• 한국음향학회지
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• 제21권4호
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• pp.339-438
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• 2002

본 논문은 3차원으로 표현된 가상의 옥외 공간에서 소음이 전파되는 방법을 컴퓨터로 시뮬레이션하기 위한 방법을 제시한다. 소음은 음원에서 발생하여 수음자로 직접전파 혹은 많은 반사를 거쳐서 간접적으로 전파되기도 한다. 결과적으로 수음자에 들리는 소음은 음원과 수음자 사이의 최단 거리, 반사 거리, 반사횟수 등에 따라 영향을 받으며, 반사시키는 물체의 특성 및 주파수에 따라서 전달되는 양의 차이가 있을 수 있다. 본 논문에서는 음원에서 수음자에 전달되는 소리를 추적함에 있어서 정방향 추적 (forward tracing)을 사용하는 방법에 대한 문제점들을 제시하고, 다른 접근방법인 기하학적 계산에 의한 시뮬레이션 방법을 제시한다. 즉 소리 추적벡터 (tracing vector)를 정의함에 있어서 음원에서 발생하는 소리벡터를 추적하는 정방향 추적 및 음원과 수음자간 발생 가능한 전파 경로를 기하학적으로 계산하는 기하학적 추적 방법에 의한 시뮬레이션 방법을 제시한다. 기하학적 계산 방법은 정방향 추적을 사용하는 경우와 비교할 때 불필요하게 버려지는 추적 벡터의 수를 현저히 줄일 수 있으므로 효과적 이라고 할 수 있다. 실험결과는 가상현실 모델링 언어 (VRML: Virtual Reality Modeling Language)로 가시화해서 보다 명확하게 알아볼 수 있다. 본 방법은 3차원 가상현실 (virtual reality)이나 멀티미디어 (multimedia), 또는 실내, 실외 등의 소음측정 시뮬레이션에도 적용이 가능하므로 확장성이 좋다고 할 수 있다.

• 한국지구과학회지
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• 제40권4호
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• pp.353-381
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• 2019

The general world model for homogeneous and isotropic universe has been proposed. For this purpose, we introduce a global and fiducial system of reference (world reference frame) constructed on a (4+1)-dimensional space-time, and assume that the universe is spatially a 3-dimensional hypersurface embedded in the 4-dimensional space. The simultaneity for the entire universe has been specified by the global time coordinate. We define the line element as the separation between two neighboring events on the expanding universe that are distinct in space and time, as viewed in the world reference frame. The information that determines the kinematics of the geometry of the universe such as size and expansion rate has been included in the new metric. The Einstein's field equations with the new metric imply that closed, flat, and open universes are filled with positive, zero, and negative energy, respectively. The curvature of the universe is determined by the sign of mean energy density. We have demonstrated that the flat universe is empty and stationary, equivalent to the Minkowski space-time, and that the universe with positive energy density is always spatially closed and finite. In the closed universe, the proper time of a comoving observer does not elapse uniformly as judged in the world reference frame, in which both cosmic expansion and time-varying light speeds cannot exceed the limiting speed of the special relativity. We have also reconstructed cosmic evolution histories of the closed world models that are consistent with recent astronomical observations, and derived useful formulas such as energy-momentum relation of particles, redshift, total energy in the universe, cosmic distance and time scales, and so forth. The notable feature of the spatially closed universe is that the universe started from a non-singular point in the sense that physical quantities have finite values at the initial time as judged in the world reference frame. It has also been shown that the inflation with positive acceleration at the earliest epoch is improbable.

• International Journal of Aeronautical and Space Sciences
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• 제17권2호
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• pp.204-213
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• 2016

A differential game theory based approach is used to develop an automated maneuver generation algorithm for Within Visual Range (WVR) air-to-air combat of unmanned combat aerial vehicles (UCAVs). The algorithm follows hierarchical decisionmaking structure and performs scoring function matrix calculation based on differential game theory to find the optimal maneuvers against dynamic and challenging combat situation. The score, implying how much air superiority the UCAV has, is computed from the predicted relative geometry, relative distance and velocity of two aircrafts. Security strategy is applied at the decision-making step. Additionally, a barrier function is implemented to keep the airplanes above the altitude lower bound. To shorten the simulation time to make the algorithm more real-time, a moving horizon method is implemented. An F-16 pseudo 6-DOF model is used for realistic simulation. The combat maneuver generation algorithm is verified through three dimensional simulations.

• 한국실내디자인학회논문집
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• 제22호
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• pp.123-131
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• 2000

The purpose of this study is to propose a new design concept and properties within new paradigm. Contemporary students of architectural design seem to redefine the mechanic and reductive approach to design method based upon Euclidean geometry. In this study, the organic space-time and holistic view-point that constitutes the background for all this is radically different from the modern design. It consists of three sections as follow: First, it presents a concept of complex system and properties of complexity that we find in new natural science and tries to combine that news geometry with architectural design to provide a methodological basis for morphogenesis and transformation. Second, the complexity in architecture is defined as a fractal shape, folded space, and irreducible organic system that cannot be fully understood by modernist idea of architecture. Third, the complexity in architecture is strategy based on the electronic paradigm that would enable the emergence of creative possibility. The complexity theory offer new insights to explain not only natural laws but also define dynamic architecture. In fine, this study places a great emphasis on the organic world-view to the spatial organization, which I hope will contribute to generating a greater number of creative possibilities for design.

