• Journal of Astronomy and Space Sciences
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• 제40권4호
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• pp.173-197
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• 2023

ShadowCam is a high-sensitivity, high-resolution imager provided by NASA for the Danuri (KPLO) lunar mission. ShadowCam calibration shows that it is well suited for its purpose, to image permanently shadowed regions (PSRs) that occur near the lunar poles. It is 205 times as sensitive as the Lunar Reconnaissance Orbiter Camera (LROC) Narrow Angle Camera (NAC). The signal to noise ratio (SNR) is greater than 100 over a large part of the dynamic range, and the top of the dynamic range is high enough to accommodate most brighter PSR pixels. The optical performance is good enough to take full advantage of the 1.7 meter/pixel image scale, and calibrated images have uniform response. We describe some instrument artifacts that are amenable to future corrections, making it possible to improve performance further. Stray light control is very challenging for this mission. In many cases, ShadowCam can image shadowed areas with directly illuminated terrain in or near the field of view (FOV). We include thorough qualitative descriptions of circumstances under which lunar brightness levels far higher than the top of the dynamic range cause detector or stray light artifacts and the size and extent of the artifact signal under those circumstances.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 춘계학술대회논문집
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• pp.132-136
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• 2007

In case of indoor gymnastics training floor, in view of its characteristics, since it is simultaneously required the related smooth communication between the coach and the player, also the acoustic performance regarding to the Clearness of Music, besides the sport activity, the consideration about the acoustic character has entered the stage as an indispensable element. On such viewpoint, on the object of the recently built dome-typed gymnastics training floor, after making the optimized acoustic design with the remodeling through acoustic simulation, by means of measurement and valuation on human's psychological(sensual) degree utilizing Auralization that enables to experience the virtual sound field at the stage of design, this thesis has attempted to survey of the acoustic satisfaction degree and its reaction about the gymnastics training floor. As the result of investigation about the research on the space of object, it could be known that the valuation regarding to the acoustic performance of 'After-Improvement' was distinctly more refined than that of 'Before-Improvement'. It is now considering that such result of the study can be utilized as the useful data which enables to improve the retrenchment effect of the construction cost as well as the acoustic capability, by means of the prediction control on the acoustic problem from the stage of design, for the occasion when the similar indoor sport gymnasium is planning to build for the near future.

• 한국음향학회지
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• 제18권8호
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• pp.32-41
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• 1999

본 논문은 chirp신호와 두 개의 근거리 청음기를 이용한 해저퇴적층의 음향학적 특성치 역산기법을 제시한다. 역산문제를 확률론적 모델로 정식화하고, 역산의 해를 역산인자의 a priori분포와 유사도함수의 곱으로 표현되는a posteriori 확률분포로 정의하였다. 퇴적층의 음속과 층두께의 a priori정보를 파형 매칭 기법으로 추정한 후 다수의 퇴적층이 존재하는 환경모델을 부분퇴적층모델로 치환하고, 계측신호와 모의신호의 L₂노음을 이용하여 정의된 목적함수에 대해 반복적인 유전자알고리즘 탐색을 수행하여 탐색공간의 축소로 인한 탐색효율과 결과의 향상을 얻었다. A posteriori 확률분포의 다중적분의 형태로 정의되는 인자의 주변확률분포와 평균의 추정은 유전자알고리즘의 탐색과정에서 선택된 탐색점들을 이용하여 수행되었다. 제시된 역산기법의 검증을 위해 두 가지 퇴적층 환경모델을 설정하고 잡음을 첨가한 합성신호에 대해 역산기법을 적용하여 역산해를 추정하였고 역산결과로부터 본 역산기법의 유용성을 확인하였다.

• 한국음향학회지
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• 제37권4호
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• pp.196-205
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• 2018

본 논문은 선박소음 데이터에 음선 역전파 기법을 적용하여 수동 선박 위치 추정 알고리듬을 제시한다. 기존의 방법 [S. H. Abadi, D. Rouseff and D. R. Dowling, J. Acoust. Soc. Am. 131, 2599-2610 (2012)]은 음선 기반 블라인드 디컨벌루션 및 음선 역전파 기법을 활용하여 배열의 기울기가 없는 근거리 환경에서 음원의 위치를 추정하였다. 하지만 위 방법은 배열의 기울기에 따른 위치 추정 오차가 크게 발생한다는 단점이 존재한다. 이를 극복하기 위해 본 논문에서는 음선 기반 블라인드 디컨벌루션 및 음선 역전파 기법을 사용하되, 배열의 기울기를 보정하여 음원의 위치를 추정할 수 있는 알고리듬을 제안한다. 제안된 알고리듬의 성능은 SAVEX15(Shallow-water Acoustic Variability EXperiment in 2015)해상 실험의 선박소음 데이터를 이용하여 검증하였다.

• 비파괴검사학회지
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• 제22권2호
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• pp.187-192
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• 2002

서로 연결되어 있는 강관의 결함을 검사할 수 있도록 하기 위한 개폐식 탐촉자를 제작하였다. 본 탐촉자는 기존의 외삽형 와전류 탐촉자로서는 탐상이 불가능한 설치 가동중인 튜브류의 검사를 위한 것이다. 리본 케이블과 커넥터로 구성된 여기 코일은 접합/단락이 가능하게 하였으며 감지 코일은 튜브 외벽 근처에 원주 방향으로 어레이 형태로 배치하였는데 여기 코일로부터 튜브 직경의 약 1.5배정도 떨어진 위치이다. 제작된 탐촉자를 강관에 적용한 결과, 감도나 결함 크기 구분 등의 성능은 자기 포화형 탐촉자에 미치지 못하나 비교적 큰 결함의 발견이나 위치 파악 등에는 적용 가능한 것으로 나타났다. 크랙 형태의 표면 결함의 경우 두께의 19% 이상의 결함을 찾을 수 있었다.

