• Journal of the Society of Naval Architects of Korea
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• v.29 no.2
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• pp.132-139
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• 1992

This paper presents geometrically nonlinear formulation of shell problems using the three-dimensional curved shell element, which includs large displacements and large rotations. Formulations of the geometrically nonlinear problems can be derived in a variety of ways, but most of them have been obtained by assuming that nodal rotations are small. Hence, the tangent stiffness matrix is derived under the assumptions that rotational increments are infinitesimal and the effect of finite rotational increments have to be considered during the equilibrium iterations. To study the large displacement and large rotation problems, the restrictions are removed and the formulations of the curved shell element including the effect of large rotational increments are developed in this paper. The displacement based finite element method using this improved formulation are applied to the analyses of the geometrically nonlinear behaviors of the single and double curved shells, which are compared with the results by others.

• International Journal of Naval Architecture and Ocean Engineering
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• v.9 no.5
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• pp.552-567
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• 2017

The floating crane vessel in waves gives rise to the motion of the lifted object which is connected to the hoisting wire. The dynamic tension induced by the lifted object also affects the motion responses of the floating crane vessel in return. In this study, coupled motion responses of a floating crane vessel and a lifted subsea manifold during deep-water installation operations were investigated by both experiments and numerical calculations. A series of model tests for the deep-water lifting operation were performed at Ocean Engineering Basin of KRISO. For the model test, the vessel with a crane control system and a typical subsea manifold were examined. To validate the experimental results, a frequency-domain motion analysis method is applied. The coupled motion equations of the crane vessel and the lifted object are solved in the frequency domain with an additional linear stiffness matrix due to the hoisting wire. The hydrodynamic coefficients of the lifted object, which is a significant factor to affect the coupled dynamics, are estimated based on the perforation value of the structure and the CFD results. The discussions were made on three main points. First, the motion characteristics of the lifted object as well as the crane vessel were studied by comparing the calculation results. Second, the dynamic tension of the hoisting wire were evaluated under the various wave conditions. Final discussion was made on the effect of passive heave compensator on the motion and tension responses.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.30 no.2
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• pp.127-135
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• 2017

The computing environment has changed rapidly to enable large-scale finite element models to be analyzed at the PC or workstation level, such as multi-core CPU, optimal math kernel library implementing BLAS and LAPACK, and popularization of direct sparse solvers. In this paper, the design considerations on a parallel finite element code for shared memory based multi-core CPU system are proposed; (1) the use of optimized numerical libraries, (2) the use of latest direct sparse solvers, (3) parallelism using OpenMP for computing element stiffness matrices, and (4) assembly techniques using triplets, which is a type of sparse matrix storage. In addition, the parallelization effect is examined on the time-consuming works through a large scale finite element model.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.44 no.1
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• pp.23-29
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• 2018

In this study, sequential cross-linked collagen gels were successfully prepared with collagen, which is biomaterial, and acrylamide (AAm), which is a synthetic monomer. The elastic moduli (E) of cross-linked collagen gels were increased from 1.5 to 3.0 kPa by varying of AAm concentrations. In addition, human dermal fibroblasts were encapsulated into the porous pores introduced into the gels, and cell growth and behavior were investigated. Increasing E of the gels led to decreases in cell growth rate, while the cellular glycosaminoglycan (GAG) production level was elevated. Overall, the growth and cellular activity of skin cells were influenced by the extracellular matrix properties of the collagen gels. In conclusion, these results will be highly useful for designing reconstructive skins and various tissue engineering researches.

• Journal of the Earthquake Engineering Society of Korea
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• v.13 no.3
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• pp.21-28
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• 2009

The precise analysis of soil-pile-structure interaction requires a proper description of soil layer, pile, and structure. In commonly used finite element simulations, mesh boundaries should match the material discontinuity line. However, in practice, the geometry of soil profiles and piles may be so complex that mesh alignment becomes a wasteful and difficult task. To overcome these difficulties, a different integration method is adopted in this paper, which enables easy integration over a regular element with material discontinuity regardless of the location of the discontinuity line. By applying this integration method, the mesh can be generated rapidly and in a highly structured manner, leading to a very regular stiffness matrix. The influence of the shape of the soil profile and piles on the response is examined, and the validity of the proposed soil-pile structure interaction analysis method is demonstrated through several examples. It is seen that the proposed analysis method can be easily used on soil-pile-structure interaction problems with complex interfaces between materials to produce reliable results regardless of the material discontinuity line.

• Magazine of the Korea Concrete Institute
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• v.9 no.2
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• pp.99-108
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• 1997

Many studies on the second-order analysis of reinforced concrete columns have been dealt for symmetric sections under uniaxial loading. However, actual columns are practically subjected to hiaxial loading. In order to more accurately predict the behavior of concrete columns under biaxial loading. the interaction between bending moments of major and minor axes should be considered. In this paper, a stiffness matrix of columns under biaxial loadings was derived and a numerical method was proposed. Numerical analyses, based on the proposed method. were performed to predict behavior of concrete columns with square and rectangular sections under various loading conditions. The analytical results were compared to those using the moment magnifier method in ACI code. It was found that the ultimate strength of concrete rectangular columns, fhr some cases of' biaxial loading conditions. calculated by the moment magnifier method was larger than the values based on the proposed method and therefore. may be ovet.'stimated.

