• Journal of Ocean Engineering and Technology
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• v.32 no.3
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• pp.166-176
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• 2018

This paper presents a numerical sensitivity analysis for the simulation of the motion performance of an offshore structure in waves using computational fluid dynamics (CFD). Starting with 2D wave simulations with varying numerical parameters such as grid spacing and CFL value, proper numerical conditions were found for accurate wave propagation that avoids numerical diffusion problems. These results were mapped on 2D error distributions of wave amplitude and wave length against the numbers of grids per wave length and per wave height under a given CFL condition. Finally, the 2D numerical sensitivity result was validated through CFD simulation of the motion of a FPSO in waves showing good accuracy in motion RAOs compared with existing potential flow solutions.

• Journal of the Korean Geotechnical Society
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• v.18 no.2
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• pp.39-49
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• 2002

This paper describes a numerical method for pile foundation subjected to earthquake loading using dynamic Winkler foundation model. To verify the numerical method, shaking table tests were carried out. In shaking table tests, accelerations and pile bending moments were measured for single pile and pile groups with a spacing-to-diameter ratio of 2.5 under fixed input base acceleration. In numerical analysis, the input base and free field accelerations measured from shaking table tests were used as input base motions. Based on the results obtained, free field acceleration was magnified relative to input base acceleration, whereas pile head accelerations reduced relatively to free field acceleration for soil-pile interaction. Measured and predicted bending moments for both cases have maximum value within the distance 10cm(4d) from the pile top. However, there are some differences between the results of numerical analysis and shake table test below 10cm(4d) from the pile top.

• Proceedings of the Earthquake Engineering Society of Korea Conference
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• 2001.09a
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• pp.83-90
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• 2001

The site effects of local geological conditions on seismic ground motion are performed using 2D numerical method. For the analysis, a numerical method far ground response analysis using FE-BE coupling method is developed. The total system is divided into two parts so called far field and near field. The far field is modeled by boundary element formulation using the multi-layered dynamic fundamental solution that satisfied radiational condition of wave. And this is coupled with near field modeled by finite elements. In order to verify the seismic response analysis, the results are compared with those of commercial code. As a result, it is shown that the developed method can be an efficient numerical method to solve the seismic response analysis of the site effect in 2D problem.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2004.03a
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• pp.825-830
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• 2004

A numerical analysis based on two-dimensional and three-dimensional incompressible Navier-Stokes equations has been carried out for double-circular-arc (DCA) compressor cascades. Two types of double-circular-arc cascades were used in this analysis. The appropriate turbulence model for compressor analysis was selected among the conventional turbulence models such as Baldwin-Lomax, k-$\varepsilon$ and k-$\varepsilon$ models. The results of current study were compared with available experimental data at various incidence angles. The 2-D and 3-D computational codes based on SIMPLE/PWIM algorithm for collocated grid and hybrid scheme for the convective terms were the main features of numerical tools. As commonly known, turbulence modeling is very important for the prediction of cascade flows, which are extremely complex with separation and reattachment by adverse pressure gradient. For selection of turbulence model, 2-D analysis was performed. And then, k-$\varepsilon$ turbulence model with wall function chosen as the reasonable turbulence model for 3-D calculation was used to increase the efficiency of computation times. A reasonable result of 3-D flow pattern passing through the double-circular-arc cascade was obtained.

• Journal of Wetlands Research
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• v.15 no.1
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• pp.91-103
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• 2013

In this Research, in order to improve problems of not enough technical validation and structural and hydraulic stability evaluation when nature-friendly revetment block is applied to field, hydraulic stability evaluation according to hydraulic behavior change of porosity soil block for vegetation reinforcement that secures ecological function was reviewed. By selecting object section, numerical analysis and hydraulic model experiments were performed; for numerical analysis, by using 1-dimensional numerical analysis model HEC-RAS and 2-dimensional numerical analysis RMA-2, one-dimensional(1D) and two-dimensional(2D) numerical analysis were performed; by applying Froude's similarity law, reduced-scale hydraulic model experiments according to vegetation existence were performed. In hydraulic model experiment, for validity of experiment result, the result of velocity and tractive force of reduced-scale hydraulic model experiments was converted to prototype so that it can be compared and reviewed under the same condition of one-dimensional(1D) and two-dimensional(2D) numerical analysis result; as a result, it was confirmed that comparatively united result appeared, and by comparing prototype-converted tractive force result with revetment's allowable tractive force coming from an existing research, block's hydraulic stability was suggested.

