• Title/Summary/Keyword: 주기적 경계 조건

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Effect of Domain Size on Flow Characteristics in Simulating Periodic Obstacle Flow (주기적인 경계조건을 사용하는 수치모사에서 계산영역 크기의 영향)

  • Choi, Choon-Bum;Jang, Yong-Jun;Kim, Jin-Ho;Han, Seok-Youn;Yang, Kyung-Soo
    • Transactions of the Korean Society of Mechanical Engineers B
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    • v.33 no.5
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    • pp.349-357
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    • 2009
  • Effect of computational domain size in simulating of periodic obstacle flow has been investigated for the flow past tube banks. Reynolds number, defined by freestream velocity ($U_{\infty}$) and cylinder diameter (d), was fixed as 200, and center-to-center distance (P) as 1.5d. In-line square array and staggered square array were considered. Drag coefficient, lift coefficient and Strouhal number were calculated depending on domain size. Circular cylinders were implemented on a Cartesian grid system by using an immersed boundary method. Boundary condition is periodic in both streamwise and lateral directions. Previous studies in literature often use a square domain with a side length of P, which contains only one cylinder. However, this study reveals that the domain size is improper. Especially, RMS values of flow-induced forces are most sensitive to the domain size.

A Study on the FDTD method using Periodic Boundary Condition for PBG Performance Analysis (PBG 구조 성능 해석을 위한 주기경계조건의 FDTD 적용연구)

  • Lim, Gye-jae
    • The Journal of Korea Institute of Information, Electronics, and Communication Technology
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    • v.3 no.2
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    • pp.31-38
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    • 2010
  • It is difficult to design accurately the bandgap of metamaterial depending on metamaterial pattern and array configuration. In this paper, we propose a design method for the wanted bandgap frequency using any metamaterial pattern in 2 dimensional array. Metamaterial structure is consisted of periodic array. Therefore the calculation area in FDTD(finite difference time domain) method can be reduced by applying the periodic boundary condition to 2-D metamaterial array. The method for design and calculation the L and C values by using 2-D is also considered. So it can be designed more accurately and rapidly. For example, we designed metamaterial square pattern array in 5 GHz, and compared with the 1-D metamaterial pattern using analysis method in microstrip line. As a result, we found that the accuracy of this proposed method can be incresed to 14.7%.

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Numerical Analysis on 3-dimensional Heat transfer of Heating Surface with Periodically Arrayed Injectors (분사기가 주기적으로 배열된 가열면의 3차원 열전달 수치해석 연구)

  • Cho, Won-Kook;Kim, Young-Mog
    • Journal of the Korean Society for Aeronautical & Space Sciences
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    • v.30 no.8
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    • pp.112-119
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    • 2002
  • Three dimensional numerical heat transfer analysis was carried out against periodically arranged fuel injectors of the liquid rocket engine. A finite volume method based on SIMPLE algorithm was adapted which gave a good agreement with the published results of the heat transfer problem of a backward facing step. The Nusselt number and pressure drop increased as the distance between the injector elements decreased. When the Reynolds number increased, the Nusselt number increased but nondimensionalized pressure drop decreased slightly.

Effect of Strut Waviness on Structural Performance of Wire-Woven Bulk Kagome Cores (WBK 의 구조적 특성에 대한 와이어 굴곡 효과)

  • Lee, Ki-Won;Kang, Ki-Ju
    • Transactions of the Korean Society of Mechanical Engineers A
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    • v.35 no.9
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    • pp.1099-1103
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    • 2011
  • Since the mechanical strength and stiffness of wire-woven bulk Kagome (BK) have been theoretically estimated by assuming that WBK is composed of straight struts, the analytical solutions occasionally give substantial errors as compared with the experimental results. The struts of WBK are helically formed, which results in errors in the estimations In this study, for accurately predicting the mechanical properties of WBK, the effects of waviness and brazed part are taken into account for estimating the strength and stiffness of WBK. The results are compared with the measured experimental results and the results estimated by a finite element analysis performed on a unit cell under periodic boundary conditions (PBC).

Periodic Mesh Generation for Composite Structures using Polyhedral Finite Elements (다면체 유한요소를 이용한 복합재 구조의 주기 격자망 생성)

  • Sohn, Dongwoo;Park, Jong Youn;Cho, Young-Sam;Lim, Jae Hyuk;Lee, Haengsoo
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.27 no.4
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    • pp.239-245
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    • 2014
  • Finite element modeling of composite structures may be cumbersome due to complex distributions of reinforcements. In this paper, an efficient scheme is proposed that can generate periodic meshes for the composite structures. Regular meshes with hexahedral finite elements are first prepared, and the elements are then trimmed to fit external surfaces of reinforcements in the composite structures. The trimmed hexahedral finite elements located at interfaces between the matrix and the reinforcements correspond to polyhedral finite elements, which allow an arbitrary number of nodes and faces in the elements. Because the trimming process is consistently conducted by means of consistent algorithms, the elements of the reinforcements are automatically compatible with those of the matrices. With the additional consideration of periodicity of reinforcements in a representative volume element(RVE), the proposed scheme provides periodic meshes in an efficient manner, which are compatible for each pair of periodic boundaries of the RVE. Therefore, periodic boundary conditions for the RVE are enforced straightforwardly. Numerical examples demonstrate the effectiveness of the proposed scheme for finite element modeling of complex composite structures.

