• Composites Research
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• 제29권6호
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• pp.328-335
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• 2016

이 연구의 목적은 석회석 미분말을 사용하여 복합재료의 연성이 향상된 시멘트계 매트릭스 섬유복합재료(ECC)를 개발하고 이 재료로 제작된 구조부재의 휨성능을 평가하는 것이다. 재료 개발을 위하여 4가지 종류의 배합을 마이크로역학과 안정상태 균열 이론을 활용하였고, 이를 위하여 시멘트계 매트릭스의 파괴인성과 섬유-시멘트 매트릭스 경계면 특성을 파악하였다. 개발된 ECC의 1축 인장변형특성과 압축강도 특성이 실험적으로 평가되었다. 또한, 2개의 구조부재를 제작하여 휨실험을 수행하였고 그 결과를 재래식 콘크리트 구조부재의 성능과 비교하였다. 재료실험 결과로 석회석 미분말의 혼입률 증가에 따라 압축강도는 감소하지만 연성은 증가하였다. 부재 실험 결과, ECC 구조부재는 재래식 콘크리트 구조부재에 비하여 높은 휨연성, 높은 휨내력, 작은 균열폭을 나타내었다.

• 비파괴검사학회지
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• 제13권4호
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• pp.9-17
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• 1994

초음파법은 종래의 금속재료는 물론 최근의 금속 복합재료등과 같은 신소재의 재료특성을 비파괴적으로 평가할 수 있는 일반적인 방법이다. 그러나 이와같은 재료들의 비파괴 특성 평가를 위해 초음파법을 적용시킬 경우 무엇보다도 재료 내부를 전파하는 탄성파의 전파특성에 대한 물리적 현상에 대한 이해가 필수적이다. 본 연구에서는 금속 복합재료의 제조공정에서 일반적으로 많이 발생되는 기지재와 강화재 사이의 계면 문제 및 기지재에 분포하는 강화재의 체적함유율의 변화등에 의한 유효 평면파의 다중 산란 특성을 SiC 입자강화 6061 알루미늄 복합재료에 대해 Lax의 준 결정 근사(quasi-crystalline approximation) 이론 및 소감정리 (extinction theorem)를 기초로 하여 이론적으로 해석하였다. 그 결과 SiC 입자 강화재의 체적 함유율의 변화에 대한 유효 평면파의 위상속도 및 감쇠의 주파수 의존 특성과 금속복합재료에 있어서의 기지재와 강화재 사이의 계면층의 탄성특성에 대한 위상속도의 변화 특성이 명확하게 규명되었다.

• 한국CDE학회논문집
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• 제21권3호
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• pp.353-362
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• 2016

As ships become larger and construction of offshore plants increases recently, the amount of outsourcing has increased accordingly in the shipyard. Consequently, the system integration in terms of SCM (Supply Chain Management) of information and material flows has become much more important. Especially, since the SCM in the shipbuilding industry is operated in accordance with the production planning in connection with design, purchasing and production process which are the main components of the supply chain, the best production plan has to be established over the whole scheduling activities from the long-term planning to the short-term planning. The paper analyzes the characteristics of the SCM and the production planning system and suggests the need and the direction of APS (Advanced Planning System) development specialized in the supply chain management only for shipbuilding industry. Furthermore, propose a new SCP-Matrix (Supply Chain Planning Matrix), which is the basis of the APS development, appropriate for the shipbuilding industry and draw the core function of the APS module for the practical production plan.

• International Journal of CAD/CAM
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• 제13권1호
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• pp.1-11
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• 2013

Just by adjusting the control points iteratively, progressive iterative approximation (PIA) presents an intuitive and straightforward scheme such that the resulting limit curve (surface) can interpolate the original data points. In order to obtain more flexibility, adjusting only a subset of the control points, a new method called local progressive iterative approximation (LPIA) has also been proposed. But to this day, there are two problems about PIA and LPIA: (1) Only an approximation process is discussed, but the accurate convergence curves (surfaces) are not given. (2) In order to obtain an interpolating curve (surface) with high accuracy, recursion computations are needed time after time, which result in a large workload. To overcome these limitations, this paper gives an explicit matrix expression of the control points of the limit curve (surface) by the PIA or LPIA method, and proves that the column vector consisting of the control points of the PIA's limit curve (or surface) can be obtained by multiplying the column vector consisting of the original data points on the left by the inverse matrix of the collocation matrix (or the Kronecker product of the collocation matrices in two direction) of the blending basis at the parametric values chosen by the original data points. Analogously, the control points of the LPIA's limit curve (or surface) can also be calculated by one-step. Furthermore, the $G^1$ joining conditions between two adjacent limit curves obtained from two neighboring data points sets are derived. Finally, a simple LPIA method is given to make the given tangential conditions at the endpoints can be satisfied by the limit curve.

