• 천문학회보
• /
• 제46권2호
• /
• pp.59.2-59.2
• /
• 2021

On March 6 2021, Apophis made a close approach to the Earth with a minimum distance of 0.11 AU when the apparent magnitude reached up to V~16. This was the most favorable condition to observe this asteroid until its 2029 encounter. The observations during this apparition were extremely important to determine major physical properties, such as size, rotational state, 3D shape model, surface mineral properties. So, we organized the observation campaign during the 2021 apparition. The main goals of our campaign are to refine the spin state and 3D shape model and check the surface composition variations. The campaign involved dozens of countries and included ground-based photometry and spectroscopy, and spacecraft observations. Our timely observation campaign will provide essential data in planning the operation scenario for the space mission. In this presentation, we will report the preliminary result of the Apophis observation campaign during the 2021 apparition.

• 천문학회보
• /
• 제44권1호
• /
• pp.53.2-53.2
• /
• 2019

$H{\alpha}$ surges (i.e. cool/dense collimated plasma ejections) may act as a guide for a propagation of magnetohydrodynamic waves. We report a high-resolution observation of a surge observed with 1.6m Goody Solar Telescope (GST) on 2009 August 26, from 18:20~UT to 18:45UT. Characteristics of plasma motions in the surge are determined with the normalizing radial gradient filter and the Fourier motion filter. The shape of the surge is found to change from a 'C' shape to an inverse 'C' shape after a formation of a cusp, a signature of reconnection. There are apparent upflows seen above the cusp top and downflows below it. The upflows show rising and rotational motions in the right-hand direction, with the rotational speed decreasing with height. Near the cusp top, we find a transverse oscillation of the surge, with the period of ~2 min. There is no change of the oscillation phase below the cusp top, but above the top a phase change is identified, giving a vertical phase speed about 86kms-1. As the height increases, the initial amplitude of the oscillation increases, and the oscillation damping time decreases from 5.13 to 1.18min. We conclude that the oscillation is a propagating kink wave that is possibly excited by an x-point oscillation.

• 대한토목학회논문집
• /
• 제4권4호
• /
• pp.127-135
• /
• 1984

본 연구는 실제 하중을 받는 강재 아치구조의 최적형상을 다루었다. 목적함수로는 아치의 중량을 취했으며, 제약조건으로는 단면력, 체적, 아치리브의 길이, 아치부채 단연적의 조합으로 구성된 웅력제약초건을 고려하였다. 형상최적화문제는 아치부재의 단면척이 설계변수의 항으로 형성되었으며, 첫단계로 구조해석의 정밀도가 최적 설계의 목적함수값에 미치는 영향을 분석하였다. 형상최적화 알고리즘은 Two-space System 으로 형성되었고, Space 1 에서는 Modified Newton-Raphson Method에 의한 단면최적화, Space 2 에서는 Powell Method 에 의한 형상최적화를 시도하여 형상최적화 알고리즘을 도출하였다. 본 연구에서 도출된 최적화 알고리즘을 이용하여 아치의 단면최적화와 최적 아치형상에 관한 연구가 수행되었다. 이 알고리즘에 의해 실제 조건하에서 아치의 최적 Span-Rise 비를 구할 수 있다.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 2007년도 정기 학술대회 논문집
• /
• pp.577-582
• /
• 2007

