• 한국환경과학회지
• /
• 제20권9호
• /
• pp.1151-1163
• /
• 2011

The bed change analysis near the opening gate of a dam or weir to release deposited sediments have been conducted mostly using the numerical models. However, the use of unverified input parameters in the numerical model is able to produce the different results with natural and real conditions. Also, the bed changes near the opening gate of a dam or weir calculated with a numerical model could be varied depending on the geometry extent included the downstream area with supercritical flow in the model. In addition, the different time steps could provide different results in the bed change calculation, even though other conditions such as input parameters, geometries, and total simulation time were same. Therefore, in this study, hydraulic experiments were performed to validate the eddy viscosity coefficient which is the one of important input parameters in the RMA2 model and relevant to variation of simulation results. The bed changes were calculated using the SED2D model based on flow results calculated in the RMA2 model with the verified and selected eddy viscosity coefficient and also compared with experimental results. The bed changes near the opening gate were underestimated in the numerical model comparing with experimental results except only the numerical case without the modeling section of sediment release pipe and downstream area where the supercritical flow was produced. For the simulation of minimum time steps, different shapes of scour hole were produced in numerical and physical modeling.

• 한국지반공학회:학술대회논문집
• /
• 한국지반공학회 2006년도 춘계 학술발표회 논문집
• /
• pp.414-423
• /
• 2006

Many construction projects adopt grouting technology to prevent the leakage of groundwater or to improve the shear strength of the ground. Recognition as a feasible field procedure dates back to 1925, Since then, developments and field use have increased rapidly. According to improvement of grout materials, theoretical study on grout penetration characteristics is demanded. Fluid of grout always tends to flow from higher hydraulic potential to lower and the motion of grout is also a function of formation permeability. Viscosity of grout is changed by chemical action while grout moves through pores. Due to the increment of viscosity, permeability is decreased. Permeability is also reduced by grout particle deposits to the soil aggregates. In this thesis, characteristics of new cement grout material that is developed recently is studied: injectable volume of new grout material is tested in two different sizes of sands, and the method to calculate injectable volume of grout is suggested with consideration of change in viscosity and clogging phenomena. The calculated values are compared with injection test results. Viscosity of new grout material is found to be an exponential function of time. And lumped parameter $\theta$ of new grout material to be used for assessing deposition characteristics is estimated by comparing deposit theory with injection test results considering different soil types and different injection pressure.

• 유체기계공업학회:학술대회논문집
• /
• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
• /
• pp.451-454
• /
• 2006

This paper describes the results of cold flow test and hot firing tests of an uni-element coaxial swirl injector and hot firing tests of a subscale combustor, as to the development effort of coaxial swirl injector for high performance liquid rocket engine combustor. A major design parameter for coaxial swirl injector is the recess number of a bi-swirl injector. The results of hot firing tests of the uni-element injector combustor and the sub-scale combustor are analyzed to investigate the effect of the recess number influencing on the combustion performance and pressure fluctuation. The test results of a cold flow test of the unielement combustor shows that it was shown that the change in recess number has significant effect on mixing characteristics and efficiency, while the effect of recess number on atomization characteristic is not The results of a series of firing tests using unielement and subscale combustor show that the recess length significantly affects the hydraulic characteristics, the combustion efficiency, and the dynamics of the liquid oxygen/kerosene bi-swirl injector. As a point of combustion performance, combustion efficiencies are 90% for unielement combustor and 95% for subscale combustor. The difference in the characteristic velocities between the unielement combustor and the subscale combustor may be caused by the difference in thermal loss to the combustor wall and the relative lengths of the combustion chamber. For a mixed type coaxial swirl combustor, the pressure drop across the injector increases as recess number becomes larger. The low frequency pressure fluctuation observed in unielement combustor can be related to the propellant mixing characteristics of the coaxial bi-swirl injector. The effect of the recess number on the pressure fluctuation inside the combustion chamber is more significant in un i-element combustor than the subscale combustor, of which the phenomena are also observed in time domain and frequency domain.

