• Steel and Composite Structures
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• v.50 no.2
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• pp.135-148
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• 2024

This paper analytically investigates the free vibration analysis of functionally graded-carbon nanotube reinforced composite (FG-CNTRC) plates by dynamic stiffness method (DSM). The properties of CNTRC are determined with the extended rule of mixture. The governing differential equations of motion based on the first-order shear deformation theory of CNTRC plate are derived using Hamilton's principle. The FG-CNTRC plates are studied for a uniform and two different distributions of carbon nanotubes (CNTs). The accuracy and performance of the DSM are compared with the results obtained from closed closed-form and semi-analytical solution methods in previous studies. In this study, the effects of boundary condition, distribution type of CNTs, plate aspect ratio, plate length to thickness ratio, and different values of CNTs volume fraction on the natural frequencies of the FG-CNTRC plates are investigated. Finally, various natural frequencies of the plates in different conditions are provided as a benchmark for comparing the accuracy and precision of the other analytical and numerical methods.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.133-138
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• 2002

Microbiologically Influenced Corrosion (MIC) was suspected in a corrosion failure of cooling system of stainless piping welded joint, carrying marine water. Marine water which is used for cooling water in a plant was transferred to the laboratory and used for experiment. In the first experiment, weld metal samples were exposed to the test solution for 56 days (marine water and sterilized marine water (control)). Surface condition of experimental coupons was observed using a Scanning Electron Microscope (SEM). In another experiment, free corrosion potential of these material was monitored for 56 days. Pitting corrosion was found in the coupons exposed to marine water. Free corrosion potential ennoblement was found to be significant compared to control. It was suspected that this corrosion case was MIC. In the second experiment, coupons were exposed to diluted nutrient medium containing single culture of microbes isolated from the MIC causing marine water sample used for the first experiment. After exposure test, surface condition of experimental coupon was observed using SEM. Pitting corrosion was found in coupons exposed to some of the isolates. The results indicate that they contribute to the corrosive effect of the SUS316L welds.

• Journal of the Korean Chemical Society
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• v.31 no.3
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• pp.244-249
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• 1987

Liquid-solid extraction technique was applied to enrich volatile free acids (VFAs) from aqueous matrices. Chromosorb P was found to be an efficient solid sorbent. The unionized VFAs could be quantitatively recovered from the Chromosorb P column with ether while interfering watermiscible components were retained in the adsorbed water on the surface of Chromosorb P. The method of simple and efficient isolation-enrichment of VFAs, followed by the quantitative analysis employing stainless steel capillary column coated with Carbowax 20M containing phosphoric acid has been applied to the determination of VFAs in several aqueous samples.

• Nuclear Engineering and Technology
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• v.52 no.7
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• pp.1471-1480
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• 2020

This research presents a case study on the remediation of a radioactive waste (uranium: U) utilizing a multi-objective fuzzy optimization in an electrocoagulation process for the iron-stainless steel and aluminum-stainless steel anode/cathode systems. The incorporation of the cumulative uncertainty of result, operational cost and energy consumption are essential key elements in determining the feasibility of the developed model equations in satisfying specific maximum contaminant level (MCL) required by stringent environmental regulations worldwide. Pareto-optimal solutions showed that the iron system (0 ㎍/L U: 492 USD/g-U) outperformed the aluminum system (96 ㎍/L U: 747 USD/g-U) in terms of the retained uranium concentration and energy consumption. Thus, the iron system was further carried out in a multi-objective analysis due to its feasibility in satisfying various uranium standard regulatory limits. Based on the 30 ㎍/L MCL, the decision-making process via fuzzy logic showed an overall satisfaction of 6.1% at a treatment time and current density of 101.6 min and 59.9 mA/㎠, respectively. The fuzzy optimal solution reveals the following: uranium concentration - 5 ㎍/L, cumulative uncertainty - 25 ㎍/L, energy consumption - 461.7 kWh/g-U and operational cost based on electricity cost in the United States - 60.0 USD/g-U, South Korea - 55.4 USD/g-U and Finland - 78.5 USD/g-U.

• Journal of computational fluids engineering
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• v.2 no.1
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• pp.117-128
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• 1997

Effects of dam and weir on the fluid flow and behavior of inclusions in the continuous casting tundish have been studied using the CFD (Computational Fluid Dynamics) technique. Inclusions affecting the quality of steel products have been considered to be passive: the fluid flow has been obtained for unstaggered grid points defined on body-fitted generalized cuvilinear coordinates with no attention on inclusions, and the spatial propagation of inclusions has been determined by using the flow field data. The result show that the dam and weir direct the flow to the free surface and increase the residence time of inclusions significantly, and thereby that inclusions have much more chance to be floated to the free surface of the tundish where it is eliminated. It is also found that they offer more margin on the geometric design of exit nozzles connected to moulds. This finding is particularly important for twin casting operations where the quality of steel products from the two moulds be kept uniformly.