A variational formulation for plane elasticity problems is derived based on an isogeometric approach. The isogeometric analysis is an emerging methodology such that the basis functions in analysis domain arc generated directly from NURBS (Non-Uniform Rational B-Splines) geometry. Thus. the solution space can be represented in terms of the same functions to represent the geometry. The coefficients of basis functions or the control variables play the role of degrees-of-freedom. Furthermore, due to h-. p-, and k-refinement schemes, the high order geometric features can be described exactly and easily without tedious re-meshing process. The isogeometric sensitivity analysis method enables us to analyze arbitrarily shaped structures without re-meshing. Also, it provides a precise construction method of finite element model to exactly represent geometry using B-spline base functions in CAD geometric modeling. To obtain precise shape sensitivity, the normal and curvature of boundary should be taken into account in the shape sensitivity expressions. However, in conventional finite element methods, the normal information is inaccurate and the curvature is generally missing due to the use of linear interpolation functions. A continuum-based adjoint sensitivity analysis method using the isogeometric approach is derived for the plane elasticity problems. The conventional shape optimization using the finite element method has some difficulties in the parameterization of boundary. In isogeometric analysis, however, the geometric properties arc already embedded in the B-spline shape functions and control points. The perturbation of control points in isogeometric analysis automatically results in shape changes. Using the conventional finite clement method, the inter-element continuity of the design space is not guaranteed so that the normal vector and curvature arc not accurate enough. On tile other hand, in isogeometric analysis, these values arc continuous over the whole design space so that accurate shape sensitivity can be obtained. Through numerical examples, the developed isogeometric sensitivity analysis method is verified to show excellent agreement with finite difference sensitivity.

• 디자인학연구
• /
• 제15권4호
• /
• pp.409-416
• /
• 2002

자동차에서 실내공간 비중의 점진적 증대는 오늘에 이르러 자동차 차체 디자인의 조형개념에서 새로운 전환점을 제공하고 있으며, 이것은 차량의 차체 크기나 엔진의 배기량에 관계없이 차체에서 승객을 위한 실내 공간을 형성하는 캐빈(cabin)의 크기가 가장 높은 비중을 가지게 되는 것을 전제로 한다. 이에 따라 차체에서 실내공간을 이루는 캐빈의 비례는 차체의 다른 부분의 비례와 함께 변화되고 있다. 캐빈 이외의 공간은 차량을 구성하는 기구적 요소들을 위한 공간과 화물 수송 목적의 공간이다. 캐빈의 비례가 변화된다는 것은 종합적으로 탑승자의 공간 비중과 기구적 요소의 비례 관계가 변화됨을 의미하는 것이며, 이것은 결과적으로 차체에서의 공간개념의 변화를 초래하게 되었다. 이러한 변화로 인하여 현재의 차량은 과거의 차량에서 단순한 외형적 스타일만이 변화되는 것이 아니라, 공간 확보를 위한 차체의 구조와 형태가 차량의 운전공간과 탑승공간의 확보를 위해 변화되고 있으며, 이것은 향후의 차체 스타일에서 새로운 변화로써 나타나게될 것으로 보인다.

• 천문학회보
• /
• 제44권1호
• /
• pp.80.1-80.1
• /
• 2019

Photometric investigations of asteroids allow us to determine their rotation states and shape models (Apostolovska et al. 2014). Our main target, asteroid (2078) Nanking's perihelion distance (q) is 1.480 AU, which belongs to the Mars-crossing asteroid (1.3 < q < 1.66 AU). Mars-crossing asteroids are objects that cross the orbit of Mars and regarded as one of the primary sources of near-Earth asteroids due to the unstable nature of their orbits. We present the analysis of the spin parameters and 3D shape model of (2078) Nanking. We conducted Cousins_R-band time-series photometry of this asteroid from November 26, 2014 to January 17, 2015 at the Sobaeksan Optical Astronomy Observatory (SOAO) and for 25 nights from March to April 2016 using the Korea Microlensing Telescope Network (KMTNet) to reconstruct its physical model with our dense photometric datasets. Using the lightcurve inversion method (Kaasalainen & Torppa 2001; Kaasalainen et al. 2001), we determine the pole orientation and shape model of this object based on our lightcurves along with the archival data obtained from the literatures. We derived rotational period of 6.461 h, the preliminary ecliptic longitude (${\lambda}_p$) and latitude (${\beta}_p$) of its pole as ${\lambda}_p{\sim}8^{\circ}$ and ${\beta}_p{\sim}-52^{\circ}$ which indicates a retrograde rotation of the body. From the apparent W UMa-shaped lightcurve and its location in the rotation frequency-amplitude plot of Sheppard and Jewitt (2004), we suspect the contact binary nature of the body (Choi 2016).

