Modeling and natural mode analysis of tethered multi-aircraft systems

Two complementary simulators aimed at the dynamic analysis of airborne wind energy systems based on multi-aircraft configurations are presented. The first model considers a train of stacked aircraft linked among them by two inelastic and massless tethers with no aerodynamic drag. The architecture of the mechanical system in the second simulator is configurable, as long as the system is made of a set of aircraft linked by an arbitrary number of elastic tethers. In both cases, the aircraft are modeled as rigid bodies and the controller is incorporated in the aerodynamic torque through the deflections of control surfaces. An analysis of the symmetric equilibrium state and the corresponding natural modes of a train (stacked configuration) of aircraft was carried out. It revealed that the higher the position of the aircraft in the train, the more they participate in the modes. Tether inertial and aerodynamic drag effects increase the equilibrium angles of attack of the aircraft and the tether tension at the attachment points. The potential applications and computational performance of the two codes are discussed.This work was supported by the Ministerio de Ciencia, Innovación y Universidades of Spain and the European Regional Development Fund under the GreenKite project ENE2015-69937-R (MINECO/FEDER, UE) and continued under the GreenKite-2 project funded by Agencia Estatal de Investigación (PID2019-110146RB-I00/ AEI / 10.13039/501100011033). GSA work is supported by the Ministerio de Ciencia, Innovación y Universidades of Spain under the Grant RYC-2014-15357

Sol-gel Barium Titanate Nanohole Array as a Nonlinear Metasurface and a Photonic Crystal

The quest of a nonlinear optical material that can be easily nanostructured over a large surface area is still ongoing. Here, we demonstrate a nanoimprinted nonlinear barium titanate 2D nanohole array that shows optical properties of a 2D photonic crystal and metasurface, depending on the direction of the optical axis. The challenge of nanostructuring the inert metal-oxide is resolved by direct soft nanoimprint lithography with sol-gel derived barium titanate enabling critical dimensions of 120 nm with aspect ratios of 5. The nanohole array exhibits a photonic bandgap in the infrared range when probed along the slab axis while lattice resonant states are observed in out-of-plane transmission configuration. The enhanced light-matter interaction from the resonant structure enables to increase the second-harmonic generation in the near-UV by a factor of 18 illustrating the potential in the flexible fabrication technique for barium titanate photonic devices

The negative compatibility effect: A case for self-inhibition

In masked priming, a briefly presented prime stimulus is followed by a mask, which in turn is followed by the task-relevant target. Under certain conditions, negative compatibility effects (NCNCEs) occur, with impaired performance on compatible trials (where prime and target indicate the same response) relative to incompatible trials (where they indicate opposite responses). However, the exact boundary conditions of NCEs, and hence the functional significance of this effect, are still under discussion. In particular, it has been argued that the NCE might be a stimulus-specific phenomenon of little general interest. This paper presents new findings indicating that the NCE can be obtained under a wider variety of conditions, suggesting that it reflects more general processes in motor control. In addition, evidence is provided suggesting that prime identification levels in forced choice tasks – usually employed to estimate prime visibility in masked prime tasks – are affected by prior experience with the prime (Exp. 1) as well as by direct motor priming (Exp. 2 & 3)

Induction in Optimal Control of Multiple-Kite Airborne Wind Energy Systems

Multiple-kite Airborne Wind Energy Systems (MAWES) aim to decrease inter-mittency and cost over conventional wind turbines, while generating more power than other airborne wind energy systems. The purpose of this work is to estimate whether axial and angular induction are relevant phenomena in the modelling of pumping-cycle MAWES with two or more kites. Considering the modelling assumptions, axial induction is a relevant phenomenon and leads to significant changes in design-point, especially with respect to kite mass and secondary tether length. However, angular induction can be neglected in modelling for optimal design and control problems

<tt>AWEbox</tt>: An Optimal Control Framework for Single- and Multi-Aircraft Airborne Wind Energy Systems

In this paper, we present AWEbox, a Python toolbox for modeling and optimal control of multi-aircraft systems for airborne wind energy (AWE). AWEbox provides an implementation of optimization-friendly multi-aircraft AWE dynamics for a wide range of system architectures and modeling options. It automatically formulates typical AWE optimal control problems based on these models, and finds a numerical solution in a reliable and efficient fashion. To obtain a high level of reliability and efficiency, the toolbox implements different homotopy methods for initial guess refinement. The first type of method produces a feasible initial guess from an analytic initial guess based on user-provided parameters. The second type implements a warm-start procedure for parametric sweeps. We investigate the software performance in two different case studies. In the first case study, we solve a single-aircraft reference problem for a large number of different initial guesses. The homotopy methods reduce the expected computation time by a factor of 1.7 and the peak computation time by a factor of eight, compared to when no homotopy is applied. Overall, the CPU timings are competitive with the timings reported in the literature. When the user initialization draws on expert a priori knowledge, homotopies do not increase expected performance, but the peak CPU time is still reduced by a factor of 5.5. In the second case study, a power curve for a dual-aircraft lift-mode AWE system is computed using the two different homotopy types for initial guess refinement. On average, the second homotopy type, which is tailored for parametric sweeps, outperforms the first type in terms of CPU time by a factor of three. In conclusion, AWEbox provides an open-source implementation of efficient and reliable optimal control methods that both control experts and non-expert AWE developers can benefit from

100-GBd Waveguide Bragg Grating Modulator in Thin-Film Lithium Niobate

An integrated electro-optic modulator based on a waveguide Bragg grating in thin-film lithium niobate is introduced. The compact device with a footprint of 10 × 400 μm2 displays an optical extinction ratio of 53.8 dB at a wavelength of 1555.9 nm in the C-band. With a simple intensity modulation and direct detection scheme, data rates up to 100 Gbit/s are demonstrated with 2-, 4- and 8-level pulse-amplitude modulation formats. The optical filter characteristic of a waveguide Bragg grating modulator suppresses one optical sideband, resulting in inherent single sideband modulation. This enables transmission of a 100 Gbit/s on-off keying signal over 12 km of standard single-mode fiber at 1559.05 nm, without the need for chromatic dispersion compensation.ISSN:1041-1135ISSN:1941-017