• Journal of Advanced Marine Engineering and Technology
• /
• 제30권3호
• /
• pp.351-358
• /
• 2006

The capability of high pressure injection with small fuel quantify at all engine operating conditions is one of the main feature in common rail fuel injection system, which is used in small and light-duty Diesel engine. The key parameter for the better atomized fuel sprays and multiple injections of this common rail fuel injection control, that can be freely selected irrespective of the engine speed and load is the mechanism controlling the needle energizing and movement in high pressure Diesel injector. In the electro-hydraulic injector, the injection nozzle is being opened and closed by movement of the injector's needle which is balanced by pressure between the nozzle seat and the needle control chamber. This study describes the macroscopic spray structure characteristics of the common rail Diesel injectors with different electric driving method i.e. the solenoid-driven and piezo-driven type. The macroscopic spray characteristics such as spray tip speed. spray tip penetration and spray cone angle were investigated by the high speed spray, which is measured by the back diffusion light illumination method with optical system for the high speed temporal photography in a constant volume chamber pressurized by nitrogen gas. As the results, the prototype piezo-driven injector system was designed and fabricated for the first time in domestic case and the effect of injector's needle response driven by different drive type was compared between the solenoid and piezo-driven injector It was found therefore. that the piezo-driven injector showed faster needle response and had better needle control capability by altering the electric input value than the solenoid-driven injector.

• Nuclear Engineering and Technology
• /
• 제44권7호
• /
• pp.735-744
• /
• 2012

In order to quantify the flow distribution characteristics of APR+ reactor, a test was performed on a test facility, ACOP ($\underline{A}$PR+ $\underline{C}$ore Flow & $\underline{P}$ressure Test Facility), having a length scale of 1/5 referring to the prototype plant. The major parameters are core inlet flow and outlet pressure distribution and sectional pressure drops along the major flow path inside reactor vessel. To preserve the flow characteristics of prototype plant, the test facility was designed based on a preservation of major flow path geometry. An Euler number is considered as primary dimensionless parameter, which is conserved with a 1/40.9 of Reynolds number scaling ratio. ACOP simplifies each fuel assembly into a hydraulic simulator having the same axial flow resistance and lateral cross flow characteristics. In order to supply boundary condition to estimate thermal margins of the reactor, the distribution of inlet core flow and core exit pressure were measured in each of 257 fuel assembly simulators. In total, 584 points of static pressure and differential pressures were measured with a limited number of differential pressure transmitters by developing a sequential operation system of valves. In the current study, reactor flow characteristics under the balanced four-cold leg flow conditions at each of the cold legs were quantified, which is a part of the test matrix composing the APR+ flow distribution test program. The final identification of the reactor flow distribution was obtained by ensemble averaging 15 independent test data. The details of the design of the test facility, experiment, and data analysis are included in the current paper.

• 항공우주기술
• /
• 제6권2호
• /
• pp.205-210
• /
• 2007

75톤급 액체 로켓 엔진용 터보펌프의 산화제펌프에 대한 로터다이나믹 설계를 수행하였다. 인듀서와 임펠러 및 베어링의 축배치는 항우연에서 개발 중인 유사한 구조를 가지는 터보펌프를 근간으로 하였고, 75톤급 산화제펌프 수력 설계에 맞추어 인류서, 임펠러의 축길이가 반영되었다. 후방 베어링으로부터 임펠러까지의 거리를 베어링 하중 설계에 대한 설계 변수로 고려하였고, 전방 베어링과 후방 베어링의 강성을 변화시키면서 회전 속도에 따른 비동기 고유진동수 해석을 수행하여 산화제 펌프의 임계속도를 고찰하였다. 베어링에 적절한 하중이 부과된다면 산화제 펌프의 임계속도는 기준속도 11,000 rpm과 비교하여 충분히 높기에, sub-critical 로터로서 기준속도 이내에서 안정적인 터보펌프의 운용이 가능하리라 판단된다.

• 대한토목학회논문집
• /
• 제12권2호
• /
• pp.229-237
• /
• 1992

2차원 수평흐름에서의 비반응성 오염물 이동에 대한 연속시스템(series system) 신뢰성해석을 농도와 노출시간의 두 극한상태 함수에 대해 시행하였다. 시간에 따라 변화하는 오염원에서의 오염이동모델을 시스템 신뢰해석 모델과 결합하여 오염이 예상되는 지점의 최대농도가 주어진 기간동안에 특정농도를 초과하거나 또는 오염예상 지점이 보통의 농도에 노출되어질 시간이 특정 한계를 초과할 확률을 구하였다. 본 신뢰성 해석의 결과 상기의 두조건을 초과할 확률은 각각의 조건을 초과할 확률보다 큰 것은 확인하였으며 보다 큰 초과확률을 갖는 요소에 의하여 지배되는 것을 발견하였다. 예민도 해석은 투수계수 외에도 횡단 분산계수(transverse dispersivity)도 이차원 오염이동 신뢰성 모델의 중요한 매개 변수임을 보여주었다. 시스템 예민도는 두 요소의 예민도를 동시에 반영하고 있으며 큰 초과확률을 갖는 요소가 해(解)에 보다 큰 영향을 미치는 것을 알게 되었다.

