• Structural Engineering and Mechanics
• /
• v.64 no.6
• /
• pp.737-749
• /
• 2017

A new quasi-3D higher shear deformation theory (quasi-3D HSDT) for functionally graded plates is proposed in this article. The theory considers both shear deformation and thickness-stretching influences by a hyperbolic distribution of all displacements within the thickness, and respects the stress-free boundary conditions on the upper and lower surfaces of the plate without using any shear correction factor. The highlight of the proposed theory is that it uses undetermined integral terms in displacement field and involves a smaller number of variables and governing equations than the conventional quasi-3D theories, but its solutions compare well with 3D and quasi-3D solutions. Equations of motion are obtained from the Hamilton principle. Analytical solutions for buckling and dynamic problems are deduced for simply supported plates. Numerical results are presented to prove the accuracy of the proposed theory.

• Journal of the Korean earth science society
• /
• v.36 no.5
• /
• pp.419-426
• /
• 2015

We investigated the high dispersion spectra that had been secured at the center of the planetary nebula NGC 7027 with the Bohyunsan Optical Echelle Spectrograph (BOES) on October, 20, 2009. We analyzed the forbidden lines of [OI], [SII], [OII], [NII], [ClIII], [ArIII], [OIII], [ArIV], [NeIII], [ArV], and [CaV] in the $3770-9225{\AA}$ wavelength region. The expansion velocities were derived from double Gaussian line profiles of the emission lines, after eliminating the subsidiary line broadening effects. The radial variations of the expansion velocities were obtained by projecting the derived expansion velocities: $19.56-31.93kms^{-1}$ onto the equatorial shell elements of the inner and the outer boundaries of the main shell of 2.5(2.1)" and 3.8(3.6)", according to the ionization potential of each ion. Analysis of equatorial shell spectra indicated that the equatorial shell generally expands in an accelerated velocity mode, but the expansion pattern deviates from a linear velocity growth with radial distance. NGC 7027, of which age is about 1000 years or less, might be still at its early stage. During the first few hundred years, plausibly in its early stage, the main shell of PN expands very slowly and, later, it gradually gain its normal expansion speed.

• The Bulletin of The Korean Astronomical Society
• /
• v.39 no.2
• /
• pp.63.2-63.2
• /
• 2014

We observed a bright type Ia Supernovae SN 2014J located in the nearby starburst galaxy M82 using BOES (Bohyunsan Optical Echelle Spectrograph) for eight nights from day -11 (Jan. 22) to day +102 (May. 15) with respect to maximum brightness in B-band. We found the lines formed in the ejecta such as Si ($6300{\AA}$), whose velocity is more than 10,000km/s respect to the host galaxy as well as those formed in the circumstellar material (e.g. Na I D [$5890{\AA}$, $5896{\AA}$], 100km/s) Also, we found other weak iron ($5780{\AA}$, $5797{\AA}$, $6376{\AA}$, $6613{\AA}$, and $7543{\AA}$), carbon ($8059{\AA}$) and other unknown elements. These lines are also thought to have been formed in circumstellar material. We expect that this study will contribute to revelation of the nature of the progenitor stars.

• Publications of The Korean Astronomical Society
• /
• v.18 no.1
• /
• pp.75-79
• /
• 2003

The characteristics of the BOES (Bohyunsan Observatory Echelle Spectrograph) CCD camera is presented. In order to get optimum gain and readout noise of the CCD, we examine the variation of the gain and readout noise by changing the value of output drain voltage of the CCD and measuring the gain using transfer curve, which is defined as the plot of variance versus mean exposure level of a homogeneous light onto the CCD surface. The gain and readout noises are optimised to be 0.5e$^-$/ADU and 3e$^-$, which is good for highest signal-to-noise ratio and contrast for the low light level characteristics of the BOES. We also measure the dark count of the CCD by getting five dark images with 3600 seconds exposure time. The mean dark count from median stacked dark images is essentially zero. A table of positions of defected pixels is also presented.

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.1
• /
• pp.77.1-77.1
• /
• 2012

We present high-resolution radial velocity measurements of K2 giant ${\varepsilon}$ CrB from February 2005 to January 2012 using the fiber-fed Bohyunsan Observatory Echelle Spectrograph at Bohyunsan Optical Astronomy Observatory. We find that the RV measurements for ${\varepsilon}$ CrB exhibit a periodic variation of 418 days with a semi-amplitude of 129 m/s. There is no correlation with RV measurements and inhomogeneous surface features by examining chromospheric activity indicator (Ca II H region), the Hipparcos photometry, and bisector velocity span. Thus, Keplerian motion is the most likely explanation, which suggests that the RV variations arise from an orbital motion. Assuming a possible stellar mass of 1.7 $M_{\odot}$, for ${\varepsilon}$ CrB, we obtain a minimum mass for the planetary companion of 6.7 $M_{Jup}$ with an orbital semi-major axis of 1.3 AU, and an eccentricity of 0.11. We support that more massive stars harbor more massive planetary companions in giant hosting planetary companions (Dollinger et al. 2009), as well as, we discuss the frequency of detected planetary companions with the metallicity distribution in giant (Pasquini et al. 2007; Quirrenbach et al. 2011).

