• Journal of Korean Society of Coastal and Ocean Engineers
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• v.15 no.3
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• pp.190-195
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• 2003

For many coastal problems, such as wave transformation, tidal circulation, sediment transports and diffusion phenomena, we resort to numerical techniques. The representative numerical techniques are the method of finite differences and finite elements. The approximate algebraic equations, referred to as finite difference equations(FDEs), are subsequently solved at discrete grid points within the domain of interests. Therefore, a set of grid points within the domain, as well as the boundaries of the domain, must be specified. The generation of grids for FDEs, with uniform spacing, is very simple compared to that of finite elements. However, within a very complex domain, there are few grid generation tools we can use conveniently. Unfortunately, most of the commercial grid generation programs are developed only for finite element method. In this paper, grid generation method using digitizer, with uniform rectangular spacing, are introduced in detail. Didger and Surfer programs by Golden Software are necessary to produce comparatively accurate and simple depth data.

• Journal of the Korean Geotechnical Society
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• v.20 no.8
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• pp.59-66
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• 2004

In this study, the behavior characteristics of vertical and batter piles were analyzed by the model tests and the numerical analyses. Model steel pipe piles with the inclination of 0$^{\circ}$, 10$^{\circ}$, 20$^{\circ}$ and 30$^{\circ}$ were driven into sands with the relative density of 79%. The static compression load tests and numerical analyses using PENTAGON 3D were performed. The bearing capacities of batter piles with inclination of 10$^{\circ}$, 20$^{\circ}$ and 30$^{\circ}$ were 111, 95, and 81% of those of vertical pile in model tests, and the results of numerical analyses were similar to those of model tests. The bearing capacities p.oposed by Petrasovits and Award (1968) were similar to those of model test in the inclination of 10$^{\circ}$, but overestimated in the inclination of 20$^{\circ}$ and 30$^{\circ}$. The skin frictions and end bearing loads were the maximum in the inclination of 10$^{\circ}$ and decreased with increasing the inclination angle.

• The Journal of Engineering Geology
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• v.25 no.4
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• pp.623-627
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• 2015

To compile a flood hazard map it is essential to identify the potential risk areas. A scenario-based numerical modeling approach is commonly used to build a flood hazard map in the case of a levee-break. The model parameters that capture peak discharge, including breach formation and progress, are important in the modeling method. In this study an earth-levee-break model is constructed under the assumption that the failure mechanism and hydraulic processes are identical for all levee-break river activities. Estimation of the hydrograph at the outlet as a function of time is highlighted. The constructed hydrograph can then serve as an upper boundary condition in running the flood routing model downstream, although flood routing is not considered in this study.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.2
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• pp.146-150
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• 1996

The waves are most important dynamical factors for the analyses of structural stability and topographical changes on coastal engineering field. However, wind-generated waves are very irregular in shape and transformed through refraction, diffraction and shoaling when they propagate into shallow water where bottom topography and water depth vary significantly. Recently, Vincent and Briggs (1989) reported hydraulic model experiments for the transformation of monochromatic and directionally-spread irregular waves passing over a submerged elliptical mound. They concluded that for the case of combined refraction-diffraction of waves by a shoal, the propagation characteristics of the irregular and equivalent regular wave conditions can be vastly different. On the irregular wave transformation have been made theoretical and numerical studies for several years. Although theoretical and laboratory studies on wave transformation have progressed considerably, field measurement and comparison of numerical results with related theories are still necessary for the prediction of the phenomena in reality. In this study, field measurement of both incident and transformed waves in Youngil Bay were made using various kinds of equipments, and numerical computations were made on the transformed frequency spectra of large waves propagating over the shoal using Chae and Jeong's (1992) elliptic model. It is shown that this model results agree very well with field data, and thus the applicability of the model is now validated.

• Tunnel and Underground Space
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• v.18 no.2
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• pp.107-117
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• 2008

In this study, the failure and deformation characteristics of steel fiber reinforced shotcrete (SFRS) which is a primary tunnel support was investigated to find out ground-support mutual behavior. To this end, a mock-up of a tunnel was made and experimented with the conditions of lateral earth pressure coefficient 0.5 and 1.0. During the tests, 11 hydraulic cylinders were used for loading. for better simulation of the lateral earth pressure effect, these cylinders were controlled separately by two groups; crown and side wall. Meanwhile, the deformation of shotcrete was measured by 11 LVDTs. Backfill material was also used fur better load transfer from hydraulic cylinders to shotcrete. For the validation of the mock-up test results, 3D numerical analysis is carried out. To do numerical analysis under the same condition as a mock-up test, the load history curve which was obtained during the test was tried to be simulated using an individual FISH routine in the numerical analysis.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.10 no.2
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• pp.25-30
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• 1992

