• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.1
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• pp.54-60
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• 2004

Experimental study on combustion characteristics of double swirl coaxial injectors has been conducted for the assessment of critical injector design parameters. A reusable, subscale thrust chamber has been fabricated with a water-cooled copper nozzle. Two different configurations of injectors have been tested for the understanding of the effects of recess length on high pressure combustion. Clearly, the recess length drastically affects the combustion efficiency and hydraulic characteristics of an injector. Internal mixing of propellants in an injector with recess number of two increases a combustion efficiency and reveals sound combustion although a pressure drop required for the same amount of mass flow rates increases compared with an injector of recess number of one.

• Journal of the Korean Geotechnical Society
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• v.37 no.12
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• pp.117-125
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• 2021

The occurrence of ground subsidence and sinkhole in downtown areas, which threatens the safety of citizens, has been frequently reported. Among the various mechanisms of a sinkhole, soil erosion through the damaged part of the sewer pipe was found to be the main cause in Seoul. In this study, a random forest model for predicting the occurrence of sinkholes caused by damaged sewer pipes based on sewage pipe information was trained using the information on the sewage pipe and the locations of the sinkhole occurrence case in Seoul. The random forest model showed excellent performance in the prediction of sinkhole occurrence after the optimization of its hyperparameters. In addition, it was confirmed that the sewage pipe length, elevation above sea level, slope, depth of landfill, and the risk of ground subsidence were affected in the order of sewage pipe information used as input variables. The results of this study are expected to be used as basic data for the preparation of a sinkhole susceptibility map and the establishment of an underground cavity exploration plan and a sewage pipe maintenance plan.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.10a
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• pp.288-291
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• 2004

The spray characteristics of coaxial swirl injector under ambient high pressure conditions were investigated in this paper. Three injectors were used to study the effect of recess length and fuel injector type(open or closed). In this research, experimental conditions(ambient gas density) were calculated by Buckingham Pi-theory and spray characteristics of the injectors were represented by mass flow rate according to the injection pressure, the spray angle, mass distribution, and mean diameter of droplet.

• Journal of the Korean GEO-environmental Society
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• v.18 no.5
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• pp.35-43
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• 2017

It is a method of suppressing back ground subsidence by re-injecting groundwater back to the target ground and recovering the underground water level. In order to analyze the subsidence of the back ground due to maintaining the underground water level, indoor model experiments were conducted. Through this study, the factors influencing on the groundwater and the tendency of subsidence back ground by experiments were analyzed and the effect of ground subsidence by reinfusion of groundwater was also investigated. As a result of the subsidence analysis with considering only the influence of the underground water level, the settlement of the ground occurs as the underground water level at the time of ground excavation goes down. The closer to the back of the retaining wall, the maximum settlement occurred. Moreover, it was analyzed that the influence distance where subsidence occurs from retaining wall to the point of about 1.8 H on the basis of the ground collapse. The most effective location of water reinjection is the closet location to the back of braced-cut wall for reducing the groundwater down and also minimizing the ground settlement.

• Journal of the Korean Society of Propulsion Engineers
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• v.8 no.2
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• pp.85-94
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• 2004

Experimental study on combustion characteristics of double swirl coaxial injectors has been conducted for the assessment of critical injector design parameters. A reusable, unielement thrust chamber has been fabricated with a water-cooled copper nozzle. Two principal design parameters. a swirl angle and a recess length, have been investigated through hot firing tests for the understanding of their effects on high pressure combustion. Clearly, both parameters considerably affect the combustion efficiency, dynamics and hydraulic characteristics of an injector. Internal mixing of propellants in a recess region increases combustion efficiency along with the increase of a pressure drop required for flowing the same amount of mass flow rates. It is concluded that pressure buildup due to flame can be released by the increase of LOx flow axial momentum or the reduction of a recess length. Dynamic pressure measurements of the thrust chamber show varied dynamic behaviors depending on injector configurations.

