• Structural Engineering and Mechanics
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• 제64권1호
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• pp.93-107
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• 2017

The article presents the vibration and acoustic responses of un-baffled doubly curved laminated composite panel structure under the excitation of a harmonic point load. The structural responses are obtained using a simulation model via ANSYS including the effect various geometries (cylindrical, elliptical, spherical and hyperboloid). Initially, the model has been established by solving adequate number of available examples to show the convergence and comparison behaviour of the natural frequencies. Further, the acoustic responses are obtained using an indirect boundary element approach for the coupled fluid-structure analysis in LMS Virtual.lab by importing the natural frequency values. Subsequently, the values for the sound power level are computed using the present numerical model and compared with that of the available published results and in-house experimentally obtained data. Further, the acoustic responses (mean-square velocity, radiation efficiency and sound power level) of the doubly curved layered structures are evaluated using the current simulation model via several numerical experimentations for different structural parameters and corresponding discussions are provided in detail.

• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.240-244
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• 2005

In this study a simple model is developed that predicts impact damage in a composite laminate using an analytical model. The model uses a non-linear approximation method (Rayleigh-Ritz) and the large deflection plate theory to predict the number of failed plies and damage area in a quasi-isotropic composite circular plate (axisymmetric problem) due to a point impact load at its centre. It is assumed that the deformation due to a static transverse load is similar to that occurred in a low velocity impact. It is found that the model, despite its simplicity, is in good agreement with FEM predictions and experimental data for the deflection of the composite plate and gives a good estimate of the number of failed plies due to fibre breakage. The predicted damage zone could be used with a fracture mechanics model developed by the second investigator and co-workers to calculate the compression after impact strength of such laminates. This approach could save significant running time when compared to FEM solutions.

• 대한원격탐사학회지
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• 제16권4호
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• pp.355-365
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• 2000

The interferometric correlation, or coherence, is calculated to measure the variance of the interferometric phase and amplitude within the neighbourhood of any location within the image at a result of SAR (Synthetic Aperture Radar) interferometric process which utilizes the phase information of the images. The coherence contains additional information that is useful for detecting point targets which change their location in an area of interest (AOI). In this research, a RGB colour composite image was generated with a intensity image (master image), a intensity change image as a difference between master image and slave image, and a coherence image generated as a part of SAR interferometric processing. We developed a technique performing detection of a point target movement using SAR interferometry and applied it to suitable tandem pair images of ERS-1 and ERS-2 as test data. The possibility of change detection of a point target in the AOI could be identified with the technique proposed in this research.

• Genomics & Informatics
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• 제18권1호
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• pp.2.1-2.11
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• 2020

In this paper, we propose a new approach to detecting outliers in a set of segmented genomes of the flu virus, a data set with a heterogeneous set of sequences. The approach has the following computational phases: feature extraction, which is a mapping into feature space, alignment-free distance measure to measure the distance between any two segmented genomes, and a mapping into distance space to analyze a quantum of distance values. The approach is implemented using supervised and unsupervised learning modes. The experiments show robustness in detecting outliers of the segmented genome of the flu virus.

• Composites Research
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• 제28권5호
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• pp.277-284
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• 2015

본 연구의 목적은 고유진동 응답데이터로부터 적층된 GFRP 판구조의 섬유 물성 변화를 추정하는 것이다. 고등유한요소 상용프로그램(ABAQUS)와 연동된 알고리즘은 미시역학적 관점에서 손상된 요소를 추정할 뿐만 아니라 위치, 개수 및 정도를 탐색할 수 있다. 연동된 기법을 적용하여 역문제를 해결하기 위하여 본 연구에서는 모드형상 대신 제한된 몇 개의 고유진동수 데이터만을 적용하였다. 몇가지 수치해석 결과로부터 제안된 시스템 기법은 다양한 적층배열을 갖는 복합재료 적층판과 같은 복잡한 구조물의 섬유 강성 변화를 추정하는 데 수치해석적으로 효율적임을 보여준다.

• 한국전산구조공학회논문집
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• 제29권5호
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• pp.405-411
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• 2016

본 논문에서는 풍력 블레이드와 같이 세장비가 크고 초기 비틀림이 존재하는 복합재료로 구성된 블레이드에 대한 이차원 단면의 차원축소와 복원관계를 이론적으로 기술하였다. 그리고 VABS 이용한 보의 차원축소모델에 대한 유효성을 검증하기 위해 선행연구 모델을 활용하여 기존 연구결과를 수치적으로 비교하였다. 실물과 가장 가까운 날개 구조물 2차원 형상에 단면해석을 적용하여 정밀한 단면의 이산화를 수행하고 VABS를 이용하여 블레이드의 특성(질량행렬, 강성행렬)을 포함한 1차원 보 모델링을 수행하였다. 1차원 보 모델을 통해 세장비가 큰 날개 구조물의 거동을 확인하고 내부하중을 계산하여 단면위치에서 변형률 복원을 수치적으로 계산하고 이산화된 단면에 수치적으로 매핑하여 시각적으로 확인하고 여유마진을 계산하였다.

