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Vibration
Volume 8
Issue 1
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Vibration, Volume 8, Issue 1 (March 2025) – 5 articles

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29 pages, 3986 KiB  
Article
Soil–Structure Interaction and Damping by the Soil—Effects of Foundation Groups, Foundation Flexibility, Soil Stiffness and Layers
by Lutz Auersch
Vibration 2025, 8(1), 5; https://doi.org/10.3390/vibration8010005 - 31 Jan 2025
Viewed by 207
Abstract
In many tasks of railway vibration, the structure, that is, the track, a bridge, and a nearby building and its floors, is coupled to the soil, and the soil–structure interaction and the damping by the soil should be included in the analysis to [...] Read more.
In many tasks of railway vibration, the structure, that is, the track, a bridge, and a nearby building and its floors, is coupled to the soil, and the soil–structure interaction and the damping by the soil should be included in the analysis to obtain realistic resonance frequencies and amplitudes. The stiffness and damping of a variety of foundations is calculated by an indirect boundary element method which uses fundamental solutions, is meshless, uses collocation points on the boundary, and solves the singularity by an appropriate averaging over a part of the surface. The boundary element method is coupled with the finite element method in the case of flexible foundations such as beams, plates, piles, and railway tracks. The results, the frequency-dependent stiffness and damping of single and groups of rigid foundations on homogeneous and layered soil and the amplitude and phase of the dynamic compliance of flexible foundations, show that the simple constant stiffness and damping values of a rigid footing on homogeneous soil are often misleading and do not represent well the reality. The damping may be higher in some special cases, but, in most cases, the damping is lower than expected from the simple theory. Some applications and measurements demonstrate the importance of the correct damping by the soil. Full article
22 pages, 10136 KiB  
Article
Experiment-Based Design of Stirling Cryocooler Compressor Using Response-Controlled Testing
by Suna Güçyılmaz Çetin, Taylan Karaağaçlı and Ahmet H. Ertas
Vibration 2025, 8(1), 4; https://doi.org/10.3390/vibration8010004 - 30 Jan 2025
Viewed by 482
Abstract
Flexure-based Stirling cryocooler compressors are a critical technology in providing cryogenic temperatures in various advanced engineering fields, such as aerospace, defense, and medical imaging. The most challenging problem in the design of this type of compressor is achieving a precise alignment that preserves [...] Read more.
Flexure-based Stirling cryocooler compressors are a critical technology in providing cryogenic temperatures in various advanced engineering fields, such as aerospace, defense, and medical imaging. The most challenging problem in the design of this type of compressor is achieving a precise alignment that preserves small gaps between the components moving relative to each other and avoids severe friction and wear. This paper introduces a novel experimental procedure for designing Stirling cryocooler compressors, leveraging a recently developed nonlinear experimental modal analysis method known as response-controlled stepped-sine testing (RCT). The alignment in a compressor prototype was significantly improved in light of a series of RCT with base excitation. The enhanced compressor design was subsequently validated though a series of constant-current tests, which confirmed the elimination of the sticking/locking phenomenon observed in the initial design. Furthermore, an indirect harmonic force surface (HFS)-based approach proposed for weakly nonlinear systems was extended to identify the high and nonlinear damping (up to a 65% hysteretic modal damping ratio) observed in the enhanced compressor design due to excessive friction. As another contribution, it was shown that the extrapolation of the HFS gives accurate results in the prediction of the nonlinear modal parameters at response levels where no experimental data are available. In light of these findings, it was concluded that the enhanced design needs further design modifications to further decrease the friction and wear between the moving parts. Overall, this study provides valuable insights for designing cryocooler compressors, with implications for aerospace and medical applications. Full article
(This article belongs to the Special Issue Vibration Damping)
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25 pages, 10978 KiB  
Article
Methodology for Designing Vibration Devices with Asymmetric Oscillations and a Given Value of the Asymmetry of the Driving Force
by Mihail D. Gerasimov, Nickolai S. Lubimyi, Andrey A. Polshin, Boris S. Chetverikov and Anastasia Chetverikova
Vibration 2025, 8(1), 3; https://doi.org/10.3390/vibration8010003 - 15 Jan 2025
Viewed by 474
Abstract
In mechanical engineering, the building industry, and many other branches of industry, vibration machines are widely used, in which circular and directed oscillations predominate in the form of movement of the working equipment. This article examines methods for generating asymmetric oscillations, which are [...] Read more.
