• 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.

• Proceedings of the KSME Conference
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• 2002.08a
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• pp.245-248
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• 2002

Vortex lock-on or resonance in the flow behind a circular cylinder is visualized by a time-resolved PIV when a single frequency oscillation is superimposed on the mean incident velocity. Measurements are made of the $K{\'{a}}rm{\'{a}}n$ vortices in the wake-transition regime at the Reynolds number 360. Basically, natural shedding state is observed to compare with lock-on state. Wake motion by the change of the shedding frequency of lock-on state is investigated. When lock-on occurs, the vortex shedding frequency is found to be half the oscillation frequency as expected from previous experiments. The physical flow phenomena of natural shedding and lock-on states are analyzed with physical parameters of recirculation and vortex formation region. Consequently, it is found that the change of wake bubble plays an important role in the flow at the lock-on state. Vortex formation region is also actively changed like recirculation region as the lock-on occurs. Therefore, it is deduced that the recirculation region is closely related with the vortex formation region.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.23 no.11 s.170
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• pp.1940-1951
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• 1999

In this paper, the equations of motion of a Bernoulli-Euler cantilever beam fixed on a moving cart and carrying a lumped mass concentrated at an arbitrary position along the beam is derived. The motion of the beam-mass-cart system is analyzed through unconstrained modal analysis, and a unified characteristic equation for calculating the natural frequencies of the system is obtained. The changes of natural frequencies and the corresponding mode shapes with respect to the changes in mass ratios of the system and to the concentrated position of the lumped mass are investigated with the frequency equation, which can be generally applied to this kind of systems. The exact and assumed-mode solutions including the dynamics of the base cart are obtained, and the open-loop responses of the system by arbitrarily designed forcing function are given by numerical simulations. The results match well with physical phenomena even at the extreme cases where the concentrated mass is attached to the bottom and to the top of the beam.

• Solar Energy
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• v.9 no.1
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• pp.53-61
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• 1989

In the present investigation, experiments on the melting of a phase change material were performed to research heat transfer phenomena generated by means of conduction and natural convection in the vertical tube at inward melting. The phase change material used in the experiments is 99 percent pure n-Docosane paraffin which is measured melting temperature of $42.5^{\circ}C$, latent heat of 37.5 cal/g, heat conductivity of $0.1505W/m^{\circ}C$. Experiments were performed both in the no-subcooling which is initiating it at melting temperature of phase change material, and in the subcooling which means to initiate it under melting temperature of phase change material, in order to compare and investigate the horizontal temperature history, vertical temperature history, ratio of melting and melted mass, figure of the melting front in the vertical tube. In the experimental results, heat transfer from tube wall to phase change material were due to conduction at early stage and due to natural convection with the passage of time, and then occurred melting downward from surface by volumetric expansion. Natural convection affects temperature distribution in the tube, ratio of melting and melted mass, figure of the melting front and then progress rapidly in case of nosubcooling compared to subcooling.

• Proceedings of the Korea Water Resources Association Conference
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• 2004.05b
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• pp.908-911
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• 2004

The purpose of this study is to investigate the applicability of the two dimensional model in natural rivers. In this study, two dimensional unite element model, SMS, is used to simulate a complex flow along with the sediment movements in the natural river. The RMA-2 model embeded in SMS is used to simulate flow phenomena and SED-2D model is employed to simulate sediment transport. The model is applied to the confluence zone of the Gam River and mouth of Nakdong River. For model calibration, the result of the unsteady flow analysis is compared with the Typhoon 'Rusa' data. In addition, the runoff analysis was conducted for the determination of the project flood and the flood forecasting. The simulation results presented the characteristics of two dimensional flow with velocity vector and flow depth. The sediment transport characteristics are shown in terms of sediment concentration as well as bed elevation change. Accordingly, the SMS model in this study turned out to be very effective tool for the simulation of the hydrodynamic characteristics under the various flow conditions and corresponding sediment transports in natural rivers.

