• Journal of the Korean Institute of Intelligent Systems
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• v.26 no.2
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• pp.127-134
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• 2016

This paper presents a robust control of a reaction wheel inverted pendulum. To this end, a mathematical model is derived using physical laws, and then parameters in the model are identified as well. Based on the model, a robust position control is designed, which consists of two parts: swing-up control using passivity and robust stabilization control using LMI (Linear Matrix Inequality). When the pendulum starts to move, the swing-up control is applied. If the position of the pendulum is near the desired upright position, the control is switched to the robust stabilization control. This robust control is employed in order to deal with the uncertainties in the inertia of the pendulum dynamics. The performance of the proposed control scheme is validated not only simulation but also real experiment.

• Journal of the Korean association of regional geographers
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• v.12 no.4
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• pp.508-521
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• 2006

The results of environmental equity analysis vary dramatically depending on different methods used. The information and data available to the researcher are also often uncertain and imprecise in empirical studies. A sensitivity analysis approach was used too handle uncertainties and methodological inconsistencies in environmental equity analysis. This paper explores the sensitivity of environmental equity analysis to two spatial measures such as proximity and scale. Two experiments were implemented to evaluate the effects of two spatial measures on the environmental equity analysis using a combination of control and experimental factors. Fulton County, Georgia was selected as a case study area for these experiments. Two major data sets including demographic characteristics and toxic release inventory (TRI) database for the study area in 1990 were integrated into a GIS environment. Two statistical analyses such as independent samples t-test and coefficient of variation were performed to determine the environmental equity in the study area and to compare the relative variability in the socioeconomic characteristics of populations over different spatial measures. The findings from two experiments indicate that the outcomes of environmental equity analysis are slightly sensitive to the buffer distance used to determine the impact zones of TRI facilities, but not to the geographic scale used in the analysis. The findings also suggest that the consequences of these choices can alter spatially and statistically the results in environmental equity analysis.

• Journal of the Korean Society of Propulsion Engineers
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• v.6 no.1
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• pp.21-29
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• 2002

Hybrid propulsion systems provide many advantages in terms of stable operation and safety. However, classical hybrid rocket motors have lower fuel regression rate and combustion efficiency compared to solid propellant rocket motor. The recent research efforts are focused on the improvement of volume limitation and regression rate in the hybrid rocket engine. The present study has numerically investigated the combustion processes in the hybrid rocket engine. The turbulent combustion is represented by the eddy breakup model and Hiroyasu and Nagle and Strickland-Constable model are used for soot formation and soot oxidation. Radiative heat transfer is modeled by finite volume method. To reduce the uncertainties for convective heat transfer near solid fuel surface having strong blowing effect, the Low Reynolds number $\kappa-\varepsilon$ turbulent model is employed. Based on numerical results, the detailed discussion has been made for the turbulent combustion processes in the vortex hybrid rocket engine.

• Journal of Technology Innovation
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• v.23 no.4
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• pp.89-121
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• 2015

Recently, national energy policy tends to be approached with the long-term perspective because it became harder to cope with various energy issues fundamentally only through the short-term and piecemeal approaches. To deal with energy policy from a long-term perspective, we need new governing approach that differs from established short-term perspective. In this context, research efforts to apply transition management theory to long-term energy policy are receiving attention. In this paper, we suggest extended transition management model based on case study of Dutch energy transition model and review the transition management traits of long-term energy policy of Korea. We conclude that transition thinking and approaches are diffusing widely in the long-term energy policy formation processes, but also can find various issues that are needed to be addressed for effective transition management especially in the energy policy implementation processes.

• Journal of the Korea institute for structural maintenance and inspection
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• v.8 no.4
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• pp.153-163
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• 2004

The main objective of this study is to develop a multi-objective fuzzy optimum design program of steel structures and to verify that the multi-objective fuzzy optimum design is more reasonable than the single objective optimum design in real structural design. In the optimization formulation, the objective functions are both total weight and deflection. The design constraints are derived from the ultimate strength of service ability requirement of AISC-LRFD specification. The structural analysis was performed by the finite element method and also considered geometric non-linearity. The different importance of optimum criteria were reflected with two weighting methods ; membership weighting method and objective weighting method. Thus, designers could choose rational optimum solution of structures with application of two weighting methods.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.26 no.5C
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• pp.313-322
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• 2006

