• Journal of Environmental Impact Assessment
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• v.24 no.4
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• pp.301-316
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• 2015

The endangered species, The Red-crowned Crane and the White-naped Crane are vulnerable species to the disturbance for human beings. We examined the importance of CCZ for the cranes by comparing the crane's density in some CCZ-released areas, which are cranes' wintering site in Cheorwon. We also assessed influence of disturbance such as construction and greenhouses on core habitats of cranes. Our study results suggested that the construction and reclamation in the CCZ shrunk core habitat area while increasing core area of far from the construction and reclamation area. The CCZ has been set since March, 2011 and the number of greenhouse has rapidly increased after 2012. As the number and size of greenhouse in the area where designation of CCZ was cancelled increased, foraging area of cranes diminished. Although the area where designation of CCZ was cancelled seemed to have more human disturbance than CCZ, the foraging density of cranes did not decline and even that of white-naped cranes increased. This could be the influence of artificial food supply at their roosting site. In conclusion, if the area of CCZ decline continuously in the future, density of cranes would decrease.

• The Sea:JOURNAL OF THE KOREAN SOCIETY OF OCEANOGRAPHY
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• v.29 no.2
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• pp.116-138
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• 2024

This study presents a new tool and protocol to assess the impact of 'Marine Invasive and Harmful Species' (MIHS) on marine environments and socio-economic aspects. It addresses shortcomings in the Marine Ecosystems Conservation and Management Act in South Korea by proposing an impact assessment framework divided into marine environmental and socio-economic groups. Six distinct evaluation categories are included in each group, and a semi-quantitative five-step scale is utilized to provide a flexible approach, addressing a variety of issues from ecological disturbances to effects on health and property. The assessment tool is applied through a systematic five-stage process based on the Delphi method. This approach posters collaboration among a diverse sets of experts and stakeholders, enabling a comprehensive evaluation that incorporates various perspectives. The study also examines strategies to effectively manage uncertainties and improve the consistency of the outcomes. The application of this assessment protocol is expected to be crucial in quantifying the ecological damage caused by MIHS and in identifying management and prevention priorities. The ultimate aim of this evaluation process is to aid decision-makers in developing strategies to preserve the marine ecosystem and mitigate socio-economic impacts.

• Journal of the Korea Society of Computer and Information
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• v.16 no.12
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• pp.23-31
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• 2011

The simple bacteria cooperative optimization (sBCO) algorithm that we developed as one of optimization algorithms has shown relatively good performances, but their performances were limited by step-by-step movement of individuals at a time. In order to solve this problem, we proposed a new method that assigned a speed to each individual according to its rank and it was confirmed that it improved the performances of sBCO in some degree. In addition to the assigning of speed to the individuals, we employed a new mutation operation that most existing evolutionary algorithms used in order to enhance the performances of sBCO in this paper. A specific percent of bad individuals are mutated within an area that is proportion to the rank of the individual in the mutation operation. That is, Gaussian noise of large standard deviation is added as the fitness of individuals is low. From this, the probability that the individuals with lower ranks can be located far from its parent will be increased. This causes that the probability of falling into local optimum areas is decreased and the probability of fast escaping the local optimum areas is increased. From experimental results with four function optimization problems, we showed that the performances of sBCO with mutation operation and individual speed were increased. If the optimization function is quite complex, however, the performances are not always better. We should devise a new method for solving this problem as a further work.