• Smart Structures and Systems
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• 제23권4호
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• pp.359-371
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• 2019

As part of a structural health monitoring system, the relative geometric relationship between a ship and bridge has been recognized as important for bridge authorities and ship owners to avoid ship-bridge collision. This study proposes a novel computer vision method for the real-time geometric parameter identification of moving ships based on a single shot multibox detector (SSD) by using transfer learning techniques and monocular vision. The identification framework consists of ship detection (coarse scale) and geometric parameter calculation (fine scale) modules. For the ship detection, the SSD, which is a deep learning algorithm, was employed and fine-tuned by ship image samples downloaded from the Internet to obtain the rectangle regions of interest in the coarse scale. Subsequently, for the geometric parameter calculation, an accurate ship contour is created using morphological operations within the saturation channel in hue, saturation, and value color space. Furthermore, a local coordinate system was constructed using projective geometry transformation to calculate the geometric parameters of ships, such as width, length, height, localization, and velocity. The application of the proposed method to in situ video images, obtained from cameras set on the girder of the Wuhan Yangtze River Bridge above the shipping channel, confirmed the efficiency, accuracy, and effectiveness of the proposed method.

• 한국항공우주학회지
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• 제30권2호
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• pp.91-97
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• 2002

응축영역 에너지 방정식과 기체 영역에 관한 화염모델을 사용하여 연소실 압력 강하에 반응하는 고체 추진제의 동적 소화 특성을 살펴보았다. 화염모델에서는 기체가 반응영역을 통과하는데 걸리는 시간(잔존시간, r,)이 동적 소화 특성을 결정하는 중요한 인자임을 확인하였다. 본 논문에서는 r,을 확산과 화학반응 시간의 다양한 조합으로 가정하였으며 이를 이용하여 동적 소화 특성을 살펴보았다. 또한 연소실 부피의 유한함에 따른 압력변화와 이에 대한 연소의 동적 반응도 살펴보았다. 동적 소화는 화학반응 시간보다는 확산 시간에 의하여 커다란 영향을 받는 현상임을 확인하였다. 그리고 연소실 부피가 유한한 경우가 무한한 경우보다 복잡한 동적 소화 특성을 보여주었다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1996년도 추계학술대회논문집; 한국과학기술회관, 8 Nov. 1996
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• pp.295-300
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• 1996

In this study, the dynamic instabilities of a nonlinear elastic system subjected to follower force are investigated. The two-degree-of-freedom double pendulum model with nonlinear geometry, cubic spring, and linear viscous damping is used for the study. The constant and periodic follower forces are considered. The chaotic nature of the system is identified using the standard methods, such as time histories, phase portraits, and Poincare maps, etc.. The responses are chaotic and unpredictable due to the sensitivity to initial conditions. The sensitivities to parameters, such as geometric initial imperfections, magnitude of follower force, and viscous damping, etc. is analysed. The strange attractors in Poincare map have the self-similar fractal geometry. Dynamic buckling loads are computed for various parameters, where the loads are changed drastically for the small change of parameters.

• Wind and Structures
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• 제5권5호
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• pp.441-462
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• 2002

This paper presents a practical numerical method to determine both the spatial and temporal distribution of driving rain on buildings. It is based on an existing numerical simulation technique and uses the building geometry and climatic data at the building site as input. The method is applied to determine the 3D spatial and temporal distribution of wind-driven rain on the facade a low-rise building of complex geometry. Distinct wetting patterns are found. The important causes giving rise to these particular patterns are identified : (1) sweeping of raindrops towards vertical building edges, (2) sweeping of raindrops towards top edges, (3) shelter effect by various roof overhang configurations. The comparison of the numerical results with full-scale measurements in both space and time for a number of on site recorded rain events shows the numerical method to yield accurate results.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제13권6호
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• pp.2893-2907
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• 2019

Wireless mobile communication systems in subway tunnels have been widely researched these years, due to increased demand for the communication applications. As a result, an accurate model is essential to effectively evaluate the communication system performance. Thus, a neoteric three-dimensional (3D) geometry-based stochastic model (GBSM) is proposed for the massive multiple-input multiple-output (MIMO) fading channels in tunnel environment. Furthermore, the statistical properties of the channel such as space-time correlation, amplitude and phase probability density are analyzed and compared with those of the traditional two-dimensional (2D) model by numerical simulations. Finally, the ergodic capacity is investigated based on the proposed model. Numerical results show that the proposed model can describe the channel in tunnels more practically.

• 한국실내디자인학회논문집
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• 제16권6호
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• pp.11-18
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• 2007

Edward Hopper is one of the great American artists in the 20th Century. In the field of art, it seems that his paintings are thoroughly analyzed In terms of human alienation and emotional aspects in various ways. However, in his numerous paintings, highly interesting spatial aspects can be found. Purpose of this study is to analyze some of his painting by the spatially analytical tools to examine how his space is experienced. The tools are: relationship between each space, relationship between light and space, and geometrical composition. Among many paintings by Hopper, four of the works that depicted interior spaces are selected and further case-studied in detail: ${\ulcorner}$Rooms by the Sea${\lrcorner}$ (1951), ${\ulcorner}$Sun in an Empty Room${\lrcorner}$ (1963), ${\ulcorner}$New York Movie${\lrcorner}$ (1939) and ${\ulcorner}$Automat${\lrcorner}$ (1927). An Environmental Simulation with scale models was used to examine the relation between light and space. After the research, some unique characteristics of his space were found. Even though his paintings seem to represent the everyday spaces, there are fascinating hidden structure to make people experience in a specific way that Hopper created. Spaces In his paintings do not communicate with each other but are constantly interrupted by the element of time. The mundane everyday world is rediscovered and recreated through these multidimensional and heterogeneous space.