• 한국분무공학회지
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• 제1권3호
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• pp.37-50
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• 1996

Computational fluid dynamics was used to optimize an A/C duct. Three dimensional flow analysis in an automotive A/C duct was performed computationally using various turbulence models and compared numerical predictions such as outlet flow split, surface pressure distribution along the duct to experimental data. Additionally, we studied the effect of location variation of 2nd branch on exit flow ratio and could find optimal location of 2nd branch. The design of an A/C duct was modeled and calculated to enhance the airflow distribution in each outlet using the STAR-CD computational fluid dynamics software. In results, modified $k-\varepsilon$ turbulence model allows a successful prediction of static pressure distribution particulary at around strong curvature but little improvement flow split. In the future, adoption of CFD to design an A/C duct with modified $k-\varepsilon$ model will bring benefits of producing more accurate prediction, and also give designers more detail information much more than now.

• 천문학회보
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• 제40권2호
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• pp.41.3-41.3
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• 2015

As part of the Herschel key program "Water in Star-forming Regions with Herschel (WISH)", PACS imaging spectroscopy data have been taken toward ten massive young stellar objects (YSOs): four high mass protostellar objects (HMPOs), two hot molecular cores (HMCs), and four ultracompact HII regions (UCHIIs). The spectra cover a broad range of wavelengths (55 to 210 micron) presenting various atomic and molecular lines as well as excellent dust thermal continua. By fitting the continua utilizing a modified black-body formula we estimate mass-weighted temperature and column density distributions of warm dust and find that UCHII regions are warmer and HMCs are more deeply embedded than the other types. We also estimate rotational temperature and column density distributions of warm CO gas using the rotational diagram analysis. In addition, based on the comparison of high J CO line fluxes to the RATRAN estimates of central heating envelope models, we find that majority of warm CO is originated from bipolar outflow shocks.

• 한국정밀공학회지
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• 제16권2호통권95호
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• pp.201-210
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• 1999

One of the major limitations of productivity and quality in metal cutting is the machining accuracy of machine tools. The machining accuracy is affected by geometric and thermal errors of the machine tools. Therefore, a key requirement for improving te machining accuracy and product quality is to reduce the geometric and thermal errors of machine tools. This study models geometric error for error analysis and develops on-machine measurement system by which the volumetric erors are measured. The geometric error is modeled using form shaping function(FSF) which is defined as the mathematical relationship between form shaping motion of machine tool and machined surface. The constant terms included in the error model are found from the measurement results of on-machine measurement system. The developed on-machine measurement system consists of the spherical ball artifact (SBA), the touch probe unit with a star type stylus, the thermal data logger and the personal computer. Experiments, performed with the developed measurement system, show that the system provides a high measuring accuracy, with repeatability of ${\pm}2{\mu}m$ in X, Y and Z directions.

• 천문학회보
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• 제41권2호
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• pp.40.2-40.2
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• 2016

The attenuation of starlight by dust in galactic environments is investigated through models of radiative transfer in a spherical, clumpy interstellar medium (ISM). We show that the attenuation curves are primarily determined by the wavelength dependence of absorption rather than by the underlying extinction (absorption+scattering) curve; the observationally derived attenuation curves cannot constrain a unique extinction curve unless the absorption or scattering efficiency is specified. Attenuation curves consistent with the Calzetti curve are found by assuming the silicate-carbonaceous dust model for the Milky Way (MW), but with the $2175{\AA}$ bump suppressed or absent. The discrepancy between our results and previous work that claimed the Small Magellanic Cloud dust to be the origin of the Calzetti curve is ascribed to the difference in adopted albedos; we use the theoretically calculated albedos whereas the previous ones adopted empirically derived albedos from observations of reflection nebulae. It is found that the model attenuation curves calculated with the MW dust are well represented by a modified Calzetti curve with a varying slope and UV bump strength. The strong correlation between the slope and UV bump strength, as found in star-forming galaxies at 0.5 < z < 2.0, is well reproduced if the abundance of the UV bump carriers is assumed to be 30-40% of that of the MW-dust; radiative transfer effects lead to shallower attenuation curves with weaker UV bumps as the ISM is more clumpy and dustier. We also argue that some of local starburst galaxies have a UV bump in their attenuation curves, albeit very weak.

• 천문학회보
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• 제42권2호
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• pp.81.1-81.1
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• 2017

L1251B is an excellent example of a small group of pre- and protostellar objects in low-mass star-forming region. Previous interferometer data with a high angular resolution resolved the outflows associated with L1251B into a few components. To understand the physical conditions of the protostellar outflows in L1251B, we mapped this region spectroscopically with Spitzer/IRS and obtained spectral line data from Herschel/PACS. Spitzer/IRS provides the S(0)-S(7) pure rotational lines of H2 as well as fine-structure emissions produced in shocks such as S, [Si II], and [Fe II] and it is a powerful tool for studying shocked interstellar gas. In addition, [O I] lines observed with Herschel/PACS are described well by J-type shock models expected in the outflows from protostars. We will present an analysis of the L1251B protostellar outflow in the H2 pure rotational lines and fine-structure emissions.

