• Title/Summary/Keyword: dynamic stiffness matrix

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Analytical solution for natural frequency of monopile supported wind turbine towers

  • Rong, Xue-Ning;Xu, Ri-Qing;Wang, Heng-Yu;Feng, Su-Yang
    • Wind and Structures
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    • v.25 no.5
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    • pp.459-474
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    • 2017
  • In this study an analytical expression is derived for the natural frequency of the wind turbine towers supported on flexible foundation. The derivation is based on a Euler-Bernoulli beam model where the foundation is represented by a stiffness matrix. Previously the natural frequency of such a model is obtained from numerical or empirical method. The new expression is based on pure physical parameters and thus can be used for a quick assessment of the natural frequencies of both the real turbines and the small-scale models. Furthermore, a relationship between the diagonal and non-diagonal element in the stiffness matrix is introduced, so that the foundation stiffness can be obtained from either the p-y analysis or the loading test. The results of the proposed expression are compared with the measured frequencies of six real or model turbines reported in the literature. The comparison shows that the proposed analytical expression predicts the natural frequency with reasonable accuracy. For two of the model turbines, some errors were observed which might be attributed to the difference between the dynamic and static modulus of saturated soils. The proposed analytical solution is quite simple to use, and it is shown to be more reasonable than the analytical and the empirical formulas available in the literature.

Damage Detection in Shear Building Based on Genetic Algorithm Using Flexibility Matrix (유연도 행렬을 이용한 전단빌딩의 유전자 알고리즘 기반 손상추정)

  • Na, Chae-Kuk;Kim, Sun-Pil;Kwak, Hyo-Gyoung
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.21 no.1
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    • pp.1-11
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    • 2008
  • Stiffness estimation of a shear building due to local damages is usually achieved though structural analysis based on the assumed material properties and idealized numerical modeling of structure. Conventional numerical modeling, however, frequently causes an inevitable error in the structural response and this makes it difficult to exactly predict the damage state in structure. To solve this problem, this paper introduces a damage detection technique for shear building using genetic algorithm. The introduced algorithm evaluates the damage in structure using a flexibility matrix since the flexibility matrix can exactly be obtained from the field test in spite of using a few lower dynamic modes of structure. The introduced algorithm is expected to be more effectively used in damage detection of structures rather than conventional method using the stiffness matrix. Moreover, even in cases when an accurate measurement of structural stiffness cannot be expected, the proposed technique makes it possible to estimate the absolute change in stiffness of the structure on the basis of genetic algorithm. The validity of the proposed technique is demonstrated though numerical analysis using OPENSEES.

Dynamic Stability Analysis of Nonconservative Systems for Variable Parameters using FE Method (유한요소기법을 이용한 비보존력이 작용하는 보-기둥 구조의 다양한 제변수 변화에 따른 동적 안정성 해석)

  • Lee Jun-Seok;Min Byoung-Cheol;Kim Moon-Young
    • Journal of the Computational Structural Engineering Institute of Korea
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    • v.17 no.4
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    • pp.351-363
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    • 2004
  • Equation of motion of non conservative system considering mass matrix, elastic stiffness matrix, load correction stiffness matrix by circulatory force's direction change and Winkler and Pasternak foundation stiffness matrix is derived. Also stability analysis due to the divergence and flutter loads is performed. And the influence of internal and external damping coefficient on flutter load is investigated applying the quadratic eigen problem solution. Additionally the influence of non-conservative force's direction parameter, internal and external damping and Winkler and Pasternak foundation on the critical load of Beck's and Leipholz's and Hauger's columns are investigated.

Experimental Investigation Into the Dynamic Characteristics of Flexible Matrix Composite Driveshafts (유연복합재 구동축의 동특성에 관한 실험 분석)

  • Shin Eung-Soo
    • Transactions of the Korean Society of Machine Tool Engineers
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    • v.15 no.2
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    • pp.93-98
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    • 2006
  • This study provides a comprehensive experimental study on the dynamic characteristics of a flexible matrix composite(FMC) driveshaft. A primary objective is to verify the analytic results of the FMC drivetrain based on the equivalent complex modulus approach and the classical lamination theory. A test rig has been constructed, which consists of a FMC shaft, a foundation beam, bearings, external dampers and a driving motor. The frequency response functions and transient responses are obtained from the external excitation and the spin-up testings. It turns out that the analytic results are in good agreement with the experimental ones.

Experimental Investigation into the Dynamic Characteristics of Flexible Matrix Composite Driveshafts (유연복합재 구동축의 동특성에 관한 실험 분석)

  • Shin, Eung-Soo;Lim, Byung-Soo
    • Proceedings of the Korean Society for Noise and Vibration Engineering Conference
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    • 2005.11a
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    • pp.123-126
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    • 2005
  • This study provides a comprehensive experimental study on the dynamic characteristics of a flexible matrix composite(FMC) driveshaft. A primary objective is to verify the analytic results of the FMC drivetrain based on the equivalent complex modulus approach and the classical lamination theory. A testrig has been constructed, which consists of a FMC shaft, a foundation beam, bearings, external dampers and a driving motor. The frequency response functions and transient responses are obtained from the external excitation and the spinup testings. It turns out that the analytic results are in good agreement with the experimental ones.

