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Kim, Moonhong,Im, Seyoung Elsevier 2017 Computer methods in applied mechanics and engineer Vol.325 No.-
<P><B>Abstract</B></P> <P>An equivalent continuum model for multilayer graphene sheets (MLGSs) and its plate model are developed to analyze the deformation behavior of MLGSs. Hyperelastic material models are introduced for the MLGS continuum model by examining the atomistic structures of MLGSs and obtaining their mechanical properties by means of molecular statics simulations. The MLGS plate model, a structural model for MLGSs, is developed by applying kinematics assumptions to the MLGS continuum model subjected to infinitesimal deformation. Finite element methods (FEM) with the corotational formulation are adopted to analyze the mechanical behavior of MLGSs under small-strain deformation and large rotation conditions. The MLGS plate element passes several basic numerical tests, including patch tests, eigenvalue analyses, and geometrically nonlinear benchmark problems. Finally, the deflections of a plane-strain cantilever and spherical indentations are analyzed by the proposed MLGS plate element and molecular dynamics (MD) simulations. These results show that the MLGS plate element properly represents the deformation behaviors of MLGSs from the atomic scale to the macroscopic continuum scale.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We present a plate finite element able to analyze deformation of MLGSs. </LI> <LI> Interlayer slip and layer deformation are described by kinematics assumptions. </LI> <LI> Corotational formulation is employed for small-strain deformations & large rotations. </LI> <LI> The element is verified as a structural element and a continuum description of MLGSs. </LI> </UL> </P>
신강원,최윤석,김미연,이문홍 경성대학교 공학기술연구소 2010 공학기술연구지 Vol.16 No.-
Since the pedestrian walkway capacity (106 person/min/m) in the 2005 Korean Highway Capacity Manual (KHCM) was obtained by investigating the commuting pedestrian flow in the Seoul metropolitan area, it is ambiguous whether or not the current pedestrian walkway capacity in KHCM can be used to examine the pedestrian characteristics in other regions. Thus, this study investigates the spatial transferability of the current pedestrian walkway capacity by analyzing the pedestrian characteristics at Kyungsung university and Pukyung university subway station in the city of Busan. To analyze the pedestrian walkway capacity, a linear regression model representing the relationship between pedestrian walking speed and density is estimated using the pedestrian speed-density data observed at the study site. The pedestrian flow-density and speed-flow functions are also developed, and the pedestrian walkway capacity is estimated by using the well-known relationships between the pedestrian flow parameters. Consistent with past studies, the results show that the relationship between speed and density can be explained by a linear regression model, and the pedestrian walking speed increases as pedestrian space (m²/person) increases. However, the pedestrian walking speed-density function estimated in this study is slightly different from that in the current version of the KHCM since this study analyzes the fast moving pedestrians (e.g, students). Thus, this study shows that the future version of the KHCM needs to include more elaborate methodologies for taking into account various pedestrian types and trip purposes.
CFD-DEM 연동을 통한 함정용 채프운의 시공간 분포 해석
정욱진,김문홍,손동우,Uk Jin Jung,Moonhong Kim,Dongwoo Sohn 한국전산구조공학회 2023 전산구조공학 Vol.36 No.2
Warships widely spread numerous chaffs using a blast, which form chaff clouds that create false radar cross-sections to deceive enemy radars. In this study, we established a numerical framework based on a one-way coupling of computational fluid dynamics and discrete element method to simulate the spatiotemporal distribution of chaff clouds for warships in the air. Using the framework, we investigated the effects of wind, initial chaff cartridge angle, and blast pressure on the distribution of chaff clouds. We observed three phases for the chaff cloud diffusion: radial diffusion by the explosion, omnidirectional diffusion by turbulence and collision, and gravity-induced diffusion by the difference in the fall speed. The wind moved the average position of the chaff clouds, and the diffusion due to drag force did not occur. The direction of radial diffusion by the explosion depended on the initial angle of the cartridge, and a more vertical angle led to a wider distribution of the chaffs. As the blast pressure increased, the chaff clouds spread out more widely, but the distribution difference in the direction of gravity was not significant.