• Atmosphere
• /
• v.23 no.1
• /
• pp.93-102
• /
• 2013

Atmospheric transport pathway of an air mass is an important constraint controlling the chemical properties of the air mass observed at a designated location. Such information could be utilized for understanding observed temporal variabilities in atmospheric concentrations of long-lived chemical compounds, of which sinks and/or sources are related particularly with natural and/or anthropogenic processes in the surface, and as well as for performing inversions to constrain the fluxes of such compounds. The Lagrangian particle dispersion model FLEXPART provides a useful tool for estimating detailed particle dispersion during atmospheric transport, a significant improvement over traditional "single-line" trajectory models that have been widely used. However, those without a modeling background seeking to create simple back-trajectory maps may find it challenging to optimize FLEXPART for their needs. In this study, we explain how to set up, operate, and optimize FLEXPART for back-trajectory analysis, and also provide automatization programs based on the open-source R language. Discussions include setting up an "AVAILABLE" file (directory of input meteorological fields stored on the computer), creating C-shell scripts for initiating FLEXPART runs and storing the output in directories designated by date, as wells as processing the FLEXPART output to create figures for a back-trajectory "footprint" (potential emission sensitivity within the boundary layer). Step by step instructions are explained for an example case of calculating back trajectories derived for Anmyeon-do, Korea for January 2011. One application is also demonstrated in interpreting observed variabilities in atmospheric $CO_2$ concentration at Anmyeon-do during this period. Back-trajectory modeling information introduced in this study should facilitate the creation and automation of most common back-trajectory calculation needs in atmospheric research.

• Journal of Mechanical Science and Technology
• /
• v.15 no.12
• /
• pp.1835-1844
• /
• 2001

The turbulent flow with wake, reattachment and recirculation is a very important problem that is related to vehicle dynamics and aerodynamics. The Smagorinsky Model (SM), the Dynamics Subgrid Scale Model (DSM), and the Lagrangian Dynamic Subgrid Scale Model (LDSM) are used to predict the three-dimensional flow field around a bluff body model. The Reynolds number used is 45,000 based on the bulk velocity and the height of the bluff body. The fully developed turbulent flow, which is generated by the driver part, is used for the inlet boundary condition. The Convective boundary condition is imposed on the outlet boundary condition, and the Spalding wall function is used for the wall boundary condition. We compare the results of each model with the results of the PIV measurement. First of all, the LES predicts flow behavior better than the k-$\xi$ turbulence model. When ew compare various LES models, the DSM and the LDSM agree with the PIV experimental data better than the SM in the complex flow, with the separation and the reattachment at the upper front part of th bluff body. But in the rear part of the bluff body, the SM agrees with the PIV experimental results better than them. In this case, the SM predicts overall flow behavior better than the DSM nd the LDSM.

• Nuclear Engineering and Technology
• /
• v.53 no.7
• /
• pp.2377-2386
• /
• 2021

To model the atmospheric dispersion of radionuclides released from nuclear accident is very important for nuclear emergency. But the uncertainty of model parameters, such as source term and meteorological data, may significantly affect the prediction accuracy. Data assimilation (DA) is usually used to improve the model prediction with the measurements. The paper proposed a parameter bias transformation method combined with Lagrangian puff model to perform DA. The method uses the transformation of coordinates to approximate the effect of parameters bias. The uncertainty of four model parameters is considered in the paper: release rate, wind speed, wind direction and plume height. And particle swarm optimization is used for searching the optimal parameters. Twin experiment and Kincaid experiment are used to evaluate the performance of the proposed method. The results show that the proposed method can effectively increase the reliability of model prediction and estimate the parameters. It has the advantage of clear concept and simple calculation. It will be useful for improving the result of atmospheric dispersion model at the early stage of nuclear emergency.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
• /
• v.1
• /
• pp.181-186
• /
• 2006

