• Journal of Radiation Industry
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• v.17 no.2
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• pp.143-150
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• 2023

A graded approach applies safety requirements differentially, depending on the risk potential. An advantage of applying a graded approach is that safety assessments can be conducted repeatedly by focusing on areas with relatively higher risk than on those with low risk when decommissioning a nuclear power plant (NPP). The International Atomic Energy Agency (IAEA) recommends applying a graded approach to decommissioning NPPs worldwide. In Korea, the definition of the graded approach requires to be clarified. This study compared the decommissioning method used in Korean NPPs with the IAEA graded approach and examined whether the graded approach can be applied to decommissioning NPPs in Korea. As a result of the comparison, the preliminary decommissioning plan for Shin-Kori Units 5 and 6 showed that the decommissioning method for Korean NPPs is similar to the five-step IAEA graded approach.

• Structural Engineering and Mechanics
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• v.59 no.1
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• pp.101-122
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• 2016

Elasticity solutions for bi-directional functionally graded beams subjected to arbitrary lateral loads are conducted, with emphasis on the end effects. The material is considered macroscopically isotropic, with Young's modulus varying exponentially in both axial and thickness directions, while Poisson's ratio remaining constant. In order to obtain an exact analysis of stress and displacement fields, the symplectic analysis based on Hamiltonian state space approach is employed. The capability of the symplectic framework for exact analysis of bi-directional functionally graded beams has been validated by comparing numerical results with corresponding ones in open literature. Numerical results are provided to demonstrate the influences of the material gradations on localized stress distributions. Thus, the material properties of the bi-directional functionally graded beam can be tailored for the potential practical purpose by choosing suitable graded indices.

• Journal of Radiation Industry
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• v.18 no.3
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• pp.195-207
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• 2024

International organizations such as IAEA and EC recommend graded approach by identifying NORM industries requiring radiation protection. In Korea, single regulation rather than graded regulation for NORM industry is applied. Therefore, it consumes more manpower and costs than necessary for both regulators and workers, and is not optimized. The purpose of this study is to analyze domestic and foreign NORM industry regulatory standards and radiological characteristics for graded approach of NORM industry in Korea. Safety reports and publications such as SRS 49 and ICRP 142 published by international organizations were investigated, and domestic and foreign NORM regulatory guidelines and legislation such as Health Canada and the Act on Protective Action Guidelines Against Radiation in the Natural Environment were investigated to indicate NORM industries and regulatory standards. The radioactivity concentration of raw materials or by-products, radiation dose by industrial process of the NORM industry identified in IAEA and Korea were investigated. Nine NORM industries in Korea were identified based on the NORM industry from IAEA and KINS survey report. Foreign countries such as Canada, UK and Denmark were executing graded approach such as classification of dose level or licensing, registration, notification based on safety assessment. Radioactivity concentration of domestic and foreign NORM industries were widespread up to 200 Bq g^-1 or higher based on industrial process and work type, and numerous NORM industries that exceeded radiation dose of 1 mSv y^-1 were indicated. Therefore, it is necessary to consider handling materials and work types of identified NORM industry when establishing graded approach for NORM industry in Korea considering domestic situation. The results of this study are expected to be used as basic data for developing methodology of graded approach for NORM industry in Korea.

• Structural Engineering and Mechanics
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• v.53 no.3
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• pp.575-587
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• 2015

This paper focuses on vibration analysis of functionally graded cylindrical shell submerged in an incompressible fluid. The equation is established considering axial and lateral hydrostatic pressure based on first order shear deformation theory of shell motion using the wave propagation approach and classic Fl$\ddot{u}$gge shell equations. To study accuracy of the present analysis, a comparison carried out with a known data and the finite element package ABAQUS. With this method the effects of shell parameters, m, n, h/R, L/R, different boundary conditions and different power-law exponent of material of functionally graded cylindrical shells, on the frequencies are investigated. The results obtained from the present approach show good agreement with published results.

• Steel and Composite Structures
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• v.33 no.2
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• pp.163-180
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• 2019

A semi analytical method is employed to analyze free vibration characteristics of uniform and stepped functionally graded circular cylindrical shells under complex boundary conditions. The analytical model is established based on multi-segment partitioning strategy and first-order shear deformation theory. The displacement functions are handled by unified Jacobi polynomials and Fourier series. In order to obtain continuous conditions and satisfy complex boundary conditions, the penalty method about spring technique is adopted. The solutions about free vibration behavior of functionally graded circular cylindrical shells were obtained by approach of Rayleigh-Ritz. To confirm the dependability and validity of present approach, numerical verifications and convergence studies are conducted on functionally graded cylindrical shells under various influencing factors such as boundaries, spring parameters et al. The present method apparently has rapid convergence ability and excellent stability, and the results of the paper are closely agreed with those obtained by FEM and published literatures.

