Opal: An open source ray-tracing propagation simulator for electromagnetic characterization

Accurate characterization and simulation of electromagnetic propagation can be obtained by ray-tracing methods, which are based on a high frequency approximation to the Maxwell equations and describe the propagating field as a set of propagating rays, reflecting, diffracting and scattering over environment elements. However, this approach has been usually too computationally costly to be used in large and dynamic scenarios, but this situation is changing thanks the increasing availability of efficient ray-tracing libraries for graphical processing units. In this paper we present Opal, an electromagnetic propagation simulation tool implemented with ray-tracing on graphical processing units, which is part of the Veneris framework. Opal can be used as a stand-alone ray-tracing simulator, but its main strength lies in its integration with the game engine, which allows to generate customized 3D environments quickly and intuitively. We describe its most relevant features and provide implementation details, highlighting the different simulation types it supports and its extension possibilites. We provide application examples and validate the simulation on demanding scenarios, such as tunnels, where we compare the results with theoretical solutions and further discuss the tradeoffs between the simulation types and its performance.

New energy, angle momentum and entropy balance approach to modelling climate and macroturbulent atmospheric dynamics, heat and mass transfer at macroscale. III. Low-frequency approximation and singularities in fields of meteoelements

An generalized low-frequency approximation of energy, angle momentum and entropy balance relationships to modelling climate and macro-turbulent atmospheric dynamics, heat and mass transfer at macroscale is introduced and allow significantly to simplify the main fundamental equations. A new equilibrium approach to modelling the global mechanisms of climatic and macroturbulent atmospheric low-frequency processes, including heat and mass transfer processes, teleconnection effects, etc., is based on the use of equilibrium relations for entropy, energy, angular momentum, spectral theory of atmospheric macroturbulence and moisture turnover in connection with the continuity of forms of atmospheric circulation (teleconnection, genesis of fronts). The physical features of singularities in the fields of meteorological elements and the balance of the angular momentum as well as a generalized Arakawa-Schubert model are introduced and discussed.

Backward peaking radiation pattern from a relativistic particle accelerated by lightning leader tip electric field

<div> <p>Charged particles being accelerated by the lightning leader tip electric field emit electromagnetic radiation due to the Bremsstrahlung process (Celestin et al., JGR, 2012). Bremsstrahlung has a continuous spectrum of radiation which includes radio waves and ionising radiation such as gamma rays which can be recorded by detectors on board the ASIM payload on the International Space Station, the forthcoming TARANIS satellite, or on the ground (Abbasi et al., JGR, 2018).  </p> </div><div> <p>The radiation pattern of this Bremsstrahlung is not well known. Displays of radiation patterns of accelerated particles are normally limited either to a low frequency approximation for radio waves, or to linear acceleration in a high frequency approximation for gamma rays. Here we report the radiation patterns from accelerated relativistic particles at low and high frequencies of the Bremsstrahlung process. It is found that the radiation patterns have four relative maxima with two backward peaking and two forward peaking.  </p> </div><div> <p>The shape of the radiation pattern is only determined by the velocity of the particle whilst the intensity of the radiation pattern is determined by the velocity and the acceleration of the particle. For example, relativistic particles with a large velocity exhibit a radiation pattern which is more forward peaking when compared to a non-relativistic particle with a smaller velocity. Similarly, relativistic particles with a large acceleration exhibit a radiation pattern with a larger intensity when compared to relativistic particles with a smaller acceleration. All these radiation patterns exhibit backward peaking radiation. The asymmetry of the radiation pattern, I.e., the different intensities of forward and backward peaking lobes, is controlled by the asymmetric frequencies of the Bremsstrahlung radiation caused by the Doppler effect.  </p> </div><div> <p>These results are important because they enable a determination of particle properties which can be inferred from observations with networks of radio receivers and arrays of gamma ray detectors. </p> </div>

Passive modelling of the electrodynamic loudspeaker: from the Thiele–Small model to nonlinear port-Hamiltonian systems

The electrodynamic loudspeaker couples mechanical, magnetic, electric and thermodynamic phenomena. The Thiele/Small (TS) model provides a low frequency approximation, combining passive linear (multiphysical or electric-equivalent) components. This is commonly used by manufacturers as a reference to specify basic parameters and characteristic transfer functions. This paper presents more refined nonlinear models of electric, magnetic and mechanical phenomena, for which fundamental properties such as passivity and causality are guaranteed. More precisely, multiphysical models of the driver are formulated in the core class of port-Hamiltonian systems (PHS), which satisfies a power balance decomposed into conservative, dissipative and source parts. First, the TS model is reformulated as a linear PHS. Then, refinements are introduced, step-by-step, benefiting from the component-based approach allowed by the PHS formalism. Guaranteed-passive simulations are proposed, based on a numerical scheme that preserves the power balance. Numerical experiments that qualitatively comply with measured behaviors available in the literature are presented throughout the paper.