• 반도체디스플레이기술학회지
• /
• 제20권4호
• /
• pp.134-140
• /
• 2021

This study investigates the flow efficiency and temperature based on flow path shape. Five models are designed to the no flow path, one flow path, two flow path, three flow path, add inlet flow path and add interior space gradient. Results show that two flow model(add inlet flow path and add interior space gradient), It was confirmed that model(add inlet flow path) is the optimal shape for coolant heat transfer, and model(add interior space gradient) is the optimal shape for coolant flow, demonstrates optimal design among the five models. The results of this study can be utilized to efficiently control the coolant flow through various types of flow paths.

• 한국실내디자인학회논문집
• /
• 제15권3호
• /
• pp.92-101
• /
• 2006

This study examines placeness of the living space on the basis of Schulz's existential space and inquires into the expressional features of placeness by analyzing cases. Results of this study have shown that placeness of living space is formed by three factors as follows. First, the living space with placesness maintains inner order which structuralizes surroundings. Second, it expresses its identity through innate shape that reflects surroundings. Third, inner space has innate identity and it is much related to characteristics personality of a resident, environmental and psychological factors. It is as follows that concrete features of existential placeness shown in analyzing cases of Botta and Moore's works. There are concrete expressional features of placeness in the housing of Botta, and one is to keep order of inner space the horizontal and vertical axis reflected surroundings. Another is to show existence feeling as the shape of a stable singular mass with surroundings and regional properties. The third is to value innate features of each space inside housing and particularly to acquire placeness as combining phenomenological characteristic of light. There are concrete expressional features of placeness in the housing of Moore, and first, strong centrality formed in the inside is emphasized as extending to outside environment. Second, existence feeling is acquired as familiar form using the shape and material considered surroundings. Third, the personality of a resident is positively reflected in the design. Besides, placeness is acquired by goods and furniture as positively considering environmental and psychological sides.

• Journal of Astronomy and Space Sciences
• /
• 제30권3호
• /
• pp.179-185
• /
• 2013

Photometric observation is one of the most effective techniques for determining the physical characteristics of unknown space objects and space debris. In this research, we examine the change in brightness of the Communication, Ocean, Meteorological Satellite-1 (COMS-1) Geostationary Orbit Satellite (GEO), and compare it to our estimate model. First, we calculate the maximum brightness time using our calculation method and then derive the light curve shape using our rendering model. The maximum brightness is then calculated using the induced equation from Pogson's formula. For a comparison with our estimation, we carried out photometric observation using an optical telescope. The variation in brightness and the shape of the light curve are similar to the calculations achieved using our model, but the maximum brightness shows a slightly different value from our calculation result depending on the input parameters. This paper examines the photometric phenomenon of the variation in brightness of a GEO satellite, and the implementation of our approach to understanding the characteristics of space objects.

• International Journal of Aeronautical and Space Sciences
• /
• 제15권1호
• /
• pp.20-31
• /
• 2014

This paper deals with the development of a realistic shape optimization of damaged columns that are subjected to conservative and non-conservative forces, using the Genetic Algorithm (GA). The analysis is based on the design of the most optimized shape of the column under the constraint of constant weight, considering the Static, Vibrational, and Flutter characteristics. Under the action of conservative and non-conservative longitudinal forces, an elastic column loses its stability. A numerical analysis based on FEM has been performed on a uniform damaged column, to compute the fundamental buckling load, vibration frequency, and flutter load, under various end restraints. An optimization search based on the Genetic Algorithm is then executed, to find the optimal shape design of the column. The optimized column references the one having the highest buckling load, highest vibration frequency, and highest flutter load, among all the possible shapes of the column, for a given volume. A comparison is then made between the values obtained for the optimized damaged column, and those obtained for the optimized undamaged column. The comparison reveals that the incorporation of damage in the column alters its optimal shape to only a certain extent. Also, the critical load and frequency values for the optimized damaged column are comparatively low, compared with those obtained for the optimized undamaged column. However, these results hold true only for moderate-intensity damage cases. For high intensity damage, the optimal shape may not remain the same, and may vary, according to the severity of damage.