• Korean Journal of Computational Design and Engineering
• /
• v.11 no.3
• /
• pp.157-163
• /
• 2006

Surfaces of many engineering structures, especially, those of ships are commonly made out of either single- or double-curved surfaces to meet functional requirements. The first step in the fabrication process of a three-dimensional design surface is unfolding or flattening the surface, otherwise known as planar development, so that manufacturers can determine the initial flat plate which is required to form the design shape. In this paper, an algorithm for optimal approximated development of a general curved surface, including both single- and double-curved surfaces, is established by minimizing the strain energy of deformation from its planar development to the design surface. The unfolding process is formulated into a constrained nonlinear programming problem, based on the deformation theory and finite element. Constraints are subjected to the characteristics of the fabrication method. And the design surface, or the curved shell plate is subdivided by automatic mesh generation.

• Proceedings of the Korea Concrete Institute Conference
• /
• 2006.05b
• /
• pp.41-44
• /
• 2006

Recently, single shell lining method of construction is studied by economical method of construction to make use of high-performance shotcrete of permanent shotcrete lining concept in the UStA, Europe, Japan etc. High-performance shotcrete use is essential as permanent support that single shell lining method of construction has two functions of lining and support to shotcrete. In this research, optimum accelerator amount was decided after setting time test using alkai-free and cement mineral accelerator. Also replacement ratio of silica fume and fly-ash was determined.

• International Journal of Industrial Entomology and Biomaterials
• /
• v.7 no.2
• /
• pp.191-195
• /
• 2003

The impact of antibiotic (Norfloxacin) administration ,at different concentration (50 ppm and 100 ppm) on commercial characters of bivoltine $({CSR_2}{\times}{CR_4})$ and the cross breed race $({BL_67}{\times}{CSR_101})$ was studied. The result indicated that antibiotic administration with different concentrations significantly improved the rearing and cocoon parameters like larval duration, larval weight, growth index, single cocoon weight, single shell weight and shell ratio. The post cocoon parameters like average filament length, non-breakable filament length, raw silk percentage, raw silk recovery percentage, denier, reelability and neatness were recorded significantly higher in antibiotic treated batches. The better performances of these parameters were recorded with the increase of antibiotic concentration.

• Proceedings of the KSME Conference
• /
• 2003.11a
• /
• pp.61-66
• /
• 2003

Fouling is very serious problem in heat exchanger because it rapidly deteriorates the performance of heat exchanger. Cross-flow heat exchanger with vortex generators is developed, which enhance heat transfer and reduce fouling. In the present heat exchanger, shell and baffle are removed from the conventional shell-and-tube heat exchanger. The naphthalene sublimation technique is employed to measure the local heat transfer coefficients. The experiments are performed for single circular tube, staggered array tube bank and in-line array tube bank with and without vortex generators. Local and average Nusselt numbers of single tube and tube bank with vortex generator are investigated and compared to those of without vortex generator.

• Structural Engineering and Mechanics
• /
• v.82 no.6
• /
• pp.691-699
• /
• 2022

This paper is devoted to the presentation of a numerical study on vibration behavior of composite panels reinforced by glass fibres and carbon nanotubes (CNTs) subjected to thermal environments. The effect of temperature variation has been included as thermal load acting on in-plane direction of the panel. To model the composite material, a micromechanical model which contains random dispersion of nanotubes and single-direction fibers has been selected. The geometry of the panel has been considered to have a single curveture along its width. Based on the above assumptions, the governing equations have been derived by using thin shell theory capturing the panel curveture and also nonlinear deflections. Finally, the panel dependence on various factors such as the curveture, nanotube amount, fiber volume, fiber direction and temperature variation has been researched.

• Computers and Concrete
• /
• v.32 no.3
• /
• pp.303-311
• /
• 2023

An analysis of the Poisson's ratios influence of single walled carbon nanotubes (SWCNTs) based on Sander's shell theory is carried out. The effect of Poisson's ratio, boundary conditions and different armchairs SWCNTs is discussed and studied. The Galerkin's method is applied to get the eigen values in matrix form. The obtained results shows that, the decrease in ratios of Poisson, the frequency increases. Poisson's ratio directly measures the deformation in the material. A high Poisson's ratio denotes that the material exhibits large elastic deformation. Due to these deformation frequencies of carbon nanotubes increases. The frequency value increases with the increase of indices of single walled carbon nanotubes. The prescribe boundary conditions used are simply supported and clamped simply supported. The Timoshenko beam model is used to compare the results. The present method should serve as bench mark results for agreeing the results of other models, with slightly different value of the natural frequencies.