• 천문학회보
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• 제35권2호
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• pp.35.2-35.2
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• 2010

It is crucial to understand the dust properties in the early universe since they provide important clues about how the early cosmic star formation should be interpreted in the presence of dust extinction. GRB 071025 is an unusually red GRB that occured at high redshift, offering an unique opportunity to study the dust properties in the early universe. We investigate the extinction properties of GRB 071025 through the analysis of RIJHK data obtained with the 1-m telescope at Mt. Lemmon Optical Astronomy Observatory (LOAO) and Simultaneous Quad Infrared Imaging Device (SQIID) on the Kitt-Peak Mayall 4-m telescope. Our dataset is independent from that in a previous work (Perley et al. 2010) where a small systematic photometric errors could complicate the interpretation. After determining the temporal power law exponent with five I-band frames from LOAO, we construct a multi-band monochromatic SED of the GRB afterglow. By using various extinction laws, we find that the SED is best fitted with models that incorporate SNe II dust and derive a photometric redshift of 4.99(+0.12/-0.03). Our results strongly support the prior claim that dusts in GRB 071025 originate mainly from supernovae, implying SNe II predominantly contributed to the dust enrichment in the early universe (z ~ 5).

• 한국마린엔지니어링학회:학술대회논문집
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• 한국마린엔지니어링학회 2011년도 후기공동학술대회 논문집
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• pp.73-73
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• 2011

In fact, asynchronous motors are used widely. Asynchronous motors which have large power (compared to the source supplies) is needed to start them in various methods. The theory of application reduced voltage to motor's stator or variable resistor fed rotor for the purpose of altering the motor's torque and power consumption characteristics is an idea that has existed for many years. These concepts have flourished mainly due to the need to limit torque and limited generator/power distribution capabilities. However, how can know exactly the time of switching steps with different types of motors as well as load characteristics is very difficult. This paper focuses on the design and development mathematical models of motor[1][2], load, ACB, asynchronous machine and then is implemented in SIMULINK in order to calculate this time, special on ships where power generation station is limited. The simulation results are both compared and discussed in detail so that it can apply to conclude the most suitable and applicable starting time for new system with various motors and load.

• 한국전산유체공학회:학술대회논문집
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• 한국전산유체공학회 2007년도 춘계 학술대회논문집
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• pp.87-90
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• 2007

A general purpose program NUFLEX for the analysis 3-D thermo/fluid flow and pre/post processor in complex geometry has been developed, which consists of a flow solver based on FVM and GUI based pre/post processor. The solver employs a general non-orthogonal grid system with structured grid and solves laminar and turbulent flows with standard/RNG ${\kappa}-{\varepsilon}\;SST$ turbulence model. In addition, NUFLEX is incorporated with various physical models, such as interfacial tracking, cavitation, MHD, melting/solidification and spray model. For the purpose of verification of the program and testing the applicability, many actual problems are solved and compared with the available data. Comparison of the results with that by STAR-CD or FLUENT program has been also made for the same flow configuration and grid structure to test the validity of NUFLEX.

• 천문학회지
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• 제34권2호
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• pp.67-80
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• 2001

Chemical evolution of galaxies can be understood by studying the spatial distribution of heavy elements. We selected two nearby galaxies, M31 and M33 and investigated spectrum of their HII regions: a) the elec-tron densities have been derived from the [S II] 6717/6731 ratio along with the most recent atomic constants (Hyung & Aller 1996); b) the electron temperatures were determinated from the Pagel's empirical method. Nebula Model (Hyung 1994) has been employed to predict the spectral line intensities which gives the proper chemical abundances. The model would predict the line intensities correctly only when various input parameters such as the effective central star temperatures, gravity log g, model atmosphere as well as the geometry and the nebula physical condition are appropriate. Thus, the determination of chemical abundances of O, S, N of the two nearby galaxies M31 and M33 has been done, which shows a radial dependance of O/H and N/H: decrease with the distance, or increasing electron temperature due to the elemental deficiency. Abundances of M31 appear to be enhanced than those of M33.

• 한국태양에너지학회 논문집
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• 제24권3호
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• pp.27-38
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• 2004

A numerical investigation has been carried out for a solar system, which consists of all glass solar vacuum tubes Water is heated as it flows through the coaxial fluid conduit inserted in each tube. The space between the exterior of the fluid conduit and the glass tube is filled with antifreeze solution. This is to facilitate heat transfer from the solar heated absorber surface to water and to prevent the functional problems due to freezing in frigid weather conditions. A one-dimensional steady state model is fully described which will be used to develop three-dimensional model using STAR-CD. These models could be used efficiently in designing all-glass solar collector tubes with different geometrical parameters other than those considered in the present analysis. Results show good agreement when compared with other experimental data demonstrating the reliability of the present model.