液體 噴流의 安定 曲線에서의 臨界 레이놀즈 수의 豫測

황용하,임성빈 忠州大學校 2003 한국교통대학교 논문집 Vol.38 No.4

The first maximum point in the stability curve of liquid jet, ie, the critical point is associated with the critical Reynolds number. This critical Reynolds number should be predicted by simple means. In this work, the critical Reynolds number in the stability curve of liquid jet are predicted using the empirical correlations and the experimental data reported in the literatures. The critical Reynolds number was found to be a function of the Ohnesorge number, nozzle length-to-diameter ratio, ambient Weber number and nozzle inlet type. An empirical correlation for the critical Reynolds number as a function of the Ohnesorge number and nozzle length-to-diameter ratio is newly proposed here. Although an empirical correlation proposed in this work may not be universal because of excluiding the effects of ambient pressure and nozle inlet type, it has resonably agrees with the measured critical Reynolds number.

수제 설치에 의한 하도 안정성 평가

김기정,장창래,이경수 응용생태공학회 2019 Ecology and resilient infrastructure Vol.6 No.4

This study investigates channel stabilities with groynes by developing the assessment of it and applying a 2-dimensional numerical model, which simulates flow and sediment transport with various flows in the channel. Evaluation inventories are composed of five items, which are width to depth ratio, sinuosity, bed slopes, velocities in the flow flied, Shields number with discharges and geomorphic characteristics in the study reach. The channel stability is evaluated by applying the evaluation indicators to the channel with and without groynes in the study reach between Dalseong-weir and Gangjeonggoryeong-weir in the Nakdong river. Width to depth ratio, sinuosity, and bed slopes, which are index of river characteristics, little affect the channel stability. However, velocities in the flow flied, and Shields number, which is dimensionless tractive, near the banks of the channel strongly affect the stability. The evaluation values of the stability in the channel on the left and right banks decrease as the number of groynes increase in both the left and right banks, which means that the bank stability increases with the groynes. 본 연구에서는 본 연구에서는 2차원 수치모형을 적용하여 수제설치에 의한 흐름특성을 분석하고, 하도의 안정성을 평가할수 있는 평가방법을 개발하였다. 2차원 수치모형의 결과는 관측자료와 1차원 모형의 결과와 비교하여, 그 적용성을 검토하였다. 평가 지표는 대상구간의 수리 및 지형학적 특성을 고려하여 하폭 대 수심의 비, 사행도, 하상경사, 하안 부근에서 유속, Shields number 등 5가지 항목으로 구성하였다. 낙동강의 달성보∼강정고령보 구간의 수제 설치 전·후에 대해 평가지표를 적용하여 하도안정성을 평가하였다. 평가 항목 중에서 하폭 대 수심의 비, 사행도, 하상경사는 하도의 안정성에 영향을 크게 주지 않는 것으로평가되었다. 양안 부근에서 유속과 유사의 이동 특성을 결정하는 무차원 소류력인 Shields Number는 수제에 의하여 영향을 받으며, 수제의 수가 증가할수록 평가 값은 감소하고, 하안의 안정성은 증가하였다.

첨가제에 따른 바이오디젤 산화안정 특성 연구

강형규,송호영,도진우,박수열,나병기 한국유화학회 2015 한국응용과학기술학회지 Vol.32 No.4

바이오디젤은 지방산 중의 일부물질이 대기중의 산소와 결합하여 유기지방산 등을 형성하며 밀도, 동점도, 전산가, 산화안정도 등의 물성 특성에 영향을 준다. 바이오디젤의 산화안정성 문제를 해결 하기 위해 바이오디젤에 다양한 산화방지제를 첨가하여 물성 변화의 특성을 분석하였다. 첨가제의 함량 이 증가함에 따라 산화안정도는 증가하는 경향을 나타내고 대부분 첨가량에 비례적으로 증가하였다. 7 종의 첨가제 중 TBHQ가 가장 우수한 성능을 보이며 propyl gallate, butyl-amine, aniline, pyrogallol 등 4종의 첨가제도 목표치인 500 ppm 첨가 시 10시간 이상의 성능을 보였다. pyrogallol이 전산가에서 품질기준에 부적합하여 첨가제로서 적절하지 않은 것으로 나타났으며, hydroquinone계열의 TBHA, DTBHQ는 산화안정도에서 품질기준은 만족하나 연구과제의 목표치인 10 시간 이상에 미치지 못하는 결과를 보여 개발 첨가제로서는 결함이 있는 것으로 판단하였다. 또한 propyl gallate도 전산가에서 품질 기준에 적합하나 500 ppm 첨가 시 수치가 높고 첨가제 증가에 따른 전산가 증가 경향이 커서 첨가제 로서 부적합한 것으로 판단하였다. Some materials of fatty acids in the biodiesel affect the physical/chemical properties like density, kinematic viscosity, total acid number and oxidation stability by forming an organic fatty acid in combination with oxygen in the air. To solve the problem of the oxidative stability of biodiesel, various kinds of antioxidant has added and analyze the characteristics of the physical/chemical property changes by the addition of antioxidant. Oxidation stability increased by the increase of additives content. The TBHQ among the seven kinds of the additives showed the best performance. Also, 4 kinds of additives like propyl gallate, butyl-amine and pyrogallo has showed above 10 hr of oxidation stability at the addition of 500 ppm. In case of pyrogallo, this is not appropriate as an additive to suitable quality standards of total acid number. TBHA, DTBHQ of hydroquinone was satisfied with the quality standard of oxidation stability but the target of this research(above 10 hr) did not satisfied with oxidation stability. Propyl gallate is also a suitable at the quality standards of total acid number but it was shown not to be an appropriate to the additives due to increasing the total acid number by increasing of the content of additives at the addition of 500 ppm.

