• Knowledge Management Research
• /
• v.17 no.2
• /
• pp.27-50
• /
• 2016

Korean manufacturing industry have recently faced the catch-up of China in the mass commodity product, such as automotive, display, and smart phone in terms of market as well as technology. Accordingly, discussion on the importance of achieving catch-up in complex product systems (CoPS) has been increasing as a new innovation engine for the industry. In order to achieve successful catch-up of CoPS, we explored emerging technologies of CoPS, which are featured by the characteristics of radical novelty, relatively fast growth and self-sustaining, through the study of emerging technologies of gas turbine for power generation. We found that emerging technologies of the gas turbine are technologies for combustion nozzle and composition of electrical machine for increasing power efficiency, washing technology for particulate matter, cast and material processing technology for enhancing durability from fatigue, cooling technologies from extremely high temperature, interconnection operation technology between renewable energy and the gas turbine for flexibility in power generation, and big data technology for remote monitoring and diagnosis of the gas turbine. We also found that those emerging technologies resulted in technological progress of the gas turbine by converging with other conventional technologies in the gas turbine. It indicates that emerging technologies in CoPS can be appeared on various technological knowledge fields and have complementary relationship with conventional technologies for technology progress of CoPS. It also implies that latecomers need to pursue integrated learning that includes emerging technologies as well as conventional technologies rather than independent learning related to emerging technologies for successful catch-up of CoPS. Our findings provide an important initial theoretical ground for investigating the emerging technologies and their characteristics in CoPS as well as recognizing knowledge management strategy for successful catch-up of latecomers. Our findings also contribute to the policy development of the CoPS from the perspective of innovation strategy and knowledge management.

• Proceedings of the KWS Conference
• /
• 2002.10a
• /
• pp.661-667
• /
• 2002

Welding-induced buckling distortion is one of the most problematic concerns in both design and fabrication of welded thin-plate structures. This paper deals with experimental and numerical results of the welding-induced longitudinal and/or buckling distortion occurring in welding of 6mm-thick AH36 high strength steel plates. Effects of the heat input and the plate size on the distortion were experimentally evaluated for square plates. Bead-on-plate welding was performed with the submerged arc welding process along the middle line of plate specimens. Experimental results showed that the longitudinal distortion made a single curvature in the plate, and the distortion magnitude along the weld centerline was proportional to the heat input and the plate size. The experimental results were used to examine the validity of the numerical simulation procedure for welding-induced distortion where the longitudinal distortion mode and magnitude were numerically quantified. Three-dimensional, large deformation, welding simulations were performed for selected weld models. Numerical results of the distortion mode and magnitude were in a good agreement with experimental ones. Depending on the presence of halting the distortion growth during the cooling cycle of welding, the condition discriminating buckling distortion from longitudinal distortion was established. Eigenvalue analyses were performed to check the buckling instability of tested plates with different sizes subjected to different heat inputs. The perturbation load pattern for the analysis was extracted from longitudinal inherent strain distributions. Critical buckling curve from the eigenvalue analyses revealed that the buckling instability is manifested when plate size or heat input increases.

• Journal of Environmental Science International
• /
• v.16 no.5
• /
• pp.603-610
• /
• 2007

Recent urban sprawl has destroyed various kinds of green space in tile city. It has affected duality of people's life in the city, as well as urban ecosystem. Recent study shows the possibilities of roofs as green spaces in urban central site where the land costs are generally high. This research focuses on Jung-Gu district in Daegu Metropolitan city as a study area and calculates possible area of green roof using 2002 Autocad program based on aerial photographs and land registration maps. And the purpose of this research is to analyze environmental and economic effects of green roof. The environmental effects are as follows. It is expected that $91,106m^2$ green spaces, 12.13 % of study site, will be added if green roof is performed in the study site. It is assumed that the expanded areas could reduce the highest temperature to $0.5-1.0^{\circ}C$ during the summer in terms of environmental effect. And the following shows the economic effects. If green roof and greening urban central site are created as a same size of $91,106m^2$, it will be expected that the costs of green roof will be much more in-expensive than about 98 billions won. It will be also found that the expense of cooling energy can be saved out about 8 millions won per day in summer, if grass planting is accomplished on the possible areas of green roof in the study site. Therefore, it is desirable to take legal supports such as enacting regulations to activate green roof for more environmental and economic effects. For instance, green roof for public institutions, school and model area selection are desirable method to publicize the effect of greening program for citizen's participation.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.15 no.6
• /
• pp.129-135
• /
• 2016

