AZ31 마그네슘합금의 시편두께 조건에 따른 실험적 피로균열전파모델 평가

최선순(Choi, Seon-Soon) 한국산학기술학회 2014 한국산학기술학회논문지 Vol.15 No.2

본 논문의 목적은 AZ31 마그네슘합금의 균열성장거동의 경향을 묘사할 수 있는 실험적 피로균열전파모델을 시편두께 조건에서 평가하여 적합한 모델을 제시하는 것이다. 평가에 사용된 실험적 모델은 Paris-Erdogan 모델, Walker 모델, Forman 모델, 수정된 Forman 모델이며, 각 모델의 파라미터를 통계적으로 추정하기 위하여 최우추정법 을 사용하였다. 두께조건이 피로균열전파거동 예측에 미치는 영향을 고려하면서 적합한 모델을 평가하기 위해 시편두 께의 3가지 조건을 변화시키면서 피로균열전파실험을 수행하여 통계적 균열성장 데이터를 획득하였다. 시편두께 조건 에 따라 마그네슘합금의 균열성장거동의 경향을 잘 묘사하는 모델은 Paris-Erdogan 모델과 Walker 모델이며, 모델의 파라미터 중 피로균열성장속도지수는 시편두께가 4.75mm와 6.60mm 조건에서 재료상수가 될 수 있음을 밝혀내었다. 그러나 시편두께가 두꺼운 경우에는 양상에 차이를 보이므로 모델 선정 시 신중한 판단이 요구된다. It is the primary aim of this paper to propose the empirical fatigue crack propagation model fit to describe a crack growth behavior of AZ31 magnesium alloys under the different specimen thickness conditions. The empirical models estimated are Paris-Erdogan model, Walker model, Forman model, and modified-Forman model. The parameters of each model are estimated by maximum likelihood method. The statistical crack growth data needed for an estimation of empirical models are obtained by fatigue crack propagation tests under the three cases of specimen thickness. It is found that the good empirical models fit to describe a crack growth behavior of AZ31 magnesium alloys under the different specimen thickness conditions are Paris-Erdogan model and Walker model. It is also verified that a fatigue crack growth rate exponent of a empirical model may be a material constant at the specimen thickness conditions of 4.75mm and 6.60mm.

최대하중 조건에 따른 AZ31 마그네슘합금의 실험적 피로균열전파모델 평가

최선순(Choi, Seon-Soon) 한국산학기술학회 2012 한국산학기술학회논문지 Vol.13 No.2

본 논문의 목적은 AZ31 마그네슘합금의 균열성장거동의 경향을 묘사할 수 있는 실험적 피로균열전파모델을 평가하여 적합한 모델을 제시하는 것이다. 3가지 최대하중 조건을 변화시키면서 피로균열전파실험을 수행하여 평가에 필요한 통계적 균열성장 데이터를 획득하였다. 평가에 사용된 실험적 모델은 Paris-Erdogan 모델, Walker 모델, Forman 모델, 수정된 Forman 모델이며, 각 모델의 파라미터를 통계적으로 추정하기 위하여 최우추정법을 사용하였다. 마그네 슘합금의 균열성장거동의 경향을 잘 묘사하는 모델은 Paris-Erdogan 모델과 Walker 모델이며, 모델의 파라미터 중 피 로균열성장속도지수는 재료상수가 될 수 있음을 밝혀내었다. It is the aim of this paper to propose the empirical fatigue crack propagation model fit to describe a crack growth behavior of AZ31 magnesium alloys. The statistical data of a crack growth for an estimation are obtained by fatigue crack propagation tests under the three cases of maximum load. The empirical models estimated are Paris-Erdogan model, Walker model, Forman model, and modified-Forman model. It is found that the empirical model fit to describe a crack growth behavior of AZ31 magnesium alloys is Paris-Erdogan model and Walker model. It is also verified that a fatigue crack growth rate exponent of a empirical model is to be a material constant.

