• 제어로봇시스템학회논문지
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• 제20권8호
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• pp.875-881
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• 2014

The redundancy resolution of the seven DOF (Degree of Freedom) upper limb exoskeleton is key to the synchronous motion between a robot and a human user. According to the seven DOF human arm model, positioning and orientating the wrist can be completed by multiple arm configurations that results in the non-unique solution to the inverse kinematics. This paper presents analysis on the kinematic and dynamic aspect of the human arm movement and its effect on the redundancy resolution of the seven DOF human arm model. The redundancy of the arm is expressed mathematically by defining the swivel angle. The final form of swivel angle can be represented as a linear combination of two different swivel angles achieved by optimizing two cost functions based on kinematic and dynamic criteria. The kinematic criterion is to maximize the projection of the longest principal axis of the manipulability ellipsoid of the human arm on the vector connecting the wrist and the virtual target on the head region. The dynamic criterion is to minimize the mechanical work done in the joint space for each of two consecutive points along the task space trajectory. The contribution of each criterion on the redundancy was verified by the post processing of experimental data collected with a motion capture system. Results indicate that the bimodal redundancy resolution approach improved the accuracy of the predicted swivel angle. Statistical testing of the dynamic constraint contribution shows that under moderate speeds and no load, the dynamic component of the human arm is not dominant, and it is enough to resolve the redundancy without dynamic constraint for the realtime application.

• 대한기계학회논문집A
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• 제24권1호
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• pp.190-195
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• 2000

It has been established that a crack has an important effect on the dynamic behavior of a structure. This effect depends mainly on the location and depth of the crack. To identify the location and depth of a crack in a structure. Nikolakopoulos et. al. used the intersection point of the superposed contours that correspond to the eigenfrequency caused by the crack presence. However the intersecting point of the superposed contours is not only difficult to find but also incorrect to calculate. A method is presented in this paper which uses optimization technique for the location and depth of the crack. The basic idea is to find parameters which use the structural eigenfrequencies on crack depth and location and optimization algorithm. With finite element model of the structure to calculate eigenfrequencies, it is possible to formulate the inverse problem in optimization format. Method of optimization is augmented lagrange multiplier method and search direction method is BFGS variable metric method and one dimensional search method is polynomial interpolation.

• 대한기계학회논문집A
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• 제25권12호
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• pp.2062-2069
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• 2001

It has been established that a crack has an important effect on the dynamic behavior of a structure. This effect depends mainly on the location and depth of the crack. To identify the location and depth of a crack in a structure, a method is presented in this paper which uses synthetic artificial intelligent technique, that is, Adaptive-Network-based Fuzzy Inference System(ANFIS) solved via hybrid learning algorithm(the back-propagation gradient descent and the least-squares method) are used to learn the input(the location and depth of a crack)-output(the structural eigenfrequencies) relation of the structural system. With this ANFIS and a continuous evolutionary algorithm(CEA), it is possible to formulate the inverse problem. CEAs based on genetic algorithms work efficiently for continuous search space optimization problems like a parameter identification problem. With this ANFIS, CEAs are used to identify the crack location and depth minimizing the difference from the measured frequencies. We have tried this new idea on a simple beam structure and the results are promising.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2001년도 춘계학술대회논문집C
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• pp.182-188
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• 2001

It has been established that a crack has an important effect on the dynamic behavior of a structure. This effect depends mainly on the location and depth of the crack. To identify the location and depth of a crack in a structure, a method is presented in this paper which uses synthetic artificial intelligent technique, that is, Adaptive-Network-based Fuzzy Inference System(ANFIS) solved via hybrid learning algorithm(the back-propagation gradient descent and the least-squares method) are used to learn the input(the location and depth of a crack)-output(the structural eigenfrequencies) relation of the structural system. With this ANFIS and a continuous evolutionary algorithm(CEA), it is possible to formulate the inverse problem. CEAs based on genetic algorithms work efficiently for continuous search space optimization problems like a parameter identification problem. With this ANFIS, CEAs are used to identify the crack location and depth minimizing the difference from the measured frequencies. We have tried this new idea on a simple beam structure and the results are promising.

• 대한기계학회논문집A
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• 제41권9호
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• pp.869-876
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• 2017

기계시스템을 제어한다든지 그 부재를 설계하기 위하여 그리고 구동기의 용량을 결정하는데 있어서 구동력이나 조인트반력을 해석하는 것이 필요하다. 본 논문은 주어진 시스템의 운동을 구현하는 다양한 형태의 구동조건에 따른 구동력(또는 토크)을 조인트좌표 공간에서 계산하는 알고리즘을 제시한다. 조인트좌표를 기구학적 시스템의 일반좌표로 사용하며 운동방정식과 구속조건의 가속도식은 속도변환법을 이용하여 직교좌표공간으로부터 조인트좌표공간으로 변환한다. 수치예제를 통하여 제시된 알고리즘의 유용성을 확인한다.

