• Journal of Korean Society of Environmental Engineers
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• v.35 no.10
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• pp.710-716
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• 2013

New and renewable energy sources have drawn attention because of climate change. Many studies have been carried out in waste-to-energy field. Fast pyrolysis of waste lignocelluosic biomass is one of the waste-to-energy technologies. Bubbling fluidized bed (BFB) reactor is widely used for fast pyrolysis of the biomass. In BFB pyrolyzer, bubble behavior influences on the chemical reaction. Accordingly, in the present study, hydrodynamic characteristics and fast pyrolysis reaction of waste lignocellulosic biomass occurring in a BFB pyrolyzer are scrutinized. The computational fluid dynamics (CFD) simulation of the fast pyrolysis reactor is carried out by using Eulerian-Granular approach. And two-stage semi-global kinetics is applied for modeling the fast pyrolysis reaction of waste lignocellulosic biomass. To summarize, generation and ascendant motion of bubbles in the bed affect particle behavior. Thus biomass particles are well mixed with hot sand and consequent rapid heat transfer occurs from sand to biomass particles. As a result, primary reaction is observed throughout the bed. And reaction rate of tar formation is the highest. Consequently, tar accounts for 66wt.% of the product gas. However, secondary reaction occurs mostly in the freeboard. Therefore, it is considered that bubble behavior and particle motions hardly influences on the secondary reaction.

• Journal of Korean Society for Geospatial Information Science
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• v.24 no.1
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• pp.99-107
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• 2016

Korea has been known as volcanic disaster free area. However, recent surveying result shows that Baekdu mountain located in northernmost in the Korean peninsula is not a dormant volcano anymore. When Baekdu mountain is erupting, various damages due to the volcanic ash are expected in South Korea area. Especially, volcanic ash in the air may cause big aviation accident because it can hurt engine or gauges in the airplane. Therefore, it is a crucial issue to interrupt airplane navigation, whose route is overlapped with volcanic ash, after predicting three dimensional dispersion of volcanic ash. In this paper, we deals with 3D visualization techniques for volcanic ash dispersion prediction results. First, we introduce the data acquisition of the volcanic ash dispersion prediction. Dispersion prediction data is obtained from Fall3D model, which is volcanic ash dispersion simulation program. Next, three 3D visualization techniques for volcanic ash dispersion prediction are proposed. Firstly proposed technique is so called 'Cube in the Air', which locates the semitransparent cubes having different color depends on its particle concentration. Second technique is a 'Cube in the Cube' which divide the cube in proportion to particle concentration and locates the small cubes. Last technique is 'Semitransparent Volcanic Ash Plane', which laminates the layer, whose grids present the particle concentration, and apply the semitransparent effect. Based on the proposed techniques, the user could 3D visualize the volcanic ash dispersion prediction results upon his own purposes.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.34 no.1
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• pp.59-69
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• 2021

Recently, large-scale offshore and coastal structures have been constructed owing to the increasing interest in eco-friendly energy development. To achieve this, precise simulations of waves are necessary to ensure the safe operations of marine structures. Several experiments are required in the field to understand the offshore wave; however, in terms of scale, it is difficult to control variables, and the cost is significant. In this study, numerical waves under various wave conditions are produced using a piston-type wavemaker, and the produced wave profiles are verified by comparing with the results from a numerical wave tank (NWT) modeled using the smoothed particle hydrodynamics (SPH) method and theoretical equations. To minimize the effect by the reflected wave, a mass-weighted damping zone is set at the right end of the NWT, and therefore, stable and uniform waves are simulated. The waves are generated using the linear and Stokes wave theories, and it is observed that the numerical wave profiles calculated by the Stokes wave theory yield high accuracy. When the relative depth is smaller than two, the results show good agreement irrespective of the wave steepness. However, when the relative depth and wave steepness are larger than 2 and 0.04, respectively, the errors are negligible if the measurement position is close to the excitation plate. However, the error is 10% or larger if the measurement position is away from the excitation location. Applicable target wave ranges are confirmed through various case studies.

• Journal of computational fluids engineering
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• v.16 no.2
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• pp.1-10
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• 2011

A new computational program, which is based on the CIP/CCUP(Constraint Interpolation Profile/CIP Combined Unified Procedure) method, has been developed to numerically analyse sloshing phenomena dealt as multiphase-flow problems. For the convection terms of Navier-Stokes equations, the RCIP(Rational function CIP) method was adopted and the THINC-WLIC(Tangent of Hyperbola for Interface Capturing-Weighted Line Interface Calculation) method was used to capture the air/water interface. To validate the present numerical method, two-dimensional dam-breaking and sloshing problems in a rectangular tank were solved by the developed method in a stationary Cartesian grid system. In the case of sloshing problems, simulations by using a improved MPS(Moving Particle Simulation) method, which is named as PNU-MPS(Pusan National University-MPS), were also carried out. The computational results are compared with those of experiments and most of the comparisons are reasonably good.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.9
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• pp.891-897
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• 2008

GPS can provide precise relative navigation information. But it needs a reference station in a close range and is effected by satellite observation environment. In this paper, we propose INS and Vision sensor integrated system with a known landmark geometry. This system is supposed to overcome problems of GPS only system. Using the proposed method, a relative navigation is available without a GPS reference station. The only need for the proposed system is a landmark image which is drawn on the ground. We conduct simple simulation to check the performance of this method. As a result, we confirm that it can improve the relative navigation information.

