Do-Sam Kim

BREAKING LIMIT, BREAKING AND POST-BREAKING WAVE DEFORMATION DUE TO SUBMERGED STRUCTURES

A study of alternatives including a shoreline evolution numerical modelization has been carried out in order to both diagnose the erosion problem at the beaches located between Cambrils Harbour and Pixerota delta (Tarragona, Spain) and select nourishment alternatives.

Analytical Method of Partial Standing Wave-Induced Seabed Response in Finite Soil Thickness under Arbitrary Reflection

Most analytical solutions for wave-induced soil response have been mainly developed to investigate the influence of the progressive and standing waves on the seabed response in an infinite seabed. This paper presents a new analytical solution to the governing equations considering the wave-induced soil response for the partial standing wave fields with arbitrary reflectivity in a porous seabed of finite thickness, using the effective stress based on Biot`s theory (Biot, 1941) and elastic foundation coupled with linear wave theory. The newly developed solution for wave-seabed interaction in seabed of finite depth has wide applicability as an analytical solutions because it can be easily extended to the previous analytical solutions by varying water depth and reflection ratio. For more realistic wave field, the partial standing waves caused by the breakwaters with arbitrary reflectivity are considered. The analytical solutions was verified by comparing with the previous results for a seabed of infinite thickness under the two-dimensional progressive and standing wave fields derived by Yamamoto et al.(1978) and Tsai & Lee(1994). Based on the analytical solutions derived in this study, the influence of water depth and wave period on the characteristics of the seabed response for the progressive, standing and partial standing wave fields in a seabed of finite thickness were carefully examined. The analytical solution shows that the soil response (including pore pressure, shear stress, horizontal and vertical effective stresses) for a seabed of finite thickness is quite different in an infinite seabed. In particular, this study also found that the wave-induced seabed response under the partial wave conditions was reduced compared with the standing wave fields, and depends on the reflection coefficient.

Numerical Simulation on Seabed-Structure Dynamic Responses due to the Interaction between Waves, Seabed and Coastal Structure

Seabed beneath and near the coastal structures may undergo large excess pore water pressure composed of oscillatory and residual components in the case of long durations of high wave loading. This excess pore water pressure may reduce effective stress and, consequently, the seabed may liquefy. If the liquefaction occurs in the seabed, the structure may sink, overturn, and eventually fail. Especially, the seabed liquefaction behavior beneath a gravity-based structure under wave loading should be evaluated and considered for design purpose. In this study, to evaluate the liquefaction potential on the seabed, numerical analysis was conducted using 2-dimensional numerical wave tank. The 2-dimensional numerical wave tank was expanded to account for irregular wave fields, and to calculate the dynamic wave pressure and water particle velocity acting on the seabed and the surface boundary of the structure. The simulation results of the wave pressure and the shear stress induced by water particle velocity were used as inputs to a FLIP(Finite element analysis LIquefaction Program). Then, the FLIP evaluated the time and spatial variations in excess pore water pressure, effective stress and liquefaction potential in the seabed. Additionally, the deformation of the seabed and the displacement of the structure as a function of time were quantitatively evaluated. From the analysis, when the shear stress was considered, the liquefaction at the seabed in front of the structure was identified. Since the liquefied seabed particles have no resistance force, scour can possibly occur on the seabed. Therefore, the strength decrease of the seabed at the front of the structure due to high wave loading for the longer period of time such as a storm can increase the structural motion and consequently influence the stability of the structure.

Numerical Simulation of Irregular Airflow within Wave Power Converter Using OWC by Action of 3-Dimensional Irregular Waves

An Oscillating Water Column (OWC) wave generation system uses the air flow induced by the vertical motion of water column in the air chamber as a driving force of turbine. It is well known that OWC is one of the most efficient devices to harness wave power. This study estimated the air flow velocity from the time variation of the water level fluctuation in the air chamber under regular wave conditions using 3-dimensional numerical irregular wave tank (3D-NIT) model that can simulate the 3-dimensional irregular wave field. The applicability of the 3D-NIT model was validated by comparing numerically predicted air flow velocities with hydraulic experimental results. In addition, the characteristics of air flow frequency spectrum variation due to the incident frequency spectrum change, and the variations of frequency spectrum and wave reflection due to the existence of converter inside the air chamber were discussed. It is found that the phase difference exists in between the air flow velocity and the water level fluctuation inside the air chamber, and the peak frequency of the spectrum in water level fluctuation is amplified by the resonance in the air chamber.

