Maíra Martins da Silva

Loudness scattering due to vibro-acoustic model variability

The use of numerical simulation in the design and evaluation of products performanceis ever increasing. To a greater extent, such estimates are needed in an early designstage, when physical prototypes are not available. When dealing with vibro-acousticmodels, known to be computationally expensive, a question remains, which is relatedto the accuracy of such models in view of the well-known variability inherent to themass manufacturing production techniques. In addition, both the academia and industryhave recently realized the importance of actually listening to a products sound, either bymeasurements or by virtual sound synthesis, in order to assess its performance. In thiswork, the scatter of significant parameter variations on a simplified vehicle vibro-acousticmodel is calculated on loudness metrics using Monte Carlo analysis. The mapping from thesystem parameters to sound quality metric is performed by a fully-coupled vibro-acousticfinite element model. Different loudness metrics are used, including overall sound pressurelevel expressed in dB and Specific Loudness in Sones. Sound quality equivalent sourcesare used to excite this model and the sound pressure level at the driver’s head position isacquired to be evaluated according to sound quality metrics. No significant variation hasbeen perceived when evaluating the system using regular sound pressure level expressedin dB and dB(A). This happens because of the third-octave filters that average the resultsunder some frequency bands. On the other hand, Zwicker Loudness presents importantvariations, arguably, due to the masking effects.Keywords: sound quality, vibro-acoustic model, finite element method, Monte Carloanalysis

Computer-aided integrated design for mechatronic systems with varying dynamics

Some mechatronic systems have different spatial configurations or operation positions, and, as a consequence, their dynamic behavior, described by their most significant eigenfrequencies and mode-shapes, may vary in the configuration space. This inevitably affects the performance and the stability of the control system. Regarding the design of mechatronic systems with variable configuration, two main issues are treated in this paper: (i) the derivation of a parametric model able to capture the varying dynamics and the control actions, (ii) the integrated design of the structure and the controller. To cope with these issues, a parametric model is derived using a flexible multibody system technique based on the finite element method. A global modal parameterization is applied for model-order reduction, yielding a concise description of the flexible multibody model. A linear parameter varying controller is derived via interpolation of local controllers for the reduced models. This methodology is applied to a pick-and-place assembly robot with a gripper carried by a flexible beam. Eventually, design tradeoffs are evaluated considering the performance of the active system for different structural configurations.

An analysis on vibration damping in turning through passive shunt circuits using a nonlinear model

The use of slender tool holders is inherent to boring and turning operations. As a result, large vibrations, known as chatter, may arise, resulting in poor surface finishing and decrease in the tool life. Therefore, chatter is a recurring issue that is in need of modeling and controlling in order to improve the industrys productivity. The nonlinear and cutting friction forces, together with the mode coupling that arises from a symmetric tool holder, can lead to these extreme vibrations and possibly chaotic motion under a certain set of parameters. These nonlinearities must be studied and experimentally analyzed to be considered in chatter control mechanisms in turning. It is well known that passive shunt circuits increase the systems damping and can be used to control chatter. This paper presents a simple lumped nonlinear model of the tool holder embedded to a piezoelectric patch and an analysis of such model with and without the passive shunt circuit. The set of parameters is chosen in order to simulate a chatter condition. The resulting phase diagrams are qualitatively compared to experimental data obtained from a real turning operation made using a CNC lathe. The results show that the model is capable of appropriately simulating the chatter vibration.