• Ocean and Polar Research
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• 제42권3호
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• pp.249-261
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• 2020

This study details grain-size distributions (GSDs) of carbonate and biogenic opal fractions of the sediments retrieved from the South Korea Plateau in the East Sea and draws paleocanographic implications from them. The opal-fraction GSDs show fine modes of 10.3 ㎛ and coarse modes of 102.5 ㎛ on average. The fine-mode grains of opal fractions mainly consist of small diatoms and radiolarians including their broken frustules, while the coarse-mode grains are mostly comprised of large warm-water diatoms and radiolarians. Significant positive correlation between opal contents and abundances of the coarse-mode GSDs in the total GSDs suggests that the abundances of the coarse-mode GSDs were controlled by the increased surface productivity of warm-water diatoms during interglacial stages. The carbonate-fraction GSDs show fine modes of 2.4 ㎛ and coarse modes of 99.1 ㎛ on average. The fine-mode grains mainly consist of coccolithophores, while the coarse-mode grains are mostly comprised of intact or broken planktonic foraminifera. The abundances of coarse-mode and fine-mode GSDs were not correlated with carbonate contents, suggesting a complex control exerted by both the degree of carbonate dissolution and the productivity of coccolithophores on the carbonate-fraction GSDs.

• 한국원자력학회:학술대회논문집
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• 한국원자력학회 1997년도 춘계학술발표회논문집(1)
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• pp.458-463
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• 1997

A transient natural circulation behavior during a LOCA at hot-standby operation is evaluated for YGN Units 3/4. The plant initial condition is determined within the EOP limitation as suitable to hot-standby mode and the transient scenario is prepared as relevant to evaluation of transient natural circulation. A 0.4% cold leg break with loss of off-site power is calculated with RELAP5/MOD3.2, whose predictability has been verified for SBLOCA natural circulation test, S-NC-8B. Through one hour transient analysis, it is found that the plant has its own decay heat removal capability by natural circulation following a LOCA, at hot-standby mode. Additional calculation is performed to investigate an effect of HPSI flow on natural circulation.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2002년도 추계학술대회논문집
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• pp.988-993
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• 2002

The AVT under traffic-induced vibrations was carried out on Namhae suspension bridge in Korea. Mode shapes as well as natural frequencies up to the 15th mode were acquired exactly, and the effect of traffic mass and temperature on measured natural frequencies was investigated. The results from the AVT are compared with those from forced vibration test(FVT) and FE analysis. In the case of long span suspension bridges such as Namhae bridge which has relatively large mass, the results shows that the measured natural frequencies are not affected by vehicle mass. From the results of long-term variation of natural frequencies due to temperature change, it can be said that temperature effect may be predominant to structural demage effect. Therefore, if damage detection methods based on dynamic characteristics of bridges are to be used, the variation should be taken into consideration.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2008년도 춘계학술대회논문집
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• pp.653-658
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• 2008

LCVA has an advantage that its natural frequency can be easily controlled by changing the area ratio of the vertical column and horizontal part. The previous studies investigated the dynamic characteristics of the LCVA under harmonic load. This study experimentally obtained the first and second mode natural frequencies of the LCVA from shaking table tests using white noise and compared the values with the ones by previous study. Test results show that the measured first mode natural frequency of the LCVA has a different value compared with calculated one. The effective length($L_e$) was revised using by power equation. In the Case01 to 19, the standard deviation($s_r$) is 4.7292 and the coefficient of correlation(r) is 0.9856. In the Case21 to 61, the standard deviation ($s_r$) is 14.2143 and the coefficient of correlation(r) is 0.9935. The second mode frequency increases with the increasing area ratio, which is due to the sloshing motion effect resulting from the large area of the vertical column.

• International Journal of Naval Architecture and Ocean Engineering
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• 제5권3호
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• pp.478-491
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• 2013

Natural vibration analysis of plates with openings of different shape represents an important issue in naval architecture and ocean engineering applications. In this paper, a procedure for vibration analysis of plates with openings and arbitrary edge constraints is presented. It is based on the assumed mode method, where natural frequencies and modes are determined by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange's equations of motion. The presented solution represents an extension of a procedure for natural vibration analysis of rectangular plates without openings, which has been recently presented in the literature. The effect of an opening is taken into account in an intuitive way, i.e. by subtracting its energy from the total plate energy without opening. Illustrative numerical examples include dynamic analysis of rectangular plates with rectangular, elliptic, circular as well as oval openings with various plate thicknesses and different combinations of boundary conditions. The results are compared with those obtained by the finite element method (FEM) as well as those available in the relevant literature, and very good agreement is achieved.

