• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2017년도 학술발표회
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• pp.271-271
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• 2017

상수관망 수리해석 기법은 절점의 사용량 및 누수량을 기지의 값으로 고려하여 총 수요량이 모두 공급될 수 있다고 가정하여 해석하는 수요기반해석(Demand Driven Analysis, DDA)과 사용량과 누수량은 절점 압력수두에 의해 달라질 수 있어, 공급가능량 및 누수량과 절점의 압력수두 모두를 미지수로 고려하여 해석하는 수압기반해석(Pressure Driven Analysis, PDA)으로 구분될 수 있다. 본 연구에서는 수압기반사용량 모의(Pressure Dependent Demand, PDD)와 수압기반누수량 모의(Pressure Dependent Leakage, PDL)기능이 모두 구현되고, 다양한 시나리오 분석이 가능한 소프트웨어(SW)인 K-NRisk를 개발하였다. K-NRisk는 2016년 7월에 공개된 상수관망 해석범용모형인 EPANET3 소스코드 기반으로 개량 개발되었으며, 기존 EPANET2와 비교하였을 경우 사용자 편의성 증대를 위한 입출력 기능 및 SW 활용도 제고를 위한 대표업무분석 기능이 신규 개발, 강화되었다. 개발된 SW를 관망정비 및 공급안정성 확보 목적을 위한 수리해석 시 적용하여 그 결과를 분석하였다. 적용결과 기존 수요기반해석이 가지고 있는 한계점을 보완하고, 실제업무 시 활용가능함을 확인하였다.

• 한국수소및신에너지학회논문집
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• 제23권5호
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• pp.521-529
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• 2012

Since the energy demand for refrigeration and air-conditioning has greatly increased all over the world, thermally activated refrigeration cycle has attracted much attention. This study carries out a performance analysis of a vapor compression cycle (VCC) driven by organic Rankine cycle (ORC) utilizing low-temperature heat source in the form of sensible heat. The ORC is assumed to produce minimum net work which is required to drive the VCC without generating an excess electricity. Effects of important system parameters such as turbine inlet pressure, condensing temperature, and evaporating temperature on the system variables such as mass flow ratio, net work production, and coefficient of performance (COP) are thoroughly investigated. The effect of choice of working fluid on COP is also considered. Results show that net work production and COP increase with increasing turbine inlet pressure or decreasing condensing temperature. Out of the five kinds of organic fluids considered $C_4H_{10}$ gives a relatively high COP in the range of low turbine inlet pressure.

• Journal of Advanced Marine Engineering and Technology
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• 제25권2호
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• pp.304-310
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• 2001

This paper describes the analysis of flow field using a projection finite element method. The projection scheme with a pressure correction is presented for the analysis of an incompressible Navier-Stokes flow. The projection scheme is analyzed numerically and applied to the well-known bench marking problems such as lid driven cavity. Finally, the projection scheme is applied to a flow through the automobiles front. In the automobiles cooling system, the flow through its front is very important to a cooling performance. The results show that the flow quantity increases by locating the position of bumper to the further front position of a car. And, the improvement on the suction part below a bumper achieves the more passing flow quantity. The attachment of an air dam increases passing flow quantity causing the pressure rise to the front part and the pressure drop beneath a car.

• 대한기계학회논문집
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• 제18권3호
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• pp.624-634
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• 1994

A numerical method which combines equal-order velocity-pressure formulation originated from SIMPLE algorithm and streamline upwinding method has been developed. To verify the proposed numerical method, we considered the lid-driven cavity flow and backward facing step flow. The trend of convergence history is stable up to the error criterion beyond which the maximum value of error is oscillatory due4 to the round-off error. In the present study, all results were obtained with the single precision calculation up to the given error criterion and it was found to be sufficient for our purpose. The present results were then compared with existing experimental results using laser doppler velocimetry and numerical results using finite difference method and mixed interpolation finite element method. It has been shown that the present method gives accurate results with less memories and execution time than the coventional finite element method.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 2002년도 춘계학술대회 논문집
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• pp.680-683
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• 2002

