• 제목/요약/키워드: macro-element

검색결과 192건 처리시간 0.034초

MFC를 이용한 손상된 복합재의 능동제어 (Active Control of Damaged Composite Structure Using MFC Actuator)

  • 손정우;김흥수
    • 한국소음진동공학회:학술대회논문집
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    • 한국소음진동공학회 2013년도 추계학술대회 논문집
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    • pp.535-540
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    • 2013
  • In this work, active control algorithm is adopted to reduce delamination effects of the damaged composite structure and control performance with MFC actuator is numerically evaluated. Finite element model for the damaged composite structure with piezoelectric actuator is established based on improved layerwise theory. In order to achieve high control performance, MFC actuator, which has increased actuating force, is considered as a piezoelectric actuator. Mode shapes and corresponding natural frequencies for the damaged smart composite structure are studied. After design and implementation of active controller, dynamic characteristics of the damaged smart composite structure are investigated.

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Analysis and Improvement of MPEG-DASH-based Internet Live Broadcasting Services in Real-world Environments

  • Kim, Namgi;Lee, Byoung-Dai
    • KSII Transactions on Internet and Information Systems (TIIS)
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    • 제13권5호
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    • pp.2544-2557
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    • 2019
  • Adaptive bitrate streaming is a crucial element in the implementation of high-quality streaming of media content over the Internet. Dynamic adaptive streaming over HTTP (MPEG-DASH) has lately emerged as the de facto solution for over-the-top (OTT) video streaming services. In this paper, we perform macro-level analysis on a real-world MPEG-DASH-based Internet live broadcasting service to gain insight into its behavior throughout the end-to-end service-provision chain, from broadcasters to viewers. Based on this analysis, we propose methods to improve the quality-of-experience (QoE) of MPEG-DASH-based services, particularly with regard to reducing broadcasting delays between recording and viewing of videos, as well as synchronizing client terminals.

Shape morphing and adjustment of pantographic morphing aerofoil section structure

  • Saeed, Najmadeen M.;Kwan, Alan S.K.
    • Smart Structures and Systems
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    • 제24권2호
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    • pp.193-207
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    • 2019
  • This study concerns with morphing structures, e.g. as applied in the aerospace industry. A morphing aerofoil structure capable of variable geometry was developed, which was shown to be able to cater for the different aerodynamic requirements at different stages of flight. In this work, the useful and relatively simple method has been applied, which provides a direct method for calculating required morphing shape displacements via finding the most effective bar through calculating bar sensitivity to displacement and calculating set of length actuations for bar assembly to control/adjust shape imperfection of prestressable structural assemblies including complex elements ("macro-elements", e.g., the pantographic element), involving Matrix Condensation. The technique has been verified by experiments on the physical model of an aerofoil shaped morphing pantographic structure. Overall, experimental results agree well with theoretical prediction. Furthermore, the technique of multi-iteration adjustment was presented that effective in eliminating errors that occur in the practical adjustment process itself. It has been demonstrated by the experiments on the physical model of pantographic morphing structure. Finally, the study discusses identification of the most effective bars with the objective of minimal number of actuators or minimum actuation.

리더의 자기기만 행동이 팀학습에 미치는 영향: 심리적 안전감과 침묵풍토의 매개효과를 중심으로 (The Effect of Leader's Self-Deception Behavior on Team Learning: Mediating Effect of Psychological Safety and Silent Climate)

  • 서강석;정승철
    • 한국콘텐츠학회논문지
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    • 제21권3호
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    • pp.478-489
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    • 2021
  • 본 연구는 팀 리더의 자기기만 행동이 팀 학습에 영향을 미치는 과정에서 심리적 안전감과 침묵풍토의 이중 매개 효과를 확인하고자 하였다. 이를 위하여 국내 일반기업에서 근무하는 직원 294명을 대상으로 설문조사를 실시하였으며, SPSS 21과 Process Macro v.3.3을 활용하여 자료 분석을 하였다. 연구 결과는 다음과 같다. 우선, 팀 리더의 자기기만 행동은 팀원들의 심리적 안전감과 부적 상관, 침묵풍토와 정적 상관, 팀 학습과 부적 상관이 있는 것으로 나타났다. 그리고 팀 리더의 자기기만 행동이 팀 학습에 영향을 미치는 관계에서 심리적 안전감과 침묵풍토가 각각 매개변인의 역할을 하는 것으로 나타났으며, 이들 심리적 안전감과 침묵풍토가 순차적으로 매개역할을 하는 이중매개효과 또한 확인되었다. 본 연구는 조직의 팀 성과 향상을 위해서 팀 리더의 진정성의 관리가 중요하다는 실무적인 의의가 있으며, 마지막으로 본 연구와 관련된 시사점 및 제한점이 결론 및 논의에서 다루어졌다.

