• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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• pp.375-380
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• 2007

This paper presents optimal design of controllable magnetorheological (MR) shock absorbers for passenger vehicle. In order to achieve this goal, two MR shock absorbers (one for front suspension; one for rear suspension) are designed using an optimization methodology based on design specifications for a commercial passenger vehicle. The optimization problem is to find optimal geometric dimensions of the magnetic circuits for the front and rear MR shock absorbers in order to improve the performance such as damping force as an objective function. The first order optimization method using commercial finite element method (FEM) software is adopted for the constrained optimization algorithm. After manufacturing the MR shock absorbers with optimally obtained design parameters, their field-dependent damping forces are experimentally evaluated and compared with those of conventional shock absorbers. In addition, vibration control performances of the full-vehicle installed with the proposed MR shock absorbers are evaluated under bump road condition and obstacle avoidance test.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.27 no.5
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• pp.328-341
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• 2014

The object of this paper is to develop optimal optical filter, which can be used to identify the financial account and read the information. The five factors which affect the performance of the optical filter are identified as optical glass type, existence of Fe, Photo pic coating type, and coating form. In this study we seek to determine the optimal combination for the best design of the optical filter. For each combination, the performances of optical filter are investigated using the proper experimental equipments and methods. White-state voltage, black-state voltage, and black-state error rate are used for the performance measures. Through the statistical analysis of the performance data collected, we have determined the optimal design of the optical filter.

• International Commerce and Information Review
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• v.9 no.2
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• pp.65-86
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• 2007

This paper reviews the properties and application methods of widely used types of risk measures, identifies the rationale and business-side effects of hedging, derives the theoretical formula of optimal hedging ratio, and analyzes the various functional aspects of VaR(Value-at-risk) as a risk measure and a hedging tool. Especially this paper focuses on the characteristics of VaR compared with other risk measures in terms of their own principal determinants and identifies its stronger aspects in the dimension of hedging strategy tools. As well, this paper provides the detailed processes deriving the optimal hedge ratios based on the distributional parameters and risk factors. In addition, this paper presents the detailed and substantial processes of estimating the minimum variance hedge ratio and minimum-VaR hedge ratio using the actual data and shows that the minimum variance hedge ratio proves helpful for many cases although it is not appropriate for the non-linear portfolio including the option contracts. We demonstrate the trade-off relationship between the minimum variance hedge strategy and the minimum-VaR hedge strategy in their hedging costs and performances through calculation of the respective VaRs and variances of unhedged and hedged portfolios and the optimal hedge ratio and hedging effectiveness values for the given long position in US Dollar with the short position in Euro.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.2
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• pp.169-176
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• 2008

This paper presents optimal design of controllable magnetorheological(MR) shock absorbers for passenger vehicle. In order to achieve this goal, two MR shock absorbers (one for front suspension; one for rear suspension) are designed using an optimization methodology based on design specifications for a commercial passenger vehicle. The optimization problem is to find optimal geometric dimensions of the magnetic circuits for the front and rear MR shock absorbers in order to improve the performance such as damping force as an objective function. The first order optimization method using commercial finite element method(FEM) software is adopted for the constrained optimization algorithm. After manufacturing the MR shock absorbers with optimally obtained design parameters, their field-dependent damping forces are experimentally evaluated and compared with those of conventional shock absorbers. In addition, vibration control performances of the full-vehicle installed with the proposed MR shock absorbers are evaluated under bump road condition and obstacle avoidance test.

• Journal of Ocean Engineering and Technology
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• v.2 no.2
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• pp.37-45
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• 1988

A dynamically positioned vessel must be capable of maintaining a specified position and direction by controlling the thruster devices. The motions of a vessel are often assuned to tne sum of low frequency(LF)motions and high frequency(HF)motions. The former is mainly due to wind, current and second order wave forces, while the latter is mainly due to first order wave forces. In order to avoid the high frequency thruser modulation, the control system must include filters to estimate the low frequency motions from the measured motion signals, This paper presents a control system based on Kalman filtering technique and optimal control tyeory. Using the combined kalmam filter, LF motion estimates and HF ones are achieved from the motion measurement of the vessel. The estimated low frequency motions are used as inputs to the dynamic positioning system. The thruster modulation is minimized using the optimal control theory; Linear Quadratic Gaussian(LQG)controller. The performances of the Kalman filter and the dynamic positioned vessel are investigated by computer simulation.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.25 no.10
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• pp.677-684
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• 2015

It is often necessary to predict the vibration patterns of the structures from the signals of finite number of vibration sensors. This study presents the optimal placement of vibration sensors by applying the genetic algorithm and the modal expansion method. The modal expansion method is used to estimate the vibration response of the whole structure. The genetic algorithm is used to estimate the optimal placement of vibration sensors. Optimal sensor placement can be obtained so that the fitness function is minimized in the genetic algorithm. This paper discusses the comparison of the performances of two types of fitness functions, modal assurance criteria(MAC) and condition number( CN). As a result, the estimation using MAC shows better performance than using CN.

