• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.1
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• pp.10-15
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• 2012

Wave characteristics in the presence of energy damping are investigated using the linear shallow water equations. To get the phase and energy velocities, geometric optics approach is used and then these values are validated through numerical experiments. Energy damping affects wave height, phase and energy velocities which result in wave transformation. When the complex wavenumber is used by the Eulerian approach, it is found that the phase velocity decreases as the damping increases while the energy velocity increases showing higher values than the phase velocity. When the complex angular frequency is used by the Lagrangian approach, the energy-damping wave group is found to propagate in the energy velocity. The energy velocity is found to affect shoaling and refraction coefficient which is verified through numerical experiments for waves on a plane slope.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2014.10a
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• pp.411-414
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• 2014

Numerical modeling was conducted to estimate the amount of dislocation that may occur across a frictionless fracture during an earthquake using commercial code FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions). The applied motion was calculated to represent a Richter 6.0 magnitude earthquake at distances of 2 km from the fracture. The velocity-time history was generated from Svensk $K{\ddot{a}}arnbr{\ddot{a}}anslehantering$ AB report. In the report, The velocity field resulting from an earthquake on a fault located in the near-field (2 km distance) was modelled using a finite difference program, WAVE. The stress-time history was substituted for velocity-time history to perform dynamic analysis using FLAC3D. During the earthquake, the maximum dislocation and change of shear stress were about 1 cm and 2MPa, respectively. Because the fracture is frictionless in this study, all dislocations relax to zero after the earthquake motions have ceased.

• Journal of the Korean Society of Safety
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• v.15 no.3
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• pp.30-39
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• 2000

The present paper deals with the numerical simulation for the spray characteristics with swirling turbulent flows and dilution flows from swirl injectors in a simplified can type of gas turbine combustor. The main objective is to investigate the characteristics of swirling turbulent flows with dilution flows and to provide the qualitative results for the spray characteristics such as the droplet distribution and Sauter Mean Diameter(SMD). The gas-phase equations based on Eulerian approach were discretized by Finite Volume Method, together with SIMPLE algorithm and the Reynolds -Stress-Model. The liquid-phase equations based on Lagrangian method were used to predict the droplet behavior. The results of preliminary test are generally in good agreement with experimental data, and show that the anisotropy exists in the primary zone due to swirl velocity and injected air from primary injector, and then gradually decays due to turbulent mixing and consequently near-isotropy occurs in the region between primary and dilution zones. For the spray characteristics, it is indicated that the swirling flows of primary jet region increase the droplet atomization. In addition, it is showed that the swirling flows at the inlet region lead the air-fuel mixture to be distributed near the igniter and can significantly affect the spray behavior in the primary jet region.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.25 no.6
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• pp.559-567
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• 2012

A level set based topological shape optimization method for nonlinear structure considering hyper-elastic problems is developed. To relieve significant convergence difficulty in topology optimization of nonlinear structure due to inaccurate tangent stiffness which comes from material penalization of whole domain, explicit boundary for exact tangent stiffness is used by taking advantage of level set function for arbitrary boundary shape. For given arbitrary boundary which is represented by level set function, a Delaunay triangulation scheme is used for current structure discretization instead of using implicit fixed grid. The required velocity field in the actual domain to update the level set equation is determined from the descent direction of Lagrangian derived from optimality conditions. The velocity field outside the actual domain is determined through a velocity extension scheme based on the method suggested by Adalsteinsson and Sethian(1999). The topological derivatives are incorporated into the level set based framework to enable to create holes whenever and wherever necessary during the optimization.

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

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.10
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• pp.1793-1799
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• 2003

An optimal design of a multi-layered plate structure to endure high-velocity impact has been suggested by using size optimization after numerical simulations. The NET2D, a Lagrangian explicit time-integration finite element code for analyzing high-velocity impact, was used to find the parameters for the optimization. Three different materials such as mild steel, aluminum for a multi-layered plate structure and die steel for the pellet, were assumed. In order to consider the effects of strain rate hardening, strain hardening and thermal softening, Johnson-Cook model and Phenomenological Material Model were used as constitutive models for the simulation. It was carried out with several different gaps and thickness of layers to figure out the trend in terms of those parameters' changes under the constraint, which is against complete penetration. Also, the measuring domain has been shrunk with several elements to reduce the analyzing time. The response surface method based on the design of experiments was used as optimization algorithms. The optimized thickness of each layer in which perforation does not occur has been obtained at a constant velocity and a designated total thickness. The result is quite acceptable satisfying both the minimized deformation energy and the weight criteria. Furthermore, a conceptual idea for topology optimization was suggested for the future work.

