• Journal of Korean Association for Spatial Structures
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• v.9 no.3
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• pp.59-66
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• 2009

Dynamic characteristics such as frequency and damping ratio in the ambient state of building has been progressed in domestic and foreign. However, there has not been any deep research of dynamic characteristics of full-scale structure using vibration measurement of the building damaged up to failure. Dynamic characteristics of three-story reinforced concrete building was evaluated before and after it was damaged by using a actuator. Dynamic characteristics is reviewed and compared with previous study. Ambient vibration and human excitation test were applied. After 120mm horizontal displacement by actuator, frequency of long and short direction is reduced to 34.3%, 33.7% and damping ratio is reduced to 36.5%, 19.5% respectively.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 1995.04a
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• pp.61-66
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• 1995

본 연구에서는 스티프너를 이용한 열린 상자형 구조물의 구조변경법에 대하여 고찰해 보았고, 다음과 같은 결론을 얻었다. 1. 감도해석법을 이용하여 고유진동수 감도를 쉽게 구할 수 있었고 구해진 고유진동수 감도를 이용하여 변경할 위치를 결정할 수 있었다. 2. 최적구조변경법에 의해 변경량을 정량적으로 구할 수 있었고, 고유진동수를 목표한 값으로 바꿀 수 있었다. 3. 기둥을 이용한 구조변경에서 문제시 되었던 동위상의 고유진동모우드에 대해서도 효과적으로 고유진동수를 변경할 수 있었다. 스티프너는 설치위치에 대허여 비교적 제약을 받지 않으므로 구조물의 동특성 변경에 효과적일 것으로 생각된다. 그리고 구조변경을 더욱 효율적으로 수행하기 위해서는 구조물의 치수, 형상, 재료 등의 종합적인 설계변수를 고려하는 감도해석과 이를 바탕으로 하는 최적구조변경이 필요할 것이다.

• The Journal of the Acoustical Society of Korea
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• v.21 no.8
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• pp.757-765
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• 2002

The object of this paper is to examine the vibration characteristics of the point-symmetric radial mode in a spherical piezoelectric transducer. The differential equations of piezoelectric radial motion are derived in terms of the radial displacement and electric potential, which are functions of the radial coordinate and time. Applying mechanical and electrical boundary conditions yields the characteristic equation of radial vibration. Numerical results of the natural frequencies are compared with the experimental measurements. The paper discusses the difference between piezoelectric and elastic resonances and the dependence of the natural frequencies on the radius and thickness of the piezoelectric spheres. As a result it is concluded for the first radial mode that the natural frequency is reduced due to the piezoelectric phenomenon and that the frequency exponentially decreases as the sphere radius increases.

• Journal of the Korea institute for structural maintenance and inspection
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• v.18 no.1
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• pp.150-159
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• 2014

A simplified method for the calculation of buckling and vibrational characteristics of initially stressed rectangular plate and antisymmetric angle-ply laminated plates is presented in this paper using the natural frequencies under unloading state. The equation of motion of rectangular plate with two opposite edges simply supported is investigated on the basis of Rayleigh-Ritz method and Mindlin plate theory with effect of the curvature term. The relationships of the non-dimensional natural frequencies with initial stresses the coeffcients of critical buckling and the boundaries of the dynamic principal instability region can be characterized by the non-dimensional natureal frequencies under unloading state. Numerical examples are presented to verify the simplified equations and to illustrate potential applications of the analysis.

• Proceedings of the Korea Water Resources Association Conference
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• 2010.05a
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• pp.754-758
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• 2010

케이블 교량에서 발생하는 사장케이블의 진동현상에 대한 현상학적 특성을 명확히 이해해야, 사장케이블의 적합한 제진설계가 가능하다. 본 연구에서는 유체의 흐름과 구조물의 진동을 동적으로 연계하여 해석하기 위하여, ADINA의 CFD 및 Structure 코드를 동적으로 연계하는 FSI(Fluid Flow with Structure Interaction) 기법을 이용하였다. 바람으로 인해 이중원형실린더의 풍상측과 풍하측 실린더에서는 와류가 방출되면서 외력이 작용하게 되며, 이러한 공기력은 풍하측 실린더의 고유진동 운동과 함께 와류진동현상을 유발한다. 본 연구에서는 풍하측 실린더의 와류진동 현상의 해석에 주안점을 두었다. 본 연구에서는 흐름의 레이놀즈수와 이중원형실린더에 대한 바람의 입사각을 변화시키며 풍하측 실린더에서 발생하는 와류진동의 크기를 분석하였다. 본 연구결과, 유입풍속 및 바람의 입사각에 따라 이중원형실린더에서 발생하는 일반적인 와류방출현상과 풍하측 실린더에 작용하는 공기력 및 변위양상을 예측할 수 있었다. 특히, 바람의 입사각이 $15^{\circ}$인 경우에는 풍하측 실린더에서 방출되는 와류로 인해 풍하측 실린더에는 비대칭의 공기력이 작용하며, 이는 풍하측 실린더가 2사분면에서 4사분면 방향으로 진동하는 원인이 되는 것으로 판단된다.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.35 no.10
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• pp.1211-1222
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• 2011

