• 한국항공우주학회지
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• 제47권7호
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• pp.535-540
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• 2019

MDO(Multi-disciplinary Optimization)를 위한 서로 다른 모델 간의 결합은 계산 프레임 워크의 복잡성을 크게 증가시키는 동시에 CPU 시간과 메모리 사용을 증가시킨다. 이러한 어려움을 극복하기 위해 POD(Proper Orthogonal Decomposition)와 RBF(Radial Basis Function)를 사용하여 복합 샌드위치 구조가 항공기 날개 스킨 재료로 사용될 때 복합재와 샌드위치 코어의 두께를 결정하는 최적화 문제의 해를 구했다. POD와 RBF를 사용하여 날개 형상과 하중 데이터에 대한 대리 모델을 만들었으며 대리 모델에 의해 얻어진 목적 함수 및 제약 함수 값을 사용하여 최적해를 구하였다.

• 산업경영시스템학회지
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• 제46권4호
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• pp.53-62
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• 2023

Effects-Based Operations (EBO) refers to a process for achieving strategic goals by focusing on effects rather than attrition-based destruction. For a successful implementation of EBO, identifying key nodes in an adversary network is crucial in the process of EBO. In this study, we suggest a network-based approach that combines network centrality and optimization to select the most influential nodes. First, we analyze the adversary's network structure to identify the node influence using degree and betweenness centrality. Degree centrality refers to the extent of direct links of a node to other nodes, and betweenness centrality refers to the extent to which a node lies between the paths connecting other nodes of a network together. Based on the centrality results, we then suggest an optimization model in which we minimize the sum of the main effects of the adversary by identifying the most influential nodes under the dynamic nature of the adversary network structure. Our results show that key node identification based on our optimization model outperforms simple centrality-based node identification in terms of decreasing the entire network value. We expect that these results can provide insight not only to military field for selecting key targets, but also to other multidisciplinary areas in identifying key nodes when they are interacting to each other in a network.

• 신재생에너지
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• 제20권2호
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• pp.26-34
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• 2024

Floating offshore wind turbines (FOWTs) have been developed to overcome large water depths and leverage the abundant wind resource in deep seas. However, wind-wave misalignment can occur depending on the weather conditions, and most megawatt (MW)-class turbines are horizontal-axis wind turbines subjected to yaw errors. Therefore, the power performance and dynamic response of super-large FOWTs exposed simultaneously to these external conditions must be analyzed. In this study, several scenarios combining wind-wave misalignment and yaw error were considered. The IEA 15 MW reference FOWT (v1.1.2) and OpenFAST (v3.4.1) were used to perform numerical simulations. The results show that the power performance was affected more significantly by the yaw error; therefore, the generator power reduction and variability increased significantly. However, the dynamic response was affected more significantly by the wind-wave misalignment increased; thus, the change in the platform 6-DOF and tower loads (top and base) increased significantly. These results can be facilitate improvements to the power performance and structural integrity of FOWTs during the design process.

• 플랜트 저널
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• 제13권4호
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• pp.41-47
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• 2017

본 논문은 해양플랜트 입찰단계에서 시스템엔지니어링(Systems Engineering)기법을 이용하여 해양플랜트를 구성하고 있는 장비 배치를 검증(Verification)할 수 있는 검증수행모델에 대한 연구이다. 해양플랜트 상부구조물(Topside) 유지보수 장비들을 엔지니어링하기 위하여는 Topside 장비 Layout검증이 선행되어야 한다. 하지만 입찰단계에서 완성도가 높지않는 FEED(Front End Engineering Design)결과물로 인한 많은 오류가 존재함에도 불구하고 검토시간의 부족 등의 이유로 검증을 수행하지 못하는 경우가 존재한다. 따라서 본 논문에서는 다학제간 접근방식인 시스템엔지니어링 프로세스를 간략화하여 적용함으로써 제한된 시간내 효과적으로 장비배치를 검증할 수 있는 검증수행모델을 제안하였다. 모델의 구성은 기능전개모델(Functional Deployment Model)을 통하여 구축하였으며 사례연구를 통하여 본 Topside 장비 배치에 대한 검증 수행모델을 검증하였다.

