• Geophysics and Geophysical Exploration
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• v.6 no.4
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• pp.165-170
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• 2003

Recently, resistivity surveys have been frequently carried out over the irregular terrain such as mountainous area. Such an irregular terrain itself can produce significant anomalies which may lead to misinterpretations. In this study, topographic effects in resistivity survey were studied using the physical scale modeling as well as the numerical one adopting finite element method. The scale modeling was conducted at a pond, so that we could avoid the edge effect, the inherent problem of the scale modeling conducted in a water tank in laboratory. The modeling experiments for two topographic features, a ridge and a valley with various slope angles, confirmed that the results by the two different modeling techniques coincide with each other fairly well for all the terrain models. These experiments adopting dipole-dipole array showed the distinctive terrain effects, such that a ridge produces a high apparent resistivity anomaly at the ridge center flanked by zones of lower apparent resistivity. On the other hand, a valley produces the opposite anomaly pattern, a central low flanked by highs. As the slope of a terrain model becomes steeper, the terrain-induced anomalies become stronger, and moreover, apparent resistivity can become even negative for the model with extremely high slope angle. All the modeling results led us to the conclusion that terrain effects should be included in the numerical modeling and/or the inversion process to interpret data acquired at the rugged terrain area.

• Journal of the Korean Society of Marine Environment & Safety
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• v.28 no.4
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• pp.610-619
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• 2022

Hydrogen is emerging as an alternative fuel for eco-friendly ships because it reacts with oxygen to produce electrical energy and only water as a by-product. However, unlike regular fossil fuels, hydrogen has a material with a high risk of explosion due to its low ignition point and high flammability range. In order to safely use hydrogen in ships, it is an essential task to study the flow characteristics of hydrogen leakage and diffusion need to be studied. In this study, a numerical analysis was performed on the effect of leakage, ventilation, etc. on ventilation performance when hydrogen leaks in an enclosed space such as inside a ship. ANSYS CFX ver 18.1, a commercial CFD software, was used for numerical analysis. The leakage rate was changed to 1 q, 2 q, and 3 q at 1 q = 1 g/s, the ventilation rate was changed to 1 Q, 2 Q and 3 Q at 1 Q = 0.91 m/s, and the ventilation method was changed to type I, type II, type III to analyze the ventilation performance was analyzed. As the amount of leakage increased from 1 q to 3 q, the HMF in the storage room was about 2.4 to 3.0 times higher. Furthermore, the amount of ventilation to reduce the risk of explosion should be at least 2 Q, and it was established that type III was the most suitable method for the formation of negative pressure inside the hydrogen tank storage room.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.28 no.5B
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• pp.575-589
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• 2008

In the present work, we investigate the hydrodynamic behavior of a turbulent bore, such as tsunami bore and tidal bore, generated by the removal of a gate with water impounded on one side. The bore generation system is similar to that used in a general dam-break problem. In order to the numerical simulation of the formation and propagation of a bore, we consider the incompressible flows of two immiscible fluids, liquid and gas, governed by the Navier-Stokes equations. The interface tracking between two fluids is achieved by the volume-of-fluid (VOF) technique and the M-type cubic interpolated propagation (MCIP) scheme is used to solve the Navier-Stokes equations. The MCIP method is a low diffusive and stable scheme and is generally extended the original one-dimensional CIP to higher dimensions, using a fractional step technique. Further, large eddy simulation (LES) closure scheme, a cost-effective approach to turbulence simulation, is used to predict the evolution of quantities associated with turbulence. In order to verify the applicability of the developed numerical model to the bore simulation, laboratory experiments are performed in a wave tank. Comparisons are made between the numerical results by the present model and the experimental data and good agreement is achieved.

• Journal of the Korea Concrete Institute
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• v.23 no.6
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• pp.773-780
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• 2011

In this study, thermal stress analysis are carried out considering material properties, curing condition, ambient temperature, and casting date of the mass concrete placed in bottom slab and side wall of the in-ground type LNG tank as a super massive structure. Also, based on the numerical results, cracking possibility is predicted and counter measures to prevent the cracking are proposed. For the tasks, two optimum mix proportions were selected. From the results of the thermal stress analysis, the through crack index of 1.2 was satisfied for separately caste concrete lots except for the bottom slab caste in 2 separate sequences. For the double caste bottom slab, it is necessary introduce counter measures such as pre-cooling prior to the site construction. Also, another crack preventive measure is to lower the initial casting temperature by $25^{\circ}C$ or less to satisfy 1.2 through crack index criterion. In the $1^{st}$ and $2^{nd}$ caste bottom slab, the surface crack index was over 1.2. Therefore, the surface cracks can be controlled by implementing the curing conditions proposed in this study. Since the side wall's surface crack index was over 1.0, it is safe to assume that the counter preventive measures can control width and number of cracks.