It is necessary to use prestressed modal analysis to calculate the modal frequencies and mode shapes of a prestressed structure such as a spinning blade, a preloaded structure, or a thermally deformed pipe, because the prestress effect sometimes causes significant changes in the frequencies and mode shapes. When the finite element model under consideration has a very large number of degrees of freedom, repeated prestressed modal analyses for investigating the prestress effects might become too computationally expensive to finish within a reasonable design-process time. To alleviate these computational difficulties, a Krylov subspace-based model order reduction, which reduces the number of degrees of freedom of the original finite element model and speeds up the necessary prestressed modal analysis with the reduced order models (ROMs), is presented. The numerical process for the moment-matching model reduction is performed directly on the full order models (FOMs) (modeled in ANSYS) by the Arnoldi process. To demonstrate the advantages of this approach for performing prestressed modal analysis, the prestressed wheel and the compressor impeller under their high-speed rotation are considered as examples.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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• 2008.11a
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• pp.354-359
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• 2008

Modal characteristics of a cracked beam with a concentrated mass undergoing rotational motion are investigated in this paper. Hybrid deformation variables are employed to derive the equations of motion of a rotating cantilever beam. The flexibility due to crack, which is assumed to be open during the vibration, is calculated basing on a fracture mechanics theory. To obtain more general information, the equations of motion are transformed into a dimensionless form in which dimensionless parameters are identified. The effects of the dimensionless parameters related to the angular speed, the depth and location of a crack and the size and location of a concentrated mass on the modal characteristics of the beam are investigated numerically.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.19 no.1
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• pp.10-16
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• 2009

Modal characteristics of a cracked beam with a concentrated mass undergoing rotational motion are investigated in this paper. Hybrid deformation variables are employed to derive the equations of motion of a rotating cantilever beam. The flexibility due to crack, which is assumed to be open during the vibration, is calculated basing on a fracture mechanics theory. To obtain more general information, the equations of motion are transformed into a dimensionless form in which dimensionless parameters are identified. The effects of the dimensionless parameters related to the angular speed, the depth and location of a crack and the size and location of a concentrated mass on the modal characteristics of the beam are investigated numerically.

• Journal of the Korean Institute of Gas
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• v.20 no.6
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• pp.58-64
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• 2016

Vibrational characteristics of curved pipe structures are investigated with respect to the change of inside flow velocities. Based upon the Hamilton's principle, the equations of motions are derived, and the finite element equation is constructed to solve the frequency equation for curved pipe structures. When the initial tension is neglected in cured pipes, the natural frequencies are reduced as flow velocity increases, and the rapid decreases of the natural frequencies take place. However, when the initial tension is taken into account, the natural frequencies are not changed with the change of the flow velocity. In free vibrational simulation of pipe systems, it is necessary to calculate the initial force due to the velocity and the pressure of the fluid flow from the equilibrium. The force should be included in the equation of motion of the systems to get more accurate natural frequencies. The mechanical properties like stiffness or the location of pipe support need to be changed to avoid resonance. The natural frequencies are to be isolated from the frequency range of dominant vibration modes. The angles of elbows do not affect the change of the fundamental natural frequency, but affect the change of the third or higher natural frequencies.

• Journal of the Society of Naval Architects of Korea
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• v.38 no.4
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• pp.48-55
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• 2001

In this paper, sensitivity analysis for the coupled axial and torsional undamped free vibration of ship propulsion shafting is proposed. The purpose of this study is to effectively and optimally design the resonance frequencies of propulsion shafting affecting barred speed range of main engine by modifying the diameters of intermediate and propeller shafts. The presented method is validated by the sensitivity analysis for the natural frequencies of propulsion shafting of two real large merchant ships. In addition, the changes of natural frequency and resonance main engine speed are discussed in case that the diameter is varied within the range regulated by the rule of shipping register.