• Progress in Superconductivity and Cryogenics
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• v.14 no.3
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• pp.38-42
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• 2012

Fixtures such as bushings in terminations of high temperature superconducting(HTS) power cable systems are subjected to high voltages, which have to transition from ambient to cryogenic temperatures. As such it is imperative to ensure the integrity of the dielectrics under all operating conditions, including thermal aspects brought about by the passage of current. Gaseous helium(GHe) at high pressure is regarded as a potential coolant for superconducting cables. The dielectric aspects of cryogenic helium gas are both complex and demanding. In this experimental study we looked at the interface between a smooth epoxy surface and high pressure helium gas in a homogeneous electric field. The alternating current(AC) flashover voltages of epoxy samples are presented. The results have been analyzed by using Weibull statistics. In addition to the behavior of the epoxy in gaseous helium as a function of pressure and temperature we also present data of the characteristics of the epoxy in mineral oil and in liquid nitrogen($LN_2$). The breakdown characteristics of a uniform field gap in gaseous helium as a function of pressure and temperature under AC, direct current(DC) and lightning impulse voltages are also given. Electric field calculations have been made for one of the experimental geometries in an attempt to explain some of the anomalies in the experimental results.

• Wind and Structures
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• v.8 no.5
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• pp.325-342
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• 2005

This paper deals with the buckling behavior of thin-walled aboveground tanks under wind load. In order to do that, the wind pressures are obtained by means of wind-tunnel experiments, while the structural non linear response is computed by means of a finite element discretization of the tank. Wind-tunnel models were constructed and tested to evaluate group effects in tandem configurations, i.e. one or two tanks shielding an instrumented tank. Pressures on the roof and on the cylindrical part were measured by pressure taps. The geometry of the target tank is similar in relative dimensions to typical tanks found in oil storage facilities, and several group configurations were tested with blocking tanks of different sizes and different separation between the target tank and those blocking it. The experimental results show changes in the pressure distributions around the circumference of the tank for half diameter spacing, with respect to an isolated tank with similar dimensions. Moreover, when the front tank of the tandem array has a height smaller than the target tank, increments in the windward pressures were measured. From the computational analysis, it seems that the additional stiffness provided by the roof prevents reductions in the buckling load for cases even when increments in pressures develop in the top region of the cylinder.

• Journal of the Society of Naval Architects of Korea
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• v.32 no.2
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• pp.22-31
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• 1995

In this paper, a 3-dimensional multi-layer current simulation program is allied to real shore area near Inchon harbor with highly irregular bottom and continental geometry. The effects of bottom topography on vertical structures of the ocean tidal current is investigated through comparing the calculated results by 2-dimensional depth averaged approach and the present method. Wind induced current, which may be more dominant factor in Predicting oil spill behavior, is also simulated by the present computation algorithm. Comparison shows quite large differences not only in vertical distribution of the current but also in the direction of the surface current.

• International Journal of Naval Architecture and Ocean Engineering
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• v.4 no.4
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• pp.423-436
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• 2012

Unstiffened plates are integral part of all kinds of structures such as ship and offshore oil platforms. Openings are unavoidable and absolutely reduce the ultimate strength of structures. In this study, the finite element analysis package, ABAQUS, is used to analyze the behavior of unstiffened plate with rectangular opening. The rectangular opening form is divided into two cases. In case1, opening depth is constant, but opening width is varied. Meanwhile, in case2 opening width is fixed and opening depth is varied. Besides, for the two different form opening, the effect of plate slenderness parameter (${\beta}$), opening area ratio (AR) and opening position ratio (PR) on the ultimate strength of plate with opening under axial compression are presented. It has been found that the ultimate strength of plate ofcase1is much more sensitive to the plate slenderness parameter (${\beta}$) and opening area ratio (AR) than that of case2. However, for case1, opening position (PR) almost has no effect on the ultimate strength, whereas, regardingcase2, the influence of opening position (PR) depends on the plate slenderness parameter (${\beta}$). Based on nonlinear regression analysis, three design formulae are not only developed but also approved reasonably for the practical engineering design.

• Journal of the Korean Applied Science and Technology
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• v.31 no.1
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• pp.50-58
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• 2014

A novel fullerene derivative with photoresponsive azobenzene group was designed and synthesized, and its photoresponsive properties were reported. Starting from 4-nitrophenol, compound 1, which is containing fullerene moiety connected to azobenzene group through covalent linkage was synthesized by 5 steps. All the intermediates and the final compound were characterized by $^1H$, $^{13}C$-NMR, FAB-Mass or elemental analysis. Compound 1 exhibited the expected photoresponsive behavior. Chloroform solution($10^{-5}M$) of it served to maximize the absorption at 351 nm corresponding to the trans-azobenzene chromophore. Irradiation of this solution with 365 nm light resulted in photoisomerization to cis-azobenzene, as evidenced by decrease in the absorbance at 351 nm and an increase in absorbance at 450nm. A photostationary state was reached within about 150 s. Thermal reversion to the original spectrum was observed over the course of about 6 h at room temperature in the dark. However, exposure to bright sun light for about 5 s also effect almost complete reversion to the trans-isomer. This indicates that there is no strong steric influence on the trans-cis reversible isomerization of compound 1.

