• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2005년도 추계학술대회논문집
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• pp.772-778
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• 2005

Based on a full layerwise displacement shell theory, the vibration and damping characteristics of cylindrical sandwiched panels with viscoelastic layers are investigated. The transverse shear deformation and the normal strain of the cylindrical hybrid panels are fully taken into account for the structural damping modelling. The present finite element model is formulated by using Hamilton's virtual work principle and the cylindrical curvature of hybrid panels is exactly modeled. Modal loss factors and frequency response functions are analyzed for various structural parameters of cylindrical sandwich panels. Present results show that the full layerwise finite element method can accurately predict the vibration and damping characteristics of the cylindrical hybrid panels with surface damping treatments and constrained layer damping.

• Advances in aircraft and spacecraft science
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• 제3권3호
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• pp.299-315
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• 2016

In this work, a strategy for passive vibration control of periodic structures is proposed which involves adding a periodic array of simple resonant devices for creating band gaps. It is shown that such band gaps can be generated at low frequencies as opposed to the well known Bragg scattering effects when the wavelengths have to meet the length of the elementary cell of a periodic structure. For computational purposes, the wave finite element (WFE) method is investigated, which provides a straightforward and fast numerical means for identifying band gaps through the analysis of dispersion curves. Also, the WFE method constitutes an efficient and fast numerical means for analyzing the impact of band gaps in the attenuation of the frequency response functions of periodic structures. In order to highlight the relevance of the proposed approach, numerical experiments are carried out on a 1D academic rod and a 3D aircraft fuselage-like structure.

• 대한토목학회논문집
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• 제13권4호
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• pp.65-75
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• 1993

본 연구는 규모가 큰 지진하중에 대한 해양 가이드 타워의 비정상과정 거동해법에 주안점을 두었으며, 아울러 작은 파랑이나 조류하중이 동시에 작용할 수 있는 경우도 고려하였다. 지진에 의한 지반운동의 비정상특성은 정상과정 성분에 지수함수의 시간포락함수를 곱하는 형태로 모형화하였다. 동적거동의 비정상과정 분산값을 해석적인 방법으로 산출하였다. 운동방정식에 계류장치의 비선형 복원력과 파동에 의한 비선형 점성저항력을 추계론적 최적화기법으로 선형화하여 동적해석을 수행하였다. 지진의 발생기간동안 예상되는 중급의 파랑하중에 의한 영향을 최대거동 산정시 고려하였다. 중급 파고조건에 대한 파랑하중은 지속기간이 상당히 길어서 정상과정으로 취급할 수 있으므로 이에 대해서는 주파수 영역해석을 사용하여 동적거동을 산출하고 이 결과를 지진에 의한 비정상과정거동에 반영하였다. 예제해석으로부터 비정상과정 해석방법을 검증하고, 지진과 파랑 및 조류하중의 각 성분이 전체응답에 미치는 영향을 분석하였다.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2011년도 추계학술대회 논문집
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• pp.325-330
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• 2011

RCP(Reactor coolant pump) must be designed to preserve it's functions on normal or abnormal environments and seismic event same as operating basis earthquake(OBE) and safe shutdown earthquake(SSE). Generally, there are static and dynamic analytical method which can be applied by a floor response spectrum or time history analysis for the seismic qualification. Initially, It was accomplished a detailed structural FE-model for finite element analysis on the bases of 3-dimensional solid model which was made by the RCP drawing. As the result of dynamic characteristic using the detailed FE-model, it's shown about 12Hz natural frequency of 1st bending mode shape and maximum displacement has 11mm with the structural bending by single-point response spectrum(SPRS) method at all elevation. But maximum displacement has 7.6mm by multi-point response spectrum(MPRS) method which was applied to the three floor response spectrum at each elevation. Therefore, On a large heighten structures as RCP, The application by SPRS method causes to be more conservative results. Finally, A simpled equivalent beam model which was developed by use of iteration of detailed FE-model is shown the result more similar with those of natural frequencies and SPRS analysis. And maximum equivalent stress and displacement of the simpled beam has verified with 180MPa and 7.1mm each at 15sec as results by SSE time history method.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2009년도 추계학술대회 논문집
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• pp.797-803
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• 2009

