• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.45-48
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• 2007

In the present work, flow analysis has been performed for side channel type double stage ring blower by solving three-dimensional Reynolds-averaged Navier-Stokes equation. Shear stress transport model is used as turbulent closure. The commercial CFD code CFX 11.0 is used for the calculations. Each of two stage is calculated separately and the second stage inlet flow is same as the first stage outlet flow so that consecutive calculation is possible. Velocity and pressure fields have been analyzed at the midplane between blades. The numerical results are validated with experimental data for head coefficients at different flow coefficients.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1995.03a
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• pp.233-237
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• 1995

Effects of frictional laws on finite element solutions in bulk metal forming were investigated in this paper. The Coulomb friction and the constant shear friction law were compared through finite element anlayses of compression of ring and cylinders with different aspect rations, ring-gear forging and hot strip rollin under the isothermal condition. It has been shown that two laws may yield quite different results inthe case that the aspect ration of a process is large, for example , strip rolling and ring -gear forging and that the difference depends mainly on the aspect ratio and the friction.

• Journal of computational fluids engineering
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• v.12 no.4
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• pp.85-89
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• 2007

In the present work, flow analysis has been performed for side channel type double stage ring blower by solving three-dimensional Reynolds-averaged Navier-Stokes equation. Shear stress transport model is used as turbulent closure. The commercial CFD code CFX 11.0 is used for the calculations. Each of two stage is calculated separately and the second stage inlet flow is same as the first stage outlet flow so that consecutive calculation is possible. Velocity and pressure fields have been analyzed at the mid-plane between blades. The numerical results are validated with experimental data for head coefficients at different flow coefficients.

• Proceedings of the Korean Geotechical Society Conference
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• 2009.03a
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• pp.136-145
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• 2009

Factors influencing shear behavior of granular material include particle size, shape, distribution, relative density, particle crushing, etc. In this study, these factors are characterized by viewpoint of shear behavior using numerical analysis based on DEM. Geometrical particle shape is represented by a combination of small circular particles and influence of particle shape on crushing is studied through relative comparisons between clump (uncrushable) and cluster (crushable) models which are modeled using DEM. Also, particle shape is quantified by the dimensionless parameters such as circularity and convexity. The results indicate that particle shape indexes have a negative association with internal friction angle. Also, internal friction angle becomes reduced and failure envelop curve becomes nonlinear due to the particle crushing. It is also found that numerical results are quite good agreement with the experimental test conducted in this study.

• Structural Engineering and Mechanics
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• v.61 no.6
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• pp.701-709
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• 2017

Seismic dissipation devices can play a crucial role in mitigating earthquake damages, loss of life and post-event repair and downtime costs. This research investigates the use of ring springs with high-force-to-volume (HF2V) dissipaters to create damage-free, recentring connections and structures. HF2V devices are passive rate-dependent extrusion-based devices with high energy absorption characteristics. Ring springs are passive energy dissipation devices with high self-centring capability to reduce the residual displacements. Dynamic behaviour of a system with nonlinear structural stiffness and supplemental hybrid damping via HF2V devices and ring spring dampers is used to investigate the design space and potential. HF2V devices are modelled with design forces equal to 5% and 10% of seismic weight and ring springs are modelled with loading stiffness values of 20% and 40% of initial structural stiffness and respective unloading stiffness of 7% and 14% of structural stiffness (equivalent to 35% of their loading stiffness). Using a suite of 20 design level earthquake ground motions, nonlinear response spectra for 8 different configurations are generated. Results show up to 50% reduction in peak displacements and greater than 80% reduction in residual displacements of augmented structure compared to the baseline structure. These gains come at a cost of a significant rise in the base shear values up to 200% mainly as a result of the force contributed by the supplemental devices.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.23 no.7
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• pp.918-927
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• 1999

