• The Journal of Korean Institute of Electromagnetic Engineering and Science
• /
• v.18 no.6 s.121
• /
• pp.656-663
• /
• 2007

In this paper, when a E-polarized plane wave is incident on the grating consisting of tapered resistive strips, electromagnetic scattering is analyzed using the method of moments(MoM). The induced current density of each resistive strip in a grounded double dielectric layer is expected to blow up at both edges. To satisfy this, the induced surface current density is expanded in a series of Chebyshev polynomials of the second kind. The scattered electromagnetic fields are expanded in a series of Floquet mode functions. The boundary conditions are applied to obtain the unknown current coefficients. According to the variation of the involving parameters such as strip width and spacing and angle of the incident field, numerical simulations are performed by applying the Fourier-Galerkin moment method. The numerical results of the normalized reflected power for resistive strips case for several resistivities are obtained.

• KSCE Journal of Civil and Environmental Engineering Research
• /
• v.31 no.4C
• /
• pp.109-116
• /
• 2011

In this study, dynamic response of a vertical shaft subjected to seismic loads was evaluated by three-dimensional Finite Element (FE) approach. The emphasis was on quantifying the ground conditions, input motions and direction of motions. A series of parametric analyses were carried out. From the results of FE analysis, more than 1.7 times increase in shear force and bending moment is obtained when the stiff layer was thinker than the soft layer. And all of the maximum values were occurred near the interface between the soil layers. The dynamic behavior of vertical shaft was significantly influenced by the different frequencies of the input motion, and normalized acceleration of surrounding soil was 3 times larger than vertical shaft.

• Proceedings of the KAIS Fall Conference
• /
• 2008.11a
• /
• pp.365-367
• /
• 2008

원자로 냉각계통의 압력경계를 구성하고 있는 재료들의 부식은 재료 표면에 형성되는 산화막, 금속재료의 구성성분이 용해되어 생성된 가용성 화학종 및 산화물 입자 형태의 부식생성물들을 발생시킨다. 금속합금의 부식에 의한 가용성 화학종 및 입자들의 방출은 원자로 냉각계통에서 노심과 증기발생기를 순환하면서 연료피복관 위에 침전되어 여러 가지 문제를 야기한다. 크러드는 구조재료의 부식에 기인하여 발생한 부식생성물들이 냉각수에 부유하여 떠다니거나 피복관 표면에 침적하여 형성되며 주로 니켈과 철 산화물로 구성되어 있다. 원자로 냉각계통에서 크러드를 최소화하기 위하여 수화학 조건들을 제어하지만 장주기 고연소도 노심에서 AOA 현상을 일으키는 주된 원인이 되고 있다. 피복관 위에 침적되는 크러드는 붕소의 잠복위치를 제공할 뿐만 아니라 냉각수의 압력강하를 증가시키고 피복관의 부식 및 파손 원인을 제공하며 방사선 준위가 증가하도록 한다. 따라서 본 연구에서는 반응속도론적 관점에서 원자로 정지시의 용출 크러드 특성에 대한 연구를 수행하였다.

• Transactions of the Korean hydrogen and new energy society
• /
• v.15 no.4
• /
• pp.257-265
• /
• 2004

Numerical analysis, as EAM(Embedded Atom Method), in the atomic level is necessary to analyze the relation between the hydrogen and hydrogen absorption metals. EAM established on density functional theory was developed as a new means for calculating various properties and phenomena of realistic metal systems. In this study, we had constructed the EAM program from constitutive formulae and parameters of the hydrogen, nickel and palladium for the purpose of predicting the expansion behavior on hydrogen absorbing. In result, not only the ground state properties of metals but also lattice constants and the volume expansion ratio of metal hydrides show good agreement with Daw's data and experiment data.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.31 no.6 s.261
• /
• pp.694-700
• /
• 2007

Recently, a new cellular metal, WBK(Wire woven Bulk Kagome) has been introduced. WBK is fabricated by assembling metal wires in six directions into a Kagome-like truss structure and by brazing it at all the crossings. Wires as the raw material are easy to handle and to attain high strength with minimum defect. And the strength and energy absorption are superior to previous cellular metals. Therefore, WBK seems to be promising once the fabrication process for mass production is developed. In this paper, an upper bound solution for the mechanical properties of the bulk WBK under compression is presented. In order to simulate uniform behavior of WBK consisted of perfectly uniform cells, a unit cell of WBK with periodic boundary conditions is analyzed by the finite element method. In comparison with experimental test results, it is found that the solution provides a good approximation of the mechanical properties of bulk WBK cellular metals except for Young's modulus. And also, the brazing joint size does not have any significant effect on the properties with an exception of an idealized thin joint.