The accurate prediction of dynamic characteristics of high speed rotors, such as gas turbines, is important to avoid the possibility of operating the machinery near the critical speeds or unstable speed regions. However, the dynamic analysis methods and softwares for gas turbines have been developed in the process of producing many gas turbines by manufacturers and most of them have seldom been disclosed to the public. Recently, commercial FEM softwares, such as SAMCEF, ANSYS and NASTRAN, started supporting some rotordynamics analysis modules based on 3-D finite elements. In this paper, the dynamic analysis method using commercial S/W, especially ANSYS, is attempted for the small-size gas turbine engine rotor, and the analysis capability and limitations of its rotordyamics module are evaluated for further improvement of the module. As the preliminary procedure, the rotordyamic analysis capability of ANSYS was tested and evaluated with the reference models of the well-known dynamics. The limitations in application of the rotordynamics module were then identified. Under the current capability and limitations of ANSYS, it is shown that Lee diagram, a new frequency-speed diagram enhanced with the concept of $H{\infty}$ in rotating machinery, can be indirectly obtained from FRFs computed from harmonic response analysis of ANSYS. Finally, it is demonstrated based on the modeling and analysis method developed in the process of the S/W verification that the conventional Campbell diagram, Lee diagram, mode shapes and critical speeds of the small-size gas turbine engine rotor can be computed using the ANSYS rotordynamics module.

• 한국소음진동공학회논문집
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• 제20권1호
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• pp.36-44
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• 2010

The accurate prediction of dynamic characteristics of high speed rotors, such as gas turbines, is important to avoid the possibility of operating the machinery near the critical speeds or unstable speed regions. However, the dynamic analysis methods and softwares for gas turbines have been developed in the process of producing many gas turbines by manufacturers and most of them have seldom been disclosed to the public. Recently, commercial FEM softwares, such as SAMCEF, ANSYS and NASTRAN, started supporting some rotordynamics analysis modules based on 3-D finite elements. In this paper, the dynamic analysis method using commercial S/W, especially ANSYS, is attempted for the small-size gas turbine engine rotor, and the analysis capability and limitations of its rotordyamics module are evaluated for further improvement of the module. As the preliminary procedure, the rotordyamic analysis capability of ANSYS was tested and evaluated with the reference models of the well-known dynamics. The limitations in application of the rotordynamics module were then identified. Under the current capability and limitations of ANSYS, it is shown that Lee diagram, a new frequency-speed diagram enhanced with the concept of $H{\infty}$ in rotating machinery, can be indirectly obtained from FRFs computed from harmonic response analysis of ANSYS. Finally, it is demonstrated based on the modeling and analysis method developed in the process of the S/W verification that the conventional Campbell diagram, Lee diagram, mode shapes and critical speeds of the small-size gas turbine engine rotor can be computed using the ANSYS rotordynamics module.

• 한국재난정보학회 논문집
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• 제16권3호
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• pp.458-471
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• 2020

연구목적: 우리나라에서는 최근 지진의 발생빈도와 횟수가 매년 증가하고 있다.따라서 본 연구에서는 우리나라와 일본지진의 특성과 사례 및 이에 대한 복구체계에 대해서 비교분석하고, 우리나라 지진 방재정책의 개선사항 제안하는 데 목적을 두었다. 연구방법: 본 연구에서는 고베 대지진과 동일본 대지진 두 사례에서의 일본의 대응을 조사 및 평가하고, 경주 지진과 포항 지진 두 사태에서 우리나라의 대응책을 조사 및 평가한 후, 이를 비교하였다. 연구결과: 우리나라와 일본의 복구체계를 비교했을 때, 크게 도로교통망 복구를 위한 계획, 지역방재계획 과 BCP 개념의 도입에서 유의미한 차이를 보였다. 결론: 우리나라의 지진 위험지역과 수도의 물리적 거리를 고려할 때 시일이 소요될 수밖에 없는 현재의 중앙정부 집중형의 하향식 대응에서 벗어나 기능연속성계획(COOP)의 세부 수립을 통해 지역에서의 즉각적인 지진 대응력을 높이고, 행정BCP 개념 도입을 통해 재해 발생 시 행정기능이 정상적으로 발휘되도록, 이를 담보하기 위한 대처방안을 조속히 마련해야 할 것이다.

