• Title/Summary/Keyword: Critical Geometry

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Thermal buckling analysis of functionally graded sandwich cylindrical shells

  • Daikh, Ahmed Amine
    • Advances in aircraft and spacecraft science
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    • v.7 no.4
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    • pp.335-351
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    • 2020
  • Thermal buckling of functionally graded sandwich cylindrical shells is presented in this study. Material properties and thermal expansion coefficient of FGM layers are assumed to vary continuously through the thickness according to a sigmoid function and simple power-law distribution in terms of the volume fractions of the constituents. Equilibrium and stability equations of FGM sandwich cylindrical shells with simply supported boundary conditions are derived according to the Donnell theory. The influences of cylindrical shell geometry and the gradient index on the critical buckling temperature of several kinds of FGM sandwich cylindrical shells are investigated. The thermal loads are assumed to be uniform, linear and nonlinear distribution across the thickness direction. An exact simple form of nonlinear temperature rise through its thickness taking into account the thermal conductivity and the inhomogeneity parameter is presented.

MULTI-HARMONIC MODELS FOR BUBBLE EVOLUTION IN THE RAYLEIGH-TAYLOR INSTABILITY

  • Choi, Sujin;Sohn, Sung-Ik
    • Journal of the Korean Mathematical Society
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    • v.54 no.2
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    • pp.663-673
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    • 2017
  • We consider the multi-harmonic model for the bubble evolution in the Rayleigh-Taylor instability in two and three dimensions. We extend the multi-harmonic model in two dimensions to a high-order and present a new class of steady-state solutions of the bubble motion. The growth rate of the bubble is expressed by a continuous family of two free parameters. The critical point in the family of solutions is identified as a saddle point and is chosen as the physically significant solution. We also present the multi-harmonic model in the cylindrical geometry and find the steady-state solution of the axisymmetric bubble. Validity and limitation of the model are also discussed.

Counter-Current Flow Limit in Narrow Gap (간극에서의 역방향 유동 제한 현상 연구)

  • Kim, Yong-Hoon;Suh, Kune-Y.
    • Proceedings of the KIEE Conference
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    • 1998.11c
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    • pp.1054-1060
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    • 1998
  • Previous counter-current flow limitation (CCFL) and critical heat flux (CHF) studies included investigations on the inlet entrance, inclined channel and gap effects for the most part. In this study, the local CHF correlation was presented to be used in the numerical analysis for the 3 dimensional hemispherical geometry. Also, first-principle analyses were performed to determine the maximum heat removal capability from the debris through the gap that may be formed during a core melt accident. The maximum heat removal capability by gap cooling can be applied in quantitatively assessing the severe accident management measures.

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INVESTIGATION ON PREDICTION OF FORMING LIMIT FOR COLD UPSETTING BY UTILIZING ENERGY FRACTURE CRITERION

  • Lee Rong-Shean;Wang Shui-To;Chen Jih-Hsing
    • Proceedings of the Korean Society for Technology of Plasticity Conference
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    • 2003.10b
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    • pp.22-25
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    • 2003
  • The forming limits are studied for cold upsetting of high strength aluminium alloy in the present paper. Different geometry ratio and frictional conditions are investigated in the forgeability test to evaluate the forming limits and also to obtain the various strain paths. The critical fracture value can be obtained by integrating along the strain path till free surface crack initiation. To predict the damage evolution of cold upsetting, the computer-aided evaluation of forming limits is obtained by using the finite-element software DEFORM-3D and the modified Cockcroft-Latham criterion. The predicted theoretical limit strains agree quite well with the experimental results.

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Effects of Three-dimensional Scaffolds on Cell Organization and Tissue Development

  • Yan Li;Yang, Shang-Tian
    • Biotechnology and Bioprocess Engineering:BBE
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    • v.6 no.5
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    • pp.311-325
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    • 2001
  • Tissue engineering scaffolds play a critical role in regulating the reconstructed human tissue development. Various types of scaffolds have been developed in recent years, including fibrous matrix and foam-like scaffolds. The design of scaffold materials has been investigated extensively. However, the design of physical structure of the scaffold, especially fibrous matrices, has not received much attention. This paper compares the different characteristics of fibrous and foam-like scaffolds, and reviews regulatory roles of important scaffold properties, including surface geometry, scaffold configuration, pore structure, mechanical property and bioactivity. Tissue regeneration, cell organization, proliferation and differentiation under different microstructures were evaluated. The importance of proper scaffold selection and design is further discussed with the examples of bone tissue engineering and stem cell tissue engineering. This review addresses the importance of scaffold microstructure and provides insights in designing appropriate scaffold structure for different applications of tissue engineering.

