• Advances in aircraft and spacecraft science
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• 제4권6호
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• pp.639-650
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• 2017

The objective of this paper is to obtain three-dimensional (3D) effective properties for layered composites with imperfect interfaces using mechanics of structure genome. The imperfect interface is modeled using linear traction-displacement model that allows small infinitesimal displacement jump across the interface. The predictions obtained from the current analysis are compared with the 3D finite element analysis (FEA). In this study, it is found that the present model shows excellent agreement with the results obtained using 3D FEA by employing periodic boundary conditions. The prediction also reveals that in-plane longitudinal and shear moduli, and all Poisson's ratios are observed to be not affected by the interfacial stiffness while the predictions of transverse longitudinal and shear moduli are significantly influenced by interfacial stiffness.

• 한국전자파학회:학술대회논문집
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• 한국전자파학회 2005년도 종합학술발표회 논문집 Vol.15 No.1
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• pp.347-352
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• 2005

Scan Element Pattern(SEP) and Scan Impedance(SI) concepts are used to analyze the characteristics of open-ended waveguide array, which is the representative phased array antenna element in C-band and X-band. Transmit SEP's are calculated for 15$\sim$15 subarray and SI's are obtained by applying periodic boundary conditions for a unit cell of the given array condition. CST's MWS and Ansoft's HFSS are utilized for each analysis. Some relations are reviewed between the two results, which are based on mutual coupling effects. For validation purpose, an 8$\sim$8 subarray is constructed and tested. Transmit SEP measured in MTG's far-field range shows good agreement with the calculated transmit SEP.

• 한국해양공학회지
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• 제10권3호
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• pp.62-73
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• 1996

Numerical simulation is made of the three-dimensional wave breaking motion about a part of a floating offshore structure containing a circular cylinder mounted vertically onto a lower hull in regular periodic gravity wave generated by a numerical wave maker. TUMMAC-VIII finite-difference method is newly developed for such a problem. By use of density-function technique the three-dimensional wave breaking motion is approximately implenented in the framework of rectangular grid system. A porosity technique is devised for the implementation of the no-slip bydy boundary conditions. The generation of breaking waves by the interaction of incident waves with the structure is well simulated and interesting features of breaking waves are revealed with containing degree of quantitative and qualitative accuracy.

• 대한수학회보
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• 제53권1호
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• pp.61-81
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• 2016

In this paper, we prove some existence and uniqueness results on coincidence points for g-monotone mappings satisfying linear as well as generalized nonlinear contractivity conditions in ordered metric spaces. Our results generalize and extend two classical and well known results due to Ran and Reurings (Proc. Amer. Math. Soc. 132 (2004), no. 5, 1435-1443) and Nieto and $Rodr{\acute{i}}guez$-$L{\acute{o}}pez$ (Acta Math. Sin. 23 (2007), no. 12, 2205-2212) besides similar other ones. Finally, as an application of one of our newly proved results, we establish the existence and uniqueness of solution of a first order periodic boundary value problem.

• 한국안전학회지
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• 제33권2호
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• pp.1-7
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• 2018

The multi-scale analysis is more proper and precise for composite materials because of considering the individual microscopic structure and properties of each material for composite materials. The purpose of this study is to verify the validity of using palladium particles in carbon/fiber composites by multi-scale analysis. The palladium is a material for itself to detect leaking hydrogen by using the property of adsorbing hydrogen. The macroscopic model material properties used in this study are homogeneous material properties from microstructure. Homogenized material properties that are calculated from periodic boundary conditions in the microscopic representative volume element model of each macroscopic analysis model. In this study, three macroscopic models were used : carbon fiber/epoxy, carbon fiber/palladium, palladium/epoxy. As a result, adding palladium to carbon/epoxy composite is not a problem in terms of strength.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2007년도 춘계학술대회A
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• pp.506-511
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• 2007