• 접착 및 계면
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• 제3권4호
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• pp.44-52
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• 2002

Composite materials are created by combining two or more component to achieve desired properties which could not be obtained with the separate components. The use of reinforcing fillers, which can reduce material costs and improve certain properties, is increasing in thermoplastic polymer composites. Currently, various inorganic fillers such as talc, mica, clay, glass fiber and calcium carbonate are being incorporated into thermoplastic composites. Nevertheless, lignocellulose fibers have drawn attention due to their abundant availability, low cost and renewable nature. In recent, interest has grown in composites made from lignocellulose fiber in thermoplastic polymer matrices, particularly for low cost/high volume applications. In addition to high specific properties, lignocellulose fibers offer a number of benefits for lignocellulose fiber/thermoplastic polymer composites. These include low hardness, which minimize abrasion of the equipment during processing, relatively low density, biodegradability, and low cost on a unit-volume basis. In spite of the advantage mentioned above, the use of lignocellulose fibers in thermoplastic polymer composites has been plagued by difficulties in obtaining good dispersion and strong interfacial adhesion because lignocellulose fiber is hydrophilic and thermoplastic polymer is hydrophobic. The application of lignocellulose fibers as reinforcements in composite materials requires, just as for glass-fiber reinforced composites, a strong adhesion between the fiber and the matrix regardless of whether a traditional polymer matrix, a biodegradable polymer matrix or cement is used. Further this article gives a survey about physical and chemical treatment methods which improve the fiber matrix adhesion, their results and effects on the physical properties of composites. Coupling agents in lignocellulose fiber and polymer composites play a very important role in improving the compatibility and adhesion between polar lignocellulose fiber and non-polar polymeric matrices. In this article, we also review various kinds of coupling agent and interfacial mechanism or phenomena between lignocellulose fiber and thermoplastic polymer.

• Coupled systems mechanics
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• 제10권6호
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• pp.509-520
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• 2021

Fiber-reinforced concrete (FRC) is a composite material where small fibers made from steel or polypropylene or similar material are embedded into concrete matrix. In a material model each constituent should be adequately described, especially the interface between the matrix and fibers that is determined with the 'bond-slip' law. 'Bond-slip' law describes relation between the force in a fiber and its displacement. Bond-slip relation is usually obtained from tension laboratory experiments where a fiber is pulled out from a matrix (concrete) block. However, theoretically bond-slip relation could be determined from bending experiments since in bending the fibers in FRC get pulled-out from the concrete matrix. We have performed specially designed laboratory experiments of three-point beam bending with an intention of using experimental data for determination of material parameters. In addition, we have formulated simple layered model for description of the behavior of beams in the three-point bending test. It is not possible to use this 'forward' beam model for extraction of material parameters so an inverse model has been devised. This model is a basis for formulation of an inverse model that could be used for parameter extraction from laboratory tests. The key assumption in the developed inverse solution procedure is that some values in the formulation are known and comprised in the experimental data. The procedure includes measured data and its derivative, the formulation is nonlinear and solution is obtained from an iterative procedure. The proposed method is numerically validated in the example at the end of the paper and it is demonstrated that material parameters could be successfully recovered from measured data.

• 한국음향학회지
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• 제43권4호
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• pp.369-382
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• 2024

능동 소나 시스템에서 잔향을 제거하기 위하여 최근 비음수 행렬 분해 기법을 활용한 잔향 제거 알고리즘이 고안된 바 있다. 비음수 행렬 분해 알고리즘을 설계하기 위해서는 분해된 기저 행렬의 곱이 원본 신호와 같도록 유도하는 추정 비용 함수가 필요한데, 기존의 연구에서는 이에 대한 고찰이 없이 쿨백-라이블러 발산 함수를 활용하였다. 본 논문에서는 쿨백-라이블러 발산 함수의 선택이 좋은 선택이었는지, 혹은 성능을 개선할 수 있는 다른 추정 비용 함수가 있는지 연구하고자 하였다. 이를 위하여, 먼저 쿨백-라이블러 함수를 포함하여 일반화된 베타-발산 함수를 활용하여 수정된 잔향 제거 알고리즘을 제안하였다. 그리고 수정된 잔향 제거 알고리즘에 대해 합성된 잔향 신호를 활용한 몬테-카를로 시뮬레이션을 수행하였다. 그 결과 높은 신호대잔향비 환경에서는 쿨백-라이블러 발산 함수(β= 1)가 좋은 성능을 보이지만, 낮은 신호대잔향비 환경에서는 쿨백-라이블러 발산 함수와 유클리드 거리의 중간 특성을 가지는 함수(β= 1.25)가 더 좋은 성능을 보이는 것을 확인하였다.

