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Effect of neutron irradiation on response of reinforced concrete members for nuclear power plants
Park, Kyoungsoo,Kim, Hyung-Tae,Kwon, Tae-Hyun,Choi, Eunsoo Elsevier 2016 Nuclear engineering and design Vol.310 No.-
<P><B>Abstract</B></P> <P>In this study, the effects of long-term irradiation on the behaviors of reinforced concrete (RC) members were investigated to obtain a better understanding of the behaviors of RC structures under an irradiation environment, which include the biological shield walls and reactor vessel support structures of nuclear power plants (NPPs). The behaviors of three RC members were examined (a beam, beam-column section, and column under cyclic loading) by considering the changes in the constituent material properties due to neutron irradiation. The load capacity generally increases for a tension failure member with an increase in neutron irradiation because neutron irradiation increases the yield stress of reinforcing steel. However, the load capacity of a compression failure member decreases with a decrease in the compressive strength of concrete when the fluence of neutron radiation increases. Additionally, RC member analysis results demonstrate that the energy dissipation capacity, which is a critical factor in seismic design, decreases significantly when the fluence of neutron radiation is greater than 1.0×10<SUP>17</SUP> n/cm<SUP>2</SUP>. Therefore, the level of neutron irradiation could be critical for RC structures over the long-term operation of NPPs, and thus the effects of neutron irradiation on RC structures should be considered as age-related damage.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Effects of long-term irradiation on reinforced concrete (RC) structures were investigated. </LI> <LI> Responses of irradiated RC members were numerically investigated in terms of ductility. </LI> <LI> Results demonstrated that energy dissipation capacity decreased under radiation environment. </LI> <LI> Level of neutron radiation could be critical for RC structures during operation. </LI> </UL> </P>
Park, Kyoungsoo,Chung, Chul-Woo,Lee, Chang Joon,Kwon, Tae-Hyun Elsevier 2019 Cement and concrete research Vol.123 No.-
<P><B>Abstract</B></P> <P>Nano-structural changes of cement paste due to neutron and gamma irradiation are investigated by using small-angle neutron scattering (SANS). Disk specimens were prepared with the w/c ratios of 0.4 and 0.5, and they were exposed to the neutron fluence of 2.57 × 10<SUP>14</SUP> n/cm<SUP>2</SUP> and the gamma radiation does dosage of 38.4 Gy. Based on SANS data and a microstructural model of C-S-H gel, one observed that the size of C-S-H globules increased after irradiation. The change of C-S-H globule size may be associated with the change of surface morphology and chemical bonding of C-S-H, and thus further research on the irradiation effects on cement paste is necessary.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We propose an investigation of irradiation effects on the nano-structural changes of C-S-H gel for the first time. </LI> <LI> Nano-structural changes of cement paste due to neutron and gamma irradiation are investigated by SANS. </LI> <LI> Based on SANS data, one observed that the size of C-S-H globules increased after irradiation. </LI> <LI> Additionally, irradiation may cause breakage of the chemical bonding, which results in complexity on surface morphology. </LI> </UL> </P>
Assessment of cohesive traction-separation relationships in ABAQUS: A comparative study
Park, Kyoungsoo,Choi, Habeun,Paulino, Glaucio H. Elsevier 2016 Mechanics research communications Vol.78 No.2
<P><B>Abstract</B></P> <P>The definition of a traction-separation relationship is essential in cohesive zone models because it describes the nonlinear fracture process zone. A few models are investigated in this paper and a comparative study is conducted. Among various traction-separation relationships, the one in Abaqus is assessed by evaluating the cohesive traction and its tangent stiffness according to a given separation path. The results demonstrate that the traction-separation relationship in Abaqus can lead to non-physical responses because of a pathological positive tangent stiffness under softening condition. This is reflected in cohesive tractions that increase and decrease repeatedly while the cohesive separation monotonically increases. Thus, together with supporting information, this paper conveys the message that a traction-separation relationship should be developed and selected with great caution, especially under mixed-mode conditions.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The traction-separation relationship of Abaqus can lead to non-physical responses. </LI> <LI> Negative tangent stiffness within the softening region is not guaranteed in the Abaqus model. </LI> <LI> The consistency of the traction-separation relationships is addressed. </LI> </UL> </P>
On nonconvex meshes for elastodynamics using virtual element methods with explicit time integration
Park, Kyoungsoo,Chi, Heng,Paulino, Glaucio H. North-Holland Pub. Co 2019 Computer methods in applied mechanics and engineer Vol.356 No.-
<P><B>Abstract</B></P> <P>While the literature on numerical methods (e.g. finite elements and, to a certain extent, virtual elements) concentrates on convex elements, there is a need to probe beyond this limiting constraint so that the field can be further explored and developed. Thus, in this paper, we employ the virtual element method for non-convex discretizations of elastodynamic problems in 2D and 3D using an explicit time integration scheme. In the formulation, a diagonal matrix-based stabilization scheme is proposed to improve performance and accuracy. To address efficiency, a critical time step is approximated and verified using the maximum eigenvalue of the local (rather than global) system. The computational results demonstrate that the virtual element method is able to consistently handle general nonconvex elements and even non-simply connected elements, which can lead to convenient modeling of arbitrarily-shaped inclusions in composites.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Exploring arbitrarily-shaped polygons/polyhedra in computational mechanics. </LI> <LI> The VEM is established for elastodynamics with explicit time integration. </LI> <LI> Novel diagonal matrix-based stabilization scheme improves VEM performance (and accuracy). </LI> <LI> The critical time step is evaluated using the maximum eigenvalue of a system of equations. </LI> </UL> </P>
편광상이 고리 기반 2차 광섬유 유연 빗살 필터의 투과 스펙트럼 특성 분석
박경수(Kyoungsoo Park),이용욱(Yong Wook Lee) 한국조명·전기설비학회 2015 조명·전기설비학회논문지 Vol.29 No.12
In this paper, we propose a second-order fiber flexible comb filter based on a polarization-diversity loop(PDL). The proposed filter consists of a polarization beam splitter, four half-wave plates(HWPs), and three high birefringence fiber(HBF) segments. In the previous Solc-type second-order filter based on the PDL, HBF segments were fusion-spliced with a fixed angle offset between their principal axes with each other. But, the proposed filter implemented by inserting two HWPs between three HBF segments has a great flexibility in adjusting relative angular difference between the principal axes of two adjacent HBF segments. Owing to this flexibility, second-order transmission spectra, which had a channel spacing of ~0.8nm, could be interleaved by controlling the orientation angles of four HWPs. The output transmission spectra of the proposed filter were theoretically analyzed and experimentally verified.