Recursive Least Squares Filtering Algorithms for On-Line Viscoelastic Characterization of Biosamples

The mechanical characterization of biological samples is a fundamental issue in biology and related fields, such as tissue and cell mechanics, regenerative medicine and diagnosis of diseases. In this paper, a novel approach for the identification of the stiffness and damping coefficients of biosamples is introduced. According to the proposed method, a MEMS-based microgripper in operational condition is used as a measurement tool. The mechanical model describing the dynamics of the gripper-sample system considers the pseudo-rigid body model for the microgripper, and the Kelvin–Voigt constitutive law of viscoelasticity for the sample. Then, two algorithms based on recursive least square (RLS) methods are implemented for the estimation of the mechanical coefficients, that are the forgetting factor based RLS and the normalised gradient based RLS algorithms. Numerical simulations are performed to verify the effectiveness of the proposed approach. Results confirm the feasibility of the method that enables the ability to perform simultaneously two tasks: sample manipulation and parameters identification

Experimental analysis on squeal modal instability

International audienceIn this paper, an experimental analysis performed on a simplified brake apparatus is presented. Brake squeal is a major concern in braking design. During past years a common approach for squeal prediction was the complex eigenvalues analysis. Squeal phenomenon is treated like a dynamic instability. When two modes of the brake system couple at the same frequency, one of them becomes unstable leading to increasing vibration. The presented experimental analysis is focused on correlating squeal characteristics with the dynamic behavior of the system. The experimental modal identification of the set-up is performed and different squeal conditions and frequencies are reproduced and analyzed. Particular attention is addressed to the system dynamics in function of the driving parameters on squeal occurrence. Squeal events are correlated with the modal behavior of the system in function of the main parameters, like contact pressure, friction material properties and system geometry. The robustness of the obtained squeal events permits a further analysis on the triggering of the squeal instability during braking, including the values of parameters that bring to instability. The obtained results agree with the modal coupling approach for squeal prediction, and confirm the characterization of squeal as dynamic instabilit

Paper ESDA2008-59092 APPLICATION OF THE COMPLEX ENVELOPE VECTORIZATION TO A BOUNDARY ELEMENT FORMULATION

ABSTRACT The complex envelope vectorization (CEV) is a recent method that has been successfully applied to structural and internal acoustic problems. Unlike other methods proposed in the last two decades to solve high frequency problems, CEV is not an energy method, although it shares with all the other techniques a variable transformation of the field variable. By such transformation involving a Hilbert transform, CEV allows the representation of a fast oscillating signal through a set of low oscillating signals. Thanks to such transformation it is possible to solve a high frequency dynamic problem at a computational cost that is lower than that required by finite elements. In fact, by using finite elements, a high frequency problem usually implies large matrices. On the contrary the CEV formulation is obtained by solving a set of linear problems of highly reduced dimensions. Although it was proved that CEV is in general a successful procedure, it was shown that it is particularly appropriate when the modes of the system have a negligible role on the solution. Moreover, the numerical advantage of the CEV formulation is much more pronounced when full matrices are used. Thus, for the first time it is applied to a boundary element formulation (BEM). Both external and internal acoustic fields of increasing complexity are considered: the internal and external field generated by a pulsating sphere; the external field of a forced box, where the velocity field is determined by finite elements; a set of 4 plates that form an open cavity. The results are compared with those obtained by a BEM procedure (SYSNOISE), highlighting the good quality of the proposed approach. An estimate of the computational advantage is also provided. Finally it is worthwhile to point out that the reduction of the BE matrices allows for an in-core solution even for large problems

Aluminium foam production control by using a combined fuzzy-genetic algorithm model

Abstract This study deals with the proposal of a combined fuzzy-genetic algorithm model able to describe the inherent uncertainties related to the manufacture of aluminium foams by using the dissolution and sintering process. The combined method allows taking into account both the uncertainty related to the model and the statistical process variability, with the aim of controlling the capability of this material at absorbing compression energy, for different set of process parameters. The use of genetic algorithms allows the optimization of the fuzzy supports in order to take into account most of the experimental data in combination with the smallest uncertainty

Finite element model of a fuzzy damper for the beam-on-disc setup

Brake squeal is a complicated research topic because, on one hand, it involves several disciplines, and on the other, it deals with a complex and variable system. In fact, while there is agreement in the scientific community that squeal is a dynamic instability triggered by the modal coupling between two or three modes of the system, the interaction between the dynamics of the brake apparatus, the nonlinear aspects of the contact between disc and pad, and the tribological aspects of the wear is still object of research studies. On the other hand, when dealing with remedies to squeal occurrences, one faces the problem that any solution should be effective in different operative conditions and different environments for all the commercial life of the brake; thus, the robustness of any system for squeal suppression is a key factor. For these reasons, several researchers, focused on more simple systems that exhibit the same instability mechanism, such as the beam-on-disc setup, that is a valuable benchmark to test both effectiveness and robustness of new devices to suppress squeal. This paper presents a numerical study on the effectiveness of a fuzzy damper, based on the theory of apparent damping, that can be able to suppress squeal on the beam-on-disc setup; moreover, the numerical analysis focuses on the relation between the performances of the device and its key design parameters, showing how such a device can either work as a tuned device able to suppress a specific squeal condition, or as a wide band device able to reduce the occurrence of squeal in large frequency ranges. © 2011. MechAero Foundation for Technical Research & Education Excellence

An interdependency index for the outputs of uncertain systems

The study of mechanical systems with uncertain parameters is gaining increasing interest in the field of system analysis to provide an expedient model for the prediction of the system behavior. Making use of the Transformation Method, the uncertain parameters of the system are modeled by fuzzy numbers in contrast to random numbers used in stochastic approaches. As a result of this analysis, a quantification of the overall uncertainty of the system outputs, including a worst-case scenario, is obtained. The inputs of the resulting fuzzy-valued model are a priori uncorrelated but after the uncertainties are propagated through the model, interdependency (or interaction) between the outputs may arise. If such interdependency is neglected, a misinterpretation of the results may occur. For example, in the case of applying uncertainty analysis in the early design phase of a product to determine the relevant design-parameter space, the interdependency between the design variables may reduce significantly the available part of the design space. This paper proposes a measure of interdependency between the uncertain system outputs. The interdependency index can be derived by a postprocessing of the data gained by the analysis with the Transformation Method. Such information can be obtained by a negligible amount of extra computation time. (c) 2007 Elsevier B.V. All rights reserved