There have been many types of development and commercialization efforts for superconducting power applications with the continuous development of High Temperature Superconducting (HTS) conductors. In particular, HTS power cables are going to be commercialized in real power grids. A cryogenic refrigeration system should be used to keep it below 77 K, and its required cooling capacity continuously increases as the unit length of the HTS power cable increases. Among the many kinds of cryogenic refrigerator, a reverse Brayton refrigerator that uses turbo expanders is a promising refrigerator due to its efficiency and reliability. Among the various components in refrigerators, the cryogenic turbo-expander is the most important part for increasing efficiency and assuring reliability. The design of a 300 W class turbo-expander is described in this paper prior to the development of a 10 kW class turbo expander, which is the required capability for the commercialization of a HTS power cable. The impeller shape and rotation speed are determined based on the cycle analysis. The Eigen frequency and harmonic analysis are conducted with gas bearings at cryogenic temperatures to determine the operational stability.

• Journal of the Korean Society of Propulsion Engineers
• /
• v.15 no.2
• /
• pp.68-73
• /
• 2011

For the launch preparation of KSLV-I, gaseous nitrogen with various level of pressure and cryogenic liquid nitrogen are required. Nitrogen Supply System on launch complex has been developed to perform the production of high pressure gaseous nitrogen, the production of gaseous nitrogen with temperature of 273 ${\pm}$ 2K for protection purge of launch vehicle after loading of propellant and the supply of cryogenic liquid nitrogen for cooling of fuel (kerosene) and oxidizer (liquid oxygen). The operational instability of vaporizer mainly caused by its heat transfer characteristics which sensitively depends on the atmospheric conditions was removed by introducing parallel installation of two vaporizer and their switching operation. The developed Nitrogen Supply System carried out its function successfully in preparation of KSLV-I flight tests.

• Journal of the Korean Society for Precision Engineering
• /
• v.17 no.9
• /
• pp.189-195
• /
• 2000

RP techniques have their unique characteristics according to the working principles : star-stepped surface of parts due to layer-by-layer stacking low build speed caused by line-by-line solidification to fish one layer and post processing to improve surface finish etc The objective of this study is to propose a new RP technique Variable Deposition Mnanufacturing (VDM) which can make up for the disadvantages of the existing RP techniques and to develop an apparatus to implement the technique. The proposed process can greatly reduce the build time and improve the surface finish of parts generated. Experiments are carried out to obtain the range of temperature of molten material to maintain its fluidity and to investigate the effect of gas cooling on the preservation of the slopes. Some simple shapes such as a line-shape an S-shape and a circle-shape are fabricated from Ethylene Vinyl Acetatecopolymer(EVA) In order to examine the applicability of VDM to more general shapes a tensile specimen and a yo-yo shape were manufactured by the proposed RP method using EVA material as a trial approach. The current basic study shows a high potential of practical use of the proposed VDM process to prototyping of a general three-dimensional shape.

• Architectural research
• /
• v.17 no.3
• /
• pp.109-115
• /
• 2015

The dynamic pricing of electricity, where the electricity rate increases in a time zone with a high demand for electricity is typically applied to a building whose power reception capacity is greater than a certain size. This includes the time of use(TOU) electricity pricing in Korea which can induce the effect of reducing the power demand of a building. Meanwhile, a VRF (Variable Refrigerant Flow) system that uses electricity is regarded as one of the typical heating and cooling systems along with central air conditioning (central HVAC) for its easy operation and application to the building. Thus, to reduce power energy and operating costs of a building in which the TOU and VRF systems are applied simultaneously, we suggested a control for changing the indoor temperature setting within the thermal comfort range or limiting the rotational speed of an inverter compressor. In this study, to describe the features of the above-mentioned control and verify its effects, we evaluated the results obtained from the analysis of its operation data. Through the actual measurements in winter operations for 73 days since mid- December 2014, we confirmed a reduction of 10.9% in power energy consumption and 12.2% in operating costs by the new control. Also, a reduction of 13.3% in power energy consumption was identified through a regression analysis.

