• Steel and Composite Structures
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• v.33 no.1
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• pp.93-109
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• 2019

In the present study, vibration analysis of double bonded micro sandwich cylindrical shells with saturated porous core and carbon/boron nitride nanotubes (CNT/BNNT) reinforced composite face sheets under multi-physical loadings based on Cooper-Naghdi theory is investigated. The material properties of the micro structure are assumed to be temperature dependent, and each of the micro-tubes is placed on the Pasternak elastic foundations, and mechanical, moisture, thermal, electrical, and magnetic forces are effective on the structural behavior. The distributions of porous materials in three distributions such as non-linear non-symmetric, nonlinear-symmetric, and uniform are considered. The relationship including electro-magneto-hydro-thermo-mechanical loadings based on modified couple stress theory is obtained and moreover the governing equations of motion using the energy method and the Hamilton's principle are derived. Also, Navier's type solution is also used to solve the governing equations of motion. The effects of various parameters such as material length scale parameter, temperature change, various distributions of nanotube, volume fraction of nanotubes, porosity and Skempton coefficients, and geometric parameters on the natural frequency of double bonded micro sandwich cylindrical shells are investigated. Increasing the porosity and the Skempton coefficients of the core in micro sandwich cylindrical shell lead to increase the natural frequency of the structure. Cylindrical shells and porous materials in the industry of filters and separators, heat exchangers and coolers are widely used and are generally accepted today.

• Bulletin of the Society of Naval Architects of Korea
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• v.24 no.1
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• pp.42-50
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• 1987

The energy expressions are formulated for the axially stiffened shell treating the stiffeners as discrete elements. The principle of minimum potential energy is employed to formulate the buckling equations for a simply supported, axially stiffened shell under uniform axial compression. The displacement functions are expended into double trigonometric series. The mode assuming method employed in this paper makes it possible to reduce the matrix size of the eigenvalue problem considerably. Effects are made to investigate the transition from overall buckling to local buckling and to verify the existence of the minimum stiffness ratio of stiffener as in the case of stiffened plate. The results of the calculation show that the critical stiffener size increase linearly as the length of the shell increases. The results also show that the overall buckling load decreases and the local buckling load has a nearly constant value as the length of the shell increases. The results show very good agreements with other computational available.

• Journal of the Korean Society of Marine Environment & Safety
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• v.4 no.2
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• pp.1-12
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• 1998

This paper descirbes a series of numberical simulations of grounding accidents of four 40,000 DWT Conventional and Advanced Double Hull tanker bottom structures using LS/DYNA3D. The overall objective of this study is no understand the structural failure and energy absorbing mechanisms during grounding events for candidate double hull tanker bottom structures, which lead to the initiation of inner shell rupture and cause the kinetic energy dissipation to bring the ship to a stop. These nuberical simulations of the grounding events will contribute to future improvements in tanker safety at the design stage.

• Korean Journal of Computational Design and Engineering
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• v.11 no.3
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• pp.157-163
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• 2006

Surfaces of many engineering structures, especially, those of ships are commonly made out of either single- or double-curved surfaces to meet functional requirements. The first step in the fabrication process of a three-dimensional design surface is unfolding or flattening the surface, otherwise known as planar development, so that manufacturers can determine the initial flat plate which is required to form the design shape. In this paper, an algorithm for optimal approximated development of a general curved surface, including both single- and double-curved surfaces, is established by minimizing the strain energy of deformation from its planar development to the design surface. The unfolding process is formulated into a constrained nonlinear programming problem, based on the deformation theory and finite element. Constraints are subjected to the characteristics of the fabrication method. And the design surface, or the curved shell plate is subdivided by automatic mesh generation.

• Journal of the Korean Magnetics Society
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• v.8 no.6
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• pp.341-345
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• 1998

Magnetic shielding effect of cylinderical ahields made of commericial amorphous ribbons has been studied. The shell-arrangement-order of double shell shield has been found to show a striking differencein shielding factor. In low applied field region, a 2605CO-2705M-shield (outer shell: 2605CO, inner shell: 2705M) yields two times higher shielding factor than a 2705M-2605CO-shield (outer shell: 2705M, inner shell: 2605CO). The reasons are as follows: In case of 2605CO-2705M-shield, the outer shell is not easily saturated and effectively shields the applied field. In addition, the inner shell shows high shielding factor in the field shielded by the outer shell. In case of 2705M-2605CO-shield, the outer shell is saturated at very low-field as well as the inner shell shows low shielding factor in the field shielded by the outer shell.