• Korean Journal of Computational Design and Engineering
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• v.10 no.5
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• pp.375-379
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• 2005

Durability of rubber dust cover in the ball joint for automotive suspension parts is analyzed by FEM and compared with experimental data. Upper open area of ball joint is sealed by dust cover for preventing outflow of the lubricating oil and intrusion of send, dust, water, etc. This rubber cover undergoes repeated loadings such as tension and compression while the car is running. Analysis about rubber material needs to consider every kinds of nonlinearities arise in finite element analysis, which are geometric nonlinearity due to large displacement and small strain, materially nonlinearity and nonlinear boundary condition such as contact. The deformation behavior of dust cover is analysed by using the commercial finite element program MARC. In the study, this program could solve these kinds of nonlinear analysis accurately. Finite element model of dust cover is considered as 3-dimensional half model based on 2-dimensional axisymmetric model. Material property of rubber is modeled by Ogden model and input data for calculation takes form uniaxial tension test of rubber specimen. The final object of the study is obtaining the design specification of dust covers and the result of analysis should be a useful data to design of rubber cover.

• Proceedings of the KIEE Conference
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• 2005.04a
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• pp.277-279
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• 2005

The imbalance of energy demand and supply caused by rapid industrialization around the world and the associated environmental issues require and alternative energy source with possible renewable fuels. Political instability and depletion of cruel oils are other factors that cause fluctuation of oil price. Securing a new alternative energy source for the next century became an urgent issue that our nation is confronting with. As a matter of fact, the fuel cell technology can be widely used as next generation energy regardless of regions and climate. Specially, the ability of expansion and quick installation enable one to apply it for distributed power, where the technology is already gaining remarkable attentions for the application. Particularly, leading industrialized nations are focusing on the PEM fuel dell with anticipation that this technology will find their place of applications in the vehicles and homes. In this study, demonstrate the multi physics modeling of a proton exchange membrane(PEM) fuel cell with interdigitated flow field design. The model uses current balances, mass balance(Maxwell-Stefan diffusion for reactant, water and nitrogen gas) and momentum balance(gas flow) to simulate the PEM fuel cell behavior.

• Journal of ILASS-Korea
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• v.13 no.1
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• pp.42-50
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• 2008

In the present work, atomization characteristics of shear-thinning liquid slurry discharging from fan spray nozzles were studied experimentally for spray painting applications. The effects of solid particle size and concentration on the properties (especially on the viscosity) of suspensions and mean drop size were examined by using model fluids. In the range of low particle concentration (below 3 wt%), the fluid viscosity was primarily determined by the particle size. On the other hand, in the range of high particle concentration (higher than 10 wt%), the agglomeration phenomenon and the oil absorption capability of solid particles played major roles in determining the fluid viscosity. In the high concentration region, which most of the paints belong to, the fluid became more viscous and the shear thinning behavior appeared more prominent as the particle concentration was increased. In this region, mean drop size(SMD) decreased more rapidly with the increase of the injection pressure. Also, SMD became larger with the higher particle concentration and the larger particle size.

• YAKHAK HOEJI
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• v.22 no.4
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• pp.201-206
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• 1978

The analysis of elemental sulfur by polarography has already been reported in the literature. Only a discussion of the more important factors influencing the analysis is here presented. (1) The effects of pH on the reduction of elemental sulfur are pronounced and the use of buffered solutions for the analysis of elemental sulfur is necessary. The authors found that a pH of 4-6 was found to be reproducible polarograms by use of D.C. polarograph. However, in alkali solvents the plateau of elemental sulfur has a pronounced dip if the concentration of sulfur is as much as 30ppm. (2) A.C. polarographic method shows a very high sensitivity in the case of sulfur reduction, so that the very low concentration of sulfur can easily be determined (about 1ppm). (3) The characteristics of sulfur wave can be formulated according to Stackelberg-Hauck-Hans equation. It was found that the curve of the peak potential of elemental sulfur in A.C. polarography versus logarithm of sulfur concentration was obtained to be straight line with the slope of 29.6 millivolts. This result was well agreed with theoretical consideration. (4) It was assumed that this polarographical methods were applicable to micro-analysis of elemental sulfur in crude oil and its petrochemical products, precipitated sulfur, and sulfur ointments with accuracy and rapidity.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 2004.05b
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• pp.125-129
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• 2004

The mold transformers have been widely used in underground substations in large building and have some advantages in comparison to oil-transformer, that is low fire risk, excellent environmental compatibility, compact size and high reliability. In addition, the application of mold transformer for outdoor is possible due to development of epoxy resin. The mold transformer generally has cooling duct between low voltage coil and high voltage coil. A mold transformer made by one body molding method has been developed for small size and low loss, but it needs some cooling method because heat radiation between each winding is difficult. The life of transformer is significantly dependent on the thermal behavior in windings. Many transformer designers have calculated temperature distribution and hot spot point by FEM(finite element method) to analyze winding temperature rise. In this paper, the temperature distribution and thermal stress analysis of 100kVA pole cast resin transformer for power distribution are investigated by FEM program.