• Proceedings of the Korea Air Pollution Research Association Conference
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• 2002.11a
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• pp.395-396
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• 2002

국내 지형이 복잡하고, 대단위 배출시설들이 대도시 주변에 많이 위치하고 있기 때문에 굴뚝에서 배출된 오염물질이 주변에 미치는 영향을 정확히 파악하기 위해서는 굴뚝 주변의 건물 세류현상에 대해 세밀한 해석이 요구된다. 현재 국내 환경영향평가에서 건물세류현상을 평가하기 위해서 주로 미국 환경보호청에서 제공하고 있는 ISC3모델을 사용하고 있다(US EPA, 1995). 그러나 이 모델에서는 건물과 굴뚝간의 거리에 따른 연기확산의 차이가 발생하는 것을 고려할 수 없고, 또한 건물 주위에 형성되는 와류(wake)에 의해서 배출된 연기의 중심축이 기울어지는 것 등을 고려 할 수 없다. (중략)

• Journal of the Korean Society of Marine Environment & Safety
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• v.27 no.7
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• pp.1106-1115
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• 2021

In this study, a fin that controls ship stern flow was attached on stern hull of a 80k bulk carrier to improve resistance performance. The rectangular cross-sectional fin was attached at several locations on the hull, and angle to streamline was changed with constant length, breadth, and thickness. The resistance performance and wake on propeller plane of the hull with and without the fin were analyzed using model-scale computational fluid dynamics simulation. The analysis results were extrapolated to full-scale to compare the performance and wake of the full-scale ship. First, the fin changed path of bilge vortex that flowed into the propeller along the stern hull without the fin to transom stern. This change increased pressure of the stern hull and upper region of the propeller, so pressure resistance and total resistance of the hull were reduced - the nearer the fin location to after perpendicular (AP) and base line of the hull, the larger the reduction of the resistances. Second, nominal wake fraction of the hull with the fin was lower than that without the fin. This dif erence was in proportion to the angle of the fin, but the total resistance reduction was in proportion until a certain angle at which the reduction was maximum. The largest total resistance reduction was approximately 2.1% at 12.5% of length between perpendiculars from the AP, 10% of draft from the base line, and 14° with respect to the streamline.

• Journal of Information Technology Applications and Management
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• v.11 no.2
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• pp.149-166
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• 2004

In the wake of Fishbein and Ajzen's the Theory of Reasoned Action (TRA), Davis (1989) proposed a Technology Acceptance Model (TAM) to account for how perceived ease of use, perceived usefulness, and attitude predict behavioral intention to use Information Systems (IS). However, TAM is incomplete in one important respect: it does not account for social influence In the acceptance and utilization of new information systems. This study investigated the relationships between organizational tasks and intention to use internet using TAM. For using internet, social network is an important factor because the natural characteristic of internet is community-based. The results showed that Organizational Culture (OC) plays an important role in explaining intention to use the internet. Using O'Reilly et al. 's measurements, we extended and empirically validated the proposed model using Structured Equation Modeling (SEM). These findings enable future researchers and practitioners to apply the OC variable in the various contextual domains.

• Journal of Communications and Networks
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• v.18 no.5
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• pp.857-869
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• 2016

This paper proposes an X-MAC/BEB protocol that runs a binary exponential backoff (BEB) algorithm on top of an X-MAC protocol to save more energy by reducing collision, especially in densely populated wireless sensor networks (WSNs). X-MAC, a lightweight asynchronous duty cycle medium access control (MAC) protocol, was introduced for spending less energy than its predecessor, B-MAC. One of X-MAC 's conspicuous technique is a mechanism to allow senders to promptly send their data when their receivers wake up. X-MAC, however, has no mechanism to deal with sudden traffic fluctuations that often occur whenever closely located nodes simultaneously diffuse their sense data. To precisely evaluate the impact of the BEB algorithm on X-MAC, this paper builds an analytical model of X-MAC/BEB that integrates the BEB model with the X-MAC model. The analytical and simulation results confirmed that X-MAC/BEB outperformed X-MAC in terms of throughput, delay, and energy consumption, especially in congested WSNs.

