Performance of soft dielectric laminated composites

This paper contains a thorough investigation of the performance of electrically activated layered soft dielectric composite actuators under plane deformation. Noting that the activation can be induced controlling either the voltage or the surface charge, the overall behaviour of the system is obtained via homogenization at large strains taking either the macroscopic electric field or the macroscopic electric displacement field as independent electrical variable. The performance of a two-phase composite actuator compared to that of the homogeneous case is highlighted for few boundary-value problems and for different values of stiffness and permittivity ratios between constituents being significant for applications, where the soft matrix is reinforced by a relatively small volume fraction of a stiff and high-permittivity phase. For charge-controlled devices, it is shown that some composite layouts admit, on one hand, the occurrence of pull-in/snap-through instabilities that can be exploited to design release-actuated systems, on the other, the possibility of thickening at increasing surface charge density

Viscoelastic effects in the aeromechanics of actuated elastomeric membrane wings

AbstractThis work is a numerical investigation on the influence of viscoelastic effects on the aerodynamics of integrally actuated membrane wings. For that purpose, a high-fidelity electro-aeromechanical computational model of wings made of dielectric elastomers has been developed. The structural model is based on a geometrically non-linear description and a non-linear electro-viscoelastic constitutive material law. It is implicitly coupled with a fluid solver based on a finite-volume discretisation of the unsteady Navier–Stokes equations. The resulting framework is used for the evaluation of the dynamics of passive and integrally actuated membrane wings at low Reynolds numbers under hyperelastic and viscoelastic assumptions on the constitutive model. Numerical simulations show that the damping introduced by viscoelastic stresses can significantly reduce the amplitude of membrane oscillations and modify key features in the coupled system dynamics. The estimated wing performance metrics are in good agreement with previous experimental observations and demonstrate the need of including rate-dependent effects to correctly capture the coupled system dynamics, in particular, for highly compliant membranes

High-fidelity modelling and feedback control of bio-inspired membrane wings

This work is a numerical investigation on the performance of integrally actuated two-dimensional membrane wings made with dielectric elastomers. A high-fidelity model based on the direct numerical integration of the unsteady Navier-Stokes equations is coupled with a geometrically non-linear structural model. The rate-dependent constitutive law for the dielectric elastomer is based on a non-linear formulation, and it has been validated against experimental data. In addition, the implementation of the aeroelastic framework has been verified against the relevant literature for the low-Reynolds number flows investigated in this dissertation. Numerical simulations of the open-loop dynamics of the actuated membrane, in good agreement with experimental observations, show that integral actuation offers enough authority in the control of the wing aerodynamic performance. Dielectric elastomers can then be used as embedded actuators, coupling the advantages of passive membranes with a simple and lightweight control mechanism. Further, this work also proposes a model-reduction methodology for the fully coupled system to aid control system design. The low-order description of the actuated system can capture the main system dynamics, and can be used for the design of the control scheme of the wing. Proportional-Integral-Derivative and Linear Quadratic Gaussian feedback controllers, designed using the reduced-order model, are finally implemented in the high-fidelity model for the rejection of flow disturbances. Results show that the wing aerodynamic performance is noticeably enhanced through the actuation as the disturbances on the lift in case of gusts can be reduced up to 60%.Open Acces

Controls and guidance research

The objectives of the control group are concentrated on research and education. The control problem of the hypersonic space vehicle represents an important and challenging issue in aerospace engineering. The work described in this report is part of our effort in developing advanced control strategies for such a system. In order to achieve the objectives stated in the NASA-CORE proposal, the tasks were divided among the group based upon their educational expertise. Within the educational component we are offering a Linear Systems and Control course for students in electrical and mechanical engineering. Also, we are proposing a new course in Digital Control Systems with a corresponding laboratory

The counterbend phenomenon in flagellar axonemes and cross-linked filament bundles

Recent observations of flagellar counterbend in sea urchin sperm show that the mechanical induction of curvature in one part of a passive flagellum induces a compensatory countercurvature elsewhere. This apparent paradoxical effect cannot be explained using the standard elastic rod theory of Euler and Bernoulli, or even the more general Cosserat theory of rods. Here, we develop a geometrically exact mechanical model to describe the statics of microtubule bundles that is capable of predicting the curvature reversal events observed in eukaryotic flagella. This is achieved by allowing the interaction of deformations in different material directions, by accounting not only for structural bending, but also for the elastic forces originating from the internal cross-linking mechanics. Large-amplitude static configurations can be described analytically, and an excellent match between the model and the observed counterbend deformation was found. This allowed a simultaneous estimation of multiple sperm flagellum material parameters, namely the cross-linking sliding resistance, the bending stiffness, and the sperm head junction compliance ratio. We further show that small variations on the empirical conditions may induce discrepancies for the evaluation of the flagellar material quantities, so that caution is required when interpreting experiments. Finally, our analysis demonstrates that the counterbend emerges as a fundamental property of sliding resistance in cross-linked filamentous polymer bundles, which also suggests that cross-linking proteins may contribute to the regulation of the flagellar waveform in swimming sperm via counterbend mechanics

Reduced-order modelling and feedback control of integrally actuated membrane wings

This paper presents a numerical investigation on aerodynamic control of integrally-actuated membrane wings made of dielectric elastomers. They combine the advantages of membrane shape adaptability with the benefits of the simple, lightweight but high-authority control mechanism offered by integral actuation. For that purpose, high-fidelity numerical models have been developed to predict their performance. They include a fluid solver based on the direct numerical integration of the unsteady Navier-Stokes equations, an electromechanical constitutive material model and a non-linear three-dimensional membrane structural model. In addition, using the Eigensystem Realization Algorithm, it is obtained a very low order model description of the fully coupled aero-electromechanical system to aid the design of a simple PID control scheme for the feedback control of the wing. The resulting regulator is then implemented in the high-fidelity model and used for the mitigation of flow disturbances

In silico case studies of compliant robots: AMARSI deliverable 3.3

In the deliverable 3.2 we presented how the morphological computing ap- proach can significantly facilitate the control strategy in several scenarios, e.g. quadruped locomotion, bipedal locomotion and reaching. In particular, the Kitty experimental platform is an example of the use of morphological computation to allow quadruped locomotion. In this deliverable we continue with the simulation studies on the application of the different morphological computation strategies to control a robotic system