• 한국복합재료학회:학술대회논문집
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• 한국복합재료학회 2005년도 춘계학술발표대회 논문집
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• pp.5-8
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• 2005

In this paper, the electromechanical displacements of curved piezoelectric actuators composed of PZT ceramic and laminated composite materials are calculated based on high performance computing technology and the optimal configuration of composite curved actuator is examined. To accurately predict the local pre-stress in the device due to the mismatch in coefficients of thermal expansion, carbon-epoxy and glass-epoxy as well as PZT ceramic are numerically modeled by using hexahedral solid elements. Because the modeling of these thin layers increases the number of degrees of freedom, large-scale structural analyses are performed through the PEGASUS supercomputer, which is installed in our laboratory. In the first stage, the curved shape of the actuator and the internal stress in each layer are obtained by the cured curvature analysis. Subsequently, the displacement due to the piezoelectric force (which is resulted from applied voltage) is also calculated. The performance of composite curved actuator is investigated by comparing the displacements obtained by the variation of thickness and elastic modulus of laminated composite layers. In order to consider the finite deformation in the first analysis stage and include the pre-stress due to curing process in the second stage, nonlinear finite element analyses are carried out.

• Structural Engineering and Mechanics
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• 제53권1호
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• pp.173-188
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• 2015

Several structural calamities in the second half of the 20th century have shown that adequate collapse-resistance cannot be achieved by designing the individual elements of a structure without taking their interconnectivity into consideration. It has long been acknowledged that membrane behaviour of reinforced concrete structures can significantly increase the robustness of a structure and delay a complete collapse. An experimental large-scale test was conducted on a horizontally restrained, continuous reinforced concrete slab exposed to an artificial failure of the central support and subsequent loading until collapse of the specimen. Within this investigation the development of catenary action associated with the formation of large displacements was observed to increase the ultimate load capacity of the specimen significantly. The development of displacements, strains and horizontal forces within this investigation confirmed a load transfer process from an elastic bending mechanism to a tension controlled catenary mechanism. In this contribution a special focus is directed towards strain and crack development at critical sections. The results of this contribution are of particular importance when validating numerical models related to the development of catenary action in concrete slabs.

• Structural Engineering and Mechanics
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• 제33권2호
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• pp.159-177
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• 2009

The aim of this paper is to give a rigorous framework for the interpretation of limit analysis results including large displacements. The presentation is oriented towards unidimensional media (beams) but two-dimensional (plates) or three-dimensional media are also concerned. A single-degree-of-freedom system is first considered: it shows the basic phenomena of large displacement limit analysis or second-order limit analysis. The results are compared to those of a continuous system and the differences between both systems are discussed. Theoretical results are obtained using the kinematical approach of limit analysis. An admissible load-displacement plane is then defined, according to the yield design theory. The methodology used is applied to frame structures. The presented results are nevertheless different from those already published in the literature, as the virtual displacement field can be distinguished from the displacement field at collapse. The simplicity of large displacement limit analysis makes it attractive for practical engineering applications. The load-displacement upper bound can be used for instance in the optimal design of steel frames in seismic areas.

• Structural Engineering and Mechanics
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• 제51권4호
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• pp.601-625
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• 2014

Based on continuum mechanics and the principle of virtual displacements, incremental total Lagrangian formulation (T.L.) and incremental updated Lagrangian formulation (U.L.) were presented. Both T.L. and U.L. considered the large displacement stiffness matrix, which was modified to be symmetrical matrix. According to the incremental updated Lagrangian formulation, small strain, large displacement, finite rotation of three dimensional Timoshenko fiber beam element tangent stiffness matrix was developed. Considering large displacement and finite rotation, a new type of tangent stiffness matrix of the beam element was developed. According to the basic assumption of plane section, the displacement field of an arbitrary fiber was presented in terms of nodal displacement of centroid of cross-area. In addition, shear deformation effect was taken account. Furthermore, a nonlinear finite element method program has been developed and several examples were tested to demonstrate the accuracy and generality of the three dimensional beam element.

• 한국전산구조공학회논문집
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• 제23권5호
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• pp.475-482
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• 2010

본 논문에서는 대규모 자유도 시스템의 병렬처리를 위하여 2단계로 이루어진 영역분할법(Domain Decomposition Method) 기반의 병렬 알고리즘을 제안하였다. 분할된 영역의 내부 및 외부 경계를 상위영역문제로 정의하고 국부영역문제는 변위 경계조건이 모두 주어지는 분할영역에서의 Dirichlet 문제로 구성한다. 상위영역에서는 전체 상위영역에 대한 강성 행렬의 어셈블이 필요없는 반복법을 통하여 변위를 구하고, 이를 바탕으로 국부영역에서 Multi-Frontal Sparse Solver (MFSS)를 이용하여 변위를 계산한다. 상위영역문제의 연산에서 프로세서 간의 데이터 교환을 최소화하여 계산효율을 유지하며, 동시에 해석 가능한 자유도를 증대시키는 병렬 PCG(Preconditioned Conjugate Gradient)법 기반의 알고리즘을 개발하였다. 제안된 알고리즘을 적용하여 수치해석을 수행한 결과, 프로세서 수가 증가할수록 계산성능의 손실없이 해석 가능한 자유도가 비례하여 증가하는 선형 확장성을 관찰할 수 있었으며, 대규모 자유도 문제에 효과적으로 사용 가능함을 확인하였다.

