• Journal of the Korean Society for Aviation and Aeronautics
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• v.24 no.1
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• pp.55-61
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• 2016

In this work a guidance and control system for an a powered ram air parafoil under wind disturbance is considered. After analyzing a 6 Dof and 9 Dof nonlinear dynamic models of the parafoil, wind effect is added to them. In order to actively respond to the wind acting on the transverse direction of the vehicle a new guidance algorithm is proposed. After a Hardware-In-the-Loop Simulation (HILS) study, flight tests are performed to demonstrate its potential under wind disturbances.

• The Korean Journal of Ecology
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• v.16 no.3
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• pp.305-316
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• 1993

Stands profiles, yearly changes in growth of annual rings, age and diameter structure, and spatial distribution pattern of individuals in the Pinus densiflora stands around the Yeocheon industrial complex were investigated. Growth of annual ring in Pinus densiflora, which survived when vegetation of this area was damaged by air pollutants, was suppressed for about 10 years since 1974 when factories in this area began to operate, but since then such suppressed growth tended to be recovered. It was supposed that the suppresed growth was originated from air pollution and that improvement of growth since the suppressed period was due to the release from competition with them by death of neighbouring trees and the resuction of the amount of air pollutants. Physiognomy of Pinus densiflora stands showed mosaic pattern composed of different patches. Spatial distribution pattern of individuals an stand profiles were similar to those of Pinus densiflora stands regenerated after natural and artificial disturbances. In an age distribution diagram, age of Pinus densiflora population ranged from 1 to 33 years, Among these individuals were recrited corresponded to the suppresed period of growth of annual ring in Pinus densiflora survived when the vegetation was damaged by air pollution. On the other hand, from the result of analysis of frequency distribution diagram of diameter, it was postulated that even if whis Pinus densiflora community can be maintained as it is for the time being, it might be changed to Quercus community with the lapse of time.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.4
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• pp.711-719
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• 2002

This paper presents the synchronous vibration control of a rotor system using an active air bearing(AAB). In order to suppress the synchronous vibration, it is necessary to actively control the air film pressure or the air film thickness. In this study, active pads are used to control the air film thickness. Active pads are supported by pivots containing piezoelectric actuators and their radial position can be actively controlled by applying voltage to the actuators. Thus, disturbances, i. e. various kinds of external force can cause shaft vibration as well as change of the air film thickness. The dynamic behavior of a rotary system supported by two tilting-pad gas bearings and its active stabilization using the tilting-pads as actuators are investigated numerically. The $\mu$ synthesis are applied to the AAB system with three pads, two of which contain piezoelectric actuators. To test the validity of the theoretical method, the performance of this control method is evaluated through experiments. The experimental results also show the effectiveness of the control system for suppressing the unbalanced response of the rigid modes.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.185-190
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• 2007

In recent days, vibration isolation system is mostly required in precise measurement and manufacturing system to reduce vibration due to external disturbances and internal actuators. Among all the vibration isolation systems, air spring is widely used because of its low resonant frequency and high damping ratio. In this study, we first analyze the passive air-spring system using leveling valve, and then design the active vibration isolation system. Because the non-linearity of pneumatic characteristics, we try to design the fuzzy controller which is better than PID controller at complex and non-linear system, and then compare them both in experiment and simulation.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.6 no.4
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• pp.380-387
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• 1994

An experimental study was performed to investigate the characteristics of refrigerant flow rate control and superheat in an evaporator with an electronic expansion valve(EEV). The EEV used in this study was devised using a needle valve coupled with a stepping motor controlled by a personal computer. A Pill control equation was used to control the superheat of the evaporator and to set the superheat to $5^{\circ}C$. In order to determine an optimum running condition for the system, Pill parameters were varied for the wide range of values. The running condition of an air conditioning system with a PI control was reasonably stable compared with that of the Pill control. Experimental results for the PI control using parameter values, $K_p=1.5$, $T_i=400(sec)$ and $T_s=6(sec)$ show that the superheat reached its target value. When external disturbances were introduced to the system, the superheat target value was reached within about 3 minutes. When the EEV was applied to the air conditioning system driven by an inverter, room temperature control was excellent.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
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• v.25 no.2
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• pp.85-93
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• 2013

