• Title, Summary, Keyword: mode acceleration method

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Dynamic Analysis of Offshore Structures by the Advanced Mode Acceleration Method (개선된 Mode Acceleration Method에 의한 해양(海洋) 구조물(構造物)의 동적(動的) 해석(解析))

  • Kim, Tae Nam
    • Journal of The Korean Society of Civil Engineers
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    • v.14 no.1
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    • pp.13-20
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    • 1994
  • Determination of the number of modes to be included in the mode superposition method(MSM) is very important and difficult. Mode acceleration method(MAM) is recommended recently with the intention to overcome the problem. But the solution of the MAM is complex and complicate in frequency domain analysis. In this paper, advanced mode acceleration method(AMAM) is formulated and examined. The results from example analyses show that AMAM is a simple, accurate and reliable method compared with the MSM and the MAM.

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Efficient Mode Superposition Method for Non-Classically Damped Systems (비비례 감쇠시스템의 해석을 위한 효율적인 모드 중첩법)

  • Cho, Sang-Won;Cho, Ji-Seong;Park, Sun-Kyu;Lee, In-Won
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • pp.549-555
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    • 2000
  • The improved mode superposition methods for non-classically damped systems are presented in this paper. Generally, the mode superposition method uses a relatively small subset of the normal modes of structures. The mode acceleration method and the modal truncation augmentation method improve the results of the mode superposition method by considering effects of truncated high modes. For using these methods to analyze non-classically damped systems, the systems are approximated to the classically damped systems and thereby the errors are induced. In this paper, the mode acceleration method and the modal truncation augmentation method are expanded to analyze the non-classically damped systems. The applicability of the expanded methods is verified by closed form solutions and numerical examples. The expanded modal truncation augmentation method is conditionally stable depending on the pattern of the external loading in the non-classically damped systems whereas the expanded mode acceleration method is stable for the all cases of loading. In the stable case, the results are the same with those of the expanded mode acceleration method.

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Effects of diaphragm flexibility on the seismic design acceleration of precast concrete diaphragms

  • Zhang, Dichuan;Fleischman, Robert B.;Lee, Deuckhang
    • Computers and Concrete
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    • v.25 no.3
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    • pp.273-282
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    • 2020
  • A new seismic design methodology for precast concrete diaphragms has been developed and incorporated into the current American seismic design code. This design methodology recognizes that diaphragm inertial forces during earthquakes are highly influenced by higher dynamic vibration modes and incorporates the higher mode effect into the diaphragm seismic design acceleration determination using a first mode reduced method, which applies the response modification coefficient only to the first mode response but keeps the higher mode response unreduced. However the first mode reduced method does not consider effects of diaphragm flexibility, which plays an important role on the diaphragm seismic response especially for the precast concrete diaphragm. Therefore this paper investigated the effect of diaphragm flexibility on the diaphragm seismic design acceleration for precast concrete shear wall structures through parametric studies. Several design parameters were considered including number of stories, diaphragm geometries and stiffness. It was found that the diaphragm flexibility can change the structural dynamic properties and amplify the diaphragm acceleration during earthquakes. Design equations for mode contribution factors considering the diaphragm flexibility were first established through modal analyses to modify the first mode reduced method in the current code. The modified first mode reduced method has then been verified through nonlinear time history analyses.

Comparison of Mode Superposition Method and Mode Acceleration Method in Dynamic Analysis of Suspension Bridges under Wind Loads (풍하중을 받는 현수교의 진동 해석에 있어서 모우드 중첩법과 모우드 가속도법의 비교)

  • 김태남
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • pp.223-230
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    • 1997
  • A method of stochastic dynamic analysis of suspension bridge subjected to random wind loads has been developed in this paper. Example analyses are carried out by mode superposition method(MSM), mode acceleration method(MAM) and advanced mode acceleration method(AMAM) in frequency domain for the Nam-Hae Bridge. In this study the statistical characterics of random wind loads we assumed to be Gaussian stationary zero mean processes. The considered structural response quanties are displacements, shear forces and bending moments. The mean extreme responses are approximately calculated by three times of standard deviations. The followings are the conclusions from this study. 1. Numerical results which obtained by three methods of computer program developed in this paper agree reasonably well when the numbers of modes increase. 2. AMAM is simple, accurate, economic and reliable method compared with the MSM and the MAM.

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A Stochastic Analysis of Offshore Structures (해양구조물(海洋構造物)의 추계학적(推計學的) 한 해법(解法))

  • Lee, Yong Jae
    • Journal of The Korean Society of Civil Engineers
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    • v.5 no.4
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    • pp.65-73
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    • 1985
  • A stochastic dynamic analysis using Mode-Acceleration Method was formulated and examined in this paper. A computer program was developed using this theory and model offshore structure was analyzed by the program. Results show that the stochastic dynamic analysis using the Mode-Acceleration Method is superior to that using Mode Displacement Method. The method using the theory developed in this paper was proved to be very reliable, economic and potential.