• Journal of the Korean Society of Propulsion Engineers
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• v.11 no.1
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• pp.1-10
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• 2007

Three dimensional structures of detonation waves propagating in a square tube were investigated using a high resolution CFD code coupled with a conservation equation of reaction progress variable and an one-step irreversible reaction. The code were parallelized based on domain decomposition technique using MPI library. The computations were carried on an in-house Windows cluster with AMD processors. Three-dimensional unsteady analysis results in the smoked-foil records caused by the instabilities of the detonation waves, which showed the rectangular and diagonal modes of detonation instabilities depending on the initial condition of disturbances and the spinning detonation for case of small reaction constant.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.31 no.8
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• pp.702-710
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• 2007

Direct numerical simulation (DNS) is performed to investigate suppressed wake transition and occurrence of lock-on in the wake of a circular cylinder disturbed by sinusoidal perturbation at the Reynolds number of 220 (A-mode instability regime). The sinusoidal perturbation, of which the frequency is near twice the natural shedding frequency, is superimposed on the free stream velocity. It is shown that the wake transition behind the circular cylinder can be suppressed due to the perturbation of the free stream velocity. This change causes a jump in the Strouhal number from the value corresponding to A-mode instability regime to the value corresponding to retarded wake transition regime (extrapolated from laminar shedding regime) in the Strouhal-Reynolds number relationship. As a result, vortex shedding frequency is locked on the perturbation frequency depending not on the natural shedding frequency but on the modified shedding frequency.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1996.10a
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• pp.443-449
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• 1996

헬리콥터, 팬, 프로펠러, 터이빈같이 회전익에서 유체역학적 소음이 발생하는 장치의 설계에 있어서는 공기 역학적 성능 분석과 함께 소음에 대한 해석이 절대적으로 필요하다. 근래에 들어와서 소음에 대한 관심이 급격히 증가하고 공항 주변에서의 국제적인 규약들은 낮은 소음 수준(low noise level)을 규정하고 있으며, 이에 따라서 소음을 감소시키려는 연구가 매우 활발히 진행되고 있는 실정이다. 더욱이 컴퓨터의 냉각 팬을 비롯한 공조기기 및 산업기기에 사용되는 회전기계에서 발생되는 소음의 저감은 보다 더 쾌적한 환경을 요구하는 사회적 요구에 부합하면서 공력소음의 연구 분야가 더 넓어지고 있다. 본 논문에서는 소음예측 방법중의 하나인 음향상사(acoustic analogy)를 주파수 영역 방법(frequency domain method)을 이용하여 헬리콥터 블레이드의 고속 충격소음(High Speed Impulsive Noise)을 해석한다. 고속 충격소음은 블레이드-와류 상호작용 소음과 더불어 헬리콥터의 지배적인 소음원으로서 깃끝 속도가 큰 전진 수평비행(forward level flight)또는 제자리 비행(hovering flight)시 발생하는 소음으로 블레이드의 깃끝 마하수(critical Mach number)보다 크거나 비슷할 경우 충격파의 교란에 의해서 일어나는 충격적인 소음을 말한다. 고속 충격소음은 고주파수 스펙트럼 성분과 큰 소음강도를 가지고 있기 때문에 날카로운 금속성의 소리를 내며 먼 거리까지 전파되는 특징을 가지고 있다.

• Proceedings of the Korea Water Resources Association Conference
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• 2019.05a
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• pp.94-94
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• 2019

보의 주요한 기능은 수위 및 유량을 조절이며, 수심을 확보하거나 하상 경사를 조절하기 위하여 설치된다. 보의 설치는 평균 흐름뿐만 아니라 강한 난류 흐름을 생성한다. 보의 실용적인 측면에도 불구하고, 이러한 흐름의 교란은 보의 상류뿐만 아니라 하류에 하상 변화를 초래한다. 이는 종종 하천의 안정뿐만 아니라 보 자체의 안전에도 영향을 미친다. 보 하류의 국부 세굴은 보를 지나는 3차원 흐름 특성을 가지는 복잡한 조직구조에서 기인한다. 특히, 이러한 흐름은 보에서 발생하는 큰 박리 흐름과 이어서 나타나는 재순환 영역 및 강한 하강류로 특징지을 수 있다. 보 하류 흐름에 관한 많은 실험 및 수치모의 연구가 수행되어왔다. 그러나 실험은 보 또는 하상과 같은 벽 경계면과 수면 근처의 세밀한 흐름 특성을 파악하기 어렵다. 또한, 기존의 RANS (Reynolds averaged navier-stokes) 모형은 조직구조와 같은 3차원 흐름 특성을 파악하기에 적합하지 않다. 본 연구에서는 큰 와 수치모의 (large eddy simulation)을 이용하여 세굴공이 발달한 경우와 그렇지 않은 경우의 보 하류의 흐름 특성을 분석하였다. 보에 의해 발생한 재순환 흐름은 세굴공이 발달하면서 그 영역이 확장되며, 재순환 흐름의 하강류의 세기는 약해지는 것을 확인할 수 있었다. 또한, 세굴공이 발달하면서 최대 세굴심의 위치는 재순환 흐름의 하단 끝 부분과 일치하는 것으로 나타났다.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.17 no.2
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• pp.159-167
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• 1992

