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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
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.
Changing climate in our lifetime: A review
Paik Kyungrock,Woo Yin San 한국수자원학회 2018 한국수자원학회논문집 Vol.51 No.11
지난 수십 년 동안, 변화하는 기후를 이해하기 위해 많은 연구가 있었고, 여러 기후 변량의 변화추세가 발견되었다. 이들 추세를 설명하기는 쉽지 않 고, 때로는 서로 모순적으로 보여지기도 한다. 다양한 기후 변량의 변화추세를 일반적으로 설명하기 위한 가설을 제시하기 위해 많은 시도도 있었다. 어느 정도 지식이 축적된 이 시점에서, 우리 시대에 진행되는 기후 변화에 대해 우리가 알고 있는 것을 되돌아보고 신중히 정리해볼 필요가 있다. 여기서는 기온, 일사량, 풍속, 증발, 강수에 초점을 맞추어 변화하는 기후에 대해 우리가 얻은 지식을 종합적으로 살펴보고자 한다. 온난화, 흐 려짐, 잔잔하기로 대변되는 주요 변화추세 및 증발의 역설, 강수 변동성의 증가를 서울 지점 자료를 예시로 들어 설명한다. 이러한 변화에 대한 이해를 근거로 수문학자와 공학자들에게 네 가지 함의를 제시하려 한다. During the last decades, considerable efforts have been spent for climate studies, in particular to better understand changing climate. In turn, several significant trends in climatic variables have been reported. Explaining such trends is challenging – some of them have been considered contradictory to another. Various hypotheses have also been suggested for general description of changing climate. At this point in time, it would be beneficial to look back and carefully recollect our knowledge about climate change. In this paper, we aim to provide a comprehensive review on our forefront knowledge in this context with focus on the trends in temperature, solar radiation, wind speed, evaporation, and precipitation. Major trends, namely warming, dimming, and stilling, are demonstrated together with evaporation paradox and increasing precipitation variability, using data at Seoul. On the basis of understanding these notions, we suggest four key implications to hydrologists and engineers.
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.
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
Hybrid approach to detect water bodies and their flow paths
Kim, JongChun,Paik, Kyungrock 한국방재학회 2015 한국방재학회 학술발표대회논문집 Vol.14 No.-
Detection of water bodies and their flow paths is elemental process of terrain analysis in any application related with surface water. Several algorithms have been proposed for automatic extraction of surface flow paths from Digital Elevation Models (DEMs) (e.g., O’Callaghan and Mark, 1984; Tarboton, 1997; Paik, 2008). While these algorithms have been widely applied, DEMs-based approaches have fundamental limitation in detecting water bodies. To resolve this issue, we propose a hybrid approach that utilizes DEMs and satellite imagery together. These dataset supplement each other’s weakness, providing extra information for better detection of water bodies and flow paths. The proposed approach is tested for the Geum River, showing successfully extraction of flow boundaries and more resonable flow paths within water bodies.
Optimization Approach for 4-D Natural Landscape Evolution
IEEE 2011 IEEE transactions on evolutionary computation Vol.15 No.5
<P>This paper presents a unique optimization method developed for landscape evolution problems. An existing hypothesis of the optimal channel network states that fluvial landscape evolution can be characterized as the procedure that follows minimum total energy expenditure. Previous studies have tested this hypothesis by solving an optimization problem, i.e., finding landscapes that satisfy the minimum total energy expenditure criterion, and showed that such optimized landscapes are similar to natural landscapes in many respects. These studies have approximated a 3-D landscape as a 2-D river network. While this network-based approach has greatly simplified the formulation of the optimization problem, this approximation limits the investigation of features such as longitudinal profiles, since their representation requires the gravitational direction-wise dimension. Here, an alternative technique is devised to fully handle the optimization of 3-D landforms over time. The proposed idea is to break down the time domain and to apply an optimization algorithm sequentially for discrete time steps. For the optimization part, a heuristic algorithm motivated from adaptation strategies of natural systems (here landscape formation) is used. This method is applied to a theoretical landscape with the condition that the balance between tectonic uplift and sediment lost is satisfied. It is found that landscapes of minimum total energy expenditure exhibit the Hack's law and the power-law in the exceedance probability distribution of drainage area, which are the characteristics found in natural river networks. However, they demonstrate no systematic pattern in longitudinal profiles.</P>