• Proceedings of the Korean Society of Propulsion Engineers Conference
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• 2017.05a
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• pp.1000-1002
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• 2017

Here, the unsteady Navier-Stokes solver has been developed using implicit dual time stepping method. The implicit dual time stepping method introduced the pseudo time step for solving the new residual including the steady state residual and real time derivative. For the validation of code, Stokes 2nd problem, the laminar flow on the oscillating flat plate was selected and compare the calculating results with analytic solutions. The calculating velocity profile and skin friction has a good agreement with analytic solutions.

• Journal of Korean Institute of Industrial Engineers
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• v.25 no.2
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• pp.184-191
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• 1999

The k most vital arcs (k-MVA) of a maximum flow problem is defined as those k arcs whose simultaneous removal from the network causes the greatest decrease in the throughput capability of the remaining system between a specified pair of nodes. In this study, we present a method for determining all the k-MVA in maximum flow problem using a minimal cardinality cut algorithm and k-th minimal cut ranking algorithm. For ranking cardinality cuts, we use Hamacher's ranking algorithm for cut capacity and by comparing present residual capacity of cardinality cut with expected residual capacity of next cardinality cut, we also present termination condition for this algorithm. While the previous methods cannot find all the alternatives for this problem, a method presented here has advantage of determining all the k-MVA.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2001.10a
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• pp.233-235
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• 2001

Residual stress in the forged parts affects the resistance to mechanical failure, dimensional uniformity, and the service life of the parts. In order to elucidate the development of residual stress in open-die forging process, elasto-plastic finite element analysis was implemented to radial forging process. Super duplex stainless steel SAF 2507 was selected as workpiece material and a series of mechanical tests followed by numerical compensation to deformation heating was conducted to obtain necessary flow data. The residual stress distributions were calculated using commercial 3-D FEM code and the effects of process design were evaluated from selected results.

• International Journal of Precision Engineering and Manufacturing
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• v.2 no.2
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• pp.17-25
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• 2001

In this paper, a theoretical study has been made to reduce the residual stress and birefringence in the injection-molded parts. An optimization program has been used to minimize the residual stresses and birefringence calculated from a simulation program. The thermally induced stress has been calculated using a linear viscoelasticity model. The flow stress and birefringence has been calculated using the Leonov's viscoelasticity model. This has been applied to the injection molding of a circular disc and a plate. the optimization has been done either by changing process variables while maintaining the mold temperature constant or by varying the mold-wall temperature with time. This study shows the significant reduction in residual stress and birefringence is possible through the optimization of processing conditions.

• Journal of Welding and Joining
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• v.15 no.5
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• pp.115-123
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• 1997

The buckling strength, fatigue strength, stress corrosion cracking are considerably effected on one of initial imperfections, the residual stresses produced by a circumferential weld between axisymmetric cylinders. Therefore, we study the residual stresses, plastic strain and temperature distribution with using thermal elasto-plastic analysis which are generated by a circumferential weld between axisymmetric cylinders. It is investigated that welding residual stresses have an effect on the strength of cylinder for inner and outer shell under external pressure.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2005.09a
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• pp.17-22
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• 2005

The residual birefringence in molded plastic parts can be divided into two kinds of residual birefringence, i.e., the flow induced residual birefringence produced in flowing stages and the thermally induced residual birefringence produced in cooling stage. In this paper, the effect of new injection-press molding process with normal injection mold, i.e. I) injection-compression mode, ii) injection-press mode, on the distribution of birefringence was studied. It was found that the values of the birefringence was reduced at i) low clamping force and ii) longer mold opening length by injection-press molding.