In mechanical engineering, the building industry, and many other branches of industry, vibration machines are widely used, in which circular and directed oscillations predominate in the form of movement of the working equipment. This article examines methods for generating asymmetric oscillations, which are estimated by a numerical parameter, namely by the coefficient of asymmetry of the magnitude of the driving force when changing the direction of action in a directed motion within each period of oscillations. It is shown that for generating asymmetric mechanical vibrations, vibration devices are used, consisting of vibrators of directed vibrations, called stages. These stages form the total asymmetric driving force. The behavior of the total driving force of asymmetric vibrations and the working equipment of the vibration machine are described by analytical equations, which represent certain laws of motion of the mechanical system. This article presents a numerical analysis of methods for obtaining laws of motion for a two-stage, three-stage, and four-stage vibration device with asymmetric oscillations. An analysis of the methodology for obtaining a generalized law of motion for a vibration device with asymmetric oscillations is performed based on the application of polyharmonic oscillation synthesis methods. It is shown that the method of forming the total driving force of a vibration device based on the coefficients of the terms of the Fourier series has limited capabilities. This article develops, substantiates, and presents a generalized method for calculating and designing a vibration device with asymmetric oscillations by the value of the total driving force and a given value of the asymmetry coefficient in a wide range of rational designs of vibration machines. The proposed method is accompanied by a numerical example for a vibration device with an asymmetry coefficient of the total driving force equal to 10. Full article
(This article belongs to the Special Issue Nonlinear Vibration of Mechanical Systems)
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14 pages, 19138 KiB  
Article
Application of Homogenization Method in Free Vibration of Multi-Material Auxetic Metamaterials
by Kadir Gunaydin, Orhan Gülcan and Aykut Tamer
Vibration 2025, 8(1), 2; https://doi.org/10.3390/vibration8010002 - 13 Jan 2025
Viewed by 722
Abstract
Different additive manufacturing modalities enable the production of multi-material components which can be used in a wide range of industrial applications. The prediction of the mechanical properties of these components via finite element modelling rather than through testing is critical in terms of [...] Read more.
Different additive manufacturing modalities enable the production of multi-material components which can be used in a wide range of industrial applications. The prediction of the mechanical properties of these components via finite element modelling rather than through testing is critical in terms of cost and time. However, due to the higher computational time spent on the modelling of lattice structures, different methods have been investigated to accurately predict mechanical properties. For this purpose, this study proposes the use of a homogenization method in the two most common types of multi-material lattices: honeycomb and re-entrant auxetics. Modal analyses were performed, and the first six mode shapes were extracted from explicit and implicit models. The results were compared in terms of mode shapes and natural frequencies. The results showed that homogenization can be successfully applied to multi-material honeycomb and re-entrant auxetic lattices without compromising the accuracy. It was shown that the implicit models predict the natural frequencies with an error range of less than 6.5% when compared with the explicit models in all of the mode shapes for both honeycomb and re-entrant auxetic lattices. The Modal Assurance Criteria, which is an indication of the degree of similarity between the mode shapes of explicit and implicit models, was found to be higher than 0.996, indicating very high similarity. Full article
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25 pages, 10425 KiB  
Article
Parameter Estimation of Nonlinear Structural Systems Using Bayesian Filtering Methods
by Kalil Erazo
Vibration 2025, 8(1), 1; https://doi.org/10.3390/vibration8010001 - 31 Dec 2024
Viewed by 550
Abstract
This paper examines the performance of Bayesian filtering system identification in the context of nonlinear structural and mechanical systems. The objective is to assess the accuracy and limitations of the four most well-established filtering-based parameter estimation methods: the extended Kalman filter, the unscented [...] Read more.
This paper examines the performance of Bayesian filtering system identification in the context of nonlinear structural and mechanical systems. The objective is to assess the accuracy and limitations of the four most well-established filtering-based parameter estimation methods: the extended Kalman filter, the unscented Kalman filter, the ensemble Kalman filter, and the particle filter. The four methods are applied to estimate the parameters and the response of benchmark dynamical systems used in structural mechanics, including a Duffing oscillator, a hysteretic Bouc–Wen oscillator, and a hysteretic Bouc–Wen chain system. Based on the performance, accuracy, and computational efficiency of the methods under different operating conditions, it is concluded that the unscented Kalman filter is the most effective filtering system identification method for the systems considered, with the other filters showing large estimation errors or divergence, high computational cost, and/or curse of dimensionality as the dimension of the system and the number of uncertain parameters increased. Full article
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