• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.3B
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• pp.289-301
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• 2009

In this work, wave run-up heights and resultant wave forces on a vertical revetment due to tsunami (solitary wave) are investigated numerically using a numerical wave tank model called CADMAS-SURF (CDIT, 2001. Research and Development of Numerical Wave Channel (CADMAS-SURF). CDIT library, No. 12, Japan.), which is based on a 2-D Navier-Stokes solver, coupled to a volume of fluid (VOF) method. The third order approximate solution (Fenton, 1972. A ninth-order solution for the solitary wave. J. of Fluid Mech., Vol. 53, No.2, pp.257-271) is used to generate solitary waves and implemented in original CADMAS-SURF code. Numerical results of the wave profiles and forces are in good agreements with available experimental data. Using the numerical results, the regression curves determined from the least-square analysis are proposed, which can be used to determine the maximum wave run-up height and force on a vertical revetment due to tsunami. In addition, the capability of CADMAS-SURF is demonstrated for tsunami wave forces acting on an onshore structure using various configuration computations including the variations of the crown heights of the vertical wall and the position of the onshore structure. Based on the numerical results such as water level, velocity field and wave force, the direct effects of tsunami on an onshore structure are discussed.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.28 no.3
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• pp.132-145
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• 2016

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.

• Journal of the Korean Society of Fisheries and Ocean Technology
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• v.36 no.2
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• pp.96-104
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• 2000

By using the offshore type submersible platform, Artificial sea floor anchored at a depth of forty meters several experimental studies have been conducted successfully during 1996. The facility consists of an artificial sea floor that floats at 7 meters below the surface, a machinery hut that projects above the surface at the center of the structure and a balance weight beneath the structure. The facility can be surfaced easily by using a water discharging pump in the water tank which is located at the center of it. To find out the behavioral character and the gathering factor of fishes around the artificial sea floor, investigations were carried out during the daytime and nighttime by direct observation and by echo-sounder. Around the testing reefs and artificial sea floor, six kinds of fishes were found by diving observation and the dominants were Scomber japonicus, Sebastes thompsoni and Oplegnathus fascitus. As Scomber japonicus was distributed around the artificial sea floor in dense small school, they were not seen elsewhere in the survey area. The artificial sea floor was concluded to act as a schooling ground far Scomber japonicus, Sebastes thompsoni and Oplegnathus fascitus. were close to the testing reefs(within 10m) in the daytime, and were thought to settle on the testing reefs at nighttime, To examine the distribution of 7shes around the artificial sea floor, an acoustic survey over a 1$\times$1km area, 0-50m in depth during the all day. Around the artificial sea floor many thin scattering fish echo(TS-54.5~ -51.5dB) and dense fish echo(TS-41~-38dB) were mainly distributed. Many scattering fish echoes, which were thought to be a mixture of small squid, pelegic crustacea and ethers, were distributed over the whole survey area. A dense fish school stayed beneath the artificial sea floor for a short duration. These phenomena were concluded to show an attraction and detention function of the artificial sea floor.

• Journal of Wetlands Research
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• v.20 no.4
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• pp.353-362
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• 2018

The purpose of this study is to suggest a structure plan for improving the utilization of inactive storage in the dam for overcoming the drought. Inactive storage in the dam is composed of the emergency storage and dead storage. The emergency storage can be used for the case of emergency such as drought. But, in general, the dead storage for sedimentation is not used even for the emergency. Therefore, this study considers the part of dead storage that the sedimentation is not progressed yet can be used during the severe drought period and is called "drought storage in a dam". The accurate Sediment Level(SL) analysis for the computation of the drought storage should be performed and so the present and future SL in the dam reservoir is estimated using SED-2D linked with RMA-2 model of SMS. After the consideration of additionally available storage capacity based on the estimated SL, the drought storage is finally determined. Present data based on historical data, future predicted future climate factors by Representative Concentrarion Pathways(RCP) 8.5 scenario. Then, using the TANK model, dam inflows were determined, and future period such as SL and drought storage were suggested. As the results, we have found that the available drought storage will be reduced in the future when we compare the present drought storage with the future one. This is due to a increase variability of climate change. Therefore, we should take the necessary study for the increase of available drought storage in the future.

