• Proceedings of the Korean Geotechical Society Conference
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• 2006.03a
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• pp.1340-1347
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• 2006

Dynamic response of buried pipelines both in the axial and the transverse directions on concrete pipe and steel pipe, FRP pipe were investigated through a free vibration analysis. End boundary conditions considered herein consist of free ends, fixed ends, and fixed-free ends in the axial and the transverse direction. Guided ends, simply supported ends, and supported-guided ends were added to the transverse direction. The buried pipeline was regarded as a beam on an elastic foundation and the ground displacement of sinusoidal wave was applied to it. Natural frequencies and mode shapes were determined according to end boundary conditions. In addition, the effects of parameters on the natural frequency were evaluated. The natural frequency is affected most significantly by the soil stiffness and the length of the buried pipelines. The natural frequency increases as the soil stiffness increases while it decreases as the length of the buried pipeline increases. Such behavior appears to be dominant in the axial direction rather than in the transverse direction of the buried pipelines.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.28 no.4A
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• pp.256-266
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• 2003

In this paper, scattering characteristics of the rectangular waveguide with elliptical conducting post and equivalent impedance of post are analyzed by mode matching method and generalized scattering method. The scattcring characteristics of rectangular waveguide are varied by the height and eccentricity of elliptical conducting post. When the height of post(2.54mm, 4mm) is small, variation in scattering characteristics appears in total simulated frequency. But as the height of post(7.62mm, 9mm) is increased, it is dominant in higher frequency. The simulated result shows good agreement with the HFSS's result. Proposed structure and analysis method are easily applied to the design and manufacture of waveguide component with elliptical conducting post.

• Journal of Communications and Networks
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• v.12 no.2
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• pp.158-167
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• 2010

The energy efficiency of wireless infrastructure and terminals has been drawing renewed attention of late, due to their significant environmental cost. Emerging green communication paradigms such as cognitive radios, are also imposing the additional requirement of flexibility. This dual requirement of energy efficiency and flexibility poses new design challenges for implementing radio functional blocks. This paper focuses on the area vs. power trade-offs for the type of channel filters that are required in the digital frontend of a flexible, energy-efficient radio. In traditional CMOS circuits, increased area was traded for reduced dynamic power consumption. With leakage power emerging as the dominant mode of power consumption in nanoscale CMOS, these trade-offs must be revisited due to the strong correlation between area and leakage power. The current work discusses how the increased timing slacks obtained by increasing the parallelism can be exploited for overall power reduction even in nanoscale circuits. In this context the paper introduces the notion of 'area efficiency' and a metric for evaluating it. The proposed metric has also been used to compare the area efficiencies of different classes of time-shared filters.

• International Journal of Concrete Structures and Materials
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• v.6 no.1
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• pp.49-57
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• 2012

The main objectives of this research were to experimentally evaluate the impact of Carbon Fiber-Reinforced Polymers (CFRP) amount and strip spacing on the shear behavior of prestressed concrete (PC) beams and to evaluate the applicability of existing analytical models of Fiber-Reinforced Polymer (FRP) shear capacity to PC beams shear-strengthened with CFRP. The Ushaped CFRP strips with different spacing were applied externally to the test specimens in order to observe the overall behavior of the prestressed concrete I-beams and the mode of failure of the applied CFRP strips. Results obtained from the experimental program showed that the application of CFRP strips to prestressed concrete I-beams did in fact enhance the overall behavior of the specimens. The strengthened specimens responded with an increase in ductility and in shear capacity. However, it should be noted that the CFRP strips were not effective at all at spacing greater than half the effective depth of the specimen and that fracture of the strips was the dominant failure mechanism of CFRP. Further research is needed to confirm the conclusion derived from the experimental program.

• International Journal of Fluid Machinery and Systems
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• v.1 no.1
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• pp.10-23
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• 2008

The development of pre-set wavelength G$\ddot{o}$rtler vortices are studied in the boundary-layer flows on concave surfaces of 1.0 and 2.0 m radius of curvature. The wavelengths of the vortices were pre-set by thin wires of 0.2 mm diameter placed 10 mm upstream and perpendicular to the concave surface leading edge. Velocity contours were obtained from velocity measurements using a single hot-wire anemometer probe. The most amplified or dominant wavelength is found to be 15 mm for free-stream velocity of 2.1 m/s and 3.0 m/s on the concave surface of R = 1 m and 2 m, respectively. The velocity contours in the cross-sectional planes at several streamwise locations show the growth and breakdown of the vortices. Three different regions can be identified based on the growth rate of the vortices. The occurrence of a secondary instability mode is also shown in the form of mushroom-like structures as a consequence of the non-linear growth of the G$\ddot{o}$rtler vortices. By pre-setting the vortex wavelength to be much larger and much smaller than the most amplified one, the splitting and merging of G$\ddot{o}$rtler vortices can be respectively observed.