• The Bulletin of The Korean Astronomical Society
• /
• v.37 no.1
• /
• pp.80.1-80.1
• /
• 2012

NGC 6803 is an elliptical ring shape planetary nebula. We analyzed the high dispersion spectra which had been observed with the Hamilton Echelle Spectrograph attached to the 3-m Shane telescope of Lick Observatory. We also investigated the low dispersion UV spectral data obtained with the 60-cm interstellar ultraviolet explorer. Diverse excitation lines were found from neutral to quadruply ionized ions. The temperature diagnostic lines indicate relatively low electron temperatures, i.e., $T_{\epsilon}{\leq}9500$ K for most lines except for [ClIV] - 11,500 K. In spite of its simplistic bi-laterally symmetrical elliptical shape, the nebula appears to be very complex of a hugh density range from 1300 to 80,000 $cm^3$. A comparison of the two epoch data suggests that the density increase occurred in the high excitation line zone near the inner boundary. We derived the chemical abundances of He, C, N, O, Ne, S, Ar, Cl, and K. The chemical abundances of NGC 6803 are enhanced compared with the average Galactic planetary nebula. Our self-consistent photo-ionization model study implies that the effective temperature of the central star is 90,000 K and its luminosity is 2400 $L_{\odot}$. The evolutionary track suggests that the progenitor of NGC 6803 was about 0.9 -- 1.0 $M_{\odot}$ star, which might be born from a metal-rich zone near the galactic disk, but now relocated into the present high Galactic latitude.

• The Bulletin of The Korean Astronomical Society
• /
• v.42 no.2
• /
• pp.56.4-57
• /
• 2017

The GMT-Consortium Large Earth Finder (G-CLEF) is the very first light instrument of the Giant Magellan Telescope (GMT) to be commissioned in 2022. The instrument is a fiber feed, optical band echelle spectrograph that is capable of extremely precise radial velocity measurement. Korea Astronomy and Space Science Institute (KASI) has been involved in the development of the G-CLEF as one member of the international consortium consisted of five astronomical institutes including Smithsonian Astrophysical Observatory (SAO), Observatories of the Carnegie Institution of Washington (OCIW). It is scheduled to have KASI side Critical Design Review in December 2017. In this presentation we will report the recent progress on the critical design activities for the G-CLEF Flexure Control Camera (FCC).

• Journal of The Korean Astronomical Society
• /
• v.53 no.1
• /
• pp.27-34
• /
• 2020

We report the detection of exoplanet candidates in orbits around HD 60292 and HD 112640 from a radial velocity (RV) survey. The stars exhibit RV variations with periods of 495 ±3 days and 613±6 days, respectively. These detections are part of the Search for Exoplanets around Northern Circumpolar Stars (SENS) survey using the fiber-fed Bohyunsan Observatory Echelle Spectrograph installed at the 1.8-m telescope of the Bohyunsan Optical Astronomy Observatory in Korea. The aim of the survey is to search for planetary or substellar companions. We argue that the periodic RV variations are not related to surface inhomogeneities; rather, Keplerian motions of planetary companions are the most likely interpretation. Assuming stellar masses of 1.7 ± 0.2M_⊙ (HD 60292) and 1.8 ± 0.2M_⊙ (HD 112640), we obtain minimum planetary companion masses of 6.5 ± 1.0M_Jup and 5.0 ± 1.0M_Jup, and periods of 495.4 ± 3.0 days and 613.2 ± 5.8 days, respectively.

• Wind and Structures
• /
• v.22 no.3
• /
• pp.329-348
• /
• 2016

This work presents a simple hyperbolic shear deformation theory for analysis of functionally graded plates resting on elastic foundation. The proposed model contains fewer number of unknowns and equations of motion than the first-order shear deformation model, but the transverse shear stresses account for a hyperbolic variation and respect the tangential stress-free boundary conditions on the plate boundary surface without introducing shear correction factors. Equations of motion are obtained from Hamilton's principle. The Navier-type analytical solutions for simply-supported plates are compared with the existing solutions to demonstrate the accuracy of the proposed theory.

• Structural Engineering and Mechanics
• /
• v.57 no.4
• /
• pp.617-639
• /
• 2016

In this work, an analytical formulation based on both hyperbolic shear deformation theory and stress function, is presented to study the nonlinear post-buckling response of symmetric functionally graded plates supported by elastic foundations and subjected to in-plane compressive, thermal and thermo-mechanical loads. Elastic properties of material are based on sigmoid power law and varying across the thickness of the plate (S-FGM). In the present formulation, Von Karman nonlinearity and initial geometrical imperfection of plate are also taken into account. By utilizing Galerkin procedure, closed-form expressions of buckling loads and post-buckling equilibrium paths for simply supported plates are obtained. The effects of different parameters such as material and geometrical characteristics, temperature, boundary conditions, foundation stiffness and imperfection on the mechanical and thermal buckling and post-buckling loading capacity of the S-FGM plates are investigated.