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Displacement estimation of bridge structures using data fusion of acceleration and strain measurement incorporating finite element model

  • Cho, Soojin;Yun, Chung-Bang;Sim, Sung-Han
    • Smart Structures and Systems
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    • v.15 no.3
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    • pp.645-663
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    • 2015
  • Recently, an indirect displacement estimation method using data fusion of acceleration and strain (i.e., acceleration-strain-based method) has been developed. Though the method showed good performance on beam-like structures, it has inherent limitation in applying to more general types of bridges that may have complex shapes, because it uses assumed analytical (sinusoidal) mode shapes to map the measured strain into displacement. This paper proposes an improved displacement estimation method that can be applied to more general types of bridges by building the mapping using the finite element model of the structure rather than using the assumed sinusoidal mode shapes. The performance of the proposed method is evaluated by numerical simulations on a deck arch bridge model and a three-span truss bridge model whose mode shapes are difficult to express as analytical functions. The displacements are estimated by acceleration-based method, strain-based method, acceleration-strain-based method, and the improved method. Then the results are compared with the exact displacement. An experimental validation is also carried out on a prestressed concrete girder bridge. The proposed method is found to provide the best estimate for dynamic displacements in the comparison, showing good agreement with the measurements as well.

A Study on Evaluating a Representative Smoke Value from an Inspection Vehicle Using Integration Method over a Cycle of Free-Acceleration Test Mode (무부하 급가속 측정 사이클로 운전되는 검사 대상 디젤 차량으로부터 배출되는 매연값 적분에 의한 차량 매연 대표값 특성 연구)

  • Lee, Choong Hoon
    • Journal of ILASS-Korea
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    • v.18 no.3
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    • pp.132-139
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    • 2013
  • Smoke emissions from light duty diesel vehicles were measured using light extinction method with the free acceleration test mode. The smoke emissions for each measurement cycle of the free acceleration method showed large variations according to driver's pedal pushing pattern. The smoke values for each measurement cycle initially increased and reach a peak value. Integration of the smoke emissions with time for each measurement cycle was performed to get a representative smoke value which was obtained by averaging the integrated results. Two kinds of integration time range were used. One is range over the whole measurement cycle of the free acceleration method. The other is only the acceleration range in the measurement cycle. Overall, variation of the representative smoke values obtained by the integration method was reduced comparing to the traditional representative smoke value which was obtained from a peak smoke value over the measurement cycle. Ten vehicles of the same model with 2.5 liter diesel engines, and seven vehicles of the same model with 2.7 liter diesel engines, were tested using the free acceleration test method.

A simplified method for determining the acceleration amplitudes of long-span floor system under walking/running loads

  • Cao, Liang;Chen, Y. Frank
    • Structural Engineering and Mechanics
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    • v.75 no.3
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    • pp.377-387
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    • 2020
  • Modern long-span floor system typically possesses low damping and low natural frequency, presenting a potential vibration sensitivity problem induced by human activities. Field test and numerical analysis methods are available to study this kind of problems, but would be inconvenient for design engineers. This paper proposes a simplified method to determine the acceleration amplitudes of long-span floor system subjected to walking or running load, which can be carried out manually. To theoretically analyze the acceleration response, the floor system is simplified as an anisotropic rectangular plate and the mode decomposition method is used. To facilitate the calculation of acceleration amplitude aP, a coefficient αwmn or αRmn is introduced, with the former depending on the geometry and support condition of floor system and the latter on the contact duration tR and natural frequency. The proposed simplified method is easy for practical use and gives safe structural designs.

DADS 및 MSC/NASTRAN을 이용한 다물체계 유연물체의 동역학 해석

  • Kim, Chang-Bu;Baek, Yun-Gi
    • Journal of the Korean Society for Precision Engineering
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    • v.18 no.2
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    • pp.63-71
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    • 2001
  • This paper introduces a method for calculation of dynamic stress occurring in flexible bodies of a moving multibody system by using commercial softwares DADS for dynamic analysis and MSC/NASTRAN for finite element analysis. Three methods for model transient response analysis of a flexible body are summarized. Elastic deformation of a flexible body can be described with normal modes and static modes composed of constraint modes and residual attachment modes. The deformation modes divided into fixed-interface modes and free-interface modes can be determined by using MSC/NASTRAN and selected for dynamic analysis. The dynamic results obtained from DADS are utilized to calculate dynamic stress by using mode-displacement method or mode-acceleration method of MSC/NASTRAN. As a numerical example of the analysis, we used a three dimensional slider-crank model with a flexible connecting rod.

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Mathematical Theorem of Mode Acceleration Method (모우드 가속도법의 수학적 정리(定理))

  • 김태남
    • Journal of the Earthquake Engineering Society of Korea
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    • v.7 no.2
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    • pp.1-7
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    • 2003
  • Mode superposition method(MSM) is the most commonly used for solving linear response problems of structural dynamics. The major advantage of MSM is that usually a small number of lower mode is sufficient to analysis the response. However, the convergence is slow and many modes would be needed to give an accurate MSM in large structure with many degrees of freedom. The inaccuracies of MSM are caused by mode truncation in the solution. These demerits can be overcome by use of the mode acceleration method(MAM). Example analyses are carried out in simple beam subjected to harmonic loadings and compared the convergence of the joint displacements by the two methods. For relatively low frequency loadings, a good results was obtained by the lowest one mode in MAM, so the method is more economic in numerical analysis on an accurate solution.