Mechanical behavior of copper nanowire is investigated. An FCC nanowire model composed of 1,408 atoms is used for MD simulation. Simulations are performed within NVT ensemble setting without periodic boundary conditions. $Nos\acute{e}-Poincar\acute{e}$ MD algorithm is employed to guarantee preservation of Hamiltonian and temperature. Numerical tensile tests of Nanowire are carried out with constant strain rate. Additionally, temperature and strain rate effects are considered. Stress-strain curve is constructed from the calculated Cauchy stresses and specified strain values. In (22,4,4) Copper nanowire, non-linear behavior appears around ${\epsilon}\simeq0.09.$ At this instance, starting of structural reorientations are observed. At the onset of reorientation, the modulus characteristics are also investigated.

• Steel and Composite Structures
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• 제22권2호
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• pp.277-299
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• 2016

In this paper, free vibration, forced vibration, resonance and stress wave propagation behavior in nanocomposite plates reinforced by wavy carbon nanotube (CNT) are studied by a mesh-free method based on first order shear deformation theory (FSDT). The plates are resting on Winkler-Pasternak elastic foundation and subjected to periodic or impact loading. The distributions of CNTs are considered functionally graded (FG) or uniform along the thickness and their mechanical properties are estimated by an extended rule of mixture. In the mesh-free analysis, moving least squares (MLS) shape functions are used for approximation of displacement field in the weak form of motion equation and the transformation method is used for imposition of essential boundary conditions. Effects of CNT distribution, volume fraction, aspect ratio and waviness, and also effects of elastic foundation coefficients, plate thickness and time depended loading are examined on the vibrational and stresses wave propagation responses of the nanocomposite plates reinforced by wavy CNT.

• 천문학회지
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• 제48권1호
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• pp.67-73
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• 2015

We present a novel method to implement time-delayed propagation of radiation fields in cosmological radiative transfer simulations. Time-delayed propagation of radiation fields requires construction of retarded-time fields by tracking the location and lifetime of radiation sources along the corresponding light-cones. Cosmological radiative transfer simulations have, until now, ignored this "light-cone effect" or implemented ray-tracing methods that are computationally demanding. We show that radiative transfer calculation of the time-delayed fields can be easily achieved in numerical simulations when periodic boundary conditions are used, by calculating the time-discretized retarded-time Green's function using the Fast Fourier Transform (FFT) method and convolving it with the source distribution. We also present a direct application of this method to the long-range radiation field of Lyman-Werner band photons, which is important in the high-redshift astrophysics with first stars.

• 한국가시화정보학회:학술대회논문집
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• 한국가시화정보학회 2007년도 추계학술대회
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• pp.101-104
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• 2007

Kiwifruit vines with broad leaves are easily torn or shed by high-speed wind. In this study, the threshold wind speed at which a cane is broken was investigated experimentally with varying physical parameters of a kiwifruit vine under two different ABL (atmospheric boundary layer) conditions. In addition, the temporal variation of wind-blown young canes was visualized using a high-speed camera. The average threshold wind speeds for ABL types A and B are about 20.5 m/s and 18.9 m/s, respectively. A wind-blown young cane takes periodic up-and-down motion when it is broken off. The mean motion frequency of young canes of the kiwifruit vines was found to be about 4.5Hz.

• Bulletin of the Korean Chemical Society
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• 제24권2호
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• pp.178-182
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• 2003

The stress and the heat-flux auto-correlation functions in the Green-Kubo formulas for shear viscosity and thermal conductivity have non-decaying long-time tails. This problem can be overcome by improving the statistical accuracy by N (number of particles) times, considering the stress and the heat-flux of the system as properties of each particle. The mean square stress and the heat-flux displacements in the Einstein formulas for shear viscosity and thermal conductivity are non linear functions of time since the quantities in the mean square stress and the heat-flux displacements are not continuous under periodic boundary conditions. An alternative to these quantities is to integrate the stress and the heat-flux with respect to time, but the resulting mean square stress and heat-flux displacements are still not linear versus time. This problem can be also overcome by improving the statistical accuracy. The results for transport coefficients of liquid argon obtained are discussed.