• Earthquakes and Structures
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• v.24 no.4
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• pp.289-301
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• 2023

Developing a competent soil-bridge interaction model for the seismic analysis of piled foundation bridges is of utmost importance for investigating the seismic response and assessing fragility of these lifeline structures. To this end, ground motion histories are deemed necessary at various depths along the piles supporting the bridge. This may be effectively accomplished through time history analysis of a free-field standalone soil column extending from bedrock level to ground surface subjected to an input bedrock motion at its base. A one-dimensional site/ground response analysis (vide one-directional shear wave propagation through the soil column) is hence conducted in the present research accounting for the nonlinear hysteretic behavior of the soil stratum encompassing the bridge piled foundation. Two homogeneous soil profiles atop of bedrock have been considered for comparison purposes, namely, loose and dense sand. Analysis of the standalone soil column has been performed under a set of ten selected actual bedrock ground motions adopting a nonlinear time domain approach in an incremental dynamic analysis framework. Amplified retrieved PGA and maximum soil shear strains have been generally observed at various depths of the soil column when moving away from bedrock towards ground surface especially at large hazards associated with high (input) PGA values assigned at bedrock. This has been accompanied, however, by some attenuation of the amplified PGA values at shallower depths and at ground surface especially for the loose sand soil and particularly for cases with higher seismic hazards associated with large scaling factors of bedrock records.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.19 no.5
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• pp.418-428
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• 2007

In the calculation of wave propagation by Boussinesq equation model, it is very common to experience numerical noises generated from nonlinear interaction and breaking wave occurrence, and the numerical solution is rapidly diverged unless the noises are properly controlled. A comparative study was here undertaken for the characteristics of three different lowpass filters (FFT filter, Gaussian filter and Shapiro filter) which are all designed to be applied to the interim results of numerical calculation. The numerical results obtained with application of respective filter techniques were compared with the results of an existing hydraulic experiment for the aspects of noise suppression, conservation of main signal and altering time. The results show that the Shapiro filter can be best applied with optimal choices of its element number, pass number and filtering tune interval. The combination of the number of filter element off, pass number of 50 or less, and application interval of 100 to 200 time steps generally showed good performance in both accuracy and efficiency of the numerical calculation.

• Proceedings of the Korea Concrete Institute Conference
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• 2004.11a
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• pp.603-608
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• 2004

The paper analyzes a scheme of decontamination of radionuclides from concrete structures, in which rapid microwave heating is used to spall off a thin contaminated surface layer. The analysis is split in two parts: (1) The hygrothermal part of the problem, which consists in calculating the evolution of the temperature and pore pressure fields, and (2) the fracturing part, which consists in predicting the stresses, deformations and fracturing. The rate of the distributed source of heat due to microwaves in concrete is calculated on the basis of the standing wave normally incident to the concrete wall with averaging over both the time period and the wavelength because of the very short time period of microwaves compared to the period of temperature waves and the heterogeneity of concrete. The reinforcing bars parallel to the surface arc treated as a smeared steel layer. The microplane model M4 is used as the constitutive model for nonlinear deformation and distributed fracturing of concrete. The aim of this study is to determine the required microwave power and predict whether and when the contaminated surface layer of concrete spalls off. The effects of wall thickness, reinforcing bars, microwave frequencies and power are studied numerically. As a byproduct of this analysis, the mechanism of spalling of rapidly heated concrete is clarified.

• Earthquakes and Structures
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• v.13 no.6
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• pp.573-588
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• 2017

The earthquake input is required when the soil-structure interaction (SSI) analysis is performed by the direct finite element method. In this paper, the earthquake is considered as the obliquely incident plane body wave arising from the truncated linearly elastic layered half space. An earthquake input method is developed for the time-domain three-dimensional SSI analysis. It consists of a new site response analysis method for free field and the viscous-spring artificial boundary condition for scattered field. The proposed earthquake input method can be implemented in the process of building finite element model of commercial software. It can result in the highly accurate solution by using a relatively small SSI model. The initial condition is considered for the nonlinear SSI analysis. The Daikai subway station is analyzed as an example. The effectiveness of the proposed earthquake input method is verified. The effect of the obliquely incident earthquake is studied.

• Proceedings of the KSR Conference
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• 2007.11a
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• pp.1330-1336
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• 2007

The purpose of the study was to verify deduction of each coefficient necessary to analysis on micro-pressure waves and reliability of the analysis result. The tunnel running train model testing device used in the test was manufactured by scale of 1:60 and the study used a train model with ten cars long according to specifications of KTX model. The study applied tunnels with cross sections of $107.9m^3\;and\;95.1m^3$ and applied tunnel extensions with 1km, 0.75km and 0.5km. Also, the study tested train speed by changing it into 275, 300, 325 and 350km/h. The test device was a hydraulic launch system composed of a train model, a hydraulic launcher, a tunnel model and a brake. The study measured speed of a model trainby a speed sensor installed in the point of each 1.2m from the front of tunnel entrance and a pithead of tunnel exit and measured pressure change of internal tunnel continuously by installing pressure sensors in the entrance part of tunnel, in the middle part of tunnel and in the exit part of tunnel. As the result of the measurement, it was known that pressure slope of pressure wave happened in the entrance part of tunnel was increased by a nonlinear effect while spreading the tunnel or its pressure slope was reduced by diffusion. Also, the study compared and analyzed micro-pressure waves happened in the exit part of the tunnel by installing each kind of hoods in the entrance part of the tunnel to prevent reduction of micro-pressure waves.

