• Proceedings of the Korean Society of Soil and Groundwater Environment Conference
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• 2004.09a
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• pp.417-421
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• 2004

Self-potential (SP) survey was carried out at Pohang geothermal field. SP measurement showed clear positive anomaly at northern part of the test wells, which can be a up-flow zone of the deep geothermal water due to electrokinetic potential generated by hydrothermal circulation. To give a clearer image of the fluid flow pattern around the test wells, a two-dimensional numerical simulation was applied to construct a numerical block model of the fluid flow system based on SP and magnetotelluric survey results. The result suggests existence of two high permeability zones including the main manifestation area in the northern part of the test wells.

• Proceedings of the KSME Conference
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• 2001.06d
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• pp.97-103
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• 2001

The effects of the electrohydrodynamic (EHD) flow and turbulent diffusion on the collection efficiency of a model ESP composed of the plates with a cavity were studied through numerical computation. The electric field and ion space charge density were calculated by the Poisson equation of the electrical potential and the current continuity equation. The EHD flow field was solved by the continuity and momentum equations of the gas phase including the electrical body force induced by the movement of ions under the electric field. The RNG $k-{\varepsilon}$ model was used to analyze the turbulent flow. The particle concentration distribution was calculated from the convective diffusion equation of the particle phase. As the ion space charge increased, the particulate collection efficiency increased because the electrical potential increased over the entire domain in the ESP. The collection efficiency decreased and then increased, i.e. had a minimum value, as the EHD circulating flow became stronger when the electrical migration velocity of the charged particle was low. However, the collection efficiency decreased with the stronger EHD flow when the electrical migration of the particle was higher relatively. The collection efficiency of the model ESP increased as the turbulent diffusivity of the particle increased when the electrical migration velocity of the particle was low. However, the collection efficiency decreased for increasing the turbulent diffusivity when the electrical migration of the particle was higher relatively.

• International Journal of Naval Architecture and Ocean Engineering
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• v.10 no.5
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• pp.545-565
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• 2018

A numerical code is developed based on potential flow theory to investigate nonlinear sloshing in rectangular Liquefied Natural Gas (LNG) tanks under forced excitation. Using this code, internal free-surface elevation and sloshing loads on liquid tanks can be obtained both in time domain and frequency domain. In the mathematical model, acceleration potential is solved in the calculation of pressure on tanks and the artificial damping model is adopted to account for energy dissipation during sloshing. The Boundary Element Method (BEM) is used to solve boundary value problems of both velocity potential and acceleration potential. Numerical calculation results are compared with published results to determine the efficiency and accuracy of the numerical code. Sloshing properties in partially filled rectangular and membrane tank under translational and rotational excitations are investigated. It is found that sloshing under horizontal and rotational excitations share similar properties. The first resonant mode and excitation frequency are the dominant response frequencies. Resonant sloshing will be excited when vertical excitation lies in the instability region. For liquid tank under rotational excitation, sloshing responses including amplitude and phase are sensitive to the location of the center of rotation. Moreover, experimental tests were conducted to analyze viscous effects on sloshing and to validate the feasibility of artificial damping models. The results show that the artificial damping model with modifying wall boundary conditions has better applicability in simulating sloshing under different fill levels and excitations.

• Nuclear Engineering and Technology
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• v.52 no.4
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• pp.784-790
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• 2020

The accelerated corrosion by Flow Accelerated Corrosion (FAC) has caused unexpected rupture of piping, hindering the safety of nuclear power plants (NPPs) and sometimes causing personal injury. For the safety, it may be necessary to select some pipes in terms of condition monitoring and to measure the change in thickness of pipes in real time. Direct current potential drop (DCPD) method has advantages in on-line monitoring of pipe wall thinning. However, it has a disadvantage in that it is difficult to quantify thinning due to various thinning shapes and thus there is a limitation in application. The machine learning approach has advantages in that it can be easily applied because the machine can learn the signals of various thinning shapes and can identify the thinning using these. In this paper, finite element analysis (FEA) was performed by applying direct current to a carbon steel pipe and measuring the potential drop. The fundamental machine learning was carried out and the piping thinning model was developed. In this process, the features of DCPD to thinning were proposed.

• Geomechanics and Engineering
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• v.20 no.3
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• pp.175-189
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• 2020

A set of relatively simple five local shear and tension failure variables is presented and then implemented into a generalized poroelastic hydromechanical numerical model to analyze failure potential and stability of variably saturated geologic media. These five local shear and tension failure variables are formulated from geometrical relationships between the Mohr circle and the Mohr-Coulomb failure criterion superimposed with the tension cutoff, which approximate together the Mohr effective stress failure envelope. Finally, fully coupled groundwater flow and land deformation in two variably saturated geologic media, which are associated with a slope (Case 1) and a tunnel (Case 2), respectively, and their failure potential and stability are simulated using the resultant hydromechanical numerical model. The numerical simulation results of both cases show that shear and tension failure potential and stability of variably saturated geologic media can be analyzed numerically simply and efficiently and even better by using the five local shear and tension failure variables as a set than by using the conventional factors of safety against shear and tension failures only.

