• 산업기술연구
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• 제27권A호
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• pp.85-94
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• 2007

This study, regarding curved channel, was performed to compare and analyze hydraulic characteristics and the speed of water and water level for left bank and right bank through hydraulic model experiments and numerical analysis. Real channels that had characteristics of curved channel were selected as objectives. In order to easily operate one and two dimensional numerical analysis and comparison for total 2.4Km model channel, measuring point was set up as 200m. HEC-RAS model was applied as one dimensional numerical analysis program and SMS model was used as two dimensional numerical analysis program. In respect of speed of water, the average speed of water for right bank recorded 8.33m/s in a model experiment and 3.08m/s, 8.57m/s were average speed of water for right bank in one dimensional and two dimensional numerical analysis. The average speed of water of two dimensional numerical analysis was quite similar to that of model experiments. Also, as for water level, maximum observational errors between one and two dimensional numerical analysis for right and left bank of model experiments were 0.66m, 0.84m and 0.28m, 0.48m for each. It was found that two dimensional numerical analysis had a similar result to hydraulic model experiments. Accordingly, from the result of this study, two dimensional numerical analysis should be used rather than one dimensional numerical analysis, when numerical analysis for curved channel is conducted.

• International journal of advanced smart convergence
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• 제9권3호
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• pp.137-140
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• 2020

Orthogonal time frequency space (OTFS) modulation is considered as one of the solutions to cope with high mobility channel environments. It converts the time-varying channel to the near-constant channel response in the delay-Doppler domain. This modulation scheme also benefits from the diversity in two-dimensional modulation. According to recent researches, this method outperforms the conventional OFDM modulation, especially in high-speed channel conditions. In this paper, to investigate the performance of OTFS in a practical system, channel estimation in the delay-Doppler domain is compared with the conventional method in the time-frequency domain at different mobile speeds. Simulation results confirm that the delay-Doppler domain channel estimation brings a better performance compared to the conventional one under the same overhead rate.

• 한국통신학회논문지
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• 제37A권10호
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• pp.821-826
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• 2012

Two-dimensional magnetic recording (TDMR) is treated as the next generation magnetic recording method, but because of its high channel bit error rate, it is difficult to use in practices. In this paper, we introduce a new writing method that can decrease the nonlinear media error effectively, and it can also achieve 10 Tb/$in^2$ of user bit density on a magnetic recording medium with 20 Teragrains/$in^2$.

• 설비공학논문집
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• 제6권4호
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• pp.337-343
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• 1994

Numerical analysis was applied to a simplified two-dimensional Ondol heating model which consists of heating space on the top of it along with radiant and convective heating floor panel, flue channel in the midway and rectangular underground soil region at the bottom. These three components constitute a system thermally coupled at the top and bottom interfaces of the flue channel. Investigated in the present paper are effects with variations of the Reynolds numbers of 100, 200, and 300, Grashof numbers of $0.1{\times}10^6$ and $0.3{\times}10^6$ and aspect ratios of 15 and 20 on the heat transfer and fluid flow characteristics of two-dimensional Ondol heating model by computer simulation.

• JSTS:Journal of Semiconductor Technology and Science
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• 제3권4호
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• pp.217-222
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• 2003

A new two-dimensional analytical model for the potential distribution and drain-induced barrier lowering (DIBL) effect of fully depleted short-channel Silicon-on-insulator (SOI)-MESFET's has been presented in this paper. The two dimensional potential distribution functions in the active layer of the device is approximated as a simple parabolic function and the two-dimensional Poisson's equation has been solved with suitable boundary conditions to obtain the bottom potential at the Si/oxide layer interface. It is observed that for the SOI-MESFET's, as the gate-length is decreased below a certain limit, the bottom potential is increased and thus the channel barrier between the drain and source is reduced. The similar effect may also be observed by increasing the drain-source voltage if the device is operated in the near threshold or sub-threshold region. This is an electrostatic effect known as the drain-induced barrier lowering (DIBL) in the short-gate SOI-MESFET's. The model has been verified by comparing the results with that of the simulated one obtained by solving the 2-D Poisson's equation numerically by using the pde toolbox of the widely used software MATLAB.

• 대한기계학회논문집B
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• 제20권8호
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• pp.2707-2720
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• 1996

The aerodynamic design of the two-stages of centrifugal compressors in an 1.2MW industrial gas turbine is completed with the application of numerical analyses. The final shape of an intake, the axial guide vanes and a return channel is determined using several interactions between design and two-dimensional turbulent flow analysis, focused on the minimum loss of internal flows. The one-dimensional turbulent flow analysis, focused on the minimum loss of internal flows. The one-dimensional design and prediction of aerodynamic performances for the compressors are performed by two different methods; one is a method with conventional loss models, and the other a method with the two-zone model. The combination methods of the Betzier curves generate three-dimensional geometric shapes of impeller blades which are to be checked with a careful change of aerodynamic blade loadings. The impeller design is finally completed by the applications of three-dimensional compressible turbulent flow solvers, and the effect of minor change of design of the second-stage channel diffuser is also studied. All the aerodynamic design results are soon to the verified by component performance tests of prototype centrifugal compressors.