• Journal of Korean Tunnelling and Underground Space Association
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• v.23 no.1
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• pp.25-36
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• 2021

Hydrogen in hydrogen-electric vehicles has a wide range of combustion and explosion ranges, and is a combustible gas with a very fast flame propagation speed, so it has the risk of leakage, diffusion, ignition, and explosion. The fuel tank has a Thermally active Pressure Relief Device (TPRD) to reduce the risk of explosion and other explosions, and in the event of an accident, hydrogen inside the tank is released outside before an explosion or fire occurs. However, if an accident occurs in a semi-closed space such as an underground parking lot, the flow of air flow is smaller than the open space, which can cause the concentration of hydrogen gas emitted from the TPRD to accumulate above the explosion limit. Therefore, in this study, the leakage rate and concentration of hydrogen over time were analyzed according to the diameter of the nozzle of the TPRD. The diameter of the nozzle was considered to be 1 mm, 2.5 mm and 5 mm, and ccording to the diameter of the nozzle, the concentration of hydrogen in the underground parking lot increases in a faster time with the diameter of the nozzle, and the maximum value is also analyzed to be larger with the diameter of the nozzle. In underground parking lots where air currents are stagnant, hydrogen concentrations above LFL (Lowe Flammability Limit) were analyzed to be distributed around the nozzle, and it was analyzed that they did not exceed UFL (Upper Flammability Limit).

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.50 no.10
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• pp.701-708
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• 2022

Since the propellant tank structure of the projectile is mainly subjected to a compressive force, there is a high risk of damage due to buckling. Large and lightweight structures such as propellant tank have a complex manufacturing process. So it requires a non-destructive test method to predict buckling load to use the structure after testing. Many studies have been conducted on Vibration Correlation Technique(VCT), which predicts buckling load using the relationship between compressive load and natural frequency, but it requires a large compressive load to predict the buckling load accurately, and it tends to decrease prediction accuracy with increasing internal pressure in structure. In this paper, we analyzed the causes of the decrease in prediction accuracy when internal pressure increases and proposed a method increasing prediction accuracy under the low compressive load for being usable after testing, through VCT combined testing and FEA result. The prediction value by the proposed method was very consistent with the measured actual buckling load.

• Journal of the Society of Naval Architects of Korea
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• v.37 no.3
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• pp.11-20
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• 2000

The flow characteristics around the stern region of two VLCCs with the same forebody and slightly different afterbody are investigated along with propulsive performance of the ship. The local mean flow measurements and the resistance and self-propulsion tests are carried out in the towing tank for the two VLCC hull forms. The measured results clearly show the formation of bilge vortices and their effect on propulsive efficiency. The comparisons are made for the two VLCC hull forms and the relation between stern framelines and bilge vortex strength is explored. Experimental data can provide a good test case to validate the accuracy of numerical methods and turbulence model of CFD codes for ship flow calculation.

• Bulletin of the Society of Naval Architects of Korea
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• v.26 no.4
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• pp.3-13
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• 1989

In recent towing tank experiments, it has been observed that a ship moving near the critical speed $\sqrt{gh}$(g=gravitational acceleration, h=water depth) radiates solitons upstream in an almost periodic manner. As a ,consequence, the ship experiences considerable changes in resistance, trim and sinkage, or better known as squat. Mei and Choi(1987) developed a nonlinear theory for a slender ship by using the method of matched asymptotic expansions. For a certain class of channel width and ship slenderness, they found that the waves generated can be described by an inhomogeneous Korteweg-de Vries(KdV) equation. The leading-order solution properly predicts solitons propagating upstream, but it fails to render three-dimensional waves in the wake. In this paper a new approach has been made by choosing a different class of channel width and ship slenderness. The wave equation in the farfield turns out to be a homogeneous Kadomtsev-Petviashvili(KP) equation, which predicts solitons upstream and three-dimensional waves in the wake. Numerical results for the wave resistance, sinkage and trim reflect the experimentally identified phenomena.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2003.10a
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• pp.204-212
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• 2003

As the first step to investigate the nonlinear interactions between turbulence and marine structures inside a viscous NWT, a LES technique was applied to the turbulent channel flow for $Re_{T}=150$, in this paper. The employed models were 4 types, such as the Smagorinsky model, the Dynamic SGS model, the Structure Function model and the Generalized Normal Stress model. The simulated data in time-series for the LESs were averaged in both time and space and performed statistical analysis. And results of the LESs were compared with those of a DNS developed in the present study and two spectral methods by Yoon et al.(2003) & Kim et al.(1987). It seems to be quite difficult to evaluate their performances to the present problem, but is seen that the accuracy of LESs are still related to the number of grids(or fine grid size).

• The Journal of Engineering Geology
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• v.19 no.1
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• pp.9-14
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• 2009

In this work applicability of a sharp-interface model to well-scale problems is examined. In coastal areas one of the main concerns in groundwater development is saltwater intrusion. To determine the saltwater intrusion at a well one needs to evaluate the saltwater content from a pumping well. We conducted laboratory sand-tank experiments to determine if a sharp-interface model can simulate the saltwater content of a pumping well. Lateral saltwater intrusion experiments and freshwater lens experiments are conducted. A partially penetrating well and a fully penetrating well are used. Comparison between numerical results and observation results indicates that the sharp-interface model can determine saltwater contents reasonably well. We conclude that a sharp-interface model can be applied to well-scale groundwater flow problems in coastal areas.