Seismic Slope Stability Evaluation Considering Rock Mass Disturbance Varying in the Slope

An-Jui Li,Zhiguang Qian,Jing-Cai Jiang,Andrei Lyamin 대한토목학회 2019 KSCE JOURNAL OF CIVIL ENGINEERING Vol.23 No.3

Seismic effect is one of the most commonly considered factors in rock slope safety design. This study adopts the finite element lower bound limit analysis method to study the seismic stability of disturbed rock slopes considering inhomogeneity caused by rock mass disturbance. Moreover, this research investigates different earthquake magnitudes by considering various seismic coefficients. Results are presented as seismic rock slope stability charts. In addition, the recommended blasting damage zones are also investigated in this study. Results show the chart solutions can provide a reasonable tool for the preliminary evaluations of the seismic safety factors for rock slope stability. The case studies demonstrate that a safe design can be done if the earthquake effects are considered reasonably. Moreover, consideration of varying rock mass disturbance in the slope is helpful to capture the failure mechanism more realistically when compared to the slope case without varying rock mass disturbance. For comparison purposes, the conventional limit equilibrium analysis and the equivalent Mohr-Coulomb parameters are used to perform analyses of the rock slope stability.

혼성제 기초 마운드의 피복재 안정성에 대한 신뢰성 해석

이철응 한국해안,해양공학회 2023 한국해안해양공학회 논문집 Vol.35 No.2

Probabilistic and deterministic analyses are implemented for the armor units of rubble foundation mound of composite breakwaters which is needed to protect the upright section against the scour of foundation mounds. By a little modification and incorporation of the previous empirical formulas that has commonly been applied to design the armor units of foundation mound, a new type formula of stability number has been suggested which is capable of taking into account slopes of foundation mounds, damage ratios of armor units, and incident wave numbers. The new proposed formula becomes mathematically identical with the previous empirical formula under the same conditions used in the developing process. Deterministic design have first been carried out to evaluate the minimum weights of armor units for several conditions associated with a typical section of composite breakwater. When the slopes of foundation mound become steepening and the incident wave numbers are increasing, the bigger armor units more than those from the previous empirical formula should be required. The opposite trends however are shown if the damage ratios is much more allowed. Meanwhile, the reliability analysis, which is one of probabilistic models, has been performed in order to quantitatively verify how the armor unit resulted from the deterministic design is stable. It has been confirmed that 1.2% of annual encounter probability of failure has been evaluated under the condition of 1% damage ratio of armor units for the design wave of 50 years return period. By additionally calculating the influence factors of the related random variables on the failure probability due to those uncertainties, it has been found that Hudson’s stability coefficient, significant wave height, and water depth above foundation mound have sequentially been given the impacts on failure regardless of the incident wave angles. Finally, sensitivity analysis has been interpreted with respect to the variations of random variables which are implicitly involved in the formula of stability number for armor units of foundation mound. Then, the probability of failure have been rapidly decreased as the water depth above foundation mound are deepening. However, it has been shown that the probability of failure have been increased according as the berm width of foundation mound are widening and wave periods become shortening. 혼성제 사석 기초 마운드 상에 거치되는 피복재의 소요중량을 산정하기 위한 결정론적 해석과 더불어 신뢰성 해석을 수행하였다. 사석 기초 마운드 경사, 피해율 그리고 입사파수를 고려할 수 있도록 안정수 산정을 위한기존의 경험식을 수정하였다. 수정된 산정식은 기존 경험식을 개발하는 과정에 사용했던 것과 동일 조건에서 수학적으로 일치한다. 먼저 결정론적 설계법으로 임의의 대표단면에 대하여 여러 가지 조건을 변화시키면서 사석 기초마운드 보호에 필요한 피복재의 소요중량을 산정하였다. 사석 기초 마운드 경사가 급할수록, 입사파수가 증가할수록기존의 경험식으로 부터 산정된 피복재의 소요 중량보다 더 큰 피복재의 소요중량이 필요함을 확인하였다. 그러나허용 피해율을 크게 부여하면 반대 경향이 나타난다. 한편, 본 연구에서 처음으로 사석 기초 마운드 피복재에 대한신뢰성 해석이 수행되었는데, 이는 결정론적 설계법으로 산정된 피복재가 얼마나 안정한지를 정량적으로 확인하고, 파괴에 미치는 각 확률변수들의 불확실성에 따른 영향의 정도를 살펴보기 위함이다. 신뢰성 해석 결과에 의하면 기존 경험식이 만족하는 조건에서 산정된 피복재의 소요중량은 재현기간 50년 설계파 조건에서 단위 년에 1%의 피해가 발생할 확률 1.2%를 갖는다. 또한 영향계수 산정 결과에 의하면 입사각에 따라 약간 다르지만 전반적으로 안정계수, 파고 그리고 사석 기초 마운드상의 수심 순으로 파괴에 미치는 영향이 큼을 확인할 수 있었다. 마지막으로안정수 산정식에 음함수적으로 포함되어 그 영향이 쉽게 확인되지 않는 확률변수의 변화에 따른 민감도 분석이 수행되었다. 해석 결과에 의하면 사석 기초 마운드의 수심이 깊어 질수록 파괴확률이 급격하게 감소하였다. 그러나반대로 사석 기초 마운드의 폭이 커질수록, 입사 파랑의 주기가 짧을수록 파괴확률은 커지는 것으로 확인되었다.