Semi-empirical long-term cycle life model coupled with an electrolyte depletion function for large-format graphite/LiFePO₄ lithium-ion batteries

Park, Joonam,Appiah, Williams Agyei,Byun, Seoungwoo,Jin, Dahee,Ryou, Myung-Hyun,Lee, Yong Min Elsevier 2017 Journal of Power Sources Vol.365 No.-

<P><B>Abstract</B></P> <P>To overcome the limitation of simple empirical cycle life models based on only equivalent circuits, we attempt to couple a conventional empirical capacity loss model with Newman's porous composite electrode model, which contains both electrochemical reaction kinetics and material/charge balances. In addition, an electrolyte depletion function is newly introduced to simulate a sudden capacity drop at the end of cycling, which is frequently observed in real lithium-ion batteries (LIBs). When simulated electrochemical properties are compared with experimental data obtained with 20 Ah-level graphite/LiFePO<SUB>4</SUB> LIB cells, our semi-empirical model is sufficiently accurate to predict a voltage profile having a low standard deviation of 0.0035 V, even at 5C. Additionally, our model can provide broad cycle life color maps under different c-rate and depth-of-discharge operating conditions. Thus, this semi-empirical model with an electrolyte depletion function will be a promising platform to predict long-term cycle lives of large-format LIB cells under various operating conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Semi-empirical cycle life model with electrolyte depletion function is developed. </LI> <LI> Our model is compared with a conventional semi-empirical model. </LI> <LI> The broad cycle life color maps at various c-rate and DOD are offered. </LI> </UL> </P>

Pricing Kernel-Based Option Valuation Approach : A New Perspective

Doojin Ryu 한국재무학회 2011 한국재무학회 학술대회 Vol.2011 No.09

This study examines the empirical performance of three model-based option valuation approaches in the KOSPI200 options market. We evaluate the in-sample pricing, out-of-sample pricing and hedging performance of the approaches based on the specification of option pricing models directly (a pricing model-based approach), on the pricing kernels implied by the option pricing models (an implied pricing kernel-based approach), and on parametric pricing kernels which are independently structured to have their own explicit functional forms (a parametric pricing kernel-based approach). Two option pricing models, a GARCH option pricing model and a Black-Scholes (BS) option pricing model, and their implied pricing kernels are analyzed and two parametric pricing kernel specifications suggested by Rosenberg and Engle (2002) are compared in a unified framework which extends the GARCH process of Duan (1995) to reflect the dynamics of asymmetric volatility. We find that the empirical performance of the approaches related to the GARCH and Black-Scholes option pricing models is moderately improved when we estimate the structural parameters using options data (options-based estimation) compared to the model performances when estimating the parameters using only a time-series of underlying returns data (underlying returns-based estimation). With the estimates under the underlying returns-based estimation, the pricing modelbased option valuation approach outperforms the implied pricing kernel-based option valuation approach for both the GARCH and BS option pricing models. However, with the estimates under the options-based estimation, this relationship is reversed in pricing OTM options in the case of the GARCH option pricing model. Although the BS option pricing model is generally the worst performer with the estimates under the underlying returns-based estimation, it yields better performance for pricing ITM options and similar performance for hedging compared to the GARCH option pricing model with the estimates under the options-based estimation. The option valuation approach based on the parametric pricing kernel of which functional form is a Chebyshev polynomial performs best out of all approaches and methods considered in this study

연구논문 : 플라즈마 공정을 이용한 고추역병균(Phytophthora capsici)불활성화 모델의 적용

김동석 ( Dong Seog Kim ),박영식 ( Young Seek Park ) 한국환경과학회 2015 한국환경과학회지 Vol.24 No.11

Ten empirical disinfection models for the plasma process were used to find an optimum model. The variation of model parameters in each model according to the operating conditions (first voltage, second voltage, air flow rate, pH, incubation water concentration) were investigated in order to explain the disinfection model. In this experiment, the DBD (dielectric barrier discharge) plasma reactor was used to inactivate Phytophthora capsici which cause wilt in tomato plantation. Optimum disinfection models were chosen among ten models by the application of statistical SSE (sum of squared error), RMSE (root mean sum of squared error), r2 values on the experimental data using the GInaFiT software in Microsoft Excel. The optimum models were shown as Log-linear+Tail model, Double Weibull model and Biphasic model. Three models were applied to the experimental data according to the variation of the operating conditions. In Log-linear+Tail model, Log10(No), Log10(Nres) and kmax values were examined. In Double Weibull model, Log10(No), Log10(Nres), α, δ1, δ2, p values were calculated and examined. In Biphasic model, Log10(No), f, kmax1 and kmax2 values were used. The appropriate model parameters for the calculation of optimum operating conditions were kmax, α, kmax1 at each model, respectively.

