• Proceedings of the Korean Society of Precision Engineering Conference
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• 1995.04b
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• pp.314-319
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• 1995

The effect of liquid level on the natural frequencies and mode shapes of a partially liquid-filled circular cylindrical shell with various boundary conditions is investigated by means of a theoretical analysis based upon Fourier series expansion method and a finite element analysis using ANSYS computer program. Two dimensional mode shapes of the liquid-coupled shell structure are obtained by the ANSYS finite element analysis and show that the liquid level affect the nodal point movement. It is found that the variation of normalized naturalfrequencies (natural frequencies of liquid-filled shell/antural frequencies ofempty shell) to the liquid level is depend on the axial mode numbers and circumferential wave numbers. Additionally, it is found that the number of variational steps of normalized natural frequencies is identicial to that of axial nodal points of the mode shape.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2012.10a
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• pp.792-798
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• 2012

This study shows the vibration characteristics of an actuator with six wire-suspensions, used in optical pickups of optical disc drives (ODDs). In this paper, the vibration characteristics of this beam structure is induced mathematically. To obtain vibration modes of focusing direction, the vibration analysis is achieved in lateral and longitudinal directions of the structure. The accuracy of induced vibration characteristics is proved by comparing mode frequencies with a finite element analysis. Finally, it is shown that mode shapes can be modified by changing design parameters in mathematical expressions.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.22 no.11
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• pp.1128-1136
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• 2012

This paper analyzes the vibration characteristics of an optical pickup actuator, which has six wire-suspensions and is used in optical disc drives(ODDs). The vibration characteristics of the actuator is mathematically described by analyzing its beam configuration and motion condition confined to lateral and longitudinal directions of the beams. The accuracy of the vibration characteristics is proved by comparing mode frequencies with a finite element analysis. Finally, it is shown that mode frequencies and shapes can be modified by changing design parameters in mathematical expressions.

• Structural Engineering and Mechanics
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• v.66 no.6
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• pp.737-748
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• 2018

The current study presents a new technique in the framework of the nonlocal elasticity theory for a comprehensive buckling analysis of Euler-Bernoulli nano-beams made up of bidirectional functionally graded material (BDFGM). The mechanical properties are considered by exponential and arbitrary variations for axial and transverse directions, respectively. The various circumstances including tapering, resting on two-parameter elastic foundation, step-wise or continuous variations of axial loading, various shapes of sections with various distribution laws of mechanical properties and various boundary conditions like the multi-span beams are taken into account. As far as we know, for the first time in the current work, the buckling analyses of BDFGM nano-beams are carried out under mentioned circumstances. The critical buckling loads and mode shapes are calculated by using energy method and a new technique based on calculus of variations and collocation method. Fast convergence and excellent agreement with the known data in literature, wherever possible, presents the efficiency of proposed technique. The effects of boundary conditions, material and taper constants, foundation moduli, variable axial compression and small-scale of nano-beam on the buckling loads and mode shapes are investigated. Moreover the analytical solutions, for the simpler cases are provided in appendices.

• Smart Structures and Systems
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• v.5 no.3
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• pp.291-316
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• 2009

Damage detection using structural classical deflection flexibility has received considerable attention due to the unique features of the flexibility in the last two decades. However, for relatively complex structures, most methods based on classical deflection flexibility fail to locate damage sites to the exact members. In this study, for structures whose members are dominated by axial forces, such as truss structures, a more feasible flexibility for damage detection is proposed, which is called the Axial Strain (AS) flexibility. It is synthesized from measured modal frequencies and axial strain mode shapes which are expressed in terms of translational mode shapes. A damage indicator based on AS flexibility is proposed. In addition, how to integrate the AS flexibility into the Damage Location Vector (DLV) approach (Bernal and Gunes 2004) to improve its performance of damage localization is presented. The methods based on AS flexbility localize multiple damages to the exact members and they are suitable for the cases where the baseline data of the intact structure is not available. The proposed methods are demonstrated by numerical simulations of a 14-bay planar truss and a five-story steel frame and experiments on a five-story steel frame.