An easy way to use artificial neural network model for calculating stability number of rock armors

Lee, Anzy,Kim, Sung Eun,Suh, Kyung-Duck Elsevier 2016 Ocean engineering Vol.127 No.-

<P><B>Abstract</B></P> <P>Since Van der Meer proposed a new empirical formula to calculate the stability number of rock armors based on his own experimental data in 1987, the data have been used in the development of artificial neural network (ANN) models. However, the ANN models are seldom used probably because they did not significantly improve the accuracy compared with the empirical formula and/or the engineers are not familiar with the ANN models. To resolve these problems, first we develop an ANN model combined with a principal component analysis (PCA) that markedly improves the accuracy of the model. The by-products of the model such as weights and biases are then used to develop an explicit method to calculate the stability number. The developed method is not as simple as the empirical formula but it can be easily used by an engineer who has basic knowledge of matrix operation without requiring knowledge of ANN and PCA. It is equally accurate as the developed ANN-PCA hybrid model and more accurate than previous empirical formula and ANN models.</P> <P><B>Highlights</B></P> <P> <UL> <LI> An explicit method other than empirical formula is proposed to calculate stability number of rock armors. </LI> <LI> An ANN-PCA hybrid model is developed based on the experimental data of Van der Meer. </LI> <LI> The by-products of the hybrid model are used for the explicit method. </LI> <LI> The method is more accurate than previous empirical formulas and ANN models. </LI> <LI> The method can be used by engineers with only basic knowledge of matrix operation. </LI> </UL> </P>

민주화 이후 한국 정당체계는 불안정한가?: 유효 정당 수와 선거 유동성 세분화를 중심으로

노기우(Gi-Woo Roh),이현우(Hyeon-woo Lee) 한국정당학회 2019 한국정당학회보 Vol.18 No.4

본 연구는 한국 정당체계의 불안정성을 지적하는 일반적 해석과 달리 실증적 분석을 통해 내부적 맥락과 구조적 틀 내에서 한국 정당체계가 안정성을 유지하고 있다는 시각을 제시한다. 정당체계의 안정성을 측정하기 위해 유효 정당 수, 선거 유동성 그리고 블록 내 유동성 등 3개 지표를 사용하여 분석한 결과, 민주화 이후 한국 정당체계는 일정한 안정성을 지니고 있는 것을 확인하였다. 개별 정당의 변화와 정당체계의 변화를 구분하여 볼 때, 한국 정당체계는 이합집산이라는 표면적 수준에서 나타나는 복잡한 양상과 달리 보수계, 민주계, 진보계라는 이념적 틀 내에서 고유의 안정성을 띠고 있다. 또한 한국에서 선거 유동성이 심각하다는 연구는 지극히 대중정당론자들의 시각에서 제기된 비판으로, 정당-유권자 간 상당 수준의 안정성이 정당체계의 안정성을 설명해준다. This study critilizes the argument that the Korean party system is unstable is erroneous or exaggerated. Based on empirical evidence, it argues that the Korean party system can achieve stability through the adoption of the internal context and structural framework. For this purpose, I use three methods that are used worldwide to measure the stability level of the party system: 1) the number of effective political parties index; 2) the electoral volatility index; and internal bloc volatility. The results of this study indicate that the party system of post-democratization South Korea has a certain level of stability. In addition, the claim that the Korean party system has a high election liquidity — as a consequence of regionalism — is only delivered by the mass party model’ perspective. Contrary to expectations, the stability of Korean party system could explain a certain trust level developed between a party and the constituents. The results confirm that the Korean party system is capable of maintaining its stability even if the regionalism component is taken into consideration.