• 한국자동차공학회논문집
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• 제4권6호
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• pp.247-259
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• 1996

Kinematic design sensitivity analysis for vehicle in suspension systems design is performed. Suspension systems are modeled using composite joins to reduce the number of the constraint equations. This allows a semi-analytical approach that is computerized symbolic manipulation before numerical computations and that may compensate for their drawbacks. All the constraint equations including design variables are derived in symbolic equations for sensitivity analysis. By directly differentiating the equations with respect to design variables, sensitivity equations are obtained. Since the proposed method only requires the hard point data, sensitivity analysis is possible in suspension design stage.

• Journal of Mechanical Science and Technology
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• 제19권4호
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• pp.947-957
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• 2005

In this study a simple model is developed that predicts impact damage in a composite laminate avoiding the need of the time-consuming dynamic finite element method (FEM). The analytical model uses a non-linear approximation method (Rayleigh-Ritz) and the large deflection plate theory to predict the number of failed plies and damage area in a quasi-isotropic composite circular plate (axisymmetric problem) due to a point impact load at its centre. It is assumed that the deformation due to a static transverse load is similar to that oc curred in a low velocity impact. It is found that the model, despite its simplicity, is in good agreement with FEM predictions and experimental data for the deflection of the composite plate and gives a good estimate of the number of failed plies due to fibre breakage. The predicted damage zone could be used with a fracture mechanics model developed by the second investigator and co-workers to calculate the compression after impact strength of such laminates. This approach could save significant running time when compared to FEM solutions.

• Composites Research
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• 제33권3호
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• pp.108-114
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• 2020

Piecewise Integrated Composite (PIC) 보는 하중 유형에 따라 구간을 나누어, 각 구간마다 하중 유형에 강한 복합재료의 적층 순서를 배열한 보이다. 본 연구는 PIC 보의 구간을 머신 러닝의 일종인 k-NN(k-Nearest Neighbor) 분류를 통해 나누어 기존에 제시되었던 PIC 보에 비해 우수한 굽힘 특성을 갖게 하는 것이 목적이다. 먼저, 알루미늄 보의 3점 굽힘 해석을 통하여 참조점에서의 3축 특성(Triaxiality) 값 데이터를 얻었고, 이를 통해 인장, 전단, 압축의 레이블을 가진 학습 데이터가 만들어진다. 학습 데이터를 통해 각 면마다 독립적인 k-NN 분류 모델을 구성하는 방법(Each plane)과 전체 면에 대한 k-NN 분류 모델을 구성하는 방법(one part)을 이용하여 k-NN 분류 모델을 생성하였고, 하이퍼파라미터의 튜닝을 통하여 다양한 하중 충실도를 도출하였다. 가장 높은 하중 충실도를 가진 k-NN 분류 모델을 기반으로 보를 매핑(mapping)하였고, PIC 보에 대하여 유한요소 해석을 진행한 결과, 기존에 제시되었던 PIC 보에 비해 최대하중과 흡수 에너지가 커지는 특성을 보였다. 하중 충실도를 수동으로 조절하여 100%로 만든 PIC 보와 비교하였을 때, 최대하중과 흡수에너지가 미소한 차이가 나타났으며 이는 타당한 하중 충실도로 보여진다.

• Steel and Composite Structures
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• 제29권4호
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• pp.527-544
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• 2018

The paper presents the study on a change in modal parameters and structural stiffness of cable-stayed Fiberline Bridge made entirely of Glass Fiber Reinforced Polymer (GFRP) composite used for 20 years in the fjord area of Kolding, Denmark. Due to this specific location the bridge structure was subjected to natural aging in harsh environmental conditions. The flexural properties of the pultruded GFRP profiles acquired from the analyzed footbridge in 1997 and 2012 were determined through three-point bending tests. It was found that the Young's modulus increased by approximately 9%. Moreover, the influence of the temperature on the storage and loss modulus of GFRP material acquired from the Fiberline Bridge was studied by the dynamic mechanical analysis. The good thermal stability in potential real temperatures was found. The natural vibration frequencies and mode shapes of the bridge for its original state were evaluated through the application of the Finite Element (FE) method. The initial FE model was created using the real geometrical and material data obtained from both the design data and flexural test results performed in 1997 for the intact composite GFRP material. Full scale experimental investigations of the free-decay response under human jumping for the experimental state were carried out applying accelerometers. Seven natural frequencies, corresponding mode shapes and damping ratios were identified. The numerical and experimental results were compared. Based on the difference in the fundamental natural frequency it was again confirmed that the structural stiffness of the bridge increased by about 9% after 20 years of service life. Data collected from this study were used to validate the assumed FE model. It can be concluded that the updated FE model accurately reproduces the dynamic behavior of the bridge and can be used as a proper baseline model for the long-term monitoring to evaluate the overall structural response under service loads. The obtained results provided a relevant data for the structural health monitoring of all-GFRP bridge.