• Journal of Korea Game Society
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• v.10 no.6
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• pp.57-65
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• 2010

In this paper, mobility performance indices are proposed which may be used to estimate characteristics of output velocity space in six-degree-of-freedom parallel mechanism. In order for manipulability and condition number to not suffer from lack of the physical meaning due to dimensional inhomogeneity, output space is partitioned into translational velocity space and rotational velocity space, respectively. In each space, mobility ellipsoids corresponding to unit input space are defined and two types of mobility performance in translational velocity spaces indices are derived. Two types of mobility performance in rotational velocity spaces indices are derived.

• Fire Science and Engineering
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• v.21 no.3
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• pp.61-68
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• 2007

The purpose of this study analyzes heat flows and fire behavior through a reduced-scale model experiments about change of wind velocity in underground life space. When the wind velocity is increased the temperature rise time of the fire room was risen fast. And temperature of fire room was increased. And increase of wind velocity displayed maximum temperature at an opening of the fire room. Heat flows by fire spread increase size of smoke occurrence and flame, and displayed high temperature distribution in passageway than inside of neighborhood department promoting eddy flow spread as wind velocity increases. Finally, heat flows are decided by wind and wind velocity at fire of underground life space, and Wind velocity increases, temperature increase and decrease could confirm that is gone fast.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.46.1-46.1
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• 2011

New statistical method is proposed to coherently combine Baryon Acoustic Oscillation statistics (BAO) and peculiar velocity measurements exploiting decomposed density--density and velocity--velocity spectra in real space from the observed redshift distortions in redshift space, 1) to achieve stronger dark energy constraints, sigma(w)=0.06 and sigma(w_a)=0.20, which are enhanced from BAO or velocity measurements alone, and 2) to cross--check consistency of dark energy constraints from two different approaches; BAO as geometrical measurements and peculiar velocity as large scale structure formation observables.

• The Bulletin of The Korean Astronomical Society
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• v.42 no.2
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• pp.51.4-52
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• 2017

We present the derived kinematic characteristics of low-${\alpha}$ thin-disk and high-${\alpha}$ thick-disk stars in the Milky Way, investigated with a sample of about 33,900 G- and K-type dwarfs from the Sloan Extension for Galactic Understanding and Exploration (SEGUE). Based on the level of ${\alpha}$-element enhancement as a function of [Fe/H], we separate our sample into thin- and thick-disk stars and then derive mean velocity, velocity dispersion, and velocity gradients for the U, V and W velocity components, respectively, as well as the orbital eccentricity distribution. There are notable gradients in the V velocity over [Fe/H] in both populations: -23 km s-1 dex-1 for the thin disk and +44 km s-1 dex-1 for the thick disk. The velocity dispersion of the thick disk decrease with increasing [Fe/H], while the velocity.

• The Bulletin of The Korean Astronomical Society
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• v.44 no.2
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• pp.74.2-74.2
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• 2019

We present a possible bias in the estimation of velocity dispersions for galaxy groups due to the contribution of subgroups which are infalling into the groups. We execute a systematic search for flux-limited galaxy groups and subgroups based on the spectroscopic galaxies with r < 17.77 mag of SDSS data release 12, by using DBSCAN (Density-Based Spatial Clustering of Application with Noise) and Hierarchical Clustering Method which are well known unsupervised machine learning algorithm. A total of 2042 groups with at least 10 members are found and ~20% of groups have subgroups. We found that the estimation of velocity dispersions of groups using total galaxies including those in subgroups are underestimated by ~10% compared to the case of using only galaxies in main groups. This result suggests that the subgroups should be properly considered for mass measurement of galaxy groups based on the velocity dispersion.

