• 유체기계공업학회:학술대회논문집
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• 유체기계공업학회 2006년 제4회 한국유체공학학술대회 논문집
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• pp.345-348
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• 2006

In sheet metal forming process using press and draw die some defect can be made because of the high pressure of air pocket between draw die and the product. The purpose of this study is to develop a program to decide an optimal combination of air vent hole size and number to prevent those defect on product. The air inside air pocket is considered as ideal gas and the compression and expansion is assumed as isentropic process. The mass flow is computed in two flow condition: unchocked and chocked condition. The present computation obtains required cross-sectional area of air vent hole for not exceeding the user specified pressure such as the pressure for yielding strength of the product or the pressure for unchocked flow. To validate the program the present results are compared with the results of other researchers and commercial CFD code.

• 한국기계가공학회지
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• 제18권8호
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• pp.82-90
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• 2019

We propose an equivalent model of a sintered metal mesh filter calculated by Ergun's equation and polynomial regression for the CFD analysis of breakaway devices at a hydrogen fueling station. CFD analysis of filters that cause high pressure loss is essential because breakaway devices in high-pressure hydrogen conditions require low pressure loss. A differential pressure experiment with a filter was performed in a low-pressure air condition considering similarities. An equivalent model was developed by deriving the resistance value by the polynomial regression using the experimental results. The results of CFD analysis using the equivalent model show that there was almost no error in the operating condition of the breakaway device compared to the experimental results. Through this work, we believe that the proposed equivalent model of a filter can be applied to the analysis of breakaway devices in hydrogen fueling stations. We will study how to optimize the shape and position of the filter in breakaway devices using the developed equivalent model.

• 한국건축시공학회:학술대회논문집
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• 한국건축시공학회 2012년도 춘계 학술논문 발표대회
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• pp.201-203
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• 2012

The establishment of the technology for evaluating friction resistance and pipe pressure and the relation of the fluid characteristics and pumpability of concrete is essential for the evaluation of concrete pumping performance for high speed construction of super-tall building. So, this study focuses on quantitative evaluation of concrete fluid characteristics and surface friction resistance under the change of concrete mix proportion and pumping condition. In this study, we measured the rheology of concrete and pipe pressure and surface friction characteristics when pumping. And, relations between the rheology characteristics of concrete and pumping performance was investigated by experiment. As the result of the experiment, high regression between the surface friction and pressure gradient was confirmed. And, prediction model to evaluate the friction resistance coefficient and pipe pressure reduction coefficient was suggested.

• 한국항공우주학회지
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• 제39권4호
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• pp.348-353
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• 2011

액체 질소를 이용하여 극저온 단일 제트 유동의 특성을 관찰하였다. 고압 챔버 내부에 액체 질소를 분사하여 단일 제트를 생성, 주위기체압력을 변화시킴으로써 아임계 조건부터 초임계 조건의 주위 환경에 따른 제트의 특성 변화를 확인하였다. 또한 분사기의 길이 대 직경비 및 분사기 내부 형상의 변화에 따른 제트의 특성 변화를 파악하였다. 유동 가시화를 통하여 극저온 제트의 형상 및 액주의 지름을 측정하였으며, 이로부터 액주의 확산각을 계산하여 이전 연구 결과와 비교하였다. 아임계 조건 및 초임계 조건에서의 제트의 형상 변화를 관찰하였으며, 주위기체압력이 대기압과 동일할 경우 제트 유동에서 불안정이 발생함을 확인하였다. 또한 주위기체압력이 증가함에 따라 액주의 확산각이 점차 증가하다가 일정 압력 이상에서 거의 일정하게 유지됨을 확인하였다.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2004년도 춘계학술대회
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• pp.2146-2150
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• 2004

To evaluate the variation of spring stiffness in nuclear plant operating condition, load-displacement tests ($P-{\delta}$ test) were performed using two kinds of space grid springs in high temperature and high pressure water. With increasing temperature, stiffness of each spring gradually decreased except $100{\sim}150^{\circ}C$. It is apparently showed that spring with convex shape had a relatively high stability of spring stiffness at high temperature compared with I-shaped spring. It is suggested that the variation of spring stiffness with temperature and spring shape should be considered as an important variable in the design and analysis of the fuel assembly.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회B
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• pp.2558-2562
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• 2007

In the present work, flow characteristics analysis has been performed for steam turbine bypass control valve (single-path type). The numerical analysis is performed by solving three-dimensional Reynolds-averaged Navier-Stokes (RANS) equations. Shear stress transport (SST) model is used as turbulence closure. Symmetry condition is applied at the mid plane of the valve while adiabatic condition is used at the outer wall of the cage. Grid independency test is performed to find the optimal number of grid points. The pressure and temperature distributions on the outer wall of the cage are analyzed. Mass flow rate at maximum plug opening condition is compared with the designed mass flow rate.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.366-372
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• 2007

Self-sensing measurement of piezo inkjet and its application are discussed. The pressure wave inside the inkjet dispenser was measured by current measurement due to self-sensing capability of PZT. The pressure wave measured from current was verified by commercially available laser vibrometer. Here, two applications using self-sensing signal were discussed: waveform design for high speed jetting and condition monitoring. For waveform design, two pulse waveform was designed based on self-sensing signal such that the pressure wave after droplet formation can be minimized. For condition monitoring, self-sensing signal was shown to be effective in detecting air bubble trapped in inkjet printhead.

• 한국분무공학회지
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• 제6권3호
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• pp.17-22
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• 2001

Recently LPG engine is developed to fulfill such new requirements as improved fuel efficiency in additional to further reduced exhaust emission. This experimental study is conducted to analyze spray characteristics for pintle type injector used in a LPLi (Liquid Phase LPG injection) engine. Since spray parameters including penetration length and spray angle make a role to design injector and engine intake system, spray visualization experiment is performed under atmosphere ambient and charging condition using Mie scattering method. From the experimental result under various LPG formation, the increased propane component decreases penetration length because boiling point of propane is lower than butane. To simulate intake charging condition in MPI engine, spray visualization is performed under high pressure condition. As a result, as ambient pressure is increased from atmosphere to 3.0 bar, penetration length is decreased. However, as ambient pressure is increased from atmosphere to 3.0 bar, spray angle is increased.

• 한국해양공학회지
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• 제30권2호
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• pp.100-108
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• 2016

A high-pressure ball valve was developed, and both the structural strength and sealing performance were assessed based on a nonlinear finite element analysis. Different parts were modeled with solid elements and assembled, taking into account both contact and sliding effects. Three different loading scenarios were analyzed, including a high-pressure closure test and fire and shell test conditions. The structural safety of each part was checked under each loading condition, and the sealing performance was also investigated to validate the performance of the valve.

• 오토저널
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• 제12권4호
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• pp.75-82
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• 1990

To study on the behavior of the early stage of the spark kernel at constant pressure condition, the expressions of the thermal properties such as compressibility factor, thermal conductivity, and electrical conductivity of the high temperature air were newly suggested. The newly suggested simple expressions of the thermal properties of the high temperature air showed good results. Under the assumption of constant pressure, one dimensional numerical analysis was executed by varying surrounding conditions and discharging current of electrical spark. Numerical results show tat high surrounding pressure suppresses the growth of the spark kernel but supplies much electrical energy into the air, on the other hand high surrounding temperature increases the growth of the spark kernel but supplies less electrical energy. Also the result shows that , in case of direct current discharge, deposited electrical energy is able to be expressed in linear function of time approximately.