• 한국지하수토양환경학회지:지하수토양환경
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• 제20권7호
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• pp.90-102
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• 2015

To understand the hyrogeochemical variation of bedrock aquifer during underground space construction, various graphical methods including multiple-component plots and chemical trends were used to estimate the mixing rate between seawater and freshwater and to investigate the evolution of water quality. The water chemistry and mixing rate between fresh and sea waters, which are generally localized in the construction area (MW-7, in land), shows typical characteristics of freshwater that doesn’t affect its validity as seawater intrusion. Especially, the water chemistry of a MW-4 (coastline) was classified as Na-Cl type, Na-HCO₃ type, and Ca-Cl type due to the influence of the seawater intrusion. And hydrogeochemical and isotopic data show that local freshwater is subjected to geochemical processes, such as reverse ion-exchange. Throughout the Chadha’s diagrams, four different case histories with the temporal and spatial variation of groundwaters in the study area were proposed, which is recommended to interpret the hydrogeochemical reactions effectively.

• 터널과지하공간
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• 제3권1호
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• pp.63-79
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• 1993

The design of tunnels in rock masses often demands more informations on geologic features and rock mass properties than acquired by usual field survey and laboratory testings. In practice, the situation that a perfect set of geological and mechanical input data is given to geomechanics design engineer is rare, while the engineers are asked to achieve a high level of reliability in their design products. This study presents an artificial neural network which is developed to resolve the difficulties encountered in conventional design techniques, particulary the problem of deteriorating the confidence of existing numerical techniques such as the finite element, boundary element and distinct element methods due to the incomplete adn vague input data. The neural network has inferring capabilities to identify the possible failure modes, support requirements and its timing for underground openings, from previous case histories. Use of the neural network has resulted in a better estimate of the correlation between systems of rock mass classifications such as the RMR and Q systems. A back propagation learning algorithm together with a multi-layer network structure is adopted to enhance the inferential accuracy and efficiency of the neural network. A series of experiments comparing the results of the neural network with the actual field observations are performed to demonstrate the abilities of the artificial neural network as a new tunnel design assistance system.

• 한국전산유체공학회지
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• 제6권4호
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• pp.26-34
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• 2001

The flow past a circular cylinder forced to vibrate transversely is numerically simulated by solving the two-dimensional Navier-Stokes equations modified by the vibration velocity of a circular cylinder at a Reynolds number of 164. The higher-order finite difference scheme is employed for the spatial discretization along with the second order Adams-Bashforth and the first order backward-Euler time integration. The calculated cylinder vibration frequency is between 0.60 and 1.30 times of the natural vortex-shedding frequency. The calculated oscillation amplitude extends to 25% of the cylinder diameter and in the case of the lock-in region it is 60%. It is made clear that the cylinder oscillation has influence on the wake pattern, the time histories of the drag and lift forces, power spectral density and phase diagrams, etc. It is found that these results include both the periodic (lock-in) and the quasi-periodic (non-lock-in) state. The vortex shedding frequency equals the driving frequency in the lock-in region but is independent in the non-lock-in region. The mean drag and the maximum lift coefficient increase with the increase of the forcing amplitude in the lock-in state. The lock-in boundaries are also established from the present direct numerical simulation.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2001년도 춘계 학술대회논문집
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• pp.181-188
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• 2001

The flow past a circular cylinder forced to vibrate transversely is numerically simulated by solving the two-dimensional Wavier-Stokes equations modified by the vibration velocity of a circular cylinder at a Reynolds number of 164. The higher-order finite difference scheme is employed for the spatial discretization along with the second order Adams-Bashforth and the first order backward-Euler time integration. The calculated cylinder vibration frequency is between 0.60 and 1.30 times of the natural vortex-shedding frequency. The calculated oscillation amplitude extends to $25\%$ of the cylinder diameter and in the case of the lock-in region it is $60\%$. It is made clear that the cylinder oscillation has influence on the wake pattern, the time histories of the drag and lift forces, power spectral density and phase diagrams, etc. It is found that these results include both the periodic (lock-in) and the quasi-periodic (non-lock-in) state. The vortex shedding frequency equals the driving frequency in the lock-in region but is independent in the non-lock-in region. The mean drag and the maximum lift coefficient increase with the increase of the forcing amplitude in the lock-in state. The lock-in boundaries are also established from the present direct numerical simulation.

• 대한안전경영과학회지
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• 제17권1호
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• pp.257-264
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• 2015

"Act on Facilitation of Purchase of Small and Medium Enterprise - Manufactured Products and Support for Development of Their Markets" was created and implemented. The act states that the materials designated by the Small and Medium Business Administration are directly purchased from the small and medium enterprises and provided to the construction companies so that the materials can be provided as GFGI (Government Furnished and Government Installed) in the case of a public construction project. This thesis is aimed to analyze the current status on the problems of each project party and understand their improvement requests so that mutually beneficial plans can be sought and improved process is presented for the continuous development of the direct construction material purchase system as well as successful construction projects. And This thesis summarized the purpose of the institutions and their change histories, and related law as well as codes for the better understanding of administrative procedures for the purchase system and the analyses as well as the improved process on the difficulties in complying with the current institutions.

