• Journal of Korean Society of Steel Construction
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• v.15 no.1
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• pp.41-50
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• 2003

Nondestructive Damage Evaluation (NDE) techniques yield the damage location and its size from the modal characteristics of pre-damaged and post-damaged structures. To predict the system reliability of the aging structure, results from the NDE are integrated into the element/component failure probabilities. The element/component failure probabilities can be calculated from failure functions for each element/component with the aid of techniques from a structural reliability analysis. In this paper, a method to estimate the system reliability of a structure that is based on the reliabilities of elements/components in a given structure is presented. The efficacy of the combination of the nondestructive damage detection and the structural reliability evaluation is demonstrated using pre-damaged and post-damaged modal data obtained from numerical simulations of a rigid frame.

• Smart Structures and Systems
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• v.30 no.1
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• pp.75-88
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• 2022

Engineering structures in operation essentially belong to time-varying or nonlinear structures and the resultant response signals are usually non-stationary. For such time-varying structures, it is of great importance to extract time-dependent dynamic parameters from non-stationary response signals, which benefits structural health monitoring, safety assessment and vibration control. However, various traditional signal processing methods are unable to extract the embedded meaningful information. As a newly developed technique, variational mode decomposition (VMD) shows its superiority on signal decomposition, however, it still suffers two main problems. The foremost problem is that the number of modal components is required to be defined in advance. Another problem needs to be addressed is that VMD cannot effectively separate non-stationary signals composed of closely spaced or overlapped modes. As such, a new method named generalized adaptive variational modal decomposition (GAVMD) is proposed. In this new method, the number of component signals is adaptively estimated by an index of mean frequency, while the generalized demodulation algorithm is introduced to yield a generalized VMD that can decompose mode overlapped signals successfully. After that, synchrosqueezing wavelet transform (SWT) is applied to extract instantaneous frequencies (IFs) of the decomposed mono-component signals. To verify the validity and accuracy of the proposed method, three numerical examples and a steel cable with time-varying tension force are investigated. The results demonstrate that the proposed GAVMD method can decompose the multi-component signal with overlapped modes well and its combination with SWT enables a successful IF extraction of each individual component.

• Nuclear Engineering and Technology
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• v.41 no.3
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• pp.335-346
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• 2009

This paper deals with a hydroelastic vibration analysis of two rectangular plates partially coupled with a liquid, which is bounded by two plates and two rigid side walls. The wet displacement of each plate is assumed to be a combination of the modal functions of a dry uniform beam with a clamped boundary condition. As the liquid is assumed to be an ideal liquid, the displacement potential satisfying the Laplace equation is determined so that the liquid boundary conditions can meet the requirements at the rigid surfaces and the free liquid surface. The wet dynamic modal functions of each plate are expanded by using the finite Fourier transform to obtain an appropriate form of the compatibility requirement along the contacting surfaces between the plates and the liquid. The liquid-coupled natural frequencies of the plates are derived by using the Rayleigh-Ritz method. Finite element analyses using commercial software are carried out to verify the proposed theory. It is observed that the theoretical method agrees excellently with the three-dimensional finite element analyses results. The effects of the liquid depth and the liquid thickness on the normalized natural frequencies are investigated to identify the dynamic characteristics of the liquid coupled system.

• Transactions of the Korean Society of Mechanical Engineers A
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• v.26 no.7
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• pp.1393-1400
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• 2002

A double cantilever sandwich-beam method has been applied to the evaluation of the frequency dependence of dynamic elastic modulus and material loss factor of EPDM rubbers. The flexural vibration of a double cantilever sandwich-beam specimen with an inserted rubber layer was studied using a finite element simulation in combination with the sine-sweep test. Effects of the rubber layer length on the dynamic characteristics were also investigated: reliable values were measured when the length of the inserted rubber layer was larger than and equal to 50% of the effective specimen length. The values were compared with those obtained by the dynamic mechanical analysis and the simple resonant test. Relationships of the dynamic characteristics of rubbers with frequency could be determined using the least square error method.

• Structural Engineering and Mechanics
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• v.14 no.5
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• pp.505-520
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• 2002

Based on the modal coordinates of the structure, a finite-element and CQC (complete quadratic combination) method for analyzing the coupled buffeting response of long-span bridges is presented. The formulation of nodal equivalent aerodynamic buffeting forces is derived based on a reasonable assumption. The power spectral density and variance of nodal displacements and elemental internal forces of the bridge structure are computed using the finite-element method and the random vibration theory. The method presented is very efficient and can consider the arbitrary spectrum and spatial coherence of natural winds and the multimode and intermode effects on the buffeting responses of bridge structures. A coupled buffeting analysis of the Jiangyin Yangtse River Suspension Bridge with 1385 in main span is performed as an example. The results analyzed show that the multimode and intermode effects on the buffeting response of the bridge deck are quite remarkable.