• Journal of Advanced Marine Engineering and Technology
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• v.35 no.5
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• pp.632-639
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• 2011

In order to design a wave energy generate system, a 6-Degree of freedom motion analysis technique was applied to the three-Dimensional CFD analysis on two floating body and the behavior was interpreted according to the nature of the incoming wave. The waves are generated by the same type of wave in the model of tank using the piston type, but due to the shallow water that is generated from the bottom of the wave energy is attenuated by Ekman boundary layer. According to the wavelength of waves generated by the result of evaluating the behavior of floating body, it is concluded that 0.3m is the maximum amplitude of wavelength of 5m, and 0.15m is the minimum amplitude of wavelength of 1m. 1.06m is the maximum distance between the two floaters of wavelength of 6m.

• 한국신재생에너지학회:학술대회논문집
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• 2007.11a
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• pp.184-187
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• 2007

Hydrogen could be produced from any substance containing hydrogen atoms, such as water, hydrocarbon (HC) fuels, acids or bases. Hydrocarbon fuels couold be converted to hydrogen-rich gas through reforming process for hydrogen production. Even though fuel cell have high efficiency with pure hydrogen from gas tank, it is more beneficial to generate hydrogen from city gas (mainly methane) in residential application such as domestic or office environments. Thus hydrogen is generated by reforming process using hydrocarbon. Unfortunately, the reforming process for hydrogen production is accompanied with unavoidable impurities. Impurities such as CO, $CO_2$, $H_2S$, $NH_3$, and $CH_4$ in hydrogen could cause negative effects on fuel cell performance. Those effects are kinetic losses due to poisoning of electrode catalysts, ohmic losses due to proton conductivity reduction including membrane and catalyst ionomer layers, and mass transport losses due to degrading catalyst layer structure and hydrophobic property. Hydrogen produced from reformer eventually contains around 73% of $H_2$, 20% or less of $CO_2$, 5.8% of less of $N_2$, or 2% less of $CH_4$, and 10ppm or less of CO. Most impurities are removed using pressure swing adsorption (PSA) process to get high purity hydrogen. However, high purity hydrogen production requires high operation cost of reforming process. The effect of carbon dioxide on fuel cell performance was investigated in this experiment. The performance of PEM fuel cell was investigated using current vs. potential experiment, long run (10 hr) test, and electrochemical impedance measurement when the concentrations of carbon dioxide were 10%, 20% and 30%. Also, the concentration of impurity supplied to the fuel cell was verified by gas chromatography (GC).

• Journal of Advanced Research in Ocean Engineering
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• v.4 no.3
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• pp.124-134
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• 2018

In this study, when the stability of the structure against the ocean wave is considered for designing the offshore structures in the Pacific, Indian ocean and Atlantic regions where the cyclone is largely generated, the ocean wave caused by the cyclone as well as the storm surge which called wind induced wave shall be predicted accurately for the purpose of judgment. The predicted wind induced wave was evaluated by comparing the outcome results the model test of Nobuhiro Matsunaga (1996) and Conventional Experiment forms such as Jonswap spectral forms(Carter, 1982), Simplified Donelan / Jonswap forms(Wilson 1965), Donelan spectral forms(Donelan 1980), Revised SPM forms(Schafer Lake 2005, 2007, 2008), SPM forms(CERC 1977), the CEM forms(Kazeminezhad et al., 2005), SMB forms(Sverdrup Munk and Bretschneider 1947,1954, 1970), and Revised Wilson forms(Wilson 1965, Goda 2003). Most of these conventional experiment forms confirmed a good match when the fetch length is less than 10 km. However, normal cyclone fetch length is more than 100km, With this fetch length, the comparison result is 10.4% of deviation when used Jonswap spectral forms(Carter, 1982) but the deviation of the other forms is around 74% due to boundary limit of fetch and wind duration. Therefore, in this study, we proposed the revised forms after comparing these results with the model results. We confirmed that the deviation range is around 10% based on revisited experiment forms. Since the model test was carried out in the small water tank, the scale up factor was applied to the mode test results in order to obtain similar results to the actual environment from revisited forms.

