• Advances in aircraft and spacecraft science
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• 제4권1호
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• pp.21-35
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• 2017

Hydrogen peroxide is being considered as a monopropellant in micropropulsion systems for the next generation of miniaturized satellites ('nanosats') due to its high energy density, modest specific impulse and green characteristics. Efforts at the University of Vermont have focused on the development of a MEMS-based microthruster that uses a novel slug flow monopropellant injection scheme to generate thrust and impulse-bits commensurate with the intended micropropulsion application. The present study is a computational effort to investigate the initial decomposition of the monopropellant as it enters the catalytic chamber, and to compare the impact of the monopropellant injection scheme on decomposition performance. Two-dimensional numerical studies of the monopropellant in microchannel geometries have been developed and used to characterize the performance of the monopropellant before vaporization occurs. The results of these studies show that monopropellant in the lamellar flow regime, which lacks a non-diffusive mixing mechanism, does not decompose at a rate that is suitable for the microthruster dimensions. In contrast, monopropellant in the slug flow regime decomposes 57% faster than lamellar flow for a given length, indicating that the monopropellant injection scheme has potential benefits for the performance of the microthruster.

• The Journal of Asian Finance, Economics and Business
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• 제6권3호
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• pp.103-113
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• 2019

The effectiveness of monetary policy critically depends upon how well the transmission mechanism functions, so that the desired impact on output and inflation is achieved. The purpose of this paper is to study the transmission mechanism of monetary policy by analyzing the impact on inflation and output during multiple indicator regime (1998-99 to 2014) in an emerging economy-India. The Inflation Targeting Regime is also briefly outlined alongwith the impact on output and inflation. Using quarterly data for the period 1997 to 2017, the paper uses weighted average call money market rate as a proxy for the policy rate and evaluates the strength of the interest rate channel. We use a conventional Structural vector auto regression (SVAR) methodology to evaluate the efficacy and show the impluse response functions. Our results find that changes in the policy rate impact output growth steeply with a lag of about two quarters and the impact on inflation is maximized after three quarters. The study concludes that the monetary policy in India has a significant impact on output and inflation in the short-to-medium-run. After the policy shock, the fall in the output growth rate is of greater magnitude than the fall in inflation.

• Corrosion Science and Technology
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• 제16권2호
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• pp.59-63
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• 2017

Chelating solutions can be damaged by strong acids during oil production. To design effective corrosion inhibitors and other alternatives for corrosion control, it is important to understand not only the behavior of the system under operating condition but also the kinetics of electrochemical reactions during the corrosion process. In this study, the electrochemical behaviors of P-110 steel in aqueous fluids based on ethylenediaminetetraacetic acid (EDTA) compounds under various temperatures and hydrodynamic regime conditions were assessed. Electrochemical measurements were conducted using rotating disc electrodes manufactured. Electrolytes were prepared using aqueous compounds of EDTA like diammonium salt, disodium salt, and tetrasodium salt. Potentiodynamic polarization, electrochemical impedance, and mass loss tests were performed in order to assess the corrosion kinetic in electrolytes. Hydrodynamic effects were observed only in the cathodic polarization curve. This proves that hydrodynamic regime plays an important role in the corrosion of steel mainly in disodium and diammonium EDTA solutions. Two cathodic reactions controlled the corrosion process. However, oxygen level and pH of the electrolyte played the most important role in metal corrosion. Corrosion rates in those fluids were decreased drastically when oxygen concentration was reduced.

• 한국기계가공학회지
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• 제16권2호
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• pp.63-68
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• 2017

Friction occurs when surfaces that are in contact move relatively between solid surfaces, fluid layers, and materials slide against one another. This friction force causes wear on the contact surface, generates unwanted heat and leads to performance degradation. Thus, much research has been performed to avoid friction reduction. Among these studies, a textured surface that has micro patterns on the surface has drawn attention for its ability to reduce friction. A mathematical model is developed in this study to examine friction reduction due to the texture of a surface. Numerical simulations are carried out with respect to various factors such as the shape aspect ratio and texture depth of a diamond-shaped texture in the hydrodynamic lubrication regime. As a result, a shape aspect ratio of 1 is best for friction reduction.

