• Journal of the Korea Institute of Military Science and Technology
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• v.13 no.2
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• pp.211-217
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• 2010

This paper introduces the Hull Mounted Sonar Vertical Scanning(HMS Verscan) technique to overcome the limitation of target detection in short range shadow zone. Numerical experiments were done with the HMS Verscan taking advantage of the vertical beamforming technique for two-dimension hydrospace(range-depth). For numerical experiments, ray model and high-frequency monostatic reverberation model were used. HMS Verscan increased a sound pressure level at the short range shadow zone through reflections at the sea surface and seafloor. Inclusion of the boundary scattering improved target detection due to the sound reflected into the shadow zone.

• The Journal of Korean Institute of Communications and Information Sciences
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• v.39C no.11
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• pp.1011-1022
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• 2014

Currently, the wireless network environment of air node is constructed mainly of ground relay station. However, as the Korean Peninsula is composed of 70% mountainous region, there are multiple shadow zones. This is calling for effective measures to prevent aircraft from losing communication link during low-mid altitude missions. In this article we propose the utilization of Bezier Curve for estimation of aircraft flight path and control method for entering shadow zone. This method successfully estimated aircraft track, and analyzed the existence, disseminated the warning, and took measures to avoid the shadow zone before entering. This article, suggested after simulated experiments, proves that the method enables seamless communication during air operations.

• Tunnel and Underground Space
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• v.3 no.2
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• pp.109-117
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• 1993

The existence and exact location of cavity is very important for the stability of the large underground storage house or building. Numerical method such as finite element method and finite diference methods are widely used because of model's complexity. Preliminary tests such as calculation step test, mesh size test and model size test were tried. Upper shadow zone and lower shadow zone can be calculated from 50% amplitude level of measuring data. From these statistical methods, the calculatied position of cavity coincided nearly with actual position of model testing cavity.

• Journal of The Geomorphological Association of Korea
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• v.26 no.2
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• pp.29-38
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• 2019

This study tries to reveal influence of artificial structure construction on shoreline change using DSAS 4.3. Before breakwater extension at the Gungchon Port, beaches at the study area were dominated by long-term erosion and especially, severe shoreline retreat was prevailed at the Wonpyeong Beach that is opened to offshore. During 2 years after the extension leading formation of shadow zone, the Gungchon Beach was rapidly developed due to sand supply to the shadow zone and then stabilized. The shadow zone only affected the northern part of the Wonpyeong Beach, while beaches from the southern part of the Wonpyeong Beach to the Munam Beach was little affected. Beach nourishment and groin construction led beach development at the northern part of the Wonpyeong Beach, while beach erosion from the southern part of the Wonypeong Beach to the Munam Beach was caused by the groin. This study suggests that sufficient consideration before coastal structure construction should be made regardless of purposes.

• Transactions of the Korean Society of Mechanical Engineers
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• v.14 no.5
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• pp.1222-1233
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• 1990

The formation and oxidation processes of soot particles in a diesel flame were investigated with a rapid compression machine. A cloud of soot particles was successfully visualized by means of the instantaneous laser shadow photographs technique and the equivalence ratio of the soot formation zone was estimated from a measured fuel concentration distribution in a nonevaporating spray. The temporal and spatial variation of soot concentration in the flame was also correlated with the rate of heat release. Soot particles appears first in a region near the flame tip when diffusion combustion period starts, and its concentration is a maximum at about the end of injection, then decreases due to oxidation. The reason for soot being formed in a fuel lean region near the flame tip is the evaporated fuel requires time to be pyrolized as it travels through the burning fuel rich zone towards the flame tip.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.04a
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• pp.97-99
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• 2013

We introduced an earthquake-resistant design using acoustic rnetamaterials. There are two way in that field: one is a cloaking method and the other is a shadow zone method of seismic waves. Cloaking is a general property of a wave that changes the direction depending on the refractive index. Metamaterials control the propagation and transmission of specified parts of the wave and demonstrate the potential to render an object seemingly invisible. The shadow zone is a method of negative modulus using many huge resonators and it attenuates the amplitude of the wave exponentially. We compared and explained the fimdarnental principles of the two methods.