This paper describes a feature extraction process by using a multi-layer neural network and is applied to the Korean stroke pattern for on line hand written character recognition, In the first layer the features are detected during the writing process and in the second layer the stroke specific features are extracted. A modified Masking field algorithm for direction co9nstancy has been used in this neural network and the resulting action potential of stroke specific features represents statistical distribution of the features in the on-line input stroke pattern and these results can be used in the recognition of on-line hand written Korean characters successfully.

• Journal of Astronomy and Space Sciences
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• v.12 no.2
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• pp.216-233
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• 1995

The distributions of the ionospheric conductivities, electric potential, ionospheric currents, field-aligned currents, Joule heating rate, and particle energy input rate by auroral electrons along with the characteristics of auroral particle spectrum are examined during moderately disturbed period by using the computer code developed by Kamide et al. (1981) and the ionospheric conductivity model developed by Ahn et al. (1995). Since the ground magnetic disturbance data are obtained from a single meridian chain of magnetometers (Alaska meridian chain) for an extended period of time (March 9 - April 27, 1978), they are expected to present the average picture of the electrodynamics over the entire polar ionosphere. A number of global features noted in this study are as follows: (1) The electric potential distribution is characterized by the so-called two cell convection pattern with the positive potential cell in the morning sector extending into the evening sector. (2) The auroral electrojet system is well developed during this time period with the signatures of DP-1 and DP-2 current systems being clearly discernable. It is also noted that the electric field seems to play a more important role than the ionospheric conductivity the conductivity over the poleward half of the westward electrojet in the morning sector while the conductivity enhancement seems to be more important over its equatorward half. (3) The global field-aligned current distribution pattern is quite comparable with the statistical result obtained by Iijima and Potemra (1976). However, the current density of Region 1 is much higher than that of Region 2 current at pointed out by pervious studies (e.g.; Kamide 1988). (4) The Joule heating occurs over a couple of island-like areas, one along the poleward side of the westward electrojet region in the afternoon sector. (5) The maximum average energy of precipitating electrons is found to be in the morning sector (07∼08 MLT) while the maximum energy flux is registered in the postmidnight sector (02 MLT). Thus auroral brightening and enhancement of ionospheric conductivity during disturbed period seem to be more closely associated with enhancement of particle flux rather than hardening of particle energy.

• Proceedings of the Korean Society of Propulsion Engineers Conference
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• v.y2005m4
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• pp.281-287
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• 2005

Nonlinear behaviors such as steep-fronted wave motions and a finite amplitude limit cycle often accompanying combustion instabilities have been numerically investigated using a characteristic-based approximate Riemann solver and the well-known ${\eta}-{\tau}$ model. A resonant pipe initially subjected to a harmonic pressure disturbance described the natural steepening process that leads to a shocked N-wave. For a linearly unstable regime, pressure oscillations reach a limit cycle which is independent of the characteristics of the initial disturbances and depends only on combustion parameters and operating conditions. For the 1.5 MW gas generator under development in KARI, the numerical results show good agreement with experimental data from hot-firing tests.