• Nuclear Engineering and Technology
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• 제50권1호
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• pp.43-53
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• 2018

It is important to clarify the characteristics of flow regimes underlying the debris bed formation behavior that might be encountered in core disruptive accidents of sodium-cooled fast reactors. Although in our previous publications, by applying dimensional analysis technique, an empirical model, with its reasonability confirmed over a variety of parametric conditions, has been successfully developed to predict the regime transition and final bed geometry formed, so far this model is restricted to predictions of debris mixtures composed of spherical particles. Focusing on this aspect, in this study a new series of experiments using nonspherical particles have been conducted. Based on the knowledge and data obtained, an extension scheme is suggested with the purpose of extending the base model to cover the particle-shape influence. Through detailed analyses and given our current range of experimental conditions, it is found that, by coupling the base model with this scheme, respectable agreement between experiments and model predictions for the regime transition can be achieved for both spherical and nonspherical particles. Knowledge and evidence from our work might be utilized for the future improvement of design of an in-vessel core catcher as well as the development and verification of sodium-cooled fast reactor severe accident analysis codes in China.

• 한국수자원학회:학술대회논문집
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• 한국수자원학회 2017년도 학술발표회
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• pp.518-518
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• 2017

4대강 사업 이후, 하천변의 환경에 많은 영향과 변화가 있었다. 그 중에서도 하천을 포함한 수변환경의 식생 변화에 가장 큰 영향을 주는 수문학적 조건이 변화하였고, 이에 따른 식생 천이가 지속적으로 발생할 것이기 때문에 그 영향을 분석하는 것이 시급한 과제이다. 이에 따라서, 본 연구의 목적은 수문학적 조건에 따른 하천변의 식생조건의 변화를 분석하는 것으로서, 수문학적 조건의 정량화를 위한 연침수확률(IEPs) 개념을 새로이 제시하고 이에 따른 수변환경과 식생의 변화를 한강에 위치한 비내섬을 대상으로 고찰하였다. 연구 결과에 따라서 P=0.08 이나 그 이하의 IEPs를 가진 구역은 식생 교란이 일어나거나 또는 친수성 식물로서 천이될 것으로 나타났다. 따라서, 하천과 유량에 대한 주무기관이 하천환경에 대해서도 관리업무를 통하여 하천보호를 수행하여야 할 것으로 판단된다.

• 융합보안논문지
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• 제17권2호
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• pp.127-135
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• 2017

현재 북한에서 3대 세습체제의 김정은은 역대 김일성과 김정일 정권보다 더욱 호전적으로 핵 및 미사일 도발을 자행하고 있다. 대한민국의 역대 정부는 나름대로의 북한의 도발을 억제하는 노력과 한반도에서의 평화정착을 위한 방안을 제시하여 왔지만 결과론적으로는 통치자로서의 기본 역할에 국한되어 온 것이 사실이다. 2017년 2월 미국의 트럼프 행정부 출범에 따라 미국 대선 과정에서의 공약과 현재에는 대통령령으로서의 통치 스타일을 고려할 때 한반도 문제와 관련하여 다소 희망적이었던 것은 사실이나, 최근 들어 트럼프 대통령의 한반도 관련 다양한 발언은 우리의 상황을 암울하게 하고 있다. 이의 연장에서 김정은의 핵 및 미사일 집착은 역대 북한 정권이 기초를 닦아놓았고 이제 마무리하여 실전배치를 앞둔 상황에서 핵 및 미사일의 경량화, 고도화, 다종화를 기치로 더욱 무모한 도발을 하고 있는 현실이다. 이에 우리는 현재 안보상황을 과거처럼 타국에만 의존할 수 없으며, 대한민국 스스로 무엇을 어떻게 할 것인가를 찾기 위해 북한의 핵 및 미사일 도발을 중심으로 대응방안을 제시하고자 한다.

