• Transactions of the Korean Society of Mechanical Engineers B
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• v.38 no.1
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• pp.89-94
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• 2014

The high Young's modulus and tensile strength of carbon nanotubes has attracted great attention from the research community given the potential for developing super-strong, super-stiff composites with carbon nanotube reinforcements. Over the decades, the strength and stiffness of carbon nanotube-reinforced polymer nanocomposites have been researched extensively. However, unfortunately, such strong composite materials have not been developed yet. It has been reported that the efficiency of load transfer in such systems is critically dependent on the quality of adhesion between the nanotubes and the polymer chains. In addition, the waviness and orientation of the nanotubes embedded in a matrix reduce the reinforcement effectiveness. In this study, we carried out performed micromechanics-based numerical modeling and analysis by varying the geometry of carbon nanotubes including their aspect ratio, orientation, and waviness. The results of this analysis allow for a better understanding of the load transfer capabilities of carbon nanotube-reinforced polymer composites.

• Geomechanics and Engineering
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• v.12 no.4
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• pp.689-705
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• 2017

The present study deals with the Pressure-settlement behavior of square and rectangular skirted footing resting on sand and subjected to a vertical load through a laboratory experimental study. A series of load tests were conducted in the model test tank to evaluate the improvement in pressure-settlement behavior and bearing capacity of square and rectangular model footings with and without structural skirt. The footing of width 5 cm and 6 cm and length/width ratio of 1 and 2 was used. The relative density of sand was maintained at 30%, 50%, 70%, and 87% respectively. The depth of skirt was varied from 0.25 B to 1.0 B. All the tests were carried out using a strain controlled loading frame of 50 kN capacity. The strain rate for all test was kept 0.24 mm/min. The results of present study reveal that, the use of structural skirt improves the bearing capacity of footing significantly. The improvement in bearing capacity was observed almost linearly proportional to the depth of skirt. The improvement in bearing capacity of skirted footings over footing without skirt was observed in the range of 33.3% to 68.5%, 68.9% to 127% and 146.7% to 262% for a skirt depth of 0.25 B, 0.50 B and 1.0 B respectively. The skirted footings were found more effective for sand at relative density of 30% and 50% than at relative density of 70% and 87%. The bearing capacity was found to increase linearly with footing width for footings with and without skirts. This observation was found to be consistent for footings with different skirt depths and for relative density of sand i.e., 30%, 50%, 70%, and 87%. The obtained results from the study for footing with and without skirts were comparable with available solutions from literature.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.37 no.4
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• pp.637-645
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• 2017

Jeju Island is composed of irregular volcanic rock layers formed by several volcanic activities. Since structure such as the offshore wind turbine has to support considerably large over turning moment due to long distance from foundation to load point and relatively large horizontal load. Pile foundations are needed to economically support such structure even in the case of rock layer. Therefore, in this study, mechanical performances are estimated by mixing ratio of water, cement, and sand to figure out optimal mixing ration of filling material for pile penetrated to rocky layers, and outcomes of this study are compared and analyzed with results of other researches. In the same conditions, mechanical performances of the mortar (S/(S+C)=20~40%) are better than those of cement paste and soil cement. On the basis of major outcome of this study, appropriate range of mixing and a strengthening model are suggested.

• Journal of the Korea institute for structural maintenance and inspection
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• v.16 no.1
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• pp.44-54
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• 2012

The structural designs of RC flat plates that have no flexural stiffness by boundary beams may be governed not by strength conditions but by serviceabilities. Specially, since over-loading and tensile cracking in early-aged slabs significantly increase the immediate and long-term deflections of a flat plate system, a construction sequence and its impact on the slab deflections may be decisive factors in designs of flat plate systems. In this study, the procedure of calculating slab deflections with considering construction sequences, concrete cracking, and long-term effects is proposed. Using the proposed method, the parametric study for deflections of flat plates is performed. With various conditions for slab construction cycle, the number of shored floors, tensile or compressive reinforcement ratio, compressive strength of concrete, construction live load, and slab thickness, the immediate deflection during construction and long-term deflections after completion are analyzed. The calculated results are compared with the serviceability limits offered by the structural design code.

• Journal of Genetic Medicine
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• v.3 no.1
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• pp.29-32
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• 1999

The Apolipoprotein E type 4 allele (ApoE ${\varepsilon}4$) is genetically associated with the common late onset familial and sporadic forms of Alzheimer's disease. The BchE-k variant, which is the common variant of the BchE gene, has been reported to show allelic association with AD in subjects who are also carriers of the ${\varepsilon}4$ allele of the ApoE, especially in subjects over the age of 75. This study was performed to evaluate the distribution of the ApoE and the BchE genotypes in the healthy and AD groups and to evaluate the synergy between the BchE-k variant and the ApoE ${\varepsilon}4$ in AD. The ApoE and the BchE genotypes were determined in DNA samples from 610 healthy people and 60 LOAD patients by using ARMS by standard agarose gel electrophoresis. The effect of the ApoE ${\varepsilon}4$ was closely related to AD(p<0.05). A comparison between the AD patients and the healthy individuals, both with the ${\varepsilon}4$ allele, indicated an interaction between the BchE-k and the ApoE ${\varepsilon}4$(p<0.05). The association of the BchE-k with AD was limited to carriers of the ApoE ${\varepsilon}4$ allele, among whom the presence of the BchE-k gave an odds ratio of AD 3.48 (95% C.I. 1.3-9.2). Therefore, these results suggested that further evidence of an association between the ApoE ${\varepsilon}4$ and LOAD, and the BchE-k acts in synergy with the ApoE ${\varepsilon}4$ as a susceptibility gene for AD.

