• International Journal of Naval Architecture and Ocean Engineering
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• 제4권2호
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• pp.96-111
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• 2012

Hull Mounted Sonar (HMS) is a long range submerged vehicle's hull-mounted passive sonar system which detects low-frequency noise caused by machineries of enemy ships or submerged vehicles. The HMS needs a sound absorption /insulation multi-layer structure to shut out the self-noise from own machineries and to amplify signals from outside. Therefore, acoustic analysis of the multi-layer system should be performed when the HMS is designed. This paper simplified the HMS multi-layer system to be an infinite planar multi-layer model. Also, main excitations that influence the HMS were classified into mechanical, plane wave and turbulent flow excitation, and the investigations for each excitation were performed for various models. Stiffened multi-layer analysis for mechanical excitation and general multi-layer analysis for turbulent flow excitation were developed. The infinite planar multi-layer analysis was expected to be more useful for preliminary design stage of HMS system than the infinite cylindrical model because of short analysis time and easiness of parameter study.

• 펄프종이기술
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• 제40권5호
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• pp.36-41
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• 2008

Multi-ply sheet forming has many advantages including the possibility of using wide range of materials in a given structure, lowering production cost, making higher grammage products and so on. But, incorrect structure of sheet makes flow resistance higher so that it shows poor dewatering in press section. One of major factors that affect sheet structure and dewatering property is fines content in each layer. We, therefore, examined the press dewatering of multi-ply sheet that has the different fines content in each layer and the effect of fines distribution on physical properties of sheet to find a technology for optimum utilization of raw materials. In case of two layered sheet, the sheet which was composed of layers with the different flow resistance showed higher dewatering rate than one which has the same flow resistance. And the more difference in fines content for layers existed, the more dewatering occurred. For three layered sheets, dewatering is mainly dependent on fines content of bottom layer. Strength properties were affected by dewatering degree and multi-ply sheet structure.

• 대한기계학회논문집
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• 제19권7호
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• pp.1720-1730
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• 1995

Finite-difference analysis was conducted to study the natural convection of a stably stratified salt-water solution in an annulus due to lateral heating. The main purpose of this study is to examine in detail the multi-layered flow structure. Calculation was thus made for R $a_{\eta}$=2*10$^{5}$ and 6.5*10$^{5}$ . Formation of layered flow structure, merging process of layers, the corresponding temperature and concentration distributions, Nusselt number variations with time are examined. Numerical results show that in each layer, the temperature profile looks 'S`-shaped and the concentration profile is uniform due to the convective mixing. The formation of the roll and the layer is governed by natural convection due to the temperature gradient and the merging process of the layer by diffusion of the concentration.ation.

• 대한기계학회논문집A
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• 제24권7호
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• pp.1703-1711
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• 2000

Microstructural morphology of molded composites of thermotropic liquid crystalline polymer(LCP) and polyamide 6 (PA6) has been studied as a function of epoxy fraction. Injection-moulding of a thin composite plaque at a temperature below the melting point of the LCP fibrils by suing the extruded LCP/PA6 pellets produced multi-layered structures: 1) the surface skin layer with thickness of 65-120 ym exhibiting a transverse orientation, 2) the sub-skin layer with an orientation perpendicular to the surface skin, i.e. in the flow direction, 3) the core layer with arc-curved flow patterns. Similar microstructural orientations were observed in the respective layers for the composite plaques with different fractions of epoxy.

• 한국표면공학회:학술대회논문집
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• 한국표면공학회 2007년도 춘계학술발표회 초록집
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• pp.71-72
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• 2007

In this study, we investigated the fabrication of MLR (multi-layer resist) with a very thin diamond-like carbon (DLC) layer. ArF PR/$SiO_2$/DLC MLR structure was investigated and etching characteristics of the DLC layer was patterned using $SiO_2$ hard-mask by varying the process parameters such as different high-frequency/low-frequency combination ($f_{LF}/f_{HF}$), HF/LF power ratio ($P_{HF}/P_{LF}$), $O_2$ flow and $N_2$ flow rate in $O_2/N_2$/Ar plasmas. The results indicated an increased etch rate of DLC for the higher $f_{LF}/f_{HF}$ combination and for the increased low-frequency power ($P_{LF}$). And the etch rate of DLC was decreased with increasing the $N_2$ flow rate in $O_2/N_2$/Ar plasmas. In order to confirm the application of DLC MLR for the etching process of silicon oxide, the stack of ArF PR/BARC/$SiO_2$/DLC/TEOS/Si was investigated.

• Wind and Structures
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• 제25권6호
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• pp.589-608
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• 2017

A novel probabilistic approach is presented for estimating the equivalent static wind loads that produce a static response of the structure, which is "equivalent" in a probabilistic sense, to the extreme dynamic responses due to the unsteady pressure random field induced by the wind. This approach has especially been developed for complex structures (such as stadium roofs) for which the unsteady pressure field is measured in a boundary layer wind tunnel with a turbulent incident flow. The proposed method deals with the non-Gaussian nature of the unsteady pressure random field and presents a model that yields a good representation of both the quasi-static part and the dynamical part of the structural responses. The proposed approach is experimentally validated with a relatively simple application and is then applied to a stadium roof structure for which experimental measurements of unsteady pressures have been performed in boundary layer wind tunnel.

