• Journal of Advanced Marine Engineering and Technology
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• v.20 no.3
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• pp.110-120
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• 1996

The purpose of this study is to build up the control scheme that promptly controls the pressure in a hydraulic cylinder having small control volume, using a PCV(proportional control valve) and a digital computer. Object pressure control system has the character to be unstable easily, because the displacement-flow gain of the PCV is so large considering comparatively small volume of the hydraulic cylinder and the time delay of response of PCV is long. Considering the above-mentioned characteristics of the object pressure control system, in this study, a control system is designed with two degree of freedom scheme that is composed by adding a feed-forward control path to I-PD control system, and the reference model is used to decide control parameters. And through some experiments on FF-I-PD, the validity of this control method is confirmed.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.1
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• pp.387-392
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• 2020

This paper proposes a flow-rate control system for industrial valves. Industrial valves are used in piping systems to control the flow rate and pressure. In general, valves used in pipelines are classified into globe valves, butterfly valves, and ball valves according to the shape. Motor, hydraulic, and pneumatic systems are used for operating valves. The flow meter should measure the flow rate when configuring the flow-rate control system. On the other hand, because the flow rate of the valve can be expressed by flow coefficient, a control scheme is proposed using the pressure deviation, which measures at the front and rear of the valve. The transfer function for the valve, according to the control input, was estimated using the signal compression method. Based on the induced transfer function, the disturbance observer was designed to improve the command following the performance of the valve stem. The performance of the proposed control method is compared with the flow-rate control result using the flow meter used.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.49 no.9
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• pp.729-738
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• 2021

Feedback flow control using an artificial neural network was numerically investigated for NACA0015 Airfoil to suppress flow separation on an airfoil. In order to achieve goal of flow control which is aimed to reduce the size of separation on the airfoil, Blowing&Suction actuator was implemented near the separation point. In the system modeling step, the proper orthogonal decomposition was applied to the pressure field. Then, some POD modes that are necessary for flow control are extracted to analyze the unsteady characteristics. NARX neural network based on decomposed modes are trained to represent the flow dynamics and finally operated in the feedback control loop. Predicted control signal was numerically applied on CFD simulation so that control effect was analyzed through comparing the characteristic of aerodynamic force and spatial modes depending on the presence of the control. The feedback control showed effectiveness in pressure drag reduction up to 29%. Numerical results confirm that the effect is due to dramatic pressure recovery around the trailing edge of the airfoil.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.35 no.8
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• pp.825-829
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• 2011

We performed a dynamic characterization of passive flow-rate regulators, which compensate for inlet pressure variation and maintain a constant flow rate for precise liquid control in microfluidic systems. To measure the flow rate for a short time, much less than the period of the dynamic inlet pressure, we use the particle image velocimetry (PIV) method. DI water containing fluorescent beads with a $0.7-{\mu}m$ diameter was supplied to the flow-rate regulators, and two successive images of the particles were taken by a pulse laser and a fluorescent microscope to measure the flow velocity. For a dynamic inlet pressure of frequency 60 Hz, the flow velocity was constant with an average of 0.194 ${\pm}$ 0.014 m/s as the inlet pressure varied between 20 kPa to 50 kPa. The flow-rate regulators provided a constant flow rate of $5.82{\pm}0.29\;{\mu}l/s$ in the frequency range of the inlet pressure from 1 Hz to 60 Hz.

• Journal of the Korean Society of Propulsion Engineers
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• v.16 no.3
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• pp.34-40
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• 2012

A pressure control law to regulate pressure of gas generator is suggested. To design a model based control law, the governing equation which consists of Robert and conservation equation is built and verified through the ground burning test. PID and nonlinear adaptive control laws are designed to analyze the loop response characteristics under the system which has varying eigen properties arisen from combustion volume change. It is suggested that new approach, gain scheduling design, is required to overcome the defects identified from numerical simulation results of the two control laws. The newly suggested scheme shows good control performance even under disturbances and measurement noise.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.11a
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• pp.618-623
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• 2011

A pressure control law to regulate pressure of gas generator is suggested. To design a model based control law, the governing equation which is consisted of Robert and conservation equation is built and verified through the ground burning test. PID and nonlinear adaptive control laws are designed to evaluate the loop response characteristics under the system which has varying eigen properties as combustor volume is increased. It is suggested that new approach, gain scheduling design, is required to overcome the defects identified from numerical simulation results of the two control laws. The newly suggested scheme showed good control performance even under disturbances and measurement noise.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2006.11a
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• pp.363-366
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• 2006

