• The Journal of the Convergence on Culture Technology
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• v.9 no.3
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• pp.701-706
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• 2023

The Korean government and industry have presented a roadmap for the commercialization of UAM services and are promoting it in earnest. In order to introduce full-scale UAM services, there are various issues to be solved, such as the development of high-performance aircraft, the design of network bases and corridors, the optimization of operation management, and the establishment of related laws and systems. In this study, in terms of optimizing operation management, we will examine research trends by field, focusing on Korea, and derive research topics that need to be solved in the future. Korean researchers have suggested that research is centered on UAM service usage fees, usage intentions and acceptance models, and vertiport location selection, but operational optimization studies such as service order acceptance, aircraft repositioning, and battery charging and maintenance scheduling are needed in the future.

• Proceedings of the KSR Conference
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• 2008.06a
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• pp.765-771
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• 2008

After the KTX operation Korail has been making great effort to reliability settlement through RCM. Also maintenance cycle and method optimization for normal speed rolling stock field are lively same as high-speed rolling stock. In this paper maintenance techniques for new model electric locomotive are introduced. To find the optimal maintenance method, locomotive inspection cycle for advanced country are examined and other electric locomotive inspection cycle are compared. As a result the present time inspection cycle is totally focusing on safety aspect so the economical efficiency is quite low. Through this research optimal maintenance technique will be accomplished in the end of year 2008.

• Journal of the Korean Institute of Illuminating and Electrical Installation Engineers
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• v.24 no.8
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• pp.1-7
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• 2010

The reliability of a power system has close relationship with the maintenance of the distribution systems. This paper presents the method of the maintenance planning of the distribution systems by minimizing the interruption cost. The interruption cost for the equipment failures is formulated using time varying failure rate and minimized by optimization of the object function. The proposed method provides the priority list for the investment of the maintenance subject to the limited investment budget by the economic analysis. In order to test the proposed method, the modified distribution system of a rural area is introduced for the testing system. Test results show that the proposed method is good enough by evaluating the improvement of the reliability of the power system.

• Structural Monitoring and Maintenance
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• v.5 no.4
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• pp.489-506
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• 2018

This paper reported test of full-scale cables attached with four types of dampers: viscous damper, passive Magneto-Rheological (MR) damper, friction damper and High Damping Rubber (HDR) damper. The logarithmic decrements of the cable with attached dampers were calculated from free vibration time history. The efficiency ratios of the mean damping ratios of the tested four dampers to theoretical maximum damping ratio were derived, which was very important for practical damper design and parameter optimization. Non-ideal factors affecting damper performance were discussed based on the test results. The effects of concentrated mass and negative stiffness were discussed in detail and compared theoretically. Approximate formulations were derived and verified using numerical solutions. The critical values for non-dimensional concentrated mass coefficient and negative stiffness were identified. Efficiency ratios were approximately 0.6, 0.6, and 0.3 for the viscous damper, passive MR damper and HDR damper, respectively. The efficiency ratio for the friction damper was between 0-1.0. The effects of concentrated mass and negative stiffness on cable damping were positive as both could increase damping ratio; the concentrated mass was more effective than negative stiffness for higher vibration modes.

• Smart Structures and Systems
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• v.30 no.6
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• pp.571-582
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• 2022

Optimal life-cycle management is a challenging issue for deteriorating regional bridges. Due to the complexity of regional bridge structural conditions and a large number of inspection and maintenance actions, decision-makers generally choose traditional passive management strategies. They are less efficiency and cost-effectiveness. This paper suggests a deep reinforcement learning framework employing double-deep Q-networks (DDQNs) to improve the life-cycle management of deteriorating regional bridges to tackle these problems. It could produce optimal maintenance plans considering restrictions to maximize maintenance cost-effectiveness to the greatest extent possible. DDQNs method could handle the problem of the overestimation of Q-values in the Nature DQNs. This study also identifies regional bridge deterioration characteristics and the consequence of scheduled maintenance from years of inspection data. To validate the proposed method, a case study containing hundreds of bridges is used to develop optimal life-cycle management strategies. The optimization solutions recommend fewer replacement actions and prefer preventative repair actions when bridges are damaged or are expected to be damaged. By employing the optimal life-cycle regional maintenance strategies, the conditions of bridges can be controlled to a good level. Compared to the nature DQNs, DDQNs offer an optimized scheme containing fewer low-condition bridges and a more costeffective life-cycle management plan.

