• Progress in Superconductivity and Cryogenics
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• v.4 no.1
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• pp.45-59
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• 2002

Evaluation of the mechanical properties of Bi-2223/Ag HTS tapes was carried out by the tension and bending tests. Most of the Bi-2223/Ag tapes retained critical current up to 10 kgf/mm$_2$ axial tension stress, and 0.2% tension strain at room temperature. Applied tension strain exceeding 0.3% in superconducting tapes at 77 K leaded to rapid degradation of the critical current. It was observed that the more filaments, the better axial tension property at 77 K, self-field The influence of bending strain on critical current degradation was revealed to be less sensitive for Bi-2223/Ag HTS tapes with a more number of filaments and higher silver ratio.

• Structural Engineering and Mechanics
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• v.76 no.1
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• pp.27-56
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• 2020

In this paper, the deflection and buckling analyses of porous nano-composite piezoelectric plate reinforced by carbon nanotube (CNT) are studied. The equations of equilibrium using energy method are derived from principle of minimum total potential energy. In the research, the non-local strain gradient theory is employed to consider size dependent effect for porous nanocomposite piezoelectric plate. The effects of material length scale parameter, Eringen's nonlocal parameter, porosity coefficient and aspect ratio on the deflection and critical buckling load are investigated. The results indicate that the effect of porosity coefficient on the increase of the deflection and critical buckling load is greatly higher than the other parameters effect, and size effect including nonlocal parameter and the material length scale parameter have a lower effect on the deflection increase with respect to the porosity coefficient, respectively and vice versa for critical buckling load. Porous nanocomposites are used in various engineering fields such as aerospace, medical industries and water refinery.

• Transactions of the Korean Society of Mechanical Engineers B
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• v.25 no.4
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• pp.546-553
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• 2001

A Parametric study is numerically carried out for flow fields in a two-dimensional plane channel with thin obstacles(“baffles and blocks”) mounted symmetrically in the vertical direction and periodically in the streamwise direction. The aim of this investigation is to understand how various geometric conditions influence the critical characteristics and pressure drop. A range of BR(the ratio of baffle interval to channel height) between 1 and 5 is considered. Especially when BR is equal to 3, for which the critical Reynolds number turned out to be minimal, we add blocks in the center region in order to study their destabilizing effects on the flows. It is revealed that the critical Reynolds number is further decreased by the presence of the block.

• Proceedings of the KSME Conference
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• 2000.04b
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• pp.783-788
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• 2000

Flow fields in two-dimensional plane channels with thin obstacles("baffles and blocks") mounted symmetrically in the vertical direction and periodically in the streamwise direction are studied numerically to understand how various geometric conditions influence the critical Reynolds number and pressure drop. Changing BR(the ratio of channel to baffle interval) from 1:1 to 1.5, we computed the critical Reynolds number and pressure drop. Especially when BR is 1:3, at which the critical Reynolds number turned out to be minimal, we added blocks in the geometry in order to study their destabiliting effects on the flows.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
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• 1996.05a
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• pp.198-201
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• 1996

In order to investigate control factors to critical current density, Ag sheathed Bi2223 superconducting tapes were fabricated using PIT process. Optimizing the reduction ratio of rolling, critical current density 7f rolled Bi2223 tape could be improved with the value of 15,000 A/$\textrm{cm}^2$(77 K, zero field). The correlation between J$\_$c/ and work inhomogeneity was revealed as a dependence of COV of measured oxide layer thickness.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.12
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• pp.1161-1169
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• 2007

In this paper, the dynamic stability of a rotating cantilever pipe conveying fluid with a crack is investigated by the numerical method. That is, the influence of the rotating angular velocity, mass ratio and crack severity on the critical flow velocity for flutter instability of system are studied. The equations of motion of rotating cantilever pipe are derived by using extended Hamilton's principle. The crack section of pipe is represented by a local flexibility matrix connecting two undamaged pipe segments. The crack is assumed to be in the first mode of fracture and always opened during the vibrations. Generally, the critical flow velocity for flutter is proportional to the rotating angular velocity of a pipe. Also, the critical flow velocity and stability maps of the rotating pipe system for the variation each parameter are obtained.

• Tribology and Lubricants
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• v.15 no.4
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• pp.328-334
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• 1999

Acoustic emission (AE) sensor was used to evaluate the wear-life of CrN-coated steel disks with 1 $\mu\textrm{m}$ and 4 $\mu\textrm{m}$ coating thickness. The relationship between Af and friction signal from scratch test and sliding test was investigated. The first spatting of CrN film was detected by AR signals in the early stage of coating failures, and overall failures by friction signals. Therefore, the conservative design for coating-life should be done using the results of AE signals. Using the percent contact load, the ratio of sliding normal load to the critical scratch load and the number of cycles to failure was measured to predict the wear-life of CrN film. On the wear-life dia-gram the percent contact loads and the number of cycles to failure showed a good linear relationship on the log coordinate. As the load percentage was decreased, the diagram showed that the wear-limits, at which the coated steels survived more than 35,000 cycles, were about 4∼5% of the critical scratch loads.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.10
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• pp.976-982
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• 2007

In this paper the vibration system is consisted of a rotating cantilever pipe conveying fluid and tip mass. The equation of motion is derived by using the Lagrange's equation. The system of pipe conveying fluid becomes unstable by flutter. Therefore, the influence of a rotating angular velocity, mass ratio, the velocity of fluid flow and tip mass on the stability of a cantilever pipe by the numerical method are studied. The critical flow velocity for flutter is proportional to the angular velocity and tip mass of the cantilever pipe. Also, the critical flow velocity and stability maps of the pipe system are obtained by changing the mass ratios.

• Food Science and Biotechnology
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• v.16 no.6
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• pp.1069-1071
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• 2007

The frequency independent critical concentration (Cc) of xanthan and carob (X/C) mixed gel was determined based on the Winter-Chambon's theory. X/C mixed (X/C=1:1 ratio) gels were prepared from 0.1 to 1% of concentration. The linear viscoelastic properties, i.e., storage and loss modulus, of X/C mixed gel at $20^{\circ}C$ were measured by frequency sweep tests. The frequency independence of tangent function of phase angle (tan ${\delta}$) of X/C mixed gels was graphically determined from the intersection of the plot of phase angle against concentration at varied frequencies. The intersection (C=0.43%) was considered to be Cc of X/C mixed gel.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 2007.04a
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• pp.247-250
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• 2007

In korean traditional wooden structure, to know the critical pass of roof load transmission is very important. to know the critical pass of roof load transmission and to find the role of each dori members, used loading block and load cell. The total weight of loading blocks was 5,8880 N and the number of loading blocks were 16, The experimental fran1e has 1/2 scale. From middle-dori to outside-dori, the linearity of line can't guarantee. So, the distribution of roof load in dori is effected by the initial state of dori. In this research, to remove the effect of initial state, initial deformation was allowed by initial setting.