The proportional plus integral(PI) feedback control manner has been used in many general industrial fields such as refrigeration system because of its simple design process and favorable control performance. This paper deals with optimized PI controller design of the refrigeration system based on evaluation functions such as integrated absolute error(IAE). The suggested optimal PI gains can be easily calculated by a simple program and the optimal controllability satisfying the evaluation function can be assured. Furthermore, at the initial step of controller design, the suggested optimal gain is able to reflect some noise disturbances caused by an inverter which drives variable speed compressors. The validity of the suggested optimal gain is investigated by some simulations and experiments to verify its efficiency. From the results of comparing control performance between the optimal PI controller based on the evaluation function and the PI controller designed by the Matlab tuner which was known as the most popular gain tuner, the optimal PI controller showed more desirable control performance especially in transient responses.

• Proceedings of the SAREK Conference
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• 2009.06a
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• pp.961-966
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• 2009

This paper presents precise temperature control of oil outlet in an oil cooler with hot-gas bypass control as an industrial refrigerator. The control system was designed for obtaining precise temperature control performance even though abrupt disturbances based on flow rate control of hot-gas bypass. PID controller was adopted in feedback control system. We showed that the gain of PID could be easily determined by using gain-tuning methods without any numerical model. Through some experiments, excellent control performances such as overshoot within 1.7%, steady state temperature error within ${\pm}0.1^{\circ}C$ were established by a simple PI controller. We expect that the system can control the target temperature within error of $0.33^{\circ}C$ under abrupt disturbances.

• International Journal of Automotive Technology
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• v.8 no.5
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• pp.637-650
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• 2007

A new on-line fault detection and isolation(FDI) scheme has been proposed for engines using an adaptive neural network classifier; this paper investigates the robustness of this scheme by evaluating in a wide range of operational modes. The neural classifier is made adaptive to cope with the significant parameter uncertainty, disturbances, and environmental changes. The developed scheme is capable of diagnosing faults in the on-line mode and can be directly implemented in an on-board diagnosis system(hardware). The robustness of the FDI for the closed-loop system with crankshaft speed feedback is investigated by testing it for a wide range of operational modes, including robustness against fixed and sinusoidal throttle angle inputs, change in load, change in an engine parameter, and all changes occurring simultaneously. The evaluations are performed using a mean value engine model(MVEM), which is a widely used benchmark model for engine control system and FDI system design. The simulation results confirm the robustness of the proposed method for various uncertainties and disturbances.

• Nuclear Engineering and Technology
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• v.56 no.3
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• pp.832-845
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• 2024

Reactor cavity cooling systems (RCCSs) comprising passive safety features use the atmosphere as a coolant, which cannot be lost. However, their drawback is that they are easily affected by atmospheric disturbances. To realize the commercial application of the two types of passive RCCSs, namely RCCSs based on atmospheric radiation and atmospheric natural circulation, their safety must be evaluated, that is, they must be able to remove heat from the reactor pressure vessel (RPV) surface at all times and under any condition other than under normal operating conditions. These include both expected and unexpected natural phenomena and accidents. Moreover, they must be able to eliminate the heat leakage emitted from the RPV surface during normal operation. However, utilizing all of the heat emitted from the RPV surface increases the degree of waste heat utilization. This study aims to understand the characteristics and degree of passive safety features for heat removal by comparing RCCSs based on atmospheric radiation and atmospheric natural circulation under the same conditions. It was concluded that the proposed RCCS based on atmospheric radiation has an advantage in that the temperature of the RPV could be stably maintained against disturbances in the ambient air.

• Proceedings of the KSME Conference
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• 2007.05a
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• pp.1120-1125
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• 2007

Experimental study on the control of randomly disturbing system is conducted. External and internal disturbances are imposed to the system in combined manner. A vertical propeller system exposed horizontal weak turbulent air flow is chosen as an experimental model. The aim of the control system is to maintain the angular position of vertical propeller in parallel to air flow. Trajectory Tracking Stochastic Controller (TTSC) is designed to ensure system's stability while following system command. The Trajectory Tracking Stochastic Controller is composed of two controller, one is stochastic controller to suppress internal random noise and the other one is trajectory-tracking controller to follow the command having random noise. The proposed hybrid controller, TTSC, shows remarkable performance in pitch control of vertical propeller system in wind-tunnel test