• 한국재료학회:학술대회논문집
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• 한국재료학회 2010년도 춘계학술발표대회
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• pp.35.1-35.1
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• 2010

The Cu(In,Ga)Se2(CIGS) thin film solar cells have been achieved until almost 20% efficiency by NREL. These solar cells include chemically deposited CdS as buffer layer between CIGS absorber layer and ZnO window layer. Although CIGS solar cells with CdS buffer layer show excellent performance, many groups made hard efforts to overcome its disadvantages in terms of high absorption of short wavelength, Cd hazardous element. Among Cd-free candidate materials, the CIGS thin film solar cells with Zn compound buffer layer seem to be promising with 15.2%(module by showa shell K.K.), 18.6%(small area by NREL). However, few groups were successful to report high-efficiency CIGS solar cells with Zn compound buffer layer, compared to be known how to fabricate these solar cells. Each group's chemical bah deposition (CBD) condition is seriously different. It may mean that it is not fully understood to grow high quality Zn compound thin film on the CIGS using CBD. In this study, we focused to clarify growth mechanism of chemically deposited Zn compound thin film on the CIGS, especially. Additionally, we tried to characterize junction properties with unfavorable issues, that is, slow growth rate, imperfect film coverage and minimize these issues. Early works reported that film deposition rate increased with reagent concentration and film covered whole rough CIGS surface. But they did not mention well how film growth of zinc compound evolves homogeneously or heterogeneously and what kinds of defects exist within film that can cause low solar performance. We observed sufficient correlation between growth quality and concentration of NH3 as complex agent. When NH3 concentration increased, thickness of zinc compound increased with dominant heterogeneous growth for high quality film. But the large amounts of NH3 in the solution made many particles of zinc hydroxide due to hydroxide ions. The zinc hydroxides bonded weakly to the CIGS surface have been removed at rinsing after CBD.

• 천문학회보
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• 제40권1호
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• pp.58.3-59
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• 2015

Dynamical expansion of H II regions plays a key role in dispersing surrounding gas and therefore in limiting the efficiency of star formation in molecular clouds. We use analytic methods and numerical simulations to explore expansions of spherical dusty H II regions, taking into account the effects of direct radiation pressure, gas pressure, and total gravity of the gas and stars. Simulations show that the structure of the ionized zone closely follows Draine (2011)'s static equilibrium model in which radiation pressure acting on gas and dust grains balances the gas pressure gradient. Strong radiation pressure creates a central cavity and a compressed shell at the ionized boundary. We analytically solve for the temporal evolution of a thin shell, finding a good agreement with the numerical experiments. We estimate the minimum star formation efficiency required for a cloud of given mass and size to be destroyed by an HII region expansion. We find that typical giant molecular clouds in the Milky Way can be destroyed by the gas-pressure driven expansion of an H II region, requiring an efficiency of less than a few percent. On the other hand, more dense cluster-forming clouds in starburst environments can be destroyed by the radiation pressure driven expansion, with an efficiency of more than ~30 percent that increases with the mean surface density, independent of the total (gas+stars) mass. The time scale of the expansion is always smaller than the dynamical time scale of the cloud, suggesting that H II regions are likely to be a dominant feedback process in protoclusters before supernova explosions occurs.

• 한국자동차공학회논문집
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• 제19권1호
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• pp.101-108
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• 2011

Understanding the exhaust gas recirculation (EGR) cooler fouling in diesel engine is important factor in the durability characteristic of a EGR system. We develope a test rig and PM feeder using carbon black to examine the effect of fouling on EGR cooler devices those were consisted of flat and shell & tube type. The EGR cooler fouling process is a complex interaction involving heat exchanger shape, boundary condition, constitutes, chemistry and operating mode. As the soot deposited to EGR cooler, these formed a thin deposit layer that was less heat exchange than the fresh status of tube enclosing the exhaust gas, resulting in lower heat exchange effectiveness in both type coolers. But these deposits caused different results in pressure drop, it is increased in flat type, but decreased in Shell & tube type of EGR cooler. A cause was estimated from a change of the flow structure and a decrease of contact area as the EGR cooler fouling.

• Structural Engineering and Mechanics
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• 제54권1호
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• pp.87-103
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• 2015

This paper focuses on an analytical research on the critical buckling load of cylindrical shells with stepwise variable wall thickness under axial compression. An arctan function is established to describe the thickness variation along the axial direction of this kind of cylindrical shells accurately. By using the methods of separation of variables, small parameter perturbation and Fourier series expansion, analytical formulas of the critical buckling load of cylindrical shells with arbitrary axisymmetric thickness variation under axial compression are derived. The analysis is based on the thin shell theory. Analytic results show that the critical buckling load of the uniform shell with constant thickness obtained from this paper is identical with the classical solution. Two important cases of thickness variation pattern are also investigated with these analytical formulas and the results coincide well with those obtained from other authors. The cylindrical shells with stepwise variable wall thickness, which are widely used in actual engineering, are studied by this method and the analytical formulas of critical buckling load under axial compression are obtained. Furthermore, an example is presented to illustrate the effects of each strake's length and thickness on the critical buckling load.