등척성 팔굽 굽힘시 최대근지구력시간의 실증적 모델에 적용한 전완길이의 영향

이상식,이기영 한국정보전자통신기술학회 2023 한국정보전자통신기술학회논문지 Vol.16 No.5

등척성 팔굽 굽힘시 전완길이(florearm length)는 전완에 가해진 힘의 방향이 직각일 때 관절토크 뿐만 아니라 최대근지구력시간(maximum endurance time: MET)을 결정하는 중요한 요소이다. 본 연구의 목표는 전완의 등척성 수축시 MET의 대표적인 두 가지 실증적 모델인 지수모델과 거듭제곱모델에 전완길이를 추가요소로 적용했을 때 미치는 영향을 검토하는 것이다. 30명의 자원자가 실험에 참여하였으며, 요소변수로 사용할 참여자의 상완 및 전완의 둘레 및 길이들과 최대자율수축강도의 백분율(percent of maximum voluntary contraction intensity: %MVC)에 따른 MET를 측정하였다. 실험과정에서 ln(MET)의 다중선형회귀모델에서 유의확률을 산츨한 결과 %MVC와 전완길이가 유의한 독립변수임을 확인하였다 (P<0.05). 또한, 측정 MET와 기존의 두 가지 실증적 모델들 사이의 평균절대편차는 19.4초 였으나 전완길이를 적용한 모델을 이용한 경우 16.2초로 감소하였으며, 상관계수과 급내상관계수는 모두 평균 0.87 이었으나 전완길이를 적용했을 때 평균 0.91로 모두 증가하였다. 실험결과로부터 전완의 길이가 실증적 모델에 유의한 추가 요소임을 확인하였다. During isometric elbow flexion, forearm length should be an important factor to determine not only joint torque but also maximum endurance time (MET), when the forearm is perpendicular to the direction of the force. The purpose of this paper is to examine the effect of forearm length as an additional factor on empirical models of MET such as an exponential model and a power model during isometric elbow flexion. Thirty volunteers participated in our experiment to measure factor variables such as circumferences and lengths of their upper and lower arms. Their METs were measured according to the percent of maximum voluntary contraction intensity (%MVC). For the multiple linear regression model of ln(MET) using these measurements, significant variables could be observed in %MVC and forearm lengths (P<0.05). The empirical models were assessed by these models using forearm length as the additional factor. Mean absolute deviations (MAD) between the measured METs amd the two empirical models were about 19.4 [s], but MAD using models applied forearm lengths were reduced to about 16.2 [s]. The correlation coefficients and intraclass correlation coefficients were about 0.87, but those applied forearm lengths were increased to about 0.91. These results demonstrated that forearm length was a significant additional factor to the empirical model.

SWOT Analysis and the Development of an Evaluation Model for Electronic Trade Settlement (TSU/BPO)

주혜영(Hye Young Joo),유병부(Byoung Boo You) 중앙대학교 한국전자무역연구소 2018 전자무역연구 Vol.16 No.3

연구목적: 본 연구는 TSU/BPO 방식의 활용가능성을 높이기 위한 전략적 방안을 모색하는 것을 주요한 목적으로 한다. 이를 위해 SWOT 분석을 실시하여 TSU/BPO의 주요당사자별로 내부환경 및 외부환경의 강점과 약점, 기회와 위협요인을 도출하였다. 또한 이를 기초로 실증 분석을 위한 연구모델을 구축하였다. 논문구성/논리: 제1장 서론에서는 연구의 목적과 배경을 기술하였고 제2장에서는 TSU/BPO 제도의 특징을 살펴보았다. 제3장에서는 SWOT 분석을 실시하였고 이에 기초하여 실증분석을 위한 연구모델을 개발하였다. 제4장의 결론에서는 주요한 연구내용의 요약과 함께 시사점이 논의되었다. 결과: SWOT 분석을 통해 TSU/BPO 결제방식을 입체적으로 조망하였고 SWOT 분석결과와 기술수용모델을 결합하여 실증적 평가모델을 구축하였다. 구체적으로, TSU/BPO의 유용성, TSU/BPO의 편의성, TSU/BPO 제도의 안정성 및 TSU/BPO로의 전환비용에 따라 TSU/BPO의 활용가능성이 영향을 받는 것으로 설계되었다. 독창성/가치: TSU/BPO와 관련된 선행연구들이 거의 대부분 문헌연구를 통해 TSU/BPO에 대한 이해를 도모하고 있는데 비해 본 연구는 SWOT 분석을 통해 TSU/BPO제도를 입체적으로 조망하고 있으며 추후 TSU/BPO 활용에 관해 실증적 평가가 가능한 연구모델을 제공하고 있다는 점에서 연구의 독창성 뿐 아니라 연구의 가치가 인정된다. Purpose: The main purpose of this study is to find strategic ways to increase the utilization of the TSU/BPO method. To do this, SWOT analysis was conducted to derive the strengths, weaknesses, opportunities, and threats of internal and external environments for each major TSU/BPO party. Based on this, we constructed a research model for empirical analysis. Composition/Logic: This paper starts with background information and presents the goals of the study in Section I 1. In Section II, we discuss the characteristics of the TSU/BPO system. In Section III, SWOT analysis is conducted and a research model for empirical analysis is developed based on the SWOT analysis. In the conclusions of Section IV, implications are discussed along with a summary of the main research contents. Findings: In this study, SWOT analysis is used to view the TSU/BPO settlement method from various angles, and an empirical evaluation model is constructed by combining the SWOT analysis results with the technology acceptance model. Specifically, the model shows that the utilization of TSU/BPO is affected by its usefulness, convenience, institutional stability, and conversion costs. Originality/Value: Although previous research related to the TSU/BPO research area has mostly aimed at understanding TSU/BPO through literature reviews, this study takes an original view of the TSU/BPO system through SWOT analysis. The value of this study, as well as the originality of the research, is recognized in that it provides an empirical research model that can evaluate TSU/BPO possibilities for practical use.

