1,354,449 research outputs found
Predicting the frequency response function of a structure when adding constraints
No full textA method is developed to predict the dynamic behavior of a structure from experimental FRF data of the same system subjected to different constraints. In particular it is required that the new structure undergoes more restrained conditions, but any type of ideal constraint, involving either translational or rotational degrees of freedom, can be accounted for. Among several interesting applications, the method can be used to overcome typical experimental drawbacks on rigid tested structures and to estimate untestable FRF terms of constrained systems. Numerical and experimental results are provided to show the consistency of the method and the possible range of applications
Bias in modal parameters using the direct and iterative RFP identification procedures
No full textIn the rational fraction polynomial method [1] the identification of modal parameters is obtained through a direct linear least-square optimization technique but a particular form of fitting error is minimized. An iterative algorithm has been recently developed which uses the true fitting error [2]. In this paper a statistical analysis is developed to estimate the bias effects on the identified parameters when the data are polluted with noise. Both the direct and iterative procedures are considered. Numerical simulations are used to validate the results predicted by the theoretical analysis, which shows that the iterative approach is by far more efficient than the direct method. © 1995 Kluwer Academic Publishers
A modification method for vibration control of structures
No full textVibration and acoustics requirements are becoming increasingly important in the design of mechanical structures, but they are not usually the primary concern in the design process. So the need of varying the structural behaviour to solve noise and vibration problems often occurs at the prototype stage, giving rise to the so-called structural modification problem.
In this paper the problem of determining the best structural modifications is cast in the framework of mathematical programming, by defining a suitable optimisation problem. The method starts from a raw set of experimentally determined frequency response functions (FRFs), and avoids any identification process aimed at the creation of either a modal or a physical model of the structure.
Several dynamic requirements can be imposed, depending on the specifications to be satisfied and on the information available about the excitation forces. Typical quantities to control are: FRF modulus, response modulus, response power spectral density and response mean square value. Structural modifications that can be accounted for are lumped masses, springs, viscous dampers, dynamic absorbers and stiffening rods.
Some examples are developed to give a straightforward implementation of the method. Results are also presented which involve real-life structures, such as an engine block
A unified approach to substructuring and structural modification problems
No full textSubstructures coupling is still an important tool in several applications of modal analysis, especially structural modification and structures assembling. The subject is particularly relevant in virtual prototyping of complex systems and responds to actual industrial needs. This paper analyzes the possibility of assembling together different substructures' models. The important role of rotational DoFs is highlighted, underlying the difficulty of assembling theoretical and experimental models, for which, usually, the rotational DoFs are not available. Expansion techniques can be used to provide this information as well as appropriate modelling of joints. With this information, FRF models, modal models and FE models can be appropriately combined together and solutions for several cases of practical interest are presented. The analyzed procedures are tested on purpose-built benchmarks, showing limits and capabilities of each of them
Coupling theoretical data and translational FRFs to perform distributed structural modifications.
No full textPredicting the effect of distributed structural modifications, such as rib or plate stiffeners, on structures for which a theoretical model is not available, is not practically considered in the technical literature: this is due to the objective difficulty of coupling continuous modifications with an original structure known through its frequency response function. While this is not the case when lumped modifications are accounted for, the possibility of describing distributed modifications requires non-trivial operations involving the use of different models for the structure and the modification, an appropriate use of a condensation procedure and a careful consideration of non-local effects introduced by the above condensation. The basic requirements for a consistent modelling are here considered and some results are presented
A critical review of energy models for structural vibration in the audio-frequency range
No full textAnalysis of static and dynamic structural problems by a combined finite element-transfer matrix method
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