• Journal of Korean Society of Coastal and Ocean Engineers
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• v.14 no.1
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• pp.1-7
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• 2002

In the past, safety assessment on the site of Ulchin Nuclear Power Plants against tsunamis was carried out with probable maximum earthquake magnitude and related tsunamigenic fault parameters. Recently, however, based on the seismic gap theory, some seismologists warned about earthquakes of larger magnitudes than had been expected. In this study, we revaluated tsunami risk with a finite difference model based on linear and nonlinear shallow water equations. Firstly, we simulated the\`83 tsunami and compared the calculated water surface profile with the observed wave heights. Secondly, we evaluated the rise and drop of sea water level at the site of Ulchin Nuclear Power Plant with fault parameters of the past '83, '93 tsunamis and some dangerous faults. Finally, we showed that the cooling water intake facility of Ulchin Nuclear Power Plants would be safely operated in disastrous tsunamis.

• Journal of Ocean Engineering and Technology
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• v.29 no.3
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• pp.217-223
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• 2015

In order to predict the motions of a planing hull in waves, it is necessary to accurately estimate the force components acting on the hull such as the hydrodynamic force, buoyancy, and friction, as well as the wave exciting force. In particular, based on strip theory, hydrodynamic forces can be estimated by the summation of the forces acting on each cross-section of the hull. A non-linear strip method for planing hulls was mathematically developed by Zarnick, and his formula has been used to predict the vertical motions of prismatic planing hulls in regular waves. In this study, several improvements were added to Zarnick's formula to predict the vertical motions of warped planing hulls. Based on calm water model test results, the buoyancy force and moment correction coefficients were modified. Further improvements were made in the pile-up correction. Pile-up correction factors were changed according to variations of the deadrise angles using the results found in previous research. Using the same hull form, captive model tests were carried out in other recent research, and the results were compared with the present calculation results. The comparison showed reasonably good agreements between the model tests and present calculations.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.18 no.4
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• pp.269-282
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• 2006

We numerically studied tsunami propagation characteristics through Korean Straits based on nonlinear shallow water equation, a robust wave driver of the near field tsunamis. Tsunamis are presumed to be generated by the earthquake in Tsuhima-Koto fault line. The magnitude of earthquake is chosen to be 7.5 on Richter scale, which corresponds to most plausible one around Korean peninsula. It turns out that it takes only 60 minutes for leading waves to cross Korean straits, which supports recently raised concerns at warning system might be malfunctioned due to the lack of evacuation time. We also numerically obtained the probability of tsunami inundation of various levels, usually referred as tsunami hazard, along southern coastal area of Korean Peninsula based on simple seismological and Kajiura (1963)'s hydrodynamic model due to tsunami-generative earthquake in Tsuhima-Koto fault line. Using observed data at Akita and Fukaura during Okushiri tsunami in 1993, we verified probabilistic model of tsunami height proposed in this study. We believe this inundation probability of various levels to give valuable information for the amendment of current building code of coastal disaster prevention system to tame tsunami attack.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.1
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• pp.28-39
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• 2019

