• 유공압시스템학회논문집
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• 제7권1호
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• pp.20-27
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• 2010

Electromagnetic control valves have been used for almost 20 years. As the solenoid modulating technology advances, its applications are extending to various industrial fields such as nuclear and fossil fuel power plants, chemical plants and refineries. Proportional solenoid valve for large flow control is designed with two-stage configuration to meet the required actuating force on the main disc and its position is stabilized by the self-controlled system. In this research, main disc dynamics is analyzed with linearized system model which is derived from the mathematical equations describing its nonlinear behavior. Major design parameters of the valve control system that affect the response and stability are also studied with root locus method. The linear dynamic analysis results are verified with simulations in time-domain.

• 조명전기설비학회논문지
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• 제26권8호
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• pp.88-95
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• 2012

When controling combustion air flow in coal fired power plant the furnace safety must be considered first prior to plant efficiency. therefore it is very important to set air flow demand exactly for safe operation and maintenance. This paper analyze air flow control loop in power plant and introduce the method to improve dynamic response time. Simulation result shows this scheme is adoptable and provide better performance.

• 연구논문집
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• 통권29호
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• pp.123-130
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• 1999

Flow divider valve는 한 개의 공급라인에서 두 개 이상의 출력라인으로 유압유를 일정비율로 분배하는 유압제어밸브로서 하중압력이나 공급압력 등에 관계없이 항상 일정비율의 유량분배가 가능해야 한다. 현재 상용제품의 유량분할 정확도는 90~95% 수준이며, 이러한 유량분할오차(Flow dividing error)는 유압시스템에 누적오차로 작용하여 많은 문제점을 야기시키고 있어 보다 고정밀 유량제어가 가능한 Flow divider valve 개발이 요구된다. 본 연구에서는 외력을 고려한 스푸울의 거동을 수치적으로 정확하게 조사하여 Flow divider valve의 동특성을 규명함과 동시에 유량분할 오차를 감소시키는 최적설계방안을 제시하고자 한다. 동특성 해석은 일정한 하중저항을 입력신호로 작용하는 경우에 대해서 제시하였으며, 이때의 고정오리피스와 가변오리피스의 단면적 및 스푸울의 단면적 변화에 따른 동특성의 변화를 조사하였다.

• 한국정보통신학회논문지
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• 제9권8호
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• pp.1683-1690
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• 2005

본 논문에서는 UDP에서의 동적 흐름 제어기법을 제안하며, 기존의 동적 흐름제어에서 많이 사용되는 측정 요소인 패킷 손실과 왕복시간의 특성에 대해 분석한 후 새로운 측정요소인 RSTT를 제안한다. 제안된 RSTT를 사용한 알고리즘은 전송률을 조절하는데 있어서 현재 측정된 네트워크 상태와 과거의 상태를 고려함으로써 보다 정확한 네트워크 상태측정을 할 수 있었다. 비교실험을 위하여 전송량과 네트워크의 상태를 출력하고 네트워크의 흐름패턴에 대한 상세 정보를 보여주는 네트워크 상태측정 프로그램을 구현하였다. 이를 이용한 성능실험을 통해 제안된 알고리듬이 기존 알고리듬에 비해 낮은 패킷 손실률로 네트워크 상태에 더욱 빠르게 적응함을 보여준다.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2009년 춘계학술대회논문집
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• pp.19-19
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• 2009

Dynamic Stall is a flow phenomenon which occurs on the retreating side of helicopter rotor blades during forward flight. It also occurs on blades of stall regulated wind turbines under yawing conditions as well as during gust loads. Time scales occurring during this process are comparable on both helicopter and wind turbine blades. Dynamic Stall limits the speed of the helicopter and its manoeuvrability and limits the amount of power production of wind turbines. Extensive numerical as well as experimental investigations have been carried out recently to get detailed insight into the very complex flow structures of the Dynamic Stall process. Numerical codes have to be based on the full equations, i.e. the Navier-Stokes equations to cover the scope of the problems involved: Time dependent flow, unsteady flow separation, vortex development and shedding, compressibility effects, turbulence, transition and 3D-effects, etc. have to be taken into account. In addition to the numerical treatment of the Dynamic Stall problem suitable wind tunnel experiments are inevitable. Comparisons of experimental data with calculated results show us the state of the art and validity of the CFD-codes and the necessity to further improve calculation procedures. In the present paper the phenomenon of Dynamic Stall will be discussed first. This discussion is followed by comparisons of some recently obtained experimental and numerical results for an oscillating helicopter airfoil under Dynamic Stall conditions. From the knowledge base of the Dynamic Stall Problems, the next step can be envisaged: to control Dynamic Stall. The present discussion will address two different Dynamic Stall control methodologies: the Nose-Droop concept and the application of Leading Edge Vortex Generators (LEVoG's) as examples of active and passive control devices. It will be shown that experimental results are available but CFD-data are only of limited comparison. A lot of future work has to be done in CFD-code development to fill this gap. Here mainly 3D-effects as well as improvements of both turbulence and transition modelling are of major concern.

