Papers - CHO Yonghwan

Numerical investigation of solitary wave attenuation by a vertical plate-type flexible breakwater using an FVM-FEM coupled model. Part 1: Linear elastic isotropic material Reviewed International journal

  Vol. 285   2023.10

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Ocean Engineering  

DOI： 10.1016/j.oceaneng.2023.115368

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Development of Coupled Numerical Model between Floating Caisson and Anti-Oscillation Tanks

Shirai, K; Nakamura, T; Cho, YH; Mizutani, N; Kurahara, Y; Takeda, M

JOURNAL OF MARINE SCIENCE AND ENGINEERING   Vol. 11 ( 9 )   2023.9

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Publisher：Journal of Marine Science and Engineering  

Floating caissons can oscillate owing to ocean waves when towed to an installation site. To reduce these oscillations, free-surface anti-oscillation tanks mounted on floating caissons have been proposed. However, no coupled numerical model exists between the motion of the floating caisson and fluid flow in the tanks based on computational fluid dynamics (CFD). In this study, a coupled model is developed and compared to existing physical experiments for validation. In the coupled model, the vertical and rotational motion of the floating caisson are computed as a rigid body, and the motion of the free water in the tank is computed using a CFD model. Numerical results show the predictive capability of the coupled model in terms of the rotational motion (pitch) of the floating caisson within ±20% of experimental data, regardless of the absence or presence of water in the tank. The numerical results also show that the fluid flow with complex air–water interface motion in the tank can be analyzed in detail using the coupled model. This suggests that the coupled model developed in this study is a useful tool for quantitatively assessing the effectiveness of an anti-oscillation tank for reducing the pitch of a floating caisson.

DOI： 10.3390/jmse11091669

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Development of coupled numerical model between floating caisson and anti-oscillation tanks Reviewed International journal

  Vol. 11 ( 9 )   2023.8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Marine Science and Engineering  

Simplified BEM-based mathematical model for bottom-hinged oscillating wave surge converters under large-amplitude regular waves Reviewed International journal

  Vol. 272   2023.3

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Ocean Engineering  

DOI： 10.1016/j.oceaneng.2023.113893

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Investigation of the Spiral Wave Generation and Propagation on a Numerical Circular Wave Tank Model Reviewed International journal

Islam M.S., Nakamura T., Cho Y.H., Mizutani N.

Journal of Marine Science and Engineering   Vol. 11 ( 2 )   2023.2

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Marine Science and Engineering  

A two-phase incompressible flow model in three-dimensional cylindrical coordinates is applied for oblique wave generation in a numerical circular wave tank. The governing equations are discretized by a finite volume method, and a mass source function is added to reproduce oblique waves through a spiral wave generator positioned at the center of the tank. The volume of fluid method is implemented to track the free surfaces between the air and fluid, and the zonal embedded grid system is adopted to obtain a grid-independent solution in the cylindrical coordinates. A permeable, circumferentially sloping topography (1:7), similar to a natural beach profile, is set up for investigating wave propagation and other characteristics. The simulation and physical experimental results are compared, which show a good agreement in randomly selected water surface elevation profiles and wave heights under the same wave and sloping conditions. The spiral waves are reproduced and propagated in a phenomenon similar to that observed in the physical experiment. The results also show that the wave-breaking positions differ in different wave conditions and suggest a relationship with cross-shore and longshore velocity distribution in terms of incident wave heights and wave-breaking positions in different wave periods on the same sloping topography. Furthermore, this model can be used to investigate the mechanism of longshore current generation and the influences of beach slope on the generated wave propagation in a sloping topography.

DOI： 10.3390/jmse11020388

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EFFECTS OF REFLECTIVE WALL WIDTH ON THE MOTION OF A PENDULUM-TYPE WAVE POWER GENERATOR: AN EXPERIMENTAL STUDY

CHO Yonghwan, YAMAMOTO Kenta, NAKAMURA Tomoaki, MIZUTANI Norimi

Japanese Journal of JSCE   Vol. 79 ( 18 ) page： n/a   2023

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

<p> A three-dimensional experiment was conducted to examine the effective width for increasing the power generation efficiency of the pendulum-type wave power generator by the width of the reflection wall installed behind it. From the pendulum's equation of motion, the amount and efficiency of energy generated by the pendulum were calculated. As a result, it was revealed that the natural period of the pendulum in three-dimensional conditions was shorter than in two-dimensional conditions, indicating the need to calculate the natural period in three dimensions. When the reflecting wall is installed, the power generation efficiency is maximum at the position of the standing wave's node, and it is high for relatively short incident wave periods, the same as in the two-dimensional case. When the width of the reflecting wall decreased, the development of the standing wave in front of the reflecting wall weakened, and the influence at the node and antinode positions was small. If the position of the antinode of the standing wave is avoided, the power generation efficiency can be increased when the width of the reflecting wall is greater than 1.5 times the width of the pendulum.</p>

DOI： 10.2208/jscejj.23-18082

CiNii Research

THREE-DIMENSIONAL NUMERICAL ANALYSIS OF MOTION OF A TOWED FLOATING CAISSON UNDER REGULAR WAVES

NAKAMURA Tomoaki, MORI Kazuhiro, CHO Yong-Hwan, MIZUTANI Norimi, YAMANO Takashi

Japanese Journal of JSCE   Vol. 79 ( 18 ) page： n/a   2023

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

<p> A three-dimensional numerical analysis was conducted using a three-dimensional coupled fluidstructure-sediment-seabed interaction model (FS3M) to investigate the motion of a floating caisson towed along a straight line under regular waves. Numerical results showed that the heave and the pitch of the caisson tended to fluctuate with the same period as the apparent incident wave period observed from the caisson. Furthermore, the amplitude of the heave increased when the apparent wave period matched the natural period of the heave. The natural period of the pitch was affected by towlines; thus, the amplitude of the pitch increased when the apparent wave period matched the natural period of the pitch considering the towlines. The time-averaged value of the tension force acting on the towline increased with increasing the incident wave height and during heave and pitch resonances.</p>

DOI： 10.2208/jscejj.23-18011

CiNii Research

A STUDY ON APPLICATION OF SEDIMENT TRANSPORT MODEL XBEACH TO SURFACE PROFILE CHANGE IN GRAVEL BEACH

NAKAMURA Tomoaki, MAKI Ryota, CHO Yong-Hwan, MIZUTANI Norimi

Japanese Journal of JSCE   Vol. 79 ( 18 ) page： n/a   2023

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

<p> The sediment transport model XBeach was applied to existing hydraulic experiments on topographic change of a gravel beach to investigate the influence of parameters related to sediment transport and evaluate the predictive capability of the model through comparison with experimental results. Numerical results showed that the reflective type of beach profile change can be obtained by increasing a factor for landward bed-load sediment transport (uprushfac) greater than unity and decreasing a factor for seaward bed-load sediment transport (backwashfac) less than unity to take into account the effect of in/exfiltration across the beach surface. It was also found that the reflective type of beach profile change cannot be computed simply using the groundwater module. Furthermore, the accuracy of the spatio-temporal change of the beach profile can be improved by calibrating the static friction angle of the sediment (re-poseangle) in addition to the factors of bed-load sediment transport.</p>

