• 소성∙가공
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• 제19권2호
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• pp.79-87
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• 2010

The Pipe bending process using high frequency local induction heating is an advanced technique to bend pipes with a small bending radius and a large diameter. Even though the pipe bending process is a quite widespread engineering practice, it depends heavily upon trial and error method by field engineers with several years of experience. So it is necessary to develop an integrated methodology for optimum design of the pipe bending process. During hot pipe bending using induction heating, outward wall thickness of a pipe is thinned due to tensile stress and the reduction of wall thickness is not allowed to exceed 12.5%. Taguchi method and dynamic reverse moment is proposed to maintain a reduction ratio of thickness within 12.5%, when D/t ratio is high. An application of the proposed approach was compared with those of the finite element analysis and has good in agreements.

• 한국지반공학회논문집
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• 제23권5호
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• pp.153-162
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• 2007

치환공법을 적용하여 연약지반 상에 시공되는 보강토 옹벽에 대해 연약지반의 두께 및 강성, 치환깊이와 옹벽높이의 변화에 따른 옹벽의 거동을 연약지반 압밀현상과 시공단계를 함께 고려하는 유한요소해석으로 검토하였다. 옹벽의 거동은 벽체에 발생하는 변위와 침하량, 옹벽 기초지반에 발생하는 전단변형율로 표현하였다. 거동에 따른 옹벽의 안정성은 변위와 전단변형율의 한계값을 문헌연구로부터 정하고 이를 기준으로 평가하였다. 해석결과로부터, 옹벽의 거동은 연약지반 두께(t)와 강성, 치환깊이(d), 옹벽높이(h)의 변화에 따라 모두 영향을 받지만, 특히 d와 h의 변화에 민감한 것을 규명하였다. 또한, 옹벽의 안정성 유지를 위해 요구되는 d/h 값은 t와 h의 변화에 대하여 크게 영향을 받지 않음을 보였다. 이러한 결과로부터 연약지반 상 보강토 시공 구간 내에서 옹벽 높이가 변화하지만 그 변화정도가 극심하지 않은 경우에, 적정 치환깊이를 d/h로 나타낸 일률적인 값으로 제안할 수 있다는 결론을 얻었다.

• Journal of Magnetics
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• 제11권2호
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• pp.83-86
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• 2006

Controlling magnetic domains in soft underlayer (SUL) of perpendicular magnetic recording (PMR) is an important issue for the application of PMR in HDD. We studied the magnetic domain structures in SUL using the finite element based micromagnetic simulation (FEMM) for the SUL models with different thicknesses. The purpose is to simulate the magnetic domain wall noise when the SUL thickness and saturation magnetization are changed. The simulation results show that a 15 nm SUL forms simpler Neel wall domain wall pattern and 40 nm SUL forms complex Bloch wall. To visualize the effect of these domain walls stray field at a read sensor position, the magnetic stray field of the domain walls at air bearing surface (ABS) which is 50 nm above the SUL was simulated and the results imply that Bloch walls have stronger stray field with more complicated field patterns than Neel walls and this becomes a significant noise source. Therefore, the thickness of the SUL should be controlled to avoid the formation of Bloch walls.

• 한국안전학회지
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• 제23권3호
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• pp.17-24
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• 2008

Elbows with various shapes of local wall thinning were numerically analyzed by finite element method to get load-displacement curves and the maximum loads. Results were compared with the experimental data obtained by another study. Elastic-plastic analysis were carried out under the combined loading conditions of internal pressure and in-plane bending loads. Two types of bending loads were considered such as elbow opening mode and elbow closing mode. Also, two different wall thinning geometries were modeled. Wall thinning area located extrados or intrados of elbow inner surface was considered. Longitudinal and circumferential lengths of the thinning area and the thinned thickness were varied for analysis. The results showed that the maximum load of the wall-thinned elbow decreased with increasing of the circumferential thinning length and the thinned thickness in both of extrados and intrados thinning locations in both loading types. The maximum load obtained by the analysis were in good agreement with the experimentally measured maximum load with the same wall thinning type and dimensions. This supports accuracy of the analysis results obtained in this study.

• Structural Engineering and Mechanics
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• 제51권1호
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• pp.15-37
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• 2014

In this study, the optimum silo dimensions for the barrel-type steel-concentrated silo with a conical outlet port usable in the hazelnut storage were investigated. Three different types of silo models as Model 1 (1635 tons), Model 2 (620 tons) and Model 3 (1124 tons) were used in the study. Varying wall thicknesses were used for Model 1 (10, 11, 12, 13, 14, 15 and 20 mm), Model 2 (10, 15 and 20 mm) and Model 3 (10, 15 and 20 mm) silos. For Model 1 silo has the most storage capacity here, to determine its optimum wall thickness, the wall thicknesses of 11, 12, 13 and 14 mm were used as different from the other models. Thus the stresses occurring in different lines with ANSYS finite element software were examined. In the study it was determined that the 10, 11 and 12 mm wall thicknesses of the Model 1 silo are not safe in terms of the stresses caused by the vertical pressure loads in the filling conditions. From the view of the filling and discharge conditions, other wall thicknesses and model silos were diagnosed to be secure. The optimum silo dimensions which won't cause any structural problems have been found out as the Model 1 silo with a 13 mm wall thickness when the filling capacity and the maximum von Mises stresses are taken into account. This barrel-type silo with conical outlet port sets forth the most convenient properties in hazelnut storing in terms of engineering.

