| 1. |
- Abbasiverki, Roghayeh, et al.
(author)
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Nonlinear Behaviour of Concrete Buttress Dams under High-Frequency Excitations Taking into Account Topographical Amplifications
- 2021
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In: Shock and Vibration. - : Hindawi Limited. - 1070-9622 .- 1875-9203. ; 2021, s. 1-22
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Journal article (peer-reviewed)abstract
- Concrete buttress dams could potentially be susceptible to high-frequency vibrations, especially in the cross-stream direction, due to their slender design. Previous studies have mainly focused on low-frequency vibrations in stream direction using a simplified foundation model with the massless method, which does not consider topographic amplifications. This paper therefore investigates the nonlinear behaviour of concrete buttress dams subjected to high-frequency excitations, considering cross-stream vibrations. For comparison, the effect of low-frequency excitations is also investigated. The influence of the irregular topography of the foundation surface on the amplification of seismic waves at the foundation surface and thus in the dam is considered by a rigorous method based on the domain-reduction method using the direct finite element method. The sensitivity of the calculated response of the dam to the free-field modelling approach is investigated by comparing the result with analyses using an analytical method based on one-dimensional wave propagation theory and a massless approach. Available deconvolution software is based on the one-dimensional shear wave propagation to transform the earthquake motion from the foundation surface to the corresponding input motion at depth. Here, a new deconvolution method for both shear and pressure wave propagation is developed based on an iterative time-domain procedure using a one-dimensional finite element column. The examples presented showed that topographic amplifications of high-frequency excitations have a significant impact on the response of this type of dam. Cross-stream vibrations reduced the safety of the dam due to the opening of the joints and the increasing stresses. The foundation modelling approach had a significant impact on the calculated response of the dam. The massless method produced unreliable results, especially for high-frequency excitations. The free-field modelling with the analytical method led to unreliable joint openings. It is therefore recommended to use an accurate approach for foundation modelling, especially in cases where nonlinearity is considered.
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| 2. |
- Josefsson, Andreas, et al.
(author)
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Bias errors due to leakage effects when estimating frequency response functions
- 2012
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In: Shock and Vibration. - : IOS Press. - 1070-9622 .- 1875-9203. ; 19:6, s. 1257-1266
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Journal article (peer-reviewed)abstract
- Frequency response functions are often utilized to characterize a system's dynamic response. For a wide range of engineering applications, it is desirable to determine frequency response functions for a system under stochastic excitation. In practice, the measurement data is contaminated by noise and some form of averaging is needed in order to obtain a consistent estimator. With Welch's method, the discrete Fourier transform is used and the data is segmented into smaller blocks so that averaging can be performed when estimating the spectrum. However, this segmentation introduces leakage effects. As a result, the estimated frequency response function suffers from both systematic (bias) and random errors due to leakage. In this paper the bias error in the H 1 and H2-estimate is studied and a new method is proposed to derive an approximate expression for the relative bias error at the resonance frequency with different window functions. The method is based on using a sum of real exponentials to describe the window's deterministic autocorrelation function. Simple expressions are derived for a rectangular window and a Hanning window. The theoretical expressions are verified with numerical simulations and a very good agreement is found between the results from the proposed bias expressions and the empirical results.
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| 3. |
- Lindberg, Eskil, et al.
(author)
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Component mode synthesis using undeformed interface coupling modes to connect soft and stiff substructures
- 2013
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In: Shock and Vibration. - 1070-9622 .- 1875-9203. ; 20:1, s. 157-170
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Journal article (peer-reviewed)abstract
- Classical component mode synthesis methods for reduction are usually limited by the size and compatibility of the coupling interfaces. A component mode synthesis approach with constrained coupling interfaces is presented for vibro-acoustic modelling. The coupling interfaces are constrained to six displacement degrees of freedom. These degrees of freedom represent rigid interface translations and rotations respectively, retaining an undeformed interface shape. This formulation is proposed for structures with coupling between softer and stiffer substructures in which the displacement is chiefly governed by the stiffer substructure. Such may be the case for the rubber-bushing/linking arm assembly in a vehicle suspension system. The presented approach has the potential to significantly reduce the modelling size of such structures, compared with classical component mode synthesis which would be limited by the modelling size of the interfaces. The approach also eliminates problems of nonconforming meshes in the interfaces since only translation directions, rotation axes and the rotation point need to be common for the coupled substructures. Simulation results show that the approach can be used for modelling of systems that resemble a vehicle suspension. It is shown for a test case that adequate engineering accuracy can be achieved when the stiffness properties of the connecting parts are within the expected range of rubber connected to steel.
