Seungil Kim

Development of Structural Composite Hybrid Systems and their Application with regard to the Reduction of CO2 Emissions

This paper discusses the development of a new structural composite hybrid system that is able to replace a conventional residential structural system in which space is partitioned using concrete walls. The new structural system consists of structural tees and wide flange steel beams, with the bottom flange and/or portion of the web partially encased in pre-cast concrete, which is then mechanically anchored by headed stud shear connectors both to the bottom flange and the web of the structural tees. In composite frame built apartments, materials known to be heavy carbon dioxide (CO2) emitters can then be either excluded or reduced with consequent reduction in CO2 emissions. This study has investigated 36 selected multi-residential apartment buildings of linear shape to compare the CO2 emissions of the new composite hybrid and conventional multi-residential apartments. The CO2 emissions resulting from the composite hybrid apartments were reduced to approximately 75—80% in comparison to the emissions occurring from the construction of conventional load-bearing wall apartments. This was achieved by reducing the main sources responsible for CO2 emission.

A Feasibility Study of Green Frame(GF) for the Implementation of Low-carbon Emissions & Long-life Housing

The bearing wall apartments which occupy the majority of multi-residential apartment buildings built in Korea, are known for having limited architectural plan flexibility, posing challenges in terms of maintenance and remodeling. The economic losses and environmental issues resulting from the reconstruction of bearing wall apartments are now accumulating to the extent that they are becoming a national concern. Multi-residential apartment buildings, which are now the dominant form of residence in Korea, must accommodate diverse customer needs and changes in life style. A new concept of Rahmen structure with architectural flexibility is Green Frame. GF multi-residence housing is expected to reduce construction costs and shorten the construction schedule by overcoming the shortcomings of conventional bearing wall apartments. This goal is consistent with the national policies that target the reduction of resource and energy consumption. In addition, GF will be established as a core contributor to achieving a reduction in emissions, which will enable the sustainable growth of domestic construction industry, and address the low-carbon green growth drive implemented by the government.

Optimized Schwarz Method with Complete Radiation Transmission Conditions for the Helmholtz Equation in Waveguides

In this paper, we present a nonoverlapping optimized Schwarz algorithm with a high-order transmission condition for the Helmholtz equation posed in waveguides. We introduce the new high-order transmission conditions based on the complete radiation boundary conditions (CRBCs) that have been developed for high-order absorbing boundary conditions. We obtain the convergence rate of the algorithm in terms of reflection coefficients of CRBCs, which decrease exponentially with the order of CRBCs. It will be shown that damping parameters involved in the transmission conditions can be selected in an optimal way for enhancing the convergence of the Schwarz algorithm. Also, this algorithm can be employed efficiently for a preconditioner in GMRES implementations based on the substructured form as in [M. J. Gander, F. Magoules, and F. Nataf, SIAM J. Sci. Comput., 24 (2002), pp. 38--60]. Finally, numerical examples confirming the theory will be presented.

Optimized double sweep Schwarz method by complete radiation boundary conditions

We present an optimized double sweep nonoverlapping Schwarz method for solving the Helmholtz equation in semi-infinite waveguides. The domain is decomposed into nonoverlapped layered subdomains along the axis of the waveguide and local wave propagation problems equipped with complete radiation conditions for high-order absorbing boundary conditions are solved forward and backward sequentially. For communication between subdomains, Neumann data of local solutions in one domain are transferred to the neighboring subdomain in the forward direction and Dirichlet data are exploited in the backward direction. The complete radiation boundary conditions enable us to not only minimize reflection coefficients for most important modes in an optimal way but also find Neumann data without introducing errors that would be produced if finite difference formulas were used for computing Neumann data. The convergence of the double sweep Schwarz method is proved and numerical experiments using it as a preconditioner are presented to confirm the convergence theory.

Convergence of the supercell method for computation of defect modes in one-dimensional photonic crystals

Abstract In this paper, we analyze the spectrum induced by the supercell method for studying locally defected one-dimensional photonic crystals. By using the propagation matrix method, we show that the continuous spectrum of the periodic structure of the supercell converges to that of the defected photonic crystal. Also, it can be shown that frequencies of localized defected modes in the bandgap are included in a narrow interval (whose length diminishes exponentially with increasing size of the supercell) of the continuous spectrum of the supercell method.

Analysis of an approximate cloaking for acoustic scattering problems in R 3

Abstract In this paper, we consider the acoustic cloaking based on singular transformations and its approximation in the context of scattering problems in R 3 . The cloaking based on singular transformations can not avoid a singularity of the resulting Laplace–Beltrami operator because singular transformations blow up one point to a sphere. In order to treat the singularity properly, we use the variational method proposed in Greenleaf et al. (2007) [1] and prove the possibility of the perfect cloaking. To design an approximation scheme that avoids the singularity of the perfect cloaking, we regularize the singular transformation and show that transmitted fields into the cloaked region in H 1 -norm and scattered fields on any compact set outside of the cloaked region in L ∞ -norm converge to zero as a regularization (approximation) parameter approaches zero provided that wave number is not a Neumann eigenvalue of the Helmholtz equation in the cloaked region.