• Title/Summary/Keyword: Surface Active Element

검색결과 61건 처리시간 0.026초

폐광지역에서의 싱크홀 발생 규명을 위한 Active-Passive-Active 유한요소 기법 연구 (Analysis of Sinkhole Formation over Abandoned Mine using Active-Passive-Active Finite Elements)

  • ;신희순;최성웅
    • 터널과지하공간
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    • 제14권6호
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    • pp.411-422
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    • 2004
  • 폐광지역에서 흔히 발생하는 싱크홀 형태의 지반침하는 인근 지역 주민의 안전은 물론, 지상구조물에 심각한 위해 요소로 작용할 수 있다. 본 연구에서는, 이러한 싱크홀의 발생양상을 수치해석적으로 규명하기 위해, 아주 특별한 형태의 유한요소해석을 실시하였다. 특히, 갱도 천반의 붕락에 의해 야기되는 공간이나, 파쇄된 암반이 쌓여서 이루는 폐석더미 등 기존의 수치해석기법으로서는 쉽사리 표현할 수 없었던 현실적인 문제들을 수치적으로 모사하기 위해 active-passive-active 유한요소를 사용하였다. Active 요소 즉 고체 요소는 싱크홀이 형성되는 영역 내에서 인장파괴 기준식을 만족하게 되면 passive 요소 즉 공간 요소로 전환될 수 있다. 싱크홀이 완전히 형성되게 되면 이들 passive요소들은 다시 active요소로 바뀌면서 폐석더미를 수치적으로 모사할 수 있게 된다. 채굴적의 폭, 심도, 천반의 상태 및 붕락 암반의 부피팽창율 등이 싱크홀에 미치는 영향을 검토하기 위해 여러 가지 조건에 의한 유한요소모델이 해석되었다. 본 연구는, 이와 같이 싱크홀이 발생하는 과정이나 천반이 붕락하는 현상 등을 해석하기 위해 수치해석상에서 active-passive-active유한요소들이 효과적으로 사용될 수 있음을 보여준다.

Representative Volume Element Analysis of Fluid-Structure Interaction Effect on Graphite Powder Based Active Material for Lithium-Ion Batteries

  • Yun, Jin Chul;Park, Seong Jin
    • 한국분말재료학회지
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    • 제24권1호
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    • pp.17-23
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    • 2017
  • In this study, a finite element analysis approach is proposed to predict the fluid-structure interaction behavior of active materials for lithium-ion batteries (LIBs), which are mainly composed of graphite powder. The porous matrix of graphite powder saturated with fluid electrolyte is considered a representative volume element (RVE) model. Three different RVE models are proposed to consider the uncertainty of the powder shape and the porosity. P-wave modulus from RVE solutions are analyzed based on the microstructure and the interaction between the fluid and the graphite powder matrix. From the results, it is found that the large surface area of the active material results in low mechanical properties of LIB, which leads to poor structural durability when subjected to dynamic loads. The results obtained in this study provide useful information for predicting the mechanical safety of a battery pack.

컨포멀 위상 배열 안테나의 패턴 합성에 대한 고찰 (Study on Pattern Synthesis of Conformal Phased Array Antenna)

  • 박동철;권오혁;류홍균;이규송
    • 한국전자파학회논문지
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    • 제26권12호
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    • pp.1031-1043
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    • 2015
  • 본 논문에서는 Enhanced Adaptive Genetic Algorithm(EAGA)를 이용하여 두 가지 종류의 컨포멀 배열 안테나의 패턴 합성 과정을 기술하였다. 한 종류는 2차 함수 형태의 실린더 도체 위에 배열된 $1{\times}16$ 배열 안테나이고, 다른 종류는 2차 함수 곡선의 회전체 곡면 도체 위에 배열된 18개 소자 배열 안테나이다. 패턴 합성시 각 소자의 능동 소자 패턴을 이용하였고, 특히 회전체형 배열 안테나의 경우, 합성 시간을 크게 줄이기 위해 동심원형 평면 배열 안테나의 능동 소자 패턴을 구한 뒤 이를 변환하여 사용하였다. 제안한 합성 기법의 타당성을 검증하기 위해 MATLAB 내에서 합성된 배열 안테나의 패턴과 MWS(Microwave Studio) 내에서 구현된 배열 안테나의 패턴을 비교하였으며, 또한, $1{\times}16$ 배열 안테나의 경우는 측정 패턴과 합성 패턴도 비교하였다.

