• 한국전산유체공학회:학술대회논문집
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• 2010.05a
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• pp.581-583
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• 2010

The report summarizes research activities in the Multiscale Energy System Laboratory at Sogang University during September 2009 and February 2010. They are mostly about molecular dynamics simulation of osmotic flows at nanoscale.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.18 no.4
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• pp.465-472
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• 2008

An automotive windshield wiper system is modeled mainly for vibration analysis purpose. The model is composed of solid links, ideal joints, imperfect joints to simulate unavoidable manufacturing defects and bushings having stiffness, contact between a wiper blade and a wind screen glass, friction, a spring and an actuator. Main stream of wiper dynamics analysis has been obtaining a closed form of system of equations using Newton's or Lagrange's formula and doing a numerical simulation study to understand and predict the behavior of it. However, the modeling process is complex since a wiper system is of multibody and a contact problem occurs. When imperfection, such as dead zone of a joint and stiffness of a rubber bushing, should be included, the added complexity makes the modeling difficult. Since the imperfection is understood as main cause of problematic vibration, the dynamics model of a wiper system aiming vibration analysis should include such unavoidable manufacturing defects in the model. An open form of dynamic model of a automotive windshield wiper system with imperfect joints using a commercial software is obtained and a simulation analyssis is conducted for vibration reduction study.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.928-942
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• 2020

The pressure responsiveness property of a skirt-cushion system, which is closely related to the overall performance of Air Cushion Vehicles (ACVs), has always been the difficulty and challenging problem involving cushion aerodynamics and flexible skirt dynamics. Based on a widely used bag and finger skirt-cushion system, the pressure responsiveness properties are investigated numerically. The physical process and mechanism are analyzed and a numerical method for evaluating the pressure responsiveness property is proposed. A cushion-skirt information communication platform is also presented for interchanging the force and the skirt configuration between cushion aerodynamics and flexible skirt dynamics. The pressure responsiveness of a typical skirt-cushion system is calculated and the results demonstrate that the pressure responsiveness property helps alleviate the influence of the cushion height changing on the overall performance of ACVs. Finally, the influences of skirt geometrical and cushion aerodynamic parameters on the pressure responsiveness properties are discussed systematically, giving insight into the design of skirt-cushion systems.

• Korean System Dynamics Review
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• v.17 no.3
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• pp.91-120
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• 2016

This study explores hedge fund characteristics that affect hedge fund performance, namely, fund size, fund age, and performance fee. Previous studies have examined relationships between hedge fund characteristics and fund performance using singular and static thinking to report inconsistent findings without providing full understanding of the causal relationships among variables. To identify that comprehensive causal relationships between hedge fund characteristics and hedge fund performance, this research applies the system dynamics perspective, which allowed demonstration of the interactions within the overall system beyond the singular causal relationships between hedge fund characteristics and performance found in existing traditional research. This study contributes to existing literature in the following ways. First, it overcomes the limitations of singular research methodologies by looking at the integrated system of hedge fund characteristics and fund performance from a bird's eye view based on their dynamic feedback relationships. Second, policy suggestions in terms of regulation and education are presented as growth strategies for the sustainable development of the Korean hedge fund market.

• Transactions on Control, Automation and Systems Engineering
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• v.1 no.2
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• pp.94-98
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• 1999

Optical scanning systems use glavanometers to point the laser beam to the desired position on the workpiece. The angular speed of a galvanometer is typically controlled using Proportional+Integral+Derivative(PID) control algorithms. However, natural variations in the dynamics of different galvanometers due to manufacturing, aging, and environmental factors(i.e., process uncertainty) impose a hard limit on the bandwidth of the galvanometer control system. In general, the control bandwidth translates directly into efficiency of the system response. Since the optical scanning system must have rapid response, the higher control bandwidth is required. Auto-tuning PID algorithms have been accepted in this area since they could overcome some of the problems related to process uncertainty. However, when the galvanometer is attached to a larger mechanical system, the combined dynamics often exhibit resonances. It is well understood that PId algorithms may not have the capacity to increase the control bandwidth in the face of such resonances. This paper compares the achieable performance and robustness of a galvanometer control system using a PID controller tuned by the Ziegler-Nichols method and a controller designed by the Quantitative Feedback Theory(QFT) method. The results clearly indicate that-in contrast to PID designs-QFT can deliver a single, fixed controller which will supply high bandwidth design even when the dynamics is uncertain and includes mechanical resonances.