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| 4. |
- Mackerle, Jaroslav
(author)
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Finite element computational dynamics of rotating systems
- 1999
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In: Shock and Vibration. - 1070-9622 .- 1875-9203. ; 6:4
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Other publication (other academic/artistic)abstract
- This bibliography lists references to papers, conference proceedings and theses/dissertations dealing with finite element analysis of rotor dynamics problems that were published in 1994-1998. It contains 319 citations. Also included, as separate subsections, are finite element analyses of rotor elements - discs, shafts, spindles, and blades. Topics dealing with fracture mechanics, contact and stability problems of rotating machinery are also considered in specific sections. The last part of the bibliography presents papers dealing with specific industrial applications.
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| 5. |
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| 6. |
- Mackerle, Jaroslav
(author)
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Finite element vibration analysis of beams, plates and shells - A bibliography (1994-1998)
- 1999
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In: Shock and Vibration. - 1070-9622 .- 1875-9203. ; 6:2, s. 97-109
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Research review (peer-reviewed)abstract
- This bibliography lists references to papers, conference proceedings and theses/dissertations dealing with finite element vibration analysis of beams, plates and shells that were published in 1994-1998. It contains 361 citations. Also included, as separated subsections, are vibration analysis of composite materials and vibration analysis of structural elements with cracks/contacts.
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| 7. |
- Mackerle, Jaroslav
(author)
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Finite element vibration and dynamic response analysis of engineering structures - A bibliography (1994-1998)
- 2000
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In: Shock and Vibration. - : Hindawi Publishing Corporation. - 1070-9622 .- 1875-9203. ; 7:1, s. 39-56
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Journal article (peer-reviewed)abstract
- This bibliography lists references to papers, conference proceedings, and theses/dissertations dealing with finite element vibration and dynamic response analysis of engineering structures that were published from 1994 to 1998. It contains 539 citations. The following types of structures are included: basic structural systems, ground structures, ocean and coastal structures, mobile structures, and containment structures.
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| 8. |
- Paul, Satyam, 1981-, et al.
(author)
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Recent Advances in Bidirectional Modeling and Structural Control
- 2016
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In: Shock and Vibration. - : Hindawi Publishing Corporation. - 1070-9622 .- 1875-9203. ; 2016
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Research review (peer-reviewed)abstract
- This paper provides an overview of building structure modeling and control under bidirectional seismic waves. It focuses on different types of bidirectional control devices, control strategies, and bidirectional sensors used in structural control systems. This paper also highlights the various issues like system identification techniques, the time-delay in the system, estimation of velocity and position from acceleration signals, and optimal placement of the sensors and control devices. The importance of control devices and its applications to minimize bidirectional vibrations has been illustrated. Finally, the applications of structural control systems in real buildings and their performance have been reviewed.
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| 9. |
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| 10. |
- Saldner, Henrik O.
(author)
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Calibrated noncontact exciters for optical modal analysis
- 1996
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In: Shock and Vibration. - 1070-9622 .- 1875-9203. ; 3:2, s. 107-115
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Journal article (peer-reviewed)abstract
- Two types of exciters were investigated experimentally. One of the exciters uses a small permanent magnet fastened on the object. The force is introduced by the change in the electromagnetic field from a coil via an air gap. The second exciter is an eddy-current electromagnet one. The amplitude of the forces from these exciters are calibrated by using dynamic reciprocity in conjunction with electronic holography. These forces strongly depend upon the distance between the exciter and the object.
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