• International Journal of Naval Architecture and Ocean Engineering
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• 제10권6호
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• pp.692-710
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• 2018

The Three-dimensional (3-D) dynamical behaviors of a fluid-conveying pipe subjected to vortex-induced vibration are investigated with different internal flow velocity ${\nu}$. The values of the internal flow velocity are considered in both subcritical and supercritical regimes. During the study, the 3-D nonlinear equations are discretized by the Galerkin method and solved by a fourth-order Runge-Kutta method. The results indicate that for a constant internal flow velocity ${\nu}$ in the subcritical regime, the peak Cross-flow (CF) amplitude increases firstly and then decrease accompanied by amplitude jumps with the increase of the external reduced velocity. While two response bands are observed in the In-line (IL) direction. For the dynamics in the lock-in condition, 3-D periodic, quasi-periodic and chaotic vibrations are observed. A variety of CF and IL responses can be detected for different modes with the increase of ${\nu}$. For the cases studied in the supercritical regime, the dynamics shows a great diversity with that in the subcritical regime. Various dynamical responses, which include 3-D periodic, quasi-periodic as well as chaotic motions, are found while both CF and IL responses are coupled while ${\nu}$ is beyond the critical value. Besides, the responses corresponding to different couples of ${\mu}_1$ and ${\mu}_2$ are obviously distinct from each other.

• 한국사회정책
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• 제24권2호
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• pp.217-244
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• 2017

이 연구는 다양한 문화적 분화도를 보이는 OECD 회원국을 대상으로 객관적 지표를 이용해 각국 이민자의 사회통합을 1)선주민과 비교한 상대적 기준과 2)이민자의 복지수준을 고려한 절대적 기준에서 비교분석하려는 목적으로 이루어졌다. 복수의 국제 데이터를 통합한 2차 데이터를 이용했으며 주요 변수 사이의 산점도를 산출하여 이민자 사회통합의 국가별 지형을 분석했다. 분석결과에 의하면, 상대적 기준의 사회통합은 전통적 이민국 레짐에 해당하는 호주, 캐나다, 미국이 이상적인 국가들로 나타났다. 절대적 기준의 사회통합이 높은 국가는 전통적 이민국 레짐과 적극적 이민국 레짐이 혼합된 형태를 보였다. 상대적 기준과 절대적 기준 모두에서 이민자의 사회통합 수준이 비교적 높은 국가는 전통적 이민국 레짐과 아일랜드, 포르투칼, 슬로베니아 등 일부 신이민국 레짐에 속한 국가들로 나타났다. 이와 같은 결과는 이민자의 사회통합은 이민국 레짐으로 대표되는 이민정책이나 문화적 분화도를 통해 설명할 수 있는 부분은 제한적이며, 이민자의 사회통합은 개별국가의 사회보장정책 등을 함께 고려해 이해되어야 함을 시사했다.

• Tribology and Lubricants
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• 제33권4호
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• pp.153-167
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• 2017

The aim of this study is to find the change in trend in the eccentricities of two journal bearings supporting the crankshaft of a single cylinder engine and the degree of misalignment of the shaft. We analyze the change in oil film thickness considering the wear scar under mixed-elasto-hydrodynamic lubrication regime at potential wear regions. For this, we first calculate the central eccentricities of the two journal bearings by using the mobility method. Then we calculate the outer end eccentricity by using the geometry of the bearings. Further, the tilting angle and degree of misalignment of the shaft are calculated by using the eccentricities of the two bearings. We show that the eccentricity of bearing #1, on which higher load is applied, increases at the beginning of the start-up cycle and during the coast-down cycle. However, the eccentricity of bearing #2, on which lower load is applied, decreases at the beginning of the start-up cycle and increases during the coast-down cycle. From the results of the analysis of oil film thickness, we show that the mixed-elasto-hydrodynamic lubrication regime for a misaligned shaft is at the initial stages of the start-up cycle for both bearing #1 and #2 and at the final stage of the coast-down cycle for only bearing #1.