In this paper, generation mechanisms of ocean freak waves are briefly introduced in the context of wave-current interaction phenomena. The present model of the fluid motion is based on the Navier-Stokes equations incorporating velocity-pressure formulation because of need to model the nonlinear wave interaction with spatially non-uniform current field. In order to deal with the free surface motion, an Arbitrary Lagrangian-Eulerian (ALE) description is adopted. As an accurate and efficient numerical tool, the spectral element method is presented with general features and specific treatment for the wave-current interaction problem. As an intermediate stage of development, solution procedure and characteristics aspects of the present modeling and numerical method are addressed in detail, and preliminary numerical results prove its accuracy and convergence.

• Journal of Korean Society of Coastal and Ocean Engineers
• /
• v.29 no.6
• /
• pp.350-362
• /
• 2017

The Eulerian nearshore current model is more advantageous than the Lagrangian model in the way that numerical results from the Eulerian model can be directly compared with the measurements by the stationary equipment. It is because the wave mass flux is not included in the computed mass flux of Euleran nearshore current model. In addition, the Eulerian model can simulate the longshore currents with depth varying parabolic profile. However, the numerical models proposed by different researcher have different forms of the wave stress terms. For example, wave stresses in Newberger and Allen's (2007) model is constant over the depth, while those of Chun (2012) are vertically distributed. In the present study, these wave stress terms were compared against Hamilton et al.'s (2001) laboratory experiments to see the effects of different wave stress terms performed on the computation of nearshore currents.

• Wind and Structures
• /
• v.20 no.2
• /
• pp.143-168
• /
• 2015

A numerical model for analyzing air-train-track interaction is proposed to investigate the dynamic behavior of a high-speed train running on a track in crosswinds. The model is composed of a train-track interaction model and a train-air interaction model. The train-track interaction model is built on the basis of the vehicle-track coupled dynamics theory. The train-air interaction model is developed based on the train aerodynamics, in which the Arbitrary Lagrangian-Eulerian (ALE) method is employed to deal with the dynamic boundary between the train and the air. Based on the air-train-track model, characteristics of flow structure around a high-speed train are described and the dynamic behavior of the high-speed train running on track in crosswinds is investigated. Results show that the dynamic indices of the head car are larger than those of other cars in crosswinds. From the viewpoint of dynamic safety evaluation, the running safety of the train in crosswinds is basically controlled by the head car. Compared with the generally used assessment indices of running safety such as the derailment coefficient and the wheel-load reduction ratio, the overturning coefficient will overestimate the running safety of a train on a track under crosswind condition. It is suggested to use the wheel-load reduction ratio and the lateral wheel-rail force as the dominant safety assessment indices when high-speed trains run in crosswinds.

• Journal of the Korean Geotechnical Society
• /
• v.32 no.10
• /
• pp.17-29
• /
• 2016

A debris flow analysis model has been developed to simulate the erosion and entrainment of soil layer. Special attention is given to the model which represents strength softening behaviour of soil layer due to velocity of deformation. The 3D FE analysis by Coupled Eulerian-Lagrangian (CEL) model is conducted to simulate the debris flow. The model is validated using published data on laboratory experiment (Mangeny et al., 2010). It has been definitely shown that proposed model is in good agreement with the results of laboratory data. Futhermore, the FE analysis is conducted to ensure capability of simulating the real scale debris flow. The result of Ramian watershed, Korea shows that the debris flow has increased the volume and speed and it is in good agreement with field investigation. Based on this, it is confirmed that proposed model shows good agreement of the behavior of the actual and analytical debris flow.

• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 2008.10a
• /
• pp.406-407
• /
• 2008

• Proceedings of the Korea Air Pollution Research Association Conference
• /
• 2007.10a
• /
• pp.87-89
• /
• 2007

• Proceedings of the Korean Radioactive Waste Society Conference
• /
• 2018.11a
• /
• pp.529-530
• /
• 2018