• Journal of Korean Tunnelling and Underground Space Association
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• v.20 no.2
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• pp.235-253
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• 2018

Groundwater flow induced by cracks in a buried pipe causes ground loss in the vicinity of it which can lead to underground cavities and sinkhole problems. In this study, the ground collapse mechanism and the failure mode based on an aperture in the pipe located in cohesionless ground were investigated through a series of physical model studies. As the influence parameters, size of the crack, flow velocity in the pipe, groundwater level, ground cover depth and ground composition were adopted in order to examine how each of the parameters affected the behavior of the ground collapse. Influence of every experimental condition was evaluated by the final shape of ground failure (failure mode) and the amount of ground loss. According to the results, the failure mode appeared to be a 'Y' shape which featured a discontinuous change of the angle of erosion when a groundwater level was equal to the height of the ground depth. While in the case of a water table getting higher than the level of ground cover depth, the shape of the failure mode turned to be a 'V' shape that had a constant erosion angle. As the height of the ground depth increased, it was revealed that a mechanism where a vertically collapsed area which consisted of a width proportional to the ground height and a constant length occurred was repeated.

• Maxillofacial Plastic and Reconstructive Surgery
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• v.29 no.2
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• pp.167-173
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• 2007

The temporalis fascia graft has been widely used in the correction of nasal deformities. The fascia can be used alone or combined for augmentation rhinoplasty. The fascia graft provides adequate coverage, contour, and bulk on the profile of the nose, as well as an inconspicuous donor site. A depressed radix area can be successfully corrected by the fascia graft. We present two cases of nasal radix augmentation by using temporalis fascia graft. Two male patients presented with the skeletal class III malocclusion and the depressed radix. A planned orthognathic surgery and the temporalis fascia graft to the radix were performed. The malocclusion and the profile of the patients were markedly improved after the operation. Not only the radix but also the nose was improved in its size and length. There was no noticeable resorption or displacement of the radix area at follow-up. The temporalis fascia graft could be an appropriate surgical technique in radix augmentation and nose lengthening.

• Journal of the Korean Geographical Society
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• v.43 no.4
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• pp.466-476
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• 2008

Gurin Cave, 442 m long, is a lava tube developed on the northern slope of Mount Halla. Seventy-three meters of its lower reach became a river channel since Byeongmun River flowed into a window after roof collapse took place. The subterranean channel has a width of 447 cm and a height of 501 cm, respectively. Its banks show well-developed lava shelves of a typical lava tube, while its floor has sculpted forms which characterize a bed of a bedrock stream. The reach is likely to be collapsed and then has four collapsed windows since its roof has the densely developed testudinal joints and consists of thin lavas with a thickness of 30 to 60 cm. Before the subterranean channel appeared, a ground channel flowed over the cave and joined into a main channel of Byeongmun River at 653 m in altitude. However, the subterranean channel substituted the ground channel since a bed of the ground channel collapsed into the cave. The new channel, flowing through the cave, joined into a main channel at 660 m in altitude. As the drainage area of Byeongmun River expanded upstream the cave, the new channel changed into a main channel. Since floodwater flows down the ground channel as well as the subterranean channel, a distributary stream has temporarily appeared at the collapsed window. Lava tubes are likely to have an affect on the development of river system in Jeiu Island, in that the caves have constantly shown roof-fall.

• The Korean Journal of Soil Zoology
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• v.7 no.1_2
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• pp.45-49
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• 2002

Meloidogyne marylandi Jepson & Golden, 1987 is described from Zoysia grass collected in Cheonan, Korea. The nematode did not produce galls, and females were generally surrounded by a massive egg sac. Perineal patterns of female were a high to rounded arch with shoulders, wavy striae usually forming a rough. Vulva and anus were sunken. Second-stage juvenile body length was 390.3 $\mu\textrm{m}$ (290-430), tail length 55.1 $\mu\textrm{m}$ (49-59) and lateral field with 4 incisures. Male stylet length was 18.1 $\mu\textrm{m}$ (15-24), spicules length 26.2 $\mu\textrm{m}$ (23-29) and lateral field with 4-5 incisures.

• Magazine of the Korea Concrete Institute
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• v.14 no.3
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• pp.64-70
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• 2002

도시 주민생활에 없어서는 안될 주요한 사회간접자본시설로서 하수도, 하수도처리시설 등의 콘크리트 구조물에 대한 부식열화는 현재 세계 각국에서 급속히 진행되고 있다. 콘크리트 구조물이 반영구적이라는 것으로 인식되어 있으나, 실제로는 사용수명이 급속히 단축되어, 특히 콘크리트가 처해있는 환경 중에 황화수소(H$_2$S) 등의 황산화합물이 다량으로 존재하고 있는 환경에서는 하수관 콘크리트의 부식에 의해 도로가 함몰되는 사례도 보도되는 등 시민생활에 큰 위험성을 동반하는 가능성을 배제할 수 없다.(중략)