• Structural Engineering and Mechanics
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• v.67 no.1
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• pp.33-43
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• 2018

The dynamic output-feedback robust control method based on linear matrix inequality (LMI) method is presented for suppressing vibration response of a functionally graded material (FGM) beam with piezoelectric actuator/sensor layers in this paper. Based on the reduced model obtained by using direct mode truncation, the linear fractional state space representation of a piezoelectric FGM beam with material properties varying through the thickness is developed by considering both the inherent uncertainties in constitution material properties as well as material distribution and the model error due to mode truncation. The dynamic output-feedback robust H-infinity control law is implemented to suppress the vibration response of the piezoelectric FGM beam and the LMI method is utilized to convert control problem into convex optimization problem for efficient computation. In numerical studies, the flexural vibration control of a cantilever piezoelectric FGM beam is considered to investigate the accuracy and efficiency of the proposed control method. Compared with the efficient linear quadratic regulator (LQR) widely employed in literatures, the proposed robust control method requires less control voltage applied to the piezoelectric actuator in the case of same control performance for the controlled closed-loop system.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.19 no.1
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• pp.108-113
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• 2020

Pinions are generally heavy and integrated with a shaft. Thus, fabricating a pinion is a material- and machining-intensive task characterized by low productivity. Contact of the output pinion with a sliding surface or a cloud contact causes loss of power because of friction. Consequently, the output pinion undergoes considerable wear and tear at its ends, which adversely affects the overall transmission efficiency of decelerators. To improve transmission efficiency and extend gear life, an optimum output pinion design is required. To this end, in this study, an output pinion for worm gear decelerators was designed and optimized by means of product verification through prototyping and performance evaluation to improve gear life and productivity. The optimized design was validated and subjected to structural analysis.

• Smart Structures and Systems
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• v.26 no.5
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• pp.591-603
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• 2020

Dynamic deflection monitoring is an essential and critical part of structural health monitoring for high-speed railway bridges. Two critical problems need to be addressed when using inclinometer sensors for such applications. These include constructing a general representation model of inclination-deflection and addressing the ill-posed inverse problem to obtain the accurate dynamic deflection. This paper provides a dynamic deflection monitoring method with the placement of optimal inclinometer sensors for high-speed railway bridges. The deflection shapes are reconstructed using the inclination-deflection transformation model based on the differential relationship between the inclination and displacement mode shape matrix. The proposed optimal sensor configuration can be used to select inclination-deflection transformation models that meet the required accuracy and stability from all possible sensor locations. In this study, the condition number and information entropy are employed to measure the ill-condition of the selected mode shape matrix and evaluate the prediction performance of different sensor configurations. The particle swarm optimization algorithm, genetic algorithm, and artificial fish swarm algorithm are used to optimize the sensor position placement. Numerical simulation and experimental validation results of a 5-span high-speed railway bridge show that the reconstructed deflection shapes agree well with those of the real bridge.

• Journal of Power System Engineering
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• v.3 no.3
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• pp.83-90
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• 1999

제어이론분야에서의 발전은 그러한 이론을 다방면으로 응요할 수 있는 분야를 더더욱 폭넓게 제공해 주고 있다. 자동화와 관련된 분야뿐만 아니라, 건축 및 토목분야에서도 고도의 제어어이론을 응용한 예를 쉽게 접할 수 있게 되었으며, 지진동에 의한 구조물의 진동을 억제하려는 방책이 그 ??ㅣ다. 이에 관한 많은 연구에서도 알 수 있듯이, 일반적으로 구조물의 수학적 모델에만 의존하여, 즉 구조물의 설계파라미터는 이미 설계되어져 있다는 가정하에 제어계를 설계하고 있다. 그러나 이러한 설계법에 있어서는 설계자로 하여금 구조물의 설계파라미터를 조정할 수 있는 자유도는 전혀 주어지지 않게 되며 단지 제어계의 파라미터를 조정하는 자유도만 허용된다. 이러한 문제점을 극복하기 위해 구조계 및 제어기의 설계파라미터를 동시에 조절할 수 있는 자유도가 허용되는 '구조계/제어계의 동시 최적화' 기법이 있다. 따라서 본 논문에서는 교량의 주탑 및 해양구조물 등의 진동제어 문제에 이러한 설계기법을 이용하여 주어진 설계사양을 만족하도록 구조계 및 제어계의 파라미터를 최적화 한다. 특히 본 논문에서는 제어계 설계 문제에 있어서의 일반적인 경우를 고려하여 상태의 일부가 관측된다고 가정하고 출력피드백의 경우에 대해 고찰하고 있다. 이때의 설계사양은 선형행렬부등식(LMI)으로 주어지며, 실험을 통하여 본 논문에서 소개하는 설계기법의 유효성을 검증한다.