• Journal of Surface Science and Engineering
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• v.40 no.2
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• pp.91-97
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• 2007

In this study we investigated the oxygen effect on the nucleation and its residual stress during unbalanced magnetron sputtering. Up to 0.5% in oxygen flow rate, cubic phase (c-BN) was dominated with extremely small fraction of Hexagonal phase (h-BN) of increasing trend with oxygen concentration, whereas hexagonal phase is dominated beyond 0.75% flow rate. Interestingly, the residual stress in cubic-phase-dominated films was substantially reduced with small amount of oxygen (${\sim}0.5%$) down to a low value comparable to the h-BN case. This may be because oxygen atoms break B-N $sp^3$ bonds and make B-O bonds more favorably, increasing $sp^2$ bonds preference, as revealed by FTIR and NEXAFS. It was confirmed by experimental facts that the threshold bias voltage for nucleation and growth of cubic phase were increased from -55 V to -70 V and from -50 V to -60 V respectively. The reduction of residual stress in O-added c-BN films is seemingly resulting from the microstructure of the films. The oxygen tends to increase slightly the amount of h-BN phase in the grain boundary of c-BN and the soft h-BN phase of 3D network including surrounding nano grains of cubic phase may relax the residual stress of cubic phase.

• Proceedings of the Korean Geotechical Society Conference
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• 2000.03b
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• pp.481-488
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• 2000

The mechanism of soil-geotextile system has been studied among researchers since the application of geotextile as a replacement of graded granular filters is rapidly growing. The interaction of soils with geotextile is rather complicated so that its design criteria are mostly based on empiricism. Hence, it is essential to study the characteristics of fine particles transport into geotextile induced by the groundwater flow In this study, the permeability reduction in the soil-filter system due to clogging phenomenon is evaluated. An extensive research program is performed using two typical weathered residual soils which are sampled at Shinnae-dong and Poi-dong area in Seoul. Two separate simulation tests with weathered residual soil are peformed: the one is the filtration test(cross-plane flow test): and the other is the drainage test(in-plane flow test). Needle punched non-woven geotextiles are selected since it is often used as a drainage material in the field. The compatibility of the soil-filter system is investigated with emphasis on the clogging phenomenon. The hydraulic behaviour of the soil-filter system is evaluated by changing several testing conditions.

• Journal of Ocean Engineering and Technology
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• v.10 no.1
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• pp.100-107
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• 1996

In this paper, we report the results of the experimental study on the flow and the mass transport around a square harbor driven by a tidal effect. The model harbor is composed of a uniform water-depth with a straight breakwater. The harbor is connected to the outer ocean by an entrance region having the same shape as the harbor. We investigated two cases, one having another breakwater in the place between the entrance region and the outer ocean, and the other without it, The surface and bottom flow patterns of the model container are visualized by using light particles and dye, respectively. It was shown that the inner harbor and the entrance region have well-organized, large vortical residual flows, and the material transport between the entrance and outer region is however significantly different for two cases; when the breakwater is built between the two regions, the transport is far better than that without it, which is clearly contrary to our common sense that the breakwater would block the dispersion of the materials between the harbor and the outer ocean.

• Proceedings of the KSEEG Conference
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• 2005.04a
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• pp.148-151
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• 2005

Field-scale DNAPL dissolution is controlled by the topology of DNAPL distributions with respect to the velocity field. A high resolution percolation model was developed and employed to simulate the distribution of DNAPL within source zones. Statistically anisotropic permeability values and capillary parameters were generated for 10${\times}$10${\times}$10 m domains at a resolution of 0.05 to 0.1 m for various statistical properties. TCE leakage was simulated at various rates and the distribution of residual DNAPL in 'fingers' and 'lenses' was computed. Variations in finger and lens geometries, frequencies, average DNAPL saturations, and overall source topology were predicted to be strongly influenced by statistical properties of the medium as well as by injection rate and fluid properties. Model results were found to be consistent with observations from controlled DNAPL release experiments reported in the literature. The computed distributions of aquifer properties and DNAPL were utilized to perform high-resolution numerical simulations of groundwater flow and dissolved transport. Simulations were performed to assess the effect of grout or foam injection in bore holes within the source zone and of shallow point-releases of fluids with various properties on dissolution in DNAPL dissolution rate, even for widely spaced injection points. The results indicate that measures that induced partial flow reductions through DNAPL source zones can significantly decrease dissolution rates from residual DNAPL. The benefit from induced partial flow reductions is two-fold: 1) local flow reduction in DNAPL contaminated zones reduces mass transfer rates, and 2) contaminant flux reductions occur due to the decrease in groundwater velocity