DOI： 10.2208/jscejj.23-18058

CiNii Research

STUDY ON IMPROVING THE ACCURACY OF WAVE ESTIMATION USING WEATHER INFORMATION AND COASTAL IMAGES BY DEEP LEARNING

MIYASHITA Yurika, NAKAMURA Tomoaki, KIKU Masami, CHO Yonghwan, MIZUTANI Norimi

Japanese Journal of JSCE   Vol. 79 ( 18 ) page： n/a - n/a   2023

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> It is important to understand wave information in coastal management. In this study, a wave estimation model with high accuracy was constructed at the heavily eroding Shichiri-Mihama-Ida beach by applying deep learning to orthomosaic images and meteorological information. It is shown that the third-generation wave estimation model SWAN can estimate the waves at the NOWPHAS observation point off the coast of Mie-Owase, and that a CNN can be applied to both the SWAN estimation results and coastal images to obtain a good estimation of significant wave heights. The results also showed that applying the CNN to both the waves estimated by applying LSTM to the wind speed data and the coastal image improved the accuracy of the significant wave height and wave direction and gave the good estimation of the significant wave period compared to the results obtained by applying the CNN only to the coastal image.</p>

DOI： 10.2208/jscejj.23-18094

CiNii Research

EXPERIMENTAL ASSESSMENT ON EVALUATION OF IMPACT FORCE OF TSUNAMI-DRIFTING VESSEL ON SEAWALL BEHIND DUNE

CHO Yonghwan, KANEKO Ryotaro, NAKAMURA Tomoaki, MIZUTANI Norimi, SUGIMOTO Wataru

Japanese Journal of JSCE   Vol. 79 ( 18 ) page： n/a   2023

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

<p> This study examines the behavior of small vessels drifting in a tsunami and the impact force of the drifting vessels on a seawall built behind a sand dune by means of a 1/100-scale hydraulic experiment. As a result, it was determined that the likelihood of a ship colliding with the seawall increases when the non-dimensional initial location (distance from the shoreline) becomes less than 0.6. The bouncing water mass of a tsunami generated in front of the seawall tends to reduce the impact power of a ship on a seawall. When there is a structure in front of the seawall, the influence of the bouncing water mass on the impact force can be estimated by considering the ship's drifting speed and the time lag between the tsunami and the ship reaching the seawall.</p>

DOI： 10.2208/jscejj.23-18080

CiNii Research

EXPERIMENTAL STUDY ON EFFECT OF SUSPENDED SEDIMENT ON TSUNAMI INUNDATION, RUN-UP, PRESSURE, AND FORCE

NAKAMURA Tomoaki, YAGI Ryota, CHO Yong-Hwan, MIZUTANI Norimi

Japanese Journal of JSCE   Vol. 79 ( 18 ) page： n/a   2023

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

<p> The effect of suspended sediment on inundation, run-up, wave pressure, and wave force caused by a black tsunami was investigated using hydraulic experiments with clear water and turbid water containing kaolin as bottom sediment. From experimental results, it was found that tsunami inundation can be locally accelerated in kaolin mixed water. Furthermore, the maximum value of surge-front wave pressure was reduced on average by mixing the kaolin. However, large surge-front wave pressure could occur at high concentration due to the high variability. The maximum value of quasi-steady wave pressure increased proportionally to an increase in the apparent fluid density due to the kaolin.</p>

DOI： 10.2208/jscejj.23-18092

CiNii Research

Influence of Tsunami-Driven Shipping Containers' Layout on Their Motion Reviewed International journal

Hou, YD; Nakamura, T; Cho, YH; Mizutani, N; Tomita, T

JOURNAL OF MARINE SCIENCE AND ENGINEERING   Vol. 10 ( 12 )   2022.12

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Marine Science and Engineering  

This study investigated the interaction between containers under extreme hydrodynamic conditions modeled on tsunamis to assess whether the number and layout of containers affect their motion and to guide future studies on numerical simulations describing tsunami-debris motion. The three-dimensional Fluid–Structure–Sediment–Seabed Interaction Model (FS3M), which can compute tsunami–container interaction, was used as a numerical test model, and numerical results for the specific target of the simulation were compared with experimental data to check the validity and computational accuracy of the FS3M. The study showed that the number of rows (Nx), columns (Ny), and stacks (Nz) in the initial arrangement of containers constitute the main factor affecting the area where the containers spread and their drift motion velocity. An increase in Nx and Nz can effectively reduce the container drift velocity. Conversely, as Ny increases, the drift motion velocity of the center of gravity of the entire group increases. The results of this study can facilitate the development of more realistic building structure scenarios in future research that consider the proposed characteristic damage estimation and comprehensive assessment methods laid out herein.

DOI： 10.3390/jmse10121911

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Performance enhancement of a bottom-hinged oscillating wave surge converter via resonant adjustment Reviewed International journal

Liu, Y; Mizutani, N; Cho, YH; Nakamura, T

RENEWABLE ENERGY   Vol. 201   page： 624 - 635   2022.12

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Renewable Energy  

Based on the boundary element method, the frequency-domain dynamic equations of bottom-hinged oscillating wave surge converters under regular and irregular waves in shallow waters were derived. The nonlinear hydrostatic restoring moment and drag moment were linearized as time-independent stiffness and constant damping, respectively. A Python code was developed to efficiently solve the response without significantly sacrificing accuracy. The feasibility of performance enhancement via adjusting Power Take-Off (PTO) parameters was discussed. Under regular waves, the adjusting approaches are classified as no artificial resonance, ideal resonance, and near resonance. The adjustment towards resonance can boost the capturing power, although the flap-type absorber was recognized as a wave torque dominating device. A near-resonance situation, found by scanning the PTO parameters, is more effective to improve the hydrodynamic performance than the ideal resonance, where the amplification of the damping item is disadvantageous. An increasing hysteretic phase angle of velocity relative to wave torque with the increase of wave period represents the best status of wave energy harvesting. Under irregular waves, two adjusting approaches are presented: no artificial resonance and adjusting towards resonance. The performance at short peak periods can be improved by adjusting PTO stiffness, while, adjusting PTO inertia torque is almost ineffective.

DOI： 10.1016/j.renene.2022.10.130

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深層学習による海岸画像を用いた波浪推定に関する検討 Reviewed

宮下侑莉華，中村友昭，菊　雅美，趙　容桓，水谷法美

土木学会論文集Ｂ２（海岸工学）   Vol. 78 ( 2 ) page： 127 - 132   2022.11

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 土木学会  

橋台背面盛土と基礎地盤の侵食が橋桁への作用津波力とその評価式に与える影響 Reviewed

中村友昭，熊澤諒大，趙　容桓，水谷法美

土木学会論文集Ｂ２（海岸工学）   Vol. 78 ( 2 ) page： 223 - 228   2022.11

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 土木学会  

減揺タンク付浮遊ケーソンの動揺に与える波浪諸元の影響に関する実験的研究 Reviewed

中村友昭，竹山俊介，白井開斗，趙　容桓，水谷法美，倉原義之介，武田将英

土木学会論文集B3（海洋開発）   Vol. 78 ( 2 ) page： 253 - 258   2022.10

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 土木学会  

DOI： 10.2208/jscejoe.78.2_I_253

Experimental Investigation on the Mechanism of Longshore Sediment Transport Using a Circular Wave Basin Reviewed

