• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.17 no.3 s.120
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• pp.257-263
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• 2007

Detection of structural damage is an inverse problem in structural engineering. There are three main questions in the damage detection: existence, location and extent of the damage. In concept, the natural frequency and mode shapes of any structure must satisfy an eigenvalue problem. But, if a potential damage exists in a structure, an error resulting from the substitution of the refined analytical finite element model and measured modal data into the structural eigenvalue equation will occur, which is called the residual modal forces, and can be used as an indicator of potential damage in a structure. In this study, a useful damage detection method is proposed and compared with other two methods. Two degree-of-freedom system and Cantilever beam are used to demonstrate the approach. And the results of three introduced method are compared.

• Journal of the Computational Structural Engineering Institute of Korea
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• v.15 no.4
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• pp.619-628
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• 2002

This paper deals with the FE analysis for the free vibration of sloshing in horizontal cylindrical tank with baffles. We use Laplace equation based on potential theory as governing equation. This problem is solved by FEM using lineal isoparametric elements. We assume that the tank as well as baffles is rigid body and by separating nodes into two at the baffle location, baffle effect is obtained by separating nodes into two at the baffle location. For the calculation of natural frequencies and mode shapes, we introduce Lanczos transformation and Jacobi iteration methods. Numerical results of the first longitudinal and transverse modes, while comparing with literature cited, are very good. In order for the baffle effects on the free vibration of sloshing, various combinations of baffle parameters, which are location, inner diameter and number, are examined.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.10a
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• pp.191-196
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• 1995

지지부에 비틀림 하중을 받는 Elstica는 비틀림 운동을 하며, 그 가진 주파수가 굽힘모드 근처일 때는 해당하는 굽힘 모드의 운동까지도 동시에 존재하게 된다. 이때 가진력의 크기가 작을때는 주기적인 운동이 된다. 가진력의 크기가 증가함에 따라 굽힘 운동은 굽힘 1차 모드와 연성된 유사주기운동이 발생하며, 이떤 범위 이상이 되면 굽힘 운동과 비틀림 운동이 결합된 진폭이 매우 크고 불규칙적인 비평면 운동(out of plane motion)이 발생하게 되며 이 때의 운동은 혼돈운동이다. Elastica가 굽힘 3차 고유진동수 근방의 주파수로 비틀림 하중을 받을 때의 정확한 이론적 해석을 위해서는 굽힘 3차모드 까지는 반영할 수 있는 식이 모델링 되어야 할 것으로 보인다. 이것은 복잡한 비평면운동을 할 때 굽힘 3차 모드까지 관찰된다는 사실에 근거한다.

• Journal of the Korea Academia-Industrial cooperation Society
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• v.17 no.12
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• pp.652-658
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• 2016

In this paper, the theoretical research and simulation using the Finite Element Method (FEM) to design and form a micro-pattern for an ultrasonic horn is described. The present method is based on an initial design estimate obtained by FEM analysis. The natural and resonant frequencies required for the ultrasonic tool horn used for forming the fine pattern were predicted by finite element analysis. FEM analysis using ANSYS S/W was used to predict the resonant frequency for the optimum technical design of the ultrasonic horn vibration mode shape. When electrical power is supplied to the ultrasonic transducer, it is converted into mechanical movement energy, leading to vibration. The RFID TAG becomes the pattern formed on the insulating sheet by using the longitudinal vibration energy of the ultrasonic tool horn. The FEM analysis result is then incorporated into the optimal design and manufacturing of the ultrasonic tool horn.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.3
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• pp.84-92
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• 2014

In this study, vibrational tendon tension measurement methods are applied to estimate tension of external tendons used in segmental post-tensioned bridges. The acceleration of various length type of tendons is measured and natural frequencies are obtained using FFT (Fast Fourier Transform). The obtained natural frequencies are within 1% error regardless of sensor direction and location. On the basis of natural frequency of tendon, estimation of the tendon tension is performed by using many types of solutions such as string theory equation, multi mode estimation, practical formula estimation and stiff string with clamped-clamped boundary conditions. The results are compared with each other and have shown that the flexural stiffness is not negligible in tendons of this type causing the vibration mode to be inharmonically related. The results have shown that the method using stiff string equation with clamped-clamped boundary conditions is more accurate than the other methods. Application example of in-service bridges has shown that force distribution effects from friction at deviation blocks can be effectively detected.

• Journal of Korean Society of Steel Construction
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• v.28 no.5
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• pp.365-371
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• 2016

In the case of the superstructure which is consist of two I girders and slab, the section can behave as II section, so that the neutral axis with respect to out of plane direction flexure can be regarded as major axis. Therefore in-plane flexural mode might govern the free vibration mode. Meanwhile, horizontally curved girders always experience not only bending moments but also torsional moments although the primary load is usually supposed to be gravitational load. The interaction due to bending and torsional moments make the behavior complicated and torsional mode may govern the free vibration mode. In other words, structure can have different dynamic characteristic due to its initial curvature. In this research, using 3-dimensional sell elements, free-vibration analyses are carried out due to initial curvature. The analysis models are assumed to be composite and non-composite and finally natural frequency and eigen mode are discussed.

• Journal of Korean Association for Spatial Structures
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• v.9 no.1
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• pp.61-68
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• 2009

This paper is concerned with the investigation of the structural behavior of waffle structure. Parametric variation on waffle floor thickness, main beam depth and column sizes are imposed to study the effects on mode shapes and natural frequencies of waffle structures. Comparisons between FEM models using shell and 3D-solid elements have also been made. The analysis result has shown that the mode frequencies increase with i) increase in main beam depth at level 2 and ii) decrease in waffle slab thickness at level 3. Both 3D and 2D model shown similar mode shapes. Besides, there is a consistent difference in mode frequencies between 3D and 2D model ranging from 25% to 36%.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2011.10a
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• pp.72-77
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• 2011

In this study, the natural frequencies and mode shape of an external mounting pod were verified using the modal analysis and modal testing technique for a pod mounted on an aircraft. The procedure associated with the FEM building of an external mounted pod to predict the dynamic behavior of aircraft structures is described. The simplified FEM reflecting the results of the modal testing of a pod is built through the optimization, applied to the structural dynamic model of an Aircraft, used to verified the stability of vibration and flutter of an aircraft.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.26 no.4
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• pp.406-411
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• 2016

The natural frequencies and mode shapes of a system composed of subsystems on a supporting structure have been derived approximately. The system is modeled as a discrete system, and it is assumed that the masses of subsystems are much smaller than the mass of a supporting structure. It has been found that the fundamental frequency corresponds to the supporting structure, and each higher frequency corresponds to each subsystem. A relation between the vibration amplitudes of the supporting structure and subsystems is also derived for the case when the supporting structure is excited by a harmonic force.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2013.10a
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• pp.860-861
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• 2013