• Structural Engineering and Mechanics
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• v.86 no.2
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• pp.249-260
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• 2023

The uncertainties involved in structural performances are of importance when the optimum number and property of seismic retrofit devices are determined. This paper proposes a seismic retrofit design framework for asymmetric soft-first-story buildings, considering uncertainties in the soil condition and seismic retrofit device. The effect of the uncertain parameters on the structural performance is used to find a robust and optimal seismic retrofit solution. The framework finds a robust and optimal seismic retrofit solution by finding the optimal locations and mechanical properties of the seismic retrofit device for different realizations of the uncertain parameters. The structural performance for each realization is computed to evaluate the effect of the uncertainty parameters on the seismic performance. The framework utilizes parallel processing to decrease the computationally intensive nonlinear dynamic analysis time. The framework returns a robust design solution that satisfies the given limit state for every realization of the uncertain parameters. The proposed framework is applied to the seismic retrofit design of a five-story asymmetric soft-first-story case study structure retrofitted with a viscoelastic damper. Robust optimal parameters for retrofitting a structure to satisfy the limit state for the different realizations of the uncertain parameter are found using the proposed framework. According to the performance evaluation results of the retrofitted structure, the developed framework is proved effective in the seismic retrofit of the asymmetric structure with inherent uncertainties.

• Journal of the Earthquake Engineering Society of Korea
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• v.12 no.2
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• pp.9-22
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• 2008

This paper presents an integrated optimal design technique of a hybrid structure-damper system for improving the seismic performance of the structure. The proposed technique corresponds to the optimal distribution of the stiffness and dampers. The multi-objective optimization technique is introduced to deal with the optimal design problem of the hybrid system, which is reformulated into the multi-objective optimization problem with a constraint of target reliability in an efficient manner. An illustrative example shows that the proposed technique can provide a set of Pareto optimal solutions embracing the solutions obtained by the conventional sequential design method and single-objective optimization method based on weighted summation scheme. Based on the stiffness and damping capacities, three representative designs are selected among the Pareto optimal solutions and their seismic performances are investigated through the parametric studies on the dynamic characteristics of the seismic events. The comparative results demonstrate that the proposed approach can be efficiently applied to the optimal design problem for improving the seismic performance of the structure.

• Journal of Korean Society of Forest Science
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• v.104 no.1
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• pp.90-97
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• 2015

The objective of this study was to find optimal amount of fertilization of container seedling production for Zelkova serrata, Ulmus parvifolia, Betula costata and Tilia amurensis. To reach our goal, we measured root collar diameter (RCD), height, biomass and seedling quality index (SQI) of container seedlings of four deciduous hardwood species grown at three different fertilization treatments ($0.5g{\cdot}L^{-1}$, $1.0g{\cdot}L^{-1}$ and $2.0g{\cdot}L^{-1}$). Z. serrata seedlings grown at $2.0g{\cdot}L^{-1}$ fertilization and B. costata seedlings grown at $0.5g{\cdot}L^{-1}$ fertilization showed the highest RCD, height, biomass and SQI. The RCD and height of U. parvifolia and T. amurensis seedlings showed no significant differences by fertilization treatments. Seedlings of two species at $0.5g{\cdot}L^{-1}$ fertilization showed the lowest SQI, however, SQI at 1.0 and $2.0g{\cdot}L^{-1}$ fertilization treatments were not significantly different. Based on these results, it is appeared that container seedlings of Z. serrata at minimum $2.0g{\cdot}L^{-1}$ fertilization, U. parvifolia and T. amurensis at $1.0g{\cdot}L^{-1}$ fertilization and B. costata at maximum $0.5g{\cdot}L^{-1}$ fertilization were optimal nutrient conditions. Practice of optimal fertilization rate will make us get better quality seedlings and reduction of production costs in the container nursery system as well as good field performances with higher survival rate after planting.

• Journal of Korea Technology Innovation Society
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• v.11 no.4
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• pp.431-449
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• 2008

I analyzed the relationships among motives, strategies, and performances of the university-initiated R&D activities in the Information Technology Research Center(ITRC) Projects. I suggested a research model and 3 hypothesis about them through analysis of a lot of literatures. And I also made an empirical test on the hypothesis through statistical methods. The data which were used in this analysis were gathered through a questionnaire survey to the head of R&D projects in the ITRCs. I would make several useful suggestions to the head of university's ITRCs and the policy makers. Firstly, the type of university's R&D strategy were influenced from several motives such as technology development and acquisition, co-utilizations of research facilities, and utilization and rearing of the expertise. Secondly, to select an optimal type of R&D strategy, the university should considered the efficient methods which were related to forecasting market size of new product and new technology, and to using the useful information on technology development, and to securing the expertise. Thirdly, the researcher and manager of ITRCs had to recognize the correct forecast of future market size of new product and new technology and a useful information about technology development, as the most important factors in improving performances of R&D projects. Lastly, They had to make an effort of getting the efficient methods to secure the expertise, research facilities, and rational compensation system.