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REFERENCE LINKING PLATFORM OF KOREA S&T JOURNALS
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Journal of the Computational Structural Engineering Institute of Korea
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Journal DOI :
The Computational Structural Engineering Institute
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Volume & Issues
Volume 27, Issue 6 - Dec 2014
Volume 27, Issue 5 - Oct 2014
Volume 27, Issue 4 - Aug 2014
Volume 27, Issue 3 - Jun 2014
Volume 27, Issue 2 - Apr 2014
Volume 27, Issue 1 - Feb 2014
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Design Sensitivity Analysis of Coupled MD-Continuum Systems Using Bridging Scale Approach
Cha, Song-Hyun ; Ha, Seung-Hyun ; Cho, Seonho ;
Journal of the Computational Structural Engineering Institute of Korea, volume 27, issue 3, 2014, Pages 137~145
DOI : 10.7734/COSEIK.2014.27.3.137
We present a design sensitivity analysis(DSA) method for multiscale problems based on bridging scale decomposition. In this paper, we utilize a bridging scale method for the coupled system analysis. Since the analysis of full MD systems requires huge amount of computational costs, a coupled system of MD-level and continuum-level simulation is usually preferred. The information exchange between the MD and continuum levels is taken place at the MD-continuum boundary. In the bridging scale method, a generalized Langevin equation(GLE) is introduced for the reduced MD system and the GLE force using a time history kernel is applied at the boundary atoms in the MD system. Therefore, we can separately analyze the MD and continuum level simulations, which can accelerate the computing process. Once the simulation of coupled problems is successful, the need for the DSA is naturally arising for the optimization of macro-scale design, where the macro scale performance of the system is maximized considering the micro scale effects. The finite difference sensitivity is impractical for the gradient based optimization of large scale problems due to the restriction of computing costs but the analytical sensitivity for the coupled system is always accurate. In this study, we derive the analytical design sensitivity to verify the accuracy and applicability to the design optimization of the coupled system.
An Criterion to Minimize FE Mesh-Dependency in Concrete Plate under Impact Loading
Kwak, Hyo-Gyoung ; Gang, Han-Gul ; Park, Lee-Ju ;
Journal of the Computational Structural Engineering Institute of Korea, volume 27, issue 3, 2014, Pages 147~154
DOI : 10.7734/COSEIK.2014.27.3.147
In the context of an increasing need for safety in concrete structures under blast and impact loading condition, the behavior of concrete under high strain rate condition has been an important issue. Since concrete subjected to impact loading associated with high strain rate shows quite different material behavior from that in the static state, several material models are proposed and used to describe the high strain rate behavior under blast and impact loading. In the process of modelling high strain rate conditions with these material models, mesh dependency in the used finite element(FE) is the key problem because simulation results under high strain-rate condition are quite sensitive to applied FE mesh size. This paper introduces an criterion which can minimize the mesh-dependency of simulation results on the basis of the fracture energy concept, and HJC(Holmquist Johnson Cook) model is examined to trace sensitivity to the used FE mesh size. To coincide with the purpose of the perforation simulation with a concrete plate under a projectile(bullet), the residual velocities of projectile after perforation are compared. The analytical results show that the variation of residual velocity with the used FE mesh size is quite reduced and accuracy of simulation results are improved by applying a unique failure strain value determined according to the proposed criterion.
Isogeometric Shape Design Optimization of Power Flow Problems at High Frequencies
Yoon, Minho ; Ha, Seung-Hyun ; Cho, Seonho ;
Journal of the Computational Structural Engineering Institute of Korea, volume 27, issue 3, 2014, Pages 155~162
DOI : 10.7734/COSEIK.2014.27.3.155
Using an isogeometric approach, a continuum-based shape design optimization method is developed for steady state power flow problems at high frequencies. In case the isogeometric method is employed to the shape design optimization, the NURBS basis functions used in CAD geometric modeling are directly utilized to embed the exact geometry into the computational framework so that the design parameterization for shape optimization is much easier than that in the finite element method and consequently provides the enhanced smoothness of design perturbations. Thus, exact geometric models can be used in both the response and the shape sensitivity analyses, where normal vector and curvature are continuous over the whole design space so that enhanced shape sensitivity can be expected. Through numerical examples, the developed isogeometric sensitivity is compared with finite difference one to provide excellent agreement. Also, it turns out that the proposed method works very well in the shape optimization problems.
No Collapse Design for Typical Bridges
Kook, Seung-Kyu ;
Journal of the Computational Structural Engineering Institute of Korea, volume 27, issue 3, 2014, Pages 163~172
DOI : 10.7734/COSEIK.2014.27.3.163
The purpose of earthquake resistant design for typical bridges is the No Collapse Design and the Earthquake Resistant Design Part of Roadway Bridge Design Code provides a design process to construct the Ductile Failure Mechanism for the bridge structure. However, if it is not practical to provide the Ductile Failure Mechanism due to structure types or site conditions, the Brittle Failure Mechanism is an alternative way to get the No Collapse Design. As well as the existing design process constructing the Ductile Failure Mechanism, the Earthquake Resistant Design Part provides a ductility-based design process as an appendix, which is prepared for bridges with reinforced concrete piers. According to the new design process, designer determines a required response modification factor for substructure and transverse reinforcement for confinement therefrom. In this study, a typical bridge with steel bearing connections and reinforced concrete piers is selected for which the existing as well as the ductility-based design processes are applied and different results from the two design processes are identified. Based on the results, an earthquake resistant design procedure is proposed in which designers should consider the two design processes.
