• Journal of Multimedia Information System
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• v.7 no.4
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• pp.269-276
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• 2020

The small craft including jet-board for leisure are commonly smaller than the general commercial vessels. For the floating vessel, the motion analysis is significantly important component to design the shape. It is, however, hardly predicting its behavior by using conventional boundary element method due to violating small amplitude assumption for potential theory. The computational fluid dynamics method can afford to simulate such small craft, but its grid system was not able to calculate motion, because movable body disturbs the grid system by confliction. The dynamics fluid body interaction model with over-set mesh system can be dealt with movable floating body under irregular ocean wave. In this study, several cases were considered to reveal that DFBI is essential method to predict floating body motion. The single phase simulate was conducted to establish the shape perfection, and then the validated vessel was simulated with ocean waves weather DFBI option on or off. Through the comparison, the results between the cases of DFBI on and off shows significantly difference. It was claimed that the DFBI was necessary not only to calculation body motion, but also to predict accurate drag and lift force on the floating body for small size craft.

• Earthquakes and Structures
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• v.23 no.1
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• pp.101-113
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• 2022

A new type of fabricated subway station construction technology can effectively solve these problems. For a new type of metro structure form, it is necessary to clarify its mechanical properties, especially the seismic performance. A soil-structure elastoplastic finite element model is established to perform three-dimensional nonlinear dynamic time-history analysis based on the first fabricated station structure-Yuanjiadian station of Changchun Metro Line 2, China. Firstly, the nonlinear seismic response characteristics of the fabricated and cast-in-place subway stations under different seismic wave excitations are compared and analyzed. Then, a comprehensive analysis of several important parameters that may affect the seismic response of fabricated subway stations is given. The results show that the maximum plastic strain, the interlayer deformation, and the internal force of fabricated station structures are smaller than that of cast-in-place structure, which indicates that the fabricated station structure has good deformation coordination capability and mechanical properties. The seismic responses of fabricated stations were mainly affected by the soil-structure stiffness ratio, the soil inertia effect, and earthquake load conditions rarely mentioned in cast-in-place stations. The critical parameters have little effect on the interlayer deformation but significantly affect the joints' opening distance and contact stress, which can be used as the evaluation index of the seismic performance of fabricated station structures. The presented results can better understand the seismic responses and guide the seismic design of the fabricated station.

• ALGAE
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• v.37 no.1
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• pp.63-74
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• 2022

Perennial stipitate kelps are globally distributed and individual species can inhabit broad latitudinal ranges, expressing notably longevous persistence. Despite the foundational role kelps provide to their communities, little is known about the variability in persistence of the stipitate kelps at local spatial scales. We studied the population persistence of Eisenia arborea, a heat- and wave force-tolerant perennial stipitate kelp with a distributional range extending from British Columbia to south of the range limit of all other northeast Pacific kelps, in Baja California Sur, Mexico. Persistence characteristics for E. arborea among sites were compared and used to test the hypothesis that stand persistence varied at local spatial scales around Isla Natividad, a Pacific island off the Baja California peninsula with documented spatiotemporal environmental heterogeneity. Collected individuals around the island were "aged" using the previously validated age estimation technique of counting annual cortical dark rings. After detecting no significant differences among sites in the covariation between estimated ages for collected individuals and stipe length, we utilized in-situ population-level stipe length measurements to more rapidly predict age structures within six stands around the island. Predicted age structures, and associated stand densities, revealed persistence characteristics and density varied at local scales and a strong positive relationship existed between stand density and stand mean and maximum ages. We speculate that stands responded differently to deterministic influences (e.g., the 2014-2016 marine heatwave and / or competition with Macrocystis) resulting in heterogenous local persistence of this foundation species.

• The Magazine of the Society of Air-Conditioning and Refrigerating Engineers of Korea
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• v.13 no.4
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• pp.215-222
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• 1984

An analytical study on the thermal instability of fluid in a vertical solt between two permeable walls has been carried out using fast converging power series solution method. For given values of prandtl number Pr and permeability paramter ${\sigma}$, the critical Grashof number $Gr_c$ and the critical wave number ac are found as eigenvalues of the problem formulated by the stability equations and the appropriate boundary conditions which are derived on the basis of linear stability theory. In the case of ${\sigma}\;>\;10^4$, the results approach those of solid boundary case, but in the case of ${\sigma}\;<\;10^3$, the decrease of $Gr_c$ and $a_c$become more prominent. In other words, the permeable walls cause the flow to be more unstable than the solid walls. This is considered to be due to the slip of the fluid on the wail, which decrease the friction force.