• Clean Technology
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• v.28 no.2
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• pp.154-162
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• 2022

Microstructured Al@Al₂O₃ and Al@Ni-Al LDH (LDH = layered double hydroxide) core-shell metal-ceramic composites are prepared by hydrothermal reactions of aluminum (Al) metal substrates. Controlled hydrothermal reactions of Al metal substrates induce the hydrothermal dissolution of Al ions at the Al-substrate/solution interface and reconstruction as porous metal-hydroxides on the Al substrate, thereby constructing unique metal-ceramic core-shell composite structures. The morphology, composition, and crystal structure of the core-shell composites are affected largely by the ions in the hydrothermal solution; therefore, the critical physicochemical and surface properties of these unique metal-ceramic core-shell microstructures can be modulated effectively by varying the solution composition. A Ni/Al@Al₂O₃ catalyst with highly dispersed catalytic Ni nanoparticles on an Al@Al₂O₃ core-shell substrate was prepared by a controlled reduction of an Al@Ni-Al LDH core-shell prepared by hydrothermal reactions of Al in nickel nitrate solution. The reduction of Al@Ni-Al LDH leads to the exolution of Ni ions from the LDH shell, thereby constructing the Ni nanoparticles dispersed on the Al@Al₂O₃. The catalytic properties of the Ni/Al@Al₂O₃ catalyst were investigated for CO₂ methanation reactions. The Ni/Al@Al₂O₃ catalyst exhibited 2 times greater CO₂ conversion than a Ni/Al₂O₃ catalyst prepared by conventional incipient wetness impregnation and showed high structural stability. These results demonstrate the high effectiveness of the design and synthesis methods for the metal-ceramic composite catalysts derived by hydrothermal reactions of Al metal substrates.

• Special Issue of the Society of Naval Architects of Korea
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• 2013.12a
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• pp.81-84
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• 2013

일반적인 Bulk carrier는 Single deck, Double bottom, Hopper side tank, Top side tank와 함께 Single side skin 또는 Double side skin으로 구성되어 Single hull bulk carrier 또는 Double hull bulk carrier라 불린다. 본 논문의 연구선박인 Double hull bulk carrier는 CSR에서 규정짓고 있는 Double hull bulk carrier의 특징 중 Hopper side tank가 없기에 일반적인 Double hull bulk carrier와는 다른 구조를 가진다. 구조적 특징으로는 Inner bottom과 Inner hull 연결부위에 응력 집중 발생, Side shell의 Shear에 대해 구조적 안전성, Double hull에 대한 CSR for bulk carrier의 Rule적용 여부에 대한 판단 등이 있다. 따라서 본 연구에서는 Double hull bulk carrier의 구조적 특징과 구조해석을 통한 응력 집중 부위의 평가 및 Fatigue analysis을 통한 피로수명을 계산하여 이를 통해 구조의 안전성을 살펴보고자 한다.

• Polymer(Korea)
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• v.36 no.6
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• pp.699-704
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• 2012

Double-layered polymeric carrier was designed for release control of hydrophilic drug in oral administration. Biopolymeric chitosan and alginate were examined as polar absorbents, poly(D,L-lactide) as a hydrophobic shell, and theophylline and diclofenac sodium as loading drugs. The fabrication of the carriers was prepared in the form of double-layered microsphere for delayed and successively extended release, which consisted of outer shell of poly(D,L-lactide) and inner core of alginate or chitosan with drugs. Morphologies and drug-release behaviors of the carriers were investigated, which were influenced by a combination of polarity between carrier and drug. It was confirmed that the relative polarities of the carriers, the drugs, and the environmental pH affected significantly the drug-release property.

• Korean Chemical Engineering Research
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• v.60 no.1
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• pp.139-144
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• 2022

This study reports a microfluidic approach to produce monodisperse hydrogel microparticles in a simple and highly efficient manner. Specifically, we produce double emulsion drops with a thin oil shell surrounding an aqueous prepolymer solution, which is solidified via UV-induced free radical polymerization. When they are dispersed in an aqueous solution, the oil shell is dewetted due to the absence of surfactants, resulting in production of highly uniform hydrogel microparticles (C.V.=1%). Results show that production of monodisperse hydrogel microparticles with controllable size and composition can be achieved with minimal use of oil unlike water-in-oil (w/o) single emulsion-based approach. Furthermore, in-depth study of flow patterns in microfluidic device using a phase diagram exhibits a crucial relationship among relative flow rates while providing windows of readily controllable parameters for reliable manufacturing of hydrogel microparticles.

• The Bulletin of The Korean Astronomical Society
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• v.36 no.1
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• pp.53.2-53.2
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• 2011

A small number of active galactic nuclei are known to exhibit prominent double peak emission profiles indicating the presence of a relativistic accretion disk model. Using a Monte Carlo technique, we compute the linear polarization of a double peaked broad emission line. A Keplerian accretion disk is adopted for the double peak emission line region and the Schwarzschild geometry is assumed in the emission region. Far from the accretion disk where flat Minkowski geometry is appropriate, we place a scattering region in the shape of a spherical shell sliced. We generate a line photon in the accretion disk in an arbitraray direction in the local rest frame and follow the geodesic of the photon until it hits the scattering region. The profile of the polarized flux is mainly determined by the relative location of the scattering region with respect to the emission source. When the scattering region is in the polar direction, the linear degree of polarization also shows a double peak structure. Under a favorable condition we show that up to 1% of linear degree of polarization may be obtained.