• Title, Summary, Keyword: mode superposition method

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Seismic Response Prediction of a Structure Using Experimental Modal Parameters from Impact Tests (충격시험에 의한 실험모드특성을 이용한 구조물의 지진응답 예측)

  • Cho, Sung-Gook;Joe, Yang-Hee;So, Gi-Hwan
    • Journal of the Earthquake Engineering Society of Korea
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    • v.14 no.2
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    • pp.75-84
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    • 2010
  • An in-cabinet response spectrum should be generated to perform the seismic qualification of devices and instruments mounted inside safety-related electrical equipment installed in nuclear power plants. The response spectrum is available by obtaining accurate seismic responses at the device mounting location of the cabinet. The dynamic behavior of most of electrical equipment may not be easily analyzed due to their complex mass and stiffness distributions. Considering these facts, this study proposes a procedure to estimate the seismic responses of a structure by a combination of a test and subsequent analysis. This technique firstly constructs the modal equations of the structure by using the experiment modal parameters obtained from the impact test. Then the seismic responses of the structure may be calculated by a mode superposition method. A simple steel frame structure was fabricated as a specimen for the validation of the proposed method. The seismic responses of the specimen were estimated by using the proposed technique and compared with the measurements obtained from the shaking table tests. The study results show that it is possible to accurately estimate the seismic response of the structure by using the experimental modal parameters obtained from the impact test.

Dynamic Behavior and Resonance Reduction of Two-Span Continuous Bridges for Korean Train eXpress (KTX용 2경간 연속교량의 동적거동 및 공진감소)

  • Oh, Juwon
    • Journal of The Korean Society of Civil Engineers
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    • v.28 no.1A
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    • pp.95-104
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    • 2008
  • Dynamic behaviors of the two-span continuous bridge which is one of prototypes on Gyoung-Bu high-speed railway are analyzed and some methods for reducing the resonance of the bridge are proposed. The bridge is modeled as a two-span continuous beam and the load is a vehicle of TGV-K (2p+18T) with length of 380.15 meter traveling on the railway bridge at some constant velocity. The equations governing the dynamic behaviors of the bridge are partial differential equations produced by using a system with distributed mass and elasticity. The analysis of the governing equations is performed by the mode superposition method which has modal coordinates solved by Duhamel's integral. Without considering the train velocity the dynamic reponses can be greatly reduced at some special lengths of bridge. It is different from the results of simple bridges researched so far. When the dynamic responses increase rapidly to make a resonance phenomenon depending on the train velocities, the several methods are proposed to deduce the resonance.

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Determination of the Natural Frequencies and Mode Shapes of Large Structures by Accelerated Newton-Raphson Method (Accelerated Newton-Raphson 방법에 의한 대형구조물의 자유진동수와 모우드형의 결정)

  • Kim, Man Cheol;Lee, In Won
    • Journal of The Korean Society of Civil Engineers
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    • v.14 no.5
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    • pp.1105-1113
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    • 1994
  • For the design of various structures, the dynamic analysis of the structures is essential. Eigenproblem must be first computed when the mode superposition method is used in the dynamic analysis of the structures. However, since most of solution time is spent on calculating the eigenpairs of the system, the development of more efficient solution method is required. The purpose of this paper is to present the efficient solution method that combines the Robinson-Lee's method and accelerated Newton-Raphson method to improve numerical stability and increase convergence. Effectiveness of the proposed method is verified through numerical examples.

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Analysis for Catenary Voltage of The ATs-Fed AC Electric Railroad System (단권변압기 교류전기철도 급전시스템의 전차선 전압해석)

  • 정현수;이승혁;김진오
    • The Transactions of the Korean Institute of Electrical Engineers A
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    • v.52 no.9
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    • pp.493-499
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    • 2003
  • This paper presents exact Autotransformers(ATs)-fed AC electric Railroad system modeling using constant current mode for locomotives. An AC electric railroad system is rapidly changing single-phase load, and at a feeding substation, 3-phase electric power is transferred to paired directional single-phase electric power. As the train moves along a section of line between two adjacent ATs. The proposed AC electric railroad system modeling method considers the line self-impedances and mutual-impedances. The constant current mode model objectives are to calculate the catenary and rail voltages with the loop equation. When there are more than one train in the AC electric railroad system, the principle of superposition applies and the only difference between the system analyses for one train. Filially, this paper shows the general equation of an AC electric railroad system, and that equation has no relation with trains number, trains position, and feeding distance.

Seismic Analysis of an Axial Blower Using a Commercial FEM Code (상용 유한요소해석 프로그램을 이용한 축류송풍기의 내진해석)

  • 정진태;임형빈;김강성;허진욱
    • Transactions of the Korean Society for Noise and Vibration Engineering
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    • v.12 no.3
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    • pp.181-186
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    • 2002
  • A seismic analysis is one of crucial design procedures of an axial blower used in nuclear power Plants. The blower should be operated even in ar emergency such as an earthquake. The blower should be designed in order to stand against an earthquake. For the seismic analysis, Ive perform the modal analysis and then evaluate the required response spectrum (PRS) from the given floor response spectrum (FRS). A finite element model of the blower is established by using a commercial FEM code of ANSYS. After the finite element modeling. the natural frequencies. the mode shapes and the participation factors are obtained from the modal analysis. The PRS is acquired by a numerical approach on the basis of the principle of mode superposition. We verify the structura safety of the axial blower and confirm the validity of the present seismic analysis results.