• 한국소음진동공학회논문집
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• 제25권8호
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• pp.575-582
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• 2015

This paper deals with the dispersion relation of the waves sustained in a cylindrical shell submerged in the fluid. The waveguide finite method and the boundary element method are used to predict the dispersion characteristic of the cylindrical shell. The dispersion diagram of the cylinder is estimated from the eigenvalue problem and the forced vibration response. It follows that the water-loading leads to the decrease of the cut-on frequencies and the phase speeds of the bending waves. On the contrary, the longitudinal waves and the torsional waves are hardly affected by the fluid, and therefore the order of the cut-on frequencies of the waves is changed. The acoustic dispersion diagram is also estimated from the forced acoustic response to identify the characteristics of the wave radiated to the fluid. It follows that the acoustic waves on and near the surface of the cylinder are the same as those in the structure. But at the far field the acoustic waves caused by subsonic waves e.g., the bending waves disappear as the increase of the distance. Conclusively, the characteristics of waves in cylindrical shells are significantly affected by water-loading in terms of the cut-on frequency, the wave speed, the order of the cut-on and radiation.

• 천문학논총
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• 제27권4호
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• pp.363-365
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• 2012

We report a search for fluctuations of the sky brightness toward the North Ecliptic Pole with AKARI, at 2.4, 3.2, and $4.1{\mu}m$. The stacked images with a diameter of 10 arcminutes of the AKARI-Monitor Field show a spatial structure on the scale of a few hundred arcseconds. A power spectrum analysis shows that there is a significant excess fluctuation at angular scales larger than 100 arcseconds that cannot be explained by zodiacal light, diffuse Galactic light, shot noise of faint galaxies, or clustering of low-redshift galaxies. These findings indicate that the detected fluctuation could be attributed to the first stars of the universe, i.e., Population III stars.

• 터널과지하공간
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• 제7권2호
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• pp.116-129
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• 1997

The objective of this study is to predict the minimization effect of the noise and vibration during the construction and the train operation regarding to the design modification of the Taegu Subway Line No. 1. It was suggested optimal control blasting methods to reduce the causing vibration Nuance to the resident in City Taegu and also proposed the better governing method to decrease the environmental hazard to the near buildings and residents during the train operation. When the high-density gaseous reaction of explosion products exerts a high pressure in motion outward, a dynamic stress field will be created in the surrounding buildings. Therefore, in the region close to the charge, permanent damage begins to occur at a great critical level of partial velocity, that is difficult from different structure as working conditions. It is reliable to predict that the damages could be reduced if we know the peak velocity and the exact reasons through the conducting of detail studies of structural analysis of the related buildings with the optimal blasting designs. A blasting technique should be deemed to take advantage of the reduction of damage of the surrounding rocks and structures to improve the in-city blasting. This is a typical in-city blasting operation where success depends on closely controlling the ground vibrations in case of better designed blasting methods. There are techniques that can be applied to prevent large vibrations from damaging the important buildings through the Route Modification of the Taegu Subway Line No. 1.

• Ocean and Polar Research
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• 제37권3호
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• pp.235-247
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• 2015

The main purpose of procuring the oceanographic research vessel with state-of-the-art technology is to provide a floating laboratory to conduct field work on the global oceans. The vessel should be properly utilized to locate and evaluate unexplored natural resources as well as to contribute international efforts to better understand and manage global environmental issues. Top priorities in the vessel design are high safety standards, noise and vibration control efficiency, and effective application of research equipment. For the accomplishment of all activities, the vessel length over all should be extended ~100 m with a gross tonnage of ~5,900 ton. In particular, the dynamic positioning system II will essentially operate at sea state 6. The high efficiency emissions reduction system will also be adopted in preparation for entry into force of 3rd exhaust emission control (Tier III). About 130 navigational and scientific instruments will be installed. The final design and model test of the new research vessel were reviewed and completed, respectively, in 2014. Currently, the ship is being built on schedule and expected to be delivered in December 2015. Within the near future, the new vessel will assume the role of carrying out multidisciplinary oceanographic researches of the highest standards in a technologically advanced and environment friendly manner.

• 한국군사과학기술학회지
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• 제12권4호
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• pp.540-547
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• 2009

In the near future, military robots are likely to be substituted for military personnel in the field of battle. The power system of a legged robot is considerably more complex than the one used for a land vehicle because of the coordination and stability issues due to the large number of degree of freedom. In this paper, a servovalve-piston combination system for a straight-line motion of robot leg is modeled as three degree of freedom based on double inputs and single output transfer function. The output is the displacement of piston from neutral. The inputs are valve displacement from neutral and arbitrary load force in this system. LQR(Linear Quadratic Regulator) technique is applied in order to achieve robust stability and fast responses of the system. The Kalman filter loop, rejection of disturbance and noise, riccati equation, filter gain matrix, and frequency domain equality are analyzed and designed.