Most algorithms in computer vision and digital photogrammetry assume that digital stereo pairs are registered in epipolar geometry. But, an aerial stereo pair is not likely to be in epiplar geometry since the attitude of the camera at the instant of exposure is different at every exposure station. In this paper, stereo digital imagery is obtained from aerial stereo pair by scanner. Then procesure to resample the digital imagery to epipolar geometry using exterior orientation elements after absolute orientation is described. As a result, a stereo imagery in epipolar geometry is produced from stereo digital imagery. Epipolar imagery in this paper is applied to the image matching method by digital image correlation technique. Then, a digital elevation model is produced from the result of image matching. The digital elevation model in this paper is compared to the other digital elevation model produced by analytical plotter. As a result, an economical method to generate digital elevation model is presented.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.2
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• pp.166-177
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• 2006

The accuracy impact of using high-order Boussinesq-type model as compared to the typical order model is examined in this paper. The multi-layer model developed by Lynett and Liu(2004a) is used for simulating of wave breaking over a shelf region. The nonlinearity of the waves tested, ${k_0}{A_0}$, ranges from 0.029 to 0.180. The overall agreement between the two-layer model and the hydraulic experiments are quite good. The one-layer model overshoals the wave near the breakpoint, while the two-layer model shoals at a rate more consistent with the experimental data.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.6 no.3
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• pp.216-225
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• 1994

By use of laboratory experiment data set for an elliptic shoal by Berkhoff et al. (1982), both accuracy and Performance tests of numerical results between PCGM (Preconditioned Conjugate Gradient Method) and PA(Parabolic Approximation) are compared. Although both results show good agreement with the experimental data the PA model gives better reproduction of the relatively high amplitudes in the section 4-5 downwave of the shoal, in comparison with the PCGM. The PA model has been proved to be a useful tool for predicting wave transformationsin large shallow water region, but it can be applied only to the case of negligible reflection. On the other hand, there is a need to improve the computational efficiency of the PCGM model which is a finite difference scheme directly derived from the mild slope equation and can handle reflection. By taking the results of th PA model as an input data of the PCGM, the CPU time can be reduced by about 40%.

• Journal of Korea Water Resources Association
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• v.48 no.4
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• pp.281-290
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• 2015

Numerical simulations of free surface flow over a broad-crested rectangular weir are conducted by using the volume of fraction (VOF) method and three different turbulence models, the k-${\varepsilon}$, RNG k-${\omega}$ and k-${\omega}$ SST models. The governing equations are solved by a second-order accurate finite volume method and the grid sensitivity study of solutions is carried out. The numerical results are evaluated by comparing the solutions with experimental and numerical results of Kirkgoz et al. (2008) and some non-dimensionalized experimental results obtained by Moss (1972) and Zachoval et al. (2012). The results show that the present numerical model can reasonably reproduce the experimental results, while three turbulent models yield different numerical predictions of two distinct zones of flow separation, the first zone is in front of the upstream edge of the weir and the second is created immediately behind the upstream edge of the weir where the flow is separated to form the separation bubble. The standard k-${\varepsilon}$ model appears to significantly underestimate the size of both separation zones and the k-${\omega}$ SST model slightly over-estimates the first separation zone in front of the weir. The RNG k-${\varepsilon}$ model predicts both separation zones in overall good agreement with the experimental measurement, while the k-${\omega}$ SST model yields the best numerical prediction of separation bubble at the upstream edge of the weir.

• Journal of the Korean Society of Surveying, Geodesy, Photogrammetry and Cartography
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• v.19 no.2
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• pp.147-154
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• 2001

The development of equipments which are for the collection and processing of digital images in digital photogrammetry is actively performed at the research about practical use. The close-range digital photogrammetry is widely using to determine accurate position, feature, and size of objects. The goal of this study is to judge the precise surveying possibility of a streamline object, like a vehicle, using digital close-range photogrammetry. The standard deviation of the calculated coordinates is respectively ${\sigma}_x$=0.434mm, ${\sigma}_y$=0.619mm, ${\sigma}_z$=0.387mm. The result values is enough to converge an accuracy required for the field of an automobile design. Therefor we suggest that the digital close-range photogrammetry could be use for the majority of industries.