• Transactions of the Korean Society of Mechanical Engineers A
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• v.36 no.6
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• pp.653-663
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• 2012

The study considers the high maneuverability flight and path optimization is conducted to investigate the appropriate generation of the lift and thrust considering the angle of the stroke plane. The path optimization problem is defined according to the various purposes of the high maneuverability flight. The flying purposes are to maximize thrust force, lift force and both lift and thrust forces. The flapping motion of the airfoil is made by a combined sinusoidal plunging and pitching motion in each problem. The optimization process is carried out by using well-defined surrogate models. The surrogate model is determined by the results of two-dimensional computational fluid dynamics analysis. The Kriging method is used to make the surrogate model and a genetic algorithm is utilized to optimize the surrogate model. The optimization results show the flapping motions for the high maneuverable flight. The effects on the generation of lift and thrust forces are confirmed by analyzing the vortex.

• Journal of Korea Water Resources Association
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• v.30 no.6
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• pp.597-610
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• 1997

One-dimensional numerical models using finite difference methods for unsteady sediment transport on alluvial river channel are developed. The Preissmann implicit scheme and the Lax-Wendroff two-step explicit scheme with the Method of Characteristics for water motion and a forward time centered space explicit scheme for sediment motion are developed to simulate the sediment transport rate and the variation of channel bed level. The program correctness of each model is successfully verified using volume conservation tests. The sensitivity studies show that higher peak stage level, steeper channel slope and longer flooding duration produce more channel bed erosion. and median grain size, $D_{50}=0.4mm$ give maximum volume loss in this study. Finally, the numerical models are found to produce reasonable results from the various sensitivity tests which reveal that the numerical models have properly responded to the changes of each model parameter.

• Journal of the Korean Society for Marine Environment & Energy
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• v.2 no.1
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• pp.40-48
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• 1999

Wave absorbing system is needed at various kinds of wave basins (wave flume, towing tank, square tank) for the model test related to the ocean engineering. In this paper, the performance of wave absorbing system with new concept is estimated throughout the experiments. Herein, the wave absorbing system is designed by punching plate with a given porosity which is installed horizontally and submerged near the water surface. As the incident wave generated by a wave maker advances above a punching plate, the strong jet flow is formed near a hole of punching plate. As a result, wave energy is dissipated into heat energy, Systematic model tests were conducted at KRISO to verify the performance of the wave absorber using a punching plate. It was found that the reflection coefficient of wave absorber is deeply dependent on both the porosity and the submerged depth of a punching plate. Inclined installation of a punching plate shows better performance than a horizontal one within a certain inclined angle.

• Journal of the Korean Geotechnical Society
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• v.21 no.2
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• pp.121-126
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• 2005

It is not uncommon to observe tilt of buildings and towers as a result of unexpected differential foundation settlements. Over the years, a number of engineering methods including the soil extraction technique have been attempted to reduce inclination of buildings and towers. In this research, a series of novel geotechnical centrifuge model tests by using a state-of-the-art in-flit robotic manipulator have been conducted to study key factors which govern the restoration of building tilts. In the centrifuge model tests, the robotic manipulator was used to drill and extract soil in-flight near an initially tilted model building. The soil extraction was to induce stress release, thereby mitigating the inclination of the model building. Insights into the effects of different configurations, soil density and sequences of drilling observed during the centrifuge model tests on the restoration of the model building are to be investigated.

• The Journal of the Acoustical Society of Korea
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• v.20 no.6
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• pp.75-81
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• 2001

In this paper we analyzed the localization error of near-field detection algorithm in the sea. The near-field detection algorithms using triangulation and wavefront curvature basically assume a signal in two dimension of bearing and range. But the assumption causes localization error because there is three dimension of bearing, range, and depth in the sea. Even through three dimensional effect is considered, the localization error is occurred if multipath propagation in the sea is ignored. To analyze the localization error in the sea, we simulate the near-field localization using acoustic propagation model and focused beamforming considering wavefront curvature. The simulation results indicate that localization error always occurs in the sea and the error varied with sound velocity profile, water depth, bottom slope, source range, etc.

• Journal of the Korean Wood Science and Technology
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• v.12 no.4
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• pp.47-52
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• 1984