• 한국생산제조학회지
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• 제19권6호
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• pp.883-888
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• 2010

This study have goal with conceptual design for Offshore Structures of high pressure control valve for localization. Ball valve for development accomplished with flow analysis based on provision of ANSI B16.34, ANSI B16.10, ANSI B16.25 In order to localize the Offshore Structures high pressure control valve. Numerical simulation using CFD (Computational Fluid Dynamic) in order to predict a mass flow rate and a flow coefficient form flow dynamic point of view. The working fluid assumed the glycerin (C3H8O3). The valve inlet and outlet setup a pressure boundary condition. The outlet pressure was fixed by atmospheric pressure and calculated until increasing 1bar to 10bar. CFD analysis used STAR-CCM+ which is commercial code and Governing equations were calculated by moving mesh which is rotated 90 degrees when ball valve operated opening and closing in 1 degree interval. The result shows change of mass flow rate according to opening and closing angle of valve, Flow decrease observed open valve that equal percentage flow paten which is general inclination of ball valve. Relation with flow and flow coefficient can not be proportional according to inlet pressure when compare with mass flow rate. Because flow coefficient have influence in flow and pressure difference. Namely, flow can be change even if it has same Cv value. The structural analysis used ANSYS which is a commercial code. Stress analysis result of internal pressure in valve showed lower than yield strength. This is expect to need more detail design and verification for stem and seat structure.

• 설비공학논문집
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• 제15권6호
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• pp.480-488
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• 2003

The purpose of this research Is to derive the principal design parameters governing the dynamic characteristics of the high response flow control servo valve. For this purpose, a numerical modeling of the servo valve system and a parameter sensitivity analysis to a frequency response characteristics was peformed. As a result of these analysis, a basis for improvement of a dynamic characteristics of servo valve was arranged.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1992년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 19-21 Oct. 1992
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• pp.724-729
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• 1992

A transient hydraulic flow rate computation scheme is described here so that the transient hydraulic flow rate can be determined using the dynamic pressure measurements at the ends of a straight flowline with a dynamic, model of the hydraulic line. Simulation results indicate that the method is relatively robust to realistic levels of uncertainties in the fluid properties.

• 대한기계학회논문집B
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• 제20권1호
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• pp.284-294
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• 1996

In this paper, dynamic characteristics of an AT clutch system were investigated considering the dynamics of check ball and hydraulic control valves. Dynamic model of a pressure control solenoid valve (PCSV) was obtained by Bondgraph and permeance method. Also, the clutch piston and check ball dynamics were modeled by considering the effect of centrifugal force of the oil entrapped in the clutch chamber. In order to validate the dynamic models obtained, plunger displacement of PCSV and pressure response of the clutch supply lines were compared with the available experimental data, which were in good accordance with the numerical results. Using the dynamic model of the clutch system, simulations were performed to investigate the effect of the rotational speed on the response of clutch cylinder pressure, clutch piston and check ball displacement, and oil flow rate into the cylinder and flow rate out of the check valve.

• Journal of Power Electronics
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• 제16권5호
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• pp.1743-1751
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• 2016

The increasing demand for high voltage DC grids resulting from the continuous installation of offshore wind farms in the North Sea has led to the concept of multi-terminal direct current (MTDC) grids, which face some challenges. Power (current) flow control is a challenge that must be addressed to realize a reliable operation of MTDC grids. This paper presents a reduced switch count topology of a current flow controller (CFC) for power flow and current limiting applications in MTDC grids. A simple control system based on hysteresis band current control is proposed for the CFC. The theory of operation and control of the CFC are demonstrated. The key features of the proposed controller, including cable current balancing, cable current limiting, and current nulling, are illustrated. An MTDC grid is simulated using MATLAB/SIMULINK software to evaluate the steady state and dynamic performance of the proposed CFC topology. Furthermore, a low power prototype is built for a CFC to experimentally validate its performance using rapid control prototyping. Simulation and experimental studies indicate the fast dynamic response and precise results of the proposed topology. Furthermore, the proposed controller offers a real solution for power flow challenges in MTDC grids.