• Journal of Ocean Engineering and Technology
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• v.38 no.2
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• pp.53-63
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• 2024

Submerged breakwaters can be installed underneath floating structures to reduce the external wave loads acting on the structure. The objective of this study was to establish an optimization analysis framework to determine the corresponding shape and position of the submerged breakwater that can minimize or maximize the external forces acting on the floating structure. A two-dimensional frequency-domain boundary element method (FD-BEM) based on the linear potential theory was developed to perform the hydrodynamic analysis. A metaheuristic algorithm, the advanced particle swarm optimization, was newly coupled to the FD-BEM to perform the optimization analysis. The optimization analysis process was performed by calling FD-BEM for each generation, performing a numerical analysis of the design variables of each particle, and updating the design variables using the collected results. The results of the optimization analysis showed that the height of the submerged breakwater has a significant effect on the surface piercing body and that there is a specific area and position with an optimal value. In this study, the optimal values of the shape and position of a single submerged breakwater were determined and analyzed so that the external force acting on a surface piercing body was minimum or maximum.

• Tunnel and Underground Space
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• v.25 no.6
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• pp.568-576
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• 2015

In this study, scenarios based on the leakage of highly compressed air and fire occurrence turned out to be high risks in an operation stage of CAES facility were constructed and estimated. By combining Bernoulli equation with momentum equation, an expression to calculate an impact force of a jet flow of compressed air was derived. An impact force was found to be proportional to the square of diameter of fracture and the pressure of compressed air. Four types of fire scenarios were composed to evaluate an effects that seasonal change and location of fire source have on the spread behavior of smoke. Smoke from the fire ignited in the vicinity of CAES opening descended more quickly below the limit line of breathing than one from the fire occurred 10 m away from CAES opening, which is expected to occur due to a propagation of wave front of smoke. It was shown that a rate of smoke spread of the winter fire is faster than one of the summer fire and smoke from the winter fire spreads farther than one of the summer fire, which are dependent on the direction of air flow into access opening. Evacuation simulation indicated that the required safe evacuation time(RSET) of the summer and winter fires are 262, 670 s each.

• Journal of the Korean Society of Hazard Mitigation
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• v.11 no.3
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• pp.219-228
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• 2011

In this paper, the design procedure of substructure of the steel-type breakwater was described and the actual foundation design was performed for the test bed. The site investigation was executed at the Osan-port area, in Uljin, Gyeongbuk, where the steeltype detached breakwater is constructed. The foundation mainly depends on the lateral load and uplift force due to the wave force. Since the superstructure is stuck out about 9.0m from the ocean bed, the foundation must resist on the lateral force and bending moment. After considering various factors, the foundation type of this structure was determined by the steel pipe pile(${\varphi}711{\times}t12mm$). On the stability of pile foundation, the safety factors of the pile on the compressive, lateral and uplift forces were grater than the minimum factor of safety. The displacements of pile under the working load were evaluated as the values below the permissible ones. Based on the subgrade reaction method, we evaluated the relationship of subgrade reaction and displacement for the lateral and the vertical directions in the layers. The structural analyses along with the foundation were perfomed and the effect of pile foundations were compared quantitatively.

• Journal of Navigation and Port Research
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• v.42 no.6
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• pp.427-436
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• 2018

In this study, experimental and numerical analysis were performed on the survivability of a long pipe-type buoy structure in waves. The buoy structure is an articulated tower consisting of an upper structure, buoyancy module, and gravity anchor with long pipes forming the base frame. A series of experiment were performed in the ocean engineering basin of KRISO with the scaled model of 1/ 22 to evaluate the survivability of the buoy structure at West Sea in South Korea. Survival condition was considered as the wave of 50 year return period. Additional experiments were performed to investigate the effects of current and wave period. The factors considered for the evaluation of the buoy's survival were the pitch angle of the structure, anchor reaction force, and the number of submergence of the upper structure. Numerical simulations were carried out with the OrcaFlex, the commercial program for the mooring analysis, with the aim of performing mutual validation with the experimental results. Based on the evaluation, the behavior characteristics of the buoy structure were first examined according to the tidal conditions. The changes were investigated for the pitch angle and anchor reaction force at HAT and LAT conditions, and the results directly compared with those obtained from numerical simulation. Secondly, the response characteristics of the buoy structure were studied depending on the wave period and the presence of current velocity. Third, the number of submergence through video analysis was compared with the simulation results in relation to the submergence of the upper structure. Finally, the simulation results for structural responses which were not directly measured in the experiment were presented, and the structural safety discussed in the survival waves. Through a series of survivability evaluation studies, the behavior characteristics of the buoy structure were examined in survival waves. The vulnerability and utility of the buoy structure were investigated through the sensitivity studies of waves, current, and tides.

