• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 1998년도 춘계학술대회논문집; 용평리조트 타워콘도, 21-22 May 1998
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• pp.629-633
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• 1998

본 연구에서는 연성손실계수가 구조물의 진동에 미치는 영향을 살펴보았다. 세부시스템의 두께가 동일할 경우 평판으로 이루어진 구조물이 접수되면 연성손실계수가 감소하게 된다. 특히, 저주파수 대역에서 연성손실계수가 크게 낮아졌다. 그 주된 원인은 접수로 인해 평판에서 전파되는 굽힘파의 그룹속도가 줄어들기 때문이며, 접수로 인한 파워투과계수의 변화는 크지 않았다. 내부에 격벽을 가진 steel box에 공기중 연성손실계수와 접수시 연성손실계수를 적용하여 세부시스템의 속도를 구한 결과, 공기중 연성손실계수를 이용하여 구한 속도가 접수시 연성손실계수를 이용하여 구한 속도보다 약 2-3 dB정도 높게 나타났다. 선박과 같은 복잡한 구조물인 경우 연성손실계수에 의한 속도 차이는 더욱 커질 것으로 추정된다. 따라서, SEA를 이용한 접수 구조물의 진동해석에서 해석오차를 줄이기 위해서는 연성손실계수에 접수의 영향을 고려해 주어야 함을 확인하였다. 특히, 접수효과가 고려된 연성손실계수를 사용하면 SEA가 큰 오차를 보이는 중, 저주파수 대역에서 해석 결과에 대한 신뢰성을 높일 것으로 판단된다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.751-752
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• 2013

• 한국소음진동공학회논문집
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• 제22권8호
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• pp.800-807
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• 2012

In this paper, radiation efficiency of the plate surround by an infinite rigid baffle is studied. The plate is simply supported and one side is in contact with air, while other side with water. The pressure and normal velocity over the plate surface are assumed as modal summations, from which a set of linear equations is obtained for fluid-structure coupled problem. It is shown that neglect of the cross modes results in overestimation of the radiation efficiency specifically for mid-frequency ranges. Based on the fact that the responses are mainly determined from the first few cross modes in addition to the diagonal terms, a new algorithm is proposed, where banded matrix is iteratively solved in computing radiation efficiency. In numerical examples, it is found that radiation efficiency obtained from banded matrix is in excellent agreement with the one from the full matrix, while computing time is significantly reduced. It is also found that as frequency grows larger, radiation efficiency considering only diagonal terms is a good approximation.

• 한국소음진동공학회논문집
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• 제24권1호
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• pp.21-27
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• 2014

In this paper, an approximate formula for radiation efficiency of the plate surround by an infinite rigid baffle is studied. The plate is simply supported and one side is in contact with air, while other side with water. By assuming an infinite plate, the fluid loading effect is derived in terms of an effective mass. Based on the observation that the fluid loading effect decreases as frequency increases, the radiation efficiency formula at high frequency, which was originally derived for a plate vibrating in the air, is modified as the approximate formula for a submerged plate. The fluid loading effect is taken into account in the wavenumber of the plate. Comparisons of the approximate formula with the numerical results shows that they match well except the mid-frequency range in which numerical results show many oscillations. In numerically solving the fully coupled equations of motion, fourfold integrals of the impedance coefficients are reduced to single nonsingular integrals, which results in substantial reduction in computing time.

• 한국소음진동공학회논문집
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• 제22권1호
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• pp.29-37
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• 2012

This paper is concerned with the natural vibration characteristics of a rectangular plate with a rectangular hole in contact with the water. The addressed problem was solved by using the Rayleigh-Ritz method combined with the Green function method. This study presents the numerical approach, numerical results and experimental results. In addition, the validity of the approximate formula which mainly depends on the so-called non-dimensionalized added virtual mass incremental factor and the natural mode shape change due to the presence of the water were investigated. Experiments were also carried out to validate theoretical results. The theoretical results are in good agreement with the experimental results. It was found that the effect of a square hole on the natural frequencies of the square plate in contact with water is different from the effect of a square hole on the natural frequencies of the square plate in air and the approximate formula can predict lower natural frequencies in water with a good accuracy.

