• Journal of the Korean Geosynthetics Society
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• v.16 no.2
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• pp.183-194
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• 2017

When a borehole is drilled, the load distributed by the removal is taken to re-establish equilibrium. As a result, the stresses around the borehole is redistributed. If there is no hydrostatic support pressure by drilling fluid (mud) introduced into the borehole, failure in the formation may take place. The mud pressure boundary that keeps the borehole stable is defined as a mud window. To predict the potential for failures around the borehole, a series of numerical analysis were performed and compared with a mud window. The effect of failure criterion and the intial stress ratio adopted on the mud window was also studied.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.7 no.1
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• pp.12-23
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• 1995

Currents driven by irregular waves are modelled using numerical model with various empirical relations improved. Kitaigorodskii's equilibrium equation is refined to account for shoaling effect and used for checking the breaking condition. In order to compute the bottom friction realistically. equivalent roughness blights are estimated considering the ripple shape and bed load transport which may be significant the surf zone. Two sets of equations are employed to evaluate the ripple shape: one is suggested by Nielsen and the other by Madsen and Rogengaus. Both equations give similar shape of ripples. but Madsen et al. give lower value of ripple factor than Swart suggesting that the equivalent roughness becomes relatively small. Optimization technique is used to determine the proper values for the empirical parameters of $\kappa$-ι equations, and the longshore current velocity is computed using the values of empirical parameters determined by the optimization technique.

• Proceedings of the KIEE Conference
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• 2001.07d
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• pp.2789-2791
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• 2001

데이터 마이닝을 통해 우리는 숨겨진 지식, 예상되지 않았던 경향 그리고 새로운 법칙들을 방대한 데이터에서 이끌어내고자 한다. 본 논문에서 우리는 사용자의 구매 패턴을 발견하여 사용자가 원하는 상품을 미리 예측하여 추천하는 알고리즘을 소개하고자 한다. 제안하고 있는 item dependency map은 구매된 상품간의 관계를 수식화 하여 행렬의 형태로 표현한 것이다. Item dependency map의 값은 사용자가 A라는 상품을 구매한 후 B상품을 살 확률이다. 이런 정보를 가지고 있는 item dependency map은 홉필드 네트윅(Hopfield network)에서 연상을 위한 패턴 값으로 적용된다. 홉필드 네트웍은 각 노드사이의 연결가중치에 기억하고자 하는 것들을 연상시킨 뒤 어떤 입력을 통해서 전체 네트워크가 어떤 평형상태에 도달하는 방식으로 작동되는 신경망 중의 하나이다. 홉필드 네트웍의 특징 중의 하나는 부분 정보로부터 전체 정보를 추출할 수 있는 것이다. 이러한 특징을 가지고 사용자들의 일반적인 구매패턴을 일부 정보만 가지고 예측할 수 있다. Item dependency map은 홉필드 네트윅에서 사용자들의 그룹별 패턴을 학습하는데 사용된다. 따라서 item dependency map이 얼마나 사용자 구매패턴에 대한 정보를 가지고 있는지에 따라 그 결과가 결정되는 것이다. 본 논문은 정확한 item dependency map을 계산해 내는 알고리즘을 주로 논의하겠다.

• Fire Science and Engineering
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• v.25 no.2
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• pp.114-119
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• 2011

Explosion limit and flash point are the major combustion properties used to determine the fire and explosion hazards of the flammable substances. In this study, in order to predict upper explosion limits (UEL) for acids and ketones, the upper flash point of these were measured under the VLE (vaporliquid equilibrium) state by using Setaflash closed cup tester (ASTM D3278). The UELs calculated by Antoine equation by using the experimental upper flash point are usually lower than the several reported UELs. From the given results, using the proposed experimental and predicted method, it is possible to research the upper explosion limits of the other flammable substances.