In the fully developed internal flow fields, there are complex transition flows caused by interaction of the cross flow and jet when jet is Injected Into the flow. These interactions are studied by means of the flow visualization methods. An instantaneous laser tomographic method is used to reveal the physical mechanism and the structure of vortices formation in the branch pipe flow. The velocity range of cross flow of the pipe is 0.7m/s and the corresponding Reynolds number $R_{cf}$, based on the duct height is $5.6{\times}10^3$, diameter/height ratios(d/H) 0.14 and velocity ratios 3.0. Oil mist with the size of $10{\mu}m$ diameter is used for the scattering particle. The instantaneous topological features of the vortex ring roll-up of the jet shear layer and characteristics of this flow are studied in detail by performing flow visualization in rectangular duct flow. It is found that the formation and roll-up of ring vortices is a periodic phenomenon. The detailed topology of the vortices in the near field of a cross -flow jet and the mechanism associated with them give enforced hints of vortex breakdown within the vortex system due to the interaction of the jet and the cross-flow.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.11 no.4
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• pp.26-33
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• 2002

One characteristic of Fine-Blanking is that the size and the direction of stress and strain are very complex in the plastic flow according to the condition of blanking. Especially, they are affected by the clearance of punch and die, by the force of blanking holder and by the force of counter punch. The purpose of this research is to how the deformation behavior in shear zone more clearly, based on Green & Cauch's large deformation theory. The deformation behavior and cracks were investigated in each step of shear, according to punch penetration increase, the use of V-indenter ring and the hardness of materials. This research found that the transforming behavior was the same as pure discretion and the cracks could be prevented when hardness is low.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.1 s.256
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• pp.21-28
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• 2007

The use of drug-eluting stents has dramatically reduced the incidence of restenosis however, much remains to be teamed about the performance of these stouts. In the present study, we tested the hypothesis that the design of drug-eluting stents influences the efficacy of local drug delivery to the arterial wall and that this effect depends on both arterial geometry and the prevailing flow conditions. We performed computational simulations in which the coupled Navier-Stokes and advection-diffusion equations were solved to determine the flow field and drug concentration in the vicinity of model drug-eluting stouts It is found that the characteristics of flow phenomena can be influenced greatly by the ratio of stent diameter to vessel diameter. The presence of drug-eluting stent may have profound effect on wall shear stresses, recirculation sizes and drug distributions. The results show that recirculation zone is influenced by the imposed flow conditions and stent diameter. In pulsatile flow, the low wall shear stress and high drug concentration occur along the arterial wall during the decelerating flow conditions. These results could provide the guideline for future drug-eluting stent designs toward reducing restenosis by affecting local wall shear stress distributions associated with neointimal hyperplasia.

• Journal of the Korean Geotechnical Society
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• v.23 no.12
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• pp.33-42
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• 2007

The assessment of shear wave velocity($V_s$) in soft soils is extremely difficult due to the soil disturbances during sampling and field access. After a ring type field $V_s$ probe(FVP) has been developed, it has been applied at the southern coastal area of the Korean peninsular. This study presents the upgraded FVP "blade type FVP", which minimizes soil disturbance during penetration. Design concerns of the blade type FVP include the tip shape, soil disturbance, transducers, protection of the cables, and the electromagnetic coupling between transducers and cables. The cross-talking between cables is removed by grouping and extra grounding of the cables. The shear wave velocity of the FVP is simply calculated by using the travel distance and the first arrival time. The large calibration chamber tests are carried out to investigate the disturbance effect due to the penetration of FVP blade and the validity of the shear waves measured by the FVP. The blade type FVP is tested in soils up to 30m in depth. The shear wave velocity is measured every 10cm. This study suggests that the upgraded blade type FVP may be an effective device for measuring the shear wave velocity with minimized soil disturbance in the field.

• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.2
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• pp.1-12
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• 1990

Interactions between a propeller and vortex system contained in a ship stern flow is treated theoretically. A new formulation to determine the effective velocity distributions is developed, which may be immediately applicable to the design and analysis of compound propulsors under the influence of severe vortical cross-flows around ship stern. An axisymmetric shear flow is represented by a system of ring vortices and the axial variation of the stream lines due to the action of propeller is represented by a cubic function. The strengths of ring vortices, which are varying along the stream lines, are determined by the conservation of angular momentum. Two simplified effective velocity models are proposed to confirm the theory. Sample calculations using the simplified models are made to compare with the results by other investigators.