Islam, MS; Akita, N; Nakamura, T; Cho, YH; Mizutani, N

JOURNAL OF MARINE SCIENCE AND ENGINEERING   Vol. 10 ( 9 )   2022.9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Marine Science and Engineering  

In this paper, a hydraulic model experiment was conducted to investigate the mechanism of longshore sediment transport on a sloping beach of 1:7 using a circular wave tank equipped with a spiral wave maker. The experimental results revealed that cross-shore sediment transport was predominant up to the formation of equilibrium cross-section. Then the longshore sediment transport was actively dominant near the bar after the development of equilibrium topography. The wave-breaking positions and the characteristics of sand displacement in the vicinity of the wave-breaking zone were observed throughout the installation of fluorescent sands in different cross-sections under several wave conditions on the same terrain to presume the coastal erosion. From the outcomes, it was confirmed that the gradient of the average water level due to the obliquely incident waves breaking and the differences in breaking positions along the shoreline accelerated the generation of longshore currents and longshore sediment transport in the sloping beach profile. Moreover, the actively longshore sediment transport tendency throughout the breaking waves and the longshore current had been confirmed in this study where the gradually increasing wave heights influenced the stronger degree of wave breaking on the sloping beach, which enhanced the sediment transport procedure to deform the beach profile.

DOI： 10.3390/jmse10091189

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Nonlinear hydrodynamic analysis and optimization of oscillating wave surge converters under irregular waves Reviewed International journal

Ocean Engineering   Vol. 250 ( 15 )   2022.4

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Ocean Engineering  

DOI： 10.1016/j.oceaneng.2022.110888

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Study on the Resonant Behaviors of a Bottom-Hinged Oscillating Wave Surge Converter Reviewed International journal

Liu Yao, Cho Yong-Hwan, Mizutani Norimi, Nakamura Tomoaki

JOURNAL OF MARINE SCIENCE AND ENGINEERING   Vol. 10 ( 1 )   2022.1

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Marine Science and Engineering  

DOI： 10.3390/jmse10010002

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INFLUENCE OF SEDIMENT TRANSPORT PARAMETERS ON LOCAL SCOURING AROUND PILES OF PILE-TYPE STRUCTURES AND ITS EVALUATION USING MACHINE LEARNING

NAKAMURA Tomoaki, NAITO Ryunosuke, CHO Yong-Hwan, MIZUTANI Norimi, YAMANO Takashi

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 78 ( 2 ) page： I_61 - I_66   2022

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> FS3M, a numerical model that can compute dynamic interaction between waves and topographic change, was applied to local scouring around piles to investigate the influence of three sediment transport parameters. Machine learning models, XGBoost and LightGBM, were trained using numerical results and the influence of the parameters was also evaluated from the machine learning. Results showed that the final scour depth increased with an increase in a coefficient of the pick-up function <i>C<b>p</b></i>, which had the largest contribution to the final scour depth. Furthermore, the height of the tangential flow velocity <i>z<b>vel</b></i> from the surface of the sediment substrate used to compute the friction velocity and the vertical cell height <i>Δz_surf</i> near the surface of the sediment substrate had the smaller contribution than <i>C<b>p</b></i>. Based on the results, a method for determining the parameter values was proposed.</p>

DOI： 10.2208/jscejoe.78.2_i_61

CiNii Research

Mechanism of tsunami-induced erosion of bridge-abutment backfill and its countermeasures Reviewed International journal

Nakamura Tomoaki, Sugiyama Chisato, Cho Yong-Hwan, Mizutani Norimi

WATER   Vol. 13 ( 24 )   2021.12

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Water (Switzerland)  

DOI： 10.3390/w13243529

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Other Link： https://www.mdpi.com/2073-4441/13/24/3529

Numerical Reproducibility of Wave Response for an Oscillating Wave Surge Converter Using Inverted Triangle Flap Reviewed International coauthorship International journal

Kim, T.-G, Kim, D.-S., Cho, Y.-H., Lee, K.-H.

Journal of Korean Society of Coastal and Ocean Engineers   Vol. 33 ( 5 ) page： 203 - 216   2021.10

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Language：Korean   Publishing type：Research paper (scientific journal)  

Analyzing various wave interactions with oscillating wave surge converters (OWSC) is essential because they must be operated efficiently under a wide range of wave conditions and designed to extract optimal wave energy. In the conceptual design and development stage of OWSC, numerical analysis can be a good alternative as a design tool. This study performed a numerical analysis on the behavioral characteristics of the inverted triangle flap against the incident waves using open source CFD to examine the essential behavioral attributes of OWSC. Specifically, the behavioral characteristics of the structure were studied by calculating the free water surface displacement and the flap rotation angle near the inverted triangular flap according to the change of the period under the regular wave conditions. By comparing and examining the numerical analysis results with the hydraulic model experiments, the validity of the analysis performed and the applicability in analyzing the wave-structure interactions related to OWSC was verified. The numerical analysis result confirmed that the hydrodynamic behavior characteristic due to the interactions of the wave and the inverted triangle flap was well reproduced.

DOI： 10.9765/KSCOE.2021.33.5.203

Motion of floating caisson with extended bottom slab under regular and irregular waves Reviewed International journal

Nakamura, T., Nagayama, N., Cho, Y.-H., Mizutani, N., Kurahara, Y., Takeda, M.

Journal of Marine Science and Engineering   Vol. 9 ( 10 ) page： 1129   2021.10

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Marine Science and Engineering  

DOI： 10.3390/jmse9101129

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Other Link： https://www.mdpi.com/2077-1312/9/10/1129

Simple Breaker Index Formula Using Linear Model Reviewed International coauthorship International journal

Lee Kwang-Ho, Cho Yong-Hwan

JOURNAL OF MARINE SCIENCE AND ENGINEERING   Vol. 9 ( 7 ) page： 731   2021.7

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Marine Science and Engineering  

Breaking waves generated by wave shoaling in coastal areas have a close relationship with various physical phenomena in coastal regions. Therefore, it is crucial to accurately predict breaker indexes such as breaking wave height and breaking depth when designing coastal structures. Many studies on wave breaking have been carried out, and many experimental data have been documented. Representative studies on wave breaking provide many empirical formulas for the prediction of breaking index, mainly through hydraulic model experiments. However, the existing empirical formulas for breaking index determine the coefficients of the assumed equation through statistical analysis of data under the assumption of a specific equation. This study presents an alternative method to estimate breaker index using representative linear-based supervised machine learning algorithms that show high predictive performance in various research fields related to regression or classification problems. Based on the used machine learning methods, a new simple linear equation for the prediction of breaker index is presented. The newly proposed breaker index formula showed similar predictive performance compared to the existing empirical formula, although it was a simple linear equation.

