• Solar Energy
• /
• v.18 no.4
• /
• pp.1-10
• /
• 1998

Polymer induced turbulent drag reduction in a rotating disk apparatus was investigated using four different molecular weights of poly(ethylene oxide)(PEO) in a synthetic seawater solution for the purpose of potential application to the cold water piping in the Ocean Thermal Energy Conversion(OTEC) system. To apply drag reduction to the OTEC we measured the temperature dependence on the drag reduction efficiency. From this study, it was found that the drag reduction efficiency increases with the temperature and the concentration. To measure the drag reduction efficiency during the operation period, the drag reduction behavior was detected as a function of time and the results obtained from the experiment was compared to the Brostow's model equation.

• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2001.06a
• /
• pp.346-353
• /
• 2001

Zirconia powder containing 3 mol% yttria(3Y-PSZ) with and with out Fe$_2$O$_3$ addition was coated on tile cast iron substrate by plasma spraying method. The erosion experiments were performed at temperatures from $25^{\circ}C$ to $600^{\circ}C$. A gas blast type erosion tester was used to examine erosion behavior of the specimens. The results of 3Y-PSZ coatings showed that tile erosion rate had maximum value at 40$0^{\circ}C$. It coincided with tile results of phase transformation tetragonal phase to monoclinic phase caused by low temperature thermal degradation. The tensile stress relaxation and the micro-hardness improvement significantly influenced on the erosion rate at $600^{\circ}C$. In the case of Fe$_2$O$_3$ added 3Y-PSZ coatings, the erosion rate of tested at $25^{\circ}C$ showed maximum value at 5.0 mol% Fe$_2$O$_3$ added coating. This tendency is caused by the improvement of mechanical properties and the tensile residual stress. The erosion rate at 200'c and 400'L showed significantly decrease by Fe203 addition. This decrease is believed to be the stabilization of the tetragonal phase and the increase of micro-hardness.

• Elastomers and Composites
• /
• v.38 no.1
• /
• pp.27-37
• /
• 2003

This work presents a comparative study of the morphology and structure related properties of thermoplastic elastomer blends based on SEBS/PP/Oil and dynamically vulcanized EPDM/PP/Oil. A combination of ruthenium oxide staining and low voltage scanning electron microscopy (LVSEM) was found to be suitable for the study of morphology of these highly oil extended blends. h close analogy was found in the mechanical, thermal and rheological properties of the two systems made in an internal Brabender mixer and co-rotating turin screw extruder. The morphology of the blends, as made by the two techniques, was found to be significantly different. In the case of TPVs, the blonds made in the extruder had smaller EPDM domains and better tensile properties. In the case of SEBS, the blends made in the Brabender had more co-continuous phases and showed better tensile properties. Crystallization behavior of the isotactic polypropylene in the blends was found to be influenced by the type of rubber. Blends of SEBS/PP crystallized at a lower temperature than the TPVs. These differences were probably caused by differences in the nucleating ability of the two rubbers.

• Steel and Composite Structures
• /
• v.29 no.5
• /
• pp.669-680
• /
• 2018

The rapidly decreasing natural resources and the global variation of the climate push us to find intelligent and efficient structural systems to provide more people with fewer resources. This paper proposed a kinematic cable-strut system to realize sustainable structures in responding to changing environmental conditions. At first, the concept of the kinematic system based on crystal-cell pyramid (CP) cable-strut unit was given. Then the deployment of the structure was studied experimentally. After that, the static behaviors in the fully deployed state under the symmetric and asymmetric load cases were investigated. Moreover, the effects of thermal loading and the initial prestress distribution were also discussed. Comparative studies between the proposed structure and other deployable cable-strut system under three times of design load cases were carried out. Finally, the robustness of the system was studied by removal of one passive cable at one time.

• Journal of the Korean Wood Science and Technology
• /
• v.47 no.4
• /
• pp.442-450
• /
• 2019

Despite its potential as a renewable source for fuels and chemicals, lignin valorization still faces technical challenges in many aspects. Overcoming such challenges associated with the chemical recalcitrance of lignin can provide many opportunities to innovate existing and emerging biorefineries. In this work, we leveraged a biomass genetic engineering technology to produce phenolic aldehyde-rich lignin structure via downregulation of cinnamyl alcohol dehydrogenase (CAD). The structurally altered lignin obtained from the Arabidopsis thaliana CAD mutant was pyrolyzed to understand the effect of structural alteration on thermal behavior of lignin. The pyrolysis was conducted at 400 and $500^{\circ}C$ using an analytical pyrolyzer connected with GC/MS and the products were systematically analyzed. The results indicate that aldehyde-rich lignin undergoes fragmentation reaction during pyrolysis forming a considerable amount of C6 units. Also, it was speculated that highly reactive phenolic aldehydes facilitate secondary repolymerization reaction as described by the lower yield of overall phenolic compounds compared to wild type (WT) lignin. Quantum mechanical calculation clearly shows the higher electrophilicity of transgenic lignin than that of WT, which could promote both fragmentation and recondensation reactions. This work provides mechanistic insights toward biomass genetic engineering and its application to the pyrolysis allowing to establish sustainable biorefinery in the future.

