• 전기학회논문지
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• 제57권11호
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• pp.1954-1961
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• 2008

Microgrid usually consists of a cluster of distributed generators(DGs), energy storage systems and loads, and can operate in the grid-connected mode and the islanded mode. This paper presents detailed descriptions of two different options for controlling the active power of DGs in the microgrid. One is regulating the power injected by the unit to a desired amount(Unit output power control) and the other is to regulate the flow of active power in the feeder where the unit is installed to a constant(Feeder flow control). Frequency-droop characteristics are used to achieve good active power sharing when the microgrid operates in the islanded mode. The change in the frequency and the active power output of DGs are investigated according to the control mode and the configuration of DGs when the microgrid is disconnected from the main grid. From the analysis, this paper proposes a method to determine the droop constant of DGs operating in the feeder flow control mode. Simulation results using the PSCAD/EMTDC are presented to validate the approach, which shows good performance as opposed to the conventional one.

• 한국전산유체공학회지
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• 제11권4호
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• pp.62-66
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• 2006

High-speed flight vehicle have various cavities. The supersonic cavity flow is complicated due to vortices, flow separation, reattachment, shock waves and expansion waves. The general cavity flow phenomena includes the formation and dissipation of vortices, which induce oscillation and noise. The oscillation and noise greatly affect flow control, chemical reaction, and heat transfer processes. The supersonic cavity flow with high Reynolds number is characterized by the pressure oscillation due to turbulent shear layer, cavity geometry, and resonance phenomenon based on external flow conditions. The resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, we performed numerical analysis of cavities by applying the unsteady, compressible three dimensional Reynolds-Averaged Navier-Stokes(RANS) equations with the ${\kappa}-{\omega}$ turbulence model. The cavity model used for numerical calculation had a depth(D) of 15mm cavity aspect ratio (L/D) of 3, width to spanwise ratio(W/D) of 1.0 to 5.0. Based on the PSD(Power Spectral Density) and CSD(Cross Spectral Density) analysis of the pressure variation, the dominant frequency was analyzed and compared with the results of Rossiter's Eq.

• 드라이브 ㆍ 컨트롤
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• 제12권3호
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• pp.52-59
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• 2015

An electro hydraulic poppet valve (EHPV) and a variable orifice poppet are assembled in a single block, which is referred to as a RHINO but is also generally called a pilot-operated flow control valve. In this study, we analyzed the structure and the operating principle for a RHINO applied in a 21-ton electric excavator system. The RHINO was experimentally tested to measure the dynamic responses and the pressure energy loss. In this test, we investigated the variation in the conductance coefficient according to the increase in the supply pressure under a constant current and a variation in the flow rate according to the increase in the current. Then, the geometrical shapes and the spring stiffness of the RHINO were considered to develop an analysis model. The characteristics (current-force and hysteresis) for the solenoid based on the experimental data were reflected in the analysis model that was developed, and the reliability of the analysis model was also verified by comparing the experimental and analytical results. The developed model is thus considered to be reliable for use in a wide range of applications, including optimum design, sensitivity analysis, parameter tuning, etc.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2002년도 학술대회지
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• pp.603-606
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• 2002

Numerical analysis and its inverse design process of 2nd stage of JT8D aircraft engine is described. One of the most important factors that affect the performante of turbomachine is secondary flow in the blade passage, so that the performance of turbomachine can be improved by controlling secondary flow. In this paper, as a method to control secondary flow, commercial inverse design program, TurboDesign is used. Meridional derivative of angular momentum is selected as a parameter to control blade leading in this program, To validate inverse designed model, computational analysis is applied which includes rotor-stator-interaction. In this paper, CFB results of both original and inverse designed model are compared to examine how much the performance improves without reduction of work output.

• 제어로봇시스템학회논문지
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• 제18권2호
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• pp.110-117
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• 2012

This paper describes a new design of optical flow estimation system with three cameras. Optical flow provides useful information of camera movement; however a unique solution is not usually available for unknowns including the depth information. A camera and two tilted cameras are used to have different view of angle and direction of movement to the camera axis. Geometric analysis is performed for cases of several independent movements. The ideas of taking advantage of the extra information for robot navigation are discussed with experimental results.

• 한국생산제조학회지
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• 제22권3호
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• pp.465-471
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• 2013

Flow rate control is the uppermost concern for a trochoid hydraulic pump. Cavitation within the flow field of the pump has the greatest effect on the flow control during high-speed pump rotation of approximately 3500~4000 RPM. In this paper, based on AMESim$^{(R)}$ and Solid Works$^{(R)}$, we will present a method to simulate cavitation by analyzing the control factors of a trochoid pump, including the hydraulic pressure change at the outlet, flow rate based on the rotation speed of the inner rotor, leakage through the gap between the outer and inner rotors, and discharging angle of the outlet. The proposed methodology of the [cavitation simulation will enable field engineers to more easily design trochoid pumps, and will allow more concrete control over the flow rate of the pump by realizing an analysis model similar to the actual product model.

• 한국산학기술학회논문지
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• 제17권7호
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• pp.734-739
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• 2016

선형으로 움직이는 글로브 밸브의 목적은 주로 유량을 제어할 수 있도록 설계 되어 있으며, 디스크의 움직임으로 인해서 유량을 제어가 가능하게 된다. 본 논문은 유량계수를 예측하기 위해서 전산유동해석 프로그램인 ANSYS-CFX로 유동해석을 진행 하였고 본 해석에서 사용되는 글로브 밸브 모델을 시제품과 동일한 형상의 크기로 설계하였다. 유량계수는 밸브 전개 시 $16.5^{\circ}C$의 맑은 물이 전후의 압력차 1psi로 흐를 때 그때의 유량을 말한다. 다시 말해서 밸브의 크기를 결정할 수 있는 중요한 요인이 된다. 밸브의 유량계수와 유량을 해석을 통해서 얻어낼 수 있었고, 그 해석으로 인해서 분당 0~0.1gal 유량을 제어할 수 있는 정밀제어 글로브 밸브를 개발 할 수 있었다. 유동해석과 실험의 결과로 유량계수를 서로 비교하였으며 그 결과로 인해서 유량계수의 오차율이 매우 작음을 확인하였고, 해석의 신뢰성을 확보하였다. 따라서 실험 없이 해석만으로 충분히 유량계수의 경향성을 파악하는데 크게 어려움이 없음을 보여주었다.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2010년도 춘계학술대회 논문집
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• pp.279-280
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• 2010

• 한국지하수토양환경학회:학술대회논문집
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• 한국지하수토양환경학회 2005년도 INTERNATIONAL SYMPOSIUM ON SOIL & GROUNDWATER ENVIRONMENT
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• pp.195-196
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• 2005

• 드라이브 ㆍ 컨트롤
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• 제11권1호
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• pp.8-13
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• 2014

Hydraulic servo valves are widely used in various fluid power systems because of their fast response and precision control. In this paper, we studied the effect of metering notch shapes and amount of their openings on the flow characteristics within the spool valve using a computational fluid dynamic (CFD) code, FLUENT. To obtain the results for more realistic operating conditions, viscous heating due to the jet flow and viscosity variation of the hydraulic fluid with temperature were considered. For two types of notch shape, streamlines, oil temperature and viscosity distributions, and variations of flow and friction forces acting on spool were showed. The flow and friction forces affected by the metering notch shapes and their openings, and oil temperature rise near metering notch was significant enough to results in the jamming phenomenon. A thermohydrodynamic (THD) flow analysis adopted in this paper can be used in optimum design of hydraulic servo valves.