• Transactions of the Korean Society of Automotive Engineers
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• v.24 no.5
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• pp.596-604
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• 2016

In this study, we used a stochastic approach for guaranteeing the reliability and robustness of the performance with regard to the design of polymer components, while taking into consideration the degradation properties and operating conditions in automobiles. Creep and tensile tests were performed for obtaining degradation properties. The Prony series, which described the viscoelastic models, were calculated to use the creep data by the Maxwell fluid model. We obtained the stress data from the frequency response analysis of the polymer components while considering the degradation properties. Limit state functions are generated by using these data. Reliability assessments are conducted under the variation of the degradation properties and area of frequency at peak response. For this study, the input parameters are assumed to be a normal distribution, and the reliability under the yield stress criteria is evaluated by using the Monte Carlo Simulation. As a result, the reliabilities, according to the three types of polymer materials in automotive components, are compared to each other and suggested the applicable possibility of polymeric materials in automobiles.

• Journal of the Korean Society for Library and Information Science
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• v.52 no.1
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• pp.231-258
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• 2018

This study attempted to identify dynamically changing structure and analyze factors of collaboration. In order to perform this study, 1,631 articles in SCI journals were collected, and 3,898 researchers' information were extracted. To examine the dynamics of collaboration networks, the co-authorship data collected from 2001 to 2015 were divided into three sets, and were analyzed with respect to each period. The results of this study were summed up as: 1) "Co-authorship of the last year" was entirely significant factors while research career was significant only in the period of 2 to 3. 2) It was found that "Influence of the researchers" and "Emergence of the researchers" were significant factors in the period of 2 to 3 and in the period of 1 to 2. 3) "Same institutions", "Same subject", and "Journal similarity" were significant factors in all periods.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.7
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• pp.779-785
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• 2019

By applying an ergonomically developed Bismuth shield to the endovascular treatment of cerebral aneurysm the radiation dose of the scalp and lens from the medical radiation exposure was reduced. The enrtance surface dose was analyzed by measuring the occipital parts, bilateral temporal parts, bilateral quadriceps, and nasal tip of the developed bismuth shield using a photostimulable fluorescence dosimeter before (Group A) before use (Group B). Signal to noise ratio (SNR) and contrast to noise ratio (CNR) analysis were used to evaluate the image quality when Bismuth shielding was used. The mean entrance surface dose of A group and B group was 26.92% lower than that of A group. The analysis of CNR and SNR was the same for both Roadmap and DSA. The use of Bismuth shielding is an alternative that can reduce the radiation impairment due to temporary hair loss and other stochastic effects that may occur after cerebrovascular intervention.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.7
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• pp.869-874
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• 2019

Performing preventive maintenance on a system reduces unexpected downtime caused by system aging and increases its availability. In general, preventive maintenance can be largely divided into two broad categories: time-based maintenance policy and condition-based maintenance policy. In the time-based maintenance policy the preventive maintenance is triggered at scheduled time epochs with fixed time intervals, while in the condition-based maintenance policy the preventive maintenance is performed when system state is checked to satisfy a specific condition. Condition-based maintenance has some benefits in improving maintenance efficiency, compared to time-based one. This paper presents a stochastic model for analyzing a system with condition-based preventive maintenance, where the preventive maintenance is performed after a random time since the system aging occurs, and provides an analytical solution for the steady-state availability and the corresponding profit.

• Journal of the Korea Institute of Information and Communication Engineering
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• v.23 no.2
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• pp.201-206
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• 2019

Rejuvenating a system periodically during the most idle time of the system reduces unexpected downtime caused by software aging and increases its availability. In general, software rejuvenation can be largely divided into two broad categories: time-based rejuvenation policy and condition-based rejuvenation policy. In time-based rejuvenation policy the software rejuvenation is triggered at scheduled time epochs with fixed time intervals, while in condition-based rejuvenation policy the software rejuvenation is performed when system state is checked to satisfy a specific condition. Conditionbased policy adds extra cost to the system due to system monitoring and aging estimation. This paper presents a stochastic model for analyzing time-based software rejuvenation mechanism, where the rejuvenation is triggered at scheduled time epochs with fixed time intervals, and provides an analytical solution for the steady-state availability, the user-perceived availability, and the corresponding cost.

• Smart Structures and Systems
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• v.29 no.3
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• pp.499-512
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• 2022