• Journal of Advanced Research in Ocean Engineering
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• v.1 no.1
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• pp.1-13
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• 2015

Post-Katrina investigations revealed that most earthen levee damage occurred on the levee crest and landward-side slope as a result of either wave overtopping, storm surge overflow, or a combination of both. In this paper, combined wave overtopping and storm surge overflow of a levee embankment strengthened with high performance turf reinforcement mat (HPTRM) system was studied in a purely Lagrangian and meshless approach, two-dimensional smoothed particle hydrodynamics (SPH) model. After the SPH model is calibrated with full-scale overtopping test results, the overtopping discharge, flow thickness, flow velocity, average overtopping velocity, shear stress, and soil erosion rate are calculated. New equations are developed for average overtopping discharge. The shear stresses on landward-side slope are calculated and the characteristics of soil loss are given. Equations are also provided to estimate soil loss rate. The range of the application of these equations is discussed.

• Journal of Environmental Science International
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• v.3 no.1
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• pp.39-47
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• 1994

Dispersion characteristics of air pollutants in the mountainous coastal area are investigated in considering with the mesoscale local circulations using a two dimensional numerical model with two kinds of topograpy of 500m and 300m. In the model, land-sea breezes and mountain-valley wind are mainly considered under the condition of the absence of large scale prevailing flow in the circulation analysis, and the pollutants dispersion is traced by the Lagrangian methods. According to the results, the wind velocity is affected by topography and is stronger in the case of 500m height mountain than that of 300m, the Pollutants that source is near the coast transported over the mountain and dispersed to behind inland area. It is classified that the topography change control affects the wind velocity and the circulations. The pollutants that source is different transported and concentrated to behind inland and/or diffused to the sea area by the combination of the wind system with topographic changes. The results can be applied to the air pollution control with the arrangement design of industrial area and the planning of coastal developments.

• Journal of Korean Society for Atmospheric Environment
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• v.23 no.4
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• pp.478-486
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• 2007

Numerical analysis had been performed to understand flow characteristics of the flue gas and slurry in the absorber of a flue gas desulphurization (FGD) system using computational fluid dynamics (CFD) technique. Two-fluid(Euler-Lagrangian) model had been employed to simulate physical phenomenon, which slurry particles injected through slurry spray nozzles fall down and bump into the flue gas inflowing through inlet duct. It was not necessary to adopt pre-defined pressure drop inside the absorber because interaction between flue gas and slurry particles was considered. Hundreds of slurry spray nozzles were considered with the spray velocity at the nozzles, swirl velocity and spreading angle. The results note that the flow disturbance of flue gas is found at the bottom of the absorber, and the current rising with high speed stream is observed in the opposite region of the inflow duct. The high speed stream is reduced as the flue gas goes up, because the high speed stream of flue gas dumps falling slurry particles due to momentum exchange between flue gas and slurry particles. In spite of some disproportion in slurry distribution inside the absorber, escape of slurry particles from the absorber facility is not observed. The pressure drop inside the absorber is mainly occurred at the bottom section.

• Journal of ILASS-Korea
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• v.16 no.2
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• pp.69-75
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• 2011

This article presents computational fluid dynamics (CFD) simulations of sub-micron particle movements and flow characteristics in laboratory-scale electrostatic precipitator (ESP) without corona discharge, and for simulation, it uses the commercial CFD program (CFD-ACE) including electrostatic theory and Lagrangian-based equation for sub-micron particle movement. For validation of CFD results, a simple cylindrical type of ESP is simulated and numerical prediction shows fairly good agreement with the analytical solution. In particular, the present study investigates the effect of particle diameter, inlet flow rate, and applied electric potential on particle collection efficiency and compares the numerical prediction with the experimental data, showing good agreement. It is found that the particle collection efficiency decreases with increasing inlet flow rate because the particle detention time becomes shorter, whereas it decreases with the increase in sub-micron particle diameter and with the decrease of applied electric voltage resulting from smaller terminal electrostatic velocity.