• KSCE Journal of Civil and Environmental Engineering Research
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• v.29 no.5A
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• pp.447-456
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• 2009

The design comparison and flexural reliability analysis of continuous span composite plate girder bridges are performed. The girders are designed by the methods of allowable stress design (ASD) and load and resistance factor design (LRFD). For the LRFD design, the design specification under development mainly by KBRC, based on AASHTO-LRFD specification in case of steel structures, is applied with the newly proposed design live load which has been developed by analyzing domestic traffic statistics from highways and local roads. For the ASD based design, the current KHBDC code with DB-24 and DL-24 live loads is used. The longest span length for the 3-span continuous bridges with span arrangement ratio of 4:5:4 is assumed to be from 30 m to 80 m. The amount of steel, performance ratios, and governing design factors for the sections designed by the ASD and LRFD methods are compared. In the reliability analysis for the flexural failure of the sections designed by two methods, the statistical properties on flexural resistance based on the yield strength statistics for over 16,000 domestic structural steel samples are applied.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.21 no.3
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• pp.569-575
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• 2020

Recently, research on renewable energy technologies has come into the spotlight due to rising concerns over the depletion of fossil fuels and greenhouse gas emissions. Demand for portable electronic and wearable devices is increasing, and electronic devices are becoming smaller. Energy harvesting is a technology for overcoming limitations such as battery size and usage time. In this paper, the V-I characteristic curve and internal resistance of thermal electric devices were analyzed, and MPPT control methods were compared. The Perturbation and Observation (P&O) control method is economically inefficient because two sensors are required to measure the voltage and current of a Thermoelectric Generator(TEG). Therefore, this paper proposes a new MPPT control method that tracks MPP using only one sensor for the regulation of the output voltage. The proposed MPPT control method uses the relationship between the output voltage of the load and the duty ratio. Control is done by periodically sampling the output voltage of the DC-DC converter to increase or decrease the duty ratio to find the optimal duty ratio and maintain the MPP. A DC-DC converter was designed using a cascaded boost-buck converter, which has a two-switch topology. The proposed MPPT control method was verified by simulations using PSIM, and the results show that a voltage, current, and power of V=4.2 V, I=2.5 A, and P=10.5 W were obtained at the MPP from the V-I characteristic curve of the TEG.

• Journal of the Korea institute for structural maintenance and inspection
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• v.24 no.4
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• pp.10-17
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• 2020

The recent earthquake in Korea caused large and small damages to many school building. School building is an important building that is used as a shelter in the event of disaster. Among the seismic retrofit methods, the internal steel braced frame type method is used for its relatively easy construction and excellent performance. In this study, the maximum shear force and displacement were compared and examined by applying the brace frame to existing concrete school buildings. As a result, we verified the adequacy of the analytical model and compared and examined the effect of brace-height ratio on the span of the existing school buildings. The adequacy of the maximum shear force and displacement relationship can be confirmed in the model with a length of 0.3. In addition, seismic frame was applied to the actual non-seismic reinforced concrete school building, and the seismic performance was evaluated by nonlinear static analysis(Push-over analysis) according to the ratio of brace-height. As a result, the increase of the brace-height according to the brace-height ratio has the effect of increasing the maximum shear force and maximum load at the performance point. But the collapse of the braced frame due to the increase in the lateral stiffness occurred, indicating that seismic retrofit according to the proper brace-height is necessary. Therefore, in the seismic retrofit design of brace frame of existing school building, it is necessary to select the proper brace-height after retrofit analysis according to the brace-height ratio.

• Proceedings of the KIEE Conference
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• 2004.07c
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• pp.1909-1911
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• 2004

It is caused that insulation paper, which had got a lot of thermal stress by over-load after installation, should have been deteriorated in electrical and mechanical characteristics. Beside, insulation material is decreased the insulating property and accelerated aging of them in case of dielectric loss when transformers are manufactured with some moisture or transformers would have been them because of moisture-permeation, Therefore, in this study we experienced the influence of moisture content in case of the thermal aged insulation paper. we have measured tan ${\delta}$ and breakdown voltage in the ratio of paper' moisture content before the aging and then taken the same tests again after insulation paper thermally accelerating-aged. There is a purpose to gain data for a life-design and to establish aging mechanism in order to continuously study life expectancy of the insulation paper.

• International Journal of Naval Architecture and Ocean Engineering
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• v.6 no.2
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• pp.257-268
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• 2014

In this study, flow-driven rotor simulations with a given load are conducted to analyze the operational characteristics of a vertical-axis Darrieus turbine, specifically its self-starting capability and fluctuations in its torque as well as the RPM. These characteristics are typically observed in experiments, though they cannot be acquired in simulations with a given tip speed ratio (TSR). First, it is shown that a flow-driven rotor simulation with a two-dimensional (2D) turbine model obtains power coefficients with curves similar to those obtained in a simulation with a given TSR. 3D flow-driven rotor simulations with an optimal geometry then show that a helical-bladed turbine has the following prominent advantages over a straight-bladed turbine of the same size: an improvement of its self-starting capabilities and reduced fluctuations in its torque and RPM curves as well as an increase in its power coefficient from 33% to 42%. Therefore, it is clear that a flow-driven rotor simulation provides more information for the design of a Darrieus turbine than a simulation with a given TSR before experiments.