• 한국소음진동공학회논문집
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• 제15권12호
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• pp.1408-1415
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• 2005

Active vibration control of smart hull structure using Macro Fiber Composite (MFC) actuator is performed. Finite element modeling is used to obtain governing equations of motion and boundary effects of end-capped smart hull structure. Equivalent interdigitated electrode model is developed to obtain piezoelectric couplings of MFC actuator. Modal analysis is conducted to investigate the dynamic characteristics of the hull structure, and compared to the results of experimental investigation. MFC 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 and structural vibration is controlled effectively.

• 한국소음진동공학회논문집
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• 제21권7호
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• pp.643-649
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• 2011

This work presents an active vibration control of a stiffened hull structure using a flexible macro fiber composite(MFC) actuator. As first step, the governing equation of the hull structure is derived in a matrix form and its dynamic characteristics such as natural frequency are obtained via a finite element analysis(FEA). The natural frequencies obtained from the FEA are compared with those determined from experimental measurement. After formulating the control model in a state space representation, an optimal controller is designed in order to attenuate the vibration of the stiffened hull structure. The controller is then empirically realized through dSPACE and control responses are evaluated in time domain.

• 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.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.217-222
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• 2005

Active vibration control of smart hull structure using Macro Fiber Composite (MFC) actuator is performed. Finite element modeling is used to obtain governing equations of motion and boundary effects of end-capped smart hull structure. Equivalent interdigitated electrode model is developed to obtain piezoelectric couplings of MFC actuator. Modal analysis is conducted to investigate the dynamic characteristics of the hull structure, and compared to the results of experimental investigation. MFC 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 and structural vibration is controlled effectively.

• 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.

• 벤처창업연구
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• 제16권4호
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• pp.101-113
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• 2021

이 연구는 기업벤처캐피탈에 대한 거시적경제, 산업구조적 관점에서 기업벤처케피탈 투자에 영향을 미치는 요인들에 대해 탐색한다. 기업벤처캐피탈 투자에 관한 기존 연구들이 모기업의 사업 다각화, 신규 사업 진출을 위한 기업벤처링(Corporate Venturing) 등 모기업과의 관련성을 중심으로 기업벤처캐피탈의 정체성과 투자목적에 대해 논의해온 것과 달리, 본 연구는 변화하는 거시경제적, 산업구조적 환경적 요인에 영향을 받고 이에 대응하는 독립적, 재무적 투자자로서의 기업벤처캐피탈의 정체성에 주목하여, 기업벤처캐피탈 투자에 미치는 영향을 분석한다. 이를 위해 구체적으로 산업 호황, 외생적 위기, 경제 성장, 산업 내 경쟁 강도 등과 같은 거시적 요인들이 기업벤처캐피탈 투자에 미치는 영향에 대해 1996년부터 2017년까지 84개 미국 기업벤처캐피탈의 2,306건의 투자데이터를 기반으로 실증분석하였다. 분석결과 일반적인 독립벤처캐피탈과 마찬가지로 산업이 호황이고, 경제가 성장할 때는 기업벤처캐피탈도 투자를 늘리고, 외생적 위기가 발생하거나, 기업벤처캐피탈들 간 경쟁 강도가 강할수록 투자가 줄어들 것이라는 가설이 모두 지지되었다. 주로 모기업과의 관계, 피투자회사와 모기업 사업의 관련성 등을 중심으로 기업벤처캐피탈 투자에 대해 논의했던 선행 연구들과 달리, 기업벤처캐피탈의 재무적 투자자로서의 정체성과 기업벤처캐피탈 투자에 미치는 거시경제적, 산업구조적 요인들의 영향에 대해 환기함으로써 기업벤처캐피탈 투자에 대한 논의의 폭을 확장하고, 기업벤처캐피탈 투자의사결정자들에게 거시경제적, 산업구조적 요인들에 대한 대응을 시사한다는 점에서 의의가 있다.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 1999년도 학회창립 10주년 기념 1999년도 가을 학술발표회 논문집
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• pp.159-162
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• 1999

The paper presents results of an investigation on the permeability characteristics and pore structure of concrete containing different levels of fly ash, silica fume, or blast furnace slag. The total cementitious content was 351kg/㎥, and the water/cementitious materials ratio was 0.55. The porosity and pore structure of representative pastes of the matrix were measured using mercury intrusion porosimetry, and the permeability characteristics of concrete were also determined by water and oxygen permeability, chloride ion penetration. The results show that significant reduction in permeability of concrete containing pozzolanic materials due to formation of a discontinuous macro-pore system which inhibits flow. And, the permeability of concrete and pore structure(capillary porosity or total porosity) shows linear relationship.

• 소성∙가공
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• 제10권6호
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• pp.471-477
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• 2001

Milli-structure components are classified as a component group whose size is between macro and micro scales, that is, about smaller than 20mm and larger than 1mm. The forming of these components has a typical phenomenon of bulk deformation with thin sheets because of the forming size. In this study, milli-structure rectangular cup drawing is analyzed and measured using the finite element method and experiments. Special containers or cases of cellular phone vibrator to save installation space are produced by rectangular-shaped drawing. A systematic approach is established for the design and the experiment of the forming processes for rectangular milli-structure cases. To verify the simulation results, the experimental investigations were also carried out on a real industrial product. The numerical analysis by FEM shows good agreement with the experimental results in view of the deformation shape of the product.

• 한국도로학회논문집
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• 제17권2호
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• pp.143-150
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• 2015

PURPOSES : The authors set out to estimate the related carbon emissions, energy use, and costs of the national freeways and highways in Korea. To achieve this goal, a macro-level methodology for estimating those amounts by road type, road structure type, and road life cycle was developed. METHODS : The carbon emissions, energy use, and costs associated with roads vary according to the road type, road structure type, and road life cycle. Therefore, in this study, the road type, road structure type, and road life cycle were classified into two or three categories based on criteria determined by the authors. The unit amounts of carbon emissions and energy use per unit road length by classification were estimated using data gathered from actual road samples. The unit amounts of cost per unit road length by classification were acquired from the standard cost values provided in the 2013 road business manual. The total carbon emissions, energy use, and cost of the national freeways and highways were calculated by multiplying the road length by the corresponding unit amounts. RESULTS: The total carbon emissions, energy use, and costs associated with the national freeways and highways in Korea were estimated by applying the estimated unit amounts and the developed method. CONCLUSIONS: The developed method can be employed in the road planning and design stage when decision makers need to consider the impact of road construction from an environmental and economic point of view.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 추계학술대회논문집
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• pp.466-471
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• 2008

Structural vibration and noise are hot issues in underwater vehicles such as submarines for their survivability. Therefore, active vibration and noise control of submarine, which can be modeled as hull structure, have been conducted by the use of piezoelectric materials. Traditional piezoelectric materials are too brittle and not suitable to curved geometry such as hull structures. Therefore, advanced anisotropic piezoceramic actuator named as Macro-Fiber Composite (MFC), which can provide great flexibility, large induced strain and directional actuating force is adopted for this research. In this study, dynamic model of the smart hull structure is established and active vibration control performance of the smart hull structure is evaluated using optimally placed MFC. Actuating performance of MFC is evaluated by finite element analysis and dynamic modeling of the smart hull structure is derived by finite element method considering underwater condition. In order to suppress the vibration of hull structure, Linear-Quadratic-Gaussian (LQG) algorithm is adopted. After then active vibration control performance of the proposed smart hull structure is evaluated with computer simulation and experimental investigation in underwater. Structural vibration of the hull structure is decreased effectively by applying proper control voltages to the MFC actuators.