• The Journal of Engineering Geology
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• v.32 no.3
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• pp.351-361
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• 2022

Numerical analysis performed to predict the behavior of Ipseok-dae columnar joints in Mudeungsan National Park to understand their stability and movement. The numerical analysis technique, 3DEC, is based on the discrete element method that can analysis discontinuities. The analysis used data for material properties derived from laboratory tests, which found that average density was 2.68 kN/m³, average normal stiffness was 3.15 GPa/m, average shear stiffness was 1.00 GPa/m, average cohesion was 0.51 MPa, and the average friction angle was 33°. The Ipseok-dae columnar joints were modeled on the basis of the field survey data for 15 joints located between the observation platform and the hiking trail. The numerical analysis assessed the behavior of each columnar joint by interpreting the displacement of the edges of its upper and lower surfaces. The greatest maximum displacement was found in columnar joint No. 6, and the greatest minimum displacement was found in joint No. 11. Analyzing the movements of five discontinuities in joint No. 11 indicated that the maximum displacement occurred at the 2nd level. The other levels were ordered 5th, 4th, 1st, and 3rd in terms of subsequent greatest displacements. Considering the total displacement in the 15 studied joints, the Ipseok-dae columnar joints are judged to be stable. However, considering the cultural and historical value of Mudeungsan National Park, it is regarded that the currents slope stability should be maintained by monitoring the individual rock blocks of the joints.

• Structural Engineering and Mechanics
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• v.81 no.4
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• pp.523-527
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• 2022

The objective of this study is to simulate the flow in pipes with various boundary conditions. Free-pressure fluid model, is used in the pipe based on Navier-Stokes equation. The models are solved by using the numerical method. A problem called "stability of pipes" is used in order to compare frequency and critical fluid velocity. When the initial conditions of problem satisfied the instability conditions, the free-pressure model could accurately predict discontinuities in the solution field. Employing nonlinear strains-displacements, stress-strain energy method the governing equations were derived using Hamilton's principal. Differential quadrature method (DQM) is used for obtaining the frequency and critical fluid velocity. The results of this paper are analyzed by hyperbolic numerical method. Results show that the level of numerical diffusion in the solution field and the range of well-posedness are two important criteria for selecting the two-fluid models. The solutions for predicting the flow variables is approximately equal to the two-pressure model 2. Therefore, the predicted pressure changes profile in the two-pressure model is more consistent with actual physics. Therefore, in numerical modeling of gas-liquid two-phase flows in the vertical pipe, the present model can be applied.

• Proceedings of the Korean Vacuum Society Conference
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• 2012.08a
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• pp.220-220
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• 2012

The supercapacitors with extraordinarily high capability for energy storage are attracting growing attention for their potential applications in portable electronic equipments, hybrid vehicles, cellular devices, and so on. The nanostructuring of the electrode surface can provide large surface area and consequently easy diffusion of ions in the capacitors. In addition, compared to two-dimensional nanostructures, the three-dimensional (3D) nano-architecture is expected to lead to significant enhancement of mechanical and electrical properties such as capacitance per unit area of the electrode. Polyaniline (PANi) is known as promising electrode material for supercapacitors due to its desirable properties such as high electro activity, high doping level and environmental stability. In this context, we fabricated well-ordered 3D PANi nanostructures on 3D polystyrene (PS) nanospheres which was arrayed by layer-by-layer stacking method. The height of the PANi nanostructures could be controlled by the number of PS layers stacked. 3D PANi hollow nanospheres were also fabricated by dissolving inner PS nanospheres, which resulted in further enhancement of the surface area and capacitance of the electrode.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.6
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• pp.1862-1871
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• 1996

The puopose of this paper is sto modify the current LBB criteria. The validity of current LBB criteria and current standard LBB analysis mehtod are evaluated using linear elastic fracture mechanics and elastic-plastic fracture mechanics. The results of evaluation demonstrate that the current LBB driteria are very conservative and some level of margins already exist in the standard LBB analysis method. Thus, the margin on load .root. and margin on crack size 2 can be eliminated to extend LBB application for the samller diameter pipe.