• Earthquakes and Structures
• /
• v.17 no.4
• /
• pp.399-409
• /
• 2019

This paper presents the experimental investigations on the seismic performance of a peculiar steel-concrete vertical hybrid structural system referred to as steel truss-RC tubular column hybrid structure. It is typically applied as the supporting structural system to house air-cooled condensers in thermal power plants (TPPs). Firstly, pseudo-dynamic tests (PDTs) are performed on a scaled substructure to investigate the seismic performance of this hybrid structure under different hazard levels. The deformation performance, deterioration behavior and energy dissipation characteristics are analyzed. Then, a cyclic loading test is conducted after the final loading case of PDTs to verify the ultimate seismic resistant capacity of this hybrid structure. Finally, the failure mechanism is discussed through mechanical analysis based on the test results. The research results indicate that the steel truss-RC tubular column hybrid structure is an anti-seismic structural system with single-fortification line. RC tubular columns are the main energy dissipated components. The truss-to-column connections are the structural weak parts. In general, it has good ductile performance to satisfy the seismic design requirements in high-intensity earthquake regions.

• Nuclear Engineering and Technology
• /
• v.54 no.8
• /
• pp.2960-2973
• /
• 2022

Since Fukushima nuclear power plant (NPP) accident in 2011, the importance of research on various severe accident phenomena has been emphasized. Particularly, detailed analysis of combustion risk is necessary following the containment damage caused by combustion in the Fukushima accident. Many studies have been conducted to evaluate the risk of local hydrogen concentration increases and flame propagation using computational code. In particular, the potential for combustion by local hydrogen concentration in specific areas within the containment has been emphasized. In this study, the process of flame propagation generated inside a reactor core to containment during a loss of coolant accident (LOCA) was analyzed using MELCOR 2.1 code. Later in the LOCA scenario, it was expected that hydrogen combustion occurred inside the reactor core owing to oxygen inflow through the cold leg break area. The main driving force of the oxygen intrusion is the elevated containment pressure due to the molten corium-concrete interaction. The thermal and mechanical loads caused by the flame threaten the integrity of the containment. Additionally, the containment spray system effectiveness in this situation was evaluated because changes in pressure gradient and concentrations of flammable gases greatly affect the overall behavior of ignition and subsequent containment integrity.

• Steel and Composite Structures
• /
• v.43 no.5
• /
• pp.673-688
• /
• 2022

Post-earthquake fire is a major threat since most structures are designed allowing some damage during strong earthquakes, which will expose a more vulnerable structure to post-earthquake fire compared to an intact structure. A series of experimental research on steel-concrete composite beam-to-column joints subjected to fire after cyclic loading has been carried out and a clear reduction of fire resistance due to the partial damage caused by cyclic loading was observed. In this paper, by using ABAQUS a robust finite element model is developed for exploring the performance of steel-concrete composite joints in post-earthquake fire scenarios. After validation of these models with the previously conducted experimental results, a comprehensive numerical analysis is performed, allowing influential parameters affecting the post-earthquake fire behavior of the steel-concrete composite joints to be identified. Specifically, the level of pre-damage induced by cyclic loading is regraded to deteriorate mechanical and thermal properties of concrete, material properties of steel, and thickness of the fire protection layer. It is found that the ultimate temperature of the joint is affected by the load ratio while fire-resistant duration is relevant to the heating rate, both of which change due to the damage induced by the cyclic loading.

• Fashion & Textile Research Journal
• /
• v.24 no.6
• /
• pp.812-824
• /
• 2022

This study proposes to develop a 3D printed re-entrant(RE) strip by shape memory thermoplastic polyurethane that can be deformed and recovered by thermal stimulation. The most suitable 3D printing infill density condition and temperature condition during shape recovery for mechanical behavior were confirmed. As the poisson's ratio indicated, the higher the recovery temperature, the closer the poisson's ratio to zero and the better the auxetic properties. After recovery testing for five minutes, it appeared that the shape recovery ratio was the highest at 70℃. The temperature range when the shape recovery ratio appeared to be more than 90% was a recovery temperature of more than 50℃ and 60℃ when deformed under a constant load of 100 gf and 300 gf, respectively. This indicated that further deformation occurred after maximum recovery when recovered at a temperature of 80℃, which is above the glass transition temperature range. As for REstrip by infill density, a shape recovery properties of 100% was superior than 50%. Additionally, as the re-entrant structure exhibited a shape recovery ratio of more than 90%, and exhibited auxetic properties. It was confirmed that the infill density condition of 100% and the temperature condition of 70℃ are suitable for REstrips for applying the actuator.

• Journal of the Korean Geotechnical Society
• /
• v.39 no.11
• /
• pp.53-62
• /
• 2023

The characteristics of unfrozen water content in frozen soils significantly impact the thermal, hydraulic, and mechanical behavior of the ground. A thorough analysis of the unfrozen water content characteristics of the target subsoil material is crucial for evaluating the stability of frozen ground. This study conducted indoor experiments to measure the freezing point and unfrozen water content of sandy soil while considering pore water salinity. Utilizing the experimental data, we introduced a novel empirical model to conveniently estimate the unfrozen water retention curve. Furthermore, the validity of the unfrozen water retention curve was assessed by comparing the experimental data with the results of a simulation model that utilized the proposed empirical model as input data.