1,721,047 research outputs found
Modern Spacecraft Guidance, Navigation, and Control - Introduction
No full textThis chapter introduces the main concepts contained in the book “Modern Spacecraft Guidance, Navigation, and Control: From System Modeling to AI and Innovative Applications.” It lists the content of each chapter of the book and the suggestions to read and use the book. It contains a brief historical review of spacecraft Guidance, Navigation, and Control (GNC) and the main GNC terminology. It offers a general introduction on the design process of a GNC system, from requirements to preliminary design and verification. Finally, it is concluded with the notation rules and the main acronyms used along the book
XML Technology for the Diffusion of the Awareness of Water Resources
No full textThis paper illustrates the requirements, problems and XML-based architectural proposals relating to a specialized Water Semantic Web System for the diffusion and the evolution of the awareness of water resources. The real and true themes connected to the awareness of water resources are presented, including those related to the artistic and social aspects destined to integrate the purely technological and organizational ones already present in the current information offer of other web systems specialized on water. We, therefore, present the technological instruments considered most adequate for the creation of the Water Semantic Web System. In conclusion a possible XML-based architecture for the system is presented and some of the initial results obtained are illustrated
Water Protection Information Management by Syntactic and Semantic Interoperability of Heterogeneous Repositories
No full textTwo dimensional vorticity dynamic studied with two different particle methods
No full textSUMMARY.
In this paper two dimensional vorticity dynamic is studied using two different particle methods.
The first one is a Diffusive Vortex Method (DVM) and the second one is a Smoothed Particle Hydrodynamics
(SPH) method. These two popular methods presents some similarities linked to their meshless nature but they are based on different numerical approaches. In this work advantages and drawbacks are highlighted testing the particle methods on selected test-cases and performing heuristic
convergence measurements. The DVM discussed in this work is characterized by the use of a computational grid to perform the vorticity diffusion process. This mesh redistribution avoid excessive
clustering or rarefaction of the vortex particles ensuring robustness and high accuracy of the method
Two-dimensional viscous flow studied using vortex particle methods
No full textVortex particle methods are alternative methods to Eulerian approaches for the solution of the incompressible Navier-Stokes equations in vorticity-velocity variables. They are characterized by the inherent ability to adapt to the flow due to their Lagrangian formulation for the advection and additionally by the decoupling of the pressure from the momentum equation. In this work, we study these methods using the Lagrangian vortex particle method Diffused Vortex Hydrodynamics that uses the operator splitting in time of Chorin. Numerical results are obtained for problems containing solid boundaries in the domain for different test cases. We compare the results with a finite volume solver that discretizes the velocity-pressure formulation of Navier-Stokes and uses artificial compressibility to evolve the solution in time, also introduced by Chorin. The comparison is obtained based on local and global derived quantities. Finally, an application of the method to a physical study is presented regarding the flow past an elliptical cylinder
A fast algorithm for free-surface particles detection in 2D and 3D SPH methods
No full textThe present paper aims at proposing a fast algorithm
permitting to detect the free-surface in particle simulations,
and next to define a level-set function on a cartesian grid. The
latter allows for analyzing in detail the free surface shape of
three-dimensional simulations as well as internal features of
the flow, by using standard visualization tools. The algorithms
proposed for detecting the free-surface particles are described
in both two and three dimensions, and are validated on simple
and complex flow simulations. Then, the derivation of the level-set
function is detailed and the usefulness of the proposed method to
post-process and analyze complex flows are illustrated on realistic
2D and 3D examples
An accurate SPH modeling of viscous flows around bodies at low and moderate Reynolds numbers
No full textA weakly compressible SPH scheme has been used to describe the evolution of viscous flows around blunt bodies at Reynolds numbers ranging from 10 to 2400. The simulation of such a wide range, rarely addressed to in the SPH literature, has been possible thanks to the use of a proper ghost-fluid technique and to an accurate enforcement of the boundary conditions along the solid boundaries. In this context, a new numerical technique based on previous works by Takeda et al. (1994) [48], Marrone et al. (2011) [28] and De Leffe et al. (2011) [16] has been proposed, along with a new method for the evaluation of the global loads on bodies. Particular care has been taken to study the influence of the weakly-compressibility assumption and of different ghost-fluid techniques on the numerical results. An in-depth validation of the model has been performed by comparing the numerical outcome with experimental data from the literature and other numerical references. The influence of the domain size has been discussed in order to avoid wall side effects and, at the same time, to limit the computational costs. The convergence of the numerical solutions has been checked on both global and local quantities by choosing appropriate Reynolds-cell number. © 2013 Elsevier Inc
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