• Journal of ILASS-Korea
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• v.19 no.4
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• pp.167-173
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• 2014

The spray characteristics of Gas-Centered Swirl Coaxial Injector was investigated that there were different characteristics with or without gas flow. As gas flow was accelerated, the momentum of gas was transferred to the momentum of liquid in the low liquid Reynolds number. Therefore, the axial velocity of liquid was increased and the measured value was smaller than without gas flow. However, in the high momentum flux ratio, the momentum transfer hardly occurred and the results had constant values. As the recess length was increased, the mixing area of gas and liquid also was increased, the results were decreased.

• Journal of ILASS-Korea
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• v.20 no.3
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• pp.168-174
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• 2015

Combustion instability is critical problem in developing liquid rocket engine. There have been many efforts to solve this problem. In this study, the method was sought through the injector as part of these efforts to suppress combustion instability. If the injector can suppress the disturbance coming from the supply line as a kind of buffer it will serve to reduce combustion instability. Especially we target at gas propellant oscillation in gas-centered swirl coaxial injector. The phenomenon is simulated with acoustic excitation of speaker. The film thickness response at injector exit was measured by using a liquid film electrode. Also the response of spray to the disturbance was observed by high-speed photography. Gas-liquid momentum flux ratio and the frequency of feeding gas oscillation were changed to investigate the effect of these experimental parameters. The trend of response by varying these parameters and the cause of weak points was studied to suggest the better design of injector for suppressing combustion instability.

• International Journal of Aeronautical and Space Sciences
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• v.14 no.4
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• pp.398-407
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• 2013

Optical tomography was used to measure the pattern of spray cross-section. The maximum-likelihood estimation (MLE) algorithm was used to reconstruct the spray cross-section from the measured transmission rate of the spray. A swirl-type injector was used to form an optically dense spray, and the test was carried out in a high-pressure chamber, to control the pressure condition of the test site. Before the experiment, the reliability of the MLE-based reconstruction algorithm was verified, by comparing it with a conventional filtered back projection reconstruction (FBP) method. The MLE algorithm showed superior reconstruction of the image. In the spray patternation experiment, the results of the optical tomography and optical line patternator, which uses Mie scattering signal information, were compared. While measuring the cross-section of optically dense spray, the intensity of the scattering signal had attenuated to an uncorrectable level, which led to incorrect spray pattern measurement by the optical line patternator. However, reliable results were obtained by optical tomography, under the same condition. Finally, the pattern of the optically dense spray was measured at various chamber pressures, of up to 3 MPa. As the chamber pressure increased, the hollow cone-shaped swirl spray shrank, and the attenuation coefficient value of the inner region increased.

• Journal of ILASS-Korea
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• v.22 no.2
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• pp.62-68
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• 2017

It is important to study on the combustion instability to develop liquid rocket engines for preventing lower combustion efficiency and destruction of combustion chamber. There are many researches on simplex injector with liquid pulsation to solve this problem. In real rocket engine system, however, they use coaxial injectors. Therefore, research on coaxial injector with liquid pulsation is essential. In this study, we investigate dynamic characteristics of gas centered swirl coaxial injector varying tangential inlet diameter. A mechanical pulsator was used to generate an excitation in the liquid flow, and the response characteristics of the injector were confirmed. As tangential inlet diameter increased, mass flow rates increased and spray angle decreased. As tangential inlet diamter decreased, gain decreased because the pressure fluctuation in the injector manifold rarely passed through the inlet. Additionally, it was confirmed that a sufficiently small tangential inlet served as a damper.

• International Journal of Aeronautical and Space Sciences
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• v.15 no.4
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• pp.444-453
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• 2014