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MAGNETIC RECONNECTION IN SHEARED SOLAR MAGNETIC ARCADES

  • CHOE G. S.
    • Journal of The Korean Astronomical Society
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    • v.29 no.spc1
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    • pp.303-305
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    • 1996
  • The evolution of solar magnetic arcades is investigated with the use of MHD simulations imposing resistivity on sheared magnetic fields. It is found that there is a critical amount of shear, over which magnetic reconnection can take place ill an arcade-like field geometry to create a magnetic island. The process leading to reconnect ion cannot. be solely attributed to a tearing instability, but rather to a reactive evolution of the magnetic arcade under resistivity. The natures of the arcade reconnection are governed by the spatial pattern of resistivity. A fast reconnection with a small shock angle can only be achieved when the diffusion region is localized. In this case. a highly collimated reconnect ion outflow can tear the plasmoid into a pair, and most of principal features in solar eruptive processes are reproduced.

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AN INTEGRATED SYSTEM FOR COMPUTATIONAL AERODYNAMIC, STRUCTURAL AND RF STEALTH ANALYSIS (공력-구조-RF 스텔스 통합 전산해석 시스템 연구)

  • Park, G.R.;Yang, Y.R.;Jung, S.K.;Myong, R.S.;Cho, T.H.
    • 한국전산유체공학회:학술대회논문집
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    • 2010.05a
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    • pp.78-82
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    • 2010
  • An integrated multi-disciplinary design system plays a critical role in the preliminary design of an aircraft. In this paper such system is developed for the multi-disciplinary computation and design; aerodynamics elasticity, and radio frequency stealth. Common data base of geometry and structured grids is generated and used for aerodynamic, structural and eletromagnetics analysis. The Navier-Stokes CFD, FEM, and CEM technique are used for aerodynamic, structural, and RF stealth computations respectively.

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Buckling of Composite Cylindrical Shells Sugjected ot Torsion of Lateral Pressure (비틀림 및 횡압럭을 받고 있는 복합재 원통쉘의 좌굴)

  • Han, Byeong-Gi;Lee, Seong-Hui;Yu, Taek-In
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.5
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    • pp.1436-1444
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    • 1996
  • The problem ofinstability of laminated circular cylindrical shell under the action of torsio or lateral pressure is investigated. The analysis is based on the Sander's theory for finite deformations of thin shell. The buckling is elastic for thin compoisite shell nad the geometry is assumed to be free of initial imperfections. The equilibrium equations are obrained by usitn the p[erturbation technique. Solution procedure is based on the Galerkin mehtod. The computer program for numerical results is made for several stacking sequence, length-to-radius ratio, and radius-to-thickness ratio. The numerical results of buckling load are present.

Study on the Behavior of a Center Crack under Thermal Impact by the Dislocation Theory (전위이론에 의한 열충격하의 균열거동에 관한 연구)

  • Cho, Chong-Du;Ahn, Soo-Ick
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.20 no.10
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    • pp.3408-3414
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    • 1996
  • This paper investigated plane strain stress intensity factors caused by thermal impact on a center-crack strip. The crack was aligned perpendicularly to the strip boundary. The problem was analysed by determining the dislocation density function in the singular integral equations formulated by the dislocation theory. Under the abrupt temperature change along the edge, the center crack behaved as a mode I crack due to the symmetric geometry. The value of maximum stress intensity factor monotonically increased until the ratio of dimensionless crack length approached to about 0.3, followed by gradual decrease. As a result, a critical corresponding crack length was determined.

Thrbulent Wake Structure behind Rectangular Cylinders in a Uniform Shear Flow (균일한 전단류에 놓인 각주 후류의 난류구조)

  • 부정숙;양종필;구명섭
    • Journal of Advanced Marine Engineering and Technology
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    • v.18 no.1
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    • pp.101-113
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    • 1994
  • This research has presented and experimental investigation on the characteristics of turbulent wake past a rectanular cylinder, according to various width/height ratio such as B/H=2.0, 2.79, 3.0, and 4.0 in a uniform shear flow. In order to perform this study, a special shear flow generator which produces the uniform shear flow has been designed and manufactured. It is found that the characteristics of the wake in a uniform shear flow are quite different from those of a uniform flow and vary with shear rate. And also, the formation of regular vortex structure is concerned with shear rate.

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