• Structural Engineering and Mechanics
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• 제12권3호
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• pp.297-312
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• 2001

The accurate finite element (FE) simulation of reinforced concrete (RC) slabs, having different boundary conditions and subjected to uniformly distributed loading, has led to the use of the developed FE models for generating results of ultimate loads from predictions of 'computer-model' RC slabs having different material and geometric properties. Equations derived from these results constitute the primary database of an intelligent computer-aided-design (CAD) system developed for accurate and fast information retrieval on arbitrary slabs. The system is capable of generating a secondary database through systems of interpolation and can be used for design assistance purposes.

• 소성∙가공
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• 제19권2호
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• pp.127-131
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• 2010

Carbon-epoxy prepreg has been introduced in the forming of the upper and lower swash plates that control the pitch of rotor blade of unmanned helicopter because of its lightweight. Taguchi experimental method has been used by introducing the variables such as arrangement angle, laminated number and forming temperature, in order to obtain the proper forming method by using prepreg satisfying the required strength of the swash plate. In the evaluation of structural safety for the swash plates, three kinds of models are considered by using FE-analysis. In comparison of the hot forged products with Al6061-T6 and the formed products with prepreg, it was found that ultimate tensile strength of the products with prepreg is three times higher than that of the Al6061-T6, and the weight reduction of 68.5g can be achieved by using prepreg swash plates.

• Structural Engineering and Mechanics
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• 제69권1호
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• pp.105-120
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• 2019

In this paper, a new efficient method for structural modal reanalysis is proposed, which can handle large finite element (FE) models requiring frequent design modifications. The global FE model is divided into a residual part not to be modified and a target part to be modified. Then, an automated matrix permutation and substructuring algorithm is applied to these parts independently. The reduced model for the residual part is calculated and saved in the initial analysis, and the target part is reduced repeatedly, whenever design modifications occur. Then, the reduced model for the target part is assembled with that of the residual part already saved; thus, the final reduced model corresponding to the new design is obtained easily and rapidly. Here, the formulation of the proposed method is derived in detail, and its computational efficiency and reanalysis ability are demonstrated through several engineering problems, including a topological modification.

• 천문학회보
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• 제44권1호
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• pp.68.3-68.3
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• 2019

Even though the initial mass function (IMF) of the first generation of stars played important roles in reionization of the universe, subsequent star formation, and chemical enrichment of the universe, it is still very uncertain. In this study, among the several indirect ways of estimating the IMF of the population III (Pop III) stars, we make use of extremely metal-poor (EMP; [Fe/H] < -3.0) stars in the Milky Way, in order to infer the characteristic mass range of Pop III stars. As the progenitors of many of the EMP stars are known to be Pop III stars, we attempt to construct the characteristic mass range of the progenitors (e.g., Pop III stars) of the EMP stares by comparing their observed abundance pattern of various chemical elements with chemical yields from supernova models.

• Bulletin of the Korean Chemical Society
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• 제7권5호
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• pp.341-346
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• 1986

The electrical conductivity of the system ${\alpha}-Fe_2O_3-CoO$ was measured in the temperature range 200-1000$^{\circ}C$ and PO$_{2}$ range 10$^{-7}-2{\times}10^{-1}$ atm. Possible defect models were suggested on the basis of conductivity data, which were measured as a function of temperature and of oxygen partial pressure. The observed activation energies were 0.50 eV and 1.01 eV in the low- and high-temperature regions, respectively. The observed conductivity dependences on PO$_{2}$ were ${\sigma}\;{\alpha}\;PO_2^{-1/6}$ in the PO$_{2}$ range $10^{-7}-10^{-4}$ atm and ${\sigma}\;{\alpha}\;PO_2^{-1/4}$ at PO$_{2}$ 's of $10^{-4}-2{\times}10^{-1}$ atm at temperatures from 300-1000$^{\circ}C$. An extrinsic electron conduction due to an Vo defect and an intrinsic electron conduction due to an Fei' defect were suggested at different temperature and oxygen partial pressure regions, respectively.

