• 한국공간구조학회논문집
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• 제5권2호
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• pp.47-55
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• 2005

공기막구조물의 공간형성방법은 크게 단일공기막과 이중공기막 방식으로 나뉜다. 내압으로 인해 평형곡면이 형성되는 공기막구조물의 형상은 형태의 변화가 외력에 의해 크게 변형되거나 응력이 집중되지 않는 등장력 곡면으로 많이 이용된다. 따라서 본 연구에서는 공기막 구조물의 초기 형성된 형상에 대해서 설계하중조합에 대한 구조해석을 비선형 전용해석프로그램인 NASS를 이용하여 수행한 후 변형형상을 살펴보고, 최대응력을 이용하여 안전성을 검토한다. 해석 모델은 사면에서 지지되는 장방형 단일공기막 구조물을 대상으로 하며, 직교이방성을 고려하여 비선형 증분해석을 수행한다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 춘계학술대회논문집
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• pp.1061-1066
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• 2002

This study proposes an analytic method that determines an optimal arrangement of absorptive materials on an enclosure surface. Under the optimal arrangement, a quiet zone in the enclosure has the minimum $\varepsilon$$\sub$p/ (acoustic potential energy density). The proposed method has been implemented by using a BEM simulation and a genetic algorithm. The BEM simulation evaluates the $\varepsilon$$\sub$p/ under the prescribed arrangement of the absorptive materials. The genetic algorithm searches the optimal arrangement by referring the ep evaluated from the BEM simulation. In the BEM simulation, the absorptive material arrangement is expressed as a vector, which is denoted as in absorptive material arrangement (AMA) vector. Besides, an admittance vector of which elements are admittances of available absorptive materials and an AMA matrix that transforms the admittance vector into the AMA vector are defined. The AMA matrix is also used as a chromosome in the genetic algorithm so that it functions to relate the BEM simulation to the genetic algorithm. As a verification example, the proposed method is applied to make the quiet zone in a parallelepiped enclosure.

• Safety and Health at Work
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• 제9권2호
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• pp.180-183
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• 2018

Background: This research investigates the degrees of slipperiness felt by the participants who walk on contaminants applied to a floor surface to decide degrees of slipperiness for various contaminants. Methods: For the experiment, 30 participants walked on a floor to which six contaminants were applied. All participants took the analytic hierarchy process (AHP)-based slipperiness questionnaire survey for the six kinds of contaminants, and the results were compared with the coefficient of friction. Results: The results of slip risk from the AHP indicate that grease is the most slippery of the six contaminants, followed by diesel engine oil, hydraulic oil, cooking oil, water-soluble cutting oil, and water in a decreasing order of slipperiness. When the results of slip risk from the AHP are compared with the static coefficient of friction for each contaminant, the order of slip risk follows the same trend. Although the results of slip risk from the AHP coincide with the static coefficient of friction, further study would be needed to investigate this relationship. Conclusion: This study will contribute as reference material for future research on preventing industrial accidents that result in falls from high places due to slipping.

• 대한조선학회논문집
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• 제29권1호
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• pp.81-92
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• 1992

본 논문은 비정상 공동 프로펠러의 영향하에 있는 선체표면의 경계치 문제를 해석하고, 이로부터 선체표면에 유기되는 변동압력을 추정할 수 있는 프로그램의 개발과정을 다루고 있다. 본 논문에서는 개발된 프로그램을 캐비티를 표현하는 쏘오스의 영향하에 있는 구 주위의 유동해석에 적용하여 Butler의 해석해와 비교한 것을 싣고 있으며, 특히 자유수면 조건을 고주파수 근사방식 또는 강체벽 근사방식으로 근사화하였을때 변동압력에 미치는 영향을 조사하였다. 또한 실제 RO-RO선을 대상으로 예제 계산을 수행하여, 선박설계과정에서 선체표면 기진력의 해석에 사용될 수 있음을 보였다.

• 한국해양공학회지
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• 제16권2호
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• pp.38-43
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• 2002

Die-less forming is a cold forming process which is to bend thick flat plates into compound curved plates using two asymmetric rollers. This forming method has several advantages compared with line heating which is widely used to fabricate compound curved pieces in shipyards. The die-less forming, however, has scarcely been studied. Even the deformation mechanism in this forming process has not been understood clearly. So, in this paper, the deformation characteristics of die-less forming is investigated analytically and numerically. for the analytic investigation, slab method based on equilibrium equation is applied. And the mechanism of curvature generation is derived for the asymmetry in roller applied. And three dimensional numerical analyses are performed with realistic modeling of interactions between the rollers and work-piece using finite element program, ABAQUS. It is shown that curvature generation is mainly due to the difference of normal positive strain distribution between the top and bottom surface of the work-piece. And a convex-type curved plate is formed if the center region of the work-piece is rolled with asymmetric rollers of which the lower is larger than the upper in diameter.

