8,327 research outputs found
Simulations of propelling and energy harvesting articulated bodies via vortex particle-mesh methods
The emergence and understanding of new design paradigms that exploit flow
induced mechanical instabilities for propulsion or energy harvesting demands
robust and accurate flow structure interaction numerical models. In this
context, we develop a novel two dimensional algorithm that combines a Vortex
Particle-Mesh (VPM) method and a Multi-Body System (MBS) solver for the
simulation of passive and actuated structures in fluids. The hydrodynamic
forces and torques are recovered through an innovative approach which crucially
complements and extends the projection and penalization approach of Coquerelle
et al. and Gazzola et al. The resulting method avoids time consuming
computation of the stresses at the wall to recover the force distribution on
the surface of complex deforming shapes. This feature distinguishes the
proposed approach from other VPM formulations. The methodology was verified
against a number of benchmark results ranging from the sedimentation of a 2D
cylinder to a passive three segmented structure in the wake of a cylinder. We
then showcase the capabilities of this method through the study of an energy
harvesting structure where the stocking process is modeled by the use of
damping elements
Computational methods and software systems for dynamics and control of large space structures
Two key areas of crucial importance to the computer-based simulation of large space structures are discussed. The first area involves multibody dynamics (MBD) of flexible space structures, with applications directed to deployment, construction, and maneuvering. The second area deals with advanced software systems, with emphasis on parallel processing. The latest research thrust in the second area involves massively parallel computers
The nuclear energy density functional formalism
The present document focuses on the theoretical foundations of the nuclear
energy density functional (EDF) method. As such, it does not aim at reviewing
the status of the field, at covering all possible ramifications of the approach
or at presenting recent achievements and applications. The objective is to
provide a modern account of the nuclear EDF formalism that is at variance with
traditional presentations that rely, at one point or another, on a {\it
Hamiltonian-based} picture. The latter is not general enough to encompass what
the nuclear EDF method represents as of today. Specifically, the traditional
Hamiltonian-based picture does not allow one to grasp the difficulties
associated with the fact that currently available parametrizations of the
energy kernel at play in the method do not derive from a genuine
Hamilton operator, would the latter be effective. The method is formulated from
the outset through the most general multi-reference, i.e. beyond mean-field,
implementation such that the single-reference, i.e. "mean-field", derives as a
particular case. As such, a key point of the presentation provided here is to
demonstrate that the multi-reference EDF method can indeed be formulated in a
{\it mathematically} meaningful fashion even if does {\it not} derive
from a genuine Hamilton operator. In particular, the restoration of symmetries
can be entirely formulated without making {\it any} reference to a projected
state, i.e. within a genuine EDF framework. However, and as is illustrated in
the present document, a mathematically meaningful formulation does not
guarantee that the formalism is sound from a {\it physical} standpoint. The
price at which the latter can be enforced as well in the future is eventually
alluded to.Comment: 64 pages, 8 figures, submitted to Euroschool Lecture Notes in Physics
Vol.IV, Christoph Scheidenberger and Marek Pfutzner editor
KE-formulacija za aplikacije virtualne stvarnosti
Virtual reality (VR), as a novel technology, represents one of the most powerful tools to assist or even play the major role in many areas, such as development of new designs, training medical practitioners or assembly operators, entertaining industry, etc. On the other hand, the finite element method (FEM) imposed itself as an essential technical support for the needs of computing flexible bodies’ deformational behavior. FEM together with CAD are important ingredients of VR. In the VR applications that imply interactive simulations with flexible bodies included, the efficiency of FEM formulations is of crucial importance. The paper presents a co-rotational FEM-formulation developed to meet the needs of simulating geometrically nonlinear deformational behavior at interactive frame rates. It is presented here in combination with a rather simple linear tetrahedral element. The formulation is enriched with a coupled-mesh technique to enable the usage of rougher FEM models to compute deformational behavior of