Parametric reduced order models for aeroelastic design of very flexible aircraft

A description for flutter and dynamic loads prediction is laid out based on state-space systems around a nonlinear equilibrium. In order to reduce the computational times associated with building and manipulating these systems, a newmethodology is proposed to build parametric reduced-order models of the unsteady aerodynamic systems from optimal Latin-Hypercube design of experiments, frequency-limited balancing techniques and interpolation on the transfer functions of the resulting reduced systems. Optimization of the kernels encapsulating the parametric dependence is also studied. The developed tools are employed for the aeroelastic design optimization of a very flexible strut-braced wing with flutter constraints. Results show a promising approach to be deployed in design problems where dynamics and stability are to be included in the analysis and geometrically nonlinear effects are to be accounted for

REFLUJO VESICO-URETERAL

Arch Esp Urol. 2006 Nov;59(9):924. [Vesico-ureteral reflux] [Article in Spanish] Palacios A, de Castro R, Reis A. Servicio de Urología, Hospital Pediátrico Maria Pía, Porto, Portugal. [email protected] PMID: 17190222 [PubMed - indexed for MEDLINE

Nonlinear modal aeroservoelastic analysis framework for flexible aircraft

A nonlinear formulation in modal coordinates of the equations of motion of a flexible aircraft is presented. It relies on the projection of the intrinsic equations of geometrically nonlinear composite beams on the linear normal modes at a reference condition, which are coupled with two-dimensional unsteady aerodynamics. The resulting description is suitable for nonlinear dynamic analysis and control design, whereas the description in modal coordinates links directly to linear aeroservoelastic analysis methods. Results are presented on and compared to cantilever wings and full aircraft configurations previously studied in the literature. Linear H∞H∞ control synthesis and closed-loop nonlinear simulations are finally explored on a highly flexible flying wing under large-amplitude discrete gusts. Results show the ability of the proposed framework to capture the nonlinear dynamics of the aeroelastic system, while providing a seamless integration with linear methods, as well as its strength in identification of the dominant contributors to the nonlinear response

Low-cost technology for the integration of micro- and nanochips into fluidic systems on printed circuit board: fabrication challenges

Nowadays, micro- and nanochips are usually\ud fabricated with Silicon and/or glass. A simple, low-cost and\ud reliable integration packaging method that provides flexibility\ud to the incorporation of electronic and fluidic devices into a\ud system has not been fully developed yet. The use of Printed\ud Circuit Board material as substrate to create dry film resist\ud microfluidic channels is the core technology to provide such an\ud integration method. The feasibility and potential of the\ud proposed packaging method is demonstrated in this wor

Non-linear response of single-molecule magnets: field-tuned quantum-to-classical crossovers

Quantum nanomagnets can show a field dependence of the relaxation time very different from their classical counterparts, due to resonant tunneling via excited states (near the anisotropy barrier top). The relaxation time then shows minima at the resonant fields H_{n}=n D at which the levels at both sides of the barrier become degenerate (D is the anisotropy constant). We showed that in Mn12, near zero field, this yields a contribution to the nonlinear susceptibility that makes it qualitatively different from the classical curves [Phys. Rev. B 72, 224433 (2005)]. Here we extend the experimental study to finite dc fields showing how the bias can trigger the system to display those quantum nonlinear responses, near the resonant fields, while recovering an classical-like behaviour for fields between them. The analysis of the experiments is done with heuristic expressions derived from simple balance equations and calculations with a Pauli-type quantum master equation.Comment: 4 pages, 3 figures. Submitted to Phys. Rev. B, brief report

Generalized Kelvin–Voigt damping models for geometrically nonlinear beams

Strain-rate-based damping is investigated in the strong form of the intrinsic equations of three-dimensional geometrically exact beams. Kelvin–Voigt damping, often limited in the literature to linear or two-dimensional beam models, is generalized to the three-dimensional case, including rigid-body motions. The result is an elegant infinite-dimensional description of geometrically exact beams that facilitates theoretical analysis and sets the baseline for any chosen numerical implementation. In particular, the dissipation rates and equilibrium points of the system are derived for the most general case and for one in which a first-order approximation of the resulting damping terms is taken. Finally, numerical examples are given that validate the resulting model against a nonlinear damped Euler–Bernoulli beam (where detail is given on how an equivalent description using our intrinsic formulation is obtained) and support the analytical results of energy decay rates and equilibrium solutions caused by damping. Throughout the paper, the relevance of damping higher-order terms, arising from the geometrically exact description, to the accurate prediction of its effect on the dynamics of highly flexible structures is highlighted