• 한국항공우주학회지
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• 제43권5호
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• pp.396-404
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• 2015

무인기의 날개는 고고도 장기체류에 적합하도록 가로세로비가 크며, 비행 중 구조 대변형이 발생한다. 비행 중 날개 구조의 실시간 변형 상태 파악을 위해 변위-변형률 관계를 이용하여 비행체의 구조 건전성 및 관련 하중 상태 평가, 이상 진동 현상 발견 및 조종성 향상과 같은 영역에서 활용할 수 있다. 본 논문에서는 비행 중 변형이 발생하는 날개 구조물을 외팔보로 가정하여 구조 대변형을 보다 간편하게 예측하기 위한 변형률 기반의 비선형성을 고려한 변위 예측 알고리즘을 작성하였다. 변위 예측식은 외팔보의 다양한 끝단 변위 조건에서 이루어진 구조 실험과 유한요소 해석 결과의 비교를 통하여 검증하였다. 변형률은 스트레인 게이지로부터 취득한 값을 사용하였으며, 변형률을 이용하여 예측된 변위는 레이저 변위 센서로 측정한 변위와 잘 일치하였다.

• 한국항해항만학회지
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• 제27권5호
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• pp.519-526
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• 2003

초대형 부유식 구조물의 초기 설계단계에서 부체구조물과 상부구조물을 분리하여 해석하는 것이 일반적이며, 부체의 탄성응답해석의 변형모드를 이용하여 상부구조물의 주각부에 강제수직변위를 입력하여 파랑하중에 의한 영향을 고려한다. 하지만 이와 같은 해석법의 경우 각 지점에 변위하중을 입력하는데 어려움이 있다. 본 논문에서는 파랑하중을 지점변위하중으로 직접 입력하지 않고 고정하중과 적재하중에 의한 강도설계 결과를 이용하여 파랑하중의 영향을 증폭계수의 형태로 도출하는 근사 실용정적해석법을 제안한다. 이 연구에서는 4경간 3층 구조물을 예제로 하여 파랑하중의 진폭과 주기, 보 경간을 매개변수로 한 증폭계수의 추이를 분석하였으며 보 모멘트의 증폭계수는 특정회귀방정식으로 나타내었다.

• Journal of Electrical Engineering and Technology
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• 제6권1호
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• pp.76-80
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• 2011

This paper proposes a method to calculate magnetostrictive forces, displacement, and vibration modes of a large-scale Brushless DC(BLDC) motor by using a magneto-mechanically strong coupling formulation. The force is calculated using the energy method with magnetostrictive stress tensor. The mechanical vibration modes are also analyzed by using the principle of Hamilton and the calculated magneto-elastic forces acting on the surfaces of the stator. To verify the algorithm, 3 MW BLDC motor is simulated, and the forces, displacements, and vibration modes are calculated. The result shows that the mechanically stressed core has more deformation or displacements than those of the normal condition.

• Structural Engineering and Mechanics
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• 제23권3호
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• pp.233-247
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• 2006

Most codes of practice state that for large in-plane structures it is necessary to account for the spatial variability of earthquake ground motion. There are essentially three effects that contribute for this variation: (i) wave passage effect, due to finite propagation velocity; (ii) incoherence effect, due to differences in superposition of waves; and (iii) the local site amplification due to spatial variation in geological conditions. This paper discusses the procedures to be undertaken in the time domain analysis of a cable-stayed bridge under spatial variability of earthquake ground motion. The artificial synthesis of correlated displacements series that simulate the earthquake load is discussed first. Next, it is described the 3D model of the International Guadiana Bridge used for running tests with seismic analysis. A comparison of the effects produced by seismic waves with different apparent propagation velocities and different geological conditions is undertaken. The results in this study show that the differences between the analysis with and without spatial variability of earthquake ground motion can be important for some displacements and internal forces, especially those influenced by symmetric modes.

• Smart Structures and Systems
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• 제5권5호
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• pp.507-515
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• 2009

The present work is an alternative methodology in order to balance a nonlinear highly flexible rotor by using neural networks. This procedure was developed aiming at improving the performance of classical balancing methods, which are developed in the context of linearity between acting forces and resulting displacements and are not well adapted to these situations. In this paper a fully experimental procedure using neural networks is implemented for dealing with the adaptive balancing of nonlinear rotors. The nonlinearity results from the large displacements measured due to the high flexibility of the foundation. A neural network based meta-model was developed to represent the system. The initialization of the learning procedure of the network is performed by using the influence coefficient method and the adaptive balancing strategy is prone to converge rapidly to a satisfactory solution. The methodology is tested successfully experimentally.