• Transactions of the Korean Society of Mechanical Engineers
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• v.9 no.4
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• pp.430-439
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• 1985

Conjugate natural convection in double enclosed annuli between horizontal concentric cylinders has been studied by the numerical analysis and experimental measurements. The interface conditions between the liquid and the solid of middle shell are obtained through the correlation factor based on the ratio of solid to fluid thermal conductivities and the Prandtl number. The characteristics of conjugate heat transfer are discussed under various dimensionless parameters such as conductivity ratios, shell thickness, diameter ratios, Prandtl number, and Rayleigh number. It is found that the average equivalent conductivity K over var $_{eq}$ does not depend on the conductivity ratios and shell thickness. The K over bar $_{eq}$ however, depends on the Prandtl number and the Rayleigh number.

• Structural Engineering and Mechanics
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• v.36 no.6
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• pp.729-744
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• 2010

There is world wide concern for safety of nuclear power installations after the terrorist attack on World Trade Center in 2001 and several other civilian structures in the last decade. The nuclear containment structure in many countries is a double shell structure (outer shell a RCC and inner a prestressed concrete). The outer reinforced concrete shell protects the inner shell and is designed for external loading like impact and blast. A comparative study of non-linear response of reinforced concrete nuclear containment cylindrical shell subjected to impact of an aircraft (Phantom) and explosion of different amounts of blast charges have been presented here. A material model which takes into account the strain rate sensitivity in dynamic loading situations, plastic and visco-plastic behavior in three dimensional stress state and cracking in tension has been developed earlier and implemented into a finite element code which has been validated with published literature. The analysis has been made using the developed software. Significant conclusions have been drawn for dissimilarity in response (deflections, stresses, cracks etc.) of the shell for impact and blast loading.

• Journal of Korean Tunnelling and Underground Space Association
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• v.8 no.3
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• pp.273-287
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• 2006

This study investigates the failure mechanism and load-carrying capacity of a single-shell lining which has no disturbance in transfer of shear force, with respect to a conventional double-shell lining which has separation between layers of shotcrete lining and secondary concrete lining by water-proof membrane. In order to evaluate the capacity, a 2-D numerical investigation is preliminarily carried out and then real-scale loading tests with tunnel lining section specimens are performed on the condition given by the numerical investigation. In the test, a concentrated load is applied for considering a released ground load or rock wedge load. Through this study, it appears that the single-shell lining takes the load-bearing capacity 20% higher than in case of the double-shell lining. In addition, a possibility of a composite single-shell shotcrete layer composed by multiple bonded layers partly involving different contents of high-capacity additives is shown thereby leading to use of less amount of the high-capacity additives on the condition of taking a similar load-bearing capacity.

• Structural Engineering and Mechanics
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• v.61 no.2
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• pp.231-244
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• 2017

The aim of this study is to develop a semi-analytical method to investigate fluid-structure coupling of concentric double shells with different lengths and elastic behaviours. Co-axial shells constitute a cylindrical circular container and a baffle submerged inside the stored fluid. The container shell is made of functionally graded materials with mechanical properties changing through its thickness continuously. The baffle made of steel is fixed along its top edge and submerged inside fluid such that its lower edge freely moves. The developed approach is verified using a commercial finite element computer code. Although the model is presented for a specific case in the present work, it can be generalized to investigate coupling of shell-plate structures via fluid. It is shown that the coupling between concentric shells occurs only when they vibrate in a same circumferential mode number, n. It is also revealed that the normalized vibration amplitude of the inner shell is about the same as that of the outer shell, for narrower radial gaps. Moreover, the natural frequencies of the fluid-coupled system gradually decrease and converge to the certain values as the gradient index increases.

• Advances in concrete construction
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• v.9 no.6
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• pp.577-588
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• 2020

In this paper, vibration attributes of chiral double-walled carbon nanotubes (CNTs) based on nonlocal elastic shell model have been investigated. The impact of small scale is being perceived by establishing Flügge shell model. The wave propagation is engaged to frame the ruling equations as eigen value system. The influence of nonlocal parameter subjected to different end supports has been overtly examined. A suitable choice of material properties and nonlocal parameter been focused to analyze the vibration characteristics. The new set of inner and outer tubes radii investigated in detail against aspect ratio and length. The dominance of boundary conditions via nonlocal parameter is shown graphically. Whereas for lower aspect ratio the frequencies coincide but as it continues to expand the difference between all respective boundary conditions slightly tend to increase. The results generated furnish the evidence regarding applicability of nonlocal shell model and also verified by earlier published literature.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1991.10a
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• pp.33-39
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• 1991

This Paper presents a geometrically nonlinear behaviors of shell problems by using the three-dimensional curved shell element, which includs large displacements and large rotations. The standard formulation of the geometrically nonlinearity is restricted to the assumption of infinitesmal rotation increments. This standard formulation for the displacement function is numerically improved by considering the second order expansions of Tayler series. The nonlinear behaviors of the single and double curved shells are compared wi th the other results.

