Fixed-distance multipoint formulas for the scattering amplitude from phaseless measurements

We give new formulas for finding the complex (phased) scattering amplitude at fixed frequency and angles from absolute values of the scattering wave function at several points $x_1,..., x_m$. In dimension $d\geq 2$, for $m>2$, we significantly improve previous results in the following two respects. First, geometrical constraints on the points needed in previous results are significantly simplified. Essentially, the measurement points $x_j$ are assumed to be on a ray from the origin with fixed distance $\tau=|x_{j+1}- x_j|$, and high order convergence (linearly related to $m$) is achieved as the points move to infinity with fixed $\tau$. Second, our new asymptotic reconstruction formulas are significantly simpler than previous ones. In particular, we continue studies going back to [Novikov, Bull. Sci. Math. 139(8), 923-936, 2015].

A simulation chain for reflectometry and non-linear MHD: type-I ELM case

A complete chain from a non-linear MHD plasma model simulation through full-wave code simulations implementing synthetic conventional reflectometry is established. For this purpose, the two-dimensional full-wave code REFMUL is employed together with MHD descriptions obtained from the JOREK code. First results of the integrated modeling are presented here where a type-I ELM crash, leading to a fast collapse of the H-mode pedestal, was taken as case-study. The REFMUL simulations were customized to implement synthetic reflectometry in conventional set-up using fixed frequency probing with O-mode waves. Posing challenging conditions for reflectometry, the type-I ELM crash reveals some of the merits and caveats of the diagnostic technique. This work also opens up the possibility to extend modeling to other MHD or ELM studies and provide support to experimental observations with reflectometry.

Large-eddy simulations of a swirling flow in a model Francis turbine

We performed Large-eddy simulations of the flow in a model air Francis turbine in a range of low-load regimes with a swirler rotating at fixed frequency. All investigated regimes revealed the presence of coherent helical vortex structure in the draft tube: the precessing vortex core. We identified the frequency of this instability and obtained mean flow velocity fields to be utilized in further works.

Adaptive Tracking Method of Distorted Voltage Using IMM Algorithm under Grid Frequency Fluctuation Conditions

This paper newly proposes an interactive multiple model (IMM) algorithm to adaptively track distorted AC voltage with the grid frequency fluctuation. The usual tracking methods are Kalman filter (KF) algorithm with a fixed frequency and KF algorithm with frequency identifier. The KF algorithm with a fixed frequency has a larger covariance parameter to guarantee the tracking robustness. However, it has a large tracking error. The KF algorithm with frequency identifier overly depends on the accuracy and stability of frequency identifier. The advantage of the proposed method is that it is decoupled from frequency detection and does not depend on frequency detection accuracy. First, the orthogonal vector dynamic (OVD) tracking model of the sine wave is established. Then, a model set covering the grid frequency fluctuation range is formed, and a new OVD-IMM tracking algorithm is proposed in combination with IMM algorithm. In the end, the effectiveness and accuracy of the proposed OVD-IMM algorithm are verified through simulations and experiments.

Topological wave energy harvesting in bistable lattices

In this paper, we present an input-independent energy harvesting mechanism exploiting topological waves. Transition waves in discrete bistable lattices entail energy radiation in the form of trailing phonons. We observe numerically and experimentally that the most dominant frequencies of these phonons are invariant to the details of the input excitations as long as transition waves are generated. Most of the phonon energy at each unit cell is clustered around a single invariant frequency, enabling input-independent resonant energy transduction. An electromagnetic conversion mechanism is implemented to demonstrate that bistable lattices behave as generators of fixed-frequency electrical sources upon transition wave propagation. The presented mechanism fundamentally breaks the link between the unit cell size and the metamaterial’s operating frequencies, offering a broadband solution to energy harvesting, particularly robust for low-frequency input sources. We also investigate the effect of lattice discreteness on the energy harvesting potential, observing two performance gaps and a topological wave harvesting pass band where the potential for energy conversion increases almost monotonically. The observed frequency-invariant phonons are intrinsic to the discrete bistable lattices, enabling broadband energy harvesting to be an inherent metamaterial property.