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Dynamic Characteristics Analysis of a Machine-Tool Spindle System (공작기계 주축계의 진동특성해석에 관한 연구)

  • Kim, Seok-Il;Gwak, Byeong-Man;Lee, Hu-Sang;Jeong, Jae-Ho
    • Journal of the Korean Society for Precision Engineering
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    • v.8 no.2
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    • pp.57-68
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    • 1991
  • In this study, to analyse the dynamic characteristics of a machine-tool spindle system, the spindle is mathematically represented by a Timoshenko beam including the internal damping of beam material, and each bearing by four bearing coefficients; stiffness and damping coefficients in moment and radial directions. And the dynamic compliance of the system is calculated by introducing the transfer matrix method, and the complex modal analysis method has been applied for the modal parameter identification. The influence of the bearing coefficients, material damping factor and bearing span on the dynamic characteristics of the system is parametrically examined.

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A Study of Vibration Analysis Due to Structual Changes of Dynamic Structure (동적 구조물의 구조변화에 의한 진동해석 연구)

  • 현천성;이기형;정인성
    • Transactions of the Korean Society of Mechanical Engineers
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    • v.16 no.11
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    • pp.2033-2048
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    • 1992
  • This paper presents the theoretical development and qualitative evaluation of a new concept in the mathematical modeling of dynamic structures. We use both test data and analytical approximations to identify the parameters of an incomplete model. The model has the capability of predicting the response of the points of interest on the structure over the frequency range of interest and can be used to predict the changes in natural frequencies and normal modes due to structural changes. The theory was tested by running simulated tests on a relatively simple structure, identifying the parameters of the incomplete model, and using this model to predict the effects on frequency and mode shapes of several mass and stiffness changes. The conditions of the tests were varied by selecting different numbers of points of measurement, varying the frequency range, and by including assumed measurement error. It is recommended that the theoretical development be continued and that applications to more complex structures be carried out in order to develop a better understanding of the limitations and capabilities of the method. A successful, more definitive sevaluation could lead to immediate practical applications.

Vibration Analysis for IHTS Piping System of LMR Conveying Hot Liquid Sodium (고온소듐 내부유동을 갖는 액체금속로 중간열전달계통 배관에 대한 진동특성 해석)

  • Koo, Gyeong-Hoi;Lee, Hyeong-Yeon;Lee, Jae-Han
    • Proceedings of the KSME Conference
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    • 2001.06b
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    • pp.386-391
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    • 2001
  • In this paper, the vibration characteristics of IHTS(Intermediate Heat Transfer System) piping system of LMR(Liquid Metal Reactor) conveying hot liquid sodium are investigated to eliminate the pipe supports for economic reasons. To do this, a 3-dimensional straight pipe element and a curved pipe element conveying fluid are formulated using the dynamic stiffness method of the wave approach and coded to be applied to any complex piping system. Using this method, the dynamic characteristics including the natural frequency, the frequency response functions, and the dynamic instability due to the pipe internal flow velocity are analyzed. As one of the design parameters, the vibration energy flow is also analyzed to investigate the disturbance transmission paths for the resonant excitation and the non-resonant excitations.

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Reanalysis for Correlating and Updating Dynamic Systems Using Frequency Response Functions (FRF를 이용한 동적 구조 시스템의 구조추정 및 재해석)

  • 한경봉;박선규
    • Proceedings of the Computational Structural Engineering Institute Conference
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    • 2004.04a
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    • pp.49-56
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    • 2004
  • Model updating is a very active research field, in which significant efforts has been invested in recent years. Model updating methodologies are invariably successful when used on noise-free simulated data, but tend to be unpredictable when presented with real experimental data that are-unavoidably-corrupted with uncorrected noise content. In this paper, Reanalysis using frequency response functions for correlating and updating dynamic systems is presented. A transformation matrix is obtained from the relationship between the complex and the normal frequency response functions of a structure. The transformation matrix is employed to calculate the modified damping matrix of the system. The modified mass and stiffness matrices are identified from the normal frequency response functions by using the least squares method. One simulated system is employed to illustrate the applicability of the proposed method. The result indicate that the damping matrix of correlated finite element model can be identified accurately by the proposed method. In addition, the robustness of the new approach uniformly distributed measurement noise Is also addressed.

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Comparisons of Elasto-Fiber and Fiber & Bernoulli-Euler reinforced concrete beam-column elements

  • Karaton, Muhammet
    • Structural Engineering and Mechanics
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    • v.51 no.1
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    • pp.89-110
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    • 2014
  • In this study, two beam-column elements based on the Elasto-Fiber element theory for reinforced concrete (RC) element have been developed and compared with each other. The first element is based on Elasto Fiber Approach (EFA) was initially developed for steel structures and this theory was applied for RC element in there and the second element is called as Fiber & Bernoulli-Euler element approach (FBEA). In this element, Cubic Hermitian polynomials are used for obtaining stiffness matrix. The beams or columns element in both approaches are divided into a sub-element called the segment for obtaining element stiffness matrix. The internal freedoms of this segment are dynamically condensed to the external freedoms at the ends of the element by using a dynamic substructure technique. Thus, nonlinear dynamic analysis of high RC building can be obtained within short times. In addition to, external loads of the segment are assumed to be distributed along to element. Therefore, damages can be taken account of along to element and redistributions of the loading for solutions. Bossak-${\alpha}$ integration with predicted-corrected method is used for the nonlinear seismic analysis of RC frames. For numerical application, seismic damage analyses for a 4-story frame and an 8-story RC frame with soft-story are obtained to comparisons of RC element according to both approaches. Damages evaluation and propagation in the frame elements are studied and response quantities from obtained both approaches are investigated in the detail.