온간단조 공정의 계면열전달계수 (Contact Heat Transfer Coefficient for Finite Element Analysis in Warm Forging Processes)

  • 강종훈;고병호;제진수;강성수
    • 소성∙가공
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    • 제15권3호
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    • pp.183-188
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    • 2006
  • Heat transfer coefficients have great influence on finite element analysis results in elevated temperature forging processes. Experimentally calculated contact heat transfer coefficient is not suitable for one-time finite element analysis because analyzed temperature will be appeared to be too low. To get contact heat transfer coefficient for one-time finite element analysis, tool temperature in operation was measured with thermocouple and repeated finite element analysis was performed with experimentally calculated contact and cooling heat transfer coefficient. Surface temperature of active tool was obtained comparing measurement and analysis results. Contact heat transfer coefficient for one-time finite element analysis was achieved analyzing surface temperature between repeated finite element analysis and one-time finite element analysis results.

On FEM modeling of piezoelectric actuators and sensors for thin-walled structures

  • Marinkovic, Dragan;Marinkovic, Zoran
    • Smart Structures and Systems
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    • 제9권5호
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    • pp.411-426
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    • 2012
  • Thin-walled adaptive structures render a large and important group of adaptive structures. Typical material system used for them is a composite laminate that includes piezoelectric material based sensors and actuators. The piezoelectric active elements are in the form of thin patches bonded onto or embedded into the structure. Among different types of patches, the paper considers those polarized in the thickness direction. The finite element method (FEM) imposed itself as an essential technical support for the needs of structural design. This paper gives a brief description of a developed shell type finite element for active/adaptive thin-walled structures and the element is, furthermore, used as a tool to consider the aspect of mesh distortion over the surface of actuators and sensors. The aspect is of significance for simulation of behavior of adaptive structures and implementation of control algorithms.

압전형 센서/액추에이터를 이용한 진동구조물의 능동-수동제어 (Active-passive control of flexible sturctures using piezoelectric sensor/actuator)

  • 고병식
    • 소음진동
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    • 제5권3호
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    • pp.313-325
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    • 1995
  • Two active/passive vibration dampers were designed to control a cantilever beam first mode of vibration. The active element was a piezoelectric polymer, polyvinlidene fluoride (PVDF). The passive damping was provided by the application of a viscoelastic layer on the surface of the steel beam. Two substantially different damper configurations were designed and tested. One damper consisted of a piezoelectric actuator bonded to one face of the beam, with a viscoelastic layer applied to the other surface of the beam. The second one was composed of a layer viscoeastic layer with one surface bonded to the beam, and with other being constrained by nine piezoelectric actuators connected in parallel. A control law based on the sign of the angular velocity of the cantilever beam was implemented to control the beam first mode of vibration. The piezoelectric sensor output was digitally differentiated to obtain the transverse linear velocity, and its sign was used in the control algorith. Two dampers provided the system a damping increase of a factor of four for the first damper and three for the second damper. Both dampers were found to work well at low levels of vibration, suggesting that they can be used effectively to prevent resonant vibrations in flexible structure from initiating and building up.

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Novel Synthesis and Nanocharacterization of Graphene and Related 2D Nanomaterials Formed by Surface Segregation

