• Selected Papers of The Society of Naval Architects of Korea
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• v.2 no.1
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• pp.18-28
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• 1994

In the vibration analysis of submerged or floating bodies such as ships and offshore structures, the coupled system between fluid and structure should be considered using the compatibility conditions on the wetted surface. It is well known that the hydroelastic vibration analysis of structures in contact with fluid can be done by applying the finite element method(FEM) to structures and the boundary element method(BEM) to the fluid domain. However, such an approach is impractical due to the characteristics of the fully coupled added mass matrix of fluid on the entire wetted surface. To overcome this difficulty, an efficient approach based on a reanalysis scheme is proposed in this paper. The proposed method can be applied for cases of higher local modes and beam-like modes for which three-dimensional reduction factors are not known. The three dimensional reduction factors are not needled and thus the restrictions can be removed in the analyses of non-beam like modes or local vibration modes by considering fluid-structure interaction. The validity and calculation efficiency of the proposed method are proved through numerical examples.

• Journal of the Korean Society for Precision Engineering
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• v.17 no.10
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• pp.200-205
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• 2000

This paper presents the vibration characteristics of a rectangular plate with 45$^{\circ}$oblique crack and a smooth plate subjected to a uniaxial tension. The experiment is adopted by the time-average holography method. The natural frequency and mode shape are considered accurate according to the increasement of tensile load in the study. When tensile load is zero, the vibration modes are almost agreed with the smooth and the 45$^{\circ}$obliquely cracked plate. But since then, according to the increasement of load, it is shown that vibration modes are extremely varied. The effects of the crack length in the vibration characteristic are discussed in detail. It is indicated that the increase of the crack length makes the variation of the frequencies and modes complicate in the range of even a small load.

• Proceedings of the KSME Conference
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• 2000.11a
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• pp.618-622
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• 2000

This paper describes the correlation between the interior noise and the trunk wall vibration. Using the vibro-acoustic reciprocity, effect of the trunk wall vibration on the compartment noise is investigated on a medium size car. In the low frequency range, vehicle interior noise is dominated by several acoustic modes of the passenger compartment and the vibration modes of the surrounding shell parts. Especially, vibration of the trunk wall radiates sound and it is transferred through holes on the package tray into the passenger compartment. This paper experimentally reveals that sound can be well produced at some particular vibration modes of the trunk lid and it strongly influences the compartment noise through package tray holes. Contributions of the trunk walls to the interior noise are estimated by measuring the acoustic-structural transfer function, based on the vibro-acoustical reciprocity theorem.

• Journal of Ocean Engineering and Technology
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• v.34 no.5
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• pp.325-333
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• 2020

As regulations concerning ship vibration and noise are becoming stricter, considerable attention is being drawn to prediction technologies for ship vibration and noise. In particular, the resonance and lock-in phenomena caused by vortex-induced vibration (VIV) have become considerably important with increases in the speed and the size of ships and ocean structures, which are known to cause structural problems. This study extends the fluid-structure interaction (FSI) analysis method to predict resonances and lock-in phenomena of high modes and VIV of ship rudders. Numerical stability is secured in underwater conditions by implementing added mass, added damping, and added stiffness by applying the potential theory to structural analysis. An expanded governing equation is developed by implementing displacements and twist angles of high modes. The lock-in velocity range and resonant frequencies of ship rudders obtained using the developed FSI method agree well with the experimental results and the analytic solution. A comparison with local vibration guidelines published by Lloyd's Register shows that predictions of resonances and lock-in phenomena of high modes are necessary in the shipbuilding industry due to the possible risks like fatigue failure.

