The Special Case of Sea Mines

In this chapter, work carried out at the Royal Military Academy regarding sea mines and mine countermeasures is summarized. Three sensors used for the detection and identification of sea mines are studied here: sonar, gradiometer and infrared camera. These sensors can be applied to detect different types of sea mines. Some signal and image processing techniques developed to extract relevant information for the detection of underwater objects are presented in this chapter. These techniques are validated using data collected in the frame of different European and NATO projects

Embedded symmetric positive semi-definite machine-learned elements for reduced-order modeling in finite-element simulations with application to threaded fasteners

We present a machine-learning strategy for finite element analysis of solid mechanics wherein we replace complex portions of a computational domain with a data-driven surrogate. In the proposed strategy, we decompose a computational domain into an "outer" coarse-scale domain that we resolve using a finite element method (FEM) and an "inner" fine-scale domain. We then develop a machine-learned (ML) model for the impact of the inner domain on the outer domain. In essence, for solid mechanics, our machine-learned surrogate performs static condensation of the inner domain degrees of freedom. This is achieved by learning the map from (virtual) displacements on the inner-outer domain interface boundary to forces contributed by the inner domain to the outer domain on the same interface boundary. We consider two such mappings, one that directly maps from displacements to forces without constraints, and one that maps from displacements to forces by virtue of learning a symmetric positive semi-definite (SPSD) stiffness matrix. We demonstrate, in a simplified setting, that learning an SPSD stiffness matrix results in a coarse-scale problem that is well-posed with a unique solution. We present numerical experiments on several exemplars, ranging from finite deformations of a cube to finite deformations with contact of a fastener-bushing geometry. We demonstrate that enforcing an SPSD stiffness matrix is critical for accurate FEM-ML coupled simulations, and that the resulting methods can accurately characterize out-of-sample loading configurations with significant speedups over the standard FEM simulations

Performing thinking in action: the meletē of live coding

Within this article, live coding is conceived as a meletē, an Ancient Greek term used to describe a meditative thought experiment or exercise in thought, especially understood as a preparatory practice supporting other forms of critical — even ethical — action. Underpinned by the principle of performing its thinking through 'showing the screen', live coding involves 'making visible' the process of its own unfolding through the public sharing of live decision-making within improvisatory performance practice. Live coding can also be conceived as the performing of 'thinking-in-action', a live and embodied navigation of various critical thresholds, affordances and restraints, where its thinking-knowing cannot be easily transmitted nor is it strictly a latent knowledge or 'know how' activated through action. Live coding involves the live negotiation between receptivity and spontaneity, between the embodied and intuitive, between an immersive flow experience and split-attention, between human and machine, the known and not yet known. Moreover, in performing 'thinking-in-action', live coding emerges as an experimental site for reflecting on different perceptions and possibilities of temporal experience within live performance: for attending to the threshold between the live and mediated, between present and future-present, proposing even a quality of atemporality or aliveness

Study of grains and granular matter under electric fields

Electric fields have been used to modify properties of dilute and dense granular materials. For the dilute case, we showed that electric fields can be used to inject kinetic energy on the material. We studied the dynamics of a single bead, two beads and three beads systems. The dynamics is described by a mathematical model which is in quantitative agreement with experiments. A synchronization effect is observed and it is described by a phase coupled oscillators model. We also show that electric fields can be used to tune the cohesion of dense granular media. A transition of the geometry of the flow is observed. Intermittences are induced by the electric field.Des champs électriques ont étés utilisés pour modifier les propriétés de matériaux granulaires denses et dilués. Pour le cas dilué, nous avons montré que les champs électriques peuvent être utilisés pour injecter de l'énergie cinétique dans le matériau. Nous avons étudié la dynamique d'une seule bille, d'un système de deux ou de trois billes. La dynamique est décrite par un modèle mathématique qui est en accord quantitatif avec les expériences. Une synchronisation apparaît et elle est décrite par un modèle d'oscillateurs couplés. Nous montrons que des champs électriques peuvent être utilisés pour induire de la cohésion dans les matériaux granulaires denses. Une transition de la géométrie du flux est observée. Des intermittences sont induites par le champ électrique