1,721,242 research outputs found
On the variational approach to axisymmetric magnetohydrodynamic equilibria
No full textThe variational formulation of the axisymmetric magnetohydrodynamic equilibrium equations with plasma flows is addressed and a more comprehensive method is presented that allows, in particular, for open boundary conditions and discontinuous (shock) solutions. A numerical procedure based on the variational formulation is described and a validation test for an open conical geometry, including also hydrodynamic shocks, is investigated. (c) 2008 American Institute of Physics
Magnetized plasma flows and magnetoplasmadynamic thrusters
No full textAn axisymmetric magnetohydrodynamics (MHD) model of the acceleration channel of an applied-field magnetoplasmadynamic thruster is presented. A set of general relationships between the flow features and the thruster performance is obtained. The boundary conditions and the flow regime, which depends on the Alfven Mach number, are shown to provide the ideal limits of steady state thruster operation. In the present analysis, a Hamiltonian formulation of the MHD plasma flow model is adopted. This formulation makes it possible to cast the model equations in a variational form, which is then solved by using a finite element numerical algorithm. (C) 2010 American Institute of Physics. [doi : 10.1063/1.3447876
Sensors and Electronic Control Unit for Optimize Rotary Harrow Soil Tillage Operation
No full textAgricultural operations, and in particular tillage practices, can have a relevant influence on environmental as well as economic sustainability. The possibility of optimizing tillage operation is thus interesting in order to allow not only improvement of soil structure and cloddiness, but also better management of residues, minimization of soil disturbance and of vertical translocation of organisms, and reduction of energetic costs. The present paper reports on a research study carried out for the development of a power harrow equipped with sensors, which quantify the working depth, the height and load on the levelling bar. Data are managed by an ECU (Electronic Control Unit) which provides a feedback signal for the optimization of the working depth and the position of the levelling bar. Field tests were carried out in order to validate the effectiveness of the approach. For the scope, specific analyses were concurrently carried out to validate the proposed solution, including fuel consumption, power absorption and soil analyses (sieving, three-dimensional roughness and permanence time in the rotary harrow chamber). Finally, it is shown how the proposed approach can help maximization of the constancy of working depth and avoidance of excessive tillage intensity
Hamiltonian magnetohydrodynamics: Lagrangian, Eulerian, and dynamically accessible stability - Examples with translation symmetry
No full textBecause different constraints are imposed, stability conditions for dissipationless fluids and magnetofluids may take different forms when derived within the Lagrangian, Eulerian (energy- Casimir), or dynamically accessible frameworks. This is in particular the case when flows are present. These differences are explored explicitly by working out in detail two magnetohydrodynamic examples: convection against gravity in a stratified fluid and translationally invariant perturbations of a rotating magnetized plasma pinch. In this second example, we show in explicit form how to perform the time-dependent relabeling introduced in Andreussi et al. [Phys. Plasmas 20, 092104 (2013)] that makes it possible to reformulate Eulerian equilibria with flows as Lagrangian equilibria in the relabeled variables. The procedures detailed in the present article provide a paradigm that can be applied to more general plasma configurations and in addition extended to more general plasma descriptions where dissipation is absent
Hamiltonian magnetohydrodynamics: Lagrangian, Eulerian, and dynamically accessible stability - Theory
No full textStability conditions of magnetized plasma flows are obtained by exploiting the Hamiltonian structure of the magnetohydrodynamics (MHD) equations and, in particular, by using three kinds of energy principles. First, the Lagrangian variable energy principle is described and sufficient stability conditions are presented. Next, plasma flows are described in terms of Eulerian variables and the noncanonical Hamiltonian formulation of MHD is exploited. For symmetric equilibria, the energy-Casimir principle is expanded to second order and sufficient conditions for stability to symmetric perturbation are obtained. Then, dynamically accessible variations, i.e., variations that explicitly preserve invariants of the system, are introduced and the respective energy principle is considered. General criteria for stability are obtained, along with comparisons between the three different approaches
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