Numerical Simulation of Dynamic Response of Seabed and Structure due to the Interaction among Seabed, Composite Breakwater and Irregular Waves (II)

Seabed beneath and near coastal structures may undergo large excess pore water pressure composed of oscillatory and residual components in the case of long durations of high wave loading. This excess pore water pressure may reduce effective stress and, consequently, the seabed may liquefy. If liquefaction occurs in the seabed, the structure may sink, overturn, and eventually increase the failure potential. In this study, to evaluate the liquefaction potential on the seabed, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank to account for an irregular wave field. In the condition of an irregular wave field, the dynamic wave pressure and water flow velocity acting on the seabed and the surface boundary of the composite breakwater structure were estimated. Simulation results were used as input data in a finite element computer program for elastoplastic seabed response. Simulations evaluated the time and spatial variations in excess pore water pressure, effective stress, and liquefaction potential in the seabed. Additionally, the deformation of the seabed and the displacement of the structure as a function of time were quantitatively evaluated. From the results of the analysis, the liquefaction potential at the seabed in front and rear of the composite breakwater was identified. Since the liquefied seabed particles have no resistance to force, scour potential could increase on the seabed. In addition, the strength decrease of the seabed due to the liquefaction can increase the structural motion and significantly influence the stability of the composite breakwater. Due to limitations of allowable paper length, the studied results were *관동대학교 에너지자원플랜트공학과 조교수(Dept. of Energy Resources and Plant Eng., Kwandong Univ., Gangwon 210-701, Korea, Tel:+82-33-649-7598, Fax:+82-33-647-3436, klee@kd.ac.kr) **한국해양대학교 대학원 토목환경공학과 박사과정(Dept. of Civil Eng., Korea Maritime and Ocean Univ., 727 Taejong-ro, Yeongdo-ku, Busan 606-791, Korea, Tel:+82-51-410-4941, Fax:+82-51-403-0656, assassin10@naver.com) ***한국해양대학교 건설공학과 교수(Corresponding author; Dept. of Civil Eng., Korea Maritime and Ocean Univ., 727 Taejong-ro, Yeongdoku, Busan 606-791, Korea, Tel:+82-51-410-4463, Fax:+82-51-403-0656, kimds@kmou.ac.kr) ****한국해양대학교 건설공학과 교수(Dept. of Civil Eng., Korea Maritime and Ocean Univ., 727 Taejong-ro, Yeongdo-ku, Busan 606-791, Korea, Tel:+82-51-410-4465, Fax:+82-51-410-4460, kth67399@kmou.ac.kr) *****경상대학교 해양토목공학과 교수(Dept. of Ocean Civil Eng., Gyeongsang Univ., 38 Cheondaegookchigil, Gyeongnam, Korea, Tel:+82-55772-9126, Fax:+82-55-772-9120, bks7265@hanmail.net) 불규칙파-해저지반-혼성방파제의 상호작용에 의한 지반과 구조물의 동적응답에 관한 수치시뮬레이션 (I) 161 divided into two portions; (I) focusing on the dynamic response of structure, acceleration, deformation of seabed, and (II) focusing on the time variation in excess pore water pressure, liquefaction, effective stress path in the seabed. This paper corresponds to (I).

Effects on the Jeju Island of Tsunamis Caused by Triple Interlocked Tokai, Tonankai, Nankai Earthquakes in Pacific Coast of Japan

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.