• Journal of Astronomy and Space Sciences
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• v.17 no.1
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• pp.107-116
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• 2000

This paper presents the preliminary survey and simulation results of the prediction of Leonid stream's orbital motion. Based on the model survey on eject velocity and perturbation of meteoroid particles, a simulation program was developed and applied to orbital motion of Leonid stream. The Jones ejection distribution model was used to describe the particle's eject velocity and the orbital dynamic model includes perturbations of major planet's gravity. DE405 ephemeris file generated by Solar System Dynamics Group at Jet Propulsion Laboratory in NASA was used for the planet's ephemeris calculations. Solar radiation pressure were also considered in the simulation and 8th order Runge-Kutta algorithm was used a numerical integration method.

• Journal of Korean Society for Atmospheric Environment
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• v.34 no.5
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• pp.697-707
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• 2018

A fast running model comprising the climate change effects is proposed for urban heat environment simulations so as to be used in urban heat island studies and/or the urban planning practices. By combining Hot City Model, a high resolution urban temperature prediction model utilizing the Lagrangian particle tracing technique, and the numerical weather simulation data which are constructed up to year of 2100 under the climate change scenarios, an efficient model is constructed for simulating the future urban heat environments. It is applicable to whole city as well as to a small block area of an urban region, with the computation time being relatively short, requiring the practically manageable amount of the computational resources. The heat environments of the entire metropolitan Seoul area in South Korea are investigated with the aid of the model for the present time and for the future. The results showed that the urban temperature gradually increase up to a significant level in the future. The possible effects of green roofs on the buildings are also studied, and we observe that green roofs don't lower the urban temperature efficiently while making the temperature fields become more homogeneous.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.1
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• pp.123-130
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• 1999

The objective of the current study is to understand steady 3-dimensional flow phenomena in a bifurcated duct experimentally. A bifurcation model is fabricated with transparent acrylic resin to visualize the whole flow field with the PIV system. The gray level cross-correlation method is applied to the image processing algorithm. The subpixel and the area interpolation methods are used to obtain the final velocity vectors. The finite volume predictions are used to analyze the flow patterns in the bifurcation model. The results of the computer simulation and the PIV experiment for three-dimensional flow show the recirculation zone and the formation of the paired secondary flow distal to the apex of the bifurcation model. The results obtained with the two methods also show that the branch flow strongly strikes the inner wall due to the inertial effect and accompanied helical motion as it flows toward the outer wall.

• Journal of the Society of Naval Architects of Korea
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• v.45 no.1
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• pp.1-9
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• 2008

The free-surface motions interacting with structures are investigated numerically using the Moving Particle Semi-implicit (MPS) method proposed by Koshizuka et al. (1996) for solving incompressible flow. In the method, Lagrangian moving particles are used instead of Eulerian approach using grid system. Therefore the terms of time derivatives in Navier-Stokes equation can be directly calculated without any numerical diffusion or instabilities due to the fully Lagrangian treatment of fluid particles and topological failure never occur. The MPS method is applied to the numerical study on the fluid impact loads for wet-drop tests in a LNG tank, and the results are compared with experimental ones.

• Proceedings of the Korea Information Processing Society Conference
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• 2005.11a
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• pp.713-716
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• 2005

차세대 원자로로 부각되고 있는 고온가스냉각 원자로에서는 고온 안정성 및 핵분열생성물 차단 성능이 우수한 TRISO(Tri-Isotropic) 핵연료를 사용하고 있다. TRISO 핵연료 입자는 직경이 약 1mm인 구 형태로 입자의 중심에는 직경 $0.35^{\sim}0.6\;{\mu}m$의 핵연료 입자가 포함되며 입자 외곽을 코팅 층이 에워 싸고 있다. 이 코팅층은 완충(buffer) PyC 층, 내부 PyC 층, 외부 PyC 층으로 구성되어 있다. 각 코팅 층의 두께를 수십$^{\sim}$백 ${\mu}m$ 범위이며 사양으로 정해져 있어 핵연료 입자 제조 후 사양을 만족하는지를 검사해야 한다. 본 연구에서는 TRISO 핵연료 입자 정보를 컴퓨터로 생성하고 가상의 X-선 래디오그래피 방법을 이용하여 투시 영상을 구성한 후 Filtered Backprojection 기법을 이용하여 단면 영상을 재구성하고 이 단면 영상을 이용하여 코팅 층의 두께를 정밀하게 측정하기 위한 모의 실험을 수행하였다. 경계선이 불명확한 투시영상이 아닌 경계선이 명확한 재구성 단면 영상을 이용하여 코팅 층의 두께를 약 2.3% 이내의 오차율로 정밀하게 측정하였다.