A throttleable rocket engine enables operational possibilities such as the docking of spacecraft, maneuvering in a certain orbit and landing on a planet's surface, altitude control, and entrance to atmosphere-less planets. Thus, throttling methods have long been researched. However, dual-manifold injectors, which represent one throttling method, have been investigated less than others. In this study, dual-manifold and single-manifold injectors were compared to determine the characteristics of dual-manifold injectors. Also, the effects of gas injection were investigated with various F/O ratios. To investigate the characteristics, mass flow rate, spray pattern, spray angle, and droplet size were measured. The spray angle and droplet size were captured by indirect photography. About 30 images were taken to assess the spray patterns and spray angle. Also, 700 images were analyzed to understand the droplet distribution and targeting area, moving to the right from the centerline with 1.11-cm intervals. The droplet size was obtained from an image processing procedure. From the results, the spray angle showed two transition regions, due to swirl momentum in the swirl chamber regardless of the F/O ratio. The droplet size showed similar trends in both dual-manifold and single-manifold injectors except in the low mass flow rate region. In the case of the dual- manifold injector, the spray cone was not fully developed in the low mass flow rate region due to low angular momentum in the swirl chamber.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.43 no.10
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• pp.868-874
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• 2015

Thrust variation is an essential parameter in a space mission such as landing on an atmosphereless planet or docking a spacecraft. In order to achieve the thrust variation control, using throttleable injector is a representative and general method. A dual-manifold injector, one of throttleable injectors, was used to control mass flow rate. Five kinds of injectors were designed and investigated in order to compare the spray characteristics of the dual-manifold injector with various tangential entries. Spray angles and patterns were measured to determine external flow characteristics and film thicknesses were measured in order to investigate the internal flow patterns.

• Journal of The Korean Association For Science Education
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• v.28 no.1
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• pp.89-99
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• 2008

In this study, we investigated the effects of explicit and reflective instruction about nature of science (NOS) using episodes from the history of science upon students' understanding about NOS, achievement, and enjoyment of science lessons. Four classes of ninth graders (N=129) at a coed middle school were divided into the control and the treatment groups. The students were taught about the composition of material for 11 classes. Before the instruction, most of the students in both the control and the treatment groups held naive views about NOS. After the instructions, the views about NOS of the control group students did not change, whereas the students in the treatment group held more adequate views about NOS. The high-level students in the treatment group showed more adequate views about NOS than the low-level students. However, there were no significant differences between the test scores of the two groups in the achievement and the enjoyment of science lessons.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.29 no.3
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• pp.134-146
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• 2011

Gyeokgu is a group ball game transmitted into the Joseon Dynasty period as acquiring a great vogue among the royal palace and people in Goryeo Dynasty after being introduced into the country from China. This research aimed through historical investigation to look into the form in which the Goryeo dynasty's kings enjoyed Gyeokgu game, and the historical-spatial signification and the locational characteristics of Gujeong(the ground where play Gyeokgu) which is the courtyard where Gyeokgu game was held centering around the Goryeo dynasty's palace where Gyeokgu was prosperous most. We researched and analyzed the data for research after extracting the records related to Gyeokgu from three historical data of the true records of the Goryeo Dynasty. Upon investigation, twelve among 34 kings of the past generations were concerned with Gyeokgu in Gyeokgu game participation form, and 46 times were recorded in historical records in total. In the participation form, kings participated personally in 9 times among 46 Gyeokgu games, and viewed games in case of 37 times. Among these kings, the 18th generation king Uijong was recorded most as 17 times(36.9%) in Gyeokgu records. Places where Gyeokgu were held were 25 places in total including royal palace, detached palace, Lu-jeong, Buddhist temple, private residences, markets and streets, other outside of the royal court and so on, and 46 time-Gyeokgu games in total were held in these places. 21 time(45.6%)-Gyeokgu games were held in only 5 detached place among these places. So, detached palace were used most for Gyeokgu games. In particular, Gyeokgu games were held most in Suchanggung palace and Jangwonjeong palace among these detached palaces, and all these things were recorded during the reign of King Uijong. Gyeokgu game which was prevalent by the end of the Goryeo Dynasty showed a progression to a national festival which kings, personally coming into streets or Jeoja(an archaic word for "market"), enjoyed with the crowd.