A Study on the Control of Short-period Waves by Resonator

In this study, the control performance of resonator was reviewed through numerical analysis and 3-dimensional hydraulic model experiments by attaching the resonator suggested in the existing studies to the openings of rectangular harbor and breakwater placed in a straight line to reduce short-period waves. In the numerical analysis, linear analysis method of singularity distribution method based on vertical-line Green function and full non-linear analysis method by 3D-NIT model were applied, and the validity of the numerical analysis methods was verified through comparative analysis between results of hydraulic experiments and numerical analysis results. In addition, effectiveness of the resonator was confirmed by reviewing its control performance on the short-period waves through review on the comparison with the case in which the resonator is not attached.

Regular Waves-induced Seabed Dynamic Responses around Submerged Breakwater

In case of the seabed around and under gravity structures such as submerged breakwater is exposed to a large wave action long period, the excess pore pressure will be generated significantly due to pore volume change associated with rearrangement soil grains. This effect will lead a seabed liquefaction around and under structures as a result from decrease in the effective stress. Under the seabed liquefaction occurred and developed, the possibility of structure failure will be increased eventually. In this study, to evaluate the liquefaction potential on the seabed quantitatively, numerical analysis was conducted using the expanded 2-dimensional numerical wave tank model and the finite element elasto-plastic model. Under the condition of the regular wave field, the time and spatial series of the deformation of submerged breakwater, the pore water pressure (oscillatory and residual components) and pore water pressure ratio in the seabed were estimated.

A study on the optimal shape of wave energy conversion system using an oscillating water column

ABSTRACT Shin, S., Lee, K.-H., Kim, D.-S., Kim, K.-H., and Hong, K., 2013. A study on the optimal shape of wave energy conversion system using an oscillating water column With the intention of diversifying energy sources, the use of natural and renewable energy sources such as sunlight, wind, tides, geothermal heats and waves is attracting favorable attention. Furthermore, current environmental issues, including global warming, ozone depletion and nuclear problems, promote development of renewable energy technologies. Many renewable energy technologies are however still under progress. Among these, the wave energy conversion system using an oscillating water column (OWC) is nearing commercial stage. OWC use the air flow induced by the vertical motion of water column in the air chamber as a driving force of turbine. Although it is well known that OWC is one of the most efficient devices to harness wave power, there is still much uncertainty about the relationship between the optimal shape and its hydrodynamic performance under the confined wave conditions. In this study, we propose a new computational fluid dynamics solver using on the immiscible two-phase (gas and water) flow model to simulate an OWC system in a two and three dimensional numerical wave tank. The numerical experiments focus on air flow velocity directly related to the working of turbine to survey the optimal shape. In order to validate the developed numerical model, laboratory experiments for the simplified OWC are carried out in a wave tank under regular wave conditions. The comparisons between the results of the developed numerical model and experimental data reveal a favorable agreement between the air flow velocity as well as the water surface profiles. Based on the validated numerical model, the effects of the inlet and chamber shapes including length, height, width and slope on the maximum air flow velocity are numerically investigated. As a result, in case the non-dimensional chamber width normalized by the incident wave length is in the range of 0.12 to 0.43, the maximum air flow velocity occurs with the increase of the inlet height and shortness of the inlet length.

Extreme Case Study of Quay Wall Stability under Earthquake and Tsunami

This study was conducted to determine the stability of a quay wall under the combined action of an earthquake and tsunami. Adopting the limit equilibrium method, the stability of the quay wall was assessed for both the sliding and overturning modes under passive and active conditions. The variation in the stability of the quay wall was determined by parametric studies, including those for the tsunami wave height, seismic acceleration coefficient, internal friction angle of soil, wall friction angle, and pore water pressure ratio. The stability of the wall was also compared with the case of no earthquake and tsunami forces. When the earthquake and tsunami were considered simultaneously, the stability of the wall under the passive condition decreased significantly. The critical mode of the quay wall under the earthquake and tsunami forces was found to be that of the overturning mode. In the active condition, the safety factors for sliding and overturning increased, because the tsunami acted as a resisting force. However, it should be noted that, if a tsunami wave spills over the quay wall and then flows backward to the wall active condition, the tsunami no longer acts as a resisting force.