Navigation, localization and stabilization of formations of unmanned aerial and ground vehicles

A leader-follower formation driving algorithm developed for control of heterogeneous groups of unmanned micro aerial and ground vehicles stabilized under a top-view relative localization is presented in this paper. The core of the proposed method lies in a novel avoidance function, in which the entire 3D formation is represented by a convex hull projected along a desired path to be followed by the group. Such a representation of the formation provides non-collision trajectories of the robots and respects requirements of the direct visibility between the team members in environment with static as well as dynamic obstacles, which is crucial for the top-view localization. The algorithm is suited for utilization of a simple yet stable visual based navigation of the group (referred to as GeNav), which together with the on-board relative localization enables deployment of large teams of micro-scale robots in environments without any available global localization system. We formulate a novel Model Predictive Control (MPC) based concept that enables to respond to the changing environment and that provides a robust solution with team members' failure tolerance included. The performance of the proposed method is verified by numerical and hardware experiments inspired by reconnaissance and surveillance missions

Organic Agriculture

The “Organic Agriculture” (OA) book provides anyone interested in this type of farming with a practically focused textbook. The book gives a basic summary of work covering all relevant themes on which the most competent authors, coordinated by Czech experts - Borivoj Šarapatka and Jirí Urban, provide definitive contributions valid not only within the Czech Republic. The book is recommended for practical farming but also as a textbook for teachers and students. The real value of the book is in the fact that it has been compiled by a number of OA specialists and institutions focusing on this area of agriculture - to meet the demand for a comprehensive publication. The book includes chapters on the history and present status of OA in Europe, the legal status of organic agriculture methods (in accordance with European Council Regulation (EC) No. 834/2007 and Commission Regulation No. 889/2008), the environmental effects of OA, plant production, soil, plant nutrition and fertilization, cultivation of crops, weed control, permanent grassland, organic fruit and vegetable-growing, organic viticulture and wine-making, animal husbandry and animal breeding

Model-based characterization of mili-reactor

This thesis focuses on development of a functioning, reliable and representative computation fluid dynamics model of milli-reactors in OpenFOAM in order to characterize them. Characterization and validation of the model was done by residence time distribution analyses, where model data were compared with experimental measurements. The model was developed for Fluitec reactor with CSE-X4 static mixer elements with diameter of 21 mm. The residence time distribution was calculated for various flow conditions in the laminar flow regime. The model followed the experimental procedure where residence time distribution is measured by injection of tracer and evaluation of its concentration at the outlet from the reactor.The comparison of calculated and experimental integrated residence time distribution curves showed good agreement. Although, it would be possible to improve the model if more information of the experimental system were provided. It was also possible spot some dead zones inside the reactor, but the experimental data suggest that it was not successfully found all of them

Model-based characterization of mili-reactor

This thesis focuses on development of a functioning, reliable and representative computation fluid dynamics model of milli-reactors in OpenFOAM in order to characterize them. Characterization and validation of the model was done by residence time distribution analyses, where model data were compared with experimental measurements. The model was developed for Fluitec reactor with CSE-X4 static mixer elements with diameter of 21 mm. The residence time distribution was calculated for various flow conditions in the laminar flow regime. The model followed the experimental procedure where residence time distribution is measured by injection of tracer and evaluation of its concentration at the outlet from the reactor. The comparison of calculated and experimental integrated residence time distribution curves showed good agreement. Although, it would be possible to improve the model if more information of the experimental system were provided. It was also possible spot some dead zones inside the reactor, but the experimental data suggest that it was not successfully found all of them

An Aggregation Multigrid Solver for Convection-diffusion Problems on Unstructured Meshes.

We study an extension of the concept of smoothed aggregation to convection-diffusion equations. Since the approximation of the hyperbolic part of the equations yields unsymmetric matrices, the use of symmetric prolongator smoother is not efficient for the construction of the coarse convection matrices. This leads us to extend the concept of smoothed aggregation to the use of non-symmetric one-sided prolongator smoothers. In this paper, we also clarify the relationship that must exist between the degree of the prolongator polynomial smoother and the aggregation strategy. This work concludes by some numerical experiments illustrating the performance of the proposed method. AMS-MOS Classification Primary: 65N55. Secondary: 65N220, 65T20. Keywords : multigrid, cell centered discretization, finite volume, Aggregation methods 1 Introduction A method that solves a N-unknowns problem in O(N logN) operations is called optimal. For problems coming from the discretisation of partial differenti..

Multilevel Algebraic Elliptic Solvers

: We survey some of the recent research in developing multilevel algebraic solvers for elliptic problems. A key concept is the design of a hierarchy of coarse spaces and related interpolation operators which together satisfy certain approximation and stability properties to ensure the rapid convergence of the resulting multigrid algorithms. We will discuss smoothed agglomeration methods, harmonic extension methods, and global energy minimization methods for the construction of these coarse spaces and interpolation operators. 1 Introduction There has been a recent resurgence of interest in algebraic multilevel elliptic solvers. Part of the motivation for considering the multilevel approach is that it is the only general method for deriving scalable solvers for large problems. Another reason is that multilevel methods are often naturally parallelizable. The main motivation for considering algebraic solvers is ease of use as often the user need only supply the problem in purely matrix-ve..

Analysis of an algebraic Petrov-Galerkin smoothed aggregation multigrid method

We give a convergence estimate for a Petrov-Galerkin Algebraic Multigrid method. In this method, the prolongations are defined using the concept of smoothed aggregation while the restrictions are simple aggregation operators. The analysis is carried out by showing that these methods can be interpreted as variational Ritz-Galerkin ones using modified transfer and smoothing operators. The estimate depends only on a weak approximation property for the aggregation operators. For a scalar second order elliptic problem using linear elements, this assumption is shown to hold using simple geometrical arguments on the aggregates. (C) 2007 IMACS. Published by Elsevier B.V. All rights reserved