  • Fujita, Daisuke
    • 한국진공학회:학술대회논문집
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    • 한국진공학회 2015년도 제49회 하계 정기학술대회 초록집
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    • pp.60-60
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    • 2015
  • Nanosheets of graphene and related 2D materials have attracted much attention due to excellent physical, chemical and mechanical properties. Single-layer graphene (SLG) was first synthesized by Blakely et al in 1974 [1]. Following his achievements, we initiated the growth and characterization of graphene and h-BN on metal substrates using surface segregation and precipitation in 1980s [2,3]. There are three important steps for nanosheet growth; surface segregation of dopants, surface reaction for monolayer phase, and subsequent 3-D growth (surface precipitation). Surface phase transition was clearly demonstrated on C-doped Ni(111) by in situ XPS at elevated temperatures [4]. The growth mode was clarified by inelastic background analysis [5]. The surface segregation approach has been applied to C-doped Pt(111) and Pd(111), and controllable growth of SLG has been demonstrated successfully [6]. Recently we proposed a promising method for producing SLG fully covering an entire substrate using Ni films deposited on graphite substrates [7]. A universal method for layer counting has been proposed [8]. In this paper, we will focus on the effect of competitive surface-site occupation between carbon and other surface-active impurities on the graphene growth. It is known that S is a typical impurity of metals and the most surface-active element. The surface sites shall be occupied by S through surface segregation. In the case of Ni(110), it is confirmed by AES and STM that the available surface sites is nearly occupied by S with a centered $2{\times}2$ arrangement. When Ni(110) is doped with C, surface segregation of C may be interfered by surface active elements like S. In this case, nanoscopic characterization has discovered a preferred directional growth of SLG, exhibiting a square-like shape (Fig. 1). Also the detailed characterization methodologies for graphene and h-BN nanosheets, including AFM, STM, KPFM, AES, HIM and XPS shall be discussed.

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향상된 적응형 유전 알고리즘을 이용한 회전체형 컨포멀 배열 안테나의 패턴 합성 (Pattern Synthesis of Rotated-type Conformal Array Antenna Using Enhanced Adaptive Genetic Algorithm)

  • 성철민;권오혁;박동철
    • 한국전자파학회논문지
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    • 제26권8호
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    • pp.758-764
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    • 2015
  • 본 논문에서는 2차 함수 곡선의 회전체형 도체 곡면 위에 있는 컨포멀 배열 안테나의 패턴을 EAGA(Enhanced Adaptive Genetic Algorithm)를 이용하여 합성한 내용을 보이고 있다. 다양한 곡면의 회전체 도체를 고찰하기 위해 2차 함수의 계수를 바꿔 세 가지 유형의 회전체형 곡면을 형성시켰고, 각 유형의 컨포멀 배열 안테나 패턴을 합성하였다. 패턴 합성에 소요되는 시간의 단축을 위해 3차원 컨포멀 배열 안테나의 능동 소자 패턴 대신에 2차원 평면 배열 안테나의 능동 소자 패턴을 구한 후, 이를 오일러 변환(Euler transform)시켜 이용하였다. EAGA를 이용하여 합성된 패턴의 검증을 위해 MWS(Microwave Studio)를 통해 구한 패턴과 비교하였으며, 두 패턴은 전반적으로 유사하였다.

경계요소법을 이용한 원통형 배열센서의 지향성/무지향성 모드에 대한 음향특성해석 (Acoustic Characteristics Analysis of Cylindrical Array for the Directional and Omni-directional mode Using the Boundary Element Method)

  • 이정민;서희선;조요한;백광렬
    • 한국소음진동공학회논문집
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    • 제19권9호
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    • pp.922-927
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    • 2009
  • The transducers used in active sonar on surface ships are packed in a specific geometry in the array drum in order to meet the requirements such as the source level, directional beam pattern, etc. This paper describes the acoustic characteristics of the cylindrical array which is based on a 64 vertical staves arrangement, each stave composed 5 independent transducers. Firstly, the single transducer on the rigid baffle in the water is analyzed with the Finite Element Method. From the result of the FE analysis nodal velocities on the radiation surface is calculated and used with the boundary conditions of the transducers mounted on the array drum. Then the acoustic pressure is calculated in the field points using the Boundary Element Method and the other acoustic informations, the source level, beam pattern, near field and far-field distance, were acquired.

지능형 Hull구조물의 능동 진동제어 (Active Vibration Control of Smart Hull Structures)

  • 손정우;최승복;김흥수
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2005년도 춘계학술대회논문집
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    • pp.192-195
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    • 2005
  • In this study, dynamic characteristics of an end-capped hull structure with surface bonded piezoelectric actuators are studied. Finite element modeling is used to obtain practical governing equation of motion and boundary conditions of smart hull structure. Modal analysis is conducted to investigate the dynamic characteristics of the hull structure. Piezoelectric actuators are attached where the maximum control performance can be obtained. Active controller based on Linear Quadratic Gaussian (LQG) theory is designed to suppress vibration of smart hull structure. It is observed that closed loop damping can be improved with suitable weighting factors in the developed LQG controller.

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