• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2007.05a
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• pp.1008-1016
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• 2007

The purpose of this paper is to investigate the Natural Frequency behavior characteristic of Wind Turbine Tower model, and calculated the stress values of thrust load, wave load, wind load, current load, and gravity load. The offshore Jacket Type Tower which was installed in Vitenam South China Sea is used for the study. Natural frequency and mode shape are calculated with commercial program using the measured vibration. The finite element analysis is performed with commercial F.E.M program(ANSYS) on the basis of the natural frequency and mode shape.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.20 no.7
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• pp.2174-2181
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• 1996

Equations of chordwise and flapwise bending motions of pretwisted rotatin cantilever beams are derived. The two motions are coupled to each other due to the pretwist angle of the beam cross section. As the angular speed, hub radius ratio, and pretwist angle vary, the vibration characteristics of the beam change. It is found that engenvalue loci veering phenomena and associated mode shape variations occur between two vibration modes due to the pretwist angle. The effect of the pretwist angle on the critical angular speed is also investigated.

• Proceedings of the Korea Committee for Ocean Resources and Engineering Conference
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• 2006.11a
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• pp.150-153
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• 2006

점탄성 복합재는 간단한 작업으로 큰 감쇠 효과를 볼 수 있어 사용이 날로 늘어나고 있다. 그런데 점탄성 복합재의 특성은 온도에 민감하게 반응하며 변화한다. 그러므로 점탄성 복합재의 모드해석 시 온도 변화에 따른 해석이 필요하다. 본 논문에서는 한쪽면에 점탄성재를 부착한 Oberst beam을 일단고정 상태로 설치하여 실험 온도를 $-15{\sim}45^{\circ}C$로 변화시켜가며 전달함수를 이용하여 실험모드해석을 실행하였다. 그리고 온도 차이에 따른 모드형상을 비교하였다.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2003.11a
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• pp.284-284
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• 2003

The free vibration characteristics of the cylindrical shell submerged in water is investigated using by FEM and experiment. In the FE analysis, the fluid-structure interaction effect is concerned. The restraint condition is clamped-free. In the results, the natural frequency and mode shape characteristics are evaluated with various water height. This results are compared with those of experiment to verify the validation of the FE analysis. The change of damping ratio is also presented by experiment.

• Transactions of the Korean Society of Machine Tool Engineers
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• v.17 no.6
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• pp.124-131
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• 2008

There are many factors which affect the acoustical properties of a micro-speaker. Among the factors, the shape of the diaphragm is considered in this study. As an investigating method, the finite element methods and measurement techniques applied to study the acoustical properties according to diaphragm shape. In order to vary the stiffness of the diaphragm, the some patterns of comb teeth, such as the angle and the number of comb teeth, are applied to diaphragm. We can confirm that the change of the stiffness by the changing diaphragm shape affects the vibration and sound properties of the speaker. As a result, the reduction of the angle of the comb teeth increases the diaphragm stiffness and shifts the resonance frequency to a higher frequency range. The number of the comb teeth is related to the stiffness of the edge part.

• Journal of the Korean Society for Precision Engineering
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• v.20 no.4
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• pp.49-58
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• 2003

In this study, the equation of motion of impacting elastic structures was derived through the theory, and the shape control of impact force using correlations of the dynamic characteristics and impact force history between two elastic structures was accomplished. Through numerical analysis and experiments, the classical contact mechanisms were verified, and the effects of the relative motion between impactor and elastic structure on the impact force shape were studied, and then the shape change of impact force depending on the impact position and mode shape of cantilever beam were analyzed. The 2-DOF impactor was designed and used. Reconstruction characteristics of impact force in cantilever beam were reviewed .

• Journal of the Institute of Electronics and Information Engineers
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• v.51 no.7
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• pp.71-81
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• 2014

In this paper, the performance variations of tri-gate FinFET are analyzed for different fin shapes and source/drain epitaxy types using a 3D device simulator(Sentaurus). If the fin shape changes from a rectangular shape to a triangular shape, the threshold voltage increases due to a non-uniform potential distribution, the off-current decreases by 72.23%, and the gate capacitance decreases by 16.01%. In order to analyze the device performance change from the structural change of the source/drain epitaxy, we compared the grown on the fin (grown-on-fin) structure and grown after the fin etch (etched-fin) structure. 3-stage ring oscillator was simulated using Sentaurus mixed-mode, and the energy-delay products are derived for the different fin and source/drain shapes. The FinFET device with triangular-shaped fin with etched-fin source/drain type shows the minimum the ring oscillator delay and energy-delay product.

• Structural Engineering and Mechanics
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• v.29 no.5
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• pp.531-550
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• 2008

This paper adopts the numerical assembly method (NAM) to determine the exact solutions of natural frequencies and mode shapes of a multi-span and multi-step beam carrying a number of various concentrated elements including point masses, rotary inertias, linear springs, rotational springs and springmass systems. First, the coefficient matrix for an intermediate station with various concentrated elements, cross-section change and/or pinned support and the ones for the left-end and right-end supports of a beam are derived. Next, the overall coefficient matrix for the entire beam is obtained using the numerical assembly technique of the conventional finite element method (FEM). Finally, the exact solutions for the natural frequencies of the vibrating system are determined by equating the determinant of the last overall coefficient matrix to zero and the associated mode shapes are obtained by substituting the corresponding values of integration constants into the associated eigenfunctions.

• Smart Structures and Systems
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• v.23 no.6
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• pp.653-667
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• 2019

Using cross-ties to connect cables together when forming a cable network is regarded as an efficient method of mitigating cable vibrations. Cross-ties have been extended and fixed on bridge decks or towers in some engineering applications. However, the dynamics of this kind of system need to be further studied, and the effects of extending cross-links to bridge decks/towers on the modal response of the system should be assessed in detail. In this paper, a system of two cables connected by an inter-supported cross-link with another lower cross-link extended to the ground is proposed and analyzed. The characteristic equation of the system is derived, and some limiting solutions in closed form of the system are derived. Roots of cable system with special configurations are also discussed, attention being given to the case when the two cables are identical. A predictable mode behavior was found when the stiffness of inter-connection cross-link and the cross-link extended to the ground were the same. The vector of mode energy distribution and the degree of mode localization index are proposed so as to distinguish global and local modes. The change of mode behaviors is further discussed in the case when the two cables are not identical. Effects of cross-link stiffness, cross-link location, mass-tension ratio, cable length ratio and frequency ratio on $1^{st}$ mode frequency and mode shape are addressed.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.1549-1552
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• 2003

The front-end side members of automobiles absorb most of the energy in a front-end collision. The front-end side members are required to have a high stiffness together with easiness to collapse sequentially to absorb more impact energy. The axial static collapse test (5mm/mim) was conducted by using UTM with respect to the single hat shaped section members which are the standard section shape of the spot welded section members, to the single cap shaped section members, to the double cap shaped section members and to the double hat shaped section members whose section shape are changed in order to give more stiffness. As a result of test, the energy absorbing characteristic was analyzed for different section shapes. That is, it was analyzed that the change of section shape influenced the absorbing energy, the mean collapse load and the maximum collapse load, and that the relation between the change of section shape and the collapse mode.