• 한국전자파학회논문지
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• 제27권8호
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• pp.735-741
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• 2016

배기관에 도파관 배열을 삽입하여 일정수준의 차폐효과를 만족시키기 위해서는 도파관 배열의 전체길이가 늘어나야 한다. 이때, 공정의 난이도와 비용이 증가하게 되며, 유체의 흐름을 방해하게 된다. 이를 보완하기 위해, 여러 개의 도체판으로 접합시켜 만든 도파관을 교차시켜 다층 구조 도파관을 제안하였다. 2층 구조에서부터 8층 구조까지 증가시키며, 차폐효과를 확인한 결과, 52 dB에서 75 dB로 향상되는 것을 확인하였다. 또한, 다층 구조 도파관이 설치된 배기관에 대해서 유속 시뮬레이션을 진행한 결과, 주입구 유속이 1m/s일 경우, 2층 구조에서부터 8층 구조까지 입구 및 출구 측 유속이 각각 0.88m/s에서 0.77m/s, 0.63m/s에서 0.68m/s로 단일 사각형 도파관 배열의 유속 결과 값인 0.79m/s와 0.53m/s에 비해서 속도 손실이 줄어드는 것을 확인하였다.

• 대한기계학회논문집B
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• 제26권4호
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• pp.578-586
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• 2002

Flow structures around a rectangular prism have been investigated by using a PIV(Particle Image Velocimetry) technique. A thick turbulent boundary layer was generated by using spires arid roughness elements. The boundary layer thickness, displacement thickness and momentum thickness were 650mm, 117.4mm and 78mm, respectively. The ratio between the model height(40mm) and the boundary layer thickness H/$\delta$, was 0.06. The Reynolds number based on the free stream velocity and the height of the model was 7.9$\times$10$^3$. The PIV measurements were performed at three different wall normal planes. Three recirculation regions at forward facing step, top of the roof and backward facing step are clearly seen and show three dimensional features. Dramatic changes of flow patterns are observed in the wake regions in the different spanwise wall normal planes. Instead of reattachment and recirculation zone, rising streamlines are depicted at the normal planes near the side wall due to the interaction with a rising horse shoe vortex. The peak of turbulent kinetic energy occurs at the separation bubble on top of the roof and the magnitude is 2.5 times higher compared with that of the wake region.

• 한국재료학회지
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• 제20권4호
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• pp.187-193
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• 2010

Chromium nitride (CrN) samples with two different layer structures (multilayer and single layer) were coated on bipolar plates of polymer electrolyte membrane fuel cells (PEMFC) using the reactive sputtering method. The effects with respect to layer structure on corrosion resistance and overall cell performance were investigated. A continuous and thin chromium nitride layer ($Cr_{0.48}\;N_{0.52}$) was formed on the surface of the SUS 316L when the nitrogen flow rate was 10 sccm. The electrochemical stability of the coated layers was examined using the potentiodynamic and potentiostatic methods in the simulated corrosive circumstances of the PEMFC under $80^{\circ}C$. Interfacial contact resistance (ICR) between the CrN coated sample and the gas diffusion layer was measured by using Wang's method. A single cell performance test was also conducted. The test results showed that CrN coated SUS316L with multilayer structure had excellent corrosion resistance compared to single layer structures and single cell performance results with $25\;cm^2$ in effective area also showed the same tendency. The difference of the electrochemical properties between the single and multilayer samples was attributed to the Cr interlayer layer, which improved the corrosion resistance. Because the coating layer was damaged by pinholes, the Cr layer prevented the penetration of corrosive media into the substrate. Therefore, the CrN with a multilayer structure is an effective coating method to increase the corrosion resistance and to decrease the ICR for metallic bipolar plates in PEMFC.

• 대한기계학회논문집B
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• 제21권11호
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• pp.1422-1436
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• 1997

Numerical investigations were conducted to study the convective phenomena of an initially stably stratified salt water solution with lateral heating in a uniformly rotating annulus. The method of investigation is the finite difference analysis of the basic conservation equation for an axisymmetric, unsteady, double-diffusive convection and calculation is made for R $a_{\eta}$=2*10$^{5}$ and Ta=10$^{7}$ ~ 2.5*10$^{8}$ . Formation of layered flow structure, merging process of layers, the corresponding temperature and concentration distributions, Nu variation with time are examined. Numerical results show that in each layer, the temperature profile looks 'S'-shaped and the concentration profile is uniform due to the convective mixing. At the interface between adjacent layers, the temperature changes smoothly but the concentration changes rapidly. As the effect of the rotation increases, the generation of rolls at hot wall, the formation and merging of layers are delayed. The average Nu shows the trend of conduction heat transferees the effect of the rotation increases.n increases.