• Structural Engineering and Mechanics
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• 제11권4호
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• pp.423-442
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• 2001

This paper presents a method of elastic-plastic analysis for planar steel frames that provides the accuracy of distributed plasticity methods with the computational efficiency that is greater than that of distributed plasticity methods but less than that of plastic-hinge based methods. This method accounts for the effect of spread of plasticity accurately without discretization through the cross-section of a beam-column element, which is achieved by the following procedures. First, nonlinear equations describing the relationships between generalized stresses and strains of the cross-section are derived analytically. Next, nonlinear force-deformation relationships for the beam-column element are obtained through lengthwise integration of the generalized strains. Elastic-plastic flexibility coefficients are then calculated by differentiating the above element force-deformation relationships. Finally, an elastic-plastic stiffness matrix is obtained by making use of the flexibility-stiffness transformation. Adding the conventional geometric stiffness matrix to the elastic-plastic stiffness matrix results in the tangent stiffness matrix, which can readily be used to evaluate the load carrying capacity of steel frames following standard nonlinear analysis procedures. The accuracy of the proposed method is verified by several examples that are sensitive to the effect of spread of plasticity.

• Structural Engineering and Mechanics
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• 제87권6호
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• pp.555-574
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• 2023

An efficient optimization algorithm and damage-sensitive objective function are two main components in optimization-based Finite Element Model Updating (FEMU). A suitable combination of these components can considerably affect damage detection accuracy. In this study, a new hybrid damage-sensitive objective function is proposed based on combining two different objection functions to detect the location and extent of damage in structures. The first one is based on Generalized Pseudo Modal Strain Energy (GPMSE), and the second is based on the element's Generalized Flexibility Matrix (GFM). Four well-known population-based metaheuristic algorithms are used to solve the problem and report the optimal solution as damage detection results. These algorithms consist of Cuckoo Search (CS), Teaching-Learning-Based Optimization (TLBO), Moth Flame Optimization (MFO), and Jaya. Three numerical examples and one experimental study are studied to illustrate the capability of the proposed method. The performance of the considered metaheuristics is also compared with each other to choose the most suitable optimizer in structural damage detection. The numerical examinations on truss and frame structures with considering the effects of measurement noise and availability of only the first few vibrating modes reveal the good performance of the proposed technique in identifying damage locations and their severities. Experimental examinations on a six-story shear building structure tested on a shake table also indicate that this method can be considered as a suitable technique for damage assessment of shear building structures.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 1991년도 한국자동제어학술회의논문집(국내학술편); KOEX, Seoul; 22-24 Oct. 1991
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• pp.174-178
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• 1991

In this paper, we present a unified approach for the control of manipulator motions and active forces based on the operational space formulation. The end-effector dynamic model is used in the development of a control system in which the generalized operational space end-effector forces are selected as the command vector. A "generalized position and force specification matrix" is used for the specification of space of motions and forces in which manipulator is to be controlled. Flexibility in the force sensor, end-effector, and environment are discussed.discussed.

• 로봇학회논문지
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• 제9권3호
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• pp.178-184
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• 2014

Tendon driven robot mechanisms have many advantages such as allowing miniaturization and light-weight designs and/or enhancing flexibility in the design of structures. When designing or analyzing tendon driven mechanisms, it is important to determine how the tendons should be connected and whether the designed mechanism is easily controllable. Graph representation is useful to view and analyze such tendon driven mechanisms that are complicatedly interconnected between mechanical elements. In this paper, we propose a method of generalized graph representation that provides us with an intuitive analysis tool not only for tendon driven manipulators, but also various other kinds of mechanical systems which are combined with tendons. This method leads us to easily obtain structure matrix - which is the one of the most important steps in analyzing tendon driven mechanisms.

• 대한기계학회논문집
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• 제18권4호
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• pp.887-902
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• 1994

Within the framework of anisotropic thermoelasticity, the problem of an interlaminar crack in a laminated fiber-reinforced composite subjected to a uniform heat flow is investigated. Under a state of generalized plane deformation, dissimilar anisotropic half-spaces with different fiber orientations are considered to be bound together by a matrix interlayer containing the crack. The interlayer models the matrix-rich interlaminar region of the fibrous composite laminate. Based on the flexibility/stiffness matrix approach, formulation of the current crack problem results in having to solve two sets of singular integral equations for temperature and thermal stress analyses. Numerical results are obtained, illustrating the parametric effects of laminate stacking sequence, relative crack size, crack location, crack surface partial insulation, and fiber volume fraction on the values of mixed mode thermal stress intensity factors.

• 제어로봇시스템학회논문지
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• 제20권6호
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• pp.631-634
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• 2014

We propose a measurement state feedback controller for a class of nonlinear systems that have uncertain nonlinearity and sensor noise. The new design method based on the matrix inequality approach solves the measurement feedback control problem of a class of nonlinear systems. As a result, the proposed methods using a matrix inequality approach has the flexibility to apply the controller. In addition, the sensor noise can be attenuated for more generalized systems containing uncertain nonlinearities.

• Nuclear Engineering and Technology
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• 제55권6호
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• pp.2172-2194
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• 2023

A variational nodal method (VNM) with unstructured-mesh is presented for solving steady-state and dynamic neutron diffusion equations. Orthogonal polynomials are employed for spatial discretization, and the stiffness confinement method (SCM) is implemented for temporal discretization. Coordinate transformation relations are derived to map unstructured triangular nodes to a standard node. Methods for constructing triangular prism space trial functions and identifying unique nodes are elaborated. Additionally, the partitioned matrix (PM) and generalized partitioned matrix (GPM) methods are proposed to accelerate the within-group and power iterations. Neutron diffusion problems with different fuel assembly geometries validate the method. With less than 5 pcm eigenvalue (k_eff) error and 1% relative power error, the accuracy is comparable to reference methods. In addition, a test case based on the kilowatt heat pipe reactor, KRUSTY, is created, simulated, and evaluated to illustrate the method's precision and geometrical flexibility. The Dodds problem with a step transient perturbation proves that the SCM allows for sufficiently accurate power predictions even with a large time-step of approximately 0.1 s. In addition, combining the PM and GPM results in a speedup ratio of 2-3.