Second order Temporal Finite Element Methods in Linear Elasticity through the Mixed Convolved Action Principle
Kim, Jinkyu ;
Journal of the Computational Structural Engineering Institute of Korea, volume 27, issue 3, 2014, Pages 173~182
DOI : 10.7734/COSEIK.2014.27.3.173
The mixed convolved action principle provides a new rigorous weak variational formalism for a broad range of initial boundary value problems in mathematical physics and mechanics in terms of mixed formulation, convolution, and fractional calculus. In this paper, its potential in the development of numerical methods for transient problems in various dynamical systems when adopting temporally second order approximation is investigated. For this, the classical single-degree-of-freedom linear elastic dynamical systems are primarily considered to investigate computational characteristics of the developed algorithms. For the undamped system, all the developed algorithms are symplectic with respect to the time step. For the damped system, they are shown to be accurate with good convergence characteristics.
A Study on the Development of Shape Functions of Polyhedral Finite Elements
Kim, Hyun-Gyu ;
Journal of the Computational Structural Engineering Institute of Korea, volume 27, issue 3, 2014, Pages 183~189
DOI : 10.7734/COSEIK.2014.27.3.183
In this paper, a polyhedral element is presented to solve three-dimensional problems by developing shape functions based on Wachspress coordinates and moving least square approximation. A subdivision of polyhedrons into tetrahedral domains is performed for the construction of shape functions of polyhedral elements, and numerical integration of the weak form is carried out consistently over the tetrahedral domains. The weight functions for moving least square approximation are defined by solving Laplace equation with boundary values based on Wachspress coordinates on polyhedral element faces. Polyhedral elements presented in this paper have similar properties to conventional finite element regarding the continuity, the completeness, the node-element connectivity and the inter-element compatibility. Numerical examples show the effectiveness of the present method for solving three-dimensional problems using polyhedral elements.
Structural Integrity Evaluation of Reactor Pressure Vessel Bottom Head without Penetration Nozzles in Core Melting Accident
Lee, Yun Joo ; Kim, Jong Min ; Kim, Hyun Min ; Lee, Dae Hee ; Chung, Chang Kyu ;
Journal of the Computational Structural Engineering Institute of Korea, volume 27, issue 3, 2014, Pages 191~198
DOI : 10.7734/COSEIK.2014.27.3.191
In this paper, structural integrity evaluation of reactor pressure vessel bottom head without penetration nozzles in core melting accident has been performed. Considering the analysis results of thermal load, weight of molten core debris and internal pressure, thermal load is the most significant factor in reactor vessel bottom head. The failure probability was evaluated according to the established failure criteria and the evaluation showed that the equivalent plastic strain results are lower than critical strain failure criteria. Thermal-structural coupled analyses show that the existence of elastic zone with a lower stress than yield strength is in the middle of bottom head thickness. As a result of analysis, the elastic zone became narrow and moved to the internal wall as the internal pressure increases, and it is evaluated that the structural integrity of reactor vessel is maintained under core melting accident.
Evaluation of Response Variability of Functionally Graded Material Beam with Varying Sectional Area due to Spatial Randomness in Elastic Modulus along Axial Direction
Noh, Hyuk Chun ;
Journal of the Computational Structural Engineering Institute of Korea, volume 27, issue 3, 2014, Pages 199~206
DOI : 10.7734/COSEIK.2014.27.3.199
In this paper, a scheme to evaluate the response variability for functionally graded material (FGM) beam with varying sectional area is presented. The randomness is assumed to appear in a spatial domain along the beam axis in the elastic modulus. The functionally graded material categorized as composite materials, however without the drawbacks of delamination and occurrence of cracks due to abrupt change in material properties between layers in the conventional composite materials. The functionally graded material is produced by the gradual solidification through thickness direction, which endows continuous variation of material properties, which makes this material performs in a smooth way. However, due to difficulties in tailoring the gradients, to have uncertainty in material properties is unavoidable. The elastic modulus at the center section is assumed to be random in the spatial domain along the beam axis. Introducing random variables, defined in terms of stochastic integration, the first and second moments of responses are evaluated. The proposed scheme is verified by using the Monte Carlo simulation based on the random samples generated employing the spectral representation scheme. The response variability as a function of correlation distance, the effects of material and geometrical parameters on the response variability are investigated in detail. The efficiency of the proposed scheme is also addressed by comparing the analysis time of the proposed scheme and MCS.