DOI： 10.3390/jmse9070731

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Other Link： https://www.mdpi.com/2077-1312/9/7/731

Development of Numerical Model for Mixed Soil Problems Using Dry Bulk Density and Investigation of Its Numerical Stability Reviewed International coauthorship International journal

Journal of Korean Society of Coastal and Ocean Engineers   Vol. 33 ( 3 ) page： 110 - 121   2021.6

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Authorship：Lead author,　Last author   Language：Korean   Publishing type：Research paper (scientific journal)  

DOI： 10.9765/KSCOE.2021.33.3.110

STUDY ON SEA LEVEL RISE EFFECTS ON SHORELINE RETREAT ON A GRAVEL BEACH

FLORENTINA Sinta, NAKAMURA Tomoaki, CHO Yonghwan, MIZUTANI Norimi, TAKEUCHI Masayuki

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 77 ( 2 ) page： I_301 - I_306   2021

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> Climate change effects have become global concern through decades due to its emerging hazards. Sea Level Rise (SLR) is one of the effects which may cause harm to the coastal communities due to the risk of damages, such as shoreline retreat and beach erosion. There are many previous studies regarding the effect of SLR on sandy beaches. However, the study regarding gravel beach response under SLR is still rare. Therefore, this study is conducted to investigate the effect of SLR on the past shoreline change by using Bruun rule on currently eroded gravel beach, Ida beach in Shichiri-mihama coast, Mie Prefecture. By comparing the calculation result with the past shoreline change data obtained from network camera system, the proportion of SLR contribution in shoreline change can be assessed. Results shows that SLR contribution is ranging between 5.1 – 8.7% of the actual shoreline retreat from November 2017 to November 2019. This indicates that there are other factors such as extreme waves playing more dominant role in the shoreline change compared to SLR in this gravel beach.</p>

DOI： 10.2208/jscejoe.77.2_i_301

CiNii Research

CHARACTERISTICS OF TOPOGRAPHIC CHAGE FOCUSED ON THE VARIATION OF DRY BULK DENSITY BY SLIP-OUT

AKAHOSHI Rei, CHO Yong-hwan, WATANABE Mikiya, NAKAMURA Tomoaki, MIZUTANI Norimi

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 77 ( 2 ) page： I_949 - I_954   2021

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> We conducted numerical analysis on changes in dry bulk density, hydraulic experiments on changes in fine particle fraction under uniform flow. The effect of the change in density on the change characteristics of the topography consisting of mixed sediment was investigated. As a result, when considering the total suspended amount, in sandy mixed earth and sand, it was suggested that it is necessary to consider the increase in the total suspended amount due to the increase in the proportion of fine particles and the decrease in the suspended amount due to the increase in the adhesive strength in the adhesive mixed sediment and sand.</p>

DOI： 10.2208/jscejoe.77.2_i_949

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EVALUATION OF EFFECT OF WALL BEHIND BOTTOM-HINGED OWSC UNDER REGULAR WAVES

SATO Harutaka, CHO Yonghwan, NAKAMURA Tomoaki, MIZUTANI Norimi

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 77 ( 2 ) page： I_223 - I_228   2021

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> Two-dimensional hydraulic experiments were conducted using a reversed triangular bottom-hinged flap with the reflection wall behind it. Electricity generation performance when the power take-off system is installed was evaluated from the experimental result based on linear theory. Efficiency is lowest near the antinodes of the standing waves. There are some cases in which D/L when efficiency is highest is slightly different from nodes depends on wave period. Efficiency is high when the wave period is short and the water depth is small. There is a possibility that there is a specific wave period in which efficiency is extremely high. The increasing ratio of efficiency by installing the wall reached 6 at most and 2 at least.</p>

DOI： 10.2208/jscejoe.77.2_i_223

CiNii Research

EXPERIMENTAL STUDY ON EFFECTIVENESS AND MECHANISM OF ANTI-OSCILLATION TANKS AGAINST MOTION OF FLOATING CAISSON

NAKAMURA Tomoaki, SHIRAI Kaito, CHO Yonghwan, MIZUTANI Norimi, KURAHARA Yoshinosuke, TAKEDA Masahide

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 77 ( 2 ) page： I_619 - I_624   2021

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> The effectiveness and mechanism of flume-type anti-oscillation tanks against the motion of a floating caisson under regular waves was investigated from hydraulic experiments. From experimental results, it was found that the amplitude of heave was little affected by free water filled in the anti-oscillation tanks. In contrast, the maximum value of the amplitude of pitch tended to decrease with an increase in the mass of free water. From anti-oscillation moment due to free water estimated from image analysis, it was revealed that gravitational force due to the free water accounted for a substantial fraction of the anti-oscillation moment, while horizontal inertia force had an effect of increasing the amplitude of the anti-oscillation moment. Furthermore, analytical solutions of the amplitude of pitch estimated from the anti-oscillation moment agreed reasonably well with experimental results. This suggested that the mechanism of anti-oscillation tanks can be explained in the same way as in the field of naval architecture.</p>

DOI： 10.2208/jscejoe.77.2_i_619

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A Proposal of New Breaker Index Formula Using Supervised Machine Learning Reviewed International coauthorship

Byung-Jong Choi, Chang-Wook Park, Yong-Hwan Cho, Do-Sam Kim, Kwang-Ho Lee

Journal of Korean Society of Coastal and Ocean Engineers   Vol. 32 ( 6 ) page： 384 - 395   2020.12

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Publishing type：Research paper (scientific journal)  

DOI： 10.9765/KSCOE.2020.32.6.1

Modeling Tsunami-Induced Erosion of Bridge-Abutment Backfill Reviewed International journal

Tomoaki Nakamura, Yuto Nakai, Yong-Hwan Cho and Norimi Mizutani

Journal of Marine Science and Engineering   Vol. 8 ( 11 ) page： 1 - 16   2020.11

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/jmse8110922

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An Experimental Study of a Bottom-Hinged Wave Energy Converter with a Reflection Wall in Regular Waves-Focusing on Behavioral Characteristics Reviewed International coauthorship International journal

Cho Yong-Hwan, Nakamura Tomoaki, Mizutani Norimi, Lee Kwang-Ho

Applied Sciences   Vol. 10 ( 19 ) page： 1 - 23   2020.10

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Applied Sciences (Switzerland)  

The hybrid system of wave energy converters (WECs) using coastal structures is an attractive issue in terms of a decrease in construction costs and an improvement of the ability to capture wave energy. Most studies on the utilization of reflected waves from structures, which is one of the hybrid systems, are limited to mathematical analysis based on linear theories. Therefore, this paper presents fundamental experimental results in the presence of a reflection wall simplified as a coastal structure behind a bottom-hinged flap-type WEC under unidirectional regular waves. The behavioral characteristics and the power generation efficiency ke of the flap were investigated, focusing on wave steepness, initial water depth, and distance from the reflection wall. The results show that the condition of the initial water depth being smaller than the flap height is more effective in terms of avoiding unstable rotating of the flap. The maximum ke appeared slightly far from the node position of the standing waves because the flap shape and the power take-off (PTO) damping induce the phase difference between the reciprocating behavior of the flap and the period of the standing wave. The results imply that the optimum position of a WEC is dependent on WEC shape, PTO damping, and installation water depth.

DOI： 10.3390/app10196734

Web of Science

Scopus

Other Link： https://www.mdpi.com/2076-3417/10/19/6734

Experimental study on spatiotemporal profile change in gravel beach Reviewed International journal

Kim, S., Nakamura, T., Cho, Y., and Mizutani, N.