• Proceedings of the IEEK Conference
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• 2001.10a
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• pp.514-519
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• 2001

Converter has been slag produced 10 million tons per year in Japan. It is a steel making by product produced in the same way as the blast-furnace slag. Though blast-furnace slag is being used effectively as a concrete admixture, the converter stag has never been used effectively because of the expansion action of contained free lime and iron oxide. This is an important environmental problem in the steel industry. Beta-2CaOSiO$_2$(beta-C$_2$S) is contained 40 percent in converter slag, therefore it is very promising as a concrete admixture. We proposed an accelerated aging processes capable of stabilizing the converter slag in a short time. The converter slag is dipped into alkali aqueous solution after heating at low temperature. It was subsequently ground to a grain size of 75 ${\mu}{\textrm}{m}$ , inner 30 percent of OPC. The properties of mortar and concrete using the blended cement were determined. As a result, it has become apparent that the expansion was reduced and long term compressive strength was increased while that at early ages was not so remarkable. The hydration exotherm rate was lower than that of the OPC.

• Journal of Welding and Joining
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• v.24 no.4
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• pp.39-49
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• 2006

The austenite grain growth model in low alloyed steel HAZ without precipitates was proposed by analyzing isothermal grain growth behavior. Steels used in this study were designed to investigate the effect of alloying elements. Meanwhile, a systematic procedure was proposed to prevent inappropriate neglect of initial grain size (D0) and misreading both time exponent and activation energy for isothermal grain growth. It was found that the time exponent was almost constant, irrespectively of temperature and alloying elements, and activation energy increased with the addition of alloying elements. From quantification of the effect of alloying elements on the activation energy, an isothermal grain growth model was presented. Finally, combining with the additivity rule, the austenite grain size in the CGHAZ was predicted.

• Journal of Korean Society of Steel Construction
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• v.9 no.4 s.33
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• pp.673-682
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• 1997

The main purpose of this paper is to investigate the effects of rotatory inertia and shear deformation on the natural frequencies of arches with variable curvature. The differential equations are derived for the in-plane free vibration of linearly elastic arches of uniform stiffness and constant mass per unit length. The governing equations are solved numerically for parabolic, circular and elliptic geometries with hinged-hinged, hinged-clamped and clamped-clamped end constraints. For each cases, the four lowest frequency parameters are presented as functions of the two dimensionless system parameters; the arch rise to span length ratio, and the slenderness ratio.

• Journal of the Korean Society for Heat Treatment
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• v.19 no.2
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• pp.90-95
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• 2006

Nitriding or carburizing of carbon steels results in good mechanical properties such as high surface hardness and wear resistance but it has no affection on the corrosion resistance. Corrosion properties of nitriding and carburizing steels could be deteriorated. So, recently, there have been great demand for oxi-nitriding to enhance both mechanical properties and corrosion resistance. In this study, the corrosion resistance of carbon steel, S35C, and free cutting steel, SUM222, are prepared by vacuum nitriding and vacuum post-oxidation were compared with those treated by nitriding. After vacuum post-oxidation, $5{\mu}m$ oxide layer was formed on the nitride layer with $20{\sim}30{\mu}m$ depth. Potentio-dynamic polarization curve in corrosion test showed that the corrosion potential after post oxidation was increased from 200 mV to 800 mV in S35C and from 600 mV to 1200 mV in SUM222. SEM analyses showed that pores was increased and surface roughness became rougher with post oxidation. However, the formation of $Fe_3O_4$ resulted in the enhanced corrosion resistance of steels.

• Proceedings of the Korean Institute of Building Construction Conference
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• 2021.05a
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• pp.187-188
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• 2021

In the case of the Busan North Port, where the Busan Opera House is located, it is an environment exposed to various external deterioration factors such as frequent strong winds, seawater and salty winds, and an exterior material using UHPC (Ultra High Performance Concrete), a highly durable exterior material as a solution to this. Has been adopted. in this study, an economical production and construction direction was reviewed by applying UHPC to the exterior panels of atypical buildings that cannot cope with GFRC, metal, and glass, which are the main exterior finishing materials applied so far. When steel fibers are used, structural performance may be better than organic fibers, but due to environmental factors in Busan, corrosion due to exposure to steel fibers or problems with safety management after construction and completion may occur. Therefore, the site used the newly developed SACF fiber. Facade design of atypical buildings, which will increase in the future, is an important part, and the scope of use of UHPC panels is expected to increase in the future as design trends and demand for high durability increase.