Browsing by Author "Maia, N. M. M."
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- An iterative uncoupling technique for the identification of the dynamic properties of jointsPublication . Batista, F. C.; Maia, N. M. M.The identification of the dynamic properties of joints is a very important subject in structural dynamics. However, classic uncoupling methods are often very difficult to apply. In the present paper an iterative technique is proposed, trying to circumvent the well-known ill-conditioning problems that arise due to any small perturbations existing in the experimental data. Various cases are simulated and discussed to illustrate the technique, including situations where it is not possible to take measurements on the joint itself; the results are compared with the ones obtained with other methods.
- Dynamics modelling of spot welded jointsPublication . Silva, J. M. M.; Batista, F. C.; Maia, N. M. M.The determination of the dynamic characteristics of joints connecting structural components is a not yet solved problem of great importance when one intends to establish a theoretical model of the dynamic behaviour of a complex structure. Many of the problems found in such a process are in fact due to the difficulties related to the theoretical modelling of joints, be these connections of the classical type ? welded, bolted, riveted, etc. - or still more complicated, as elastic supports, ribbons, etc. Given the complexity of the problem, it is convenient to approach it considering each specific type of joint separately. In the present case, the work will focus on spot-welded joints of the type found in the body of automobile vehicles. Spot-welds connect laminated foils, limiting to small areas the effective connecting zones. As a consequence, the application of common finite element techniques to the analysis of the dynamic behaviour of the vehicle body, yields not very accurate results given the fact that the effects of the welded connections are not accounted for. The objective of this work is to develop a numeric model that characterizes those joints, so that a more accurate model of this type of structures may be available.
- Estimation of unmeasured frequency response functionsPublication . Batista, F. C.; Maia, N. M. M.In the present work, the authors propose a new methodology for the estimation of Frequency Response Functions (FRFs) that for some reason cannot be measured in a structure. With such an objective, one uses FRFs that are obtained through a finite element modelization of the structure. Due to instrumentation limitations, in the majority of the cases the FRFs that are associated to rotationaldegrees-of-freedom are often problematic. In the examples that are given in this paper those kind of FRFs are the ones to be estimated. Various examples are numerically simulated and the results obtained are discussed in order to assess the robustness of the method to the presence of noise in the data.
- Uncoupling techniques for the dynamic characterization of sub-structuresPublication . Batista, F. C.; Maia, N. M. M.The characterization of the dynamic behavior of sub-structures may be of great importance in certain complex structures. A possible approach is through the use of uncoupling techniques. This is the subject of the present paper, where various issues are raised and different possibilities to circumvent the encountered problems are discussed. These problems are mostly due to numerical instabilities associated to the calculation procedures, namely to the ill-conditioning that often appears and causes complications in the inversion of the involved matrices. The location of the possible points of measurement may also influence the results. Several variations to the main algorithms are tried in order to reduce the numerical problems. This study will be based on numerical simulations to compare the various approaches and to draw some final conclusions.