International Journal of Offshore and Polar Engineering   Vol. 30 ( 3 ) page： 349 - 356   2020.9

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.17736/ijope.2020.hc19

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Scopus

Influence of Tidal Current, Wind, and Wave in Hebei Spirit Oil Spill Modeling International coauthorship International journal

Lee Kwang-Ho, Kim Tag-Gyeom, Cho Yong-Hwan

JOURNAL OF MARINE SCIENCE AND ENGINEERING   Vol. 8 ( 2 )   2020.2

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Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.3390/jmse8020069

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STUDY ON TSUNAMI FORCE ACTING ON INLAND STRUCTURE BEHIND COASTAL PROTECTION FACILITY WITH RESILIENT STRUCTURE COMBINED WITH COASTAL DIKE AND EMBANKMENT

NAKAMURA Tomoaki, SUZUKI Ryota, CHO Yonghwan, MIZUTANI Norimi

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 76 ( 2 ) page： I_156 - I_161   2020

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> Tsunami-induced force acting on an inland building located at the landward side of a coastal protection facility with resilient structure combined with a coastal dike and an embankment was investigated numerically. Numerical results showed that the relationship between the tsunami force considering the erosion of the embankment and that assuming the constant profile of the embankment was affected by the scale of the erosion. This suggested that it is essential to take into account the erosion process of an embankment in assessing tsunami force acting on inland buildings.</p>

DOI： 10.2208/jscejoe.76.2_i_156

CiNii Research

BEACH DEFORMATION ANALYSIS BY COMBINING NETWORK CAMERA AND UAV-SFM/MVS SURVEY

CHO Yonghwan, NAKAYAMA Ryoya, KIKU Masami, NAKAMURA Tomoaki, MIZUTANI Norimi

Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)   Vol. 76 ( 2 ) page： I_655 - I_660   2020

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> This study describes the improvement of the image analysis of network camera using the orthomosaic created from UAV-SfM/MVS survey and the morphological characteristics of Shichiri-Mihama Ida beach based on the estimated shoreline positions extracted by a network camera and DEM obtained by UAV-SfM/MVS survey. The estimated shoreline extracted from the network camera image denotes the position in the range of 1~2 m above sea level by comparison with the DEM so that it was located on the land side from the actual shoreline. The application of the network camera including UAV-SfM/MVS survey makes it possible to identify the waves that caused the beach deformation between observations.</p>

DOI： 10.2208/kaigan.76.2_i_655

CiNii Research

EFFECT OF WAVE FIELD ON TIME SCALE OF EROSION OF SAND SEABED UNDER RUBBLE MOUND OF COMPOSITE BREAKWATER COVERED WITH WAVE DISSIPATING BLOCKS

MURAOKA Hiroki, NAKAMURA Tomoaki, CHO Yonghwan, MIZUTANI Norimi

Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)   Vol. 76 ( 2 ) page： I_865 - I_870   2020

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> Numerical analyses of 1/55.8-scale small experiments and 1/4-scale large experiments on sand erosion under the rubble mound of a composite breakwater were conducted to investigate the effect of wave field on the time scale of the erosion. Numerical results showed that the time for the averaged flow inside the mound to be offshore throughout the mound and the time for the wave field around the breakwater to be equilibrium were longer in the small-scale experiments than in the large-scale experiments, and consequently the erosion observed in the large-scale experiments was underestimated in the small-scale experiments. This suggested that the time for the erosion to reach the same depth as that of the large-scale experiments was longer than that estimated according to the Froude similarity law.</p>

DOI： 10.2208/kaigan.76.2_i_865

CiNii Research

FUNDAMENTAL STUDY ON POWER GENERATION CHARACTERISTICS OF BOTTOM-HINGED WAVE ENERGY CONVERTER

CHO Yonghwan, HONG Hyeonseon, KIM Shinwoong, NAKAMURA Tomoaki, MIZUTANI Norimi

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 76 ( 2 ) page： I_899 - I_904   2020

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> The paper presents power generation characteristics of the proposed wave energy converter based on the bottom-hinged pendulum. The pendulum behavior becomes unstable and the power generation efficiency decreases when the wave energy is small, and the pendulum is installed at the position of <i>D/L</i> ≈ 0.5, which is the antinode of the standing wave. When the initial water depth was deeper than the pendulum, it was found that larger wave energy was required to rotate the pendulum stably. The maximum power generation efficiency (<i>k_e</i> = 0.77) was obtained at the position of <i>D/L</i> ≈ 0.32.</p>

DOI： 10.2208/jscejoe.76.2_i_899

CiNii Research

NUMERICAL ANALYSIS OF WAVE DAMPING MECHANISM OF TEMPORARY FLOATING BREAKWATER

NAKAMURA Tomoaki, YOSHIMURA Kazuki, CHO Yonghwan, MIZUTANI Norimi, KOTAKE Yasuo, SHIBUTANI Yoko

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 76 ( 2 ) page： I_372 - I_377   2020

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> A temporary floating breakwater has been proposed to keep calm wave conditions in an offshore construction site. In this study, its wave damping mechanism was investigated from numerical simulations. Numerical results showed that the trend of the transmission coefficient can be predicted reasonably well. Furthermore, an energy damping coefficient of the breakwater changed depending on the breakwater width relative to the wavelength, and the change was explained in terms of vortices formed inside and under the breakwater. From numerical experiments, it was found that the barrier height of the breakwater and the free water depth poured inside the breakwater for most effectively reducing transmitted waves were dependence on the breakwater width relative to the wavelength.</p>

DOI： 10.2208/jscejoe.76.2_i_372

CiNii Research

STUDY ON INFLUENCE OF FOOTING WIDTH ON MOTION OF FLOATING CAISSON

NAKAMURA Tomoaki, NAGAYAMA Naoto, CHO Yonghwan, MIZUTANI Norimi, KURAHARA Yoshinosuke, TAKEDA Masahide

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 76 ( 2 ) page： I_366 - I_371   2020

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> In order to reduce the motion of a floating caisson, the effectiveness of a footing was investigated in terms of its width. Free oscillation experiments showed that the natural period of the pitch and the nonlinear extinction coefficients of the heave and pitch increased with the relative footing width. Forced oscillation experiments showed that the amplitude of the heave became large when the wave period was the same as the natural period of the heave. Similarly, the amplitude of the pitch increased when the wave period was one or two times larger than the natural period of the pitch. These suggested that it is essential to determine footing width considering the findings of this study.</p>

DOI： 10.2208/jscejoe.76.2_i_366

CiNii Research

MORPHOLOGICAL EVOLUTION OF CLAY/SAND MIXTURE FOCUSING ON CLAY LOSS Reviewed International journal

Cho Y. H., Watanabe M., Nakamura T., Mizutani N.

    page： 593 - 599   2020

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：APAC 2019 - Proceedings of the 10th International Conference on Asian and Pacific Coasts  

DOI： 10.1007/978-981-15-0291-0_82

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Scopus

Sediment transport calculation considering cohesive effects and its application to wave-induced topographic change Reviewed

Cho Y.H., Nakamura T., Mizutani N., Lee K.H.

Proceedings of the 7th International Conference on Asian and Pacific Coasts, APAC 2013     page： 338 - 345   2020

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：Proceedings of the 7th International Conference on Asian and Pacific Coasts, APAC 2013  

A sediment transport calculation considering cohesive force is proposed to deal with the transport phenomena of cohesive sediment. In the proposed calculation, each sand particle is assumed to be surrounded by a thin layer of clay. The critical Shields parameter and bed-load sediment transport rate are modified to include the cohesive force acting on the sand particle. The proposed calculation is incorporated into a two-way coupled fluid-structure-sediment interaction model, and applied to wave-induced topographic change of an artificial shallow. Numerical results show that an increase in the content ratio of the clay, cohesive resistance force per unit surface area and water content cause increases in the critical Shields parameter and decreases in the bed-load sediment transport rate, reducing the topographic change of a shallow without changing its trend. This suggests that mixing clay in the pores of the sand particles can reduce the topographic change of shallows.