complex geometries. The advantages of an iterative solver and the solution procedure for both static and dynamic analyses are discussed.Virtualna stvarnost (VR), kao nova tehnologija, predstavlja jednu od najmoćnijih alatki koje podržavaju rad ili čak igraju glavnu ulogu u mnogim područjima, kao što su razvoj novih dizajna, trening liječnika ili montažera, industrija zabave, itd. S druge strane, metoda konačnih elemenata (MKE) se nametnula kao osnovna tehnička podrška za potrebe proračunavanja deformacijskog ponašanja elastičnih tijela. MKE je zajedno s CAD-om, važan dio VR-a. U VR aplikacijama koje podrazumijevaju interaktivnu simulaciju s elastičnim tijelima, efikasnost MKE formulacije je od presudne važnosti. Rad predstavlja korotacijsku MKE formulaciju razvijenu s ciljem simuliranja geometrijski nelinearnog ponašanja u interaktivnoj domeni. Formulacija je predstavljena u kombinaciji s vrlo jednostavnim linearnim elementom tipa tetraedra. Formulacija je proširena tehnikom spregnutih mreža kako bi se omogućilo korištenje grubljih MKE modela za određivanje deformacijskog ponašanja složenih geometrija. Razmotrene su prednosti iterativnog solvera kao i procedura rješavanja statičke i dinamičke analize
Preconditioner-Based Contact Response and Application to Cataract Surgery
International audienceIn this paper we introduce a new method to compute, in real-time, the physical behavior of several colliding soft-tissues in a surgical simulation. The numerical approach is based on finite element modeling and allows for a fast update of a large number of tetrahedral elements. The speed-up is obtained by the use of a specific preconditioner that is updated at low frequency. The preconditioning enables an optimized computation of both large deformations and precise contact response. Moreover, homogeneous and inhomogeneous tissues are simulated with the same accuracy. Finally, we illustrate our method in a simulation of one step in a cataract surgery procedure, which require to handle contacts with non homogeneous objects precisely
A consistent bending model for cloth simulation with corotational subdivision finite elements
Modelling bending energy in a consistent way is decisive for the realistic simulation of cloth. With existing approaches characteristic behaviour like folding and buckling cannot be reproduced in a physically convincing way. We present a new method based on a corotational formulation of subdivision finite elements. Due to the non-local nature of the employed subdivision basis functions a C1-continuous displacement field can be defined. It is thus possible to use the governing equations of thin shell analysis leading to a physically accurate bending behaviour. Using a corotated strain tensor allows the large displacement analysis of cloth while retaining a linear system of equations. Hence, known convergence properties and computational efficiency are preserved
An improved assumed strain solid-shell element formulation with physical stabilization for geometric non-linear applications and elastic-plastic stability analysis
In this paper, the earlier formulation of the SHB8PS finite element is revised in order to eliminate some persistent membrane and shear locking phenomena. This new formulation consists of a solid-shell element based on a purely three-dimensional approach. More specifically, the element has eight nodes, with displacements as the only degrees of freedom, as well as an arbitrary number of integration points, with a minimum number of two, distributed along the 'thickness' direction. The resulting derivation, which is computationally efficient, can then be used for the modeling of thin structures, while providing an accurate description of the various through-thickness phenomena. A reduced integration scheme is used to prevent some locking phenomena and to achieve an attractive, low-cost formulation. The spurious zero-energy modes due to this in-plane one-point quadrature are efficiently controlled using a physical stabilization procedure, whereas the strain components corresponding to locking modes are eliminated with a projection technique following the assumed strain method. In addition to the extended and detailed formulation presented in this paper, particular attention has been focused on providing full justification regarding the identification of hourglass modes in relation to rank deficiencies. Moreover, an attempt has been made to provide a sound foundation to the derivation of the co-rotational coordinate frame, on which the calculations of the stabilization stiffness matrix and internal load vector are based. Finally to assess the effectiveness and performance of this new formulation, a set of popular benchmark problems is investigated, involving geometric non-linear analyses as well as elastic-plastic stability issues
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