• Proceedings of the KOSOMBE Conference
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• v.1994 no.05
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• pp.115-118
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• 1994

Three-dimensional steady and pulsatile flows in an end-to-side anastomosis were investigated using a finite difference method in order to understand the flow dynamics in the preferential development of distal anastomotic intimal hyperplasia or thrombosis. Steady flow results revealed that a double helical vortex was formed in the host artery and flow recirculations near tow and heel regions were limited due to the secondary flow. Oscillating wall shear stress with significant secondary flow might be the flow dynamic reason of developing intimal hyperplasia or thrombosis.

• Tribology and Lubricants
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• v.12 no.3
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• pp.85-91
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• 1996

An analysis for turbulent hybrid beatings with fluid inertia and swirl injection effect was derived for studying static characteristics of swirl-controlled hybrid journal. The swirl-controlled hybrid journal beating is considered to have more freedom in stability control in high speed rotating machinery. Current analysis is compared with experimental results with 3-recess hydrostatic journal bearing. The analysis revealed that the fluid momentum exchange at orifice discharge could produce pressure rise inside the recess region which can control the shear flow induced by journal rotation. The analysis also shows that the swirl-controlled hybrid journal beating has a capability of controlling load carrying capacity and stability by manipulating supply pressure and injection angle.

• Journal of the Korean Society of Manufacturing Process Engineers
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• v.2 no.3
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• pp.84-89
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• 2003

The joint method and characteristics of lubricant Impregnated MC nylon and metal are analyzed. Considering the productivity and economics, two materials are Joined with the process of turning, knurling, and induction heating. The Joint strength is determined by adhesion of the melted nylon, the size of knurl, and the interference from the difference of the diameters. The parameters affecting induction heating process are analyzed. The adhesion strength of the melted nylon is measured. Finally the joint strength is analyzed in the environments of low, room, and high temperature. The nylon/metal Joined material is expected to be widely used as the sliding machine elements with good friction and shear strength.

• Journal of KSNVE
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• v.6 no.4
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• pp.431-438
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• 1996

The channel type structure which has large openings is frail with respect to torsional strength, and the horizontal-torsional motion is highly coupled, because of the large difference between the centroil and the shear center. Also, a discontinuous boundary phase is came from tansition section between the opened section and the closed section. To analyze the Bending- Torsional coupled mode parameters for the channel type structure, the Transfer Matrix Method was used. Comparing the result of F.D.M.T.M.M yields good results in relatively low frequency region.

• Journal of the Semiconductor & Display Technology
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• v.3 no.3
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• pp.5-9
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• 2004

A new wafer level packaging scheme is presented as an alternative to MEMS package. The proof-of-concept structure is fabricated and evaluated to confirm the feasibility of the idea for MEMS wafer level packaging. The scheme of this work is developed using an electroplated tin (Sn) solder. The critical difference over conventional ones is that wafers are laterally bonded by solder reflow after LEGO-like assembly. This lateral bonding scheme has merits basically in morphological insensitivity and its better bonding strength over conventional ones and also enables not only the hermetic sealing but also its electrical interconnection solving an open-circuit problem by notching through via-hole. The bonding strength of the lateral bonding is over 30 Mpa as evaluated under shear and the hermeticity of the encapsulation is 2.0$\times10^{-9}$mbar.$l$/sec as examined by pressurized Helium leak rate. Results show that the new scheme is feasible and could be an alternative method for high yield wafer level packaging.

• Water for future
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• v.23 no.1
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• pp.119-127
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• 1990

The concentration of cohesive suspended sediment is determined by the circulation of water and the material dispersion. The equations of the two-dimensional, depth-integrated dispersive transport are the Reynolds equation, continuity equation, and advection-dispersion equation based on the Fick's law. A finite difference method has been applied to two models of circulation and dispersion transport. The circulation model is solved by the explicit scheme and the dispersion transport model is solved by multi-operational scheme. It is investigated wheter advective terms are included when the equation of circulation is applied to the model. For advection-dispersion equation, it was also investigated about variations of suspended sediment concentration with respect to the critical shear stresses.

