-monotonic trend. We suggest a sectional model and a change-point test based on the Schwarz information criterion(SIC) to describe the non-monotonic trend. Maximum likelihood is also suggested to estimate parameters of sectional model. The suggested methods are applied to field data from an repairable system.

• Journal of Communications and Networks
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• v.6 no.1
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• pp.78-87
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• 2004

This paper presents deterministic, worst-case analysis of a queueing system whose multiple homogeneous input streams are regulated by the associated leaky buckets and the queueing system that has a single stream regulated by the jumping-window. Queueing delay averaged over all items is used for performance measure, and the worst-case input traffic and the worst-case performance are identified for both queueing systems. For the former queueing system, the analysis explores different phase relations among leaky-bucket token generations. This paper observes how the phase differences among the leaky buckets affect the worst-case queueing performance. Then, this paper relates the worst-case performance of the former queueing system with that of the latter (the single stream case, as in the aggregate streams from many users, whose item arrivals are regulated by one jumping-window). It is shown that the worst-case performance of the latter is identical to that of the former in which all leaky buckets have the same phase and have particular leaky bucket parameters.

• Communications of the Korean Mathematical Society
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• v.23 no.4
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• pp.529-540
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• 2008

This paper deals the global existence and blow-up properties of the following non-Newton polytropic filtration system, $${u_t}-{\triangle}_{m,p}u=u^{{\alpha}_1}\;{\int}_{\Omega}\;{\upsilon}^{{\beta}_1}\;(x,\;t)dx,\;{\upsilon}_t-{\triangle}_{n,p}{\upsilon}={\upsilon}^{{\alpha}_2}\;{\int}_{\Omega}\;u^{{\beta}_2}\;(x,{\;}t)dx,$$ with homogeneous Dirichlet boundary condition. Under appropriate hypotheses, we prove that the solution either exists globally or blows up in finite time depends on the initial data and the relations of the parameters in the system.

• International Journal of Reliability and Applications
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• v.14 no.2
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• pp.55-70
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• 2013

This paper deals with the Bayesian analysis of the failure data of a repairable mechanical system subject to minimal repairs and periodic overhauls. The effect of overhauls on the reliability of the system is modeled by a proportional age reduction model and the failure process between two successive overhauls is assumed to be 2-parameter Engelhardt-Bain process (2-EBP). Power Law Process (PLP) model has a disadvantage which 2-EBP can overcome. On the basis of the observed data and of a number of suitable prior densities, point and interval estimation of model parameters, as well as quantities of relevant interest are found. Also hypothesis tests on the effectiveness of performed overhauls have been developed using Bayes factor. Sensitivity analysis of improvement parameter is carried out. Finally, a numerical application is used to illustrate the proposed method.

• Journal of the Korean Operations Research and Management Science Society
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• v.24 no.3
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• pp.109-123
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• 1999

Fleet sizing and empty equipment redistribution are two of the most critical problems in managing a fleet of equipment over a transportation network. Where the demand pattern followed the compound Poisson process(CPP) which can be generated one or more at a time under homogeneous Poisson process(HPP), this paper presented a mathematical model to determine control parameters of a decentralized distribution policy and fleet size in case of the pure hub-and-spoke system, a popular form of a logistics system. and validated this model by simulation. That is, where the number of demanded equipments followed geometric and binomial distributions, respectively, cost models on the pure hub-and-spoke logistics system with deterministic trans-portation times, which could be solved analytically, were established and analyzed. We also compared the deterministic case with stochastic one that the transportation time follows some probability distributions.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.3
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• pp.581-593
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• 1990

A semi-solid alloy in which solid and liquid phase are co-existing is obtained by strirring of Al7075 molten metal. A semi-solid alloy is dependent on the corresponding temperature within the solid-liquid range, and the process parameters should be controlled accurately to obtain the homogeneous semi-solid alloy. The possibility o homogeneous fiber-reinforce aluminum alloy by addition of $Al_{2}$O$_{3}$ short fibers with vigorous agitation was investigated. The billet of composite materials was fabricated by squeeze casting, and homogeneous dipersion state of fibers in billet of fabricated metal matrix composites was observed. A slurry of semi-solid short fiber metal matrix composites is used in the direct rolling process, and this process showed the fabrication possibility of metal matrix composite sheets. The fabricated sheet was tested regarding vickers hardness, elongation and micro-structure. It has become clear that mashy state processing and working are very useful to obtain parts of composites material closed to near net shape.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.11 no.4
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• pp.1239-1247
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• 2010

In this paper, we were researched decision problem called an optimal release policies after testing a software system in development phase and transferring it to the user. The applied model of release time exploited infinite failure non-homogeneous Poisson process This infinite failure non-homogeneous Poisson process is a model which reflects the possibility of introducing new faults when correcting or modifying the software. The intensity function used Gompertz, Preto and Log-logstic pattern which has the efficient various property. Thus, optimal software release policies which minimize a total average software cost of development and maintenance under the constraint of satisfying a software reliability requirement becomes an optimal release policies. In a numerical example, after trend test applied and estimated the parameters using maximum likelihood estimation of inter-failure time data, estimated software optimal release time.

• Korean Journal of Environmental Biology
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• v.24 no.4
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• pp.368-371
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• 2006

The complex analysis of male reproductive system of vines and fruit-tyees growing in zone of the Armenian Nuclear Power Plant (ANPP) is realized. The obtained data demonstrate that the homogeneous pollen with high fertility and optimal morphometric parameters in all variants is formed. The obtained results demonstrate that there is no one-sided effect of ANPP on the development and formation of investigated male generative system of vines and fruit trees. Thus, on the base of obtained results we can't confirm its deleterious effect on the environment.

• Smart Structures and Systems
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• v.16 no.1
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• pp.195-211
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• 2015

This paper presents nonlinear analysis of a functionally graded square plate integrated with two functionally graded piezoelectric layers resting on the Winkler-Pasternak foundation. Geometric nonlinearity was considered in the strain-displacement relation based on the Von-Karman assumption. All the mechanical and electrical properties except Poisson's ratio can vary continuously along the thickness of the plate based on a power function. Electric potential was assumed as a quadratic function along the thickness direction and trigonometric function along the planar coordinate. The effect of non homogeneous index was investigated on the responses of the system. Furthermore, a comprehensive investigation has been performed for studying the effect of two parameters of assumed foundation on the mechanical and electrical components. A comparison between linear and nonlinear responses of the system presents necessity of this study.

• Coupled systems mechanics
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• v.13 no.1
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• pp.21-41
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• 2024

This paper is concerned with the disturbances in a transversely isotropic new modified couple stress homogeneous thermoelastic rotating medium under the combined influence of Hall currents, magnetic fields, and mechanical sources represented by inclined loads. The application of Laplace and Fourier transform techniques are used for the derivation of analytical expressions for various physical quantities. As an application,the bounding surface is subjected to uniformly and linearly distributed force (mechanical force). Present model contains length scale parameters that can capture the size effects. Numerical inversion techniques has been used to provide insights into the system's behavior in the physical domain. The graphical representation of numerical simulated results has been presented to emphasize the impact of rotation and inclined line loads on the system, enhancing our understanding of the studied phenomena. Further research can extend this study to investigate additional complexities and real-world applications.