Foto del docente

Alessandro Zanarini

Assistant professor

Department of Industrial Engineering

Academic discipline: ING-IND/13 Applied Mechanics


Keywords: Full field optical measurement techniques ESPI - full field displacement measurements High Speed DIC - Digital Image Correlation SLDV - Scanning Laser Doppler Vibrometry experimental modal analysis structural dynamics fatigue vibro-acustic modelling non destructive testing flexible multibody analysis component mode synthesis signal processing for diagnostics bearing tool cutting forces gear light weight structures rotordynamics spatial mechanisms dynamic analysis dynamic strains-stresses

1) Understand the benefit that the extreme number of degrees of freedom and consistency of optical measurements (ESPI, LDV and Image Correlation) can give of the dynamic analysis of complex-shaped components; to increase the accuracy in the evaluation of dynamic strains and stresses; to assess the fatigue life of a component due to wide-spectra dynamic loading and enhance its reliability; to evaluate the sound emission of vibrating surfaces; to test the materials for defects by means of optical non-destructive techniques.

2) Formulation of the linearized modal model of complex spatial mechanisms around all the kinematically compatible positions that can be explored in the working domain, by means of multibody techniques, modal analysis and Lagrange multipliers, to be able to define the boundary and constraint conditions of the problem and the flexibility of the mechanism components. This study aims at exploring the kinematics-based variability of the dynamic behaviour of the spatial mechanisms.

3)Diagnostics and modelling of faults in mechanical components (gears and bearings);fault identification by means of signal processing on vibro-acustic signals; rotordynamics.

4) Improvement of the cutting force measurements in milling machines by means of a filtering of the inertia force components related to the rigid body motion of the measuring set-up/fixtures on an instrumented dynamometric table. Rigid body properties identification

1) Displacement measurement analysis, by means of laser ESPI technique, for dynamic characterization, modal identification, stress&strain evaluation, fatigue behaviour analysis and non-destructive testing of mechanical components.
This topic continues the studies started in the "Speckle interferometry for industrial needs" project at Dantec Ettemeyer GmbH, Ulm (Germania), during the European Commission Marie Curie Post Doctoral Host Fellowship in 2004-2005. The research first aims at checking the portability of full-field optical measurement datasets toward the traditional modal analysis domain (estimation and sharing of Frequency Response Functions). Then a better insight about the influence of the high degree of freedom number (100K to 2M dofs) and of the spatially highly defined displacement fields over modal model estimation and over dynamic analysis of complex and lightweight structures is searched. On these latter, the high modal density and eigenshape complexity result in a difficult set-up for traditional measurement devices, like accelerometer arrays. From highly defined displacement fields and object shape-contour description it might also be possible to evaluate the strain&stress field on the surface directly from dynamic event measurements: such a full-field based dynamic strain or modal model might be employed in fatigue and durability estimation of complex objects.
The usage of full field datasets as input/boundary condition in sound radiation estimation will be also considered, being this a part of a wider research, interested in the vibro-acustic modeling of complex systems: the dynamic signature of the components affects the emitted sound pressure of the whole system, coming from the vibrating surfaces.
The high density of spatial information contained in full field datasets will be also studied for non-destructive testing procedures, considering techniques deriving from image processing and compression, beside others computationally suited for the size of the problem.

Key words:

ESPI, dynamic analysis, light structures, experimental full-field measurements, stress-strain, fatigue, Non Destructive Testing.

2) Development of methods for the study of the elastodynamic behaviour of complex spatial mechanisms, by means of multibody and modal substructuring approaches.

The research activity aims at an approach for the dynamic behaviour analysis of spatial mechanisms (from the simple ones to vehicles, robots, automatic and tooling machines), constituted by rigid and/or flexible parts coupled together by kinematical constraints with varying relative dofs and elastic lumped elements. Linearized modal models of the system will be formulated in the neighborhood of the kinematically admissible configurations, the latter being functions of the selected motion laws in the working domain of the mechanism. The linearized modal model will be assembled by means of numerical techniques, such as multibody modeling and Lagrange multipliers, to model the boundary conditions and the flexibility of the parts (by a modal base, either experimental or analytical-numerical). A numerical code will result from this research activity, implementing the above described procedure with different kinematic and elastic lumped constraints and able to automatically write and solve the related equations. Testing on real prototypes should follow for the validation of the approach.

Key words:

flexible multibody, spatial mechanisms, component mode synthesis, modal analysis, model optimization

3) Diagnostics of mechanical systems by means of signal processing.

This activity starts with a literature survey on consistent diagnostics techniques for complex mechanical systems, focusing in particular on defect modeling in mechanical components like gears and bearings, and on damage identification by means of signal processing techniques on vibro-acustic signals. Non conventional techniques will be also explored. Experiments to test the fault identification procedures will be carried on, both in the laboratory and on field, in industrial environment.

For the diagnosis of rotating machinery, rotordynamics and fluid-related phenomena in bearings will be investigated by means of literature readings, construction of a testing rig, acquisition and analysis software tools, with the aim to prepare an integrated diagnostic tool.

Key words:

Diagnostics, signal processing, fault diagnosis, gears, bearings, rotordynamics

4) Development of methodologies to estimate the cutting forces in tooling machines, by means of an instrumented dynamometric table.

The first part of the activity was aimed at obtaining the FE model of the tooling machine Giuliani MT3 C, acquired by DIEM for researches about active controlled vibrations in industrial machinery. Useful information, about the dynamic behaviour and about design guidelines for the dynamometric table, came from the modal analysis of the frame coupled to the sledges and to the item-carrying table. The dynamic behaviour of the whole system induces inertia actions on the instrumented table, due to the rigid body motion of the latter, even if fixed, through the force transducers, to the main structure. The procedure, object of this study, will thus take account for filtering out, from the cutting force estimation, the inertia forces deriving from the rigid body constrained motion of the instrumented table. By means of processing the force and acceleration signals coming from the table, an equivalent inertia force system is pursued, the latter having to be subtracted from the force transducer signals to obtain a more precise estimation of the cutting forces in working conditions. Rigid body properties of the measurement system will be evaluated by means of identification algorithms applied to the available signals coming from the transducers on the instrumented table.

Key words:

tool-cutting force, inertia forces, filtering, dynamic analysis