• Nuclear Engineering and Technology
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• 제46권3호
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• pp.343-352
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• 2014

Uncertainty and sensitivity analyses with respect to nuclear data are performed with depletion calculations for BWR and PWR fuel assemblies specified in the framework of the UAM-LWR Benchmark Phase II. For this, the GRS sampling based tool XSUSA is employed together with the TRITON depletion sequences from the SCALE 6.1 code system. Uncertainties for multiplication factors and nuclide inventories are determined, as well as the main contributors to these result uncertainties by calculating importance indicators. The corresponding neutron transport calculations are performed with the deterministic discrete-ordinates code NEWT. In addition, the Monte Carlo code KENO in multi-group mode is used to demonstrate a method with which the number of neutron histories per calculation run can be substantially reduced as compared to that in a calculation for the nominal case without uncertainties, while uncertainties and sensitivities are obtained with almost the same accuracy.

• Journal of Chest Surgery
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• 제20권2호
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• pp.300-308
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• 1987

Clinical and pathologic data were reviewed in 20 patients who had have surgery for isolated aortic valvular heart disease between April 1978 and April, 1987. Hospital mortality was 10%, with no additional late mortality during a mean follow-up period of 24.1 months. Prosthetic valve failure developed in 3 patients and two had reoperation. Niety four percent of the survivors who were in NYHA Funtional class III or IV before operation are now in class I or II. Ninety percent of all patients are still alive at a maximum follow up of 9 years. The clinical histories, gross and histologic examination of valves estabilished the causes for isolated aortic valve disease: 3 rheumatic, 2 congenital bicuspid, 2 hypertention, 2 aortitis and each one case of floppy valve, medial cystic necrosis of aorta, bacterial endocarditis. But etiology was unknown in 8 cases. Sixteen patietns had myxoid degeneration, defined as significant disruption of the valve fibrosa and its replacement by acid mucosaccharides and cystic changes. Myxoid degeneration was also the primary pathologic abnormality in the patients with 2 hypertention, 2 rheumatic, 1 aortitis, 1 bacterial endocarditis, 1 floppy valve, 1 congenital bicuspid. The patients with myxoid degeneration of uncertain origin were 8. Histologic finding of all of them revealed nonspecific patients with myxoid degeneration of uncertain orgin were 8. Histologic finding of all of them revealed nonspecific chronic valvulitis with myxoid degeneration. This finding may indicate that the etiology w uld be infectious.

• 한국정밀공학회지
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• 제24권2호
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• pp.110-117
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• 2007

In this paper, probabilistic distribution of chassis component fatigue life is determined statistically by applying the design of experiments and the Pearson system. To construct p - ${\varepsilon}$ - N curve, the case that fatigue data are random variables is attempted. Probabilistic density function (p.d.f) for fatigue life is obtained by the design of experiment and using this p.d.f fatigue reliability, any aimed fatigue life can be calculated. Lower control arm and rear torsion bar of chassis components are selected as examples for analysis. Component load histories which are obtained by multi-body dynamic simulation for Belsian load history are used. Finite element analysis is performed by using commercial software MSC Nastran and fatigue analysis is performed by using FE Fatigue. When strain-life curve itself is random variable, the probability density function of fatigue life has very little difference from log-normal distribution. And the cases of fatigue data are random variables, probability density functions are approximated to Beta distribution. Each p.d.f is verified by Monte-Carlo simulation.

• 지구물리
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• 제5권2호
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• pp.99-109
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• 2002

전자탐사는 매우 다양한 탐사 방법론 및 탐사 장비가 개발되어 있으며 그 적용 분야 또한 매우 넓다. 전자탐사는 탐사기법 및 사용되는 기기 즉, 특정 송 · 수신 배열이나 사용 주파수 대역 등에 따라 탐사심도 및 분해능이 서로 다른 결과를 제공한다. 또한 현대의 전자탐사 측정장비는 그 복잡성에 비추어 장비의 이동성이 뛰어나므로 지반조사 및 환경 오염대의 조사와 같은 지반 · 환경 물리탐사에 적용이 용이하다. 비록 전자탐사는 이론이 복잡하지만, 최근 급속한 컴퓨터 기술의 발달에 힘입어 정확한 모델링 및 역산 기법이 지속적으로 개발되고 있다. 여기서는 다양한 전자탐사 방법 중에서 환경분야 및 지반조사에 효과적이고 현재 국내에서 수행 가능한 방법 및 조속한 시일 내에 국내에 도입 가능한 전자탐사법의 원리 및 방법을 간략하게 소개하고 각 방법에 대한 현장자료를 소개한다.

• Geomechanics and Engineering
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• 제14권3호
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• pp.257-269
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• 2018

Analysis of slope stability failures, as one of the complex natural hazards, is one of the important research issues in the field of civil engineering. Present paper adopts and investigates four soft computing-based techniques for this problem: Patient Rule-Induction Method (PRIM), M5' algorithm, Group Method of data Handling (GMDH) and Multivariate Adaptive Regression Splines (MARS). A comprehensive database consisting of 168 case histories is used to calibrate and test the developed models. Six predictive variables including slope height, slope angle, bulk density, cohesion, angle of internal friction, and pore water pressure ratio were considered to generate new models. The results of test studies are used for feasibility, effectiveness and practicality comparison of techniques with each other, and with the other available well-known methods in the literature. Results show that all methods not only are feasible but also result in better performance than previously developed soft computing based predictive models and tools. It is shown that M5' and PRIM algorithms are the most effective and practical prediction models.