• Proceedings of the Korean Vacuum Society Conference
• /
• 2014.02a
• /
• pp.380.2-380.2
• /
• 2014

Direct synthesis of graphene using a chemical vapor deposition (CVD) has been considered a facile way to produce large-area and uniform graphene film, which is an accessible method from an application standpoint. Hence, their fundamental understanding is highly required. Unfortunately, the CVD growth mechanism of graphene on Cu remains elusive and controversial. Here, we present the effect of graphene growth parameters on the number of graphene layers were systematically studied and growth mechanism on copper substrate was proposed. Parameters that could affect the thickness of graphene growth include the pressure in the system, gas flow rate, growth pressure, growth temperature, and cooling rate. We hypothesis that the partial pressure of both the carbon sources and hydrogen gas in the growth process, which is set by the total pressure and the mole fraction of the feedstock, could be the factor that controls the thickness of the graphene. The graphene on Cu was grown by the diffusion and precipitation mode not by the surface adsorption mode, because similar results were observed in graphene/Ni system. The carbon-diffused Cu layer was also observed after graphene growth under high CH4 pressure. Our findings may facilitate both the large-area synthesis of well-controlled graphene features and wide range of applications of graphene.

• Korean Journal of Materials Research
• /
• v.23 no.4
• /
• pp.246-249
• /
• 2013

Nano-sized ${\beta}$-SiC nanoparticles were synthesized combined with a sol-gel process and a carbothermal process. TEOS and carbon black were used as starting materials for the silicon source and carbon source, respectively. $SiO_2$ nanoparticles were synthesized using a sol-gel technique (Stober process) combined with hydrolysis and condensation. The size of the particles could be controlled by manipulating the relative rates of the hydrolysis and condensation reactions of tetraethyl orthosilicate (TEOS) within the micro-emulsion. The average particle size and morphology of synthesized silicon dioxide was about 100nm and spherical, respectively. The average particles size and morphology of the used carbon black powders was about 20nm and spherical, respectively. The molar ratio of silicon dioxide and carbon black was fixed to 1:3 in the preparation of each combination. $SiO_2$ and carbon black powders were mixed in ethanol and ball-milled for 12 h. After mixing, the slurries were dried at $80^{\circ}C$ in an oven. The dried powder mixtures were placed in alumina crucibles and synthesized in a tube furnace at $1400{\sim}1500^{\circ}C$ for 4 h with a heating rate of $10^{\circ}C$/min under flowing Ar gas (160 cc/min) and furnace cooling down to room temperature. SiC nanoparticles were characterized by XRD, TEM, and SAED. The XRD results showed that high purity beta silicon carbide with excellent crystallinity was synthesized. TEM revealed that the powders are spherical shape nanoparticles with diameters ranging from 15 to 30 nm with a narrow distribution.

• Composites Research
• /
• v.30 no.6
• /
• pp.350-355
• /
• 2017

The new liquid crystalline (LC) epoxy was designed by substituting the phenylcyclohexyl (PCH) mesogen moiety with an alkyl chain at the 2,5 position of the diglycidyl terephthalate. The mesomorphic properties were evaluated by differential scanning calorimetry (DSC) and polarized optical microscopy (POM). All LC epoxy derivatives exhibited an enantiotropic smectic phase upon heating and cooling process. The LC phase temperature range was widened by mixing the eutectic mixture of LC epoxies. Interestingly, the cured LC epoxy exhibited the highest thermal conductivity of $0.4W{\cdot}m^{-1}{\cdot}K^{-1}$. The novel LC epoxy with high thermal conductivity might be used as a composite material for electronic and display devices.