• Transactions of the Korean Society of Mechanical Engineers
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• v.11 no.5
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• pp.781-788
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• 1987

The state variables estimated in an observer were useed in feedback control of a hydraulic servosystem to increase the system stability and to enhance the system performance. The nonlinear hydraulic servosystem with the inherent nonlinearities due to the square root function of flow equation, the Coulomb friction and so on, was modelled as a fourth order linear hydraulic servosystem. Also, a second order linear system was derived for the observer-controller design. For these models, a fourth order linear observer and a second order linear observer were constructed respectively to evaluate the performance of the observer-based hydraulic servosystem. The results obtained from series of simulation showed that the system which had shown oscillatory phenomenon under proportional control became stable with the same maximum acceleration and velocity that it had started under proportional control.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.20 no.2
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• pp.115-121
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• 2010

Periodic vortex separations generate periodic vertical forces acting on a trailing edge of an airfoil. When a natural frequency of the trailing edge of the airfoil is close to a vortex shedding frequency, an amplitude of the edge oscillation becomes maximal; it makes intensive noise called singing. Motion of the trailing edge may also feedback to the vortex shedding so that self-sustained oscillation appears, and a resonant frequency is locked in some interval of the speed of the incident flow. In this study, a theoretical model is proposed and applied for modeling an airfoil singing. Results are compared with experimental measurements which are carried out in an anechoic wind tunnel.

• Journal of The Korean Association For Science Education
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• v.25 no.6
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• pp.642-649
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• 2005

Argumentative discussion is one of the important components of an educational program, which allows students not only to learn the process of social negotiation through discussions, but also to improve students' overall research abilities. The purpose of this study was to examine a) the changes between inquiry of before-argumentative discussion and inquiry of after-argumentative discussion, and b) the connections between the inquiry changes and online argumentative discussion. This study analysed 726 messages in an online argumentative discussion, as well as in first research reports and second research reports. The results of the study indicate that science-gifted students' research abilities were improved through on-line argumentative discussion that provided them with feedback based on interactive discussions, and encouraged them to re-examine hypotheses and experiment processes. The science-gifted students showed knowledge and abilities for identifying simple errors in research processes and arguing problems in the flow of the whole logic of research.

• Proceedings of the KSME Conference
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• 2008.11a
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• pp.917-922
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• 2008

In order to reduce energy consumption, secondary controlled system has been applied to many types of equipments. In lifting equipments or press machines using hydraulic cylinder, a hydraulic transformer is used as a control component instead of a valve for motion control and a component for recovering potential energy of load. The transformer is combination of a variable displacement pump/motor as a secondary controlled element and a fixed displacement pump/motor. Based on the nominal model derived from mathematical model, the feedback type two-degree-of-freedom controller is designed and implemented. From simulation results, the disturbances including nonlinear friction torque, leakage flow and load force can be compensated and good positioning accuracy is obtained. It show that the proposed controller is effective.

• Journal of Korean Society for Geospatial Information Science
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• v.5 no.2 s.10
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• pp.29-43
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• 1997

An integrated optimal control modelhas been formulated to address dynamic freeway diversion control process. The purpose of this paper is to develop an effective and efficient approach for simultaneous]v solving optimal control measures, including on-ramp metering rates, off-ramp diversion rates, and g/C ratios for traffic signals, on a real-time basis. By approximating the flow-density relation with a two-segment linear function, the non-linear optimal control problem can be simplified into a set of piece-wised linear programming models and solved with the proposed SLP algorithm. consequently, an effective on-line feedback method has been developed for integrated freeway corridor control in the framework of the ITS

• Korean System Dynamics Review
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• v.2 no.2
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• pp.97-118
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• 2001

To solve the policy problem between transportation and environment in trade-offs, above all, it is necessary to understand the complicated relationship between transportation and environment clearly before selecting policy alternatives. From this point of view, this study will propose the logic structure to examine the complex interaction of transportation and environment and investigate theoretically what kinds of impact would appear by the air related polices. In this research, we used ’system-dynamics’ which investigates the complexity through the flow of information and materials and the interaction of elements, which constitutes systems. System Dynamics is an approach that the variables to decide structural relationship in a system affect one another not in only-way but in inter-way and the power of influence changes time by time. This research is trying to examine the complex interaction of transportation and air pollution. For achieving this purpose, causal maps in System Dynamics approach were used. The main issues are as follows; first, to investigate the dynamic relationship between transportation and air pollution caused by exhaust emission gas. Second, to structuralize the logic of simulation to experiment the impacts of policies to relieve air pollution.

• Journal of Biosystems Engineering
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• v.25 no.1
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• pp.11-18
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• 2000

In precision chemical application increment of biological efficacy with less chemical is the virtue. spraying rate and droplet size is closely related to biological efficacy. this study was performed to develope a spray-control-system that could control spraying rate and droplet size independently. Twin-fluid nozzles were selected and tested to certify if the nozzles were suitable for the objective of this study. Characteritics of the nozzles i.e., spraying rte and droplet size change u8nder the changes of spraying pressure and air pressure were statistically modeled. The model had I to 1 matching property between dependent variables and independent variables. Using the property and the model, inverse relationship could be determined between variables. A feedback spray control system was developed and tested with predetermined error of 5 % in pressure. The system showed 4 % error in spraying rate and 9 % error in droplets size. Performance of the system could be upgraded by fine tuning but, in practical sense keeping air pressure in the field sprayer was the bottle neck of commercialization of the spray system.

• 한국연소학회:학술대회논문집
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• 2002.11a
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• pp.223-229
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• 2002

Spark plug ionization signal could be useful in an internal combustion engine as a feedback signal for combustion diagnostics such as misfire detection, knocking detection and lambda control, but the signal has high level of cyclic fluctuation in an internal combustion engine due to residual gas, pressure, temperature, mixture composition in the spark gap. Because of this reason it is very difficult to apply ion signal to commercial engine control. In this Study, a correlation between A/F and spark plug ionization signal was studied in a constant volume chamber. Constant volume chamber with gas phase fuel(Propane) has homogeneous fuel composition , no mixture flow, same pressure and temperature on each test. The results show that mean chemi-ion signal has the highest correlation with A/F and intial pressure change has on effect on the thermal-ion signal and not on chemi-ion signal.

• Journal of Korean Society for Quality Management
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• v.25 no.4
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• pp.185-205
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• 1997

Reliability management requires many activities such as conceptual design, detail design, reliability evaluation and analysis, life testing, and environmental screening, etc.. To perform these activities effectively, a lot of information are required : information for failure mechanism, failure modes, part characteristics, and environmental conditions, etc.. These information should be managed to be used effectively and accurately in reliability activities and feedback to product design and manufacturing. This study identified and characterized these information and classified them according to the reliability activities commonly adopted in many manufacturing industries. IDEF1 was used to define and characterize the flow and the relationship of these reliability information and model is proposed which represents the structure of reliability information systems. The proposed model can be used as a basis for developing reliability management softwares.

• Journal of the korean Society of Automotive Engineers
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• v.13 no.5
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• pp.73-80
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• 1991

Air/fuel ratio control system for gasoline engines has been analyzed to determine the control gain of the system. In this analysis the engine is modelled to be a simple time delaying element and the ramp-and-jump method is used to control air/fuel ratio. The result shows that it is necessary to measure the air flow rate accurately to enhance the control performance. And also it is shown that the control gain must be determined in some bounded region to meet the fast dynamic response and high catalyst conversion efficiency together.