• Journal of the Korean Society for Precision Engineering
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• v.28 no.4
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• pp.490-495
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• 2011

A slide-rail system is widely used in home appliances, furniture, mechanical rigs, and so many other applications; due to its high strength and performance for easy moving heavy objectives. In general, a pair of side slide-rails is set on both sides of a drawer to support and move it. So an unbalanced sliding motion can occur during opening and closing a drawer with pull and push force. To settle this problem, single central slide-rail having three collapsible rail-bodies was firstly proposed in this work. 'H'-beam shaped rail-body was newly designed to have enough bending and twisting strength. The experimental test showed that the proposed rail could be applied to large-size home appliances for easy moving drawer with heavy weight.

• International Journal of Highway Engineering
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• v.17 no.3
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• pp.13-25
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• 2015

PURPOSES : This paper aims at the implementation of a balanced scorecard that can be widely applied to modern business management for use in the public road management sector. METHODS : This study applied the newly developed LOS-based balanced scorecard system instead of a traditional Key Performance Index (KPI) for better decision making in asset management planning. As an evaluation technique, a" hierarchical alignment and cascading method" is also suggested. Finally, the suggested system has been empirically applied to a regional government. RESULTS : To provide stable and sustainable road services, the balanced scorecard informs the regional government of needed improvements in its asset management plans regarding budget optimization, structural management, the development of inner-business processes, and human resources. CONCLUSIONS : An LOS-based balanced scorecard for managing road services and organizations in a quantitative manner has been successfully developed and tested through a field study. The developed scorecard is a timely topic and a useful analytical tool for coping with the new phases of an aging infrastructure, tighter budgets, and demand for greater public accountability.

• KSII Transactions on Internet and Information Systems (TIIS)
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• v.8 no.11
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• pp.4087-4102
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• 2014

Two-way relaying is an effective way of improving system spectral efficiency by making use of physical layer network coding. However, energy efficiency in OFDM-based bidirectional relaying with asymmetric traffic requirement has not been investigated. In this study, we focused on subcarrier transmission mode selection, bit loading, and power allocation in a multicarrier single amplified-and-forward relay system. In this scheme, each subcarrier can operate in two transmission modes: one-way relaying and two-way relaying. The problem is formulated as a mixed integer programming problem. We adopt a structural approximation optimization method that first decouples the original problem into two suboptimal problems with fixed subcarrier subsets and then finds the optimal subcarrier assignment subsets. Although the suboptimal problems are nonconvex, the results obtained for a single-tone system are used to transform them to convex problems. To find the optimal subcarrier assignment subsets, an iterative algorithm based on subcarrier ranking and matching is developed. Simulation results show that the proposed method can improve system performance compared with conventional methods. Some interesting insights are also obtained via simulation.

• Korean Journal of Materials Research
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• v.24 no.3
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• pp.123-128
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• 2014

To realize high-performance thin film solar cells, we prepared CIGS by the co-evaporation technique on both sodalime and Corning glass substrates. The structural and efficient properties were investigated by varying the thickness of the Mo:Na layer, where the total thickness of the back contact was fixed at 1${\mu}m$. As a result, when the Mo:Na thickness was 300 nm on soda-lime glass, the measured Na content was 0.28 %, the surface morphology was a plate-like compact structure, and the crystallinity by XRD showed a strong peak of (112) preferential orientation together with relatively intense (220) and (204) peaks as the secondary phases influenced crystal formation. In addition, the substrates on soda-lime glass effected the lowest surface roughness of 2.76 nm and the highest carrier density and short circuit current. Through the optimization of the Mo:Na layer, a solar conversion efficiency of 11.34% was achieved. When using the Corning glass, a rather low conversion efficiency of 9.59% was obtained. To determine the effects of the concentration of sodium and in order to develop a highefficiency solar cells, a very small amount of sodium was added to the soda lime glass substrate.

• Journal of Ocean Engineering and Technology
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• v.27 no.2
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• pp.27-32
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• 2013

A valve is a marine structure that is subjected to multiple seawater loads. Therefore, it is necessary to define the kind of loads applied to it to confirm whether the structure has sufficient strength. In this research, we aimed to find the optimal solution for the stress and deformation of valves under various loads. We first selected design variables and implement a finite element analysis according to changes in the thickness of each component of a valve based on a central composite design. Next we developed a regression model of the response surface. Using this model, we calculated the optimal objective value based on NSGA-II. Finally, to confirm the correspondence between the optimal objective value and the real FEM value, we compared the optimal result and structural analysis result to verify the performance of NSGA-II.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.31 no.2 s.257
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• pp.245-252
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• 2007

Since the new millennium, truss PCMs(Periodic Cellular Metals) have drawn attention because of their superior specific stiffness, strength and multi-functionality. Prior studies have focused on the structural design and optimization. Kagome truss PCM has been proved to have the higher resistance to plastic buckling, more plastic deformation energy and lower anisotropy than other truss PCMs. In this study, we introduce a new idea to fabricate multi-layered Kagome truss PCM from continuous wires which can gain high strength as in piano wires and can be controlled to be defect free owing to drawing process. The relative density, the stiffness and the strength under bending and compressive load are estimated through elementary mechanics and compared with the results from experiments and FEA. The failure mechanisms are analyzed, and also mechanical performance and production are discussed.