NASCOM에 의한 실험결과 예측 (Verification of NASCOM : Nonlinear Finite Element Analysis for Structural Concrete)

  • 조순호
    • 콘크리트학회지
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    • 제8권3호
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    • pp.187-195
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    • 1996
  • 콘크리트 구조요소의 비선형거동을 예측하기 위하여 압축응력장 이론의 기본개념인 압축강도 연화 현상, 거시적 및 회전균열 모델을 고려한 유한요소해석이 제시되었다. 수치해석상의 효율성 및 최대하중 이후의 거동에 주안점을 두어 초기재료 강성을 채택한 변위증분법 논리 및 빠른 수렴을 위한 Over-Relaxation 방법이 Isoparametric계의 8-Node 요소에 포함.유도되었다. 상기에 근거하여 제작된 비선형 프로그램, NASCOM은 다조하중을 지지하는콘크리트 구조요소의 내력, 변형특성, 균열 분포 상황 및 보강근의 항복 분포를 예측하는데 사용할 수 있다. NASCOM의 성능을 검토하기 위하여 이러한 목적에 빈번히 사용되는 Bhide의 패널(PB21) 및 Leonhardt의 춤이 큰보에 대한 해석이 실시되었다. 패널에 대한 해석결과는 대체로 변형이력 및 강도가 강한 거동을 나타내는 반면에, 춤이 큰보에 대해서는 변형이력이 유연한 거동을 나타내고있어, 향후 보다 정확한 결과를 예측하기 위해서는 콘크리트의 인강강화 및 압축강도 연화현상에 대하여 좀더 향상된 재료모델의 고려가 필요한 것으로 판단되었다.

Effects of macroporosity and double porosity on noise control of acoustic cavity

  • Sujatha, C.;Kore, Shantanu S.
    • Advances in aircraft and spacecraft science
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    • 제3권3호
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    • pp.351-366
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    • 2016
  • Macroperforations improve the sound absorption performance of porous materials in acoustic cavities and in waveguides. In an acoustic cavity, enhanced noise reduction is achieved using porous materials having macroperforations. Double porosity materials are obtained by filling these macroperforations with different poroelastic materials having distinct physical properties. The locations of macroperforations in porous layers can be chosen based on cavity mode shapes. In this paper, the effect of variation of macroporosity and double porosity in porous materials on noise reduction in an acoustic cavity is presented. This analysis is done keeping each perforation size constant. Macroporosity of a porous material is the fraction of area covered by macro holes over the entire porous layer. The number of macroperforations decides macroporosity value. The system under investigation is an acoustic cavity having a layer of poroelastic material rigidly attached on one side and excited by an internal point source. The overall sound pressure level (SPL) inside the cavity coupled with porous layer is calculated using mixed displacement-pressure finite element formulation based on Biot-Allard theory. A 32 node, cubic polynomial brick element is used for discretization of both the cavity and the porous layer. The overall SPL in the cavity lined with porous layer is calculated for various macroporosities ranging from 0.05 to 0.4. The results show that variation in macroporosity of the porous layer affects the overall SPL inside the cavity. This variation in macroporosity is based on the cavity mode shapes. The optimum range of macroporosities in poroelastic layer is determined from this analysis. Next, SPL is calculated considering periodic and nodal line based optimum macroporosity. The corresponding results show that locations of macroperforations based on mode shapes of the acoustic cavity yield better noise reduction compared to those based on nodal lines or periodic macroperforations in poroelastic material layer. Finally, the effectiveness of double porosity materials in terms of overall sound pressure level, compared to equivolume double layer poroelastic materials is investigated; for this the double porosity material is obtained by filling the macroperforations based on mode shapes of the acoustic cavity.