• Korean Journal of Hydrosciences
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• 제5권
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• pp.1-16
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• 1994

In this paper distributed models for simulating spatially and temporally varied moving storm in a watershed were developed. The complete simulation in a watershed is achieved through two sequential flow simulations which are overland flow simulation and channel network flow simulation. Two dimensional continuity equation and momentum equation of kinematic approximation were used in the overland flow simulation. On the other hand, in the channel network simulation two types of governing equations which are one dimensional continuity and momentum equations between two adjacent sections in a channel, and continuity and energy equations at a channel junction were applied. The finite difference formulations were used in the channel network model. Macks Creek Experimental Watershed in Idaho, USA was selected as a target watershed and the moving storm on August 23, 1965, which continued from 3:30 P.M. to 5:30 P.M., was utilized. The rainfall intensity fo the moving storm in the watershed was temporally varied and the storm was continuously moved from one place to the other place in a watershed. Furthermore, runoff parameters, which are soil types, vegetation coverages, overland plane slopes, channel bed slopes and so on, are spatially varied. The good agreement between the hydrograph simulated using distributed models and the hydrograph observed by ARS are Shown. Also, the conservations of mass between upstreams and downstreams at channel junctions are well indicated and the wpatial and temporal vaiability in a watershed is well simulated using suggested distributed models.

• 한국전산유체공학회지
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• 제15권3호
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• pp.54-59
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• 2010

A parametric study has been carried out to elucidate the characteristics of channel flow with a streamwise-periodic array of cylinders. This flow configuration is relevant to heat exchanger applications. The presence of cylinders in channel flow causes the attached wall boundary layer to separate, leading to significant change in flow instabilities. There exist two kinds of instabilities; flow undergoes a primary instability (Hopf bifurcation) at a lower Reynolds number, and the unsteady two-dimensional flow becomes unstable to three-dimensional disturbances at a higher Reynolds number. We report here the dependencies of the primary instability as well as the flow characteristics of the subsequent unsteady flow, including flow-induced forces and Strouhal number of vortex shedding, on the distance between the cylinder and the channel wall.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집B
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• pp.591-596
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• 2000

Flow through compliant tubes with linear taper in wall thickness is numerically simulated by finite element analysis. Two models are examined: a planar two-dimensional channel, and an axisymmetric tube. For verification of the numerical method, flow through a compliant stenotic vessel is simulated and compared to existing experimental data. Computational results for an axisymmetric tube show that as cross-sectional area falls with a reduction in downstream pressure, flow rate increases and reaches a maximum when the speed index (mean velocity divided by wave speed) is near unity at the point of minimum cross-section area, indicative of wave speed flow limitation or "choking" (flow speed equals wave speed) in previous one-dimensional studies. For further reductions in downstream pressure, flow rate decreases. Cross-sectional narrowing is significant but localized. When the ratio of downstream-to-upstream wall thickness is ${\le}$ 2 the area throat is located near the downstream end; as wall taper is increased to ${\ge}$ 3 the constriction moves to the upstream end of the tube. In the planar two-dimensional channel, area reduction and flow limitation are also observed when outlet pressure is decreased. In contrast to the axisymmetric case, however, the elastic wall in the two-dimensional channel forms a smooth concave surface with the area throat located near the mid-point of the elastic wall. Though flow rate reaches a maximum and then falls, the flow does not appear to be choked.

• 한국통신학회논문지
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• 제38A권9호
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• pp.739-743
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• 2013

본 논문에서는 비트 패턴드 자기기록 저장장치 채널을 위한 2차원 변조부호를 제안한다. 패턴드 미디어 기록장치는 하나의 자성점에 한 비트의 정보를 저장한다. 정보저장 기록 밀도를 높이기 위하여 인접한 트랙 사이의 간격을 아주 좁게 만들기 때문에 인접한 트랙간 간섭(intertrack interference, ITI)과 인접한 심볼간 간섭(intersymbol interference, ISI)이 문제가 된다. 따라서 한 비트 신호의 진폭은 2차원 간섭에 의해 변형된다. 같은 값으로 둘러싸인 비트의 신호가, 특히 어느 한 비트의 값이 둘러싸인 여덟 비트의 값과 동일한 경우 영향을 받는다. 제안된 변조부호 방법은 기존의 변조부호보다 좋은 부호율을 가지면서 위와 같은 최악의 경우가 발생하지 않도록 하므로써 패턴드 미디어의 기록 성능을 향상시키도록 한다.