• Proceedings of the Computational Structural Engineering Institute Conference
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• 1998.10a
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• pp.35-42
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• 1998

Response spectrum analysis method(RSA) rather than time history analysis method(THA) continues to e used by the profession for evaluating maximum dynamic responses of structures subjected to earthquake excitations. Nevertheless, this simple and practical method can cause significant errors in some cases with unproper modal combination method and so on. To obtain more exact responses based n RSA many studies have been carried out considering displacement of top story, base shear and overturning moment. The purpose of this study is to verify error characteristics in RSA with respect to various responses including displacement shear force and overturning moment of each story. It's shown that RSA appears to yield underestimated responses when compared to THA calculations. Also, errors involved in RSA computations grow with an increase in total number of stories.

• Transactions of the Korean Society for Noise and Vibration Engineering
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• v.13 no.2
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• pp.99-107
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• 2003

The finite element method(FEM) is the most widely used and powerful method for structural analysis. In general, in order to analyze complex and large structures, we have used the FEM. However, it is necessary to use a large amount of computer memory and computation time for solving accurately by the FEM the dynamic problem of a system with many degree-of-freedom, because the FEM has to deal with very large matrices in this case. Therefore, it was very difficult to analyze the vibration for plate structures with a large number of degrees of freedom by the FEM on a personal computer. For overcoming this disadvantage of the FEM without the loss of the accuracy, the finite element-transfer stiffness coefficient method(FE-TSCM) was developed. The concept of the FE-TSCM is based on the combination of modeling technique in the FEM and the transfer technique in the transfer stiffness coefficient method(TSCM). The merit of the FE-TSCM is to take the advantages of both methods, that is, the convenience of the modeling in the FEM and the computation efficiency of the TSCM. In this paper, the forced vibration analysis algorithm of plate structures is formulated by the FE-TSCM. In order to illustrate the accuracy and the efficiency of the FE-TSCM, results of frequency response analysis for a rectangular plate, which was adopted as a computational model, were compared with those by the modal analysis method and the direct analysis method which are based on the FEM.

• Earthquakes and Structures
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• v.14 no.4
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• pp.297-303
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• 2018

Seismic behavior of Osmanli and Senyuva stone bridges was addressed in this study. A combination of FEM and DEM was employed for getting closer to the real behavior of the bridge. One of the unique features of this combinational method is simulation close to reality. Modal numerical analysis was also used to verify the modeling. At the end of earthquake, a part of two lateral walls of Osmanli bridge was broken. The growth of arch cracks also increased during the earthquake. A part of right-hand wall of Senyuva Bridge was destructed during the earthquake. The left-hand side of the bridge wall was damaged during the earthquake but was not destructed.

• Journal of KSNVE
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• v.4 no.2
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• pp.137-146
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• 1994

An analytical method for linear free vibration of fully liquid-filled circular cylindrical shell with various boundary conditions is developed by the Fourier series expansion based on the Stokes' transformation. A set of modal displacement functions and their derivatives of a circular cylindrical shell is substituted into the Sanders' shell equations in order to explicitily represent the Fourier coefficients as functions of the end point displacements, forces, and moments. For the vibration relevant to the liquid motion, the velocity potential of liquid is assumed as a sum of linear combination of suitable harmonic functions in the axial directions. The unknown parameter of the velocity potential is selected to satisfy the boundary condition along the wetted shell surface. An explicit expression of the natural frequency equation can be obtained for any kind of classical boundary conditions. The natural frequencies of the liquid-filled cylindrical shells with the clamped-free, the clamped-clamped, and the simply supported-simply supported boundary conditions examined in the previous works, are obtained by the analytical method. The results are compared with the previous works, and excellent agreement is found for the natural frequencies of the shells.

• Structural Engineering and Mechanics
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• v.47 no.1
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• pp.119-129
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• 2013

Nonlinear Static Procedures (NSPs) have been developed as a practical tool to estimate the seismic demand of structures. Several researches have accomplished to minimize errors of NSPs, namely pushover procedures, in the Nonlinear Time History Analysis (NTHA), as the most exact method. The most important issue in a typical pushover procedure is the pattern and technique of loading which are extracted based on structural dynamic fundamentals. In this paper, the coefficients of modal force combination is focused involving a meta-heuristic optimization algorithm to find the optimum load pattern which results in a response with minimum amount of errors in comparison to the NTHA counterpart. Other parameters of the problem are based on the FEMA recommendations for pushover analysis of building structures. The proposed approach is implemented on a high-rise 20 storey concrete moment resisting frame under three earthquake records. In order to demonstrate the effectiveness and robustness of the studied procedure the results are presented beside other well-known pushover methods such as MPA and the FEMA procedures, and the results show the efficiency of the proposed load patterns.