A Study on the Modeling for Boom Structural Behaviors of the Triaxial Woven Fabric Composite (3-방향 직물 복합재료 모델링 및 붐 구조물의 거동 연구)

  • Seon-Woo, Byun;Ji-Yoon, Yang;Soo-Yong, Lee;Jin-Ho, Roh
    • Journal of Aerospace System Engineering
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    • v.16 no.6
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    • pp.99-105
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    • 2022
  • This paper studied the mechanical characteristics of boom structures by verifying the modeling method of representing unit cells of triaxial woven fabric (TWF) composites. The modeling of the representative unit cell obtained the ABD matrix by analysing the behaviour of tensile, shear, bending, and torsion using the periodic boundary conditions for the beam element. This study aimed to validate the ABD matrix by comparing the tensile analysis output from a finite element program with the experimental results from an MTS 810 machine. Additionally, the mechanical characteristics of a TWF composite boom structure were determined through bending analysis and experiments. The findings of this research are expected to be beneficial for developing structures using TWF composites.

Moving boundary condition for simulation of inundation (범람 모의를 위한 이동경계조건)

  • Lin, Tae-hoon;Lee, Bong-Hee;Cho, Dae-Hee;Cho, Yong-Sik
    • Journal of Korea Water Resources Association
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    • v.36 no.6
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    • pp.937-947
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    • 2003
  • A shoreline, which has no the water depth, moves continuously as waves rise up and recede. Therefore, a special boundary treatment is required to track properly the movements of the shoreline in numerical modeling of the behavior of tsunamis or tides near a coastal zone. In this study, convective terms in nonlinear shallow-water equations are discretized explicitly by using a second-order upwind scheme to describe a moving shoreline more accurately. An oscillatory flow motion in a circular paraboloidal basin has been employed to validate the performance of the developed numerical model. Computed results of instantaneous free surface displacements are compared with those of analytical solutions and existing numerical solutions. The run-up heights in the vicinity of a circular island have also been calculated and obtained numerical results have been shown against available laboratory measurements. A good agreement has been observed.

An Analysis of the Sound Stopband in Periodically Corrugated 2-D Ducts (반복 주름을 갖는 이차원 덕트의 음파차단 해석)

  • Kim, Hyun-Sil;Kim, Jae-Seung;Kim, Bong-Ki;Kim, Sang-Ryul;Lee, Seong-Hyun
    • The Journal of the Acoustical Society of Korea
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    • v.31 no.1
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    • pp.11-18
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    • 2012
  • In this paper, the occurrence of a stopband phenomenon when an acoustic wave propagates through periodically corrugated ducts is discussed using theoretical and BEM analyses. A 2-D duct with sinusoidally corrugated upper and lower walls is considered. When the magnitude of the sinusoidal corrugation is sufficiently small compared to the duct's height, the wave equation is solved with the multiple scaling perturbation method. Then stopbands for Bragg and non-Bragg resonances are computed from the condition where frequency becomes a complex number. A 2-D BEM analysis is performed to compute insertion loss of the duct, and stopbands are confirmed as predicted by analytical analysis.

Prediction of the Equivalent Coefficient of Thermal Expansion of Fiber Reinforced Plastic Lamina and Thermal Pointing Error Analysis of Satellites (섬유강화 복합재료 등가열팽창계수 예측 및 인공위성 열지향오차 해석)

  • You, Won Young;Lim, Jae Hyuk;Kim, Sun Won;Kim, Chang-Ho;Kim, Sung-Ho
    • Aerospace Engineering and Technology
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    • v.13 no.1
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    • pp.76-85
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    • 2014
  • In this paper, the equivalent coefficient of thermal expansion (CTE) of fiber reinforced plastic composite material is investigated with various CTE prediction schemes. Although there are several methods for predicting the equivalent CTEs, most of them have some limitations of are not much accurate when comparing prediction results with test results. In the framework of computational homogenization, a representative volume element is taken from the predefined fiber-volume ratio, and modelled with finite element mesh. Finally, the equivalent CTEs are obtained by applying periodic boundary condition. To verify the performance of the proposed method, the results obtained are compared with those by the existing methods and test results. Additionally, the thermal pointing error analysis for star tracker support structure is conducted and its accuracy is estimated according to CTE prediction schemes.

Prediction of the Equivalent Elastic Properties of Fiber Reinforced Composite Materials and Structural Analysis of Composite Satellite Panel (섬유강화 복합재료 등가탄성계수 예측과 복합재료 위성패널의 구조해석)

  • You, Won-Young;Lim, Jae Hyuk;Sohn, Dongwoo;Kim, Sun-Won;Kim, Sung-Hoon
    • Aerospace Engineering and Technology
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    • v.12 no.2
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    • pp.48-56
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    • 2013
  • In this paper, the equivalent elastic properties of fiber reinforced plastic laminar are investigated using various homogenization schemes. Although there are several methods for predicting the equivalent elastic properties such as analytical formula or semi-empirical formula, most of them have some limitations or are not much accurate when handling new composite material consisting of various fiber, matrix and fiber-volume fraction ratio. To resolve the issues, computational homogenization scheme is adopted with a representative volume element (RVE) comprised of a set of finite elements. Finally, the equivalent elastic properties are obtained by applying periodic boundary conditions. The obtained results are compared with those by the existing methods and test results. Also its effect on structural analysis results of the composite satellite panel is investigated.