In the design process of counter measures against the beach erosion, information like the main sediment transport mode and yearly net amount of longshore and cross shore transport is of great engineering value. In this rationale, we numerically analyzed the yearly sediment budget of the Mang-Bang beach which is suffering from erosion problem. For the case of cross sediment transport, Bailard's model (1981) having its roots on the Bagnold's energy model (1963) is utilized. In doing so, longshore sediment transport rate is estimated based on the assumption that longshore transport rate is determined by the available wave energy influx toward the beach. Velocity moments required for the application of Bailard's model (1981) is deduced from numerical simulation of the nonlinear shoaling process over the Mang-Bang beach of the 71 wave conditions carefully chosen from the wave records. As a wave driver, we used the consistent frequency Boussinesq Eq. by Frelich and Guza (1984). Numerical results show that contrary to the Bailard's study (1981), Irribaren NO. has non negligible influence on the velocity moments. We also proceeds to numerically simulate the yearly sediment budget of Mang-Bang beach. Numerical results show that for ${\beta}=41.6^{\circ}$, the mean orientation of Mang-Bang beach, north-westwardly moving longshore sediment is prevailing over the south-eastwardly moving sediment, the yearly amount of which is simulated to reach its maxima at $125,000m^3/m$. And the null pint where north-westwardly moving longshore sediment is balanced by the south-eastwardly moving longshore sediment is located at ${\beta}=47^{\circ}$. For the case of cross shore sediment, the sediment is gradually moving toward the shore from the April to mid October, whereas these trends are reversed by sporadically occurring energetic wind waves at the end of October and March. We also complete the littoral drift rose of the Mang-Bang beach, which shows that even though the shore line is temporarily retreated, and as a result, the orientation of Mang-Bang beach is larger than the orientation of null pont, south-eastwardly moving longshore sediment is prevailing. In a case that the orientation of Mang-Bang beach is smaller than the orientation of null pont, north-westwardly moving longshore sediment is prevailing. And these trend imply that the Mang-Bang beach is stable one, which has the self restoring capability once exposed to erosion.

• Journal of the Earthquake Engineering Society of Korea
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• v.11 no.1 s.53
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• pp.67-77
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• 2007

Site coefficients in IBC and KBC codes have some limits to predict the rational seismic responses of a structure, because they take into account only the effect of the soil amplification without the effects of the structure-soil interaction. In this study, upper and lower limits of the site coefficients are estimated through the pseudo 3-D elastic seismic response analyses of structures built on the linear or nonlinear soil layers taking Into account the effects of the structure-soil interaction. Soil characteristics of site classes of A, B and C were assumed to be linear, and those of site classes of D and E were done to be nonlinear and the Ramberg-Osgood model was used to evaluate shear modulus and damping ratio of a soil layer depending on the shear wave velocity of the soil layer, Seismic analyses were performed with 12 weak or moderate earthquake records scaled the peak acceleration to 0.1g or 0.2g and deconvoluted as earthquake records at the bedrock located at 30m deep under the outcrop. With the study results of the elastic seismic response analyses of structures, new standard response spectrum and upper and lower limits of the site coefficients of $F_{a}\;and\;F_{v}$ at the short period range and the period of 1 second are suggested including the effects of the structure-soil interaction, and new site coefficients for the KBC code are also suggested.

• Korean Journal of Fisheries and Aquatic Sciences
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• v.34 no.6
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• pp.661-665
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• 2001

This paper deals with optimal mooring system to secure fish cage in a desired location, Through field investigation and paper works, we surveyed disasters by breakdown of cage frame and mooring system due to higher wave attack and selected compliant buoy mooring method for shallow water mooring system against severe coastal external forces. To analyze interaction between external forces and compliant buoy mooring system, theoretical model has developed as quasi-static nonlinear analysis. After verifying the feasibility of the numerical model compared with experiment, static analysis has tried for various mooring systems with different angle of array, number of mooring points, length of horizontal and inclined rope. Optimal mooring method using compliant buoy has selected for fish cage through numerical simulation. This results can apply for preliminary design for cage mooring system.

• Smart Structures and Systems
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• v.4 no.6
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• pp.727-740
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• 2008

A down hole vertical seismic array is a sequence of instruments installed at various depths in the earth to record the ground motion at multiple points during an earthquake. Numerous studies demonstrate the unique utility of vertical seismic arrays for studying in situ site response and soil behavior. Examples are given of analyses made at two sites to show the value of data from vertical seismic arrays. The sites examined are the Lotung, Taiwan SMART1 array and a new site installed at Jingliao, Taiwan. Details of the installation of the Jingliao array are given. ARX models are theoretically the correct process models for vertical wave propagation in the layered earth, and are used to linearly map deeper sensor input signals to shallower sensor output signals. An example of Event 16 at the Lotung array is given. This same data, when examined in detail with a Bayesian inference model, can also be explained by nonlinear filters yielding commonly accepted soil degradation curves. Results from applying an ARMAX model to data from the Jingliao vertical seismic array are presented. Estimates of inter-transducer soil increment resonant frequency, shear modulus, and damping ratio are presented. The shear modulus varied from 50 to 150 MPa, and damping ratio between 8% and 15%. A new hardware monitoring system - TerraScope - is an affordable 4-D down-hole seismic monitoring system based on independent, microprocessor-controlled sensor Pods. The Pods are nominally 50 mm in diameter, and about 120 mm long. An internal 16-bit micro-controller oversees all aspects of instrumentation, eight programmable gain amplifiers, and local signal storage.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.8 no.4
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• pp.23-32
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• 1988