• Journal of the Korean Institute of Navigation
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• v.17 no.1
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• pp.37-48
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• 1993

When the vessel is running at the very low Froude numbers, the free-surface is difficult to be disturbed, wave-making is negligible, and the double -model velocity potential gives a very good approximation for calculating the velocity distribution just outside the boundary layer. If the speed of incident flow is gradually increased, the most perceptible change is the rise of the flow surface at stem. With further increase in speed, the nature of the flow at the bow changes completely, The flow ahead of the bow becomes more distrubed, the rise at the stem to stagnation height disappear, and the first wave crest, of less than the stagnation height, appears a small distance downstream from the stem. The present study is concerned with a small region of this flow, mainly in the bow region. The present investigation is primarily an experimental study of the flow in the bow region of s ship model, and it is undertaken in order to investigated systematically, the effect of bow geometry on this flow. The long-range objective is to use these results to guide the development of a mathematical model for predicting the flow about a ship's bow.

• Korean Chemical Engineering Research
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• v.57 no.6
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• pp.883-890
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• 2019

Two-phase flow near the wellbore in volatile oil reservoirs causes complications in well test analysis. In this study, the flow behavior of volatile oil reservoirs below the bubble-point pressure and the potential of radial composite model for interpretation of two-phase well test in volatile oil reservoirs was investigated. A radial composite model was used for two-phase well test analysis. A new procedure was developed to interpret well test data and estimate the radius of the two-phase region. The changes in fluid composition near the wellbore during drawdown test were found to increase the saturation pressure, which affects the saturation profile during build-up. Well test results showed that the radial composite method is a powerful tool for well test characterization and estimation of reservoir parameters. The proposed procedure was able to estimate the reservoir parameters and radius of the two-phase region with acceptable accuracy.

• Journal of Ship and Ocean Technology
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• v.10 no.4
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• pp.1-11
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• 2006

The finite volume based multi-block RANS code, WAVIS developed at MOERI is applied to the numerical self-propulsion test. WAVIS uses the cell-centered finite volume method for discretization of the governing equations. The realizable $k-{\epsilon}$ turbulence model with a wall function is employed for the turbulence closure. The free surface is captured with the two-phase level set method and body forces are used to model the effects of a propeller without resolving the detail blade flow. The propeller forces are obtained using an unsteady lifting surface method based on potential flow theory. The numerical procedure followed the self-propulsion model experiment based on the 1978 ITTC performance prediction method. The self-propulsion point is obtained iteratively through balancing the propeller thrust, the ship hull resistance and towing force that is correction for Reynolds number difference between the model and full scale. The unsteady lifting surface code is also iterated until the propeller induced velocity is converged in order to obtain the propeller force. The self-propulsion characteristics such as thrust deduction, wake fraction, propeller efficiency, and hull efficiency are compared with the experimental data of the practical container ship. The present paper shows that hybrid RANS and potential flow based numerical method is promising to predict the self-propulsion parameters of practical ships as a useful tool for the hull form and propeller design.

• Proceedings of the KSME Conference
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• 2001.06b
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• pp.476-481
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• 2001

In this paper, based on the developed dynamic model of a vacuum circuit breaker mechanism, the development of the new circuit breaker with less energy mechanism is focused. The energy flow analysis of the original mechanism is carried out to show where the elastic potential energies of pre-loaded springs are transmitted. Through energy flow analysis, the concept design of the new circuit breaker with less energy mechanism is proposed, and then the detailed design is carried out through the design process based on the verified dynamic model. Comparing simulation results with experiment using a high-speed camera, the appropriateness of the proposed design procedures for the rapid circuit breaker mechanism is shown.

• Journal of Ocean Engineering and Technology
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• v.23 no.4
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• pp.38-46
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• 2009

Two sets of numerical simulations were carried out for a planing hull model ship. In the first, the WAVIS 1.4 linear and nonlinear potential solver was utilized with the free support condition, in which the running posture was determined during calculation. The linear and nonlinear potential calculation results showed qualitative agreement in the trim and resistance coefficient with the MOERI towing tank test. However, the nonlinear potential calculation gave better results than the linear method. In the next simulation, Fluent 6.3.26 with a VOF model and the WAVIS 1.4 nonlinear potential solver were used with the given running posture from the measurement carried out in the MOERI towing tank. Fluent with the VOF method had substantially better agreement with model test results than the results from the WAVIS nonlinear potential calculation for the total resistance coefficient, and for the bow and stern wave patterns, in spite of the much greater computational costs. Both methods can be utilized in planing hull design when their limitations are perceived, and the running posture should be predicted correctly.