• 한국음향학회지
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• 제14권2호
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• pp.80-91
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• 1995

타이어와 노면의 상호작용에 의해 발생하는 소음에 대한 이론적인 모델에 대하여 연구하였다. 모델은 레디얼 타이어의 벨트 운동을 얇은 셀 방정식들로 가정하고 Bohm이 유도한 운동방정식을 기초로 하였으며 이들 방정식에 요구되는 구조적인량은 타이어의 재질적인 특성을 기초로 유도하였다. 타이어의 회전형태는 이들 방정식들의 정상상태로 부터 계산되고 진통 응답은 전체 종속적인 셀 방정식에 의해 구하였다. 타이어 노면 접지면에서의 힘은 타이어 트레드의 기하학적인 형상과 접지압의 분포를 기초로 계산하였고 소음방사는 심프슨 적분에 의해 계산된다. 여러가지 설계인자의 변화에 대한 효과를 조사하여 저소음 타이어 설계의 기초자료를 확보하는데 목적이 있다.

• 소성∙가공
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• 제22권3호
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• pp.150-157
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• 2013

Fiber metal laminates (FMLs) are layered materials comprised of thin metal sheets and fiber reinforced plastic (FRP). This paper presents the numerical study of the formability enhancement of FMLs composed of an aluminum alloy and self-reinforced polypropylene (SRPP) composite. In this study, a numerical simulation based on finite element (FE) modeling is proposed to evaluate the formability of FMLs using ABAQUS/Explicit. The FE model, which included a single layer of solid and shell elements to model the blank, used discrete layers of the solid element with a contact model and shell elements with a friction based model for the aluminum alloy-composite interface conditions. This method allowed the description of each layer of FMLs and was able to simulate the interaction between the layers. It is noted through this research that the proposed numerical simulation described properly the formability enhancement of the FMLs and the simulation results showed good agreement with experimental results.

• Earthquakes and Structures
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• 제18권5호
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• pp.637-648
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• 2020

In this study, a new steel cylindrical shell configuration of the dissipative energy device is proposed to improve lateral ductility and to reduce the damage of the structures against seismic forces. Four nested-eccentric- cylindrical shells are used to constructing this device; therefore, this proposed device is named nested-eccentric-cylindrical shells damper (NECSD). The particular configuration of the nested-eccentric-cylindrical shells is applied to promote the mechanical characteristics, stability, and overall performance of the damper in cyclic loads. Shell-type components are performed as a combination of series and parallel non-linear springs into the in-plan plastic deformation. Numerical analysis with respect to dimensional variables are used to calculate the mechanical characteristics of the NECSD, and full-scale testing is conducted for verifying the numerical results. The parametric study shows the NECSD with thin shells were more flexible, while devices with thick shells were more capacious. The results from numerical and experimental studies indicate that the NECSD has a stable behavior in hysteretic loops with highly ductile performance, and can provide appropriate dissipated energy under cyclic loads.

• 대한기계학회논문집
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• 제10권5호
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• pp.758-769
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• 1986

본 연구에서는 직교이방성 복합재료 원통셀의 진동 방정식을 Sanders, Love 및 Donnell의 셸이론에 기초하여 유도하고 이를 통일된 형태로 표현하였으며 등방성 원통셸에 대한 Chung의 해석법을 채용하여 임의의 경계조건을 갖는 직교이벙성 복합 재료 원통셸에 대해서 간편히 이용할 수 있는 유용한 해석방법을 제시하였다.

• Steel and Composite Structures
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• 제20권1호
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• pp.147-166
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• 2016

The paper presents comprehensive quasi-static stability analysis results for a real funnel-flow cylindrical steel silo composed of horizontally corrugated sheets strengthened by vertical thin-walled column profiles. Linear buckling and non-linear analyses with geometric and material non-linearity were carried out with a perfect and an imperfect silo by taking into account axisymmetric and non-axisymmetric loads imposed by a bulk solid following Eurocode 1. Finite element simulations were carried out with 3 different numerical models (single column on the elastic foundation, 3D silo model with the equivalent orthotropic shell and full 3D silo model with shell elements). Initial imperfections in the form of a first eigen-mode for different wall loads and from 'in-situ' measurements with horizontal different amplitudes were taken into account. The results were compared with Eurocode 3. Some recommendations for the silo dimensioning were elaborated.

• Structural Engineering and Mechanics
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• 제57권1호
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• pp.45-63
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• 2016

Fiber metal laminates (FMLs) represent a high-performance family of hybrid materials which consist of thin metal sheets bonded together with alternating unidirectional fiber layers. In this study, the buckling behavior of a FML circular cylindrical shell under axial compression is investigated via both analytical and finite element approaches. The governing equations are derived based on the first-order shear deformation theory and solved by the Navier solution method. Also, the buckling load of a FML cylindrical shell is calculated using linear eigenvalue analysis in commercial finite element software, ABAQUS. Due to lack of experimental and analytical data for buckling behavior of FML cylindrical shells in the literature, the proposed model is simplified to the full-composite and full-metal cylindrical shells and buckling loads are compared with the available results. Afterwards, the effects of FML parameters such as metal volume fraction (MVF), composite fiber orientation, stacking sequence of layers and geometric parameters are studied on the buckling loads. Results show that the FML layup has the significant effect on the buckling loads of FML cylindrical shells in comparison to the full-composite and full-metal shells. Results of this paper hopefully provide a useful guideline for engineers to design an efficient and economical structure.