• Proceedings of the Korea Water Resources Association Conference
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• 2016.05a
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• pp.400-400
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• 2016

자연하천에서 다양한 목적으로 설치된 수공구조물을 볼 수 있으며 대표적으로 교량의 교각을 들 수 있다. 교각 주위에서 발생하는 국부세굴은 교량붕괴의 가장 큰 원인이므로 이에 대한 연구는 필수적이다. 수리실험 또는 수치모형을 이용하여 교각주변의 국부세굴에 관한 많은 연구들이 수행되었지만 세굴인자의 특성 및 메커니즘에 대한 연구는 여전히 부족하다. 본 연구에서는 LES(large-eddy simulation)에 유사이송 및 하상변동 모형과 결합하여 2개의 원형교각 주변의 흐름 및 세굴을 수치모의 하였다. LES와 유사이송 및 하상변동 모형의 결합은 난류의 영향을 직접 모형에 고려할 수 있기 때문에 교각 주변에서 발생하는 말굽형 와 구조와 같은 복잡한 흐름에 의한 영향이 반영된다. 계산영역은 흐름방향으로 10 m, 횡 방향으로 2.4 m로 하였고, 지름(D) 0.16 m를 가지는 원형교각을 유입부로부터 2.4 m 떨어진 위치에 배치하였다. 이때 두 개 교각사이의 각은 $0^{\circ}{\sim90^{\circ}$이고 원형교각 사이의 거리는 5D로 하였다. 수치모의에 사용된 조건은 이전의 수리실험(Khosronejad et al., 2012)을 참고하여 접근평균유속은 0.25 m/s, 수심은 0.15m를 사용하였다. 수치모의는 원형교각 주변의 최대세굴심이 평형상태에 이를 때 까지 수행하였다. 접근각도 변화에 따른 원형교각 주변의 세굴과정 및 특성을 분석하였으며 최대 세굴심 결과를 Hannah(1978)의 수리실험결과와 비교하였다.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2011.04a
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• pp.356-359
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• 2011

In this study, applicable to Sounding Rocket about the development of high-performance propellant was studied. Sounding Rocket requires generally multistage rocket system for atmospheric research. This study describes the development of two types solid propellant compositions which are based on HTPB/AP for the two-stage rocket. CEA code of NASA and internal ballistic analysis were used for confirming the theoretical performance of designed propellants. The strand burner and JANNAF tensile test was used to measure ballistic and mechanical properties of designed propellants. Finally, static fired test of standard motors was performed to prove the possibility of development.

• Journal of the Korean Society of Propulsion Engineers
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• v.25 no.3
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• pp.1-13
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• 2021

Effects of the nozzle wall angles on the supersonic flow field in a thrust optimized nozzle were numerically investigated. The combustor and operating condition of 30-tonf rocket engine was selected to study the optimum nozzle shape. The nozzle flow of combustion products was realized by the shifting equilibrium calculation for the propellant of kerosene-LOx. The change of nozzle wall angles induced different developing patterns of the internal and secondary shock wave. The optimum nozzle was obtained when the internal shock was in a specific position at the nozzle outlet. The nozzle wall angles of the optimum nozzle were very similar to those of the optimum nozzle which does not consider the shock wave.

• Journal of the Korean Chemical Society
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• v.29 no.3
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• pp.239-246
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• 1985

The equilibria of chemical reaction between [Cu(dl-trans-[14]-diene)]$^{2+}$ and L$^{n-}$(S$_2$O$_3^{2-}$, SCN$^-$, I$^-$, NO$_2^-$) ions were studied by the spectrophotometric method in the range of 15 to 35$^{\circ}C$ and 1 to 1500bar. The equilibrium constants(K) for L$^{n-}$ = S$_2$O$_3^{2-}$, SCN$^-$, I$^-$ and NO$_2^-$ ions at 25$^{\circ}C$ and 1500bar were 3.0, 1.9, 0.6 and 0.5, respectively. The values of K decreased with increasing pressure and temperature. From the temperature effect on equlibrium constant, the thermodynamic parameters(${\Delta}G^{\circ}$, ${\Delta}H^{\circ}$, ${\Delta}S^{\circ}$) of reaction were evaluated and the reactions of [Cu(dl-trans-[14]-diene)]2+ ion with S$_2$O$_3^{2-}$, SCN$^-$ and I$^-$ except NO$_2^-$ ion were exothermic. The volume changes of reaction(${\Delta}$V) had positive values for all the used anions. The values of ${\Delta}$V in cm$^3$/mole for S$_2$O$_3^{2-}$ ion at 1,500, 1,000 and 1,500bar were 26, 22, 19 and 16, and those for S$_2$O$_3^{2-}$, SCN$^-$, I$^-$ and NO$_2^-$ ions at atmospheric pressure 26, 30, 64 and 45, respectively. Bonding character between Cu(Ⅱ)-complex ion and L$^{n-}$ was discussed by comparing both the equlibrium constants experimentally determined and those calculated according to Fuoss's ion-pair equation in case of S$_2$O$_3^{2-}$ ion.