WRF-SMOKE-CMAQ(MADRID)을 이용한 한반도 봄철 황사(PM10)의 농도 추정

문윤섭,임윤규,이강열 한국지구과학회 2011 한국지구과학회지 Vol.32 No.3

In this study a modeling system consisting of Weather Research and Forecasting (WRF), Sparse Matrix Operator Kernel Emissions (SMOKE), the Community Multiscale Air Quality (CMAQ) model, and the CMAQ-Model of Aerosol Dynamics, Reaction, Ionization, and Dissolution (MADRID) model has been applied to estimate enhancements of PM_10 during Asian dust events in Korea. In particular, 5 experimental formulas were applied to the WRF-SMOKE-CMAQ (MADRID) model to estimate Asian dust emissions from source locations for major Asian dust events in China and Mongolia: the US Environmental Protection Agency (EPA) model, the Goddard Global Ozone Chemistry Aerosol Radiation and Transport (GOCART) model, and the Dust Entrainment and Deposition (DEAD) model, as well as formulas by Park and In (2003), and Wang et al. (2000). According to the weather map, backward trajectory and satellite image analyses, Asian dust is generated by a strong downwind associated with the upper trough from a stagnation wave due to development of the upper jet stream, and transport of Asian dust to Korea shows up behind a surface front related to the cut-off low (known as comma type cloud) in satellite images. In the WRF-SMOKE-CMAQ modeling to estimate the PM_10 concentration, Wang et al.’s experimental formula was depicted well in the temporal and spatial distribution of Asian dusts, and the GOCART model was low in mean bias errors and root mean square errors. Also, in the vertical profile analysis of Asian dusts using Wang et al's experimental formula, strong Asian dust with a concentration of more than 800μg/m^3 for the period of March 31 to April 1, 2007 was transported under the boundary layer (about 1 km high), and weak Asian dust with a concentration of less than 400 μg/m^3 for the period of 16-17 March 2009 was transported above the boundary layer (about 1-3 km high). Furthermore, the difference between the CMAQ model and the CMAQ-MADRID model for the period of March 31 to April 1, 2007, in terms of PM10 concentration, was seen to be large in the East Asia area: the CMAQ-MADRID model showed the concentration to be about 25 μg/m^3 higher than the CMAQ model. In addition, the PM10 concentration removed by the cloud liquid phase mechanism within the CMAQ-MADRID model was shown in the maximum 15 μg/m^3 in the Eastern Asia area. 본 연구에서는 한반도 황사 사례 동안 WRF 기상모델과 SMOKE 배출량모델, CMAQ 및 CMAQ-MADRID 대기질 모델을 이용하여 다양한 황사 발생량 경험식에 대한 PM10의 농도를 추정하였다. 특별히 Wang et al.(2000), US EPA 모델, Park and In(2003), GOCART 모델, DEAD 모델의 5가지 황사 발생 경험식이 중국과 몽골 등의 황사 발생량을 추정하기 위해 WRF-SMOKE-CMAQ(MADRID) 모델에 적용되었다. 일기도, 후방궤적 및 위성이미지 분석에 따르면 한반도로의 황사 수송은 절리저기압(위성에서 콤마형 구름)과 관련된 지상 전선의 뒤쪽에서, 그리고 상층 제트류의 발달에 기인한 파의 정체현상과 함께 상층 골에서의 풍속이 하층으로 전이되는 풍하 바람에 의해 생성되었다. 그리고 WRF-SMOKE-CMAQ 모델링 결과, 황사의 시·공간적 분포에 있어서는 Wang et al.(2000)의 경험식이, 평균 편의및 평균 제곱근 오차에서의 정확도 부분에서는 GOCART 모델의 경험식이 관측값을 보다 잘 모사하는 것으로 나타났다. 또한 Wang et al.의 경험식을 이용한 황사의 연직분포 분석 결과에서 강한 황사 사례(2007년 3월 31에서 4월 1일800 μg/m^3 이상)의 경우는 황사 수송이 한반도 상공 대기 경계층 내를 통과하였기 때문으로, 약한 황사 사례(2009년 3월 16일과 17에 400 μg/m^3 이하)의 경우는 황사 수송이 경계층 위를 통과하였기 때문으로 나타났다. 또한 CMAQ 모델과 CAMQ-MADRID 모델에서의 미세먼지(PM10) 민감도 분석 결과에서는 CMAQ-MADRID 모델이 CMAQ 모델에 비해 한반도를 포함한 동아시아 지역에서 최대 25 μg/m^3 정도가 높게 모사되었고, 모델 내 구름 액상과정에 의해서는 최대 15 μg/m^3 정도가 제거되는 것으로 나타났다.

