Daniel Alazard

Jose Alvaro Perez, Christelle Pittet, Daniel Alazard et al.

This study presents the integrated control/structure design of a Large Flexible Structure, the Extra Long Mast Observatory (ELMO). The integrated design is performed using structured $\mathcal{H}_\infty$ control tools, developing the Two-Input Two-Output Port (TITOP) model of the flexible multi-body structure and imposing integrated design specifications as $\mathcal{H}_\infty$ constraints. The integrated control/structure design for ELMO consists of optimizing simultaneously its payload mass and control system for low-frequency perturbation rejection respecting bandwidth requirements.

Pierre Vuillemin, Charles Poussot-Vassal, Daniel Alazard

In this paper, a new simple but yet efficient spectral expression of the frequency-limited H2-norm, denoted H2w-norm, is introduced. The proposed new formulation requires the computation of the system eigenvalues and eigenvectors only, and provides thus an alternative to the well established Gramian-based approach. The interest of this new formulation is in three-folds: (i) it provides a new theoretical framework for the H2w-norm-based optimization approach, such as controller synthesis, filter design and model approximation, (ii) it improves the H2w-norm computation velocity and it applicability to models of higher dimension, and (iii) under some conditions, it allows to handle systems with poles on the imaginary axis. Both mathematical proofs and numerical illustrations are provided to assess this new H2w-norm expression.

Jose Alvaro Perez, Thomas Loquen, Daniel Alazard et al.

This study presents a generic TITOP (Two-Input Two-Output Port) model of a substructure actuated with embedded piezoelectric materials as actuators (PEAs), previously modeled with the FE technique. This allows intuitive assembly of actuated flexible substructures in large flexible multi-body systems. The modeling technique is applied to an illustrative example of a flexible beam with bonded piezoelectric strip and vibration attenuation of a chain of flexible beams.

Ervan Kassarian, Francesco Sanfedino, Daniel Alazard et al.

Conventional robust H2/H-infinity control minimizes the worst-case performance, often leading to a conservative design driven by very rare parametric configurations. To reduce this conservatism while taking advantage of the stochastic properties of Monte Carlo sampling and its compatibility with parallel computing, we introduce an alternative paradigm that optimizes the controller with respect to a stochastic criterion, namely the conditional value at risk. We present the problem formulation and discuss several open challenges toward a general synthesis framework. The potential of this approach is illustrated on a mechanical system, where it significantly improves overall performance by tolerating some degradation in very rare worst-case scenarios.

Jose Alvaro Perez, Daniel Alazard, Thomas Loquen et al.

The main objective of this study is to propose a methodology to build a parametric linear model of Flexible Multibody Systems for control design. This approach uses a combined Finite Element - State Space Approach based on component modes synthesis and double-port approach. The proposed scheme offers the advantage of automatic assembly of substructures, preserving the elastic dynamical behavior of the whole system. Substructures are connected following the double-port approach; i.e, through the transfer of accelerations and loads at the connection points, which take into account the dynamic coupling among them. In addition, parametric variations can be included in the model for accomplishing integrated control/structure design purposes. The method can be applied to combinations of chain-like or/and star-like flexible systems, and it is validated through its comparison with the assumed modes method for the case of a rotatory spacecraft.