Search results for "shooting"

Thermally unstable throughflow of a power–law fluid in a vertical porous cylinder with arbitrary cross–section

2021

Abstract The present paper investigates how the cross–sectional shape of a vertical porous cylinder affects the onset of thermoconvective instability of the Rayleigh–Benard type. The fluid saturating the porous medium is assumed to be a non–Newtonian power–law fluid. A linear stability analysis of the vertical thorughflow is carried out. Three special shapes of the cylinder cross–section are analysed: square, circular and elliptical. The effect of changing the power–law index is investigated. The stability of a steady base state with vertical throughflow is analysed. The resulting stability problem is a differential eigenvalue problem that is solved numerically through the shooting method. …

Robotic Pancreaticoduodenectomy: Technical Considerations

2017

Robotic surgery can help to overcome some technical limitations of laparoscopic pancreaticoduodenectomy thanks to EndoWrist instrumentations and the 3D view. Despite the potential benefits, its employment is still low and controversial. We focused on some important technical details crucial for a safe robotic pancreatectomy. After performing 52 robotic pancreatic resections that included 10 pancreatoduodenectomies, the authors describe their technique. The review of literature on robotic and laparoscopic duodenopancreatectomy is also performed in order to evaluate possible benefits of the robotic platform. We describe the step-by-step surgical procedure, analyzing all possible troubleshooti…

“Tirare al selvatico”: modalità. Una voce del Vocabolario-Atlante delle pratiche venatorie siciliane .

2020

Viene presentato un saggio di voce del "Vocabolario-atlante delle pratiche venatorie siciliane", secondo il modello elaborato in seno all’Atlante Linguistico della Sicilia (ALS). Con una nuova messe di dati e tenendo conto del modello di voce elaborato per il Vocabolario-atlante, in questo contributo, che vuole essere un ideale ampliamento della voce "sparari" pubblicata nel 1980 da Giovanni Ruffino in questo stesso Bollettino, sono prese in esame le numerose locuzioni venatorie relative alle modalità di ‘tirare al selvatico’, concetto che nel lessico venatorio siciliano è generalmente espresso con il tipo lessicale "sparari". A sample of the entry of the "Vocabolario-atlante delle pratiche…

nalysis, Modeling and Simulation of Mechatronic Systems using the Bond Graph Method

2011

The Bond Graph is the proper choice of physical system used for: (i) Modeling which can be applied to systems combining multidisciplinary energy domains, (ii) Analysis to provide a great value proposition for finding the algebraic loops within the system enabling the process of troubleshooting and eliminating the defects by using the proper component(s) to fix the causality conflict even without being acquainted in the proper system, and (iii) Simulation facilitated through derived state space equations from the Bond Graph model is solved using industrial simulation software, such as 20-Sim. The Bond Graph technique is a graphical language of modeling, in which component energy ports are co…

Thermoconvective instability and local thermal non-equilibrium in a porous layer with isoflux-isothermal boundary conditions

2014

The effects of lack of local thermal equilibrium between the solid phase and the fluid phase are taken into account for the convective stability analysis of a horizontal porous layer. The layer is bounded by a pair of plane parallel walls which are impermeable and such that the lower wall is subject to a uniform flux heating, while the upper wall is isothermal. The local thermal non-equilibrium is modelled through a two-temperature formulation of the energy exchange between the phases, resulting in a pair of local energy balance equations: one for each phase. Small-amplitude disturbances of the basic rest state are envisaged to test the stability. Then, the standard normal mode procedure is…

Latvijas Vēstures Institūta Žurnāls. 2013, Nr. 1 (86)

2013

Méthodes géometriques en mécanique spatiale et aspects numériques

2005

We present in this thesis two research projectson the optimal control of the space vehicles.In the first, we have dealt with the orbit transferproblem. We study the minimum time control of a satellite that we want to reach a geostationary orbit. Our contribution is of two kinds. Geometric, first, since we study the controllability of the system together with the geometry of the transfer (structure of the command) by means of geometric control without state constraint tools (minimum principle). Then we present shootingalgorithm and homotopy method. These approaches allow the numerical resolution of problems with strong or low thrust satellites.The second project concerns to the calculation o…

Optimal control of the atmospheric arc of a space shuttle and numerical simulations with multiple-shooting method

2005

This article, continuation of previous works, presents the applications of geometric optimal control theory to the analysis of the Earth re-entry problem for a space shuttle where the control is the angle of bank, the cost is the total amount of thermal flux, and the system is subject to state constraints on the thermal flux, the normal acceleration and the dynamic pressure. Our analysis is based on the evaluation of the reachable set using the maximum principle and direct computations with the boundary conditions according to the CNES research project\footnote{The project is partially supported by the Centre National d'Etude Spatiales.}. The optimal solution is approximated by a concatenat…

3D Geosynchronous Transfer of a Satellite: Continuation on the Thrust

2003

The minimum-time transfer of a satellite from a low and eccentric initial orbit toward a high geostationary orbit is considered. This study is preliminary to the analysis of similar transfer cases with more complicated performance indexes (maximization of payload, for instance). The orbital inclination of the spacecraft is taken into account (3D model), and the thrust available is assumed to be very small (e.g. 0.3 Newton for an initial mass of 1500 kg). For this reason, many revolutions are required to achieve the transfer and the problem becomes very oscillatory. In order to solve it numerically, an optimal control model is investigated and a homotopic procedure is introduced, namely cont…

On local optima in minimum time control of the restricted three-body problem

2016

International audience; The structure of local minima for time minimization in the controlled three-body problem is studied. Several homotopies are systematically used to unfold the structure of these local minimizers, and the resulting singularity of the path associated with the value function is analyzed numerically.