• 대한기계학회논문집
• /
• 제9권4호
• /
• pp.430-439
• /
• 1985

본 연구에서는 유한차분법을 사용하여 지배방정식의 수치해를 구하였으며, 특 히 유체와 고체 사이의 접촉면조건에서 correlation인자를 도입하여 K/$_{s}$/ $K_{f}$ 비가 큰 값에서는 수치해를 얻을 수가 있었다. 그리고 실험에서 여러가지 $K_{s}$/ $K_{f}$값에 대하여 온도를 측정하였으며, 여기서 계산치와 비교하면서 correlation인 자의 신뢰도를 조사하였다. 수평 이중 환상밀폐공간에서 유선 및 등온선을 여러가지 무차원 변수에 대하여 나타내었다. 등가 열전도도(equivalent conductivity)를 정의 하여 도입하고 $K_{s}$/ $K_{f}$값 중간 셸 두께, Prandtl 그리고 Rayleigh수에 대한 영향을 조사하여 이중 밀폐공간에서의 conjugate 자연대류 열전달특성을 연구하였다..였다..

• Structural Engineering and Mechanics
• /
• 제36권6호
• /
• pp.729-744
• /
• 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.

• 한국터널지하공간학회 논문집
• /
• 제8권3호
• /
• pp.273-287
• /
• 2006

본 연구에서는 숏크리트 라이닝과 2차 콘크리트 라이닝 사이에 방수막으로 분리된 기존 이중구조의 터널 라이닝과 터널 라이닝 단면상에 전단력 전달을 저해하는 장치를 포함하지 않은 일체화 싱글쉘 구조의 터널 라이닝의 파괴양상 및 하중 지지성능에 관해 고찰한다. 하중지지력 평가를 위하여 우선적으로 수치해석적인 사전 평가가 실시되었으며, 새롭게 고안된 실대형 터널 라이닝 하중재하 실험이 실시되었다. 이때, 이완하중이나 암괴하중을 모사하기 위해 터널 천단부 집중하중이 고려되었다. 본 연구를 통하여, 동일한 터널라이닝 강도 관리기준에서 이중구조 라이닝보다 싱글쉘 라이닝 구조가 약 20%정도 높은 지지력을 보였으며, 다중 숏크리트 타설 단계마다 고성능 첨가재료 투입량의 조절로 복합재료 싱글쉘 라이닝 구조를 형성함으로써 보다 적은 고성능화 첨가재료 투입량으로 유사한 지지성능을 확보할 수 있는 가능성을 보였다.

• Structural Engineering and Mechanics
• /
• 제61권2호
• /
• pp.231-244
• /
• 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
• /
• 제9권6호
• /
• pp.577-588
• /
• 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.

• 한국전산구조공학회:학술대회논문집
• /
• 한국전산구조공학회 1991년도 가을 학술발표회 논문집
• /
• pp.33-39
• /
• 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.

• 천문학논총
• /
• 제11권1호
• /
• pp.91-107
• /
• 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.

• 천문학회보
• /
• 제35권2호
• /
• pp.73.1-73.1
• /
• 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.

• 한국터널지하공간학회 논문집
• /
• 제10권2호
• /
• pp.167-175
• /
• 2008

터널공사비에 대한 국내외의 사례 조사 결과 싱글쉘 터널은 기존의 콘크리트 라이닝을 설치하는 이중쉘 터널에 비하여 공사비가 저렴하였다. 그러나 암반 상태가 불량해 질수록 싱글쉘 터널의 경제성은 급격히 저하되었다. 따라서 싱글쉘 공법은 암반상태가 양호한 지반에 적용해야 한다. 국내의 경우 일반적으로 여러 암반 등급이 다양하게 나타나므로 양호한 암반과 불량한 암반의 비율을 고려하여 싱글쉘 공법의 적용 여부를 판단해야 한다. 싱글쉘에 이용되는 숏크리트 및 록볼트는 영구지보재로서 고품질이어야 하므로 지보재료의 저렴한 공급여부에 따라서 싱글쉘 공법의 적용 대상 암반이 확대될 수 있을 것으로 기대된다.

• 천문학회지
• /
• 제53권2호
• /
• pp.35-42
• /
• 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.