• Journal of Mechanical Science and Technology
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• v.16 no.1
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• pp.32-38
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• 2002

The purpose of this study is to analyze the collapse characteristics of widely used spot welded section members (hat and double hat section, nembers of vehicles) which possess the greatest energy absorbing capacity In an axial impact collapse. This study also suggests how the collapse load and deformation mode are obtained under impact. In the program system presented in this study, an explicit finite element code, LS-DY7A3D, is adopted for simulating complicated collapse behavior of the hat and double hat shaped section members with respect to section dimensions and spot weld pitches. Comparing the results with experiments, the simulation has been verified under a velocity of 7.19 m/sec (impact energy of 1034J)

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.12 no.3
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• pp.181-186
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• 2002

A seismic analysis is one of crucial design procedures of an axial blower used in nuclear power Plants. The blower should be operated even in ar emergency such as an earthquake. The blower should be designed in order to stand against an earthquake. For the seismic analysis, Ive perform the modal analysis and then evaluate the required response spectrum (PRS) from the given floor response spectrum (FRS). A finite element model of the blower is established by using a commercial FEM code of ANSYS. After the finite element modeling. the natural frequencies. the mode shapes and the participation factors are obtained from the modal analysis. The PRS is acquired by a numerical approach on the basis of the principle of mode superposition. We verify the structura safety of the axial blower and confirm the validity of the present seismic analysis results.

• Structural Engineering and Mechanics
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• v.35 no.6
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• pp.717-733
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• 2010

The dynamic stiffness matrix is formulated for an axially loaded slender double-beam element in which both beams are homogeneous, prismatic and of the same length by directly solving the governing differential equations of motion of the double-beam element. The Bernoulli-Euler beam theory is used to define the dynamic behaviors of the beams and the effects of the mass of springs and axial force are taken into account in the formulation. The dynamic stiffness method is used for calculation of the exact natural frequencies and mode shapes of the double-beam systems. Numerical results are given for a particular example of axially loaded double-beam system under a variety of boundary conditions, and the exact numerical solutions are shown for the natural frequencies and normal mode shapes. The effects of the axial force and boundary conditions are extensively discussed.

• 한국연소학회:학술대회논문집
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• 2003.05a
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• pp.167-171
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• 2003

Acoustic characteristics of baffled combustion chamber to elucidate suppressing effect of baffle on combustion instability are numerically investigated by linear acoustic analysis. A hub-blade baffle of 5 blades is selected as a candidate one and five variants of baffles with various configuration are designed. Resonant-frequency shift and damping factor are analyzed quantitatively as damping parameters. When the hub is located radially at the pressure node, the decrease of resonant frequency and increase of damping factor in 1R mode are dominant. But sub-1T mode is formed within hub, therefore, there would be a possibility of initiating 1T mode in unbaffled region, which would occur another problem. For smaller hub size, four kinds of axial baffle length is selected. As the axial baffle length increases, resonant frequency shift and increase of damping factor of transverse acoustic modes is obtained. Especially, two close acoustic modes such as 1L and 1T could be overlapped for a certain axial length, resulting in extreme increase of damping factor. The present study based on linear acoustic analysis is expected to be a useful confirming tool to predict acoustic field and design a passive control devices such as baffle and acoustic cavity.

• Steel and Composite Structures
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• v.32 no.3
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• pp.411-422
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• 2019

Six shear-critical square tubed steel reinforced concrete (TSRC) columns using the high-strength concrete ($f_{cu,150}=86.6MPa$) were tested under constant axial and lateral cyclic loads. The height-to-depth ratio of the short column specimens was specified as 2.6, and the axial load ratio and the number of shear studs on the steel shape were considered as two main parameters. The shear failure mode of short square TSRC columns was observed from the test. The steel tube with diagonal stiffener plates provided effective confinement to the concrete core, while welding shear studs on the steel section appeared not significantly enhancing the seismic behavior of short square TRSC columns. Specimens with higher axial load ratio showed higher lateral stiffness and shear strength but worse ductility. A modified ACI design method is proposed to calculate the nominal shear strength, which agrees well with the test database containing ten short square TSRC columns with shear failure mode from this study and other related literature.