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Brake disk cooling performance optimization with DFSS
Sangyeol Choi(최상열),Semoon Choi(최세문),Younghoon Kim(김영훈),Yongsuk Kim(김용석) 한국자동차공학회 2012 한국자동차공학회 부문종합 학술대회 Vol.2012 No.5
The cooling performance of ventilated brake disk of vehicle which depends on convective heat transfer rate governed by air flow entering into brake system is the main property to determine the brake disk size. To achieve competitive brake disk size will contribute the mass reduction that is one of most significant challenges for fuel economy in recent automotive industry. To improve the cooling performance of brake disk without disk size increasing, it is obvious that the cooling air flow should be induced to brake system inside wheel rim effectively by design optimization of vehicle front end and underbody configurations. However, there are little correlation studies between vehicle geometry and brake cooling performance. So, it is necessary that it should be preceded to find the correlation with each geometric change. In the present study, DFSS method is used for analyzing which design parameter affect on brake cooling performance and how it works on. According to the results, brake cooling performance is proportional to mass flow rate into wheel and it should be controlled to achieve desired brake sizing and cooling performance.
Maximum entropy test for infinite order autoregressive models
Sangyeol Lee,Jiyeon Lee,Jungsik Noh 한국데이터정보과학회 2013 한국데이터정보과학회지 Vol.24 No.3
In this paper, we consider the maximum entropy test in infinite order autoregressive models. Its asymptotic distribution is derived under the null hypothesis. A bootstrap version of the test is discussed and its performance is evaluated through Monte Carlo simulations.
Forecasting value-at-risk by encompassing CAViaR models via information criteria
Sangyeol Lee,Jungsik Noh 한국데이터정보과학회 2013 한국데이터정보과학회지 Vol.24 No.6
This paper proposes a new method of VaR forecasting using the conditional au-toregressive VaR (CAViaR) models and information criteria. Instead of using a single CAViaR model, we propose to utilize several candidate CAViaR models during a forecasting period. By adopting the Akaike and Bayesian information criteria for quantile regression, we can update not only parameter estimates but also the CAViaR specifications. We also propose extended CAViaR models with a constant location parameter. An empirical study is provided to examine the performance of the proposed method. The results suggest that our method shows more stable performance than those using a single specification.
Dependence structure analysis of KOSPI and NYSE based on time-varying copula models
Sangyeol Lee,Byungsoo Kim 한국데이터정보과학회 2013 한국데이터정보과학회지 Vol.24 No.6
In this study, we analyze the dependence structure of KOSPI and NYSE indices based on a two-step estimation procedure. In the first step, we adopt ARMA-GARCH models with Gaussian mixture innovations for marginal processes. In the second step,time-varying copula parameters are estimated. By using these, we measure the de-pendence between the two returns with Kendall`s tau and Spearman`s rho. The two dependence measures for various copulas are illustrated.
Monitoring parameter change for bivariate time series models of counts
Lee Sangyeol,Kim Dongwon 한국통계학회 2023 Journal of the Korean Statistical Society Vol.52 No.3
In this study, we consider an online monitoring procedure to detect a parameter change for bivariate time series of counts, following bivariate integer-valued generalized autoregressive heteroscedastic (BIGARCH) and autoregressive (BINAR) models. To handle this problem, we employ the cumulative sum (CUSUM) process constructed from the (standardized) residuals obtained from those models. To attain control limits, we develop limit theorems for the proposed monitoring process. A simulation study and real data analysis are conducted to affirm the validity of the proposed method.
홍최상열(Sangyeol Choi),이동현(Donghyun Lee),하종백(Jongpaek Ha) 한국자동차공학회 2010 한국자동차공학회 학술대회 및 전시회 Vol.2010 No.11
Recently, wheels in road vehicle are being developed to be stiffed and lighten from the standpoint of vehicle dynamics and fuel economy, respectively. In addition, design and shape of wheels are being diversified more and more. So, understanding air flow characteristics by those changes of wheel design and shape are very important on production vehicle, because it affect on not only aerodynamic performance which can be sensitized by geometric complexity near wheel, but also thermal performance which can be depended on convective heat transfer rate governed by cooling air flow entering into thermal objectives inside wheel rim like a brake assembly. The objective of this investigation is to analyze aerodynamic performances on the wheel spokes which were designed virtually using NACA airfoil. According to the results, air flow through the wheel opening area could be controlled by NACA airfoil spokes with angle of attack, and also drag coefficient and lift coefficient were changed by the changes of air flow patterns. The results are intended to be used in guiding the establishment of optimum wheel design for future aerodynamic friendly vehicle.
Oh, Sangyeol,Jeong, Jichai,Lee, Jaehoon IET 2015 Electronics letters Vol.51 No.25
<P>A common noise suppression filter in a differential pair using the coupled microstrip line (CML) to edge-coupled coplanar waveguide (ECCPW) transition is proposed. The filter consists of CMLs, ECCPWs, and shorting via holes that connect the CMLs and ECCPWs, and provides wideband common noise signal suppression using an even-mode impedance mismatching technique between the CMLs and ECCPWs and wideband differential signal propagation for high-speed circuit systems. A bandgap effect is realised in even mode, based on the CML to ECCPW transition without a multilayer. This method was verified using the three-dimensional full-wave high-frequency structure simulator and experimental measurements.</P>
이상열(SangYeol Lee) 한국부패학회 2011 한국부패학회보 Vol.16 No.1
1945 police constitution since then police organization corruption exposing and ethical ceremony cultivation and integrity from above mass produced a various countermeasure raising with the fact that, cannot be effective extra ordinary evaluation is receiving. The police organization cannot be trusted the citizens without being able there is a various reason but is biggest and this new is in order for the integrity to be low. Finally the integrity is low the thing is a possibility of saying that originates to the insufficiency of police internal control, Namely, the control middle which is the possibility discipline of doing the conduct self-control of the police officer the internal control is feeble and police officer each person voluntary and acts with egoistic and even at the time of character does not display a regulation power well. The internal efforts for police corruption control flowing, corruption control are big, the degree substitution the huge result the self-purification will of the police officers and forms the corruption control atmosphere of police organization leading which is not and calls there was an effect.