Analysis for Catenary Voltage of The ATs-Fed AC Electric Railroad System (교류전기철도 급전시스템의 전차선 전압해석)

  • 이승혁;정현수;김진오
    • Proceedings of the KSR Conference
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    • pp.490-496
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    • 2002
  • This paper presents exact Autotransformers(ATs)-fed AC electric Railroad system modeling using constant current mode far locomotives. An AC electric railroad system is rapidly changing single-phase load, and at a feeding substation, 3-phase electric power is transferred to paired directional single-phase electric power. As the train moves along a section of line between two adjacent ATs. The proposed AC electric railroad system modeling method considers the line self-impedances and mutual-impedances. The constant current mode model objectives are to calculate the catenary and rail voltages with the loop equation. When there are more than one train in the AC electric railroad system, the principle of superposition applies and the only difference between the system analyses for one train. Finally, this paper shows the general equation of an AC electric railroad system, and that equation has no relation with trains number, trains position, and feeding distance.

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Estimation of floor response spectra induced by artificial and real earthquake ground motions

  • Pu, Wuchuan;Xu, Xi
    • Structural Engineering and Mechanics
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    • v.71 no.4
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    • pp.377-390
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    • 2019
  • A method for estimating the floor response spectra (FRS) of elastic structures under earthquake excitations is proposed. The method is established based on a previously proposed direct estimation method for single degree of freedom systems, which generally overestimates the FRS of a structure, particularly in the resonance period range. A modification factor is introduced to modify the original method; the modification factor is expressed as a function of the period ratio and is determined through regression analysis on time history analysis results. Both real and artificial ground motions are considered in the analysis, and it is found that the modification factors obtained from the real and artificial ground motions are significantly different. This suggests that the effect of ground motion should be considered in the estimation of FRS. The modified FRS estimation method is further applied to a 10-story building structure, and it is verified that the proposed method can lead to a good estimation of FRS of multi-story buildings.

On the eigenvalues of a uniform rectangular plate carrying any number of spring-damper-mass systems

  • Chen, Der-Wei
    • Structural Engineering and Mechanics
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    • v.16 no.3
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    • pp.341-360
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    • 2003
  • The goal of this paper is to determine the eigenvalues of a uniform rectangular plate carrying any number of spring-damper-mass systems using an analytical-and-numerical-combined method (ANCM). To this end, a technique was presented to replace each "spring-damper-mass" system by a massless equivalent "spring-damper" system with the specified effective spring constant and effective damping coefficient. Then, the mode superposition approach was used to transform the partial differential equation of motion into the matrix equation, and the eigenvalues of the complete system were determined from the associated characteristic equation. To verify the reliability of the presented theory, all numerical results obtained from the ANCM were compared with those obtained from the conventional finite element method (FEM) and good agreement was achieved. Since the order of the property matrices for the equation of motion obtained from the ANCM is much lower than that obtained from the FEM, the CPU time required by the ANCM is much less than that by the FEM.

A natural frequency sensitivity-based stabilization in spectral stochastic finite element method for frequency response analysis

  • Lee, Gil-Yong;Jin, Seung-Seop;Park, Yong-Hwa
    • Structural Engineering and Mechanics
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    • v.75 no.3
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    • pp.311-325
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    • 2020
  • In applying the spectral stochastic finite element methods to the frequency response analysis, the conventional methods are known to give unstable and inaccurate results near the natural frequencies. To address this issue, a new sensitivity based stabilized formulation for stochastic frequency response analysis is proposed in this paper. The main difference over the conventional spectral methods is that the polynomials of random variables are applied to both numerator and denominator in approximating the harmonic response solution. In order to reflect the resonance behavior of the structure, the denominator polynomials is constructed by utilizing the natural frequency sensitivity and the random mode superposition. The numerator is approximated by applying a polynomial chaos expansion, and its coefficients are obtained through the Galerkin or the spectral projection method. Through various numerical studies, it is seen that the proposed method improves accuracy, especially in the vicinities of structural natural frequencies compared to conventional spectral methods.

Analysis of Dynamic Deformation of 4-Bar Linkage Mechanism (1) Finite Element Analysis and Numerical Solution (4절 링크 기구의 동적 변형 해석 (I) 유한 요소 해석 및 수치해)

  • Cho, Sun-Whi;Park, Jong-Keun;Lee, Jin
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.4
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    • pp.737-752
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    • 1992
  • Analysis of elasto-dynamic deformation of flexible linkage mechanism is conducted using the finite element method. The equations of motion of the system are derived from the static structural problem in which dynamic inertia, gravitational and driving forces are treated as external loads. Linear spring model is included in the formulation of equation of motions to represent the effects of deformation of elastic bearings of revolute joints on the system behavior. A computer program is constructed and applied to analyze a specific crank-lever 4-bar mechanism. The algorithm of the program is as follows. First, the natural frequencies and the mode shapes of the system are calculated by solving the eigenproblem of the mechanism system which can be considered as a static structure by assuming the input shaft (crank shaft) to be fixed at any given configuration of mechanism. And finally, the elasto-dynamic deformation of the whole system is obtained using mode superposition method for the case of constant input speed. The effect of geometric stiffness on the mechamism is included in the program with the axial forces of links obtained through the quasi-static displacement analysis. It is found that the geometric stiffness exerts an important effect upon the elasto-dynamic behavior of the flexible linkage mechanism. Elastic deformation of bearing lowers the natural frequencies of the system, resulting smaller elastic displacement at the mid-point of the links and bigger elestic displacement at the ends of the links than rigid bearing. The above investigation of flexible linkage mechanism shows that the effects of the elastic deformation of bearing on the mechanism should be considered to design the mechanism which satisfies more preciously the purpose and the condition of design.