In this paper, it has been investigated that the design and simulation of vacuum pump driven by linear motor. Vacuum pump consists of unified plunger and piston part, coils, inlet valve and outlet valve. Operating principal of vacuum pump show that air is to flow to go inside through the inlet valve when the magnetic force (16N) is exerted, whereas, air is to flow to go outside through outlet valve when spring farce (14.8N) is exerted. The results of simulation. it was turned out that reached vacuum pressure was about -0.55 bar at 150 seconds, magnetic force was loaded with 16 Newton, displacement of actuator was about 8mm.

• 한국전산유체공학회지
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• 제4권2호
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• pp.39-46
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• 1999

The FVM(Finite Volume Method) have been used mainly for the flow analyses in the piston-cylinder. The objective of the present study is to analyze numerically the piston-driven intake flows using the FEM(Finite Element Method). The FEM algorithm used in this study is 4-step time-splitting method which requires much less execution time and computer storage than the velocity-pressure integrated method and the penalty method. And the explicit Lax-Wendroff scheme is applied to nonlinear convective term in the momentum equations to prevent checkerboard pressure oscillations. Also, the ALE(arbitrary Lagrangian Eulerian) method is adopted for the moving grids. The calculated results show good agreement in comparison with those by the FVM and the experimental results by the LDA.

• 한국압력기기공학회 논문집
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• 제19권1호
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• pp.44-51
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• 2023

The RCP is one of the main components in nuclear power plants and plays an important role in circulating coolant to the RCS system. Currently, nuclear plants are monitored using various monitoring systems. However, since they operate independently according to their functional purpose, it is not able to analyze vibration and operation/performance information comprehensively, and thus failure diagnosis accuracy is limited. In addition, these systems do not provide some important information (such as fault type, parts and cause) necessary for emergency actions, but provide only alarm information. To improve these technical problems, this study proposes a diagnosis technique (M/L, Rule-based model, Data-driven model, Narrow band model) and methodology for comprehensive analysis.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1989년도 한국자동제어학술회의논문집; Seoul, Korea; 27-28 Oct. 1989
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• pp.1-6
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• 1989

For the design of synergistic hydraulic motion simulator, the load locus method is introduced. The given mass property of load and its velocity profile is resolved into the load locus of each actuator which decides the suitable valve and cylinder. This asymmtic cylinder and 4 way valve system have the pressure oscillation on zero velocity. The variable structure position controller which based on linearized flow equation makes elimination of the unstable pressure oscillation.

• 한국유체기계학회 논문집
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• 제5권1호
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• pp.55-61
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• 2002

The feasibility of an oil-free, motor-driven, two-stage centrifugal compressor supported by air bump bearings is investigated. This centrifugal compressor is driven by a 75 kW motor at an operating speed of 39,000 RPM, and a pressure ratio of the compressor is set up to 4. The analysis is performed by using bearing equilibrium position, heaving stillness, Campbell diagram, unbalance response, and stability. It is demonstrated in this paper that air bump bearings can be adopted well to an oil-free, motor-driven, centrifugal compressor. Specially, Cu-coated bump bearings have enough damping force to reduce a synchronous unbalance for rigid modes of the two-stage compressor. Futhermore, this concept may be applied to the flexible rotor system such as high speed turbomachinery with a super critical speed.

• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2001년도 유체기계 연구개발 발표회 논문집
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• pp.469-474
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• 2001

The feasibility of a oil-free motor-driven two-stage centrifugal compressor supported by air bump bearings is investigated. This centrifugal compressor is driven by 75kW motor at an operating speed of 39,000RPM md a pressure ratio of the compressor is up to 4. The analysis is performed, based upon bearing equilibrium position, bearing stiffness, Campbell diagram, unbalance response and stability. It is demonstrated in this paper that air bump bearings can be adopted well to a oil-free motor-driven centrifugal compressor.