• Structural Engineering and Mechanics
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• 제77권4호
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• pp.523-533
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• 2021

The present study investigates the lateral torsional buckling behaviour of pultruded glass fiber reinforced polymer (GFRP) simply supported channel beams subjected to uniform bending about their major axis. A parametric study by varying the sectional geometry and span of channel beams is carried out by using ABAQUS software. The accuracy of the FE models was ensured by verifying them against the available results provided in the literature. The effect of geometric nonlinearity, geometric imperfections, and the dependency of finite element mesh on the lateral torsional buckling were carefully considered in the FE model. Lateral torsional buckling (LTB) strengths obtained from the numerical study were compared with the theoretical LTB strengths obtained based on the Eurocode 3 approach for steel sections. The comparison between the numerical strengths and the design procedure proposed in the literature based on Eurocode 3 approach revealed disagreements. Therefore, a simplified improved design procedure is proposed for the safe design strength prediction of pultruded GFRP channel beams. The proposed equation has been provided that might aid the structural engineers in economically designing the pultruded GFRP channel beams in the future.

• Nuclear Engineering and Technology
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• 제54권2호
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• pp.732-740
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• 2022

A piping system stress analysis need to be re-performed for structural integrity assessment after reinforcement of a pipe with significant wall thinning. For efficient stress analysis, a one-dimensional beam element for the wall-thinned pipe with reinforcement needs to be developed. To develop the beam element, this work presents analytical equations for elastic stiffness of the wall-thinned pipe with reinforcement are analytically derived for axial tension, bending and torsion. Comparison with finite element (FE) analysis results using detailed three-dimensional solid models for wall-thinned pipe with reinforcement shows good agreement. Implementation of the proposed solutions into commercial FE programs is explained.

• Steel and Composite Structures
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• 제42권3호
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• pp.363-373
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• 2022

This paper presents an experimental and a numerical investigation of a H-beam - composite box column joint fabricated with two new inner diaphragms and a continuous inner diaphragm. The main objective of the current research project is to investigate the structural performance of the newly developed inner diaphragms under a cyclic loading protocol. Hysteretic behaviour of the composite joints is analysed to investigate the structural performance of the new and continuous inner diaphragms. This paper compares the result of the finite element (FE) models with the new and continuous inner diaphragms against their counterpart experimental results. To produce a design criterion for the newly developed inner diaphragms, yielding or failure area of the inner diaphragms under tensile stress is analysed from the FE results.

• Ocean Systems Engineering
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• 제12권1호
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• pp.1-22
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• 2022

The majority of tubular joints commonly found in offshore jacket structures are multi-planar. Investigating the effect of loaded out-of-plane braces on the values of the stress concentration factor (SCF) in offshore tubular joints has been the objective of numerous research works. However, due to the diversity of joint types and loading conditions, a number of quite important cases still exist that have not been studied thoroughly. Among them are internally ring-stiffened two-planar TT-joints subjected to axial loading. In the present research, data extracted from the stress analysis of 243 finite element (FE) models, verified against available numerical and experimental data, was used to study the effects of geometrical parameters on the chord-side SCFs in two-planar tubular TT-joints reinforced with internal ring stiffeners subjected to two types of axial loading. Parametric FE study was followed by a set of nonlinear regression analyses to develop six new SCF parametric equations for the fatigue analysis and design of axially-loaded two-planar TT-joints reinforced with internal ring stiffeners.

• Ocean Systems Engineering
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• 제13권2호
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• pp.97-121
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• 2023

Through-the-thickness stress distribution in a tubular member has a profound effect on the fatigue behavior of tubular joints commonly found in steel offshore structures. This stress distribution can be characterized by the degree of bending (DoB). Although multi-planar joints are an intrinsic feature of offshore tubular structures and the multi-planarity usually has a considerable effect on the DoB values at the brace-to-chord intersection, few investigations have been reported on the DoB in multi-planar joints due to the complexity of the problem and high cost involved. In the present research, data extracted from the stress analysis of 243 finite element (FE) models, verified based on available parametric equations, was used to study the effects of geometrical parameters on the DoB values in two-planar tubular DYT-joints. Parametric FE study was followed by a set of nonlinear regression analyses to develop six new DoB parametric equations for the fatigue analysis and design of axially loaded two-planar DYT-joints.