• Journal of the Korean Association of Geographic Information Studies
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• v.9 no.1
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• pp.127-136
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• 2006

Shaded relief is used in the analysis of digital terrain model, but accurate shadow zone has not been affirmed on account of idea only shadow of terrain that would be in shadow are shaded. This study is to analyze each display difference of a digital terrain model by grasping the shadow characteristics of terrain and comparing shaded relief function used terrain display of GIS with a rendering technique. After terrain with road in subject area is selected and created to digital terrain model of TIN, shaded relief and rendering according to altitude and azimuth of the sun at 9:00 am and 3:00 pm is applied. As the results, only backward portions of the terrain that is in shadow from the sunlight are shaded in case of shaded relief. The rendering created the shadow, which is cast by terrain features. By these mutual comparison, this study represented data for understanding of shaded relief. And it is expected that the rendering method could be used to analyze sunshine influence.

• Proceedings of the Acoustical Society of Korea Conference
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• autumn
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• pp.437-440
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• 2004

HMS(Hull Mounted Sonar) 운용 시 수중음속구조의 영향에 의한 음파가 경계면(해저면, 해수면)의 반사를 통해서 근거리 음영구역(short range shadow zone)을 발생시킨다(그림 1). 따라서 본 논문에서는 다양한 수중음파탐지 무기체계 가운데 특히 단상태 (monostatic) 조건일 때 HMS에 의해 발생하는 근거리 음영구역을 최소화하는 방안을 연구하였다. 즉, 2차원 수중공간 (수심-거리)에서 빔형성기법 (beamforming)을 이용한 HMS Vertical Scanning (HMS Verscan) 기법을 제안하여 수치 실험을 수행하였다. 수치실험을 위해 HMS 운용환경에 근접한 고주파 음선모델(BELLHOP)과 잔향음 모델(HYREV)을 이용하였다. 그 결과 HMS Verscan 기법은 수평방향의 음파방사에 의해 주로 발생하는 근거리 음영구역으로 해저반사를 통하여 음파를 전달시켰고, 근거리 음영 구역에 숨어있는 표적의 탐지가능성을 높였다. 또한 실제 산란환경을 고려한 수치실험 결과에서도 부분적으로 표적이 탐지가 됨으로써 HMS Verscan 기법의 근거리 음영구역의 감소효과를 확인하였다.

• Journal of Korean Society of Coastal and Ocean Engineers
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• v.8 no.4
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• pp.297-304
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• 1996

The purpose of this study is to observe the applicability of parabolic mild-slope equations allowing relatively large angles of wave propagation based on the use of a Pade approximant or minimax approximation and also the applicability of the models with nonlinearity of diffracted waves in the shadow zone behind coastal structures. To accomplish these objectives, numerical solutions are obtained from the above parabolic models and are compared with the results from Watanabe and Maruyama's(1984) hydraulic model test on the wave field with an impermeable detached breakwater. From this study, it is found that computed wave heights increase for the nonlinear results in comparison to the linear results due to the increased diffraction effect across the geometric shadow boundary. The model with a larger aperture with respect to the principal direction was found to spread laterally to a much greater degree where spreading angle (diffraction effect) is relatively large. which causes a distortion in the overall results due to the error accumulated by the approximation of wave length.

• Journal of the Korean Institute of Telematics and Electronics A
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• v.33A no.5
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• pp.85-93
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• 1996

The far-zone scattered field patterns of a hyperbolic reflector antenna are analyzed by using uniform geometrical theory of diffraction(UTD). The main objective of this paper is to obtain the higher order diffraction contributions which provide the continuity over the shadow boundaries of the first order solution. to obtain the scattered magnetic field characteristics, the scattered field components of the secodn-order diffraction, diffraction-reflection, diffraction-reflection-diffraction terms are added to the result of the previous research. The results of the present research are compared to those of the first order solution and the method of moments. One can observe the improvemtn of the current approach over the first order solution. also, the results of the present method agree very well with those of the moment methods especially in the transition regions near the first order diffraction shadow boundaries.