동심 환형 Swirl injector에서의 Swirl number에 대한 새로운 관계식의 제안 및 수치적 분석

최재훈(Jaehoon Choi),강성원(Seongwon Kang),도형록(Hyungrok Do) 대한기계학회 2016 대한기계학회 춘추학술대회 Vol.2016 No.12

Gas turbine combustors using lean-premixed combustion often utilizes a swirling flow to generate a centraltoroidal recirculation zone (CTRZ) for flame stabilization. The characteristics of a CTRZ, such as the volume of a CTRZ, can be predicted by the swirl number at the combustor inlet (or the exit of the swirl injector). In the present study, a new correlation for the swirl number is derived to estimate the swirl number at the end of a swirl-injector pipe, especially for the pipe with a variable cross-sectional area, where existing formulas cannot be applied accurately. First, we derive a correlation for the case with a flat-vane axial swirler. Next, theoretical and numerical analyses are performed to show that the variation of the swirl number in an annular pipe is mainly dependent on the geometry of the pipe. Finally, our correlation is generalized by coupling to a correlation of a radial-type swirl generator. The suggested correlations are validated and analyzed with RANS simulations.

DYNAMICAL BEHAVIOUR OF A DRINKING EPIDEMIC MODEL

Sharma, Swarnali,Samanta, G.P. The Korean Society for Computational and Applied M 2013 Journal of applied mathematics & informatics Vol.31 No.5

In this paper we have constructed a mathematical model of alcohol abuse which consists of four compartments corresponding to four population classes, namely, moderate and occasional drinkers, heavy drinkers, drinkers in treatment and temporarily recovered class. Basic reproduction number $R_0$ has been determined and sensitivity analysis of $R_0$ indicates that ${\beta}1$ (the transmission coefficient from moderate and occasional drinker to heavy drinker) is the most useful parameter for preventing drinking habit. Stability analysis of the model is made using the basic reproduction number. The model is locally asymptotically stable at disease free or problem free equilibrium (DFE) $E_0$ when $R_0<1$. It is found that, when $R_0=1$, a backward bifurcation can occur and when $R_0>1$, the endemic equilibrium $E^*$ becomes stable. Further analysis gives the global asymptotic stability of DFE under some conditions. Our important analytical findings are illustrated through computer simulation. Epidemiological implications of our analytical findings are addressed critically.

Improved electrochemical, mechanical and transport properties of novel lithium bisnonafluoro-1-butanesulfonimidate (LiBNFSI) based solid polymer electrolytes for rechargeable lithium ion batteries

Karuppasamy, K.,Kim, Dongkyu,Kang, Yong Hee,Prasanna, K.,Rhee, Hee Woo Elsevier 2017 Journal of industrial and engineering chemistry Vol.52 No.-

<P><B>Abstract</B></P> <P>In the present work, a new methodology for improving the ionic conductivity and cation transport properties of polymer electrolytes have been synthesized by adding bulky anion based novel lithium bisnonafluoro-1-butanesulfonimidate salt and characterized for its applications in lithium ion batteries. The self-standing solid polymer electrolyte films exhibit excellent mechanical, thermal, and electrochemical stability. The ion–polymer interactions are examined thoroughly by ATR Fourier Transform-Infra Red Spectroscopy. The solid polymer electrolyte prepared with EO/Li ratio 14 exhibits a highest ionic conductivity of 10<SUP>−4</SUP> Scm<SUP>−1</SUP> at 333K. Also, it achieves a maximum lithium transference number of 0.31 and it is electrochemically stable in the scanned electrochemical window. This new type of polymer electrolytes with high ion conductivity and improved mechanical properties paves way to be a potential candidate along with lithium anode and LiCoO<SUB>2</SUB> cathode in the lithium ion batteries.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A novel LiBNFSI based SPEs have been prepared and characterized for its applications in lithium ion batteries. </LI> <LI> The prepared self-standing SPE films exhibit excellent mechanical, thermal, and electrochemical stability. </LI> <LI> These electrolytes give maximum ionic conductivity and electrochemical stability at ambient temperature. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>