• Journal of the Korean Society of Propulsion Engineers
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• v.23 no.1
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• pp.33-45
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• 2019

In this study, numerical simulations were performed to investigate the steady-state characteristics of a symmetric pintle nozzle by varying the position of the pintle and the altitude. The pintle nozzle shape was used in a linear pintle nozzle that had been analyzed prior to the study, and the boundary conditions of the chamber were considered to be according to the propellant burn-back characteristics. A software was used to perform a verification analysis of the square nozzle, pintle nozzle, and high-altitude conditions with an appropriate analytical technique. The pintle position had three different nozzle throat area conditions-: fully closed, half open, and fully open, and the altitude was set at 0, 5, and 20 km. The study compared the thrust, pintle drive load, and static stability at each condition.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.46 no.11
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• pp.883-891
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• 2018

In this paper, aerodynamic noise simulation was conducted using DES (Detached Eddy Simulation) and FW-H (Ffowcs Williams and Hawkings) acoustic analogy for the tandem cylinders which have configuration similar to a landing gear of airplanes. Numerical simulation for the tandem cylinders whose centers are 3.7D apart was carried out and results were compared with the measured data such as flow characteristics, pressure coefficients on the cylinder surfaces and far-field noise characteristics. It was confirmed that periodically shedded vortices released at the upstream cylinder and impinged on the downstream cylinder surface are major sources of aerodynamic noise. After verifying the computational method of using DES and FW-H acoustic analogy for predicting aerodynamic noise of tandem cylinders, additional simulation was conducted to examine the effect of attaching a splitter plate at the rear of the upstream cylinder. It was confirmed that the noise level in specific frequency band decreased significantly because the splitter plate changed the vortex shedding features and reduced dipole noise source.

• Journal of the Korea Convergence Society
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• v.12 no.1
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• pp.1-9
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• 2021

Recently, new types of security crimes have been steadily occurring in Korea due to environmental changes such as the development of IT technology, and responding to these threats has become a key national task for the establishment of a safe society as well as individuals and businesses. Meanwhile, as the Zero-Contact Era has arrived since the COVID-19 Pandemics, a new convergence security threat that combines the characteristics of the Zero-Contact Era with the existing IT development is threatening our society. Research to prevent and correct these new levels of threats is continuously required in this study. Chapter 1 examined the causes of new convergence security threats and Chapter 2 discussed cybersecurity, fake news, remote voting·work and video security threats as five major threats.

• Korean Chemical Engineering Research
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• v.60 no.1
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• pp.145-150
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• 2022

Dynamic contact angles have investigated by numerous researchers for understanding interfacial behavior at moving contact lines However, due to limitation of visualization techniques, previous experiments for dynamic contact angles have conducted limitedly in hydrophilic capillary tubes based on visible ray. Recently, there is continuous need for research on dynamic contact angles in hydrophobic capillary tubes on various research and industrial fields. Therefore, in this study, we measure the dynamic contact angles of water-glycerol mixture slug in hydrophobic microtubes using synchrotron X-ray imaging. Based on the visualized data, we verified the previous experimental correlations for dynamic contact angles.

• Proceedings of the Korea Water Resources Association Conference
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• 2020.06a
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• pp.339-339
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• 2020

도시화로 인한 불투수면적의 증가와 기후 변화로 인한 강우패턴의 변화 자연적 물순환 체계에 악영향을 미치며. 이를 해결하기 위하여 국내에서는 도시 내 빗물관리 및 비점오염원 저감이 가능한 저영향개발(Low Impact Development, LID)를 적용하고 있다. 건기시 도로, 주차장등 차량통행 및 유동인구가 많은 지역에서는 입자상 물질들이 많이 발생되어 노면에 축적되어 있다가 강우시 강우유출수를 통해 시설로 유입된다. 이로 인해 시설 내 오염물질 및 퇴적물이 축적되어 여재 공극막힘현상 및 침투율저하의 문제가 발생되어 시설 내 효율이 감소된다. 따라서, 레인가든의 장기 모니터링을 통해 시설 내 유입되는 오염물질의 성상 분석 및 시설 내부의 퇴적물 분석을 통해 LID시설 운영의 효율성 평가를 수행하였다. 모니터링은 강우시 모니터링과 건기시 집수구역, 침강지, 시설 상부, 중부, 하부 등 총 5곳에서 채취하여 분석을 수행하였다. 모니터링은 평균 선행건기 일수는 5.46±4.7 days, 평균 강우량은 14.31±11.4 mm, 평균 강우강도는 5.33±6.7 mm/hr의 강우사상에서 모니터링을 수행하였다. 시설 내 평균 유입수농도는 TSS 98.0 ± 32.7 mg / L, COD 133.6 ± 6.3 mg / L, TN 5.77 ± 4.05 mg, TP 0.54 ± 0.03 mg / L으로 분석되었다. 유입부 내 퇴적물 종류는 Sandy Clay Loam으로 나타났으며, Cr 0.36mg / kg, Cu 5.17 mg / kg and Pb 6.04 mg / kg으로 중금속의 함유량이 높은것으로 분석되었다. 퇴적물은 침강지 및 시설 유입부에서의 입자크기는 49-113㎛ 약 60%의 퇴적물이 축적되어 제거되는 것으로 나타났다. 시설 내 침강지에서 50㎛ 이상의 입자들이 여과, 흡착 및 침전으로 인하여 40% 이상의 입자들이 제거되는 것으로 분석되었으며, 50㎛ 미만의 입자들은 시설 내 중간부, 유출부에서 제거되는 것으로 분석되었다. 침강지에서 유입수 대부분의 입자상물질들이 흡착 및 여과로 인한 제거가 이루어지기에 침강지 여재부는 넓은 표면적, 우수한 흡착능 및 여과율을 고려하여 선정하영 하며, 잦은 교체를 위하여 중량성이 낮은 우드칩 등이 적당한 것으로 사료된다.

