• 한국항공우주학회지
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• 제31권9호
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• pp.1-8
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• 2003

연장된 앞전을 갖는 삼각날개 위에서 시위방향의 여러 위치에서 3축 hot 필름 풍속계를 사용하여 속도장 데이터를 획득하였다. 속도장 데이터는 받음각 24도와 32도에 대하여 중심 시위선을 기준으로 한 레이놀즈수 $1.76{\times}10^6$에서 날개면에 수직한 유동단면에서 측정하였다. 3축 hot 필름 프로브에 의한 세 가지 속도 성분을 측정함으로써 연장된 앞전을 갖는 삼각날개에서의 와류장을 정량적으로 분석할 수 있었다. 날개 와류와 LEX 와류는 평균 축방향 속도가 국소 최고 속도를 갖는 영역에 존재하였다. 아울러, 앞전 근처의 날개면 위에서 주와류와 반대 방향으로 회전하는 이차와류의 생성을 관찰할 수 있었다. 측정 프로브의 유동장에의 삽입은 와류 중심 위치에 크게 영향을 주지 않음을 알 수 있었다.

• 한국항공우주학회지
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• 제30권5호
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• pp.71-78
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• 2002

동축공기 수소확산 화염에서 세 가지 동축공기 조건과 화염의 유무에 따라 실험조건을 분류하고, 이에 대해 PIV를 이용하여 실험을 수행하였다. PIV를 통해 얻은 속도장을 이용하여 평균속도, 난류강도, Reynolds stress 등을 구하여 유동장을 분석하였다. 우선 단순제트에 대해 상사성을 살펴본 결과 이전의 다른 연구자의 실험결과와 일치하였다. 동축공기가 있는 경우 중심축 속도 감쇠는 $x^{-1}$에 비례하여 감소하는 것을 확인하였다. 축방향 길이를 유효밀도에 의해 정의된 유효 제트 지름으로 무차원화한 값으로 중심축 속도를 도시한 결과 하나의 선분에 떨어지는 것을 확인하였다. 평균속도 분포를 살펴보면 일정한 연료유량에 동축공기 유량을 증가시킨 경우 동축공기가 증가함에 따라 속도 분포의 형태가 바뀌게 되어 자기상사성이 유지되지 않는 것으로 보인다. 난류강도는 평균속도 분포의 경우보다 후류에서 자기상사성이 나타난다.

• 천문학회지
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• 제39권4호
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• pp.107-114
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• 2006

We conducted an analysis of a selected region from the FCRAO $^{12}CO$ Outer Galaxy Survey. The selected region is located between galactic longitude $117^{\circ}$ and $124^{\circ}$ with the velocity of -23 km $s^{-1}. Molecular clouds in this region show a peculiar velocity field, protruding from the Local Arm population. The selected region is divided into 7 clouds by spatial location. Though we were not able to identify the direct driving source for peculiar velocity of our target region, we find that there are several internal YSOs or star forming activities; there are many associated sources like an outflows, a high-mass protostellar candidate and $H_2O$ maser sources. We attribute the driving energy source to older generation of episodic star formation. Masses of main clouds(cloud 1-4) estimated using a conversion factor from $^{12}CO$ luminosity are larger than $10^4M_{\odot}$. Other components have a small mass as about $10^3M_{\odot}$. Among main clouds, cloud 2 and 4 seem to be marginally gravitational bound systems as their ratio of $M_{CO}$ to $M_{VIR}$ is about $2{\sim}3$, and the internal velocity dispersion is larger than the centroid velocity dispersion. Total mass estimated using a conversion factor from $^{12}CO$ luminosity is $7.9{\times}10^4M_{\odot}$.

• 천문학회보
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• 제35권2호
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• pp.77.2-77.2
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• 2010

We report a possible low-mass companion around the K2 III star $\varepsilon$ CrB (HD 143107). This star belongs to our sample of 55 K-giants studied for their radial velocity variations using the fiber-fed Bohyunsan Observatory Echelle Spectrograph (BOES) attached to the 1.8-m telescope at Bohyunsan Optical Astronomy Observatory (BOAO). Our precise radial velocity measurements were obtained from February 2005 to June 2010. We find an orbital solution with a period of P = 419 days, a semi-amplitude of K = 137 m/s, and an eccentricity of e = 0.14. Assuming a moderate stellar mass of $M_{\bigstar}=0.77\;M\odot$, we calculate the minimum mass for the companion of m sini = $4.2\;M_{Jup}$ with an orbital semi-major axis of 1.0 AU.