• Physical Therapy Rehabilitation Science
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• 제7권3호
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• pp.114-118
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• 2018

Objective: The left and right sides of the brain has different roles. This study investigated the differences in cognitive driving ability between stroke survivors with damage to the left brain and right brain. Therefore, the purpose of this study was to compare the driving cognitive ability of left and right hemispheric drivers following stroke. Design: Cross-sectional study. Methods: The Stroke Drivers' Screening Assessment (SDSA) from the UK was translated to the Korean Stroke Drivers' Screening Assessment (K-SDSA) to meet the specific traffic environments of Korea. The SDSA is composed of 4 tasks :1) a dot cancellation task that measures concentration and visuospatial abilities necessary for driving, 2) a directional matrix task to measure spatio-temporal executive function required for driving, 3) a compass matrix task to measure accurate direction determination ability required for driving, and 4) recognition of traffic signs and reasoning ability to understanding traffic situation. The SDSA assessment time is about 30 minutes. The K-SDSA was used to compare the cognitive driving abilities between 15 stroke survivors with left and 15 stroke survivors with right brain damage. Results: There were significant differences between the persons with stroke patients with left brain lesions (right hemiplegia) compared to the persons with stroke with right brain lesions (left hemiplegia) (p<0.05). It was found that the cognitive driving ability of those with right brain damage was lower than that of the group of left brain damage. Conclusions: This research investigated the driving cognitive ability of persons with stroke. The therapists can use this information as basis for the driving test and training purposes. It could also be used as a basis to understanding if the cognitive ability of not only stroke survivors but also those with brain damage is adequate to actually drive.

• 한국전자파학회논문지
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• 제17권12호
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• pp.1224-1230
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• 2006

본 논문에서는 제한된 피드백 정보를 사용하는 공간 다중화 시스템을 위한 preceding 기법을 제안하였다. 제안하는 precoding 기법은 unitary 행렬로 구성된 precoder 코드북내에서 preceding 행렬의 선택 정보를 송신단에 전달하는 장구간 피드백과 선택된 unitary 행렬의 열 벡터 중 전송체 사용될 열 벡터 정보를 송신단에 전달하는 단구간 피드백을 이용한다. 또한, zero-forcing 수신기를 사용하는 $2{\times}2$ MIMO 시스템에 대해 평균 throughput을 최대화하는 precoder 코드북을 디자인하였다. 모의 실험 결과에 따르면 제안된 기법은 몇 비트의 장구간 피드백 정보를 추가함으로써 평균 SNR이 20 dB인 환경에서 멀티모드 안테나 선택 기술이나 멀티모드 기저 선택 기술에 비해 throughput 성능이 각각 11.2 %, 5.1 % 증가한다.

• 한국통신학회논문지
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• 제37권7C호
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• pp.554-564
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• 2012

차량인식은 차량 후보영역 검출단계와 검출된 후보 영역에서 특징을 기반으로 차량을 검증하는 차량 검증단계로 나누어진다. 선형 변환 방식의 특징은 차원 감소 효과와 통계적인 특징을 지니게 되어, 이동이나 회전에 강인한 특성을 갖는다. 선형 변환 방식 중 비음수행렬분해(Non-negative Matrix Factorization, NMF)는 부분 기반 표현 방식으로 차량의 국소적인 특징을 기저벡터로 사용하여 희소성을 갖는 특징을 추출할 수 있기 때문에 도심영상에서 발생하는 차폐 영역에 따른 인식률 저하를 방지할 수 있다. 본 논문에서는 차량 인식에 적합한 NMF 특징 추출 방법을 제안하고, 인식률을 검증하였다. 또한 희소성 제약 조건을 이용하여 기저 벡터에 희소성을 가지는 SNMF(Sparse NMF)와 LVQ2(Learning Vector Quantization) 신경 회로망을 결합하여 차폐 영역에 대한 차량 인식 효율을 기존의 NMF를 이용한 방법과 비교하였다. NMF를 이용하는 특징은 차량이 혼재되어 차폐 영역이 빈번히 발생하는 도심에서도 강건한 특징임을 보였다.