• Proceedings of the Korea Water Resources Association Conference
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• 2022.05a
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• pp.262-262
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• 2022

토석류는 산지 사면에서 발생하여 지형변화에 큰 영향을 미치는 대표적인 자연재해 중 하나로 국내에서 발생하는 토석류는 홍수, 태풍 등 타 재해에 비하여 상대적으로 매우 짧은 시간에 발생하며, 사후대응이 어려우므로 사전대비가 필수적이다. 토석류로 인한 피해를 효과적으로 대비하기 위해서는 국내의 지질, 지형 그리고 강우에 따라 발생하는 토석류에 대한 보다 체계적인 정밀현장조사를 통한 자료 구축과 이를 분석한 토석류의 발생원인, 이동경로와 침식 및 퇴적에 관한 연구가 필요하다. 최근의 토석류 연구에서는 침식-퇴적 및 연행작용에 의한 효과를 반영한 수치모의 연구들이 있으나, 모형의 검증을 위한 침식-퇴적 거동에 대한 자료는 현재까지 매우 부족한 실정이다. 토석류 발생에 따른 침식-퇴적 거동특성은 그 자체로도 공학적으로 중요한 요소이며, 수치해석 모의에 필요한 매개변수 추정에도 필요한 항목이다. 토석류 모의의 검증자료로 활용될 수 있는 토석류에 대한 실험적 연구는 토석류의 확산 형태 및 확산 길이에 대한 내용이 대부분으로 흐름수로에서의 침식 및 퇴적에 대한 연구는 찾아보기 어려운 상태이다. 본 연구에서는 토석류 발생에 따른 흐름부에서의 침식 및 퇴적에 대한 거동 특성을 분석하기 위하여 함수비, 흐름수로 경사, 상부 붕괴토조의 토사깊이, 흐름수로 침식가능 깊이 등 다양한 조건으로 실내모형실험을 수행하였다. 상부 토조의 토사 함수비가 30~80% 실험에서는 퇴적 현상이 탁월하였고, 100% 이상인 실험에서는 침식 현상이 확연하게 나타나 토사의 함수비가 높아지면 집중호우 등 선행강우로 인한 산지 지역에서 발생되는 토석류 현상과 유사하고, 함수비가 낮으면 토석류(Debris flow)가 아닌 입상유동(Granular flow)으로 보는 것이 적절한 것으로 판단된다. 상부 토조의 함수비를 100% 이상으로 변화하여 침식이 발생한 실험에서 상부 토조의 액화 된 토사는 빠른 속도로 흐름이 진행되면서 함수비와 붕괴 체적이 증가할수록 흐름수로 상류부에 침식이 크게 나타나고, 상류부의 토사를 중류부를 거쳐 하류부까지 연행(Entrainment)하는 것으로 판단된다.

• Journal of the Korean Geosynthetics Society
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• v.15 no.3
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• pp.27-37
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• 2016

Although many studies on the Granular Compaction Pile (GCP) have been done by many researchers, the GCP design has not been systematically done due to the absence of the rational design methodology. As the GCP design has been mostly done by engineers' own experiences, some failure cases have been reported to occur. For this reason, it is very difficult to confirm definite causes of the failure and establish the prevention plans for the failure. Therefore, this study aims to investigate the optimal mixing ratio of gravel and sand, the effects of the internal friction angle of the GCP on the stress concentration ratio and the vertical and horizontal settlements. In order to analyze the behavior of the soft ground reinforced with the GCP depending on the different design parameters such as the stress concentration ratio and the internal friction angle, a number of finite element (FE) analyses were performed. From the direct shear test, the optimal mixing ratio of gravel to sand was found to be 70:30. Based on the numerical analyses, as the internal friction angle increased, the stress concentration ratio increased and it converged to a constant value. In addition, the larger the internal friction angle, the smaller the settlements. Consequently, the use of the optimal mixing ratio of gravel and sand can lead to reducing both the lateral flow and the heaving phenomenon.