• KCI Concrete Journal
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• 제14권4호
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• pp.151-159
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• 2002

This study investigates experimentally the optimum mix proportion and design factors of the stabilizing liquid used for excavation of the massive and deep slurry wall in LNG in-ground tank before pouring concrete. Considering those site conditions, the stabilizing liquid used for excavation of slurry wall has to be satisfied with some requirements including specific gravity, fluid loss, cake thickness, funnel viscosity and sand content in order to construct the safe and qualified slurry wall. For this purpose, we select materials including bentonite, polymer and dispersion agent. After performing many tests for materials and mix design process, we propose the optimum mix proportion that the upper limit ratio of bentonite is $2.0\%$, polymer is $0.1\%$ considering the funnel viscosity and dispersion agent is $0.05\%$considering the fluid loss of the stabilizing liquid. Also, we select all materials which are consisted of GTC4 as bentonite, KSTP as polymer and Bentocryl 86 as dispersion agent. Based on the results of this study, the optimum mix proportion of the stabilizing liquid is applicable to excavate the deep and massive slurry wall in LNG in-ground tank successfully.

• 대한기계학회논문집B
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• 제27권5호
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• pp.543-552
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• 2003

The effects of a directionally emitting and reflecting dielectric surface on the wall heat flux and medium temperature distribution are studied. The system is an infinite square duct enclosing an absorbing and emitting medium. The emissivity and reflectivity of opaque and gray wall vary with direction. Combined effect of conductive and radiative heat transfer is analyzed using finite difference and the direct discrete-ordinates method. The parameters under study are conduction to radiation parameter, optical depth, refractive index ratio. The results with directional and diffuse properties deviate each other when the conduction to radiation parameter is less than around 0.01. The wall heat flux differs fur optical thickness less than around 0.1. However, the medium temperature profiles differ for optical thickness greater than around 1. Deviations from diffuse property calculations are larger for hot wall with directional property than cold wall with directional property. As n increases from 1.5, the trend changes are observed fur refractive index ratio about n=6.10

• 대한기계학회논문집B
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• 제25권10호
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• pp.1451-1458
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• 2001

The effects of a specularly reflecting surface on the wall heat flux and medium temperature distribution are studied. The system is an infinite square duct enclosing an absorbing and emitting medium. The walls are opaque, and black or gray. The walls emit diffusely but reflect diffusely or speculary. Heat is transferred by the combined effect of conduction and radiation. The radiative heat transfer is analyzed using direct discrete-ordinates method. The parameters under study are conduction, to radiation parameter, optical depth, wall emissivity, and reflection characteristics. The specular reflection and diffuse reflection show sizeable differences when the conduction to radiation parameter is less than around 0.01. The differences appear only either on the side wall heat flux or on the medium temperature profiles for the range of this study. The differences on the side wall heat flux are observed for optical thickness less than around 0.1 However the differences on the medium temperate profiles are found for optical thickness greater than around 1. The difference increase with increasing reflectance. The specular reflection increases the well heat flux gradient along the side wall.

• 한국구조물진단유지관리공학회 논문집
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• 제11권1호
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• pp.153-162
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• 2007

1988년 이전에 건설된 벽식 구조 아파트는 내진규정의 적용을 받지 않아 리모델링을 위해서는 현행법규에 적합한 내진보강이 필요하다. 본 연구에서는 벽체 신설 공법에 의한 내진 보강효과를 분석하기 위하여, 개발된 리모델링 건축 평면 내에서 전단벽의 신설이 가능한 위치별 보강 효과와 벽량 및 벽두께의 변화에 따른 내진 보강 효과를 분석하도록 하였다. 내진성능의 평가는 층간 횡 변위를 이용하여 허용 층간변위의 만족여부에 의하여 분석하였으며, 건축물의 구조 모델은 슬래브의 횡 방향 기여도를 고려한 유효보 모델을 사용하였다. 본 연구의 결과에 따르면 리모델링 시 단위 모듈별 내진보강이 가능하며, 전단벽의 신설 위치와 벽량에 따라 건물 건체의 거동에 영향을 받는 것을 확인 할 수 있다.

• 대한토목학회논문집
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• 제26권6B호
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• pp.633-639
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• 2006

여러 가지 두께의 유공벽을 이용하여 다양한 파 조건에 대한 반사율 실험을 실시하고 기존 이론식의 타당성을 검토하였다. 그 결과 유공벽의 두께가 두꺼우면 에너지손실계수가 기존 이론식에 사용된 예연오리피스 공식의 약 62% 정도로 감소하며, 관성저항길이는 벽의 두께가 증가함에 따라 선형적으로 증가하는 것으로 나타났다. 관성저항의 길이가 증가할수록 최소반사율을 주는 유수실 폭이 감소한다. 그러므로 본 연구에서 얻어진 결과는 유공벽 설계시 유용하게 사용될 수 있을 것으로 판단된다.