• 한국전산유체공학회:학술대회논문집
• /
• 2011.05a
• /
• pp.518-522
• /
• 2011

Cartesian grid system has mainly been used in the casting simulation even though it does not nicely represent sloped and curved surfaces. These distorted boundaries cause several problems. A special treatment is necessary to clear these problems. A cut cell method on Cartesian grids has been developed to simulate three-dimensional mold filling Cut cells at a cast-mold interface are generated on Cartesian grids. Governing equations were computed using volume and areas of cast at cut cells. In this paper, we propose a new method that can consider the cutting cells which are cut by casting and mold based on the patial cell treatment (PCT). This method provides a better representation of geometry surface and will be used in the computation of velocities that are defined on the cell boundaries in the Cartesian gird system. Various test examples for several casting process were computed and validated. The analysis results of more accurate fluid flow pattern and less momentum loss owing to the stepped boundaries in the Cartesian grid system were confirmed. We can know the momentum energy at the cut cell is conserved by using the cut cell method. By using the cut cell method. performance of computation gets better because of reducing the whole number of meshes.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.10 no.1
• /
• pp.54-63
• /
• 2006

Ejector system are used to transport a low momentum flow to the higher pressure flow by the momentum change between high and low momentum flows. This system is used to simulate the high altitude and Mach number condition over altitude 20 km and Mach 4 of the supersonic test facility. We applied the design and the performance analysis technique(EISIMP code) of the Ramjet Test Facility(RJTF) air system in JAXA to the ejector system of the ramjet test facility in KARI. After preliminary design of the ejector system, we performed a computational study using FLUENT and investigated shock structures and flow characteristics of the ejector system.

• Computers and Concrete
• /
• v.30 no.1
• /
• pp.19-32
• /
• 2022

This paper presents an investigation into the failure of RC columns under impact loadings. A numerical simulation of 19 identical RC columns subjected to single and repeated impact loadings was performed. A free-falling hammer was dropped at midspan with the same total kinetic energy input but varying mass and momentum. The specimens under the repeated impact test were struck two times at the same location. The colliding index, defined as the impact energy-momentum ratio, was proposed to explain the different impact responses under equal-energy impacts. The increase of colliding index from low to high indicates the transition of the impact response from static to dynamic and failure mode from flexure to shear. This phenomenon was more evident when the column had a greater axial load and was impacted with a high colliding index. The existence of the axial load had an inhibitory effect on the crack development and increased the shear resistance. The second impact changes the failure mode from flexural to brittle shear as found in the specimen with 20% axial load subjected to high a colliding index. Moreover, a deflection prediction equation based on the impact energy and force was limited to the low colliding index impact.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.50 no.6
• /
• pp.413-422
• /
• 2022

In this paper, the fault analysis of the momentum wheel, which is a high-speed rotary machinery of 'Control Moment Gyro' for medium and large satellite, was described. For fault diagnosis, envelope spectrum analysis was performed using Hilbert transformation method and signal demodulation method to find the impact signals periodically generated from amplitude modulated signals. Through this, the fault of the momentum wheel was diagnosed by analyzing whether there was a harmonic component of the rotational frequency and a bearing fault frequency in a specific frequency band with a high peak.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.38 no.1
• /
• pp.64-72
• /
• 2010

Due to the interaction between main oxidizer flow and the wall injected flow resulting from the regression process, a specific time characteristics identified in the frequency spectrum of streamwise velocity is generated in the hybrid rocket motor. In order to understand the response of the turbulent flow to two different types of external momentum forcing, LES analysis was conducted without considering the combustion. It turns out that both concentrated and distributed forcings do not lead to the disastrous resonance phenomenon. Energy contents are enhanced due to the added momentum but the peak frequency was not modified in the turbulent flow near the end of the rocket motor. Natural frequency of the flow system should be taken into account to further pursue the instability issue by using external forcing.

