Modal confidence factor in vibration testing

Ibrahim, S. R.

doi:10.2514/3.28014

Cited by 72 publications

(30 citation statements)

References 1 publication

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“…These methods determine the modal parameters indirectly by imposing a linear multiple-degree-of-freedom model on the measurement. Popular multiple-degree-offreedom time domain system identification methods are Ibrahim time domain (Ibrahim 1977), least squares complex exponential method (LSCE) algorithm (Brown et al 1979), eigensystem realization algorithm (ERA) Pappa 1985 and, and autoregressive moving average model and its derivatives (e.g., ARMAX, ARMAVX) (Ljung 1999). Some of these multiple-degree-of-freedom time domain methods are also implemented in the frequency domain.…”

Section: Experimental Modal Analysismentioning

confidence: 99%

Calibration under uncertainty for finite element models of masonry monuments

Atamturktur¹,

Hemez²,

Unal³

2010

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About the Cover:The figures on the cover illustrate three aspects of the validation of a computational model developed to predict the vibration response of historic masonry monuments. Top right: The National Cathedral, Washington, DC, where vibration response of vaults is experimentally measured to assess the effect of structural damage. The measurements provide acceleration time series used to verify and validate predictions of the numerical simulation. Top left: The computational finite element model is shown to illustrate the mesh discretization of a vault. The model is analyzed to simulate the vibration response. Colors represent different material properties whose uncertainties are propagated through the calculation. Bottom: The measurement of a vibration mode shape of the structure (solid line) is compared to the prediction of the finite element model (dashed line). Crosses illustrate the uncertainty of predictions due to variability of the boundary conditions and material properties. Statistical tests are implemented to quantify the accuracy of the finite element model, given measurement variability and prediction uncertainty. Tables Table 3- Calibration Under Uncertainty for Finite List of Figures List of ABSTRACTHistorical unreinforced masonry buildings often include features such as load bearing unreinforced masonry vaults and their supporting framework of piers, fill, buttresses, and walls. The masonry vaults of such buildings are among the most vulnerable structural components and certainly among the most challenging to analyze. The versatility of finite element (FE) analyses in incorporating various constitutive laws, as well as practically all geometric configurations, has resulted in the widespread use of the FE method for the analysis of complex unreinforced masonry structures over the last three decades. However, an FE model is only as accurate as its input parameters, and there are two fundamental challenges while defining FE model input parameters: (1) material properties and (2) support conditions. The difficulties in defining these two aspects of the FE model arise from the lack of knowledge in the common engineering understanding of masonry behavior. As a result, engineers are unable to define these FE model input parameters with certainty, and, inevitably, uncertainties are introduced to the FE model.As the complexity of the building increases, as is the case for historical unreinforced masonry buildings, the errors and uncertainties in the analysis also increase. In the presence of high and numerous uncertainties originating from multiple sources, deterministic approaches in which parameters are defined as constant values assumed to be known with certainty cannot be implemented reliably. Probabilistic methods, however, provide a rigorous and rational means in treating the uncertainty present in the FE analysis of historical unreinforced masonry buildings. The way in which uncertainty in historical unreinforced masonry construction is treated is one of the novel and main contributions...

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Section: Experimental Modal Analysismentioning

confidence: 99%

Calibration under uncertainty for finite element models of masonry monuments

Atamturktur¹,

Hemez²,

Unal³

2010

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“…Table 3. The modal assurance criterion (MAC) is used to estimate the correctness of different mode shape [8].…”

Section: Vibration Testing Of the Ac Dipolementioning

confidence: 99%

Vibration research of the AC dipole-girder system for CSNS/RCS

Liu

et al. 2014

Chinese Phys. C

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China Spallation Neutron Source (CSNS) is a high intensity proton accelerator based facility, and its accelerator complex includes two main parts: an H-linac and a Rapid Cycling Synchrotron (RCS). The RCS accumulates the 80MeV proton beam, and accelerates it to 1.6GeV, with a repetition rate of 25Hz. The AC dipole of the CSNS/RCS is operated at a 25 Hz sinusoidal alternating current which causes severe vibration. The vibration will influence the long-term safety and reliable operation of the magnet. The dipole magnet of CSNS/RCS is active vibration equipment which is different with ground vibration accelerator. It's very important to design and research the dynamic characteristic of the dipole-girder system. This paper takes the AC dipole and girder as a specific model system, a method for researching the dynamic characteristic of the system is put forward by combining theoretical calculation with experimental testing. The ANSYS simulation method plays a very important role in the girder structure design stage. With the method the mechanical resonance phenomenon was avoided in the girder design time. At the same time the dipole vibratory force will influence the other equipment through the girder. It's necessary to isolate and decrease the dipole vibration. So a new isolator was designed to isolate the vibratory force and decrease the vibration amplitude of the magnet.

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“…While this approach has also been frequently applied in the field of structural dynamics Thomson, 1974, 1977;Ibrahim and Mikulcik, 1973, 1977Ibrahim and Pappa, 1982;Ibrahim, 1977Ibrahim, , 1978Ibrahim, , 1983Junkins, 1978;Beck and Jennings, 1980;Yao, 1985;Torkamani and Hart, 1975;Shinozuka et al, 1982;Rajaram and Junkins, 1985;Hac and Spanos, 1987), there is a paucity of studies that are concerned with the problems encountered by this approach when applied to realistic problems arising in the vibration field. Consequently, the present section of this paper is devoted to presenting an indepth, unified, and efficient approach for using least-squares…”

Section: Time-domain Identification Of Linear System Matricesmentioning

confidence: 99%

Identification of Nonlinear Vibrating Structures: Part I—Formulation

Masri

Miller

Saud

et al. 1987

Journal of Applied Mechanics

118

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A self-starting multistage, time-domain procedure is presented for the identification of nonlinear, multi-degree-of-freedom systems undergoing free oscillations or subjected to arbitrary direct force excitations and/or nonuniform support motions. Recursive least-squares parameter estimation methods combined with non-parametric identification techniques are used to represent, with sufficient accuracy, the identified system in a form that allows the convenient prediction of its transient response under excitations that differ from the test signals. The utility of this procedure is demonstrated in a companion paper.

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Modal confidence factor in vibration testing

Cited by 72 publications

References 1 publication

Calibration under uncertainty for finite element models of masonry monuments

Calibration under uncertainty for finite element models of masonry monuments

Vibration research of the AC dipole-girder system for CSNS/RCS

Identification of Nonlinear Vibrating Structures: Part I—Formulation

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