2-D meso-scale complex fracture modeling of concrete with embedded cohesive elements

  • Shen, Mingyan;Shi, Zheng;Zhao, Chao;Zhong, Xingu;Liu, Bo;Shu, Xiaojuan
    • Computers and Concrete
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    • 제24권3호
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    • pp.207-222
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    • 2019
  • This paper has presented an effective and accurate meso-scale finite element model for simulating the fracture process of concrete under compression-shear loading. In the proposed model, concrete is parted into four important phases: aggregates, cement matrix, interfacial transition zone (ITZ), and the initial defects. Aggregate particles were modelled as randomly distributed polygons with a varying size according to the sieve curve developed by Fuller and Thompson. With regard to initial defects, only voids are considered. Cohesive elements with zero thickness are inserted into the initial mesh of cement matrix and along the interface between aggregate and cement matrix to simulate the cracking process of concrete. The constitutive model provided by ABAQUS is modified based on Wang's experiment and used to describe the failure behaviour of cohesive elements. User defined programs for aggregate delivery, cohesive element insertion and modified facture constitutive model are developed based on Python language, and embedded into the commercial FEM package ABAQUS. The effectiveness and accuracy of the proposed model are firstly identified by comparing the numerical results with the experimental ones, and then it is used to investigate the effect of meso-structure on the macro behavior of concrete. The shear strength of concrete under different pressures is also involved in this study, which could provide a reference for the macroscopic simulation of concrete component under shear force.

초탄성 복합재의 평균장 균질화 데이터 기반 멀티스케일 해석 (A Data-driven Multiscale Analysis for Hyperelastic Composite Materials Based on the Mean-field Homogenization Method)

  • 김수한;이원주;신현성
    • Composites Research
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    • 제36권5호
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    • pp.329-334
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    • 2023
  • 기존의 멀티스케일 유한요소법(Multiscale finite element, FE2 )은 거시 스케일의 모든 적분점에서 대표 체적요소(representative volume element, RVE)의 미시 경계치 문제를 반복적으로 계산하기 때문에 긴 해석 시간과 많은 데이터 저장 공간을 필요로 한다. 이를 해결하기 위해 본 연구에서 평균장 균질화 데이터 기반 멀티스케일 해석 기법을 개발하였다. 데이터 기반 전산역학(data-driven computational mechanics, DDCM) 해석은 변형률-응력 데이터 셋을 직접적으로 사용하는 모델-프리(model-free)접근 방식이다. 멀티스케일 해석을 수행하기 위해, 평균장 균질화(mean-field homogenization)를 활용하여 복합재의 미세구조에 대한 변형률-응력 데이터베이스(database)를 효율적으로 구축하고, 이를 기반으로 데이터 기반 전산역학 시뮬레이션을 수행하였다. 본 논문에서는 개발한 멀티 스케일 해석 프레임워크(framework)를 예제에 적용하여, 초탄성(hyperelasticity) 복합재의 미세 구조를 고려한 데이터 기반 전산역학 시뮬레이션 결과를 확인하였다. 따라서, 데이터 기반 전산역학 접근 방식을 활용한 멀티스케일 해석기법은 다양한 재료 및 구조에 적용될 수 있으며, 멀티스케일 해석 연구 및 응용 가능성을 열어줄 것으로 기대된다.

한국 기록관리와 '거버넌스'에 대한 역사적 접근 (A Historical Approach to the Development of Democracy and the Archival Society in Korea)