• Smart Structures and Systems
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• 제30권6호
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• pp.673-686
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• 2022

Deep learning algorithms for Structural Health Monitoring (SHM) have been extracting the interest of researchers and engineers. These algorithms commonly used loss functions and evaluation indices like the mean square error (MSE) which were not originally designed for SHM problems. An updated loss function which was specifically constructed for deep-learning-based structural damage detection problems has been proposed in this study. By tuning the coefficients of the loss function, the weights for damage localization and quantification can be adapted to the real situation and the deep learning network can avoid unnecessary iterations on damage localization and focus on the damage severity identification. To prove efficiency of the proposed method, structural damage detection using convolutional neural networks (CNNs) was conducted on a truss bridge model. Results showed that the validation curve with the updated loss function converged faster than the traditional MSE. Data augmentation was conducted to improve the anti-noise ability of the proposed method. For reducing the training time, the normalized modal strain energy change (NMSEC) was extracted, and the principal component analysis (PCA) was adopted for dimension reduction. The results showed that the training time was reduced by 90% and the damage identification accuracy could also have a slight increase. Furthermore, the effect of different modes and elements on the training dataset was also analyzed. The proposed method could greatly improve the performance for structural damage detection on both the training time and detection accuracy.

• 한국실천공학교육학회논문지
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• 제3권1호
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• pp.76-83
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• 2011

본 논문에서는 센서공학분야의 실습교육에 NI-ELVIS(National Instrument Educational Laboratory Virtual Instrumentation Suite)를 활용하는 방안을 제시하였다. ELVIS는 LabView 기반의 계측시스템 설계와 프로토타이핑 환경을 제공하는 개발 플랫폼을 지칭한다. ELVIS는 가상 계측장치와 다기능 데이터 수집 장치(DAQ) 및 벤치탑 워크스테이션, 프로토타이핑보드 등으로 구성되어 있기 때문에 사용자가 의도하는 다양한 형태의 계측시스템을 PC에서 소프트웨어적으로 구성할 수 있다. 따라서 고가의 계측 장비를 이용하지 않고도 전기전자 분야의 효과적인 실험 실습 교육을 진행할 수 있다는 장점이 있다. 특히 센서계측공학의 경우 센서 기술, 전기전자공학, 신호처리, 데이터 분석 등 다양한 분야가 혼합된 영역임에도 복잡한 실험 장치에 의존하지 않아도 실습교육에 활용이 가능하다. 본 논문에서 제시한 계측공학 실습교육에서의 적용 외에도 전기전자 실험이 필요한 다양한 교과목에 높은 학습효과를 기대할 수 있다.

• Earthquakes and Structures
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• 제8권6호
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• pp.1363-1386
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• 2015

The October 23 2011 Van Earthquake is studied from an earthquake engineering point of view. Strong ground motion processing was performed to investigate features of the earthquake source, forward directivity effects during the rupture process as well as local site effects. Strong motion characteristics were investigated in terms of peak ground motion and spectral acceleration values. Directiviy effects were discussed in detail via elastic response spectra and wide band spectograms to see the high frequency energy distributions. Source parameters and slip distribution results of the earthquake which had been proposed by different researchers were summarized. Influence of the source parameters on structural response were shown by comparing elastic response spectra of Muradiye synthetic records which were performed by broadband strong motion simulations of the earthquake. It has been emphasized that characteristics of the earthquake rupture dynamics and their effects on structural design might be investigated from a multidisciplinary point of view. Seismotectonic calculations (e.g., slip pattern, rupture velocity) may be extended relating different engineering parameters (e.g., interstorey drifts, spectral accelerations) across different disciplines while using code based seismic design approaches. Current state of the art building codes still far from fully reflecting earthquake source related parameters into design rules. Some of those deficiencies and recent efforts to overcome these problems were also mentioned. Next generation ground motion prediction equations (GMPEs) may be incorporated with certain site categories for site effects. Likewise in the 2011 Van Earthquake, Reverse/Oblique earthquakes indicate that GMPEs need to be feasible to a wider range of magnitudes and distances in engineering practice. Due to the reverse faulting with large slip and dip angles, vertical displacements along with directivity and fault normal effects might significantly affect the engineering structures. Main reason of excessive damage in the town of Erciş can be attributed to these factors. Such effects should be considered in advance through the establishment of vertical design spectra and effects might be incorporated in the available GMPEs.