• 제어로봇시스템학회:학술대회논문집
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• 1996.10b
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• pp.739-742
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• 1996

Several figures representing velocity transmission from joint space to task space are analyzed and compared with each other. The figures include velocity ellipsoid derived from Jacobian matrix, scaled velocity ellipsoid derived from normalized joint velocities, polytope derived by numerical scaling, and polytopes derived by linear combinations of Jacobian column vectors. The results show that the optimal directions given by the measures are not the same and the conventional velocity ellipsoid is not good choice as optimization measure as far as the moving direction is concerned. Simulation examples for 3 d.o.f. redundant robot manipulators in 2-dimensional task space are given for comparison study.

• Journal of The Korean Astronomical Society
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• v.29 no.1
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• pp.75-81
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• 1996

We mapped the $^{13}CO$ line in the dark nebula L134 using the 14-m Taeduck radio telescope with a 57 arcsec beam and one beam spacing. The cloud has a spherical shape with an intensity peak ridge extended from the northwest to the southeast directions. The halfwidth and the radial velocity of the lines peak at the region of the cloud center. The radial velocity decreases from the cloud center towards the north and south directions. The integrated line intensity distributions in the space-velocity plane show some structure and a velocity gradient. The $^{13}CO$ and $H_2CO$ clouds and dark clouds are closely related in space in shape, outer boundary, and intensity peak positions. The $^{13}CO$ integrated line intensity is linearly proportional to the visual extinction.

• Journal of ILASS-Korea
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• v.21 no.2
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• pp.71-77
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• 2016

Air pollutants nitrogen oxides are inevitably generated in the combustion reaction. Its amount trend is steadily increasing because the rapid modern industrialization and population growth. For this reason, NOx is controlled to reducing the harmful components in the exhaust gas. So Marine Environment Protection Committee (MEPC) take effect 'Tier I', 'Tier II' of air pollution regulation in 2005 and 2011 respectively. According to NOx emissions are strictly regulated management of the vessel through them. In addition, since 2016 the regulation enter into force in the next step 'Tier III' was confirmed by MEPC 66th committee. It's 80% enhanced emissions limits than the 'Tier I' Alternatively these emission regulation, research is actively being carried out about exhaust gas after-treatment methods through the vessel application of Selective Catalytic Reduction(SCR). Therefore depending on the basic specification of cell density according to the Area velocity, Space velocity, Linear velocity is studied the effects of NOx removal efficiency

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.4
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• pp.523-532
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• 2001

A simultaneous measurement of wall vorticity and near-wall streamwise velocity fluctuations has been performed using a V-type wall vorticity probe and an I-type velocity probe to investigate the relation between them. Long-time averaged space-time correlations show that the wall vorticity is highly correlated with a turbulence structure which is tilted from the wall in the streamwise direction and that there is a streamwise vortex pair near the wall. It is shown that a structure correlated with the streamwise wall vorticity is smaller than and prior to a structure correlated with the spanwise wall vorticity. Tilting angles are obtained from the phase shift between the wall vorticity and streamwise velocity fluctuations. The tilting angle of the structure correlated with the streamwise wall vorticity is larger than that of the structure correlated with the spanwise wall vorticity. The convection velocity of the near-wall streamwise velocity fluctuations obtained from the space-time correlation is in good agreement with previous results.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.14 no.5
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• pp.424-431
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• 2004

An implicit direct-time integration method for obtaining transient responses of general dynamic systems is described. The conventional Newmark method cannot be directly applied to state-space first-order differential equations, which contain no explicit acceleration terms. The method proposed here is the state-space Newmark method that incorporates the average velocity concept, and can be applied to an analysis of general dynamic systems that are expressed by state-space first-order differential equations. It is also readily coded into a program. Stability and accuracy analyses indicate that the method is numerically unconditionally stable like the conventional Newmark method, and has a period error of 2nd-order accuracy for small damping and 4th-order for large damping and an amplitude error of 2nd-order, regardless of damping. In addition, its utility and validity are confirmed by two application examples. The results suggest that the proposed state-space Newmark method based on average velocity be generally applied to the analysis of transient responses of general dynamic systems with a high degree of reliability with respect to stability and accuracy.