• Bulletin of the Korean Chemical Society
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• v.5 no.1
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• pp.37-41
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• 1984

The pseudolattice calculations in the CNDO/2 level of approximation are carried out for polymeric beryllium hydride, polyethylene and polymeric boron hydride. Since there is no evidence on the geometry for polymeric boron hydride, the two possible geometries are assumed. One is a polyethylene-type geometry and the other is a polymeric beryllium hydride-type geometry. In order to compare their relative stability, we calculate polyethylene and polymeric beryllium hydride and then compare with polymeric boron hydride having the assumed structures. The total energy calculation indicates that a polymeric beryllium bydride-type geometry is more stable than a polyethylene-type geometry. Our results obtained for polyethylene are in good agreement with those given by CNDO/2 crystal orbital. From the convergence problem with respect to the number of unit cells (M), the calculation with value of 4 for M can be considered to give the convergence limit results.

• Bulletin of the Korean Chemical Society
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• v.6 no.5
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• pp.277-279
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• 1985

Orbital interactions of the types, ${\sigma}-{\pi},\;{\sigma}^*-{\pi},\;{\sigma}-{\pi}^*\;and\;{\sigma}^*-{\pi}^*$ are investigated for the rotamers of ${\alpha}$-X-acetones (X = F and Cl) using STO-3G method of calculation. It was found that the interactions are possible only in gauche forms, and the ${\sigma}^*-{\pi}^*$ interactions are in general greater than the $\sigma-\pi$ interactions due to the greater overlap, in spite of the greater energy gap involved; the greater ${\sigma}^*-{\pi}^*$ interaction causes greater lowering of ${\pi}^*$ level relative to the lowering of ${\sigma}$ in the ${\sigma}-{\pi}$ interaction so that both ${\sigma}-{\pi}^*$ and $n-{\pi}^*$ interactions are enhanced in the gauche forms. The extra stability of the gauche form and the red shift in the $n-{\pi}^*$ transition are thus found to be natural corollaries of the greater ${\sigma}^*-{\pi}^*$ interaction in the gauche forms.

• Proceedings of the KIEE Conference
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• 2002.07c
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• pp.1515-1517
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• 2002

$MnO_2$ is used for the oxide electrode of electrochemical equipments because of its good electric conductivity and low oxygen overpotential. The effect of additives on the properties of $MnO_2$ has been investigated to enhance the electric conductivity and the stability in an acid solution. In this research, the effect of Ni addition on ${\beta}-MnO_2$ was studied by the theoretical quantum chemical method. The calculation was carried out by the discrete variation $X{\alpha}$ method, which is a sort of the first principle method and use Hatre-Fock-Slater approximation. The electron energy level, the density of state, the bond overlap population, the charge density distribution and the net ionic transfer between cations and anions were calculated and discussed. The used cluster model was $(Mn_{10}NiO_{44})^{-44}$.

• Proceedings of the Korean Radioactive Waste Society Conference
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• 2009.06a
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• pp.84-85
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• 2009