• Smart Structures and Systems
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• 제9권4호
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• pp.335-353
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• 2012

This study suggests a simple two-step method for structural vibration-based health monitoring for beam-like structures which only utilizes mode shape curvature and few natural frequencies of the structures in order to detect and localize cracks. The method is firstly based on the application of wavelet transform to detect crack locations from mode shape curvature. Then particle swarm optimization is applied to evaluate crack depth. As the Rayleigh quotient is introduced to estimate natural frequencies of cracked beams, the relationship of natural frequencies and crack depths can be easily obtained with only a simple formula. The method is demonstrated and validated numerically, using the numerical examples (cantilever beam and simply supported shaft) in the literature, and experimentally for a cantilever beam. Our results show that mode shape curvature and few estimated natural frequencies can be used to detect crack locations and depths precisely even under a certain level of noise. The method can be extended for health monitoring of other more complicated structures.

• 한국소음진동공학회논문집
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• 제19권2호
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• pp.119-126
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• 2009

LCVA has an advantage that its natural frequency can be easily controlled by changing the area ratio of the vertical column and horizontal part. The previous studies investigated the dynamic characteristics of the LCVA under harmonic load. This study experimentally obtained the first and second mode natural frequencies of the LCVA from shaking table tests using white noise and compared the values with the ones by previous study. Test results show that the measured first mode natural frequency of the LCVA has a different value compared with calculated one. The effective length($L_e$) was revised using by power equation. In the case01 to 19, the standard deviation($S_r$) is 4.7292 and the coefficient of correlation(r) is 0.9856. In the case21 to 61, the standard deviation($S_r$) is 14.2143 and the coefficient of correlation(r) is 0.9935. The second mode frequency increases with the increasing area ratio, which is due to the sloshing motion effect resulting from the large area of the vertical column.

• Coupled systems mechanics
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• 제12권2호
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• pp.127-149
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• 2023

A theoretical method is developed to analyze the free vibration of an elastic annular plate in contact with an ideal liquid. The displacement potential functions of the contained liquid are expressed as a combination of the Bessel functions that satisfy the Laplace equation and the liquid boundary conditions. The compatibility condition along the interface between the annular plate and the contained liquid is taken into account to consider the fluid-structure coupling. The dynamic displacement of the wet annular plate is assumed to be a combination of dry eigenfunctions, allowing for prediction of the natural frequencies using the Rayleigh-Ritz method. The study investigates the effect of radial liquid boundary conditions on the natural frequencies of the wet annular plate, considering four types of liquid bounding: outer container bounded, outer and inner bounded, inner bounded, and radially unbounded. The proposed theoretical method is validated by comparing the predicted wet natural frequencies with those obtained from finite element analysis, showing excellent accuracy. The results indicate that the radial liquid bounding effect on the natural frequencies is negligible for the axisymmetric vibrational mode, but relatively significant for the mode with one nodal diameter (n =1) and no nodal circle (m' = 0). Furthermore, the study reveals that the wet natural frequencies are the largest for the plate with an inner bounded cylinder among the radial liquid boundary cases, regardless of the vibration mode.

• 대한기계학회논문집
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• 제18권8호
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• pp.1899-1909
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• 1994

This work presents the experimental and FEM results for the free vibration of cantilevered, symmetrically and antisymmetrically laminated composite rectangular plates. The natural frequencies, mode shapes and contour plots of a number of CFRP, GFRP, DFRP-Aluminum, GFRP-Aluminum and DFRP-GFRP hybrid composite plates are experimentally obtained. Determination of Young's modulus and test procedures are described. The natural frequencies are determined for a wide range of parameters : e.g. , composite material constants, fiber angles and stacking sequences. Natural frequency and nondimensional frequency parameter results are compared with the finite element analysis and existing literatures. Agreement between experimental and calculated frequencies is excellent. The effects of varing the parameters upon the free vibration frequencies and mode shapes are discussed.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.1455-1458
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• 2007

Vibration characteristics of concrete slabs were investigated using a 1:10 scale model and finite element method. A 1:10 scale model of a test building with 150 and 200mm slab thicknesses was made of acrylic materials. Modal test was conducted to investigate mode shape and modal frequencies. Results show that the mode shapes of two slabs with different thickness are similar each other, whereas natural frequency is different. Through modal analysis using FEM, it was revealed that both mode shapes and natural frequencies calculated from the FEM model are similar to those of the scale model measurement. It was also found that natural frequencies increased with increment of the slab thickness.