C. M. A. Vasques

Improved passive shunt vibration control of smart piezo-elastic beams using modal piezoelectric transducers with shaped electrodes

Modal control and spatial filtering technologies for mitigation of vibration and/or structural acoustics radiation may be achieved through the use of distributed modal piezoelectric transducers with properly shaped electrodes. This approach filters out undesirable and uncontrollable modes over the bandwidth of interest in order to increase the robustness and stability of the controlled structural system, and may also yield higher values of the generalized modal electromechanical coupling coefficient, which is an important design parameter for achieving efficient passive shunt damping design. In this paper the improvements in passive shunt damping performance when using modal piezoelectric transducers with shaped electrodes are investigated for a two-layered resonant-shunted piezo-elastic smart beam structure. An electromechanical one-dimensional equivalent single-layer Euler–Bernoulli analytical model of two-layered smart piezo-elastic beams with arbitrary spatially shaped electrodes is established for modal and uniform electrode designs. The model is verified and validated by comparison with a one-dimensional discrete-layer (layerwise) finite element model, the damping performance of the shunted smart beam with shaped electrodes is investigated and assessed in terms of the generalized electromechanical coupling coefficient and frequency responses obtained when considering uniform and modally shaped electrodes and the underlying improved performance and advantages are assessed and discussed.

Active vibration control of a smart beam through piezoelectric actuation and laser vibrometer sensing: simulation, design and experimental implementation

A velocity feedback control system is evaluated in the active control of vibrations of a smart beam with a pair of surface mounted piezoelectric ceramic patches, and finite element (FE) model results are validated against measured ones. To this end, a three-layered smart beam FE model is utilized, where a partial layerwise theory and a fully coupled electro-mechanical theory are considered for the formulation of the displacement field and electric potential, respectively. Regarding the test rig, it consists of a cantilever smart aluminum beam with two piezoelectric patches mounted close to the clamped end. One of the piezoelectric patches is utilized to excite the beam while the other is utilized as an actuator in the feedback control loop. The control voltage applied to the actuator is proportional to the transverse velocity at the free end, which is measured by a laser vibrometer. First, the quasi-static actuation capacity of the piezoelectric patches is evaluated. Next, the free and forced velocity responses to an initial displacement field and harmonic excitation are analyzed. The capacity to predict instabilities and the accuracy of the FE model are demonstrated and the applicability and functionality of the velocity feedback vibration control system are discussed.

Numerical and Experimental Comparison of the Adaptive Feedforward Control of Vibration of a Beam with Hybrid Active-Passive Damping Treatments

This article concerns the adaptive feedforward control of vibration of a freely supported beam with two distinct surface mounted hybrid active—passive damping treatments. The first configuration concerns the use of an Active Constrained Layer Damping (ACLD) patch alone, where the piezoelectric constraining layer is actively utilized to increase the shear deformation of the sandwiched passive viscoelastic layer and at the same time to apply forces and moments into the structure, which will balance the power flows into the structure, and is denoted by ACLD configuration. The second configuration regards the use, as an active element in the control, of the piezoelectric patch alone, denoted by Active Damping (AD), and since the constraining layer of the ACLD treatment also bonded on the other side of the beam is not actively utilized, a Passive Constrained Layer Damping (PCLD) treatment is utilized in combination with an AD one, yielding an AD/PCLD configuration. A finite element model of the beam with the damping treatments is used for the simulation of the adaptive feedforward controller which is also implemented and tested in real-time. The aims are to compare the predicted and measured damping performances of the two treatments in terms of vibration reduction, control effort, stability and robustness, when a filtered-reference LMS algorithm is used to cancel the effects of a broadband voltage disturbance applied into a third surface mounted piezoelectric patch which is used to excite the beam.

Experimental Identification of GHM and ADF Parameters for Viscoelastic Damping Modeling

Viscoelastic materials can be used as an effective means of controlling the dynamics of structures, reducing and controlling the structural vibrations and noise radiation. They can be used as surface mounted or embedded damping treatments, utilizing passive viscoelastic materials alone, the so-called passive treatments, or in an unified way with active materials such as piezoelectrics, the so-called hybrid treatments. The use of these materials in damping treatments provides high damping capability over wide temperature and frequency ranges. The extensive use of passive or hybrid treatments using viscoelastic materials has motivated the development of damping models to be used and integrated into commercial or home-made finite element (FE) codes. The implementation of the Golla-Hughes- McTavish (GHM) and anelastic displacement fields (ADF) models in a general FE model with viscoelastic damping is presented and discussed in this paper. Additionally, a direct frequency analysis (DFA) is also described and employed.