Real-time forecasting of wave heights using EOF – wavelet – neural network hybrid model

Oh, Jihee,Suh, Kyung-Duck Elsevier 2018 Ocean engineering Vol.150 No.-

<P><B>Abstract</B></P> <P>Recently, along with the development of data-driven models, artificial neural networks (ANN) have been used in ocean wave forecasting models. Hybridization of ANN with wavelet analysis or fuzzy logic approach has also been used. The wavelet and neural network hybrid models (WNN models) show better performance than ANN models. However, their accuracy decreases with increasing lead time because they do not consider the relation between wave and meteorological variables. Moreover, the WNN model has been developed to forecast the wave height at a single location where the past wave height data are available. To resolve these problems, in this paper, a hybrid model is developed by combining the empirical orthogonal function analysis and wavelet analysis with the neural network (abbreviated as EOFWNN model). The past wave height data at multiple locations and the past and future meteorological data in the surrounding area including the wave stations are used as input data. The model then forecasts the wave heights at the locations for various lead times. The developed model is employed to forecast the wave heights at eight wave observation stations in the coastal waters around the East/Japan Sea. The EOFWNN model is shown to perform better compared with the WNN model for all lead times regardless of the decomposition level of wavelet analysis. The EOFWNN model is proven to be a promising tool for forecasting wave heights at multiple locations where the past wave height data and the past and future meteorological data in the surrounding area are available.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A real time wave height forecasting model at multiple locations is developed. </LI> <LI> A hybrid model is developed by combining EOF and wavelet analyses with neural network. </LI> <LI> The model forecasts significant wave heights at multiple locations for various lead times. </LI> <LI> The model is applied to eight wave stations in the coastal waters around the East/Japan Sea. </LI> <LI> The model is compared with a single point wave forecast model. </LI> </UL> </P>

대향류형 액체식 제습시스템의 제습 성능 예측을 위한 수치적 및 경험적 모델 비교

조혜진(Hye Jin Cho),박준영(Joon Young Park),천성용(Seong Yong Cheon),조민석(Min Seok Jo),정재원(Jae Weon Jeong) 대한설비공학회 2017 대한설비공학회 학술발표대회논문집 Vol.2017 No.6

This paper aims to propose the numerical model of counter flow type liquid desiccant (LD) system and to compare the dehumidification effectiveness between the numerical model and empirical model to verify the accuracy of the predicting performance of the proposed numerical model. A heat and mass transfer correlations using NTU as an input parameter are employed to solve this system model equations for predicting dehumidifications effectiveness. The simulation results were compared with the results from the empirical model presented in existing literatures. The 24 groups are chosen based on the air properties conditions for the liquid desiccant performance test and the valid parameter range of the empirical model. For the 24 groups of both predicted and experimental results, the overall discrepancy is within 20%, which proves that the calculated results by the model accord well with the experimental findings.