• 대한조선학회지
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• 제31권3호
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• pp.33-35
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• 1994

본 고에서는 선체국부팬널의 대종을 이루고있는 판요소, 보강판, 복판팬널 및 복합재료적층판의 진동특성을 구하는 근사방법으로서 주로 Rayleigh-Ritz방법을 적용한 연구결과들을 정리하였다. 이를 통해 향후 추가로 연구가 이루어져야 할 내용을 다음과 같이 도출하였다 1) 팬널주위의 경제조건으로서 탄성구속을 고려 할 수 있도록 정식화는 이루어져 있으나 실제 선체 팬널의 탄성구속도를 구하는 방법이 정립되어 잇지 못하기 때문에 해석결과의 정도 문제가 발생한다. 따라서 해석정도의 향상을 위해 실제 선체팬널의 탄성구속도에 대한 연구가 수행되 어야 하며, 이와 같은 연구는 조선소에서 이루어지는 것이 타당한 것으로 사료된다. 2) Mindlin 판, 복합판널, 복합재료적층판에 대한 정식화에서 경제조건이 회전방향탄성고속만 고려되고 힁방향 변위는 고정되어 자유와 단순지지 사이의 경제조건은 고려될 수 없으므오 이 에대한 보완 연구가 이루어져야 한다. 3) 본 고에서는 접수효과에 대한 연구결과의 소개는 없었으나, 이에대한 현재까지의 연구는 주로 평판에 대해 이루어졌다. 화물창내 국부판널 또는 이중저의 진동해석을 정도 노ㅍ게 수행하기 위해서는 보강판 및 복판팬널의 접수효과에 대한 연구가 적극적으로 이루어져야 한다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 추계학술대회 논문집
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• pp.279-280
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• 2013

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2007년도 추계학술대회논문집
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• pp.42-47
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• 2007

An analytical method for the free vibration of a flexible rectangular plate in contact with water is developed by the Rayleigh.Ritz method. The plate clamped along the edges is partially contacted with water at both sides. It is assumed that the water bounded by rigid walls is incompressible and inviscid. The wet mode shape of the plate is assumed as a combination of the dry mode shapes of a clamped beam. The liquid motion is described by using the liquid displacement potential and determined by using the compatibility conditions along the liquid interface with the plate. Minimizing the Rayleigh quotient based on the energy conservation gives an eigenvalue problem. It is found that the theoretical results can predict excellently the fluid.coupled natural frequencies comparing with the finite element analysis result.

• 대한조선학회논문집
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• 제55권4호
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• pp.281-288
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• 2018

Acoustic radiation efficiency is a crucial factor to estimate Underwater Radiated Noise (URN) of ships accurately. This paper describes a numerical method to analyse acoustic radiation efficiency of one side-wetted rectangular Mindlin plate with simply supported boundaries excited by a harmonic point force. Transverse displacements of plate and acoustic radiation pressures are evaluated by the mode superposition method. The acoustic radiation efficiencies analyzed by both Mindlin and thin plate theories show little differences at monopole and corner modes of low frequency regions but relatively large differences at edge and critical modes of high frequency regions. Especially, the critical frequency with the highest acoustic radiation efficiency evaluated by the Mindlin plate theory is higher than that of thin plate theory. In addition, the acoustic loading effect of fluid also increases bending wave-number of plate and its critical frequency. Finally, the acoustic radiation characteristics of plates with different aspect ratios and thicknesses through numerical analyses are investigated and discussed.

• 대한기계학회:학술대회논문집
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• 대한기계학회 2003년도 춘계학술대회
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• pp.839-844
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• 2003

The effect of water level on the free vibration of a partially water-filled two rectangular plates structure was investigated by experimental modal analysis and finite element analysis using ANSYS computer program. Modal parameters of two rectangular plates coupled with water were obtained by means of experiment and the FEM solutions were compared with the experimental solutions to verify the finite element model. As a result, the comparison between the experiment and FEM results showed excellent agreement. The transverse vibration modes, in-phase and out-of-phase, were observed alternately in the fluid-coupled system. The effect of water level and water gap size on the fluid-coupled natural frequency were investigated. It was found that the natural frequency of the partially water-filled two rectangular plates are not proportional to the water level, but depend on mode number of plates.