• Journal of the Korea Academia-Industrial cooperation Society
• /
• v.15 no.3
• /
• pp.1764-1769
• /
• 2014

Numerical investigations have been conducted on the junction that connect the multi-tubular section and the single shell section in order to evaluate applicability of hybrid sections in wind turbine towers instead of conventional single shell towers. Major characteristics in structural details include extension of multi-tubular member into shell end section, installation of wing stiffeners, and different layout of floor beams. Elastic and nonlinear incremental analyses were conducted to examine stress concentration patterns and ultimate behaviors, respectively. Based on evaluation of structural performance due to vertical and horizontal forces, it has been confirmed that installation of floor beams and wing stiffeners sensitively affect ultimate strength of global wind tower.

• Tunnel and Underground Space
• /
• v.14 no.1
• /
• pp.1-15
• /
• 2004

The development of high-performance shotcrete lining is essential in improving the long-term durability of tunnels and in introducing single-shell tunnelling methods, where shotcrete as well as rockbolts are used as permanent support members. In this paper, new and advanced admixtures to improve shotcrete performance are introduced. In addition, requirements for mechanical properties as well as test items for quality control of shotcrete are summarized. A case study on the application of the pneumatic pin penetration test which can estimate compressive strength of shotcrete more easily and quickly is also illustrated. Previous studies to analyze the behaviors of shotcrete lining by considering its transient hardening and to carry out the sensitivity analysis of the design parameters of shotcrete lining are discussed to give fundamental concepts on rock-support interactions. Representative single-shell tunnelling methods where high-performance shotcrete lining is applied as a permanent support are also introduced.

• Advances in nano research
• /
• v.12 no.1
• /
• pp.25-35
• /
• 2022

Within the framework of the density functional theory combined with the method of non-equilibrium Green's functions (DFT + NEGF), the features of electron transport in fullerene nanojunctions, which are «core-shell» nanoobjects made of a combination of fullerenes of different diameters C₂₀, C₈₀, C₁₈₀, placed between gold electrodes (in a nanogap), are studied. Their transmission spectra, the density of state, current-voltage characteristics and differential conductivity are determined. It was shown that in the energy range of -0.45-0.45 eV in the transmission spectrum of the "Au-C₁₈₀-Au" nanojunction appears a HOMO-LUMO gap with a width of 0.9 eV; when small-sized fullerenes C₂₀, C₈₀ are intercalation into the cavity C₁₈₀ the gap disappears, and a series of resonant structures are observed on their spectra. It has been established that distinct Coulomb steps appear on the current-voltage characteristics of the "Au-C₁₈₀-Au" nanojunction, but on the current-voltage characteristics "Au-C₈₀@C₁₈₀-Au", "Au-(C₂₀@C₈₀)@C₁₈₀-Au" these step structures are blurred due to a decrease in Coulomb energy. An increase in the number of Coulomb features on the dI/dV spectra of core-shell fullerene nanojunctions was revealed in comparison with nanojunctions based on fullerene C₆₀, which makes it possible to create high-speed single-electron devices on their basis. Models of single-electron transistors (SET) based on fullerene nanojunctions "Au-C₁₈₀-Au", "Au-C₈₀@C₁₈₀-Au" and "Au-(C₂₀@C₈₀)@C₁₈₀-Au" are considered. Their charge stability diagrams are analyzed and it is shown that SET based on C₈₀@C₁₈₀-, (C₂₀@C₈₀)@C₁₈₀- nanojunctions is output from the Coulomb blockade mode with the lowest drain-to-source voltage.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.30 no.2
• /
• pp.111-117
• /
• 2017

In this paper, a local deformation effect in thin-walled box beams is investigated via a finite element modal analysis. The analysis is carried out for single-cell and multi-cell box beam configurations. The single-cell box beam with and without a neck, which mimics a simple wind-turbine blade, is analyzed first. The results obtained by shell elements are compared to those of one-dimensional(1D) beam elements. It is observed that the wall thickness plays a crucial role in the natural frequencies of the beam. The 1D beam analysis deviates from the shell analysis when the wall thickness is either thin or thick. The shell modes(local deformations) are dominant as it becomes thin, whereas the shear deformation effects are significant as it does thick. The analysis is extended to the single-cell box beam with a neck, in which the shell modes are confined to near the neck. Finally the multi-cell box beam with a taper, which is quite similar to real wind-turbine blade configuration, is considered to investigate the local deformation effect. The results reveal that the 1D beam analysis cannot match with the shell analysis due to the local deformation, especially for the lagwise frequencies. There are approximately 5~7% errors even if the number of segments is increased.