• Journal of Korea Water Resources Association
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• v.33 no.3
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• pp.331-340
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• 2000

This study aims to develop a methodology of real time forecasting of mundation risk based on DAMBRK model and Kalman filter. The model is based on implicit, nonlinear finite difference approximatIons of the one-dimensional dynamic wave equations. The stochastic estimator uses on extended Kalman filter to provide optimal updating estimates. These are accomplished by combining the predictions of the determurustic model with real time observauons modified by the Kalman filter gain ractor. Inundation risks are also estimated by applying Monte Carlo simulation to consider the variability in cross section geometry and Manning's roughness coefficient. The model calibrated by applying to the floods ot South Han River on September, 1990 and August, 1995. The Kalman tilter model indicates that significant improvement compared to deteriministic analysis in flood routing predictions in the river. Overtopping risk of levee is also presented by comparing levee height with simulated flood level. level.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.1
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• pp.34-42
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• 2011

It's been reported that the global warming effect has invoked the ever increasing typhoon intensity and long-term sea level rise which jointly cause severe wave overtopping over breakwaters or shore dykes. A simple measure to cope with this undesirable change may be just to increase the crest height of the dykes and breakwaters. This is surely effective to prevent wave overtopping, but it also decreases the seaward visibility of coastal waterfront. In this paper, a dynamic deformable rubber membrane parapet which not only reduces wave overtopping in storm period but also secures seascapes in normal days is presented. Several optimal configurations of the parapet are proposed. Through numerical analyses using a nonlinear finite element model and hydraulic experiments, the air controlled expansion and contraction of the parapets, their behavior against wave overtopping and structural stability are investigated.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.23 no.4
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• pp.313-325
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• 2011

Finite element grid system using h-refinement on the Yellow Sea was constructed based on previous study (Suh, 1999b) from 14 K to 210 K and special attention was concentrated on refining the coastal zone. In grid generation, depth change between adjacent points and non-dimensional tidal wave length ratio were considered. As a result approximately a quarter of the total nodes are located nearby 5 m of shallow area. Accurate bathymetry data using 30's and ETOPO1 with open boundary conditions of 8 major tidal constituents extracted automatically from FES2004 have been applied. In tidal simulation a 3-dimensional nonlinear harmonic model was setup and tidal amplification due to changes in vertical turbulent and bottom friction were simulated. In this study not only 8 major tidal constituents but also nonlinear shallow tides $M_4,$, $MS_4$ and long period $M_f,$, $M_{sf}$ were reproduced. It is found that implication of spatial variation of friction coefficient plays a very important role in reproduction of astronomical and shallow tides which are computed by iterative computation of nonlinear terms. Also it should be considered differently with respect to tidal periods. To understand the distribution of tidal asymmetry, amplitude ratio of $M_4/M_2$ and phase differences $2g(M_2)-g(M_4)$ were calculated. Tidal distortion ratio marks up to 0.2 on the west coast showing shallow coastal characteristics and somewhat wide range of ebb-dominances in front of Mokpo area are reproduced.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.204-212
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• 2003

As the first step to investigate the nonlinear interactions between turbulence and marine structures inside a viscous NWT, a LES technique was applied to the turbulent channel flow for $Re_{T}=150$, in this paper. The employed models were 4 types, such as the Smagorinsky model, the Dynamic SGS model, the Structure Function model and the Generalized Normal Stress model. The simulated data in time-series for the LESs were averaged in both time and space and performed statistical analysis. And results of the LESs were compared with those of a DNS developed in the present study and two spectral methods by Yoon et al.(2003) & Kim et al.(1987). It seems to be quite difficult to evaluate their performances to the present problem, but is seen that the accuracy of LESs are still related to the number of grids(or fine grid size).

• Journal of Korea Water Resources Association
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• v.32 no.3
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• pp.237-246
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• 1999

A finite element model is studied to simulate unsteady free surface flow based on dynamic wave equation and collocation method. The collocation method is used in conjunction with Hermite polynomials, and resulting matrix equations are solved by skyline method. The model is verified by applying to hydraulic jump, nonlinear disturbance propagation and dam-break flow in a horizontal frictionless channel. The computed results are compared with those by Bubnov-Galerkin and Petrov-Galerkin methods. It is also applied to the North Han River to simulate the floodwave propagation. The computed results have good agreements with those of DWOPER model in terms of discharge hydrographs. The suggested model has proven to be one of the promising scheme for simulating the gradually and rapidly varied unsteady flow in open channels.