  • 오항녕
    • 기록학연구
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    • 제11호
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    • pp.15-40
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    • 2005
  • 'Governance' is a subject that is widely discussed these days in the government and the academic world. I think that the new concept, 'governance', is a strategy to develop the democracy of the society in its institutional and functional aspects. When we are going to discuss about governance, public records and their relationships, without understanding the meaning of 'public' in Korea, we cannot expect to discuss the matter precisely. It is said that Korean public service sectors are awash with authoritarianism and unreasonableness, and that they are at the center of seething corruption and bribe scandals. It is the legacy that the regimes adopted in the aftermath of the Japanese colonial rule for 35 years. The colonial legacy included not simply the practice of the Japanese colony, but also people who had collaborated the Japanese. The American military government and Rhee, Sung-Man regime also appointed the same officials to government posts. As was the same case in other areas including economy, press, education, politics, law, etc. In this point of view, "Righting historical wrongs", a controversial issue now in Korea, aims at establishing the right relationships between an individual and the public, and eventually laying the foundation of democracy for future generation, a procedure of achieving good governance. Apparently, Korea has made progress in developing democracy, as well as in reforming the government policy and organization. Many independent commissions are performing the projects instead of the government institutions that mandated to do the job, but has not played their roles. The e-government projects in Korea was launched in 2001 by the former administration. However, the confusion of records-management after the promulgation of the act is the result of the lack of strategy and the inconsistency of the vision. Good record-keeping supports effective, transparent and accountable government. Accountability is a key element of good governance. It is a recognized fact that without information, there is no guidance for decision-making, and accountability. Thus without records, there is no accountability for the decisions of actions. Transparency means that the decisions taken and their enforcement are carried out based on led-out rules and regulations. When both accountability and transparency are non-existent, good governance is bound to fail. Archival institutions have to give an attention to inner-governance because of the new trend of archival practice, namely 'macro-appraisal'. This 'macro-appraisal' is a kind of a functions-based approach. However, macro-appraisal focuses not just on function, but on the three-way interaction of function, structure and citizen, which combined reflect the functioning of the state within civil society, that is to say, its governance. In conclusion, the public and democracy are major challenges in the Korean society. The so-called good governance requires good record management. In this respect, records managers are in the front line of instituting good governance, and achieving better public and democracy for future generation, a procedure of achieving good governance.

들깨 및 차조기 유전자원의 재분화능 (Regeneration Ability in Germplasms of Perilla frutescens)

  • 이찬옥;이성호;임정대;유창연
    • 한국약용작물학회지
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    • 제12권6호
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    • pp.500-507
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    • 2004
  • 본 연구는 들깨의 기내배양에서 식물체 재분화에 영향을 미치는 최적 배지와 식물생장조절물질의 종류 및 농도의 최적조건의 구명을 위하여 수행하였다. 재분화에 요구되어지는 생장조절물질은 다른 종 및 수집장소, 혹은 인근지역에 분포하고 있는 수집종들 사이에서도 서로 차이가 나는 결과를 얻을 수 있었으며 들깨의 식물체 형성에 있어서 각 계통 간 기내배양에서의 TDZ와 BAP의 처리에 따른 재분화율은 Kocf (한국산 들깨 재배형)의 경우에서는 $1.0\;mg/{\ell}$의 BAP와 TDZ을 처리한 경우 양호한 신초형성수를 나타내었으나 Kowf (한국산 들깨 잡초형)은 저농도의 ($0.1\;mg/{\ell}$) BAP와 TDZ을 첨가한 경우 양호한 신초형성수를 나타내었다. 차조기 의 경우에서는 BAP를 첨가할 경우 고농도에서 신초형성수가 우수한 반면 TDZ을 첨가할 경우에는 저농도로 첨가하는 것이 양호한 신초형성수를 나타내었다. 조합처리에서는 TDZ $1.0\;mg/{\ell}$와 IAA $0.5\;mg/{\ell}$를 조합처리된 배지에서 캘러스 형성율도 좋은 결과를 보였으며 신초 형성이나 뿌리 유도에서도 양호한 결과를 나타내었다. 식물이 필요로 하는 탄소원 외에 배지 내의 삼투압에 중요한 역할을 하는 sucrose의 농도에 따른 재분화율은 캘러스 형성율에서는 큰 차이를 보이지 않았지만 shoot 형성이나 배발생캘러스 형성에서 3%의 sucrose의 농도에서 좋은 효율을 나타내었다. 재분화 조건에 가장 적합한 배지를 알아보기 위한 실험에서는 모든 배지에서 높은 캘러스형성율은 보였지만 완전한 식물체로의 분화는 MS 배지에서 조사되었다. Polyamine을 처리한 결과 spermine, spermidine의 경우에서는 고농도($10\;mg/{\ell}$)로 사용할 경우에 양호한 재분화율을 나타낸 반면 putrescine의 경우에는 $5\;mg/{\ell}$로 첨가한 경우 가장 양호한 신초 형성수를 나타내었다. 호르몬의 첨가 없이 기본배지의 macro elements를 조절하였을 경우와 호르몬을 첨가 했을때의 재분화 효과를 비교하기 위한 실험에서는 캘러스 형성및 shoot 형성에서는 큰 차이가 없었으나 기본배지의 macro elements를 조절한 배지에서 배발생캘러스 형성율이 높게 관찰되었다.