• Structural Engineering and Mechanics
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• 제13권6호
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• pp.615-638
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• 2002

This paper presents a method of seismic analysis for a cylindrical liquid storage structure considering the effects of the interior fluid and exterior soil medium in the frequency domain. The horizontal and rocking motions of the structure are included in this study. The fluid motion is expressed in terms of analytical velocity potential functions, which can be obtained by solving the boundary value problem including the deformed configuration of the structure as well as the sloshing behavior of the fluid. The effect of the fluid is included in the equation of motion as the impulsive added mass and the frequency-dependent convective added mass along the nodes on the wetted boundary of the structure. The structure and the near-field soil medium are represented using the axisymmetric finite elements, while the far-field soil is modeled using dynamic infinite elements. The present method can be applied to the structure embedded in ground as well as on ground, since it models both the soil medium and the structure directly. For the purpose of verification, earthquake response analyses are performed on several cases of liquid tanks on a rigid ground and on a homogeneous elastic half-space. Comparison of the present results with those by other methods shows good agreement. Finally, an application example of a reinforced concrete tank on a horizontally layered soil with a rigid bedrock is presented to demonstrate the importance of the soil-structure interaction effects in the seismic analysis for large liquid storage tanks.

• Smart Structures and Systems
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• 제20권2호
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• pp.247-261
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• 2017

In the field of dynamic measurement and structural damage identification, it is generally known that modal frequencies may be measured with higher accuracy than mode shapes. However, the number of natural frequencies within a measurable range is limited. Accessing additional forms of modal frequencies is thus desirable. The present study is concerned about the extraction of artificial boundary condition (ABC) frequencies from modal testing. The ABC frequencies correspond to the natural frequencies of the structure with a perturbed boundary condition, but they can be extracted from processing the frequency response functions (FRF) measured in a specific configuration from the structure in its existing state without the need of actually altering the physical support condition. This paper presents a comprehensive experimental investigation into the measurability of the ABC frequencies from physical experiments. It covers the testing procedure through modal testing, the data processing and data analysis requirements, and the FRF matrix operations leading to the extraction of the ABC frequencies. Specific sources of measurement errors and their effects on the accuracy of the extracted ABC frequencies are scrutinised. The extracted ABC frequencies are subsequently applied in the damage identification in beams by means of finite element model updating. Results demonstrate that it is possible to extract the first few ABC frequencies from the modal testing for a variety of artificial boundary conditions incorporating one or two virtual pin supports, and the inclusion of ABC frequencies enables the identification of structural damages without the need to involve the mode shape information.

• Journal of Advanced Research in Ocean Engineering
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• 제1권4호
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• pp.239-251
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• 2015

In this study, a spectral fatigue analysis was performed for the topside structure of an offshore floating vessel. The topside structure was idealized using beam elements in the SACS program. The fatigue analysis was carried out considering the wave and wind loads separately. For the wave-induced fatigue damage calculation, motion RAOs calculated from a direct wave load analysis and regular waves with different periods and unit wave heights were utilized. Then, the member end force transfer functions were generated covering all the loading conditions. Stress response transfer functions at each joint were produced using the specified SCFs and member end force transfer functions. fatigue damages were calculated using the obtained stress ranges, S-N curve, wave spectrum, heading probability of each loading condition, and their corresponding occurrences in the wave scatter diagrams. For the wind induced fatigue damage calculation, a dynamic wind spectral fatigue analysis was performed. First, a dynamic natural frequency analysis was performed to generate the structural dynamic characteristics, including the eigenvalues (natural frequencies), eigenvectors (mode shapes), and mass matrix. To adequately represent the dynamic characteristic of the structure, the number of modes was appropriately determined in the lateral direction. Second, a wind spectral fatigue analysis was performed using the mode shapes and mass data obtained from the previous results. In this analysis, the Weibull distribution of the wind speed occurrence, occurrence probability in each direction, damping coefficient, S-N curves, and SCF of each joint were defined and used. In particular, the wind fatigue damages were calculated under the assumption that the stress ranges followed a Rayleigh distribution. The total fatigue damages were calculated from the combination with wind and wave fatigue damages according to the DNV rule.