• 대한환경공학회지
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• 제34권6호
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• pp.365-372
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• 2012

최근의 사회는 엔지니어에게 국제사회와 미래를 이해할 수 있고, 리더십을 갖춘 전문기술자가 될 것을 요구하고 있다. 전문교양교육은 이러한 요구를 만족시켜 주어야 하며, 글로벌형 인재를 양성할 수 있도록 강화돼야 한다. 7차 교육과정 이후 소홀해진 과학교육으로 인해 저하된 이공계기초 교양교육을 강화시켜 공과대학 학생들의 전공수학능력을 향상시켜야 한다. 엔지니어의 인성 및 기초교양 교육은 2009 교육과정을 통하여 초 중 고부터 대학으로 이어지는 연속적이고 체계적인 교육과정으로 완성될 수 있다. 아울러 대학 및 학과특성화 과정을 통하여 다양한 교육의 기회를 제공해주고, 사회가 요구하는 필요한 인재를 양성하도록 해야 한다. 환경공학은 학제간 융복합적 성격이 강하기 때문에 다전공제도를 적극 활용하는 것이 바람직하고, 이공계기초 과목의 이수기준을 강화시킬 필요가 있으며, 환경공학 맞춤형 교양교육컨텐츠를 개발할 필요가 있다.

• Structural Engineering and Mechanics
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• 제86권3호
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• pp.337-348
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• 2023

The optimization of reinforced concrete (RC) cantilever retaining walls is a complex problem and requires the use of advanced techniques like metaheuristic algorithms. For this purpose, an optimization model must first be developed, which involves mathematical complications, multidisciplinary knowledge, and programming skills. This task has proven to be too arduous and has halted the mainstream acceptance of optimization. Therefore, it is necessary to unravel the complications of optimization into an easily applicable form. Currently, the most commonly used method for designing retaining walls is by following the proportioning limits provided by the ACI handbook. However, these limits, derived manually, are not verified by any optimization technique. There is a need to validate or modify these limits, using optimization algorithms to consider them as optimal limits. Therefore, this study aims to propose updated proportioning limits for the economical design of a RC cantilever retaining wall through a comprehensive parametric investigation using the genetic algorithm (GA). Multiple simulations are run to examine various design parameters, and trends are drawn to determine effective ranges. The optimal limits are derived for 5 geometric and 3 reinforcement variables and validated by comparison with their predecessor, ACI's preliminary proportioning limits. The results indicate close proximity between the optimized and code-provided ranges; however, the use of optimal limits can lead to additional cost optimization. Modifications to achieve further optimization are also discussed. Besides the geometric variables, other design parameters not covered by the ACI building code, like reinforcement ratios, bar diameters, and material strengths, and their effects on cost optimization, are also discussed. The findings of this investigation can be used by experienced engineers to refine their designs, without delving into the complexities of optimization.

• 한국해양공학회지
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• 제32권1호
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• pp.1-8
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• 2018

In order to analyze the response of the offshore structure numerically, the linear potential theory is generally applied for simplicity, and only the radiation damping is considered among various damping forces. Therefore, the results of a numerical simulation can be different from the motion of the structure in a real environment. To reduce the differences between the simulation results and experimental results, the viscous damping, which affects the motion of the structure, is also taken into account. The appropriate damping model is essential for the numerical simulation in order to obtain precise responses of the offshore structure. In this study, various damping models such as linear or quadratic damping and the nonlinear drag force from numerous slender bodies were used to simulate the free decay motion of the platform, and its characteristics were confirmed. The optimized damping model was found by comparing the simulation results to the experimental results. The hydrodynamic forces and wave exciting forces of the structure were obtained using WAMIT, and the free decay test was simulated using OrcaFlex. A free decay test of the scale model was performed by KRISO.