• International Journal of Aeronautical and Space Sciences
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• v.3 no.1
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• pp.95-104
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• 2002

Numerical solution of the full Navier-Stokes equation as well as the energy equation has been obtained for the unsteady natural convection in a rectangular enclosure. One side wall was maintained at very high temperature simulating fires. Especially the effect of surface radiation was taken into account. While the enclosed air was assumed to be transparent, the internal walls directly interacted one another through the surface radiation. Due to a significant temperature difference in the flow field, the equation of state was used instead of the Boussinesq approximation. It was found that the rapid heating of the adiabatic ceiling and floor by the incoming radiation from the hot wall made the evolution at thermo-fluid field highly unstable in the initial period. Therefore, the secondary cells brought about at the floor region greatly affected the heat transfer mechanism inside the enclosure. The heat transfer rate was augmented by the radiation, resulting in requiring less time for the flow to reach the steady state. At the steady state neglecting radiation two internal hydraulic jumps were clearly observed in upper/left as well as in lower/right comer. However, the hydraulic jump in the lower/right comer could not be observed for the case including radiation due to its high momentum flow over the bottom wall. Radiation resulted in a faster establishment of the steady state phenomena.

• Journal of Korean Society for Geospatial Information Science
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• v.12 no.1 s.28
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• pp.21-29
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• 2004

Floods are disastrous natural phenomena which result in numerous losses of life and property. It is possible to minimize the potential risk by adopting a disaster management system. Nowadays, Geo-Spatial Information System(GSIS) and computer-modelling techniques have assisted scientists and engineers with determining flood disaster assessments, GIS technologies especially have the advantage of performing spatial analysis as well as generating the model for a flood hazard. Therefore, this paper presents the flood management system based on 3D GSIS that can cope with natural disasters actively and manage flood hazard systematically by constructing the database using hydrological data, digital map, DEM, and high-resolution satellite images.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2000.11a
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• pp.150-155
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• 2000

This paper presents phenomena of vibration and noise due to acoustic resonance in tube bank of a power plant. Acoustic resonance is may arise when the vortex shedding frequency coincides with the acoustic natural frequency. At the resonance, the value of vibration in this system was 595 ${\mu}m$, p-p and the sound pressure level was maximum 103 dBA. And the resonance frequency was found to be 35 Hz. When the difference of vortex shedding frequency and acoustic natural frequency is within ${\pm}20%$, acoustic resonance is possible. In this system, the difference of these frequencies was 1.8%. We can evaluate the possibility of acoustic resonance by using damping parameter. We did eliminate acoustic resonance by installing baffle in tube bank. After installing baffle, the level of vibration and noise was reduced dramatically.

• Journal of IKEEE
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• v.25 no.4
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• pp.778-781
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• 2021

In this paper, we propose the 16-layer 3D NAND Flash memory compact modeling using SPICE. In the same structure and simulation conditions, the channel potential about Down Coupling Phenomenon(DCP) and Natural Local Self Boosting (NLSB) were simulated and analyzed with Technology Computer Aided Design(TCAD) tool Atlas(Silvaco^TM) and SPICE, respectively. As a result, it was confirmed that the channel potential of TCAD and SPICE for the two phenomena were almost same. The SPICE can be checked the device structure intuitively by using netlist. Also, its simulation time is shorter than TCAD. Therefore, using SPICE can be expected to efficient research on 3D NAND Flash memory.

• The Korean Journal of Zoology
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• v.26 no.2
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• pp.95-106
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• 1983

Selections for rapid and slow walking behavior were carried out with the populations, drived from Oregon-R and lethal free strain of Drosophila melanogaster. The behavior was measured by means of connected test-tube apparatus. The populations responded effectively to the artificial selection, and it reached the selection plateau after 7 generations. The realized heritability for the first 10 generations was estimated to be about $9\\sim14%$ for the rapid walking behavior, and those for slow walking behavior was about $11\\sim16%$. The results of hybridization analysis between selected populations at generations 8 and 10 indicated that some polygenes showing a slow walking behavior were partially dominant over polygenes controlled rapid trait. The populations selected for rapid and slow walking behavior were relaxed after 10 generations of selection. The response to natural selection of rapid population was completely returned to their neutral states after only 5 generations. Such phenomena would be explained by the genetic homeostasis resulted from an action of natural selection. However, the slow population did not make any difference from walking scores of their original artificial selection. It seems reasonable to assume that the slow walking behavior was possibly controlled by a major gene.