Modal-based nonlinear model predictive control for 3D very flexible structures

In this paper a novel NMPC scheme is derived, which is tailored to the underlying structure of the intrinsic description of geometrically exact nonlinear beams (in which velocities and strains are primary variables). This is an important class of PDE models whose behaviour is fundamental to the performance of flexible structural systems (e.g., wind turbines, High-Altitude Long-Endurance aircraft). Furthermore, this class contains the much-studied Euler-Bernoulli and Timoshenko beam models, but has significant additional complexity (to capture 3D effects and arbitrarily large displacements) and requires explicit computation of rotations in the PDE dynamics to account for orientation-dependent forces such as gravity. A challenge presented by this formulation is that uncontrollable modes necessarily appear in any finite dimensional approximation to the PDE dynamics. We show, however, that an NMPC scheme can be constructed in which the error introduced by the uncontrollable modes can be explicitly controlled. Furthermore, in challenging numerical examples exhibiting considerable deformation and nonlinear effects, it is demonstrated that the asymptotic error can be made insignificant (from a practical perspective) usingour NMPC scheme and excellent performance is obtained evenwhen applied to a highly resolved numerical simulation of thePDEs. We also present a generalisation of Kelvin-Voigt dampingto the intrinsic description of geometrically-exact beams. Finally,special emphasis is placed on constructing a framework suitablefor real-time NMPC control, where the particular structure ofthe underlying PDEs is exploited to obtain both efficient finite-dimensional models and numerical schemes

Vortex matter in superconducting mesoscopic disks: Structure, magnetization, and phase transitions

The dense vortex matter structure and associated magnetization are calculated for type-II superconducting mesoscopic disks. The magnetization exhibits generically first-order phase transitions as the number of vortices changes by one and presents two well-defined regimes: A non-monotonous evolution of the magnitude of the magnetization jumps signals the presence of a vortex glass structure which is separated by a second-order phase transition at $H_{c2}$ from a condensed state of vortices (giant vortex) where the magnitude of the jumps changes monotonously. We compare our results with Hall magnetometry measurements by Geim et al. (Nature 390, 259 (1997)) and claim that the magnetization exhibits clear traces of the presence of these vortex glass states.Comment: 4 pages, 3 figure

Surface abundances of ON stars

Massive stars burn hydrogen through the CNO cycle during most of their evolution. When mixing is efficient, or when mass transfer in binary systems happens, chemically processed material is observed at the surface of O and B stars. ON stars show stronger lines of nitrogen than morphologically normal counterparts. Whether this corresponds to the presence of material processed through the CNO cycle or not is not known. Our goal is to answer this question. We perform a spectroscopic analysis of a sample of ON stars with atmosphere models. We determine the fundamental parameters as well as the He, C, N, and O surface abundances. We also measure the projected rotational velocities. We compare the properties of the ON stars to those of normal O stars. We show that ON stars are usually helium-rich. Their CNO surface abundances are fully consistent with predictions of nucleosynthesis. ON stars are more chemically evolved and rotate - on average - faster than normal O stars. Evolutionary models including rotation cannot account for the extreme enrichment observed among ON main sequence stars. Some ON stars are members of binary systems, but others are single stars as indicated by stable radial velocities. Hence, mass transfer is not a simple explanation for the observed chemical properties. We conclude that ON stars show extreme chemical enrichment at their surface, consistent with nucleosynthesis through the CNO cycle. Its origin is not clear at present.Comment: 18 pages, 10 figures (+ appendix). A&A accepte

Lithium and magnetic fields in giants. HD 232862 : a magnetic and lithium-rich giant star

We report the detection of an unusually high lithium content in HD 232862, a field giant classified as a G8II star, and hosting a magnetic field. With the spectropolarimeters ESPaDOnS at CFHT and NARVAL at TBL, we have collected high resolution and high signal-to-noise spectra of three giants : HD 232862, KU Peg and HD 21018. From spectral synthesis we have inferred stellar parameters and measured lithium abundances that we have compared to predictions from evolutionary models. We have also analysed Stokes V signatures, looking for a magnetic field on these giants. HD 232862, presents a very high abundance of lithium (ALi = 2.45 +/- 0.25 dex), far in excess of the theoretically value expected at this spectral type and for this luminosity class (i.e, G8II). The evolutionary stage of HD 232862 has been precised, and it suggests a mass in the lower part of the [1.0 Msun ; 3.5 Msun ] mass interval, likely 1.5 to 2.0 solar mass, at the bottom of the Red Giant Branch. Besides, a time variable Stokes V signature has been detected in the data of HD 232862 and KU Peg, pointing to the presence of a magnetic field at the surface of these two rapidly rotating active stars.Comment: 11 pages, 9 figures ; accepted by Astronomy and Astrophysic