• Steel and Composite Structures
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• v.47 no.5
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• pp.569-585
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• 2023

This paper proposes an efficient approach for the structural topology optimization of bi-directional functionally graded structures by incorporating popular radial basis functions (RBFs) into an implicit level set (ILS) method. Compared to traditional element density-based methods, a level set (LS) description of material boundaries produces a smoother boundary description of the design. The paper develops RBF implicit modeling with multiquadric (MQ) splines, thin-plate spline (TPS), exponential spline (ES), and Gaussians (GS) to define the ILS function with high accuracy and smoothness. The optimization problem is formulated by considering RBF-based nodal densities as design variables and minimizing the compliance objective function. A LS-RBF optimization method is proposed to transform a Hamilton-Jacobi partial differential equation (PDE) into a system of coupled non-linear ordinary differential equations (ODEs) over the entire design domain using a collocation formulation of the method of lines design variables. The paper presents detailed mathematical expressions for BiDFG beams topology optimization with two different material models: continuum functionally graded (CFG) and mechanical functionally graded (MFG). Several numerical examples are presented to verify the method's efficiency, reliability, and success in accuracy, convergence speed, and insensitivity to initial designs in the topology optimization of two-dimensional (2D) structures. Overall, the paper presents a novel and efficient approach to topology optimization that can handle bi-directional functionally graded structures with complex geometries.

• Structural Engineering and Mechanics
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• v.64 no.4
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• pp.487-494
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• 2017

The present paper deals with a theoretical study of delamination fracture in the Crack Lap Shear (CLS) functionally graded beam configuration. The basic purpose is to analyze the fracture with taking into account the material non-linearity. The mechanical behavior of CLS was described by using a non-linear stress-strain relation. It was assumed that the material is functionally graded along the beam height. The fracture was analyzed by applying the J-integral approach. The curvature and neutral axis coordinate of CLS beam were derived in order to solve analytically the J-integral. The non-linear solution of J-integral obtained was verified by analyzing the strain energy release rate with considering material non-linearity. The effects of material gradient, crack location along the beam height and material non-linearity on fracture behavior were evaluated. The J-integral non-linear solution derived is very suitable for parametric studies of longitudinal fracture in the CLS beam. The results obtained can be used to optimize the functionally graded beam structure with respect to the fracture performance. The analytical approach developed in the present paper contributes for the understanding of delamination fracture in functionally graded beams exhibiting material non-linearity.

• Advances in materials Research
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• v.5 no.4
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• pp.299-318
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• 2016

Analytical investigations were performed of a longitudinal crack representing a cylindrical surface in circular shafts loaded in torsion with taking into account the non-linear material behavior. Both functionally graded and multilayered shafts were analyzed. It was assumed that the material is functionally graded in radial direction. The mechanical behavior of shafts was modeled by using non-linear constitutive relations between the shear stresses and shear strains. The fracture was studied in terms of the strain energy release rate. Within the framework of small strain approach, the strain energy release rate was derived in a function of the torsion moments in the cross-sections ahead and behind the crack front. The analytical approach developed was applied to study the fracture in a clamped circular shaft. In order to verify the solution derived, the strain energy release rate was determined also by considering the shaft complimentary strain energy. The effects were evaluated of material properties, crack location and material non-linearity on the fracture behavior. The results obtained can be applied for optimization of the shafts structure with respect to the fracture performance. It was shown that the approach developed in the present paper is very useful for studying the longitudinal fracture in circular shafts in torsion with considering the material non-linearity.

• Structural Engineering and Mechanics
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• v.90 no.1
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• pp.1-18
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• 2024

The present study conducts a thorough analysis of thermal vibrations in functionally graded porous nanocomposite beams within a thermal setting. Investigating the temperature-dependent material properties of these beams, which continuously vary across their thickness in accordance with a power-law function, a finite element approach is developed. This approach utilizes a nonlocal strain gradient theory and accounts for a linear temperature rise. The analysis employs four different patterns of porosity distribution to characterize the functionally graded porous materials. A novel two-variable shear deformation beam nonlocal strain gradient theory, based on trigonometric functions, is introduced to examine the combined effects of nonlocal stress and strain gradient on these beams. The derived governing equations are solved through a 3-nodes beam element. A comprehensive parametric study delves into the influence of structural parameters, such as thicknessratio, beam length, nonlocal scale parameter, and strain gradient parameter. Furthermore, the study explores the impact of thermal effects, porosity distribution forms, and material distribution profiles on the free vibration of temperature-dependent FG nanobeams. The results reveal the substantial influence of these effects on the vibration behavior of functionally graded nanobeams under thermal conditions. This research presents a finite element approach to examine the thermo-mechanical behavior of nonlocal temperature-dependent FG nanobeams, filling the gap where analytical results are unavailable.

• Structural Engineering and Mechanics
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• v.63 no.5
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• pp.585-595
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• 2017

This study aimed to presents a simple analytical approach to investigate the thermal buckling behavior of thick functionally graded sandwich by employing both the sinusoidal shear deformation theory and stress function. The material properties of the sandwich plate faces are continuously varied within the plate thickness according to a simple power-law distribution in terms of the volume fractions of the constituents. The core layer is still homogeneous and made of an isotropic material. The thermal loads are considered as uniform, linear and non-linear temperature rises across the thickness direction. Numerical examples are presented to prove the effect of power law index, loading type and functionally graded layers thickness on the thermal buckling response of thick functionally graded sandwich.