• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11b
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• pp.810-815
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• 2002

Vibration analysis of rotating blade is the main purpose of this study. In the present work, general formulation is proposed to analyze the rotating shell-type structures including the effect of centrifugal force, Coriolis acceleration and initial twist. Furthermore, simplified equations are derived for the case of an open circular cylindrical shell. Based on the concept of degenerated shell element with the Reissner-Mindlin's assumptions, the finite element method is adopted for solving the governing equations. In addition, it is investigated the effect of thermal load on the vibration characteristics of pretwisted blade. Numerical results are summarized for the various parameters such as rotating speed, angle of pretwist and stacking sequence of a composite blade. Also, present results are compared with the previous works and experimental data.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.19 no.3
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• pp.260-266
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• 2006

In this paper, We coupled fluid balance and director balance equation from Ericksen-Leslie's continuum theory and observed the motion of Liquid Crystal molecular. We simulated flow velocity and director distribution in which flow effect is considered in switching on and switching off state. We interpreted the dynamic response characteristic caused by the flow. As the result of the simulation, We could see the flow effect. In the case of Twisted Nematic(TN) cell, this flow caused abnormal twist temporarily in switching off state. We could prove that this abnormal twist is a direct cause of optical bounce phenomenon known well until now with the result of simulation. In addition, We analyzed the mechanism of the fast response due to flow in the case of Optically Compensated Bend(OCB) cell.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2002.05a
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• pp.127-130
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• 2002

Vibration analysis of rotating blade is the main purpose of the present study. In this study, general formulation is performed for rotating shell structures including the centrifugal force, Coriolis acceleration and initial twist. Furthermore, simplified equations are derived for the case of an open cylindrical shell. Based on the concept of degenerated shell element with the Reisser-Mindlin's assumptions, the finite element method is adopted for solving the problems. In addition, it is investigated the effect of the stacking sequence of the composites on the vibration characteristics of the blade. The results are summarized for the various parameters such as the speed of rotation and pre-twist of the blade. Also, present results are compared with the previous works and experimental data.

• Fibers and Polymers
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• v.3 no.1
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• pp.31-37
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• 2002

Most fibers are irregular, and they are often subjected to combined loading conditions during processing and enduse. In this paper polyester and wool fibers under the combined tensile and torsional loads have been studied for the first time using the finite element method (FEM). The dimensional irregularities of these fibers are simulated with sine waves of different magnitude and frequency. The breaking load and breaking extension of the fibers at different twist or torsion levels are then calculated from the finite element model. The results indicate that twist and level of fiber irregularity have a major impact on the mechanical properties of the fiber and the effect of the frequency of irregularity is relatively small.

• Textile Coloration and Finishing
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• v.20 no.2
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• pp.47-52
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• 2008

Nylon textured yarn is usually manufactured by disk type false twist texturing. Dyeing properties of nylon textured yam have not been studied yet. In this study, dyeing properties of nylon textured yam according to draw ratio out of process parameters were investigated. The fact that microstructure of nylon textured yarn in amorphous region particularly is transformed by draw ratio was confirmed indirectly by measurement of dyeing rate because dyeing rate was affected by the structure of amorphous region. Dyeing rate at draw ratio 1.29 was the lowest because the higher draw ratio increase amorphous orientation and disturb dye diffusion into amorphous region. The microstructure according draw ratio was indirectly confirmed by 5% strength, tenacity, elongation. But difference in K/S value and fastness was insignificant.

• Textile Coloration and Finishing
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• v.8 no.6
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• pp.55-64
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• 1996

The compression properties of the 2 folded yams such as compression linearity, compression resilience, and compression work with various wool/polyester blend ratios and with single and 2-folded yarn twists under various degrees of twisting were studied for analyzing twist characteristics, inter and intra frictional effects. A variation of single and 2-folded yarn twists was analysed in their twist structure. This structural analysis was discussed with various wool/polyester blend ratios and various single and 2-folded yarn twists.

• Proceedings of the Korean Society For Composite Materials Conference
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• 2003.10a
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• pp.95-98
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• 2003

In woven or knitted preforms for composites, the yams are often twisted for avoiding damage due to the contact with the textile machine elements. When the preforms of twisted yams are used in carbon/carbon composites, the thermal conductivity of the composites varies depending upon the degree of the yarn twist. This paper presents a thermal conductivity model of spun yarn composites. The thermal-electrical analogy and the averaging technique have been adopted in this analysis. The model prediction has been correlated with experimental results in order to confirm the model predictability. Parametric study has also been conducted to examine the effect of the yam twist on the thermal conductivity of spun yarn composites.

• Transactions of Materials Processing
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• v.12 no.8
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• pp.718-723
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• 2003

Tn order to develop springback control technology for high-strength steel sheets, several studies have been conducted: dome stretching test, stepped s-rail forming and springback measurement, and optimally shaped initial blank design. First, to find out the formability of TRIP60, dome stretching test was performed. Next, the stepped s-rail die, which was designed to form a channel type panel with large twist and wall curl, was manufactured and used to evaluate the effect of controlling forming variables, such as blank holding force and flange amount on the springback. Furthermore, new measurement method of the springback was introduced to define wall curl and twist in geometrically complex panels. Finally, the optimally shaped initial blank was employed to verify one of the best ways to control the springback in channel type. high-strength sheet panels.

• 한국초전도학회:학술대회논문집
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• v.10
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• pp.221-225
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• 2000

The effect of twisting on the microstructural evolution and critical current of BSCCO superconductor tape has been evaluated. Twisting pitches of the tapes are in the range of 8-70 mm and uniformly deformed. The critical current of twisted tape was dependent on the twist pitch. Specifically, it was observed that the critical current decreased with decreasing twist pitch, and only 50% of critical current was retained when the tape was twisted to a pitch of 8 mm. This reduction of the critical current may be related to the interface irregularity, smaller grain size, worse texture and the presence of cracks due to the induced strain during the twisting processing.

• Journal of the Korean Ceramic Society
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• v.32 no.10
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• pp.1117-1122
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• 1995

The effect of grain boundary structure on zigzag migrtion has been studied. Five kinds of a(2110)-m(1010) diffusion couples with different twist angles by 30$^{\circ}$from a [0001] common direction of each plane were prepared. When chromia (Cr2O3) was added to the diffusion couples by a vapor phase, zigzag migration of the grain boundary occurred. The fraction of zigzag migration did not essentially vary with the twist angle, but the magnitude and migration distance of individual migrating segment varied. The variation of CIGM morphology thus appears to result from the change in grain boundary mobility due to microscopic deviation of grain boundary structure out of a macroscopic grain boundary orientation.