• Journal of the Korean Institute of Navigation
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• v.21 no.1
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• pp.103-108
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• 1997

Mathematical model of maneuvering motion for a single-screw single-rudder ship is established and several applications to the special situations of maneuvering are attempted. While, the mathematical model for twin-screw twin-rudder ship is not presented so much, because that type of ship is not popular. Lee et al. have examined the characteristics of such ship by captive model tests in 1988, in Japan. This paper proposes new mathematical models for propeller effective wake (1 -${\omega}_p$) and effective neutral rudder angle ${delta}_R$ in the case of twin-screw twin-rudder ship. And some maneuvering motionse are calculated with proposed models and compared with exact simulations.

• Journal of electromagnetic engineering and science
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• v.10 no.4
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• pp.231-236
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• 2010

This study proposes a temperature compensation method of the complex permittivities of biological tissues and organs. The method is based on the temperature dependence of the Debye model of water, which has been thoroughly investigated. This method was applied to measured data at room temperature for whole blood, kidney cortex, bile, liver, and heart muscle. It is shown that our method can compensate for the Cole-Cole model using measured data at 20 $^{\circ}C$, given the Cole-Cole model based on measured data at 35 $^{\circ}C$, with a root-mean-squared deviation of 3~11 % and 2~6 % for the real and imaginary parts of the complex permittivities, respectively, among the measured tissues.

• Proceedings of the Korean Institute of Navigation and Port Research Conference
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• 1996.09a
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• pp.81-88
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• 1996

Mathematical model of maneuvering motion for a single-screw single-rudder ship is established and several applications to the special situations of maneuvering are attempted. While the mathematical model for twin-screw twin-rudder ship is not studied presented so much because that type of ship is not popular. Lee et al. have examined the characteristics of such ship by captive model tests in 1988 in Japan. This paper proposes new mathematical models for propeller effective wake (1-wp) and effective neutral rudder angle $\delta$R in the case of twin-screw twin-rudder ship. And some maneuvering motions are calculated with proposed models and compared with exact simulations.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.36 no.8
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• pp.719-727
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• 2008

A 3-D compressible Navier-Stokes solver using overlapped grids is developed to predict a flow-field around a hovering rotor. The flow solver is verified by a parametric study with the grid spacing of wake grid, spatial accuracy and turbulence model. Computations are performed with different Chimera grid systems. Computational results are compared with the experimental data of Caradonna et al. for both blade loading and the tip vortex behavior. Numerical results show good agreements with experiments for the distribution of surface pressure and tip vortex behavior. Pressure distributions over the blade have marginal differences for different numerical methods, whereas large discrepancies are seen in the prediction of the wake behavior. Results unexpectedly show that the vortex strength from an automated cut-paste Chimera grid is weaker than that from the conventional Chimera grid.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.35 no.10
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• pp.868-874
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• 2007

Noises from the helicopter rotor model are calculated numerically at various pitch angles. The aerodynamic data are calculated by using prescribed wake model and unsteady panel method. The distribution of aerodynamic loads on the blade surface are obtained from $0^{\circ}$ to $9^{\circ}$ pitch angles with equiangular increments of $1.5^{\circ}$. Although thickness noise is not related to the change of pitch angles, loading noise level increases about 3~4dBA every $1.5^{\circ}$ increment of pitch angle. The additive noise level shows sufficient value to perceive the loudness. From the result of directivity pattern the sound level at the lower region of the blade disc plane is higher than that of the upper region.

• Journal of the Korean Society for Marine Environment & Energy
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• v.16 no.4
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• pp.248-254
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• 2013

Recently, contra-rotating propellers (CRP) having higher efficiency draw much attention since the EEDI regulation of IMO has been enforced. In this paper a numerical method based on the vortex lattice potential theory with a wake model and an experimental procedure with a newly built measuring device, specifically focusing on CRPs, are introduced. And they are applied to a series of CRP known to be designed for the purpose of improving EEDI. The numerical and experimental results showed good agreement explaining the characteristics of the CRP properly. The proposed method is believed to be effectively used for various CRP related studies.