• Selected Papers of The Society of Naval Architects of Korea
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• 제2권1호
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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.

• 한국정밀공학회지
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• 제17권10호
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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.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2000년도 추계학술대회논문집A
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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.

• 한국해양공학회지
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• 제34권5호
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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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• 제10권4호
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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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• 제15권2E호
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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.

• 소음진동
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• 제3권2호
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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.

• 한국철도학회:학술대회논문집
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• 한국철도학회 2000년도 추계학술대회 논문집
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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.

• 한국가스학회지
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• 제21권1호
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• pp.18-26
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• 2017

현재의 초음파 두께 측정에 기반한 배관 감육 검사 속도를 개선하기 위해 배관 쉘 진동 모드의 고유 진동수 변화를 이용한 감육 검사 기법을 제안하였다. 감육이 발생한 부위의 축방향 수직 단면의 두께는 원주 방향을 따라 불균일하게 변화하는데, 두께가 균일한 경우에 비해 쉘 모드의 고유 진동수가 감소하거나 두 개 이상으로 분기됨을 확인하였다. 배관의 고유 진동수는 한 번의 측정으로도 평가할 수 있으므로, 제안한 방법을 이용하면 축방향 수직 단면의 평균 두께 변화를 빠르게 확인할 수 있어 초음파 두께 측정 방식에 비해 신속한 감육 검사가 가능하다. 본 논문에서는 제안 기법의 원리를 설명하고, 2차원과 3차원 감육 배관 모델 및 시편을 이용한 전산 해석과 실험을 통해 제안한 기법의 적용성을 검증하였다.

• 한국소음진동공학회논문집
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• 제27권2호
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• pp.234-242
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• 2017

단순지지-자유 경계조건과 좁은 슬롯을 포함한 짧은 후판 실린더의 음향방사 특성을 검토하였다. 유한요소 해석을 통해 얻어진 샘플 실린더(슬롯 포함)의 진동 모드를 동일한 치수의 슬롯이 없는 균일 실린더의 진동 모드들의 선형 합으로 근사화하였다. 이렇게 얻어진 근사적인 진동 모드를 기준으로 (1) 레일리 적분을 이용한 직접 계산, (2) 균일 실린더의 음향 모드들을 이용한 모드전개법 등 두 방법을 적용하여 샘플 실린더의 음향 모드들을 정의하였다. 이 결과를 이용하여 음향파워, 최대음압, 지향성 선도 등 부가적인 특성을 계산한 다음, 전체 결과를 경계요소법을 이용한 수치해석 결과와 비교하여 검증하였다. 이 결과를 바탕으로, 제시된 두 가지 방법을 이용하여 짧은 비대칭 후판 실린더의 음향방사 특성을 비교적 정확하게 예측할 수 있음을 알 수 있다. 이 방법들은 다른 형태의 비대칭성 및 경계조건을 가진 실린더에도 확대 적용 가능할 것으로 판단되며 이를 통해 실린더 형태의 실제 부품들에서 방사되는 소음을 저감방안 도출도 가능할 것으로 기대된다.