• Journal of the Korean Institute of Traditional Landscape Architecture
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• v.34 no.2
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• pp.16-26
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• 2016

In this paper, we collected information on Palgyeong of the Gangneung area that were scattered around several literatures, and analyzed and interpreted regional distribution, elements of scenery and inherent meanings from various angles. we shed light on the origin and the meaning of Palgyeong, which have been passed down in the Gangneung area. Palgyeong of the Gangneung area have been accumulated and expanded for a long period of time, since Goryeo up to the modern times, and it does not simply reflect the beauty of natural scenery, but also reflect historical facts and sentiments rooted in this region. In addition, given the comprehensive veiw of Palgyeong of the Gangneung area and in consideration of its type and distribution of the eight sceneries the most common format is similar to Sosang(瀟湘類似型). What are repeatedly appearing among them include 'smoke from cooking supper' and 'catching fish', showing the living conditions of local residents of Gangneung at the time, which refers to the fact that Palgyeong consisted of village units. Palgyeong in the Gangneung area are distributed in diverse ranges between the city and Nujung. Most of Palgyeong are clustered in the east of Gangneung city and in the region tangent to Gangdong-myeon and Gujeong-myeon. When we consider the situation where most of Palgyeong in the Gangneung area are distributed in this region, it suggests that the region occupies the heart of scenery of Gangneung. Palgyeong of the Gangneung area consists of 60% natural factors, 36% humanity factors, and 4% other factors, where the natural factors hold the beauty of nature itself and the humanities and other factors hold the legends and history contained in the targets. The sceneries expressed by Palgyeong cannot be individually separated. Namedaecheon, Jukdobong, Sumseokcheon, Sumdulmaeul, Gunseongang, Pungho and Kyungpoho were connected to Nujung and Hongjamam, and they eventually became a panorama. Hansongjung, Hwanseondeung, Hansongsa, Pungho and Gunseongang are related to Hwarang of Silla and have become representative historical sceneries of the Gangneung area. Judging from the fact that currently non-existing sceneries such as Kyeonjodo, Hansongjung and Gulsansa remained in Palgyeong and been passed, Palgyeong have positioned imaginary spaces of the Gangneung people beyond simply expressing sceneries. In conclusion, Palgyeong in the Gangneung area are aesthetical objects and while at the same time, they are historical and cultural space, and furthermore, we can see that they still remain as imaginary spaces.

• Journal of the Korean Institute of Landscape Architecture
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• v.43 no.3
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• pp.52-62
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• 2015

This study conducted an experiment to clarify the effect of rubber bands used as a root connector during the process of transplanting landscape trees on the development of the root system and the rooting process. The research period was four years, from April 2007 to April 2011, and the test conducted for this study was performed at the experimental field located at 398-2 Bangdong-ri, Sacheon-myeon, Gangneung-si, Gangwon-do. Twenty 15-year-old Pinus densiflora Siebold & Zucc. with good growth conditions were harvested and transplanted from the forest in Jebi-ri, Gujeong-myeon, Gangneung-si, Gangwon-do for the field experiment. A completely randomized design was applied for plot design, with 10 pines without rubber bands and 10 pines with rubber bands. Pinus densiflora for. multicaulis Uyeki was selected as the official tree of the pot test and was planted in a transparent pot to observe the development of the root system. A completely randomized design was applied for plot design, with 3 pines without rubber bands and 3 pines with rubber bands. The results of this research on the effect of rubber bands used as a root connector on root system development and the rooting process are as follows. 1. The rate of height growth in the field test was 4.1% lower in the trees with rubber bands when compared to trees without rubber bands. Trees with rubber bands were 4.2% wider than those without rubber bands in root diameter. The chlorophyll content was 6.8% higher in trees without rubber bands, but the rate of height growth, root diameter, and chlorophyll content were not significantly correlated. 2. In the comparison of fresh root weight in the field test, trees with rubber banding had roots weighing 1,740.0kg and those without rubber bands had roots weighing 1,433.3kg. Root dry weight was 522.3g in trees with rubber bands and 450.0g in those without rubber bands, but showed no significant difference depending on whether the rubber band was attached. 3. In a comparison of root number between surfaces touching and not touching the rubber band in trees with rubber banding, the surface touching the rubber band was observed to have more roots growing, the difference of which was deemed significant. 4. The shoot growth rate in the pot test was 1.1% higher in trees without rubber bands when compared with trees with rubber bands. The chlorophyll content was 0.02 higher in trees with rubber bands but the difference was not significant. 5. In the pot test, no significance was found in comparison of root number, root length, and root dry weight in trees with and without rubber bands. These test results imply that removing rubber bands as a connector does not present any significant effects on the ground growth or root development of transplanted pine trees. As it is shown that surface touching rubber bands grow more roots in trees with rubber bands, more active related research must be undertaken.