• Journal of the Korean Geosynthetics Society
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• v.20 no.4
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• pp.85-93
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• 2021

The seventy percentage of Korean Peninsular is covered by the mountainous area, and the depth of west sea and south sea is relatively shallow. Therefore, a large scale land reclamation from the sea has been implemented for the construction of industrial complex, residental area, and port and airport facilities. The common problem of reclaimed land is consisted of soft ground, and hence it has low load bearing capacity as well as excessive settlement upon loading on the ground surface. The hollow concrete block has been used to reinforce the loose and soft foundation soil where the medium-high apartment or one-story industrial building is being planned to be built. Recently the earthquakes with the magnitude of 4.0~5.0 have been occurred in the west coastal and southeast coastal areas. Lee (2019) reported the advantages of hollow concrete block reinforced shallow foundation through the static laboratory bearing capacity tests. In this study, the dynamic behavior of hollow concrete block reinforced sandy ground with filling the crushed stone in the hollow space has been investigated by the means of shaking table test with the size of shaking table 1000 mm × 1000 mm. Three types of seismic wave, that is, Ofunato, Hachinohe, Artificial, and two different accelerations (0.154 g, 0.22 g) were applied in the shaking table tests. The horizontal displacement of structure which is situated right above the hollow concrete block reinforced ground was measured by using the LVDT. The relative density of soil ground are varied with 45%, 65%, and 85%, respectively, to investigate the effectiveness of reinforcement by hollow block and measured the magnitude of lateral movement, and compared with the limit value of 0.015h (Building Earthquake Code, 2019). Based on the results of shaking table test for hollow concrete block reinforced sandy ground, honeycell type hollow block gives a large interlocking force due to the filling of crushed stone in the hollow space as well as a great interface friction force by the confining pressure and punching resistance along the inside and outside of hollow concrete block. All these factors are contributed to reduce the great amount of horizontal displacement during the shaking table test. Finally, hollow concrete block reinforced sandy ground for shallow foundation is provided an outstanding reinforced method for medium-high building irrespective of seismic wave and moderate accelerations.

• Geophysics and Geophysical Exploration
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• v.13 no.3
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• pp.268-276
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• 2010

Earthquake Hazard Mitigation Law was activated into force on March 2009. By the law, the obligation to monitor the effect of earthquake on the facilities was extended to many organizations such as gas company and local governments. Based on the estimation of National Emergency Management Agency (NEMA), the number of free-surface acceleration stations would be expanded to more than 400. The advent of internet protocol and the more simplified operation have allowed the quick and easy installation of seismic stations. In addition, the dynamic range of seismic instruments has been continuously improved enough to evaluate damage intensity and to alert alarm directly for earthquake hazard mitigation. For direct visualization of damage intensity and area, Real Time Intensity COlor Mapping (RTICOM) is explained in detail. RTICOM would be used to retrieve the essential information for damage evaluation, Peak Ground Acceleration (PGA). Destructive earthquake damage is usually due to surface waves which just follow S wave. The peak amplitude of surface wave would be pre-estimated from the amplitude and frequency content of first arrival P wave. Earthquake Early Warning (EEW) system is conventionally defined to estimate local magnitude from P wave. The status of EEW is reviewed and the application of EEW to Odesan earthquake is exampled with ShakeMap in order to make clear its appearance. In the sense of rapidity, the earthquake announcement of Korea Meteorological Agency (KMA) might be dramatically improved by the adaption of EEW. In order to realize hazard mitigation, EEW should be applied to the local crucial facilities such as nuclear power plants and fragile semi-conduct plant. The distributed EEW is introduced with the application example of Uljin earthquake. Not only Nation-wide but also locally distributed EEW applications, all relevant information is needed to be shared in real time. The plan of extension of Korea Integrated Seismic System (KISS) is briefly explained in order to future cooperation of data sharing and utilization.