• Proceedings of the KIEE Conference
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• 2000.07b
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• pp.825-827
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• 2000

자성체를 포함하는 자기 시스템을 해석하는데 있어 비선형과 히스테리시스(Hysteresis)는 매우 중요한 역할을 한다. 특히 재질의 히스테리시스 특성을 유한요소법(FEM)을 이용하여 계산하기 위해서 많은 방법들이 소개되었다. 단순 반복법이나 Fixed Point Technique(FPT), M-iteration 법. 뉴튼 랍슨 (Newton-Raphson) 법 등이 그 예이다. 이 방법들 중에서 뉴튼 랍슨법은 빠른 수렴 특성으로 가장 많이 사용되고 있다. 하지만 뉴튼-랍슨법을 이용하여 히스테리시스 재질을 해석할 때는 매 반복 계산 때마다 계 계수행렬(System Stiffness matrix)이 변화하기 때문에 요소의 수가 매우 많을 경우 역행렬을 계산하기 위한 시간이 많이 소요되는 단점이 있다. 특히 히스테리시스 해석의 경우에는 주로 time-step법을 이용하여 계산하므로 가장 시간이 많이 소요되는 행렬 계산 시간을 단축함으로써 전체 계산 시간을 크게 줄일 수 있다. 최근 비선형 해석에서 TLM(Transmission Line Modeling)법이 도입되어 비선형 해석 시의 계산 시간을 크게 단축할 수 있게 되었다. 본 논문에서는 비선형 해석에 적용된 TLM법을 히스테리시스 해석에 적용하는 방법을 새로 제안한다. TLM법은 뉴튼-랍슨법과 달리 각 반복 계산 때마다 계수행렬식이 변화하지 않고 단지 구동항만 변하기 때문에 행렬의 LU를 한 번 저장해 두면 forward와 backward substitution만 시행하면 된다. 따라서 요소의 수가 증가할 경우 TLM법을 사용하면 뉴튼-랍슨법에 비해 매우 큰 계산 이득을 얻을 수 있다. 본 논문에서는 TLM법을 히스테리시스에 적용하는 방법을 기술하고 간단한 모델에 이 방법을 적용하여 뉴튼-랍슨법과의 비교를 통해 TLM법의 효용성을 보인다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.16 no.1
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• pp.69-76
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• 2003

Low-tension cables have been increasingly used in recent years due to deep-sea developments and the advent of synthetic cables. In the case of low-tension cables, large displacements may happen due to relatively small restoring forces of tension and thus the effects of fluid and geometric non-linearities and bending stiffness. A Fortran program is developed by employing a finite difference method. In the algorithm, an implicit time integration and Newton-Raphson iteration are adopted. For the calculation of huge size of matrices, block tri-diagonal matrix method is applied, which is much faster than the well-known Gauss-Jordan method in two point boundary value problems. Some case studies are carried out and the results of numerical simulations are compared with a in-house program of WHOI Cable with good agreements.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.18 no.3
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• pp.291-302
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• 2005

Due to the importance of the parameter in structural response, the uncertain elastic modulus was located at the center of stochastic analysis, where the response variability caused by the uncertain system parameters is pursued. However when we analyze the so-called stochastic systems, as many parameters as possible must be included in the analysis if we want to obtain the response variability that can reach a true one, even in an approximate sense. In this paper, a formulation to determine the statistical behavior of in-plane structures due to multiple uncertain material parameters, i.e., elastic modulus and Poisson's ratio, is suggested. To this end, the polynomial expansion on the coefficients of constitutive matrix is employed. In constructing the modified auto-and cross-correlation functions, use is made of the general equation for n-th moment. For the computational purpose, the infinite series of stochastic sub-stiffness matrices is truncated preserving required accuracy. To demons4rate the validity of the proposed formulation, an exemplary example is analyzed and the results are compared with those obtained by means of classical Monte Carlo simulation, which is based on the local averaging scheme.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.22 no.4
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• pp.307-314
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• 2009

The present paper briefly describes the space frame element and the fundamental strategies in computational elastic bifurcation theory of geometrically nonlinear, single load parameter conservative elastic spatial structures. A method for large deformation(rotation) analysis of space frame is based on an eulerian formulation, which takes into consideration the effects of large joint translations and rotations with finite deformation(rotation). The local member force-deformation relationships are based on the beam-column approach, and the change in member chord lengths caused by axial strain and flexural bowing are taken into account. and the derived geometric stiffness matrix is unsymmetric because of the fact that finite rotations are not commutative under addition. To detect the singular point such as bifurcation point, an iterative pin-pointing algorithm is proposed. And the path switching mode for bifurcation path is based on the non-negative eigen-value and it's corresponding eigen-vector. Some numerical examples for bifurcation analysis are carried out for a plane frame, plane circular arch and space dome structures are described.