• Journal of Nuclear Fuel Cycle and Waste Technology(JNFCWT)
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• v.15 no.1
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• pp.35-44
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• 2017

A gamma-ray peak of $^{226}Ra$ (186.2 keV) overlaps with one of $^{235}U$ (185.7 keV) in a gamma-ray spectrometry system. Though reference peaks of $^{235}U$ can be used to correct the peak interference of $^{235}U$ in the analysis of $^{226}Ra$, this requires a complicated calculation process and a high limit of quantitation. On the other hand, evaluating $^{226}Ra$ using the correction constant in the overlapped peak can make a rapid measurement of $^{226}Ra$ without the complicated calculation process as well as overcome the disadvantage in the indirect measurement of $^{214}Bi$, which means the confinement of $^{222}Rn$ gas in a sample container and a time period to recover the secular equilibrium. About 93 samples with 6 species for raw-materials and by-products were prepared to evaluate the activity of $^{226}Ra$ using the correction constant. The results were compared with the activity of $^{214}Bi$, which means the indirect measurement of $^{226}Ra$, to validate the method of the direct measurement of $^{226}Ra$ using the correction constant. The difference between the direct and indirect measurement of $^{226}Ra$ was generally below about ${\pm}20%$. However, in the case of the phospho gypsum, a large error of about 50% was found in the comparison results, which indicates the disequilibrium between $^{238}U$ and $^{226}Ra$ in the materials. Application results of the contribution ratio of $^{226}Ra$ were below about ${\pm}10%$. The direct measurement of $^{226}Ra$ using the correction constant can be an effective method for its rapid measurement of raw materials and by-products because the activity of $^{226}Ra$ can be produced with a simple calculation without the consideration of the integrity of a sample container and the time period to recover the secular equilibrium.

• Journal of the Korean Society of Food Science and Nutrition
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• v.30 no.5
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• pp.894-899
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• 2001

Intakes and excretions of zinc and copper were determined for 8 female adolescents (aged 16.4$\pm$0.5 y; body mass index 20.4$\pm$1.3kg/$m^2$; body fat 33.3$\pm$2.5%; bone mineral density of lumbar spine in L2-L4; 0.96$\pm$0.08g/$\textrm{cm}^2$) when they consumed diets basal and high in calcium for 6 days each. All subjects consumed a basal Ca diet containing 800 mg, Korean RDA level of the subjects, and a high Ca diet containing 1200mg, RDA plus 2 SDs of calcium intake. The diets provided 58% of energy intake as carbohydrate, 25% as fat, and 17% as protein. Food, urine and fecal samples were collected during the last 3 days of each feeding period and were assayed. Mean daily intakes on the basal and high calcium diets, respectively, were 6.57 and 6.37 mg for zinc and 910 and 812 $\mu\textrm{g}$for copper. Fecal excretion of copper and zinc in relation to intake was significantly greater on the high calcium than on the basal calcium diet. Hence, apparent absorption rate was significantly lowered from 98.7% on the basal calcium diet to 97.9% on the high calcium diet for zinc from 66.3% to 56.4% for copper, respectively. Urinary loss of copper was not detectable but that of zinc was 0.38mg on the basal diet and 0.47mg on the high calcium diet. Copper retention was 899$\pm$105$\mu\textrm{g}$/day on the basal calcium diet and 792$\pm$20.8$\mu\textrm{g}$/day on the high calcium diet, and zinc retention was 3.95$\pm$0.91mg/day and 3.11$\pm$0.89mg/day. Thus, copper and zinc retention was significantly decreased on the high calcium diet (p<0.05). Summarizing the results, apparent absorption and retention of zinc and copper were significantly decreased by calcium supplementation. Therefore, it is suggested that interactions among minerals should be considered in determining RDA.