• 한국수자원학회논문집
• /
• 제44권12호
• /
• pp.955-965
• /
• 2011

본 연구에서는 광정횡월류위어의 정확한 월류량을 산정하기 위해 직사각형, 1:1 및 1:2 경사 사다리꼴 위어에 대한 형상별 흐름특성을 수리실험을 통해 확인하였다. 흐름은 사다리꼴 형상으로 사면경사가 작을수록 흐름이 안정적이었으며, 각 형상별 위어 월류량의 경우 직사각형 형상보다 1 : 1 및1 : 2 사다리꼴 형상에서 각 5.67% 및 8.57% 가량 증가해 홍수배제 능력에서도 유리한 것으로 나타났다. 기존의 유량계수식에 횡월류위어 형상에 대한 매개변수 $L/L_H$를 추가한 다중회귀분석으로 각 형상별 유량계수식과 형상을 일반화 시킨 통합 유량계수식을 제시하였다. 또한 선행연구 및 기존 연구자들의 실험자료와 본 실험의 연구자료를 이용하여, 측정된 월류량과 계산된 월류량을 비교하여 새롭게 제안하는 유량계수식의 적용성을 확인하였다.

• 한국수자원학회논문집
• /
• 제37권11호
• /
• pp.915-927
• /
• 2004

남한강 수계를 대상으로 대표 어종의 하천 어류 서식처 환경에 대한 서식처 적합도 기준을 작성하고, 어류 서식을 위한 최적유량의 산정방법을 확립하기 위하여, 생태학적 접근 방법 중 어류서식처 환경평가방법의 한가지인 점유량점증론적방법론(IFIM)의 물리적서식처모의시스템(PHABSIM)을 적용하여 어류서식처 보호 및 유지를 위한 최적유량을 산정하였다. 서식처 평가에 요구되는 수리인자의 모의를 위해 2차원 동수역학적 모델을 이용하였으며, 현장조사를 실시하여 대표어종으로 선정된 피라미의 단일변량곡선법을 적용한 서식처 적합도 기준을 작성하였다. 이러한 결과를 토대로 유황변화에 어류 서식환경이 가장 민감하게 반응하는 여울 구간과 여울이 형성되지 않음으로서 어류의 서식처 평가의 고려대상에서 제외되었던 본류 구간을 동시에 모의하여 상$\cdot$하류간의 수문학적 물질균형이 이루어짐을 확인할 수 있었다.

• Tribology and Lubricants
• /
• 제33권2호
• /
• pp.65-70
• /
• 2017

In vertical hydro/hydraulic power turbine-generator applications, traditionally, cylindrical turbine guide bearings (TGBs) are widely used to provide turbine runner shafts with smooth rotation guides and supports. All existing cylindrical TGBs with simple plain pads have drawbacks such as having no pressure generation and film stiffness at the no-load condition and in addition, at the low-load/low-eccentricity condition, having very low film stiffness values and lacking design credibility in the stiffness values themselves. In this paper, in order to fundamentally improve the low-load/low-eccentricity performance of conventional cylindrical TGBs and thus enhance their design-application availability and usefulness, we propose to introduce a rotation-directional leading-edge taper to each partitioned pad, i.e., a pad leading-edge taper. We perform a design analysis of lubrication performance on $4-Pad{\times}4-Row$ cylindrical TGBs to verify an engineering/technical usefulness of the proposed pad leading-edge taper. Analysis results show that by introducing the leading-edge taper to each pad of the cylindrical TGB one can expect a constant high average direct stiffness with a high degree of design credibility, regardless of load value, even at the low-load/low-eccentricity condition and also control the average direct stiffness value by exploring the taper height as a design parameter. Therefore, we conclude that the proposed pad leading-edge tapers are greatly effective in more accurately predicting and controlling rotordynamic characteristics of vertical hydro-power turbine-generator rotor-bearing systems to which cylindrical TGBs are applied.