• 한국음향학회지
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• 제18권7호
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• pp.39-44
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• 1999

직사각형 평판의 고유진동수와 진동모드를 연구하였다. 이중 퓨리에 사인시리즈를 직사각형 평판의 모달 변위함수로 사용하였으며, 다양한 경계조건을 가지는 자유진동 해석에 적용하였다. 유한급수 전개로써 근사해를 나타내는 고전적인 Ritz 방법을 이용해서 직사각형 평판의 고유진동수를 해석한 Leissa의 결과와 본 연구의 결과를 비교하였다. 그리고, 평판의 형상비에 따른 영향도 연구하였다. 자유경계 평판, 외팔평판, 고정평판, 그리고 모서리가 단순지지된 직사각형 평판의 진동형태를 가시화 하였다.

• 소음진동
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• 제1권1호
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• pp.45-52
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• 1991

The dynamic properties of primary-secondary structural systems are examined using analytical expressions for the modal properties. The analysis begins with a Lagrange multiplier formulation to develop a characteristic equation in terms of primary system mobilities and secondary system impedances. The complexity of the characteristic equation by developing new method, frequency window method. It is shown that the reduction of complexity can only be obtained by a reduction of accuracy, but by retaining the dominant effects of the dynamics problem, the loss of accuracy is not excessive. The reduced problem is examined further to develop simple expressions for the modal properties which provide insight into the resonance characteristics of the primary-secondary system problem. The results are useful as a complement to existing computational techniques for understanding and interpreting dynamic analysis results.

• Structural Engineering and Mechanics
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• 제63권4호
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• pp.457-469
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• 2017

This manuscript deals with a novel approach aimed at identifying multiple damaged sites in structural components through finite frequency changes. Natural frequencies, meant as a privileged set of modal data, are adopted along with a numerical model of the system. The adoption of finite changes efficiently allows challenging characteristic problems encountered in damage detection techniques such as unexpected comparison of possible shifted modes and the significance of modal data changes very often affected by experimental/environmental noise. The new procedure extends MDLAC and exploits parallel computing on modern multicore processors. Smart filters, aimed at reducing the potential damaged sites, are implemented in order to reduce the computational effort. Several use cases are presented in order to illustrate the potentiality of the new damage detection procedure.

• Structural Engineering and Mechanics
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• 제68권1호
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• pp.39-51
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• 2018

In this study, a frequency domain model updating method is presented using power spectral density (PSD) data. It uses the sensitivity of PSD function with respect to the unknown structural parameters through a decomposed form of transfer function. The stiffness parameters are captured with high accuracy through solving the sensitivity equations utilizing the least square approach. Using numerically noise polluted data, the model updating results of a truss model prove robustness of the method against measurement and mass modelling errors. Results prove the capabilities of the method for parameter estimation using highly noise polluted data of low ranges of excitation frequency.

• 한국콘크리트학회:학술대회논문집
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• 한국콘크리트학회 2005년도 추계 학술발표회 제17권2호
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• pp.113-116
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• 2005

In this study, in order to. investigate the effectiveness af tuned liquid damper (TLD) for the seismic performance enhancement af the existing reinforced concrete (RC) apartment structure which is nat seismically designed, shaking table test was conducted for the small scale five stary RC structure with TLD. TLD model was constructed to. have the frequency tuned to. the first modal frequency af the structure, $2\%$ mass ratio. af the first modal mass, and 0.08 liquid depth ratio. White noise with $0.2\~5Hz$ frequency bandwidth tests were performed using the shaking table at Korea Institute af Machinery and Materials, and the displacement and absolute acceleration af each floor were measured. Test results indicate that mare than $30\%$ seismic responses reduction can be achieved using TLD for RC structure under white noise.

• 한국소음진동공학회:학술대회논문집
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• 한국소음진동공학회 2013년도 춘계학술대회 논문집
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• pp.816-821
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• 2013

This case study presents a practical method to reduce resonant vibration of generator-motor set. The generator is driven at 1800rpm by induction integral motor. The vibration is below alarm limits, but the dominant frequency of vibration is sub-synchronous and close to that of bearing fault signal in spite of new bearings. To find an mechanism of abnormal vibration, ODS and Modal analysis is carried out. The measured modal characteristics were compared with those of FE Analysis. The ODS mode at rated speed is consistent with system natural frequency mode that is excited by bearings. To reduce vibration level, the isolation mount at system base is changed with new rubber mount for lower natural frequency.

• Smart Structures and Systems
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• 제9권5호
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• pp.441-459
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• 2012

Identification of vibration parameters from the analysis of the dynamic response of a structure plays a key role in current health monitoring systems. This study evaluates the capabilities of the recently developed Synchrosqueezed Wavelet Transform (SWT) to extract instant frequencies and damping values from the simulated noise-contaminated response of a structure. Two approaches to estimate the modal damping ratio from the results of the SWT are presented. The results obtained are compared to other signal processing methods based on Continuous Wavelet (CWT) and Hilbert-Huang (HHT) transforms. It was found that the time-frequency representation obtained via SWT is sharped than the obtained using just the CWT and it allows a more robust extraction of the individual modal responses than using the HHT. However, the identification of damping ratios is more stable when the CWT coefficients are employed.

• ETRI Journal
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• 제29권1호
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• pp.36-44
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• 2007

The wave concept iterative procedure (WCIP) is used to analyze arbitrarily shaped frequency selective surfaces (FSS). The WCIP method is developed from the fast modal transform based on a two-dimensional fast Fourier transform algorithm. Using the proposed procedure, less computing time and memory are needed to calculate the scattering parameters of the FSS structure. The method is applied to the modeling of an FSS structure of a rectangular patch and a comparison with experimental results confirms good agreement.

• Structural Engineering and Mechanics
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• 제39권5호
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• pp.703-716
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• 2011

The accurate dynamic analysis of structures is usually performed by a fine finite element discretization with very large number of degrees of freedom. Apart from modal analysis, one can reduce the number of final equations by assuming the deformed shape of the structure as a linear combination of independent Ritz vectors. The efficiency of this method relies heavily on the vectors selected. In this paper, a new set of Ritz vectors is proposed. It is primarily proved that these vectors are linearly independent. Subsequently, various two and three-dimensional examples are analyzed based on the proposed method. In each case, the results are compared with the ones obtained based on usual Ritz and modal analysis methods. It is finally concluded that the proposed method is very effective and efficient method for dynamic analysis of structures in frequency domain.

• Wind and Structures
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• 제29권5호
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• pp.361-369
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• 2019

The modal frequency responses of adhesive bonded T-joint structure have been analyzed numerically and verified with own experimental data. For this purpose, the damped free frequencies of the bonded joint have been computed using a three-dimensional finite element model via ANSYS parametric design language (APDL) code. The practical relevance of the joint structure analysis has been established by comparing the simulation data with the in-house experimental values. Additionally, the influences of various geometrical and material parameters on the damped free frequency responses of the joint structure have been investigated and final inferences discussed in details. It is observed that the natural frequency values increase for the higher aspect ratios of the joint structure. Also, the joint made up of Glass fiber/epoxy with quasi-isotropic fiber orientation indicates more resistance towards free vibration.