• Fire Science and Engineering
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• v.32 no.4
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• pp.86-94
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• 2018

A sports center fire in Jecheon caused 29 deaths and 40 injuries. This study focused only on the structural factors of the building and equipment to investigate the causes of casualties based on the fire investigation results at the sports center. The structural factors of the building and equipment were a piloti-type parking lot, lack of a fire compartment between the piloti-type parking lot and lobby, lack of an installed sprinkler system, lack of an installed fire door in the main stairs on the $1^{st}$ floor, lack of an installed fire water tank on the rooftop, an installed pocket fire door in the main entrance on the $2^{nd}$ floor, poor fire compartments in an EPS space and a pipe pit and on each floor, a leak in the joint of a drain pipe, plywood installed in the hoistway of the freight elevator and interior wall, illegal remodeling of a closed rooftop structure, which cannot discharge smoke and heat, installed styrofoam insulation in the inside of the parking lot ceiling, an installed tempered glass window, which cannot be opened in the ladies bathroom on the $2^{nd}$ floor, and a finished dryvit exterior wall.

• Geomechanics and Engineering
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• v.13 no.6
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• pp.929-946
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• 2017

Composite foundation treated with compaction piles can eliminate collapsibility and improve the bearing capacity of foundation in loess area. However, the large number of piles in the composite foundation leads to difficulties in the analysis of such type of engineering works. This paper proposes two simplified methods to quantify the stability of composite foundation treated with a large number of compaction piles. The first method is based on the principle of making the area replacement ratios of the simplified model as the same time as the practical engineering situation. Then, discrete piles arranged in a triangular shape can be simplified in the model where the annular piles and compacted soil are arranged alternately. The second method implements equivalent continuous treatment in the pile-soil area and makes the whole treated region equivalent to a type of composite material. Both methods have been verified using treated foundation of an oil storage tank. The results have shown that the differences in the settlement values obtained from the water filled test in the field and those calculated by the two simplified methods are negligible. Using stability analysis, the difference ratios of the static and dynamic safety factors of the composite foundation treated with compaction piles calculated by these two simplified methods are found to be 3.56% and 5.32%, respectively. At the same time, both static and dynamic safety factors are larger than the general safety factor, which should be greater than or equal to 2.0 according to the provisions in civil engineering. This indicates that after being treated with compaction piles, the bearing capacity of the composite foundation is effectively improved and the foundation has enough safety reserve.

• International Journal of Naval Architecture and Ocean Engineering
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• v.12 no.1
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• pp.213-225
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• 2020

Floating Offshore Wind Turbines (FOWT) installed in the deep sea regions where stable and strong wind flows are abundant would have significantly improved energy production capacity. When designing FOWT, it is essential to understand the stability and motion performance of the floater. Water tank model tests are required to evaluate these aspects of performance. This paper describes a model test and numerical simulation for a 750-kW semi-submersible platform wind turbine model-II. In the previous model test, the 750-kW FOWT model-I suffered slamming phenomena from extreme wave conditions. Because of that, the platform freeboard of model-II was increased to mitigate the slamming load on the platform deck structure in extreme conditions. Also, the model-I pitch Response Amplitude Operators (RAO) of simulation had strong responses to the natural frequency region. Thus, the hub height of model-II was decreased to reduce the pitch resonance responses from the low-frequency response of the system. Like the model-I, 750-kW FOWT model-II was built with a 1/40 scale ratio. Furthermore, the experiments to evaluate the performance characteristics of the model-II wind turbine were executed at the same location and in the same environment conditions as were those of model-I. These tests included a free decay test, and tests of regular and irregular wave conditions. Both the experimental and simulation conditions considered the blade rotating effect due to the wind. The results of the model tests were compared with the numerical simulations of the FOWT using FAST (Fatigue, Aerodynamics, Structures, and Turbulence) code from the National Renewable Energy Laboratory (NREL).