• Journal of the Korean Institute of Gas
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• v.24 no.5
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• pp.56-64
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• 2020

This study presents the hydrate induction time of PVCap according to subcooling temperature, salt concentration, and MEG concentration in order to analyze the inhibition effect of PVCap in various production environments of offshore gas fields. A high-pressure hydrate generator was made for the hydrate formation experiments. It was verified that the apparatus had sufficient reliability by comparing the results of hydrate equilibrium conditions and induction time from the apparatus with published reference data. As the subcooling temperature increased from 6.1℃ to 12.1℃, the induction time of PVCap concentration of 0.1~1 wt% decreased. When the salt concentration increased from 3 wt% to 7 wt%, the induction time was reduced by up to 78% under the condition of 0.5 wt% PVCap due to polymer structure degradation by salt effect. In the case of HHI (hybrid hydrate inhibitor) made by mixing MEG 10 wt% and PVCap, the change in induction time was not large compared to PVCap 1 wt% due to the under-inhibition effect. On the other hand, the hydrate inhibition efficiency of HHI with MEG 20wt% increased 1.7 times compared to PVCap.

• Journal of Korean Ophthalmic Optics Society
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• v.15 no.1
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• pp.39-46
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• 2010

Purpose: To assess the reliability for measuring the back vertex power of soft contact lenses by dry blotting and wet cell method using an auto-lensmeter. Methods: The soft contact lenses used for measurement were 5 types that were distributed in Korea, and 4 back vertex powers (-1.50D, -3.00D, -6.00D, -9.00D) were used. and repeatability and reproducibility were evaluated by measuring them with an auto-lensmeter by two examiners. Results: Measured powers by dry blotting method were ranged in mean differences from 0.03D to 0.18D for overall lenses, 0.10D to 0.18D for silicone hydrogel lenses, 0.03D to 0.08D for hydrogel lenses. The mean differences between two examiners were less than 0.10D, and the inter-examiner reproducibility was good for dry blotting method. The mean difference between powers determined by wet cell method were 0.09D to 0.69D, the mean differences between two examiners were 0.02D to 0.59D. The reliability of measurements and inter-examiner reproducibility were less than dry blotting method. Conclusions: The reliability of measurements for all materials was better in dry blotting than wet cell method, the re liability of measurements for silicone hydrogel lenses was low in both methods. In clinical practical which requires quick checking of back vertex power using an auto-lensmeter. dry blotting method is thought to be more efficient than wet cell one.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2005.11a
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• pp.321-331
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• 2005

Recently. three-dimensional models have been used for aquatic dispersion of radioactive effluents in relation to nuclear power plant siting based on the Notice No. 2003-12 'Guideline for investigating and assessing hydrological and aquatic characteristics of nuclear facility site' of the Ministry of Science and Technology (MOST) in Korea. Several nuclear power plants have been under construction or planed. which are Shin-Korl Unit 1 and 2, Shin-Wolsong Unit 1 and 2, and Shln-Ulchin Unit 1 and 2. For assessing the aquatic dispersion of radionuclides released from the above nuclear power plants, it is necessary to know the coastal currents around sites which are affected by circulation of East Sea. In this study, a three dimensional hydrodynamic model for the circulation of the East Sea of Korea has been developed as the first Phase, which Is based on the RIAMOM. The model uses the primitive equation with hydrostatic approximation, and uses Arakawa-B grid system horizontally and Z-coordinate vertically. Model domain is $126.5^{\circ}E\;to\;142.5^{\circ}E$ of east longitude and $33^{\circ}N\;and\;52^{\circ}N$ of the north latitude. The space of the horizontal grid was $1/12^{\circ}$ to longitude and latitude direction and vortical level was divided to 20. This model uses Generalized Arakawa Scheme. Slant Advection, and Mode-Splitting Method. The input data were from JODC, KNFRDI, and ECMWF. The model ing results are in fairly good agreement with schematic patterns of the surface circulation in the East Sea The local current model and aquatic dispersion model of the coastal region will be developed as the second phase. The oceanic dispersion experiments will be also tarried out by using ARGO Drifter around a nuclear pelter plant site.