The effectiveness of two passive control techniques for alleviating the pressure oscillation generated in a supersonic cavity flow is investigated numerically. The passive devices suggested in the present research include a triangular bump and a sub-cavity installed near the upstream edge of a rectangular cavity. The supersonic cavity flow characteristics are examined by using the three-dimensional, unsteady Wavier-Stokes computation based on a finite volume scheme. Large eddy simulation (LES) is carried out to properly predict the turbulent features of cavity flow. The results show that the pressure oscillation near the downstream edge dominates overall time-dependent cavity pressure variations. Such an oscillation is attenuated more considerably using the sub-cavity compared with other methods, and a larger sub-cavity leads to better control performance.

• Proceeding of EDISON Challenge
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• 2013.04a
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• pp.387-392
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• 2013

본 연구에서는 천음속 전투기 무장창 내부의 압력 진동을 제어하기 위해 F-111의 무장창을 2차원 공동(Cavity)으로 모델링하고, EDISON_전산열유체 시스템을 활용하여 공동의 형상 변화에 따라 발생하는 유동 특성을 분석하였다. 최근의 전투기들은 항력 감소와 스텔스 기능을 위해 무기를 기체 안에 내장하는데, 덮개를 열 때 발생하는 공동 형상에 의해 강한 압력 진동이 유발된다. 이러한 진동은 무장창과 주변 기계 장치에 구조적 진동을 일으키고 고장 또는 파괴를 유발하므로, 근본적인 해결책이 필요한 중요한 문제이다. 본 연구에서는 진동의 원인이 되는 전단층(Shear layer) 불안정성을 해결하기 위해 기존에 연구된 형상(Leading edge extension 및 Ramp)과 본 연구에서 새로 제안한 Ramp extension을 적용해 보았다. 그 결과 압력 진동의 원인이 되는 유동 특성이 줄어들고 압력 진동 역시 감소했음을 관찰할 수 있었다.

• Proceedings of the Korean Nuclear Society Conference
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• 1996.05a
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• pp.594-601
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• 1996

가압기고압력 원자로정지여유도(high pressurizer pressure trip margin)에 영향을 주는 요인들에 대한 민감도 분석을 울진 3,4호기 성능해석코드인 LTCUCN computer code틀 이용하여 수행하였다. 그 결과, 초기 가압기압력, 증기우회제어계통의 quick open지연시간, 터빈우회밸브의 quick opening시간, 원자로출력 감발계통의 용량, 원자로출력감발 제어붕 낙하시간, 가압기 살수작동 설정치 둥이 완전부하상실시 가압기압력을 상승시키는 주요인자임을 알 수 있었으며, 증기우회제어계통 및 가압기살수계통의 용량은 최대 가압기 압력에 미치는 영향이 미미한 것으로 판명되었다. 울진 3,4호기의 참조발전소인 영광 3,4호기의 as-built 자료를 토대로 울진 3,4호기의 원자로정지여유도를 계산한 결과 울진 3,4호기는 완전부하상실사건시 37 psi의 정지여유도를 가질 수 있는 것으로 판단된다. 그러나, 원자로출력감발계통이 있는 ABB-CE type의 울진 3,4호기에서는 완전부하상실사건보다 원자로출력감발계통이 동작하지 않는 부하감발사건이 최대 가압기 압력치를 유발하는 사건이고, 다양한 부하상실사건중에도 운전여유도는 확보하고 있음을 알 수 있었다.

• Tunnel and Underground Space
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• v.28 no.3
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• pp.247-257
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• 2018

High-speed trains have been developed widely in many countries in order to transport large quantity of people and commodities rapidly. When a high speed train enters a tunnel, aerodynamic resistance is generated suddenly. The resistance caused from air pressure induces micro pressure wave and discomfort to passengers in a train. Therefore, a pressure relief system should be installed in a tunnel to reduce the resistance acting against the running train in a tunnel. Additionally, the shape of a grain should be streamlined in order to reduce aerodynamic resistance caused by a high-speed train. The cross-section of a tunnel also should be carefully designed to reduce discomfort of passengers. This study represents the effect of pressure relief ducts installed between two running tunnels. The pressure relief duct was integrated with a cross-passage in order to save cost and construction time. One-dimensional network numerical simulations were carried out in order to estimate the effect of pressure relief systems.