• The Transactions of the Korean Institute of Electrical Engineers D
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• v.51 no.5
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• pp.182-189
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• 2002

This paper presents a framework of hybrid dynamic control systems for the motion control of wheeled mobile robot systems with nonholonomic constraints. The hybrid control system has the 3-layered hierarchical structure: digital automata for the higher process, mobile robot system for the lower process, and the interface as the interaction process between the continuous dynamics and the discrete dynamics. In the hybrid control architecture of mobile robot, the continuous dynamics of mobile robots are modeled by the switched systems. The abstract model and digital automata for the motion control are developed. In high level, the discrete states are defined by using the sensor-based search windows and the reference motions of a mobile robot in low level are specified in the abstracted motions. The mobile robots can perform both the motion planning and autonomous maneuvering with obstacle avoidance in indoor navigation problem. Simulation and experimental results show that hybrid system approach is an effective method for the autonomous maneuvering in indoor environments

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.38 no.1
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• pp.57-67
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• 2020

Recently, smart cities are attracting attention as a solution for a plethora of urban problems, including transportation, environment, safety, and energy. However, despite a substantial body of research dealt with the concept, trends, policy, and legal institutions of smart cities, few researchers have examined how the smart city services influence the cities from the dynamic perspective that considers the entire cycle of a city, including its growth, stagnation, and decline. Thus, it is vital to understand how the city changes with time from the view that a city is a system of sub-elements-population, industry, transportation, environment, housing, and land-closely interacting together. Within this context, this study explores how the urban dynamics of Anyang-city develop for the long term using the System Dynamics method and analyzes the effect of smart city project investment on the dynamics of Anyang-city. According to the result, Anyang-city is a "mature and stable" type, and its population is expected to decrease slowly by 2040. Specifically, the Anyang-city population will be reduced to 553,000 by 2030. It was analyzed that the number will decrease to 543,000 by 2040. It was also found that the investment in smart city projects in Anyang, based on the Plan for Anyang Smart City, would have the following effects: easing population decline, increasing number of businesses, improving urban safety index, and increasing average driving speed. The population will grow by 4,000 and the number of businesses will increase by 761 than before budget investment. The result of this paper is expected to contribute to identifying and predicting the effect of smart city policies from a long-term perspective.

• Korean System Dynamics Review
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• v.12 no.2
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• pp.5-36
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• 2011

Seoul citizens are currently suffering from high housing price. Home prices have risen more rapidly than salaries so owning a housing unit (apartment, condominium, or single-family home) in Seoul is becoming more difficult than ever. Therefore, this research examines the behavior of average Seoul citizen in owning housing unit in Seoul, Korea, particularly in terms of the length of time required to afford a house unit. This research estimates that it will take about 18.75 years in maximum after getting a job (12.75 years after purchasing the housing unit) to own housing unit in Seoul that is currently valued at $300,000 where the growth rate of income is 2.97% and consumption price increases at a rate of 2.95% per annum. Finally in this research, the optimal growth rate of housing price is estimated ranged from 3.5 to 4.0% minimizing the loan payoff period.

• Korean System Dynamics Review
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• v.5 no.1
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• pp.35-47
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• 2004

Analyzers adopt a variety of techniques in analyzing public policy. Based on the results of exploration, they explain problems and suggest prescriptions such as policy alternatives. By doing so, however, they have different degree of confidence in their own results according to what techniques they adopt. This study explores whether system dynamics apporach gives analyzers more confidence on their own simulation results than other approaches do. This study designed an experiment. Three research teams are organized. Each of them applies different analytic techniques on the same policy issue, i.e., introduction of transportation tax. It flnds that researchers using S,D. simulation technique are most confident on what they predict, while researchers adopting survey techniques show moderate degree of confidence on their results. Researchers using regression are least confident.

• Proceedings of the KIEE Conference
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• 1997.11a
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• pp.113-115
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• 1997

This paper presents an efficient method which can estimate the system with unmodeled dynamics using D-L networks. The proposed method is to estimate system with unmodeled dynamics recursively from only input-output information, which can exclude additional procedure for system description and thus reduce the required computational burden for real-time estimation. Higher convergence speed is achieved with our manner when compared with widely-used conventional methods.