• 한국전산유체공학회:학술대회논문집
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• 2007.10a
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• pp.187-193
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• 2007

The flight vehicles have cavities such as wheel wells and bomb bays. The flow around a cavity is characterized as unsteady flow because of the formation and dissipation of vortices due to the interaction between the freestream shear layer and cavity internal flow, the generation of shock and expansion waves. Resonance phenomena can damage the structures around the cavity and negatively affect aerodynamic performance and stability. In the present study, numerical analysis was performed for cavity flows by the unsteady compressible three dimensional Reynolds-Averaged Navier-Stokes (RANS) equations with Wilcox's ${\kappa}\;-\;{\omega}$ turbulence model. The cavity has the aspect ratios of 2.5, 3.5 and 4.5 for two-dimensional case, same aspect ratios with the W/D ratio of 2 for three-dimensional case. The Mach and Reynolds numbers are 0.53 and 1,600,000 respectively. The flow field is observed to oscillate in the "shear layer mode" with a feedback mechanism. Based on the SPL(Sound Pressure Level) analysis of the pressure variation at the cavity trailing edge, the dominant frequency was analyzed and compared with the results of Rossiter's formula. The MPI(Message Passing Interface) parallelized code was used for calculations by PC-cluster.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.20 no.10
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• pp.3344-3354
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• 1996

An experimental and numerical study on the three-dimensional natural convection-radiation conjugate heat transfer in the enclosure with heat generating chip has been performed. A 3-dimensional simulation model is developed by considering heat transfer phenomena by conduction-convection and radiation. Radiative transfer was analyzed with the discrete ordinates method. Experiments are conducted in order to validate the numerical model. Comparisons with the experimental data show that good agreement is obtained when the radiation effect is considered. The effects of the thermal conductivity of the substrate and power level on heat transfer are investigated. It is shown that radiation is the dominant heat transfer mode and the conductivity of the substrate has important effects on the heat transfer in the enclosure.

• Journal of the Korean Society of Costume
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• v.50 no.2
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• pp.15-28
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• 2000

This paper focuses on the sports look expressed in 20th century fashion. It is Age of Sport just as rock'n roll became dominant cultural form of the 1960's and 1970's . In the 1990's the sportsware is fashion. Designers gazing into the future are inspired by the details and functionality of clothing for snow boarding , skiing , motorbike racing and fitness. No doubt fashion in 2000 will also be full of references to it. Since the late 1960's the sportswear that was originally a term for clothing worn for various sports activities in the 1890's has changed and is now considered as fashion for day as well as evening. This has occurred primarily in the U.S. due to the adoption of less formal lifestyles by Americans. while the sportwear is the term which stemmed from the need for functionality in sports, sports look is the style inspired by the formative elements, that is, the details, the shilhouette, and the colors of the sportswear. New technologies for sports, the powerful influence of youthful culture, and the celebritizations of the sports stars made the sports look much hipper and more popular. It can be categoried into three aesthetic values, I. e., the functional sports look,, purism and no useless ornament, the street sports look with fun, androgynous and unisex mode and the mix and match of different texture and colors, and the futuristic sports look with new high tech fabrics and avant-garde style.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2000.11a
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• pp.875-879
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• 2000

In the previous report1), the grinding characteristics of quartz were investigated. In this paper, the grinding mechanisms of brittle materials including ceramics and quartz are modeled and a new parameter SDR(Surface roughness Direction Ratio) is proposed to characterize the grinding mechanisms of such materials. A set of experiments were performed to verify the effectiveness of the suggested parameter. The experimental results indicate that the plastic deformation is the dominant material removal mode at the grinding conditions which show the higher value of SDR. In the case of quartz, the material was removed by brittle fracture in a lower value of SDR and by plastic deformation in a higher value of it. SDR is not affected by wheel mesh size when brittle fracture occured. But in the plastic deformation case, SDR value increases with wheel mesh size.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.12
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• pp.2019-2027
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• 2003

Pitting wear is a dominant from of polyethylene surface damage in total knee replacements, and may originate from surface cracks that propagate under repeated tribological contact. In this study, stress intensity factors, K$\_$I/and $_{4}$, were calculated for a surface crack in a polyethylene-CoCr-bone system under the rolling and/or sliding contact pressures. Crack length and load location were considered in determination of probable crack propagation mechanisms and fracture modes. Positive K$\_$I/ values were obtained for shorter cracks in rolling contact and for all crack lengths when the sliding load was apart from the crack. $_{4}$ was the greatest when the load was directly adjacent to the crack (g/a=${\pm}$1). Sliding friction caused a substantial increase of both K$\_$I/$\^$max/ and $_{4}$$\^$max/. The effective Mode I stress intensity factors, K$\_$eff/, were the greatest at g/a=${\pm}$1, showing the significance of high shear stresses generated by loads adjacent to surface cracks. Such behavior of K$\_$eff/ suggests mechanisms for surface pitting by which surface cracks may propagate along their original plane under repeated rolling or sliding contact.