• Journal of Biosystems Engineering
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• 제25권2호
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• pp.141-150
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• 2000

This study was carried out to de develop a control strategy of a fruit harvesting redundant robot. The method of generating a safe trajectory, which avoids collisions with obstracles such as branches or immature fruits, in the 3D(3-dimension) space using artificial potential field technique and virtual plane concept was proposed. Also, the method of setting reference velocity vectors to follow the trajectory and to avoid obstacles in the 3D space was proposed. Developed methods were verified with computer simulations and with actual robot tests. Fro the actual robot tests, a machine vision system was used for detecting fruits and obstacles, Results showed that developed control method could reduce the occurrences of the robot manipulator located in the possible collision distance. with 10 virtual obstacles generated randomly in the 3 D space, maximum rates of the occurrences of the robot manipulator located in the possible collision distance, 0.03 m, from the obstacles were 8 % with 5 degree of freedom (DOF), 8 % with 6-DOF, and 4% with 7-DOF, respectively.

• Smart Structures and Systems
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• 제17권2호
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• pp.327-345
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• 2016

The existence of SH-wave in a piezomagnetic layer overlying an initially stressed orthotropic half-space is investigated. The coupled of differential equations are solved for piezomagnetic layer overlying an orthotropic elastic half-space. The general dispersion equation has been derived for both magnetically open circuit and magnetically closed circuits under the four types of boundary conditions. In the absence of the piezomagnetic properties, initial stress and orthotropic properties of the medium, the dispersion equations reduce to classical Love equation. The SH-wave velocity has been calculated numerically for both magnetically open circuit and closed circuits. The effect of initial stress and magnetic permeability are illustrated by graphs in both the cases. The velocity of SH-wave decreases with the increment of wave number.

• 한국기계가공학회지
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• 제17권5호
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• pp.131-136
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• 2018

Research on space development and satellites is being actively pursued. An interesting field is the study of reliable low-cost space launch vehicles. Since chemical fuel-based launching systems are expensive and take a lot of time and cost to maintain, the EML system, which is an electromagnetic force launching apparatus, is attracting attention. The EML system converts electrical energy stored in a capacitor into magnetic energy, and converts magnetic energy into mechanical kinetic energy, thereby accelerating the projectile. Although studies are actively conducted in the field, it is difficult to solve the equation because the impedance and speedance change with time and the nonlinearity is strong. Many researchers have solved this equation in a variety of methods. In this paper, the velocity analysis of the projectile was carried out by FEM (finite element method) using the commercial electromagnetic analysis program MAXWELL.

• 천문학회보
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• 제43권2호
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• pp.43.2-43.2
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• 2018

The line-of-sight component in the relative motion of galaxy pairs sources the redshift space distortion (RSD) in galaxy surveys. By knowing the probability density function (PDF) of pair-wise motions and projecting it to the line-of-sight direction, one can compute the RSD effect precisely. I present the pair-velocity PDF of dark matter and galaxies in the Horizon-run 4 simulation. I also derive a model motivated by the perturbation theory which fits the results fairly well. I also discuss the application of the model in constraining the cosmology.

• 로봇학회논문지
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• 제17권1호
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• pp.32-39
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• 2022

Since the mobile platform and the manipulator mounted on it move at the same time in a mobile manipulator, the risk of mutual collision increases. Most of the studies on collision avoidance of mobile manipulators cannot be applied to differential drive type mobile platforms or the end-effector tends to deviate from the desired trajectory for collision avoidance. In this study, a collision avoidance algorithm based on null space projection (CANS) that solves these two problems is proposed. To this end, a modified repulsive force that overcomes the non-holonomic constraints of a mobile platform is generated by adding a virtual repulsive force in the direction of its instantaneous velocity. And by converting this repulsive force into a repulsive velocity and applying it to the null space, the end-effector of the robot avoids a collision while moving along its original trajectory. The proposed CANS algorithm showed excellent performance through self-collision avoidance tests and door opening tests.

• 천문학회보
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• 제36권2호
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• pp.88.2-88.2
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• 2011

Fast Imaging Solar Spectrograph (FISS) is an instrument developed by Seoul National University and Korea Astronomy and Space Science Institute and installed at the 1.6 meter New Solar Telescope of Big Bear Solar Observatory. Using this instrument, we observed solar filaments and analyzed the data focusing on determining the temperature and non-thermal velocity. We inferred the Doppler absorption widths of $H{\alpha}$ and Ca II 8542$\bar{A}$ lines from the line profiles using the cloud model. From these values, we separately determined temperature and non-thermal velocity. Our first result came from a solar filament observed on 2010 July 29th. Temperature inside a small selected region of this ranges from 4500K to 12000K and non-thermal velocity, from 3.5km/s to 7km/s. We also found temperature varied a lot with time. For example temperature at a fixed point varied from 8000K to 18000K for 40 minutes, displaying an oscillating pattern with a period of about 8 minutes and amplitude of about 2000K. We will also present new results from filaments observed in 2011 summer.