• Geomechanics and Engineering
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• v.18 no.6
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• pp.639-650
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• 2019

Time-domain commercial codes are widely used to evaluate the seismic behavior of tunnels. Those tools offer a good insight into the performance and the failure mechanism of tunnels under earthquake loading. Viscous damping is generally employed in the dynamic analysis to consider damping at very small strains in some cases, and the Rayleigh damping is commonly used one. Many procedures to obtain the damping parameters have been proposed but they are seldom discussed. This paper illustrates the influence of the Rayleigh damping formulation on the tunnel visco-elastic behavior under earthquake. Four Rayleigh damping determination procedures and three soil shear velocity profiles are accounted for. The results show significant differences in the free-field and in the tunnel response caused by different procedures. The difference is somewhat decreased when the soil site fundamental frequency is increased. The conventional method which consists of using solely the first soil natural mode to determine the viscous damping parameters may lead to an unsafe seismic design of the tunnel. In general, using five times site fundamental frequency to obtain the damping formulation can provide relatively conservative results.

• The Bulletin of The Korean Astronomical Society
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• v.45 no.1
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• pp.55.1-55.1
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• 2020

In an attempt to investigate the nonlinear dynamics such as shock, shear, and turbulence associated with ultra-relativistic jets, we develop a new relativistic hydrodynamics (RHD) code based on the weighted essentially non-oscillatory (WENO) scheme. It is a 5th-order accurate, finite-difference scheme, which has been widely used for solving hyperbolic systems of conservation equations. The code is parallelized with MPI and OpenMP. Through an extensive set of tests, the accuracy and efficiency of different WENO reconstructions, and different time discretizations are assessed. Different implementations of the equation of state (EOS) for relativistic fluid are incorporated, As the fiducial setup for simulations of ultra-relativistic jets, we adopt the EOS in Ryu et al. (2006) to treat arbitrary adiabatic index of relativistic fluid, the WENO-Z reconstructions to minimize numerical dissipation without loss of stability, and the strong stability preserving Runge-Kutta (SSPRK) method to achieve stable time stepping with large CFL numbers. In addition, the code includes a high-order flux averaging along the transverse directions for multi-dimensional problems, and the modified eigenvalues for the acoustic modes to effectively control the carbuncle instability. We find that the new code performs satisfactorily simulations of ultra-relativistic jets.

• Korean Journal of Optics and Photonics
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• v.29 no.3
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• pp.99-103
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• 2018

Optical coherence elastography (OCE) is based on optical coherence tomography (OCT), which is a noninvasive, high-resolution, cross-sectional imaging technique. In this paper, we have developed dynamic optical coherence elastography to measure elasticity, a mechanical property of tissue, by phase difference. A piezoelectric actuator was used for sinusoidal mechanical loading of samples. Before applying this method to biomaterial, we assessed the feasibility of OCE with samples of sponge, eraser, and sharp lead. Cross-sectional and phase-difference images of the sample were obtained under sinusoidal loading. The strain rate was calculated from the phase-difference information. To obtain the envelope of the phase-difference oscillations along the horizontal direction, Hilbert transformation was performed at each depth. The elevation of the envelope was represented by color mapping, and we could measure the relative elasticity within the sample by comparing the elevations. Finally, there was an advantage when we calculated the shear rate using self-interference in the sample arm, instead of the interference between sample and reference arms.

• Magazine of the Korean Society of Agricultural Engineers
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• v.26 no.2
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• pp.97-105
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• 1984

We have, at present, found some studies on the optimum design of reinforced concrete about the simple slab but very few about the multi-story and multi-span slab. The aim of this study is to make a optimum design of coalesced beam and column slab constructure. Some results of the evaluation by using the optimalized algorithm that was developed in this study are as follows. 1. Slab was mainly restricted by the constraint of effective depth, bending moment, and minimum steel ratio; especially the effective depth was the preceding crifical constraint. In the optimum design of slab, therefore, the constraint about the minimum thickness should be surely considered. 2. This optimum design is good economy as much as some 3.4&~6.2% compared with the conventional design method. 3. In most case, it was converged by 3 to 6 iteratin regardless of the highest or lowest value and only in case of N=1 and case 1, there is a little oscillation after the 3rd iteration but it makes no difference in taking either the highest or lowest value because the range of oscillation is low as much as about 1.2% of the total construction cost. 4. In this study the result seeking for constraints that make no difference in the least cost design shows that shear stress and maximum steel ration may not be considered in it. 5. Bending moment was converged by one time iteration regardless of the initial value, while steel ratio, in most case, by two times because both bending moment and steel ratio are the fuction of effective depth.