• Bulletin of the Society of Naval Architects of Korea
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• v.27 no.4
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• pp.3-14
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• 1990

For a moored body on the sea surface, incident waves with narrow-banded spectra excite the body oscillations of short and long periods. Since the period of slow oscillations can be as long as the natural period of the moored body in horizontal modes, resonance can occur and resulting large motions may cause significant strains in mooring cables. By using the perturbation method of multiple scales, the large slow motion can be analyzed without solving any second-order potentials explicitly. To the leading order, the flows associated with the fast and slow motions interact only parametrically and thus they can be studied separately. It is found that the slow motion strongly depends on the mooring stiffness. In particular, if the moring stiffness is considerably weak compared to the body inertia, the slow motion is highly amplified near resonance. It is also shown that the slow motion is associated with the generation of long waves.

• Journal of the Korean Society for Aeronautical & Space Sciences
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• v.31 no.1
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• pp.8-17
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• 2003

The butt lap joint structures which are usually designed by the concept of slow crack growth damage tolerance, show frequently the behaviors of multiple site fatigue crack growth around the fastener hole edges due to the fretting between the two jointed parts. In this paper, experimental tests of fatigue crack growth have been performed of a bolted butt lap joint structure having an initial corner crack at the fastener hole edge, with different fretting conditions under a flight load spectrum. The obtained test results were reviewed to investigate the effects of fretting fatigue cracks on the damage tolerance crack growth life. Computations of corner crack growth were also carried out using an existed model to compare with test results.

• KEPCO Journal on Electric Power and Energy
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• v.5 no.2
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• pp.75-81
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• 2019

In this study 24 power transmission towers were selected by considering various variables such as power transmission capacity, height and structural type to evaluate their seismic performance using the standard design response spectrum recently announced by the government. In addition, the stresses and sectional forces generated by the current design wind loads and revised seismic ones were compared to review the effects on the design of power transmission towers when the government-required seismic standards were raised. The results of seismic performance evaluation for the target power transmission towers showed that they had seismic capacity of 0.31~0.91g, and that they met the level of the earthquake-resistant special grade, which is the 2,400-year earthquake return periods and secured seismic safety. Further, the sectional forces caused by earthquakes in the towers were 33~82.5% of the ones due to wind loads, and it was also confirmed that the design wind loads were more dominant than design earthquake ones under the elevated seismic standards.

• Journal of the Korean Society of Hazard Mitigation
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• v.2 no.1 s.4
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• pp.135-141
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• 2002

Both non-linear damping values of the deep and shallow crustal materials and seismic source parameters are found from the observed near-field seismic ground motions at the South-eastern Korean Peninsula. The non-linear numerical algorithm applied in this study is Levenberg-Marquadet method. All the 25 sets of horizontal ground motions (east-west and north-south components at each seismic station) from 3 events (micro to macro scale) were used for the analysis of damping values and source parameters. The non-linear damping values of the deep and shallow crustal materials were found to be more similar to those of the region of the Western United States. The seismic source parameters found from this study also showed that the resultant stress drop values are relatively low compared to those of the Western United Sates. Consequently, comparisons of the various seismic parameters from this study and those of the United States Seismo-tectonic data suggest that the seismo-tectonic characteristics of the South eastern Korean Peninsula is more similar to those of the Western U.S.

• Journal of Korean Ophthalmic Optics Society
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• v.5 no.1
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• pp.19-30
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• 2000

LaF, KzFS1, LBO glass were manufactured successfully by using platinum crucible in LaF and using clay crucible in the KzFS1 and LBO. There was optically transparent and the refractive indexes were measured by minum deviation method of prism. LaF, KzFS1, LBO show that the refrective indexes are $n_d$ = 1.770 in LaF, $n_d$ = 1.603 in KzFS1, $n_d$ = 1.560 in LBO. The transmittance were obtained that LaF has 85%, and KzFS1 has 83% and LBO has 89% in visible range. These glasses have no any absorption spectrum under visible range. Therefore it has no any color.

• Journal of the Korean Society for Marine Environment & Energy
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• v.18 no.3
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• pp.135-142
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• 2015

Floating offshore structures should be designed by considering the most extreme environmental loadings which may be encountered in their design life. The most severe loading on a wave-offshore wind hybrid power generation system is wave loads. The principal parameters of wave loads are wave length, wave height and wave direction. The wave loads have different effects on the structural behavior characteristic depending on the combination of wave parameters. Therefore, the process of investigation for critical loads based on the individual wave loading parameter is need. Namely, the equivalent design wave should be derived by finding the wave condition which generates the maximum stress in entire wave conditions. Through a series of analysis, an equivalent regular wave height can be obtained which generates the same amount of the hydrodynamic loads as calculated in the response analysis. The aim of this study is the determination of equivalent design wave regarding to characteristic global hydrodynamic responses for wave-offshore wind hybrid power generation system. It will be utilized in the global structural response analysis subjected to selected design waves and this study also includes an application of global structural analysis.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.27 no.3
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• pp.199-206
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• 2014

