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김경록(Kyungrock Kim),김병구(Byung-Gu Kim),이창훈(Changhoon Lee) 대한기계학회 2006 대한기계학회 춘추학술대회 Vol.2006 No.6
Recently, second-order Lagrangian stochastic model (LSM) have been broadly simulated and predicted for detailed physics such as rotational vector, dispersion at various Reynolds number. (Reynolds, 2006) In this study, we introduce more accurate modeling approach by considering first and second drift correction term, that is inhomogeneous term, which have a role to resolve more correct physics in the wall region such as viscous sub-layer and buffer layer which have sharply tilted Reynolds stresses as well as log-layer. Also we simulated by incorporating and by not incorporating cross-covariance of acceleration into second-order LSM at various acceleration variance case including DNS parameterized acceleration variance case.
김경록(Kyungrock Kim),정재달(Jaedal Jung),이창훈(Canghoon Lee) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-
In this study we perform Lagrangian stochastic model simulation for heavy particle. Reynolds(2002) construct simple LSM for heavy particle, which lack in detailed parameter study and statistics of turbulent flow within his paper. we investigate more simple but important turbulent statistics such as autocorrelation for velocity and acceleration, Lagrangian structure function and dispersion statistics parameterized by using DNS
벽 근처 가속도 모델링에 의한 확산예측과 레이놀즈 수 효과
김경록(Kyungrock Kim),김병구(Byung-Gu Kim),이창훈(Changhoon Lee) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.5
We apply a second-order stochastic dispersion model to the prediction of dispersion in the atmospheric boundary layer and comparc results in dispersion with the prediction by first-order model. Second-order stochastic model can be applied at reltively low Reynolds turbulent flows. Moreover we consider the Reynolds effects and spin statistics in the near-wall dispersion. Especially, spin and it's variance which measure rotational property of the Lagrangian particle trajectory(Sawford 1999) can explain particle dispersion properties
난류유동에서 이차 라그랑지안 스토케스틱 모델에 의한 확산
김경록(Kyungrock Kim),김병구(Byung-Gu Kim),이창훈(Changhoon Lee) 대한기계학회 2005 대한기계학회 춘추학술대회 Vol.2005 No.11
Performance of the second-order Lagrangian stochastic model of Reynolds et al.(2004) for particle dispersion in turbulent flows is assessed. We correct original Reynolds model to novel second-order Lagrangian stochastic model by modifying diffusion terms. new model give a good agreement with fundamental statistics of turbulent channel flows such as Reynolds stress Also, the statistics of spin such as the mean rotation is compared. modified model observe better prediction than Reynolds model. but high-order statistics of spin and more accurate model for predicting spin is needed.
전형규(Hyung Gyu Jeon),정경환(Kyunghwan Jung),강병문(Byungmun Kang),김대은(DaeEun Kim),임윤묵(Yun Mook Lim),김광준(Kwang Joon Kim),김창오(Chang Oh Kim),이황재(Hwang-Jae Lee),김경록(Kyungrock Kim),김윤명(Yoon-Myung Kim) 대한운동학회 2022 아시아 운동학 학술지 Vol.24 No.4
OBJECTIVES The purpose of this study was to investigate the effects of assist and resistance torque on the spatiotemporal gait characteristics, and the symmetry and asymmetry of gait using a Gait Enhancing and Motivating System (GEMS) in the elderly. METHODS A cross-sectional and repeated measure design was used. A total of 18 participants (9 males, 9 females; age: 63.5 ± 5.02 years; mass: 64.26 ± 6.87 kg; height: 164.06 ± 7.15 cm) were recruited from a local community, and spatiotemporal gait data were collected with OptoGait system and GEMS. Spatiotemporal gait variables and differences between the dominant and non-dominant legs of these variables were assessed (step length, step time, stance phase, swing phase, single support, load response, pre swing phase, stride time, stride length, double support, cadence, and gait speed). The effects of three modes including normal, assist, and resist modes using GEMS were investigated twice for each participant on a 9-meter walkway. A one-way repeated measure analysis of variance followed by Bonferroni post-hoc tests was conducted. RESULTS The assist mode increased step time, swing phase, stride time and reduced stance phase, pre-swing phase, double support, cadence, and gait speed as compared to normal mode. The resist mode increased stance phase, load response, pre-swing phase, double support, cadence, and reduced step time, swing phase, and stride time. In dominant leg, assist mode showed increased step time and reduced pre-swing phase than normal mode, and greater step time than resist mode (p < 0.05). However, there was no effect of external torque on symmetry and asymmetry between both legs (p > 0.05). CONCLUSIONS The resistance and assist torque of GEMS alter spatiotemporal characteristics during the stance and swing phase of gait in the elderly. However, the resistance torque and assist torque of GEMS did not increase or decrease the gait asymmetry between the dominant and non-dominant legs.