Scopus

INTRODUCTION OF CLAY LOSS TO MIXED SOIL CALCULATION

CHO Yonghwan, NAKAMURA Tomoaki, MIZUTANI Norimi

Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)   Vol. 75 ( 2 ) page： I_475 - I_480   2019

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> This paper describes the method to calculate sediment transport in the mixed soil condition composed of sand and clay considering the change of clay contents due to clay loss. The concepts of the four-phase soil model and the maximum clay contents classifying mixed soil status were introduced into the method. The model incorporating the proposed method was tested under the experimental conditions. From the numerical results, when all the clay in the clay activation layer where clay loss can occur was flowed out, the suspended concentration of clay decreased with time similar to the experimental results. The suspended concentration of clay was remarkable at the offshore and onshore of the movable bed consisting of sand and clay, and the decrease of the clay content on the surface of the bed was confirmed in the same locations due to clay loss. Therefore, the proposed model suggests the possibility to improve the accuracy of sediment calculation in mixed soil condition and to clarify the mechanism of clay loss from the surface of mixed soil.</p>

DOI： 10.2208/kaigan.75.i_475

CiNii Research

REAL-SCALE NUMERICAL ASSESSMENT OF ARTIFICIAL REEF IN IDA BEACH

KIM Shinwoong, NEHASHI Soraka, NAKAMURA Tomoaki, CHO Yonghwan, MIZUTANI Norimi, TAKEUCHI Masayuki

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 75 ( 2 ) page： I_971 - I_976   2019

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> In this study, to evaluate the effectiveness of the FS3M for assessing the countermeasures of beach erosion, the model was applied to the real-scale domain. We used the FS3M, which is a computational fluid dynamic model using the Navier-Stokes equation, and the survey data provided by Mie Prefecture. To address the problem of calculation cost, the numerical method called long-term estimation was used to calculate the evolution of the beach profile on the gravel beach. The validity of FS3M was investigated by applying the parameters used in the reflective type beach to the step type beach. The model reproduced well the position of the berm but shows a problem in the profile change under the water. However, in the process of wave propagation to the rear of the artificial reef, the reduction of the wave energy decreases the wave steepness, and the beach profile change for reflective type occurs predominantly. This fact shows that FS3M can be used to reproduce the beach profile change and evaluate the effects of artificial reef.</p>

DOI： 10.2208/jscejoe.75.i_971

CiNii Research

EXPERIMENTAL STUDY ON THE INFLUENCE OF SPATIAL VARIATION OF CLAY ON THE TOPOGRAPHY CONSISTING OF MIXED SOIL

AKAHOSHI Rei, CHO Yong-hwan, WATANABE Mikiya, NAKAMURA Tomoaki, MIZUTANI Norimi

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 75 ( 2 ) page： I_193 - I_198   2019

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> As a part of elucidation of the dynamic characteristics of fine particles considered to be an important factor in maintenance for tidal flat, we carried out a hydraulic model experiment focusing on the change of topography consisting of sand-clay mixed sediments by wave conditions and clay content. The characteristics of the topography and the influence of the spatial distribution of clay on the sediment characteristics of the mixed sediment were investigated. As a result, in the case of sediment consisted of clay and sand, the effect of the cohesion of clay was effective in delaying the topographic change. Mixed sediment was eroded by the movement of sand after clay particle is washed out. Moved sand covered mixed sediment and reduced the erosion.</p>

DOI： 10.2208/jscejoe.75.i_193

CiNii Research

DEVELOPMENT OF VOF-BASED NUMERICAL MODEL APPLICABLE TO UNSATURATED SOIL AND APPLICATION TO SEEPAGE AND EROSION PHENOMENA

NAKAMURA Tomoaki, CHO Yonghwan, MIZUTANI Norimi

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 75 ( 2 ) page： I_229 - I_234   2019

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> A simple method to deal with unsaturated soil for the volume-of-fluid (VOF) method was proposed and incorporated into a VOF-based numerical model, FS3M. Furthermore, the FS3M was improved to compute unsaturated seepage flow more accurately. From comparison with experimental data, the predictive capability of the improved FS3M was demonstrated for unsaturated seepage in a dike and overflow-induced erosion of an unsaturated dike. This suggested the usefulness of the improved FS3M in assessing such phenomena related to unsaturated soil.</p>

DOI： 10.2208/jscejoe.75.i_229

CiNii Research

STUDY ON EFFECTIVENESS OF CONFIGURATION CHANGE IN CAISSONS AGAINST OVERFLOW TSUNAMIS

NAKAMURA Tomoaki, KANG Jiyoung, CHO Yonghwan, MIZUTANI Norimi

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 75 ( 2 ) page： I_773 - I_778   2019

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> To prevent the overturning of caissons due to overflow tsunamis, the effectiveness of configuration change in the caissons was investigated from hydraulic experiments and numerical analyses. From experimental and numerical results, it was found that the resilience of a trapezoidal caisson was higher than that of a rectangular caisson and an L-shaped caisson because the configuration of the trapezoidal caisson prevented the separation of the overflow and the formation of a vortex reducing an increase in wave pressure acting on the landward surface of the caisson.</p>

DOI： 10.2208/jscejoe.75.i_773

CiNii Research

EXPERIMENTAL STUDY ON EFFECTIVENESS OF GABIONS AGAINST TSUNAMI SCOUR AT LANDWARD TOE OF COASTAL DIKE

NAKAMURA Tomoaki, TANIGUCHI Junya, CHO Yonghwan, MIZUTANI Norimi

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 75 ( 2 ) page： I_749 - I_754   2019

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> The effectiveness of gabions against tsunami-induced scour at the landward toe of a coastal dike was investigated from hydraulic experiments. Experimental results showed that the installation of gabions moved a scour hole landward and reduced its maximum depth. This effect was reconfirmed from the hydraulic experiments in addition to existing numerical analyses not considering the leakage of sand and the displacement of gabions. Furthermore, it was found that a scour hole grew rapidly due to sand leakage after the gabions were displaced largely. This suggested that connected gabions could be more effective to reduce the displacement of the gabions and the gaps between the gabions.</p>

DOI： 10.2208/jscejoe.75.i_749

CiNii Research

STUDY ON PERFORMANCE OF ANTI-OSCILLATION TANK AGAINST MOTION OF FLOATING CAISSON AND ITS SIMPLE ESTIMATION METHOD

NAKAMURA Tomoaki, ONUMA Fumito, CHO Yonghwan, MIZUTANI Norimi, EGUCHI Mikiko, KURAHARA Yoshinosuke, TAKEDA Masahide

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 75 ( 2 ) page： I_403 - I_408   2019

