• 천문학회보
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• 제40권2호
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• pp.30.3-31
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• 2015

We present a kinematic analysis of 172 likely member galaxies of the Ursa Major Cluster. In order to understand the dynamical state of the cluster, we investigate the correlation of the cluster morphology with rotation, the velocity dispersion profile, and the rotation amplitude parallel to the global rotation direction. Both the minor axis and the rotation are very well-aligned with the global rotation axis in the outer region at half radius (> 0.5 $R_{max}$), but not in the inner region. The cluster exhibits low velocity dispersion and rotation amplitude profiles in the inner region, but higher in the outer. Both profiles exhibit outwardly increasing trends, suggesting an inside-out transfer of angular momentum of dark matter via violent relaxation, as revealed by a recent off-axis major-merging simulation. From Dressler-Schectman plots in the plane of galactic positions, and velocity versus position angle of galaxy, we are able to divide the Ursa Major Cluster into two substructures: Ursa Major South (UMS) and Ursa Major North (UMN). We derive a mass of $3.2{\times}10^{14}M_{\odot}$ for the cluster through the two-body analysis by the timing argument with the distance information (37 for UMN and 36 for UMS) and the spin parameter of ${\lambda}=0.049$. The two substructures appear to have passed each other 4.4 Gyr ago and are moving away to the maximum separation.

• 대한기계학회논문집
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• 제15권6호
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• pp.2083-2099
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• 1991

본 연구에서는 다른 실험 조건은 일정하게 유지하면서 아래 벽면의 표면조도 를 체계적으로 변화시켜 표면조도가 후향계단 뒤의 재부착 흐름 및 재발달경계층에 미 치는 영향을 조사하고자 하며 구체적인 내응은 다음과 같다. (1) 표면조도가 재부착 길이와 재발달경계층에 미치는 영향의 조사. (2) 표면조도가 평균속도와 난류량 분포 에 미치는 영향의 조사. (3) 여러 종류 표면조도 변화에 따른 재부착길이와 재발달 경 계층 회복에 미치는 영향과 결과의 상호 비교.

• 한국해양공학회지
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• 제25권4호
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• pp.42-47
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• 2011

In this paper, wake equalizing duct (WED) form optimization was carried out using computational fluid dynamics (CFD) techniques. A WED is a ring-shaped flow vane with a foil-type cross-section fitted to a hull in front of the upper propeller area. The main advantage of a WED is the power savings resulting from the uniformity of the velocity distribution on the propeller plane, a reduction in the flow separation at the aft-body, and lift generation with a forward force component on the foil section. This paper intends to evaluate these functions and find an optimized WED form for minimizing the viscous resistance and equalizing the wake distribution. In the optimization process, the study uses four WED parameters: the angle of the section, longitudinal location, and angles of the axes for the half rings against the longitudinal and transverse planes of the ship. KRISO 300K VLCC2 (KVLCC2) is chosen as an example ship to demonstrate the WED optimization. The optimization procedure uses genetic algorithms (GAs), a gradient-based optimizer for the refinement of the solution, and Non-dominated Sorting GA-II(NSGA-II) for Multiobjective Optimization. The results show that the optimized WED can reduce the viscous resistance at the expense of the uniformity of the wake distribution.

• Wind and Structures
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• 제11권5호
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• pp.377-389
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• 2008

An experimental investigation has been conducted to determine the effectiveness of base shield plates in reducing the drag of a rough circular cylinder in a cross flow at Reynolds numbers in the range $3{\times}10^4{\leq}Re{\leq}10.5{\times}10^4$. Three model configurations were investigated and compared: a plane cylinder (PC), a cylinder with a splitter plate (MC1) and a cylinder fitted with base shield plates (MC2). Each configuration was studied in the sub and supercritical flow regimes. The chord of the plates, L, ranged from 0.22 to 1.50D and the cavity width, G, between the plates was in the range from 0 to 0.93D. It is recognized that base shield plates can be employed more effectively than splitter plates to reduce the aerodynamic drag of circular cylinders in both the sub- and supercritical flow regimes. For subcritical flow regime, one can get 53% and 24% drag reductions for the MC2 and MC1 models with L/D=1.0, respectively, compared with the PC model. For supercritical flow regime however, the corresponding drag reductions are 38% and 7%.

• 천문학회보
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• 제39권2호
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• pp.46-46
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• 2014

Interactions such as mergers and flybys play a fundamental role in shaping galaxy morphology. We used the Horizon Run 4 cosmological N-body simulations to study the frequency and the type of halo interactions as a function of the environment, the separation p, the mass ratio q, and the target halo mass. We defined targets as haloes more massive than 10^11 Msun/h, and a target is interacting if it is located within the virial radius of a neighbour halo more massive than 0.4 times the target mass. We find that the interaction rate as a function of time has a universal shape for different halo mass and large-scale density, with an increase and saturation. Larger density yield steeper slopes and larger final interaction rates, while larger masses saturate later. Most interactions happen at large-scale density contrast ${\delta}$ about 10^3, regardless of the redshift. We also report the existence of two modes of interactions in the (p,q) plane, reflecting the nature (satellite or main halo) of the target halo. These two trends strongly evolve with redshift, target mass, and large-scale density. Interacting pairs have similar spins parameters and aligned spins, with radial trajectories, and prograde encounters for non-radial trajectories. The satellite trajectories become less and less radial as time proceed. This effect is stronger for higher-mass target, but independent of the large-scale density.