This work proposes a novel contactless vibration damping and thermal isolation tripod platform based on Superconducting Magnetic Levitation (SML). This prototype is suitable for cryogenic environments, where classical passive, semi active and active vibration isolation techniques may present tribological problems due to the low temperatures and/or cannot guarantee an enough thermal isolation. The levitating platform consists of a Superconducting Magnetic Levitation (SML) with inherent passive static stabilization. In addition, the use of Operational Modal Analysis (OMA) technique is proposed to characterize the transmissibility function from the baseplate to the platform. The OMA is based on the Stochastic Subspace Identification (SSI) by using the Expectation Maximization (EM) algorithm. This paper contributes to the use of SSI-EM for SML applications by proposing a step-by-step experimental methodology to process the measured data, which are obtained with different unknown excitations: ambient excitation and impulse excitation. Thus, the performance of SSI-EM for SML applications can be improved, providing a good estimation of the natural frequency and damping ratio without any controlled excitation, which is the main obstacle to use an experimental modal analysis in cryogenic environments. The dynamic response of the 510 g levitating platform has been characterized by means of OMA in a cryogenic, 77 K, and high vacuum, 1E-5 mbar, environment. The measured vertical and radial stiffness are 9872.4 N/m and 21329 N/m, respectively, whilst the measured vertical and radial damping values are 0.5278 Nm/s and 0.8938 Nm/s. The first natural frequency in vertical direction has been identified to be 27.39 Hz, whilst a value of 40.26 Hz was identified for the radial direction. The determined damping values for both modes are 0.46% and 0.53%, respectively.

• International conference on construction engineering and project management
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• 2009.05a
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• pp.400-408
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• 2009

Simulation applications for analyzing the productivity of construction operations at operation level and project schedules at project level are crucial methods in project management. The application at two different levels should be very tightly linked to each other in practice. However, appropriate integration at the levels is not achieved in that existing systems do not support to integrate operation models into a schedule model. This paper presents a new approach named to Discrete Event Simulation-Nesting modeling approach, which supports not only productivity analysis at operation level but also schedule management at a project level. The system developed by the authors allows creating operation models at the operation level, maintaining them in operation model library, executing sensitivity analysis to find the behaviors of the operation models when different combination of resources are used as existing DES systems do. On top of the conventional functions, the new system facilitates to find the optimum solution of resource combinations which satisfy the user's interest by computing the hourly productivity and the hourly cost of the operation. By drag-and-dropping an operation model kept in the operation model library, the operation models are integrated into an activity of the schedule model. When a complete schedule model is established by nesting operation models into the schedule model, stochastic simulation based scheduling is executed. A case study is presented to demonstrate the new simulation system and verify the validity of the system.

• Journal of the Korea Society for Simulation
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• v.19 no.2
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• pp.17-28
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• 2010

Since a homing torpedo system consists of various subsystems, organic interactions of which dictate the performance of the torpedo system, it is necessary to estimate the effects of individual subsystems in order to obtain an optimized design of the overall system. This paper attempts to gain some insight into the detection mechanism of a torpedo run, and analyze the relative importance of various parameters of a torpedo system. A database for the analysis was generated using a simulation model based on the combined discrete event and discrete time architecture. Multiple search schemes, including the snake-search method, were applied to the torpedo model, and some parameters of the torpedo were found to be stochastic. We then analyzed the effectiveness of torpedo’s detection capability according to the torpedo speed, the target speed, and the maximum detection range.

• Journal of the Korean Society of Hazard Mitigation
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• v.9 no.6
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• pp.133-141
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• 2009

The main objective of water distribution system is to supply enough water to users with proper pressure. Hydraulic analysis of water distribution system can be divided into Demand Driven Analysis (DDA) and Pressure Driven Analysis (PDA). Demand-driven analysis can give unrealistic results such as negative pressures in nodes due to the assumption that nodal demands are always satisfied. Pressure-driven analysis which is often used as an alternative requires a Head-Outflow Relationship (HOR) to estimate the amount of possible water supply at a certain level of pressure. However, the lack of data causes difficulty to develop the relationship. In this study, effective supply, which is the possible amount of supply while meeting the pressure requirement in nodes, is proposed to estimate the serviceability and user's convenience of the network. The effective supply is used to calculate Subsystem Importance Index (SII) which indicates the effect of isolating a subsystem on the entire network. Harmony Search, a stochastic search algorithm, is linked with EPANET to maximize the effective supply. The proposed approach is applied in example networks to evaluate the capability of the network when a subsystem is isolated, which can also be utilized to prioritize the rehabilitation order or evaluate reliability of the network.

• School Mathematics
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• v.11 no.3
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• pp.389-413
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• 2009

This thesis assumes that the teaching objective of the Probability unit of the 8th grade textbook under the 7th National Curriculum is to enhance the ability to analyze and utilize informations. And we examine them if this point of view is fully reflected. Based on the analysis of the textbook analysis, followings are found. 1) It is necessary to emphasize more enumerating all possible cases and to induce formulae counting the number of possible cases through organizing them 2) The probability is to be decribed more clearly as a likelihood of events and to be introduced and followed through various students' experiences and the relative frequencies. Less emphasis on probability computations, while more emphasis on probability comparisons of events are recommended. 3) The term "influential events"(a kind of stochastic correlation) is ambiguous. It is necessary to make clear what it means at tile level of the 8th grade or to discard it for it is to be learned at the 10th grade again. Especially, contingency table has been introduced at the 9th grade under the 7th National Curriculum. 4) Uses of the likelihood principle in making a decision and in learning the reliability of it should be encouraged. And students are to team the hazard of transitive inferences in probability comparisons. As a consequence of above, we feel that textbook authors and related stakeholder are to be more serious about the behavioral changes of students that may come along with the didactics of specific contents of school mathematics.