Liquefaction of soil foundation is one of the major seismic damage types for infrastructures. In this paper, deterministic and probabilistic approaches for the evaluation of liquefaction potential are briefly summarized and the risk assessment method is newly proposed using seismic fragility and seismic hazard analyses. Currently the deterministic approach is widely used to evaluate the liquefaction potential in Korea. However, it is very difficult to handle a certain degree of uncertainties in the soil properties such as elastic modulus and resistant capacity by deterministic approach, and the probabilistic approaches are known as more promising. Two types of probabilistic approaches are introduced including (1) the reliability analysis (to obtain probability of failure) for a given design earthquake and (2) the seismic risk analysis of liquefaction for a specific soil for a given service life. The results from different methods show a similar trend, and the liquefaction potential can be more quantitatively evaluated using the new risk analysis method.

• Journal of Korean Society of Steel Construction
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• v.12 no.5 s.48
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• pp.503-513
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• 2000

This study treats the criteria, considering the fuzziness occurred by optimization design. And we applied two weighting methods to show the relative importance of criteria. This study develops multi-objective optimization programs implementing plain stress analysis by FEM and discrete optimization design uniformaly. The developed program performs a sample design of 10-member steel truss. This study can carry over the multi-objective optimization based on total system fuzzy-genetic algorithms while performing the stress analysis and optimization design. Especially, when general optimization with unreliable constraints is cannot be solve this study can make optimization design closed to realistic with fuzzy theory.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.3
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• pp.9-20
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• 1989

It is important to enhance the safety of ship structures as much as possible in order to prevent the disastrous collapse of structures. In fact, the strength problem of structures is closely related with the safety problem of structures. Recently, the direct calculation method using a rational approach based on the first principle is implemented into the structural design process instead of adopting empirical approach based on the rules. The structural designer have shown increased concern with the problem of adequacy of conventional design method based on the safety factor since it does not fully take into account some degree of variability of the applied loads on and the strength of ship structures. To deal with the analysis of structures effectively, it is necessary to have three stages being equally treated. The first one is load analysis, second one response analysis, third one safety analysis. For marine structures, most of research effort has been however put into the first and second stages. The third stage is normally done by simple procedures. Hence, the various probabilistic methods are compared in order to establish the reliability analysis techniques for ship structures. As a result, the advanced level 2 method is selected as a most effective and accurate reliability method. The validity of this method is further demonstrated by comparing the results with the conventional method for the problem of the longitudinal strength of hull girder of Ro-Ro ship.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.41 no.4
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• pp.417-428
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• 2021

Since future maintenance cost estimation of infrastructure involves uncertainty, it is important to make use of a failure prediction model. However, it is difficult for local governments to develop accurate failure prediction models applicable to infrastructure due to a lack of budget and expertise. Therefore, this study estimated the life expectancy of asphalt road pavement of national highways using the Bayesian Markov Mixture Hazard model. In addition, in order to accurately estimate life expectancy, environmental variables such as traffic volume, ESAL (Equivalent Single Axle Loads), SNP (Structural Number of Pavement), meteorological conditions, and de-icing material usage were applied to retain reliability of the estimation results. As a result, life expectancy was estimated from at least 13.09 to 19.61 years by region. By using this approach, it is expected that it will be possible to estimate future maintenance cost considering local failure characteristics.

• Journal of the Institute of Electronics Engineers of Korea SC
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• v.44 no.3
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• pp.64-69
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• 2007

Motion control of the system is a position control of motor. Motion control of an uncertain robot system is considered as one of the most important and fundamental research directions in the robotics. Some distinguished works using linear control, adaptive control, robust control strategies based on computed torque methodology have been reported. However, it is generally recognized within the control community that these strategies suffer from the following problems : the exact robot dynamics are needed and hard to implement, the adaptive control cannot guarantee the performance during the transient period for adaptation under the variation, the robust control algorithms such as the sliding mode control need information on the bounds of the possible uncertainty and disturbance. And it produces a large control input as well. In this dissertation, a motion control for the unmanned intelligent robot system using disturbance observer is studied. This system is affected with an impact vibration disturbance. This paper describes a stable motion control of the system with the consideration of external disturbance. To obtain the stable motion independently against the external disturbance, the disturbance rejection is strongly required. To address the above issue, this paper presents a Disturbance OBserver(DOB) control algorithm. The validity of the suggested DOB robust control scheme is confirmed by several computer simulation results. And the experiments with a motor system is performed to give the validity of applicability in the industrial field. This results make the easier implementation of the controller possible in the field.