• 대한기계학회논문집A
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• 제20권5호
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• pp.1524-1533
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• 1996

Risidual stress of cylindrical glass rods are measured by photoelasticity to study the variation of stresses with respect to heat treatment temperatures. In order to measure the stresses accurately, fringe sharpening and multiplication techniques are applied to the determination of photoelastic fringe orders. Filon's separationmethod is used to resolve circumferential and redial stress ocmponents from isochromatic fringes which are the same as in-plane maximum shearing stresses. According to the photoelastic measurements, residual stress is increased as the heat treatment temperature of the rods is raised from $560^{\circ}C$ to $650^{\circ}C$ All the circumferential stress components are changed from tensile stresses to compressive ones at approximate $R_m$/$R_o$ = 0.6, where $R_o$/ is outer radius and $R_m$any measured radius. This analysis shows that residual stresses of the glass rods approach zero if the rods are heat-treated near the strain point.

• 한국수산과학회지
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• 제48권2호
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• pp.207-220
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• 2015

This study identified the species-specific, frequency-dependent characteristics of broadband acoustic scattering that facilitate classifying fish species using the pulse compression (PC) technique. Controlled acoustic scattering laboratory experiments were conducted with nine commercially important fish species using linear chirp signals (95-220 kHz) over an orientation angle range of ${\pm}45^{\circ}$ in the dorsal plane at approximately $1^{\circ}$ increments. The results suggest that the angular-dependent characteristics of the broadband echoes and the frequency-dependent variability in target strength (TS) were useful for inferring the fish species of interest. The scattering patterns in the compressed pulse output were extremely complex due to morphological differences among fish species, but the x-ray images strongly suggested that spatial separation correlated well with scattering for the head, skeleton, bone, otoliths, and swim bladder within each specimen.

• Computers and Concrete
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• 제1권3호
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• pp.261-284
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• 2004

Two enhancements to a recently developed plastic-damage-contact model for concrete are presented. The model itself, which uses planes of degradation that can undergo damage and separation but that can regain contact according to a contact law, is described. The first enhancement is a new damage evolution function which provides a completely smooth transition from the undamaged to the damaged state and from pre-peak to post-peak regions. The second is an improved contact function that governs the potential degree of contact with increasing opening on a crack plane. The use of a damage evolution function with a pre-peak has implications for the consistent tangent matrix/stress recovery algorithm developed for the model implementation, and amendments to this algorithm to accommodate the new function are described. A series of unpublished experimental tests on notched specimens undertaken in Cardiff in the mid 1990s are then described. These include notched beam tests as well as prismatic and cylindrical torsion tests. The tests are then considered in three dimensional finite element analyses using the modified Craft model implemented in the finite element program LUSAS. Comparisons between experimental and numerical data show reasonable agreement except that the numerical simulations do not fully describe the latter stages of the softening responses for the torsion examples. Finally, it is concluded that the torsion tests described provide useful benchmark examples for the validation of three-dimensional numerical models for concrete.

• 천문학회보
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• 제43권1호
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• pp.63.4-64
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• 2018

High resolution spectroscopy of the yellow symbiotic star AG Draconis is performed with the Canada-France-Hawaii Telescope to analyse the line profiles of Raman scattered O VI broad emission features at $6825{\AA}$ and $7082{\AA}$ with a view to investigating the wind accretion process from the mass losing giant to the white dwarf. These two spectral features are formed through inelastic scattering of O $VI{\lambda}{\lambda}32$ and 1038 with atomic hydrogen. We find that these features exhibit double-component profiles with red parts stronger than blue ones with the velocity separation of ~ 60 km s-1 in the O VI velocity space. Monte Carlo simulations for O VI line radiative transfer are performed by assuming that the O VI emission region constitutes a part of the accretion flow around the white dwarf and that Raman O VI features are formed in the neutral part of the slow stellar wind from the giant companion. The overall Raman O VI profiles are reasonably fit with an azimuthally asymmetric accretion flow and the mass loss rate ~ 4 ${\times}$ 10^{-7} M_sun yr^{-1}. We also find that additional bipolar neutral regions moving away with a speed ~ 70 km s^{-1} in the directions perpendicular to the orbital plane provide considerably improved fit to the red wing parts of Raman features.

• 한국정보통신학회논문지
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• 제17권3호
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• pp.540-545
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• 2013

Fractional 푸리에변환(Fractional Fourier Transform : FRFT)은 기존의 푸리에 변환의 일반화된 형태로서, 양자역학분야에서 처음 소개되었다. FRFT가 가지는 시간-주파수 영역에서의 단순하면서도 유용한 특성으로 인하여, 지금까지 소나 및 레이더 신호처리 분야에서 많은 연구결과들이 발표되었으며, 푸리에 변환을 활용한 기존의 방법보다 우수한 연구결과를 보여 왔다. 본 논문에서는 LFM(Linear Frequency Modulation)신호들이 겹쳐져 수신되었을 경우에 이들 신호들을 검출하고 분리하기 위해 FRFT를 이용하였다. 실험결과 수신된 LFM 신호들을 FRFT 영역에서 효율적으로 검출하고 분리가 가능함을 확인하였다.