• 대한기계학회논문집A
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• 제23권11호
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• pp.2058-2066
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• 1999

The present paper proposes a new dynamic analysis method for multi-span Timoshenko beam structures supported by joints with damping subject to moving loads. An exact dynamic element matrix method is adopted to model Timoshenko beam structures. A generalized modal analysis method is applied to derive response formulae for beam structures subject to moving loads. The proposed method offers an exact and closed form solution. Two numerical examples are provided for validating and illustrating the proposed method. In the first numerical example, a single span beam with multiple moving loads is considered. A dynamic analysis on a multi-span beam under a moving load is considered as the second example, in which the flexibility and damping of supporting joints are taken into account. The numerical study proves that the proposed method is useful for the vibration analysis of multi-span beam-hype structures by moving loads.

• 한국정밀공학회:학술대회논문집
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• 한국정밀공학회 1995년도 춘계학술대회 논문집
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• pp.608-614
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• 1995

공작기계 등과 같이 복잡한 대형 구조물의 구조해석에 있어서 결합부요소의 강성과 질량특성을 모델링하는 일반적 인 방법이 없는 실정이므로 어려움이많다. 본 연구에서는 공작기계에서 흔히 쓰이는 Slide-way contact joint 결 합부를 등가의 강성행렬 요소(Generalized stiffness matrix element)로 모델링하는 방법을 제안하였다.. 기존의 유 한용소 해석법 프로그램을 이용하여 결합부 유한요소 모델의 유연도계수(Flexibility influence coefficients)를 계산하고 Guyan의 정축약이론을 이용하여 등가의 강성행렬요소로 축약시키는 방법이다. 제안된 방법을 대형 평면연 삭기 구조해석에 적용하고, 그 결과를 강결합 모델의 결과 및 Yoshimura의 등가스프링결합부 모델을 사용한 경우의 결과와 비교하므로써 본 연구에서 제안한 결합부 모델링 방법의 유용성을 확인하였다.

• 지능정보연구
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• 제29권1호
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• pp.249-263
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• 2023

대표적인 추천 시스템 방법론인 협업 필터링(Collaborative Filtering)에는 이웃기반 방법(Neighbor Methods)과 잠재 요인 모델(Latent Factor model)이라는 두 가지 접근법이 있다. 이중 행렬 분해(Matrix Factorization)를 이용하는 잠재 요인 모델은 사용자-아이템 상호작용 행렬을 두 개의 보다 낮은 차원의 직사각형 행렬로 분해하고 이들의 행렬 곱으로 아이템의 평점(Rating)을 예측한다. 평점 패턴으로부터 추출된 요인 벡터들을 통해 사용자와 아이템 속성을 포착할 수 있기 때문에 확장성, 정확도, 유연성 측면에서 이웃기반 방법보다 우수하다고 알려져 있다. 하지만 평점이 지정되지 않은 아이템에 대해서는 선호도가 다른 개개인의 다양성을 반영하지 못하는 근본적인 한계가 있고 이는 반복적이고 부정확한 추천을 초래하게 된다. 이러한 잠재요인 모델의 한계를 개선하고자 각각의 아이템 별로 사용자의 선호도를 적응적으로 학습하는 적응 심층 잠재요인 모형(Adaptive Deep Latent Factor Model; ADLFM)이 등장하였다. ADLFM은 아이템의 특징을 설명하는 텍스트인 아이템 설명(Item Description)을 입력으로 받아 사용자와 아이템의 잠재 벡터를 구하고 어텐션 스코어(Attention Score)를 활용하여 개인의 다양성을 반영할 수 있는 방법을 제시한다. 하지만 아이템 설명을 포함하는 데이터 셋을 요구하기 때문에 이 방법을 적용할 수 있는 대상이 많지 않은 즉 일반화에 있어 한계가 있다. 본 연구에서는 아이템 설명 대신 추천시스템에서 보편적으로 사용하는 아이템 ID를 입력으로 하고 Self-Attention, Multi-head attention, Multi-Conv1d 등 보다 개선된 딥러닝 모델 구조를 적용함으로써 ADLFM의 한계를 개선할 수 있는 일반화된 적응 심층 잠재요인 추천모형 G-ADLFRM을 제안한다. 다양한 도메인의 데이터셋을 가지고 입력과 모델 구조 변경에 대한 실험을 진행한 결과, 입력만 변경했을 경우 동반되는 정보손실로 인해 ADLFM 대비 MAE(Mean Absolute Error)가 소폭 높아지며 추천성능이 하락했지만, 처리할 정보량이 적어지면서 epoch 당 평균 학습속도는 대폭 향상되었다. 입력 뿐만 아니라 모델 구조까지 바꿨을 경우에는 가장 성능이 우수한 Multi-Conv1d 구조가 ADLFM과 유사한 성능을 나타내며 입력변경으로 인한 정보손실을 충분히 상쇄시킬 수 있음을 보여주었다. 결론적으로 본 논문에서 제시한 모형은 기존 ADLFM의 성능은 최대한 유지하면서 빠른 학습과 추론이 가능하고(경량화) 다양한 도메인에 적용할 수 있는(일반화) 새로운 모형임을 알 수 있다.