• Tunnel and Underground Space
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• v.14 no.1
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• pp.54-68
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• 2004

In this study, scaled model tests were performed on blasting demolition of reinforced concrete structures and the experimental results were analyzed in comparison with the results of numerical analysis. The tests were designed to induce a progressive collapse, and physical properties of the scaled model were determined using scale factors obtained ken dimension analysis. The scaled model structure was made of a mixture of plaster, sand and water at the ratio determined to yield the best scaled-down strength. Lead wire was used as a substitute for reinforcing bars. The scaled length was at the ratio of 1/10. Selecting the material and scaled factors was aimed at obtaining appropriately scaled-down strength. PFC2D (Particle Flow Code 2-Dimension) employing DEM (Distinct Element Method) was used for the numerical analysis. Blasting demolition of scaled 3-D plain concrete laymen structure was filmed and compared to results of numerical simulation. Despite the limits of 2-D simulation the resulting demolition behaviors were similar to each other. Based on the above experimental results in combination with bending test results of RC beam, numerical analysis was carried out to determine the blasting sequence and delay times. Scaled model test of RC structure resulted in remarkably similar collapse with the numerical results up to 900㎳ (mili-second).

• Proceedings of the Korean Geotechical Society Conference
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• 2003.03a
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• pp.385-392
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• 2003

Traditional forms of river and coastal structures have become very expensive to build and maintain, because of the shortage of natural rock. Geotextile tubes hydraulically or mechanically filled with dredged materials have been applied in hydraulic and coastal engineering in recent years(shore protection structure, detached breakwater, groins and jetty). Recently, new preliminary design criteria supported by model and prototype tests, and some stability analysis calculations have been studied. In this study, the numerical analysis was performed to investigate the behavior of geotextile tube with various properties of geotextile and hydraulic pumping conditions. Numerical analysis was executed to compare with the results from the large-scale field model tests, and also compared the results of 2-D plane strain analysis and 3-D FEM analysis. A geotextile tube was modeled using the commercial finite element analysis program ABAQUS and the one-quarter of tube was modeled. Behavior of geotextile tube during the hydraulic pumping procedure was analyzed by comparing the large-scale field model test and numerical analysis. The shape variation and maximum tube height between the numerical analysis results and large-scale filed test results are turned out to be a good agreement.

• 한국전산유체공학회:학술대회논문집
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• 2003.10a
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• pp.36-37
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• 2003

Three-dimensional numerical analysis of the flow around rectangular cylinders with various side ratios, D/H, from 0.2 to 2.0 is carried out for Reynolds number of 1000 by using multi-directional finite difference method in multi-grid. The predicted results are well compared with the experimental data. It is found that fluid dynamics characteristics alternate between high pressure mode. and low pressure mode of the base pressure for rectangular cylinder of D/H=0.2-0.6.

• The Transactions of The Korean Institute of Electrical Engineers
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• v.59 no.6
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• pp.1114-1119
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• 2010

This paper is concerned with an numerical analysis of electromagnetic wave propagation from randomly rough surfaces as a desert, sea surface and so on. We propose discrete ray tracing method (DRTM) for analysis of characteristics of wave propagation along one dimensional (1D) and two dimensional (2D) random rough surfaces. The point of the present method is to discretize not only rough surface but also ray tracing. This technique helps saving computer memories and does simplifying ray searching algorithm resulting in saving computation time. Numerical calculations are carried out for 1D and 2D random rough surfaces and electric field distributions are shown to check the effectiveness of the proposed DRTM.

• Journal of the Korean Geotechnical Society
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• v.22 no.7
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• pp.5-12
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• 2006

In this study, 2D shallow tunnel model test using close range photogrammetric technique was conducted with aluminium rods simulating continuum granular material. Numerical analysis was also carried out in order to identify the behaviour of subsurface deformations caused by shallow tunnelling. Direction and magnitude of displacement vectors from the model test were identical to the result of numerical analysis based on the model data. In particular, it is shown that the vector direction was toward a point below the tunnel invert level. A narrow "chimney or tulip like" pattern of vertical displacement was confirmed by both the model test and numerical analysis. This behaviour is consistent with the field data. In addition to the qualitative comparison, the quantitative result of subsurface settlements according to 2D volume loss showed good agreement between the model test and numerical analysis. Therefore, close range photogrammetric technique applied in the model test may be used to validate the result from the continuum numerical analysis.