• Proceedings of the Korea Water Resources Association Conference
• /
• 2017.05a
• /
• pp.281-281
• /
• 2017

하천에서 하도불안정(stream instability)으로 인하여 하상의 형태가 변화하고 하상파(sand wave)가 발생한다. 사련(ripple), 사구(dune) 등과 같은 하상파는 흐름저항을 유발하여 홍수시 수위를 증가시킨다. 수리실험 및 수치모형을 이용하여 사련 및 사구의 발달과정 그리고 이를 지나는 난류흐름에 대한 연구가 국외에서는 이루어지고 있지만 국내의 경우 거의 찾아보기 힘들다. 수치모형을 활용한 연구는 주로 횡방향으로 하상파가 일정하다는 가정하에 연직 2차원 수치모형을 적용하였으나 최근 컴퓨터 기술 및 수치기법의 고도화로 3차원 RANS(Reynolds averaged Navier-Stokes) 또는 LES(Large eddy simulation)를 이용한 수치모형이 개발되고 있다. 본 연구에서는 LES에 유사이송 및 하상변동 모형과 결합하여 사구발달에 대한 수치모의를 수행하였다. LES와 유사이송 및 하상변동 모형의 결합은 순간유속성분을 하상변동모형에 직접 적용되기 때문에 난류영향을 고려할 수 있는 것이 장점이다. 특히 사구의 발달에 따라 복잡한 흐름이 발생하며 3차원 와구조가 발생하므로 난류특성의 고려는 필수적이다. 수치모의는 Delft Hydraulics (Bakker et al., 1986)에서 수행한 수리실험 T39를 활용하였다. 수리실험은 길이 100 m, 폭 0.5 m 개수로에서 수행되었으며 평균유속은 0.611 m/s, 수심은 0.436 m이다. 하상파 실험에 사용된 유사입경은 0.78 mm 균일사를 사용하였다. 수치모의 조건은 수리실험과 동일하게 하였으나 계산시간의 효율을 고려하여 흐름방향의 계산영역은 4.0 m로 하고 주기경계조건(periodic boundary condition)을 부여하여 계산을 수행하였다. 수치모의 계산은 사구의 길이 및 파고가 평형상태에 이를 때까지 수행되었다. 수치모의 통해 사구발달에 따른 흐름 및 하상변동 특성을 분석하였다.

• Transactions of the Korean Society of Mechanical Engineers A
• /
• v.35 no.8
• /
• pp.957-964
• /
• 2011

This investigation presents a finite element method to obtain the transmission properties of bulk elastic waves in piezoelectric band gap structures(phonon crystals) for varying frequencies and modes. To this end, periodic boundary conditions are imposed on a three-dimensional model while both in-plane and out-of-plane modes are included. In particular, the mode decoupling characteristics between in-plane and out-of-plane modes are identified for each electric poling direction and the results are incorporated in the finite element modeling. Through numerical simulations, the proposed modeling method was found to be a useful, effective one for analyzing the wave characteristics of various types of piezoelectric phononic band gap structures.

• The Journal of the Institute of Internet, Broadcasting and Communication
• /
• v.15 no.6
• /
• pp.311-319
• /
• 2015

In this paper, in order to increase the production efficiency of the industrial plant, and predicts the resources of the manufacturing process, we have proposed a decision-making system for resource implementing the risk management effectively forecasting and risk management. A variety of information that occurs at each step efficiently difficult the creation of detailed process steps in the scenario you want to manage, is a frequent condition change of manufacturing facilities for the production of various products even within the same process. The data that is not contiguous products production cycle also not constant occurs, there is a problem that needs to check the variation in the small amount of data. In order to solve these problems, data centralized manufacturing processes, process resource prediction, risk prediction, through a process current status monitoring, must allow action immediately when a problem occurs. In this paper, the range of change in the design drawing, resource prediction, a process completion date using a regression algorithm to derive the formula, classification tree technique was proposed decision system in three stages through the boundary value analysis.

• Korean Journal of Materials Research
• /
• v.8 no.8
• /
• pp.678-684
• /
• 1998

By means of constant- pressure molecular dynamics simulations, we studied the liquid- glass- crystalline transition of a system composed of Lennard- Jones particles with periodic boundary conditions. Atomic volume and enthalpy were calculated as functions of temperature during heating and cooling processes. The Wendt- Abraham ratio derived from radial distribution function and the angular distribution function characterizing short range order were analyzed to distinguish between liquid, glass and crystalline states. A liquid phase resulting from a slow heating of an initial fee crystal amorphized on fast quench, but it crystallized on slow quench. When slowly heated, the amorphous phase from fast quench crystallized into an fee structure. A system with free surface was shown to melt from the surface inward at a lower temperature than bulk system and to have a strong tendency for crystallization even during a fast quench from a liquid state.

• Journal of the Korean Society for Aeronautical & Space Sciences
• /
• v.31 no.7
• /
• pp.41-52
• /
• 2003

In this paper, three-dimensional thermo-mechanical properties of carbon-phenolic 8-hamess satin weave composites were predicted considering geometric parameters of microstructures. The effective properties were calculated by a series of numerical experiments based on unit cell analysis. The microstructural details were modeled through macro-elements, and the periodic boundary conditions were derived for corresponding un it cell types. The Monte Carlo method was employed to consider the random phase shift between the layers, and the results were investigated on the effect of the geometric parameters of shift, number of layers and waviness ratios. Experimental tests were also performed and the results were compared.