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Namhun Lim,Paul M. Pedersen 글로벌지식마케팅경영학회 2022 Journal of Global Sport Management Vol.7 No.1
Attendance data in sports leagues are organized at more than one level and thus are nested data with factors varying by individual games (e.g. single game attendance figure), which are nested within the factors varying by teams (e.g. local population and income level, stadium). Such a nested data structure requires a multilevel modeling approach for an accurate examination of attendance. Also, although the previous application of multilevelmodeling to sport attendance research has been limited to the data aggregated and averaged by seasons or by teams, no multilevel modeling of attendance data at the individual game level is available. The uniqueness of the current study is its extension of the multilevel modeling approach by analyzing the audience data at the individual game level. Thus, this study examined the relationship between attendance determinants and single game attendance in a Major League Baseball (MLB) season by using multilevel modeling with 14 game level variables and 12 team level variables. Twelve predictors (e.g. home/visiting team playoff appearances, day of game, season progress, ticket price, stadium capacity, game uncertainty) significantly (p < .05) influenced attendance.
A Computational Study of Wall Effects on the Aeroelastic Behavior of Spanwise Flexible Wings
Namhun Lee,이승수,조해성,신상준 한국항공우주학회 2019 International Journal of Aeronautical and Space Sc Vol.20 No.3
In this paper, we present a computational aeroelastic analysis of flexible flapping wings in the vicinity of solid walls. The wall effects change the aerodynamic forces and moments of the wings, and thus the aeroelastic behavior. The numerical simulation is carried out using a fluid–structure interaction framework by coupling the computational fluid dynamics and computational structural dynamics. A preconditioned Navier–Stokes solver based on a finite volume method is used for the aerodynamic analysis. The structural analysis is performed using a nonlinear structural model based on a geometrically exact beam formulation. The method is validated using previous numerical and experimental results. The aeroelastic characteristics of the flexible wings with and without the walls are computed and compared.
Namhun Koo,Gook Hwa Cho,Soonhak Kwon IEEE 2016 IEEE Transactions on Computers Vol.65 No.1
<P>We present an r-th root extraction algorithm over a finite field F-q. Our algorithm precomputes a primitive r(s)-th root of unity if where 8 is the largest positive integer satisfying r(s)vertical bar q 1, and is applicable for the cases when is small. The proposed algorithm requires one exponentiation for the r-th root computation and is favorably compared to the existing algorithms.</P>
Modified Direct Torque Control System of Five Phase Induction Motor
Namhun Kim,Minhuei Kim 대한전기학회 2009 Journal of Electrical Engineering & Technology Vol.4 No.2
In this paper, improved direct torque control(DTC) of five-phase induction motor(IM) is proposed. Due to the additional degrees of freedom, five-phase IM drives present unique characteristics. One of them is the ability of enhancing the torque producing capability of the motor. Also fivephase motor drives possess many others advantage compared with the traditional three-phase motor drives. Such as, reducing the amplitude and increasing of frequency of torque pulsation, reducing amplitude of current per phase without increasing the voltage per phase and increasing the reliability. The direct torque control method is advantageous when it is applied to the five-phase IM. Because the fivephase inverter provides 32 space vectors in comparison to 8 space voltage vectors by the three-phase inverter. The 32 space voltage vectors are divided into three groups according to their magnitudes. The characteristics and dynamic performance of traditional five-phase DTC are analyzed and new DTC for five-phase IM is proposed. Therefore, a more precise flux and torque control algorithm for the fivephase IM drives can be suggested and explained. For presenting the superior performance of the proposed direct torque control, experimental results is presented using a 32 bit fixed point TMS320F2812 digital signal processor
Namhun Lim,Sang Keon Yoo 한국체육학회 2022 International journal of human movement science Vol.16 No.2
In order to investigate the relationship between Major League Baseball (MLB) attendance and game duration, this study analyzed the number of spectators throughout the 2010–19 MLB regular seasons (N=24,297) with attendance determinants identified in earlier studies. Also, a three-level hierarchical linear modeling (HLM) was used in consideration of the characteristics of attendance data for several seasons, teams, and individual games. A total of 27 independent variables were used in the current research, and 17 attendance determinants, including game duration (γ =4.45, p<.05), were identified as having a significant impact on the number of spectators. Furthermore, by confirming the hierarchical structure of the attendance data, this study highlights how critical it is to utilize appropriate analytical methods. Based on these findings and statistical analysis that confirmed MLB's current attendance decline, these results will help in the development of a number of strategies to increase or sustain team’s attendance to practitioners.
Low Cost Rotor Fault Detection System for Inverter Driven Induction Motor
Namhun Kim,Changho Choi 대한전기학회 2007 Journal of Electrical Engineering & Technology Vol.2 No.4
In this paper, the induction motor rotor fault diagnosis system using current signals, which are measured using axis-transformation method, and speed, which is estimated using current information, are presented. In inverter-fed motor drives unlike line-driven motor drives the stator currents have numerous harmonics components and therefore fault diagnosis using stator currents is very difficult. The current and speed signal for rotor fault diagnosis needs to be precise. Also, high resolution information, which means the diagnosis system, demands additional hardware such as low pass filter, high resolution ADC, encoder and etc. Therefore, the proposed axis-transformation and speed estimation method are expected to contribute to low cost fault diagnosis systems in inverter-fed motor drives without the need for an encoder and any additional hardware. In order to confirm validity of the developed algorithms, various experiments for rotor faults are tested and the line current spectrum of each faulty situation using Park transformation and speed estimation method are compared with the results obtained from fast Fourier transforms.
( Namhun Lim ),( Wanyong Choi ),( Paul Mark Pedersen ) 국민체육진흥공단 한국스포츠정책과학원 2019 International Journal of Applied Sports Sciences Vol.31 No.1
The location of a sports facility is one of the significant factors in economically operating and maintaining the facility. The present study used a location theory model to examine the influence of the Major League Baseball (MLB) stadium location on attendance (N = 348) for the 2006-2017 MLB regular seasons, taking into consideration the population, median income, and distance between the stadium and the population center of counties nearby the stadium. The optimal location model was determined as the inverse proportion of the squared distance of the first nearest county, and location significantly influenced the attendance (p < .05). Then, based on the results of the location model, the current study analyzed the relationship between the MLB attendance and other attendance determinants by using hierarchical linear modeling. Among 14 different determinants, six variables (i.e., stadium capacity, ticket price, season, as well as the home team’s quality, payroll, and star players) were revealed in the findings to have a significant influence on the MLB attendance (p < .05).