• 대한조선학회논문집
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• 제29권4호
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• pp.58-65
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• 1992

본 논문에서는 물체표면을 겹 3차 B-Spline 방법에 의하여 표현하고, 특이점세기를 겹선형으로 근사하는 고차판요소법을 이용하여 몰수체에 대한 조파저항을 계산하였다. 여기서 Neumann-kelvin 문제는 쏘오스분포법과 법선다이폴분포법에 의하여 해석되었다. 고차 판요소법에 의하여 계산된 결과는 Hess & Smith가 사용한 최저차 판요소법 결과와 비교하였으며, 고차 판요소법의 수렴도는 보통 판요소법보다 훨씬 좋은 것으로 나타났다. 그러나, 고차 판요소법에 의하여 계산된 조파저항도 최저차 판요소법에 의한 것과 마찬가지로 낮은 Froude 수에서는 해석해와의 차이를 보이고 있다.

• Restorative Dentistry and Endodontics
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• 제17권1호
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• pp.153-165
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• 1992

Dental composite resin is a kind of the particle - reinforced composite material, and is widely used in recent dental restoration of anterior and posterior tooth region. The purpose of this study was to investigate the fracture behaviour according to volume fractions and external findings of the filler particles for better interpretation of the fracture characteristics of posterior dental composite resins by analytic method of fracture mechanics. The plane strain fracture toughness($K_{IC}$) and Acoustic Emission were determined with three - point bending test using the single edge notch specimen according to the ASTM - E399, and its analyzed data was compared with filler volume fractions derived from the standard ashing test and scanning electron fractographs of each specimen including the unfilled experimental resin as a control. The results were that the value of fracture toughness of the composite resin material was in the range from 0.85 MPa$\sqrt{m}$ to 1.60 MPa$\sqrt{m}$ and was higher than the value of the unfilled experimental resin, and the fracture behaviours dervied from Acoustic Emission analysis show prominent differences according to the volume fraction and the size of filler particles used in each composite resin. The degree of resistance against crack propagation seems to be increase and the fractographs demonstrate the high degree of surface roughness and irregularity according with the increase of fracture toughness value.

• 한국물환경학회지
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• 제20권3호
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• pp.245-250
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• 2004

This study investigated the micropollutants present in raw water supplied for the several drinking water treatment plants in Seoul. The target sample waters were collected from the several sites, such as Jayang (JY), Kuui (KI), Paldang (PD) and Kangbuk (KB) at the Han-River stream. The analytical method used in this study enable us to detect about 300 kinds of chemicals commonly found in surface water at ppt level by GC-ion trap MS. In this study, the consideration on the analytic results focused on the four hazardous organics, such as benzenes, phenols, phthalates and pesticides. The numbers of each detected micropollutant were 1~8 kinds for benzenes, 1~7 kinds for phenols, 5~7 kinds for phthalates and 1~9 kinds for pesticides. For the pesticides, the higher concentration was detected in the water samples collected from PD and KB adjacent to the farming area, and at June and July, which is the busy farming season. The total concentrations of each micropollutants detected at all the sites were significantly lower than those of drinking water regulation in Korea as well as other advanced countries. However, the frequently detected micropollutants requires the steady and precise monitoring for the effective management of drinking water source.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2001년도 추계학술대회논문집 II
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• pp.799-804
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• 2001

Nonlinear normal mode (NNM) vibration, in a nonlinear dual mass Hamiltonian system, which has 6th order homogeneous polynomial as a nonlinear term, is studied in this paper. The existence, bifurcation, and the orbital stability of periodic motions are to be studied in the phase space. In order to find the analytic expression of the invariant curves in the Poincare Map, which is a mapping of a phase trajectory onto 2 dimensional surface in 4 dimensional phase space, Whittaker's Adelphic Integral, instead of the direct integration of the equations of motion or the Birkhotf-Gustavson (B-G) canonical transformation, is derived for small value of energy. It is revealed that the integral of motion by Adelphic Integral is essentially consistent with the one obtained from the B-G transformation method. The resulting expression of the invariant curves can be used for analyzing the behavior of NNM vibration in the Poincare Map.

• 한국지진공학회:학술대회논문집
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• 한국지진공학회 2003년도 춘계 학술발표회논문집
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• pp.50-58
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• 2003

We have developed a locally variable time-step scheme matching with discontinuous grids in the flute-difference method for the efficient simulation of seismic wave propagation. The first-order velocity-stress formulations are used to obtain the spatial derivatives using finite-difference operators on a staggered grid. A three-times coarser grid in the high-velocity region compared with the grid in the low-velocity region is used to avoid spatial oversampling. Temporal steps corresponding to the spatial sampling ratio between both regions are determined based on proper stability criteria. The wavefield in the margin of the region with smaller time-step are linearly interpolated in time using the values calculated in the region with larger one. The accuracy of the proposed scheme is tested through comparisons with analytic solutions and conventional finite-difference scheme with constant grid spacing and time step. The use of the locally variable time-step scheme with discontinuous grids results in remarkable saving of the computation time and memory requirement with dependency of the efficiency on the simulation model. This implies that ground motion for a realistic velocity structures including near-surface sediments can be modeled to high frequency (several Hz) without requiring severe computer memory