• Publications of The Korean Astronomical Society
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• v.11 no.1
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• pp.91-107
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• 1996

We determine analytically the onset of thin-shell formation time of fast wind bubble with power-law energy injection $E_{in}=E_0t^s$, and power-law ambient density structure, ${\rho}_0(r)={\bar{\rho}}(r/{\bar{r}})^{-{\omega}}$. Thin-shell formation time, $t_{sf}$ can be estimated by minimizing the total time elapsed before the complete cooling of shocked gas. For uniform medium (${\omega}=0$) and constant energy injection (s = 1), the onset of shell formation is found to be at $t_{sf}=5.2{\times}10^3yr$, which agrees Quite well with the results of FCT 1D numerical calculation. We solve the line transfer problem with previous result derived by numerical calculation in order to calculate line profile of [OIII] (${\lambda}=5007{\AA}$) forbidden line. In general, radiative outer shell causes the formation of double peaked line profile. Each peak corresponds to approaching and receeding shells with large velocities. Our line profiles show good agreements with observation of expanding shell structure.

• The Bulletin of The Korean Astronomical Society
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• v.35 no.2
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• pp.73.1-73.1
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• 2010

Using the spectroscopic data secured with the Hamilton Echelle Spectrograph attached to a 3-m telescope at the Lick Observatory, we derived the expansion velocities from various line profiles in the 3600 $\AA$ to 10,000 $\AA$ based on the full width at half maximum and double peak of the high dispersion line profiles. The symmetrical shapes of the permitted line profiles indicate that the permitted line zone is symmetrical e.g., a spherical shell or bipolar + torus structures, which might be evidence of relatively recent ejection from the central star. Most other stronger forbidden lines might be coming from a main shell which appears as a bilateral symmetrical morphology, seen in HST and other ground-based telescopic images. The overall expansion velocities of this main shell structure that are responsible for most lines, seem to show the Hubble type expansion, i.e., accelerating shell. The faster expansion velocities of the permitted OII, NII, NIII and perhaps CII lines that do not suit to the Hubble type expansion, imply the existence of a somewhat smaller inner shell inside the outer main shell. We conclude that the nebular shell consists of a swiftly expanding inner shell and an outer normal shell excited by a central star of about 55,000K. The former compact zone appears to be responsible for the permitted C, N, and O lines while the latter extended shell appears to be responsible for H, He, and forbidden lines. We present some evidence that NGC 6833 be a member of the Galactic halo.

• Journal of Korean Tunnelling and Underground Space Association
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• v.10 no.2
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• pp.167-175
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• 2008

The construction cost for the single shell tunnel is cheaper than that of the double shell tunnel according to the case studies performed in several domestic and foreign tunnels. However, the economic advantage of single shell tunnel drops drastically as the condition of the rock mass deteriorates. Therefore, the single shell tunnelling method should be applied to the good rock mass conditions. The application of the single shell tunnelling method to tunnels in Korea should be determined considering the ratio between the good rock and poor rock masses along the tunnel section. The use of the single shell tunnel is expected to offend depending on the cheap supply of high quality shotcrets and rock bolts developed for single shell tunnels.

• Journal of The Korean Astronomical Society
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• v.53 no.2
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• pp.35-42
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• 2020

We analyze high dispersion emission lines of the symbiotic nova AG Pegasi, observed in 1998, 2001, and 2002. The Hα and Hβ lines show three components, two narrow and one underlying broad line components, but most other lines, such as H_I, He_I, and He_II lines, show two blue- and red-shifted components only. A recent study by Lee & Hyung (2018) suggested that the double Gaussian lines emitted from a bipolar conical shell are likely to form Raman scattering lines observed in 1998. In this study, we show that the bipolar cone with an opening angle of 74°, which expands at a velocity of 70 km s^-1 along the polar axis of the white dwarf, can accommodate the observed double line profiles in 1998, 2001, and 2002. We conclude that the emission zone of the bipolar conical shell, which formed along the bipolar axis of the white dwarf due to the collimation by the accretion disk, is responsible for the double Gaussian profiles.