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> The effectiveness of flume-type anti-oscillation tanks installed on a floating caisson in the pitch and roll directions under regular waves and multi-directional irregular waves was investigated from hydraulic experiments, and a simple numerical method for estimating the effect of the anti-oscillation tanks was developed and applied to the hydraulic experiments. From experimental results, it was revealed that the anti-oscillation tanks can reduce the pitch of the caisson increased at around the natural frequency and its double frequency under the regular waves. Furthermore, the anti-oscillation tanks were found to be effective against not only the pitch but also the roll under the multi-directional irregular waves. From numerical results, it was found that the effect of the anti-oscillation tanks can be estimated reasonably well in terms of the amplitude of the pitch. This suggested the usefulness of the developed method in estimating the most effective water volume in anti-oscillation tanks.</p>

DOI： 10.2208/jscejoe.75.i_403

CiNii Research

EXPERIMENTAL STUDY ON WAVE HEIGHT REDUCTION EFFECT AND DYNAMIC BEHAVIOR OF TEMPORARY FLOATING BREAKWATER

NAKAMURA Tomoaki, YOSHIMURA Kazuki, CHO Yonghwan, MIZUTANI Norimi, KOTAKE Yasuo, SHIBUTANI Yoko

Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)   Vol. 75 ( 2 ) page： I_781 - I_786   2019

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> A temporary floating breakwater has been proposed to keep calm wave conditions in an offshore construction site. In this study, its transmission coefficient and dynamic behavior were investigated from hydraulic experiments. Experimental results showed that the transmission coefficient decreased with an increase in the wave steepness and relative breakwater width. Furthermore, the time from the peak of the heave to that of the sway increased with the relative breakwater width and the temporal changes in the heave and sway had a nearly opposite phase for large relative breakwater widths, resulting in the abovementioned decrease in the transmission coefficient.</p>

DOI： 10.2208/kaigan.75.i_781

CiNii Research

NUMERICAL SIMULATION OF TSUNAMI SCOUR AT LANDWARD TOE OF COASTAL DIKE AND EVALUATION OF EFFECTIVENESS OF GABIONS

NAKAMURA Tomoaki, TANIGUCHI Junya, CHO Yonghwan, MIZUTANI Norimi

Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)   Vol. 75 ( 2 ) page： I_703 - I_708   2019

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

<p> A three-dimensional coupled fluid-structure-sediment-seabed interaction model (FS3M) was applied to hydraulic experiments on the effectiveness of gabions against tsunami scour at the landward toe of a coastal dike. Numerical results showed that the predictive capability of the FS3M was demonstrated in terms of temporal change in the maximum scour depth for all conditions without the gabions and a small discharge condition with the gabions. From numerical results for a large discharge condition with the gabions, which subsided due to sand leakage in the hydraulic experiments, it was suggested that it was essential to take into account the subsidence of the gabions in accurately assessing the effectiveness of gabions.</p>

DOI： 10.2208/kaigan.75.i_703

CiNii Research

命山基部に使用したPCマクラギの耐津波安定性に関する研究 Reviewed

趙 容桓, 山田 悠貴, 中村 友昭, 水谷 法美

土木学会論文集Ｂ２（海岸工学）   Vol. 74 ( 2 ) page： I_301-I_306   2018.11

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Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 土木学会  

DOI： 10.2208/kaigan.74.I_301

消波ブロック被覆堤マウンド下部の砂地盤の侵食と石かごが与える影響に関する実験的研究 Reviewed

村岡宏紀，中村友昭，趙　容桓，水谷法美

土木学会論文集B1（水工学）   Vol. 74 ( 2 ) page： I_595-I_600   2018.11

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 土木学会  

陸上構造物に作用する津波力に与える浮遊砂の影響に関する研究 Reviewed

中村 友昭, 中井 祐斗, 趙 容桓, 水谷 法美

土木学会論文集B3（海洋開発）   Vol. 74 ( 2 ) page： I_210-I_215   2018.9

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 土木学会  

DOI： 10.2208/jscejoe.74.I_210

Experimental study on gravel beach deformations under irregular waves Reviewed

Shinwoong KIM, Ryoya NAKAYAMA, Tomoaki NAKAMURA, Soraka NEHASHI, Yonghwan CHO, Norimi MIZUTANI

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 74 ( 2 ) page： I_731-I_736   2018.9

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Society of Civil Engineers  

DOI： 10.2208/jscejoe.74.I_731

体積変化量に着目した七里御浜井田海岸の海浜変形特性に関する研究 Reviewed

趙 容桓, 小林 泰輔, 菊 雅美, 中村 友昭, 水谷 法美

土木学会論文集B3（海洋開発）   Vol. 74 ( 2 ) page： I_647-I_652   2018.9

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Authorship：Lead author   Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 土木学会  

DOI： 10.2208/jscejoe.74.I_647

消波ブロック被覆堤下部からの砂地盤の吸い出しに関する実験的研究 Reviewed

中村 友昭, 村岡 宏紀, 趙 容桓, 水谷 法美

土木学会論文集B3（海洋開発）   Vol. 74 ( 2 ) page： I_258-I_263   2018.9

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 土木学会  

DOI： 10.2208/jscejoe.74.I_258

Failure Mechanism of Armor Blocks of Submerged Breakwater Reviewed International journal

  Vol. 85   page： 1166 - 1170   2018.5

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Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Journal of Coastal Research  

This paper describes the failure mechanism of armor blocks of a submerged breakwater under regular and long period waves. Laboratory experiments with the scale of 1/50 were conducted in a wave flume. The measured normal and tangential wave forces on the damaged armor blocks were compared with 31 tests for a submerged breakwater with 3 submerged depths and 3 respective wave periods of regular and long period waves. The experimental results described the failure of armor blocks in the threshold conditions occurred mainly at the seaward edge of the crown by normal wave forces under regular waves, and the landward edge of the crown by normal and tangential wave forces under long period waves. Two-dimensional numerical analysis was carried out to investigate the effect of temporal and spatial variation of wave fields around the submerged breakwater on wave force acting on armor blocks. The results demonstrated that the dominant wave forces on armor blocks were induced by the decrease of the pressure near the damaged blocks resulting from the wave breaking for regular waves and the increase in the flow velocity for long period waves. It was confirmed the other blocks on the crown tends to be stable under long period waves.

Scopus

EXPERIMENTAL STUDY ON EROSION OF SAND SEABED UNDER RUBBLE MOUND OF COMPOSITE BREAKWATER COVERED WITH WAVE DISSIPATING BLOCKS AND EFFECTS OF GABIONS

MURAOKA Hiroki, NAKAMURA Tomoaki, CHO Yonghwan, MIZUTANI Norimi

Journal of Japan Society of Civil Engineers, Ser. B1 (Hydraulic Engineering)   Vol. 74 ( 5 ) page： I_595 - I_600   2018

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Language：Japanese   Publisher：Japan Society of Civil Engineers  

<p> In this study, 1/55.8-scale hydraulic experiments on a composite breakwater with gabions like large-scale hydraulic experiments were carried out to organize what should be considered in determining the sizes of mound gravel and seabed sand. Experimental results showed that same flow fields around the breakwater were formed as hydraulic experiments without gabions. Similar with the large-scale hydraulic experiments, sand seabed benearth the seaward part of the mound was eroded. However, the time at which this eroded depth reached to that for the large-scale hydraulic experiments needed to be longer than the time determined according to the Froude similarity law. This suggested that further studies are required for the time scale of the erosion of the sand seabed benearth the mound.</p>

DOI： 10.2208/jscejhe.74.5_i_595

CiNii Research

Suspended clay load from mixed soil under regular waves

Akahoshi R., Cho Y.H., Nakamura T., Mizutani N.

