• Composites Research
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• v.13 no.6
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• pp.47-54
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• 2000

One promising method for impact detection of composite structures is based on the use of piezopolymer thin fim (PVDf) sensor. In this paper, the relationship between the contact force and the signals of the attached strain gage and PVDF sensor to the composite plate subjected to low-velocity impact were derived. The relation for the open circuit and short circuit voltage of PVDF sensor was derived based on the equivalent circuit model of the piezoelectric sensor. The work was then extended to include experimental investigation into the use of short circuit voltage of PVDF sensor without using charge amplifier to detect low-velocity impact. The natural frequencies and damping ratio of the composite plate obtained from the vibration test were used to modify the analytical model and therefore the differences between measured and simulated signal of the modified analytical model in both forward and backward problem were considerably reduced. The reconstructed contact force and simulated sensor signals agreed well with the measured contact force, strain gage signal, and PVDF sensor singanl.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.74-79
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• 1995

모우드 밀도의 산정을 정확하게 구하기 위해 고주파수 영역에서 흔히 적용되는 3채널 측정법이 저주파수대 영역에서도 2채널법에 의한 방법보다 주파수 응답함수의 크기 및 공전주파수의 위치를 보다 더 잘 나타내 주고 있다는 것을 실험적으로 제시하였다. 2채널 측정법에 비하여 3채널 측정법이 모우드 밀도가 균일한 보의 경우에 있어서도 주파수 응답함수의 크기를 실제의 경우와 근접하게 추정해 줄 수 있을 뿐 아니라, 상대적으로 모우드 밀도가 높은 평판의 경우에 있어서도 공진주파수 대에서의 주파수 응답함수의 형태를 보다 분명히 나타내어 줄 수 있는 것으로 나타났다. 한편, 구조물과 가진기의 상호작용에 의한 고유진동수의 변동량 측정의 관점에서는 2채널 측정법과 3채널 측정법의 경우 모두 주파수 응답함수를 적절히 나타내어 주고 있는 것으로 나타났다.

• Proceedings of the KSR Conference
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• 2006.11b
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• pp.31-34
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• 2006

A new continuum damage theory (CDT) has been proposed by Lee et al. (1996) based on the SEEP. The CDT has the apparent advantage over the other related theories because the complete constitutive law can be readily derived by simply replacing the virgin elastic stiffness with the effective orthotropic elastic stiffness obtained by using the proposed continuum damage theory. In this paper, the CDT is evaluated by the numerical experiment comparing the mode shapes and natural frequencies of a square plate containing a small line-through crack with those of the same plate with a damaged site replaced with the effective orthotropic elastic stiffness computed by using the CDT.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.11a
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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.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.27 no.9
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• pp.1486-1491
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• 2003

A modeling method for the modal analysis of a composite trapezoidal plate undergoing in-plane translational acceleration is presented in this paper. The equations of motion for the plate are derived and transformed into a dimensionless form. The effects of the inclination angles, fiber orientation angle and the acceleration on the modal characteristics of the plate are investigated.

• Proceedings of the KIEE Conference
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• 1999.11d
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• pp.1145-1147
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• 1999

평판전극배열을 이용한 회전구동형 마이크로 액츄에이터의 구동력을 증대시키기 위하여 전극의 형상을 최적화 하였다. 기존 평판구동형 마이크로 액츄에이터의 형상을 변형시켜 반경에 무관하게 전극의 수직간격을 최소간격으로 일정하게 유지함으로서 구동력을 배가시키는 효과를 발생시켰다. 이러한 구동력의 증가는 결국 요구되는 변위를 만족시키면서 고유진동수를 증가시켜 마이크로액츄에이터의 구동성능을 향상시킬 수 있다.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.19 no.3 s.73
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• pp.247-258
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• 2006

For the perforated cylindrical shell submerged in fluid, it is almost impossible to develop a finite element model due to the necessity of the fine meshing of the shell and the fluid at the same time. This necessitates the use of solid shell with equivalent material properties. Unfortunately the effective elastic constants are not found in any references even though the ASME code is suggesting those for perforated plate. Therefore in this study the equivalent material properties of perforated shell are suggested by performing several finite element analyses with respect to the ligament efficiencies.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2002.11a
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• pp.389.1-389
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• 2002

An analytical study is presented on the hydroelastic vibration of two rectangular identical plates coupled with a bounded fluid by using the finite Fourier series expansion method. It is observed that the two contrastive modes, the so called the out-of-phase and in-phase modes. All natural frequency of the in-phase modes can be predicted well by the combination of the beam modes in the air, but the natural frequency of the out-of-phase mode cannot be estimated precisely. (omitted)

• Journal of the Society of Naval Architects of Korea
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• v.38 no.3
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• pp.62-73
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• 2001

The interest in evaluation of structural intensity arises for practical reasons, because net energy flow distribution offers information of energy transmission path, positions of sources, and sinks of vibration energy. In this paper, structural intensity analysis of local ship structures using finite element method(FEM) is carried out. The purpose of this analysis is to evaluate the relative accuracy according to mesh fineness. The structural intensity of unstiffened and stiffened plates varying their mesh fineness is analyzed and the results are compared with those obtained by the assumed mode method. As results, the proper mesh size in qualitative/quantitative structural intensity analysis of plate structures is proposed. In addition, the propagation phenomenon of vibration energy is investigated for the thickness-varying flat plate, L-type plate, and box-girder structures.

• Journal of the Korean Society for Nondestructive Testing
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• v.21 no.2
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• pp.182-188
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• 2001

This paper presents the vibration characteristics of a rectangular plate with $45^{\circ}$ oblique crack subjected to a uniaxial tension. The experiment is adopted by the time-average Electronic Speckle Pattern Interferometry(ESPI) method. The natural frequency and mode shape are considered accurately according to the increase of tensile load. When tensile load is zero, the vibration modes we agreed with the smooth and the $45^{\circ}$ obliquely cracked plate. But according to the increasement of load it is shown that vibration modes are extremely varied. The effects of the crack under the vibration are discussed in detail. It is indicated that the increase of load makes the variation of the frequencies and modes complicate in the range of even a small load. The results are agreed with the FEM analysis within 5%.