• Korean Chemical Engineering Research
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• v.52 no.4
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• pp.475-480
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• 2014

In the fields of researches associated with plant layout optimization, the main goal is to minimize the costs of pipelines for connecting equipment. However, what is the lacking of considerations in previous researches is to handle the multi floor processes considering the safety distances for domino impacts on a complex plant. The mathematical programming formulation can be transformed into MILP (Mixed Integer Linear Programming) problems as considering safety distances, maintenance spaces, and economic benefits for solving the multi-floor plant layout problem. The objective function of this problem is to minimize piping costs connecting facilities in the process. However, it is really hard to solve this problem due to complex unequality or equality constraints such as sufficient spaces for the maintenance and passages, meaning that there are many conditional statements in the objective function. Thus, it is impossible to solve this problem with conventional optimization solvers using the derivatives of objective function. In this study, the PSO (Particle Swarm Optimization) technique, which is one of the representative sampling approaches, is employed to find the optimal solution considering various constraints. The EO (Ethylene Oxide) plant is illustrated to verify the efficacy of the proposed method.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2005.04a
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• pp.719-726
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• 2005

The optimal design was performed for the bridge superstructure composed of steel box girders and concrete deck considering life cycle cost. The service life of the superstructure was estimated, after load carry capacity curves for steel girder and concrete deck were derived on the basis of condition grade curves and maintenance histories. The object function was determined as life cycle cost, including initial cost, total maintenance cost, disposal cost and user cost, for a period of the estimated service life. The optimal design of the superstructure was performed for the various service lifes. The annual costs were used to compare calculated results and to get the most economical design. Also this paper presents reasonable idea for the use of user cost with uncertainty.

• Proceedings of the KIEE Conference
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• summer
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• pp.740-742
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• 2004

In TWBP markets, ISO determines the maintenance schedule based on Gencos' and Transcos' offers under reasonable criterion. This paper presents ISO's alternative procedure to coordinate maintenance schedules submitted by Gencos and Transcos. ISO's coordination procedure is formulated as an optimization problem that minimizes expected losses in Gencos' revenue subject to system reserve requirement.

• Proceedings of the KIEE Conference
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• 2003.07a
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• pp.643-645
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• 2003

In competitive electricity markets, each GenCo establishes generator maintenance schedule and submits to ISO those. Then, ISO reviews and arranges maintenance schedule of each GenCo to meet the standard for reliability. This paper presents the new optimization model which can apply to competitive electricity markets. The object of this model is to minimize schedules variation of each GenCo and to satisfy system reliability.

• Structural Monitoring and Maintenance
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• v.4 no.1
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• pp.33-52
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• 2017

A cantilever beam with a breathing crack is studied to improve the breathing crack identification sensitivity by the parametric optimization of sample entropy and wavelet transformation. Crack breathing is a special bi-linear phenomenon experienced by fatigue cracks which are under dynamic loadings. Entropy is a measure, which can quantify the complexity or irregularity in system dynamics, and hence employed to quantify the bi-linearity/irregularity of the vibration response, which is induced by the breathing phenomenon of a fatigue crack. To improve the sensitivity of entropy measurement for crack identification, wavelet transformation is merged with entropy. The crack identification is studied under different sinusoidal excitation frequencies of the cantilever beam. It is found that, for the excitation frequencies close to the first modal frequency of the beam structure, the method is capable of detecting only 22% of the crack depth percentage ratio with respect to the thickness of the beam. Using parametric optimization of sample entropy and wavelet transformation, this crack identification sensitivity is improved up to 8%. The experimental studies are carried out, and experimental results successfully validate the numerical parametric optimization process.