Proceedings of the International Offshore and Polar Engineering Conference   Vol. 2018-June   page： 1387 - 1391   2018

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Publisher：Proceedings of the International Offshore and Polar Engineering Conference  

In this study, we conducted hydraulic model experiments on mixed soil containing clay and investigate the phenomenon of interParticle clay escaping from sand-clay mixed sediment with different wave conditions and clay content. Furthermore, we examine the effect of the clay escape phenomenon on the topographic change characteristics of mixed sediment. On mixed sediment having a high clay fraction, suspended clay behavior depended on bottom shear stress. On the other hands, in lower clay fraction condition, suspended interParticle clay behavior depended on wave steepness. It was also found that the corrugation gradient and the erosion rate of the clay escaping from the sand Particles have a linear relationship. Through the above investigation, it was suggested that difficult to evaluate the washout of clay from sand Particles only by evaluating critical shear stress.

Scopus

Simulation of tsunami force in the presence of beachside structures

Nakamura T., Yamashima A., Mizutani N., Cho Y.

Proceedings of the Coastal Engineering Conference   Vol. 36 ( 2018 )   2018

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Publisher：Proceedings of the Coastal Engineering Conference  

Scopus

画像解析を用いた七里御浜井田海岸における海浜地形の変化特性に関する研究 Reviewed

渡邉 博之, 趙 容桓, 菊 雅美, 中村 友昭, 水谷 法美

土木学会論文集Ｂ２（海岸工学）   Vol. 73 ( 2 ) page： I_673-I_678   2017.10

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 土木学会  

DOI： 10.2208/kaigan.73.I_673

潜堤法肩部の被覆ブロックの被災機構に関する研究 Reviewed

趙 容桓, 張 楚, 中村 友昭, 水谷 法美

土木学会論文集Ｂ２（海岸工学）   Vol. 73 ( 2 ) page： I_1099-I_1104   2017.10

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DOI： 10.2208/kaigan.73.I_1099

津波の越流により生じる海岸堤防裏法尻周辺の流動場の特徴と洗掘対策の有効性に関する数値解析 Reviewed

中村友昭，日比野加奈，趙　容桓，水谷法美

土木学会論文集B3（海洋開発）   Vol. 73 ( 2 ) page： I_114-I_119   2017.8

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DOI： 10.2208/jscejoe.73.I_114

上部斜面堤ケーソンの動揺特性に関する3次元数値解析 Reviewed

中村 友昭, 山本 勘太, 趙 容桓, 水谷 法美, 小竹 康夫

土木学会論文集B3（海洋開発）   Vol. 73 ( 2 ) page：  I_707-I_712   2017.8

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DOI： 10.2208/jscejoe.73.I_707

波作用下における混合土砂底面の粘土抜け出し効果 Reviewed

赤星 怜, 趙 容桓, 中村 友昭, 水谷 法美

土木学会論文集B3（海洋開発）   Vol. 73 ( 2 ) page： I_696-I_701   2017.8

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DOI： 10.2208/jscejoe.73.I_696

Wave hindcast and beach profile changes under high wave condition at Shichiri-Mihama Ida Beach Reviewed

土木学会論文集B3（海洋開発）   Vol. 73 ( 2 ) page： I_162-I_167   2017.8

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DOI： 10.2208/jscejoe.73.I_162

Numerical calculation of flow field and optimal operation during the drop of grab bucket Reviewed

LONG Rui, Tomoaki Nakamura, Yonghwan Cho, Norimi Mizutani, Tsuyoshi Kanazawa

JOURNAL of Yangtze River Scientific Research Institute   Vol. 34 ( 12 ) page： 7-11   2017.7

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Language：Chinese   Publishing type：Research paper (scientific journal)  

DOI： 10.11988/ckyyb.20170785

Development of fluid-sediment interaction model considering infiltration/exfiltration for long-term beach profile change and its application to gravel beach Reviewed

Kim, S.-W., Cho, Y.-H., Nakamura, T., and Mizutani, N.

Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)   Vol. 72 ( 2 ) page： I_679-I_684   2016.11

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DOI： 10.2208/kaigan.72.I_679

東北地方太平洋沖地震津波による海岸堤防裏法尻の洗掘と対策工の有効性に関する数値解析 Reviewed

中村友昭，日比野加奈，趙容桓，水谷法美，小竹康夫

土木学会論文集Ｂ２（海岸工学）   Vol. 71 ( 2 ) page： I_1099-I_1104   2015.11

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DOI： 10.2208/kaigan.71.I_1099

矢板式岸壁の腐食孔からの埋立土砂の吸い出し機構に関する研究 Reviewed

中村友昭，福田　俊，趙　容桓，水谷法美

土木学会論文集B3（海洋開発）   Vol. 72 ( 2 ) page： I_724-I_729   2015.8

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DOI： 10.2208/jscejoe.72.I_724

3次元波浪場における上部斜面堤ケーソンの動揺特性に関する実験的研究 Reviewed

中村友昭，伊藤早紀，山本勘太，趙　容桓，水谷法美，小竹康夫

土木学会論文集B3（海洋開発）   Vol. 72 ( 2 ) page： I_223-I_228   2015.8

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DOI： 10.2208/jscejoe.72.I_223

浮遊砂による流体の粘度の変化と一様流および津波による流動場に与える影響に関する研究 Reviewed

中村友昭，鈴木愛美，趙　容桓，水谷法美

土木学会論文集B3（海洋開発）   Vol. 72 ( 2 ) page： I_163-I_168   2015.8

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DOI： 10.2208/jscejoe.72.I_163

An Experimental Study on Influences of Cohesive Sediments on Sediment Transport of Mixed Soil Reviewed

Cho, Y. H., Nakamura, T., Suzuki, M., Mizutani, N.

Journal of Japan Society of Civil Engineers, Ser. B3 (Ocean Engineering)   Vol. 70 ( 2 ) page： I_738-I_743   2014.10

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DOI： 10.2208/jscejoe.70.I_738

An Experimental Study on the Wave-Induced Topographic Change in Artificial Shallows Reviewed

  Vol. 56 ( 2 ) page： 1450008_1 - 1450008_21   2014.6

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DOI： 10.1142/S0578563414500089

A Numerical Simulation of Wave-Induced Topographic Change in shallows Composed of Fine Sand Reviewed

Cho, Y. H.,Nakamura, T.,Mizutani, N.,Lee, K. H.

Journal of Advanced Simulation in Science and Engineering   Vol. 1 ( 1 ) page： 72-86   2014

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DOI： 10.15748/jasse.1.72

粘性力の影響を考慮した漂砂計算手法の提案と浅場の地形変化への適用 Reviewed

中村友昭，趙　容桓，水谷法美，李 光浩

土木学会論文集B3（海洋開発）   Vol. 69 ( 2 ) page： I_1036 - I_1041   2013.9

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：公益社団法人 土木学会  

DOI： 10.2208/jscejoe.69.I_1036

Sediment Transport Calculation Considering Cohesive Effects and Its Application to Wave-Induced Topographic Change Reviewed

Cho, Y. H., Nakamura, T., Mizutani, N., Lee, K. H.

Journal of Korean Society of Coastal and Ocean Engineers   Vol. 25 ( 6 ) page： 405 - 411   2013

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