Low-Speed Aeroelastic Modeling of Very Flexible Slender Wings with Deformable Airfoils

Published versio

On-demand Aerodynamics in Integrally Actuated Membranes with Feedback Control

This paper is a numerical investigation on model reduction and control system design of integrally actuated membrane wings. A high-fidelity electro-aeromechanical model is used for the simulation of the dynamic fluid-structure interaction between a low-Reynolds-number flow and a dielectric elastomeric wing. Two reduced-order models with different levels of complexity are then derived. They are based on the projection of the fullorder discretisation of fluid and structure on modal shapes obtained from eigenvalue analysis and Proper Orthogonal Decomposition. The low-order systems are then used for the design of Proportional-Integral-Derivative and Linear Quadratic Gaussian feedback schemes to control wing lift. When implemented in the full-order model, closed-loop dynamics are in very good agreement with the reduced-order model for both tracking and gust rejection, demonstrating the suitability of the approach. The control laws selected in this work were found to be effective only for low-frequency disturbances due to the large phase delay introduced by the fluid convective time-scales, but results demonstrate the potential for the aerodynamic control of membrane wings in outdoor flight using dielectric elastomers

Entanglement in a second order quantum phase transition

We consider a system of mutually interacting spin 1/2 embedded in a transverse magnetic field which undergo a second order quantum phase transition. We analyze the entanglement properties and the spin squeezing of the ground state and show that, contrarily to the one-dimensional case, a cusp-like singularity appears at the critical point $\lambda_c$, in the thermodynamic limit. We also show that there exists a value $\lambda_0 \geq \lambda_c$ above which the ground state is not spin squeezed despite a nonvanishing concurrence.Comment: 4 pages, 4 EPS figures, minor corrections added and title change

Generalized thick strip modelling for vortex-induced vibration of long flexible cylinders

We propose a generalized strip modelling method that is computationally efficient for the VIV prediction of long flexible cylinders in three-dimensional incompressible flow. In order to overcome the shortcomings of conventional strip-theory-based 2D models, the fluid domain is divided into “thick” strips, which are sufficiently thick to locally resolve the small scale turbulence effects and three dimensionality of the flow around the cylinder. An attractive feature of the model is that we independently construct a three-dimensional scale resolving model for individual strips, which have local spanwise scale along the cylinder's axial direction and are only coupled through the structural model of the cylinder. Therefore, this approach is able to cover the full spectrum for fully resolved 3D modelling to 2D strip theory. The connection between these strips is achieved through the calculation of a tensioned beam equation, which is used to represent the dynamics of the flexible body. In the limit, however, a single “thick” strip would fill the full 3D domain. A parallel Fourier spectral/hp element method is employed to solve the 3D flow dynamics in the strip-domain, and then the VIV response prediction is achieved through the strip-structure interactions. Numerical tests on both laminar and turbulent flows as well as the comparison against the fully resolved DNS are presented to demonstrate the applicability of this approach

Robust Control Synthesis for Gust Load Alleviation from Large Aeroelastic Models with Relaxation of Spatial Discretisation

This paper introduces a methodology for the design of gust load control systems directly from large aeroelastic models with relaxation of spatial discretisation. A convenient state-space representation of the vortex-panel unsteady aerodynamics suitable for control synthesis is presented. This allows a full understanding of the dynamics of the linearized vortex aeroelastic model and is suitable for control system design. Through the use of robust controllers, large reductions in loading could be achieved. Comparisons are also made between robust and classical control methods. It further demonstrates that controllers synthesized from models of coarse spatial discretizations and of an order of magnitude smaller in size were capable of rejecting disturbances on fully converged models, with performances comparable to expensive higher order controllers developed from full models

Structure and magnetic properties of Sm/Fe multilayers versus substrate temperature

Three Sm(2 Å)/Fe(3 Å) multilayers have been made using two electron beams in a high vacuum chamber onto very thin Kapton foils at different substrate temperatures, (Ts=40°C, 150°C and 230°C), with the same total thickness of 3000 Å. We have found that the substrate temperature strongly affects structure and magnetic properties of the samples. For a substrate temperature of 150°C the sample behaves as a three dimensional random magnet

Structural Models for Flight Dynamic Analysis of Very Flexible Aircraft

Dissimilar analysis models are considered for the large structural deformations of aircraft with high-aspect-ratio composite wings. The different approaches include displacement-based, strain-based, and intrinsic geometrically-nonlinear beam models. Comparisons are made in terms of numerical efficiency and simplicity for integration of full aircraft flexibility in flight dynamics models. An analysis procedure is proposed based on model substructuring with a (linear) modal representation of both fuselage and tail and (nonlinear) intrinsic beam elements for the flexible wings. Copyright © 2009 by Rafael Palacios and Carlos E. S. Cesnik.Published versio

Mechanical, Electrical, and Magnetic Properties of Ni Nanocontacts

The dynamic deformation upon stretching of Ni nanowires as those formed with mechanically controllable break junctions or with a scanning tunneling microscope is studied both experimentally and theoretically. Molecular dynamics simulations of the breaking process are performed. In addition, and in order to compare with experiments, we also compute the transport properties in the last stages before failure using the first-principles implementation of Landauer's formalism included in our transport package ALACANT.Comment: 5 pages, 6 figure

Consistent structural linearisation in flexible-body dynamics with large rigid-body motion

A consistent linearisation, using perturbation methods, is obtained for the structural degrees of freedom of flexible slender bodies with large rigid-body motions. The resulting system preserves all couplings between rigid and elastic motions and can be projected onto a few vibration modes of a reference configuration. This gives equations of motion with cubic terms in the rigid-body degrees of freedom and constant coefficients which can be pre-computed prior to the time-marching simulation. Numerical results are presented to illustrate the approach and to show its advantages with respect to mean-axes approximations

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