In this paper, a scheme to evaluate the response variability for functionally graded material (FGM) beam with varying sectional area is presented. The randomness is assumed to appear in a spatial domain along the beam axis in the elastic modulus. The functionally graded material categorized as composite materials, however without the drawbacks of delamination and occurrence of cracks due to abrupt change in material properties between layers in the conventional composite materials. The functionally graded material is produced by the gradual solidification through thickness direction, which endows continuous variation of material properties, which makes this material performs in a smooth way. However, due to difficulties in tailoring the gradients, to have uncertainty in material properties is unavoidable. The elastic modulus at the center section is assumed to be random in the spatial domain along the beam axis. Introducing random variables, defined in terms of stochastic integration, the first and second moments of responses are evaluated. The proposed scheme is verified by using the Monte Carlo simulation based on the random samples generated employing the spectral representation scheme. The response variability as a function of correlation distance, the effects of material and geometrical parameters on the response variability are investigated in detail. The efficiency of the proposed scheme is also addressed by comparing the analysis time of the proposed scheme and MCS.

• Journal of the Society of Cosmetic Scientists of Korea
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• v.44 no.2
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• pp.133-139
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• 2018

Chemically damaged hair is vulnerable to external stimuli in daily life due to the weakened physical properties of the hair strand itself. The purpose of this work was to determine whether chemical conjugation between hair keratin proteins restores tensile strength and thus results inpreventing further deterioration under repeated combing. A model damaged hair tress was produced by a typical perm-process. Then, it was internally crosslinked by the bifunctional crosslinker (3-aminopropyl)triethoxysilane (APTES), via both silane coupling and carbodiimide chemistry. Physical properties, including tensile strength, Young's modulus, and plateau stress, were measured to verify the effect of internal crosslinking, and the existence of crosslinking was verified by Fourier transform infrared (FT-IR) spectroscopy. The degrees of hair breakage and split ends were evaluated by repeated combing-drying tests. Physical properties of chemically damaged hair were restored by internal crosslinking. Successful crosslinking of APTES via both silane coupling and carbodiimide chemistry was verified by FT-IR spectra. Prevention of breakage and split ends after repeated combing with heat was observed. Human hair can be weakened by chemical damage including perm-processing, so restoring such properties is a major issue in the hair care industry. This work shows that internal crosslinking of damaged hair via chemical conjugation would be a potent method to restore the healthy hair.

• Journal of the Korean Geotechnical Society
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• v.38 no.12
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• pp.91-101
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• 2022

The 1995 Kobe earthquake caused a massive damage to the Port of Kobe. Therefore, it was pointed out that it was impossible to design port structures for Level II (Mw 6.5) earthquakes with quasi-static analysis and Allowable Stress Design methods. In Japan and the United States, where earthquakes are frequent, the most advanced design standards for port facilities are introduced and applied, and the existing seismic design standards have been converted to performance-based design. Since 1999, the Korean Port Seismic Design Act has established a definition of necessary facilities and seismic grades through research on facilities that require seismic design and their seismic grades. It has also established a performance-based seismic design method based on experimental verification. In the performance-based seismic design method of the breakwater proposed in this study, the acceleration time history on the surface of the original ground was subjected to a fast Fourier transform, followed by a filter processing that corrected the frequency characteristics corresponding to the maximum allowable displacement with respect to performance level of the breakwater and the filtered spectrum. The horizontal seismic coefficient for the equivalent static analysis considering the displacement was calculated by inversely transforming (i.e., subjected to an inverse fast Fourier transform) into the acceleration time history and obtaining the maximum acceleration value. In addition, experiments and numerical analysis were performed to verify the performance-based seismic design method of breakwaters suitable for domestic earthquake levels.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.37 no.4
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• pp.251-258
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• 2024

This study investigated the effect of bearing aging on the seismic response of a three-span continuous concrete girder bridge with pot bearings installed. The pot bearings were modeled as elastic springs in the longitudinal, transverse, and vertical directions of the bridge to reflect the stiffness of fixed and movable supports. The effect of bearing aging on the seismic response of the bridge was examined by considering two factors: a decrease in the horizontal stiffness of the fixed bearings and an increase in the horizontal stiffness of the movable bearings. The finite element model of the three-span continuous girder bridge was validated by comparing its numerical natural frequencies with the designed natural frequencies. Using artificial ground motions that conform to the design response spectrum specified by the KDS bridge seismic design code, the seismic responses of the bridge's girders and bearings were calculated, considering the bearing stiffness variation due to aging. The results of a numerical analysis revealed that a decrease in the horizontal stiffness of the fixed bearings led to an increase in the absolute maximum relative displacement of the bearings during an earthquake. This increases the risk of the mortar block that supports the bearing cracking and the anchor bolt breaking. However, an increase in the horizontal stiffness of the movable bearings due to aging decreased the absolute maximum shear on the fixed bearings. Despite the shear reduction in the fixed bearings, the aging of the pot bearings change could cause additional tensile bending stress in the girder section above the free bearings, which could lead to unexpected structural damage to the continuous bridge during an earthquake.