본(本) 연구(硏究)는 연필향나무(Juniperus virginiana L.) 지재(技材)내에 형성(形成)된 압축이상재(壓縮異常材)(compression wood) 및 대응재(對應材)(opposite wood)에 관한 주사전자현미경적(走査電子顯微鏡的)인 특성(特性)을 비교(比較)하기 위하여 수행(遂行)되었는데 그 결과(結果)는 다음과 같다. 1. 압축이상재(壓縮異常材)의 가도관(假導管) 이행(移行)은 연륜(年輪)의 경계부(境界部)를 제외하고는 점진적(漸進的)이나 대응재(對應材)의 가도관(假導管) 이행(移行)은 급진적(急進的)이다. 그리고 대응재(對應材)에 있어서 추재율(秋材率)은 변이(變異)가 심하며 추재(秋材) 가도관(假導管)의 배열(排列)은 불균일(不均一)하다. 2. 압축이상재(壓縮異常材) 및 대응재(對應材)의 가도관(假導管)은 그 횡단면(橫斷面)의 모양(模樣)이각각 둥근형 및 모난형이다. 그리고 압축이상재(壓縮異常材)와 대응재(對應材) 모두에서는 큰 가도관(假導管)과 작은 가도관(假導管)이 혼재(混在)되어 있으나 나선상(螺旋狀)의 째짐이 가도관(假導管)의 막(膜)에 존재(存在)하지 않으며 세포간극(細胞間隙)은 경계부(境界部)를 지니는 경우가 있는데 압축이상재(壓縮異常材)에만 존재(存在) 한다. 3. 분야막공(分野膜工)에 있어서 압축이상재(壓縮異常材)의 막공구(膜孔口)는 대응재(對應材)의 것보다 가도관(假導管)측의 막공록(膜孔綠)이 더 넓기 때문에 더 좁으며 경사(傾斜)가 급한 타원형(楕圓形)을 나타낸다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.22 no.1
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• pp.10-17
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• 2010

The interaction of oblique incident waves with a porous dual semi-cylindrical structure is investigated under the assumption of linear potential theory. The porous dual semi-cylindrical structure consists of two concentric bottom-mounted cylindrical structures that are porous in front half and transparent in back half. By changing porosity, gap, and wave characteristics(wave frequencies, incidence angle), the wave blocking performance as well as the wave loads and the wave run-up are obtained. As a convenient measure of overall wave blocking performance, the root mean square(R.M.S.) of the wave elevation in a sheltered region is used. It is found that the porous semi-cylindrical structure may significantly reduce the wave response in a sheltered region and the wave forces decrease largely compared to the impermeable structure. The dual structure is more effective in reducing the wave response in a sheltered region than the mono type in the region of high frequencies.

• Journal of the Korean Geographical Society
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• v.33 no.3
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• pp.355-364
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• 1998

Flume experiments are conducted to describe the channel morphology at a tributary junction and to examine the influence of channel arrangements and hydrologic conditions on the channel morphology. When flow momenta of two tributaries are equal, a receiving stream tends to align with an axis bisecting junction angle. It causes lateral migration of a receiving stream according to an initial channel arrangement. As a result, the post-fonfluent channel morphology varies with plan geometry of a confluence such as symmetry, transition and asymmetry. Bed scour is the most notable morphology within a junction site. Its shape is characterized by steep walls which are primarily influenced by junction angle. Key control of scour dimension is also junction angle. Although the principle of accordant junction has been undoubtedly accepted, discordance is commonly developed at model and natural stream confluences. Unit discharge ratio of confluent streams is the most crucial factor because both discharge and sediment concentration ratios have an effect on discordance at a junction.

• Journal of the Korean Crystal Growth and Crystal Technology
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• v.10 no.4
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• pp.318-323
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• 2000

The intercalated compounds of alkylsulfonates into hydrated zinc were synthesized. From the high temperature powder X-ray diffraction (HTXRD), FT-IR, and molecular size, the temperature dependence of orientation for the intercalated alkylsulfonates were determined. In the temperatures range 1, alkylsulfonates were intercalated into hexa aqua zinc layer with the bilayer structure of $32.9^{\circ}$angle for ${Zn(H_2O_4]^{2+}[C_nH_{2n+1}SO_3]_2\;^-$. In the temperatures range 2, alkylsulfonates were intercalated into tetra aqua zinc layer with the bilayer structure of $55.2^{\circ}$angle for ${Zn(C_nH_{2n+1}SO_3)_2$. In the temperatures range 3, alkylsulfonates were directly bonded to zinc ion with the bilayer structure of $76.5^{\circ}$angle for ${Zn(C_nH_{2n+1}SO_3)_2$.

• The KIPS Transactions:PartB
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• v.13B no.5 s.108
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• pp.525-532
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• 2006

This paper proposes a new class of image restoration on the Ising modeled binary 'Takbon' image by the flexible line-fitting ICM(Iterated conditional modes) method. Basically 'Takbon' image need be divided into two extreme regions, information and background one due to its stroke combinations. The main idea is the line process, comparing with the conventional ICM approaches which were based on partially rectangular structured point process. For calculating geometrical mechanism, we have defined line-fitting functions at each current pixel array which form the set of linear lines with gradients and lengths. By applying the Bayes' decision to this set, the region of the current pixel is decided as one of the binary levels. In this case, their statistical reiteration for distinct tracking between intra and extra region offers a criterion to decide the attachment at each step. Finally simulations using the binary 'Takbon' image are provided to demonstrate the effectiveness of our new algorithm