The rates of infiltration contributed to the flow fo water in an unconfined aquifer under the partially penetrated stream at an ungaged station and the corresponding base flow in channel are coupled by using the hydraulic and/or hydrologic characteristics obtained from the geomorphologic and soil maps. For the determination of groundwater flow, the linearized model which is originally Boussinesq's nonlinear equation is applied in this study. Also, a stream flow routing model for base flow in channel is based on a simplification of the Saint-venant. The distributed runoff model with piecewise spatial uniformity is presented for obtaining its solution based on a finite difference technique of the kinematic wave equations. The method developed in this study was tested to the Bocheong watershed(area : $475.5km^2$) of the natural stream basin which is one of tributaries in Geum River basin in Korea. As a result, it is suggested that the rationality of hydro-graph separation according to a wide variability in hydrogeologic properties be worked out as developing the physically based subsurface model. The results of the present model are shown to be possible to simulate a base flow due to an arbitrary rate of infiltration for ungaged basins.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.31 no.5
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• pp.320-333
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• 2019

In this study, a physics-based 3D morphology model for the estimation of an erosion rate of nourished beach is newly proposed. As a hydrodynamic module, IHFOAM toolbox having its roots on the OpenFoam is used. On the other hand, the morphology model comprised a transport equation for suspended sediment, and Exner type equation derived from the viewpoint of sediment budget with the bed load being taken to accounted. In doing so, the incipient motion of sediment is determined based on the Shields Diagram, while the bottom suspended sediment concentration, the bed load transport rate is figured out using the bottom shearing stress directly calculated from the numerically simulated flow field rather than the conventional quadratic law and frictional coefficient. In order to verify the proposed morphology model, we numerically simulate the nonlinear shoaling, breaking over the uniform beach of 1/m slope, and its ensuing morphology change. Numerical results show that the partially skewed, and asymmetric bottom shearing stresses can be successfully simulated. It was shown that sediments suspended and eroded at the foreshore by wave breaking are gradually drifted toward a shore and accumulated in the process of up-rush, which eventually leads to the formation of swash bar. It is also worth mentioning that the breaker bar formed by the sediments dragged by the back-wash flow which commences at the pinnacle of up-rush as the back-wash flow gets weakened due to the increased depth was successfully duplicated in the numerical simulation.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.24 no.4
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• pp.295-304
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• 2012

This study proposed a two-dimensional horizontal numerical model based on the nonlinear shallow water wave equations to simulate tsunami propagation and coastal inundation. We numerically investigated the possible impacts of tsunami caused by the triple interlocked Tokai, Tonankai and Nankai Earthquakes on the Jeju coastal areas, using the proposed model. The simultaneous Tokai, Tonankai and Nankai Earthquakes were created a virtual tsunami model of an M9.0 earthquake. In numerical analysis, a grid nesting method for the local grid refinement in shallow coastal regions was employed to sufficiently reproduce the shoaling effects. The numerical model was carefully validated through comparisons with the data collected during the tsunami events by 2011 East Japan Earthquake and 1983 central East Sea Earthquake (Nihonkai Chubu Earthquake). Tsunami propagation triggered by the combined Tokai, Tonanakai and Nankai, Earthquakes was simulated for 10 hours to sufficiently consider the effects of tsunami in the coastal areas of Jeju Island. The numerical results revealed that water level fluctuation in tsunami propagation is greatly influenced by water-depth change, refraction, diffraction and reflection. In addition, the maximum tsunami height numerically estimated in the coastal areas of Jeju Island was about 1.6 m at Sagye port.