Shells with Hybrid Active-Passive Damping Treatments: Modeling and Vibration Control

This paper concerns the mathematical modeling and finite element (FE) solution of general anisotropic shells with hybrid active-passive damping treatments. A fully-coupled piezo-visco-elastic mathematical model of the shell (host structure) and segmented arbitrarily stacked layers of damping treatments is considered. A discrete layer approach is employed in this work, and the weak form of the governing equations is derived for a single generic layer of the multilayer shell using Hamilton’s principle and a mixed (displacement/stresses) definition of the displacement field. First, a fully refined deformation theory of the generic layer, based on postulated out-of-plane shear stress definitions and in the in-plane stresses obtained with a Reissner-Mindlin type shell theory, is outlined. A semi-inverse procedure is used to derive the layer mixed non-linear displacement field, in terms of a blend of the generalized displacements of the Love-Kirchhoff and ReissnerMindlin theories and of the stress components at the generic layer interfaces. No assumptions regarding the thinness of the shell are considered. Regarding the definition of the electric potential, the direct piezoelectric effects are condensed into the model through effective stiffness and strains definitions, and the converse counterpart is considered by the action of prescribed electric potential differences in each piezoelectric layer. Then, the weak forms of a partially refined theory, where only the zero-order term of the non-linear fully refined transverse displacement is retained, are derived for an orthotropic doublycurved piezo-elastic generic shell layer. Based on the weak forms a FE solution is initially developed for the single layer. The degrees of freedom (DoFs) of the resultant four-noded generic piezo-elastic single layer FE are then ”regenerated” into an equivalent eight-node 3-D formulation in order to allow through-the-thickness assemblage of displacements and stresses, yielding a partially refined multilayer FE assuring displacement and shear stress interlayer continuity and homogeneous shear stress conditions at the outer surfaces. The shear stresses DoFs are dynamically condensed and the FE is reduced to a displacementbased form. The viscoelastic damping behavior is considered at the global FE model level by means of a Laplace transformed ADF model. The active control of vibration is shortly discussed and a set of indices to quantify the damping performance and the individual contributions of the different mechanisms are proposed.

Functional verification and performance tests of an ultra-low shock non-explosive actuator for hold-down and release mechanisms for space applications

This paper addresses the functional verification and performance assessment of an ultra-low shock non-explosive actuator appropriate to space applications of hold-down and release mechanisms. To demonstrate that the design implementation and manufacturing methods have resulted in an engineering model conforming to the set of functional, performance and environmental requirements specified, a space qualification test campaign is typically required. To ensure the readiness of the engineering model and the adequacy of the mechanical and electrical ground support equipment required for the entire qualification test campaign, a set of functional verification procedures and performance characterization tests were systematized and undertaken before the mechanism qualification. A preload monitoring system was developed and calibrated, and the performance of the mechanism was evaluated through the estimation of the release time and the measurement of the self-generated shock. The main results and conclusions taken from these tests are presented and discussed here.

Viscoelastic Damping Technologies: Finite Element Modeling and Application to Circular Saw Blades

A great deal of information on viscoelastic damping technologies, comprising surface mounted or embedded viscoelastic damping treatments, is nowadays available for the practical noise reduction of machinery, in general, and circular saw blades, in particular, for woodworking operations. Among the most efficient and appellative noise reduction techniques for low-noise woodworking circular saw blades demonstrated during the last decades, the use of viscoelastic damping technologies is an interesting possibility which did not receive sufficient attention and dissemination so far. These technologies are analyzed in this chapter in order to gain a preliminary insight into the interest of this noise control solution to further continuing developing more refined and efficient viscoelastic-based noise reduction designs towards the widespread use of low-noise circular saw tooling and industrial practices by woodworking companies. For that purpose, a more comprehensive and tutorial approach to the field is presented in this book chapter. Emphasis is put not also on the specific application to circular saws, which is used to illustrate the interest, applicability and design procedures of such technologies, but also on practical engineering aspects related with the use of computational tools and finite element (FE) modeling software for the mathematical modeling, design and assessment of the efficiency of damping treatments. In particular, different configurations of damping treatments, spatial FE modeling and meshing approaches, mathematical descriptions of viscoelastic frequency-dependent material damping and their implementation into FE frameworks and the use of different solution methods and commercial FE software are discussed.