New approaches for detecting, preventing and remedying environmental damage are important for protection of the environment. Procedures must be developed and implemented to reduce the amount of waste produced in chemical processes, to detect the presence and/or concentration of contaminants and decontaminate fouled environments. Contamination can be classified into three general types: airborne, surface and structural. The most dangerous type is airborne contamination, because of the opportunity for inhalation and ingestion. The second most dangerous type is surface contamination. Surface contamination can be transferred to workers by casual contact and if disturbed can easily be made airborne. The decontamination of the surface in the nuclear facilities has been widely studied with particular emphasis on small and large surfaces. The amount of wastes being produced during decommissioning of nuclear facilities is much higher than the total wastes cumulated during operation. And, the process of decommissioning has a strong possibility of personal's exposure and emission to environment of the radioactive contaminants, requiring through monitoring and estimation of radiation and radioactivity. So, it is important to monitor the radioactive contamination level of the nuclear facilities for the determination of the decontamination method, the establishment of the decommissioning planning, and the worker's safety. But it is very difficult to measure the surface contamination of the floor and wall in the highly contaminated facilities. In this study, the poly(styrene-ethyl acrylate) [poly(St-EA)] core-shell composite polymer for measurement of the radioactive contamination was synthesized by the method of emulsion polymerization. The morphology of the poly(St-EA) composite emulsion particle was core-shell structure, with polystyrene (PS)as the core and poly(ethyl acrylate) (PEA) as the shell. Core-shell polymers of styrene (St)/ethyl acrylate (EA) pair were prepared by sequential emulsion polymerization in the presence of sodium dodecyl sulfate (SOS) as an emulsifier using ammonium persulfate (APS) as an initiator. The polymer was made by impregnating organic scintillators, 2,5-diphenyloxazole (PPO) and 1,4-bis[5-phenyl-2-oxazol]benzene (POPOP). Related tests and analysis confirmed the success in synthesis of composite polymer. The products are characterized by IT-IR spectroscopy, TGA that were used, respectively, to show the structure, the thermal stability of the prepared polymer. Two-phase particles with a core-shell structure were obtained in experiments where the estimated glass transition temperature and the morphologies of emulsion particles. Radiation pollution level the detection about under using examined the beta rays. The morphology of the poly(St-EA) composite polymer synthesized by the method of emulsion polymerization was a core-shell structure, as shown in Fig. 1. Core-shell materials consist of a core structural domain covered by a shell domain. Clearly, the entire surface of PS core was covered by PEA. The inner region was a PS core and the outer region was a PEA shell. The particle size distribution showed similar in the range 350-360 nm.

• Journal of Powder Materials
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• v.17 no.6
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• pp.464-469
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• 2010

The Cu nanofluid in ethylene glycol was prepared by electrical explosion of wire, a novel one-step method. The X-ray diffraction, field emission scanning electron microscope and transmission electron microscope were used to study the properties of Cu nanoparticles. The results showed that the nanoparticles were consisted of pure face-centered cubic structure and near spherical shape with average grain size of 65 nm. Ultraviolet-visible spectroscopy (UV-Vis) confirmed Cu nanoparticles with a single absorbance peak of Cu surface plasmon resonance band at 600 nm. The nanofluid was found to be stable due to high positive zeta potential value, +51 mV. The backscattering level of nanofluid in static stationary was decreased about 2% for 5 days. The thermal conductivity measurement showed that Cu-ethylene glycol nanofluid with low concentration of nanoparticles had higher thermal conductivity than based fluid. The enhancement of thermal conductivity of nanofluid at a volume fraction of 0.1% was approximately 5.2%.

• 한국전산유체공학회:학술대회논문집
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• 2008.03a
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• pp.1-13
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• 2008

An efficient segregated algorithm for the coupling of velocity and pressure of incompressible fluid flow, called IDEAL Inner Doubly-Iterative Efficient Algorithm for Linked-Equations), has been proposed by the present authors. In the algorithm there exist double inner iterative processes for pressure equation at each iteration level, which almost completely overcome two approximations in SIMPLE algorithm. Thus the coupling between velocity and pressure is fully guaranteed, greatly enhancing the convergence rate and stability of solution process. The performance of the IDEAL algorithm for three-dimensional incompressible fluid flow and heat transfer problems is analyzed and a systemic comparison is made between the algorithm and three other most widely-used algorithms (SIMPLER, SIMPLEC and PISO). It is found that the IDEAL algorithm is the most robust and the most efficient one among the four algorithms compared. This new algorithm is used for the velocity prediction of a new interface capturing method. VOSET, also proposed by the present author. It is found that the combination of VOSET and IDEAL can appreciably enhance both the interface capture accuracy and convergence rate of computations.