• Aerospace Engineering and Technology
• /
• v.12 no.2
• /
• pp.57-63
• /
• 2013

The mission of a lot of satellites on geostationary orbit is the communication and/or the broadcasting. These satellites need a big power, so these have a large solar array. Recently, the new satellite for Earth environment monitoring is developing on geostationary orbit. The payload of Earth monitoring satellite requires better thermal condition on detector. Therefore this satellite uses a boom for the attitude stability instead of rejecting one-side solar array as a heat source. The other hand, it uses some momentum wheels being a more momentum capacity to control the large disturbance by solar pressure due to the asymmetric solar array configuration. In this paper, the analysis on the wheel allocation and the wheel off-loading for COMS is summarized and the results are verified by telemetry of COMS. COMS has no boom and a perfectly asymmetric solar array configuration, and it is operating well on geostationary orbit.

• The Journal of the Korea Contents Association
• /
• v.19 no.11
• /
• pp.619-631
• /
• 2019

Researchers are persons who are destined to produce improved knowledge, with duty, responsibility and desire for overcoming limits of the existing knowledge in continuously changing natural and social environments. In addition, both drawing research outcomes 'contributing to the society' by tapping on 'researches convergent with other disciplines', to 'deducing meaningful research outcomes' and 'operating laboratories for fostering convergence talents', for the consistency of incessant researches are the momentum for convergence researchers to continue convergence researches. However, an irony fact is that 53.1% of convergence researchers respond that they began convergence researches from happenstantial momentum (a happenstantial talk with other majors)'. This study examined what was the momentum from which convergence researches began and what was the motive with which they have been consistently conducted and suggested how to continue convergence researches.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.27 no.3
• /
• pp.152-157
• /
• 2015

Stack effect on high-rise building have negative effect on living environment, energy and life-safety aspect. Thus, it's necessary to find the measure to reduce the stack effect. As a result of field test on a 31-story building, a circulating type stack effect reduction technology was developed, which supplies air in the low stairs and discharges air in the high stairs. To evaluate the performance of this circulating type stack effect reduction technology on building stairs, a 3D numerical analysis was carried out by using Momentum Loss Model for analyzing leakage flow between compartments in a building. Consequently, numerical analysis proved that the stack effect on building stairs was reduced by a circulating type stack effect reduction technology.

• Korean Journal of Air-Conditioning and Refrigeration Engineering
• /
• v.25 no.10
• /
• pp.562-567
• /
• 2013

1D-numerical analysis of the network algorithm with the orifice equation for the relationship between pressure difference and flowrate has been mostly used to analyse leakage flow at the gap. In this study, a 3D-numerical method applying momentum loss model to the gap region in the computational domain is represented to reflect effectively the effect of leakage flow by determining the proportion of pressure difference to air passage velocity. While the 3D-numerical method is verified through the computation of the two compartments model, the numerical analysis of the stack effect in a building stairway is performed. As the temperature of air outside drops, the pressure in the upper stairway and leakage flowrate through the gap in the door rise. The change of gap area does not have an effect on pressure in the stairway for the analysis conditions.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.18 no.3
• /
• pp.635-644
• /
• 1994

This study investigated mainly on the flow characteristics of a droplet in the cross region of twin spray. The velocities of the droplet were measured along the axial and radial direction, and the flow characteristics of the droplet were statistically analyzed. For the statistical analysis, the probability density of the turbulent components has been studied, and then the Reynolds shear stress, the skewness and the flatness factors were calculated, and compared with the Gaussian value. Two pressure swirl stomizers were used for the twin spray system and kerosene was employed as the working liquid. 2-D PDA(particle dynamic analyzer) was used for the purpose of the measurement of droplet size and velocities. As a result, it was found that (1) the droplets collision was taken place strongly in the cross region. So, a large momentum loss of droplets due to the loss of natural movement direction was occurred, and momentum loss of radial direction was greater than that of axial direction. (2) The axial direction skewness factor approached to zero like the Gaussian distribution in the cross region of twin spray. (3) In the cross region of twin spray, the fluctuation instability of droplet was increased because of the development of the turbulence characteristics due to the droplet collision.