• KSII Transactions on Internet and Information Systems (TIIS)
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• 제14권5호
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• pp.2236-2257
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• 2020

Ransomware is malicious software that encrypts the user-related files and data and holds them to ransom. Such attacks have become one of the serious threats to cyberspace. The avoidance techniques that ransomware employs such as obfuscation and/or packing makes it difficult to analyze such programs statically. Although many ransomware detection studies have been conducted, they are limited to a small portion of the attack's characteristics. To this end, this paper proposed a framework for the behavioral-based dynamic analysis of high survivable ransomware (HSR) with integrated valuable feature sets. Term Frequency-Inverse document frequency (TF-IDF) was employed to select the most useful features from the analyzed samples. Support Vector Machine (SVM) and Artificial Neural Network (ANN) were utilized to develop and implement a machine learning-based detection model able to recognize certain behavioral traits of high survivable ransomware attacks. Experimental evaluation indicates that the proposed framework achieved an area under the ROC curve of 0.987 and a few false positive rates 0.007. The experimental results indicate that the proposed framework can detect high survivable ransomware in the early stage accurately.

• 대한토목학회논문집
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• 제39권1호
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• pp.147-154
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• 2019

유한요소모델 업데이팅은 계측에 의한 구조물의 실제 응답과 가장 가까운 응답을 내는 유한요소모델의 매개변수를 찾는 문제로 정의할 수 있다. 기존 연구에서는 실 구조물과 해석 모델의 응답의 오차를 최소화하는 최적화에 기반 한 방법이 개발되었다. 이 연구에서는 목표 모드 정보로부터 유한요소 모델의 매개변수를 직접 얻을 수 있는 역 고유치 문제를 구성하고 역 고유치 문제를 빠르고 정확하게 풀기 위한 깊은 신경망(Deep Neural Network)을 구성하는 방법을 제안한다. 개발한 방법의 적용 예로서 현수교의 역 고유치 함수를 모사하는 신경망을 이용한 동적 유한요소모델 업데이트를 보인다. 해석 결과 제시한 방법은 매우 높은 정확도로 목표 모드에 대응하는 매개변수를 찾아낼 수 있음을 보였다.

• 한국전문물리치료학회지
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• 제5권3호
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• pp.11-20
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• 1998

The purposes of this study were to determine the effect of different degrees of severity of diabetic neuropathy on balance function, and to evaluate dynamic balance and functional performance in diabetes patients. Twenty-four subjects with diabetes mellitus were divided into three groups according to results of sensory nerve conduction study. All subjects were evaluated for dynamic balance which was measured using computerized dynamic posturography, and functional performance which was measured using the Berg balance scale. One-way analysis of variance was used to determine whether there were any statistically differences of dynamic balance function and functional performance among the three groups. The Spearrnan's rank correlation was used to determine statistical significance between dynamic balance and age. The results were as follows: 1. Dynamic balance measured using computerized dynamic posturography was significantly lower in the no response group than in the normal amplitude group (p<0.05). 2. Functional performance tested by the Berg balance scale was not statistically different among the three groups (p>0.05). 3. an inverse relationship was found between dynamic balance measured using computerized dynamic posturography and age (r=-0.68, p<0.05). These results suggest that patients with severe diabetic neuropathy have loss of dynamic balance function. Therefore, patients with severe diabetic neuropathy need to have their balance evaluated and receive appropriate education.

• 한국구조물진단유지관리공학회 논문집
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• 제18권3호
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• pp.101-107
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• 2014

구조물의 손상 추정은 동적응답신호로부터 고유주기와 모드형상을 구한 후 이를 역해석하여 손상위치와 손상정도를 파악함으로써 이루어 진다. 건축구조물의 경우 토목구조물에 비하여 구조형식이 복잡하고 비구조요소 및 노이즈 등의 영향으로 인하여 구조물 판별에 어려움이 있다. 동적응답신호를 이용한 건물의 손상추정에 관한 최근의 연구들은 손상추정을 위하여 민감도 또는 추정치 등 간접적 지표를 사용하고 있으나, 좀 더 합리적이고 명확한 손상추정을 위하여 운동방정식으로부터 직접 유도된 변수를 손상지수로 활용할 필요가 있을 것으로 판단된다. 따라서 본 연구에서는 전단형 건물의 운동방정식으로부터 직접 유도된 층강성 감소비를 손상지수로 하는 손상추정 방법을 제안하였다. 제안된 손상지수는 손상 전 모드형상과 손상 전 후 고유진동수 차이를 알면 구할 수 있다. 제안된 손상 추정방법을 수치해석예제에 적용한 결과 손상이 발생한 층에서 층강성 변화율이 (-)부호를 나타내었으며, 크기가 다른 층에 비하여 15배 정도 크게 나타나 전단형 건물의 손상 추정지수로서 활용될 수 있을 것으로 판단된다.

• Structural Engineering and Mechanics
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• 제32권5호
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• pp.667-683
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• 2009

FE model-based dynamic analysis has been widely used to predict the dynamic characteristics of civil structures. In a physical point of view, an FE model is unavoidably different from the actual structure as being formulated based on extremely idealized engineering drawings and design data. The conventional model updating methods such as direct method and sensitivity-based parameter estimation are not flexible for model updating of complex and large structures. Thus, it is needed to develop a model updating method applicable to complex structures without restriction. The main objective of this paper is to present the model updating method based on the hybrid genetic algorithm (HGA) by combining the genetic algorithm as global optimization method and modified Nelder-Mead's Simplex method as local optimization method. This FE model updating method using HGA does not need the derivation of derivative function related to parameters and without application of complicated inverse analysis methods. In order to allow its application on diversified and complex structures, a commercial FEA tool is adopted to exploit previously developed element library and analysis algorithms. Moreover, an output-level objective function making use of measurement and analytical results is also presented to update simultaneously the stiffness and mass of the analysis model. The numerical examples demonstrated that the proposed method based on HGA is effective for the updating of the FE model of bridge structures.