• Steel and Composite Structures
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• v.10 no.4
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• pp.297-315
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• 2010

This paper is concerned with free vibration characteristics and natural frequency of horizontally curved composite plate girder bridges. Three-dimensional finite element models are developed for the girders using the software package LUSAS and analyses carried out on the models. The validity of the finite element models is first established through comparison with the corresponding results published by other researchers. Studies are then carried out to investigate the effects of total number of girders, number of cross-frames and curvature on the free vibration response of horizontally curved composite plate girder bridges. The results confirm the fact that bending modes are always coupled with torsional modes for horizontally curved bridge girder systems. The results show that the first bending mode is influenced by composite action between the concrete deck and steel beam at low subtended angle but, on the girders with larger subtended angle at the centre of curvature such influence is non-existence. The increase in the number of girders results in higher natural frequency but at a decreasing rate. The in-plane modes viz. longitudinal and arching modes are significantly influenced by composite action and number of girders. If no composite action is taken into account the number of girders has no significant effect for the in-plane modes.

• The Journal of the Acoustical Society of Korea
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• v.15 no.2E
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• pp.63-75
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• 1996

The squeal vibration of a drum is the major source of brake noise. In this system the binary flutter model of squeal vibration was employed for the drum brake of a passenger car. The vibration analysis of a drum brake was performed by using normal modes, which are obtained by variational method. An improved method for the estimation of shoe modes is proposed and the results are compared with the exact solutions. Numerical results for the coupled system of drum and shoes good agreement with the results of experimental model analysis and those obtained by FE analysis.

• Journal of KSNVE
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• v.3 no.2
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• pp.163-167
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• 1993

Suction and discharge valves of special type refrigerant compressor are designed by finite element method for effective valve design development procedure. It is well known that valve dynamic characteristics, for example, the natural frequencies and vibration modes, are necessary for the computer simulation of compressor valve dynamics, the analysis of flow patterns, noise, impact stresses and their propagation phenomena. This paper has analysed the natural frequencies and vibration modes for the first three orders under the given special boundary conditions and the experiments are conducted by laser holography. And also stress distribution is analysed and experiment by strain gage is followed.

• Proceedings of the KSR Conference
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• 2000.11a
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• pp.527-534
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• 2000

Characteristics of local vibration modes of a corrugated panel are investigated by finite element analysis and modal testing. Structural modification model in the corrugation is proposed to increase the resonance frequency. This model decreases the fall by the local resonance in the transmission loss of the corrugated pallet and improves sound insulation performance. Damping effect of tile foam filled ill tile core cavity is also estimated by experiment The results of tile study offer useful information how to predict the severe local resonances in corrugations and how to prevent their undesirable effect ell the sound insulation and the vibration transmission.

• Journal of the Korean Institute of Gas
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• v.21 no.1
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• pp.18-26
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• 2017

This work proposes an alternative pipe wall-thinning inspection method based on change of eigenfrequencies of shell vibration modes in wall-thinned pipes. It takes much time to detect wall-thinning of pipes using ultrasonic thickness gauge and only a limited number of pipes are under regular inspection. In a pipe with locally decreased thickness, stiffness varies along circumferential direction and natural frequencies of shell vibration modes of the pipe change or frequencies of same modes bifurcate into two different values. Therefore, one can monitor pipe wall-thinning by measuring change of natural frequencies or estimate wall-thinning shape qualitatively. The feasibility of the proposed method was studied by FE vibration analysis for wall-thinned pipes. Modal testing was also carried out for the pipes with artificial wall-thinned section to verify the working performance of the suggested technique.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.27 no.2
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• pp.234-242
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• 2017

This study investigates vibro-acoustic characteristics of a short, thick cylinder containing a slot given a pined-free boundaries. Using the finite element analysis results, structural modes of the asymmetric cylinder (with a slot) are expressed as the linear combinations of modes of the symmetric cylinder made of same material with identical geometry except the slot. Based on synthesized modal vibrations, acoustic modes of the asymmetric cylinder are obtained with two approaches, i.e., Rayleigh integral calculation and modal expansion of the acoustic modes of the symmetric cylinder. Also, acoustic powers, max. sound pressure and directivity pattern are obtained from acoustic modes and verified with the boundary element analyses. Based on these results, the accuracy of proposed approaches in calculating the vibro-acoustic properties of a short, thick, asymmetric cylinder has been confirmed. The procedure can be applied to the similar cylinders with other boundaries or asymmetric properties. Also, attenuation of vibration and/or sound radiation of the cylinder type practical components can be studied using these approaches.