475 research outputs found
The Rhie-Chow stabilized Box Method for the Stokes problem
The Finite Volume method (FVM) is widely adopted in many different
applications because of its built-in conservation properties, its ability to
deal with arbitrary mesh and its computational efficiency. In this work, we
consider the Rhie-Chow stabilized Box Method (RCBM) for the approximation of
the Stokes problem. The Box Method (BM) is a piecewise linear Petrov-Galerkin
formulation on the Voronoi dual mesh of a Delaunay triangulation, whereas the
Rhie-Chow (RC) stabilization is a well known stabilization technique for FVM.
The first part of the paper provides a variational formulation of the RC
stabilization and discusses the validity of crucial properties relevant for the
well-posedeness and convergence of RCBM. Moreover, a numerical exploration of
the convergence properties of the method on 2D and 3D test cases is presented.
The last part of the paper considers the theoretically justification of the
well-posedeness of RCBM and the experimentally observed convergence rates. This
latter justification hinges upon suitable assumptions, whose validity is
numerically explored.Comment: 27 pages, 6 figures, 4 table
An explicit dynamics GPU structural solver for thin shell finite elements
With the availability of user oriented software tools, dedicated architectures, such as the parallel computing
platform and programming model CUDA (Compute Unified Device Architecture) released by NVIDIA,
one of the main producers of graphics cards, and of improved, highly performing GPU (Graphics
Processing Unit) boards, GPGPU (General Purpose programming on GPU) is attracting increasing interest
in the engineering community, for the development of analysis tools suitable to be used in validation/
verification and virtual reality applications. For their inherent explicit and decoupled structure, explicit
dynamics finite element formulations appear to be particularly attractive for implementations on hybrid
CPU/GPU or pure GPU architectures. The issue of an optimized, double-precision finite element GPU
implementation of an explicit dynamics finite element solver for elastic shell problems in small strains
and large displacements and rotations, using unstructured meshes, is here addressed. The conceptual
difference between a GPU implementation directly adapted from a standard CPU approach and a new
optimized formulation, specifically conceived for GPUs, is discussed and comparatively assessed. It is
shown that a speedup factor of about 5 can be achieved by an optimized algorithm reformulation and
careful memory management. A speedup of more than 40 is achieved with respect of state-of-the art
commercial codes running on CPU, obtaining real-time simulations in some cases, on commodity hardware.
When a last generation GPU board is used, it is shown that a problem with more than 16 millions
degrees of freedom can be solved in just few hours of computing time, opening the way to virtualization
approaches for real large scale engineering problems
Perinatal variation and covariation of oxidative status and telomere length in yellow-legged gull chicks.
The perinatal period is critical to survival and performance of many organisms. In birds, rapid postnatal growth and sudden exposure to aerial oxygen around hatching markedly affect the chick redox status, with potentially negative consequences on physiology mediated by oxidative stress. In addition, telomere length (TL) undergoes reduction during birds' early life, partly depending on oxidative status. However, relatively few studies have focused specifically on the changes in oxidative status and TL that occur immediately after hatching. In this study of the yellow-legged gull Larus michahellis, we found that chicks undergo a marked increase in plasma total antioxidant capacity and a marked decrease in the concentration of pro-oxidant molecules during the first days after hatching. In addition, TL in erythrocytes decreased by 1 standard deviation over the 4 days post-hatching. Body mass and tarsus length covaried with total antioxidant capacity and concentration of pro-oxidants in a complex way, that partly depended on sex and laying order, suggesting that oxidative status can affect growth. Moreover, TL positively covaried with the concentration of pro-oxidant molecules, possibly because retention of high concentrations of pro-oxidant molecules results from mechanisms of prevention of their negative effects, including reduction in TL. Thus, this study shows that chicks undergo marked variation in oxidative status, which predicts growth and subsequent TL, prompting for more studies of the perinatal changes in the critical post-hatching stages
Multiphysics simulation of corona discharge induced ionic wind
Ionic wind devices or electrostatic fluid accelerators are becoming of
increasing interest as tools for thermal management, in particular for
semiconductor devices. In this work, we present a numerical model for
predicting the performance of such devices, whose main benefit is the ability
to accurately predict the amount of charge injected at the corona electrode.
Our multiphysics numerical model consists of a highly nonlinear strongly
coupled set of PDEs including the Navier-Stokes equations for fluid flow,
Poisson's equation for electrostatic potential, charge continuity and heat
transfer equations. To solve this system we employ a staggered solution
algorithm that generalizes Gummel's algorithm for charge transport in
semiconductors. Predictions of our simulations are validated by comparison with
experimental measurements and are shown to closely match. Finally, our
simulation tool is used to estimate the effectiveness of the design of an
electrohydrodynamic cooling apparatus for power electronics applications.Comment: 24 pages, 17 figure
High-Order Variational Time Integrators for Particle Dynamics
The general family of Galerkin variational integrators are analyzed and a complete classification of such methods is proposed. This classification is based upon the type of basis function chosen to approximate the trajectories of material points and the numerical quadrature formula used in time. This approach leads to the definition of arbitrarily high order method in time. The proposed methodology is applied to the simulation of brownout phenomena occurring in helicopter take-off and landing
Polystyrene microplastics ingestion induced behavioral effects to the cladoceran Daphnia magna
Microplastic (\u3bcPs) contamination represents a dramatic environmental problem threatening both aquatic and terrestrial organisms. Although several studies have highlighted the presence of \u3bcPs in aquatic environments, the information regarding their toxicity towards organisms is still scant. Moreover, most of the ecotoxicological studies of \u3bcPs have focused on marine organisms, largely neglecting the effects on freshwater species. The present study aimed at exploring the effects caused by 21-days exposure to three concentrations (0.125, 1.25 and 12.5 \u3bcg/mL) of two differently sized polystyrene microplastics (P\u3bcPs; 1 and 10 \u3bcm) to the Cladoceran Daphnia magna. The ingestion/egestion capability of daphnids (<24 h) and adults, the changes in individual growth and behavior, in terms of changes in swimming activity, phototactic behavior and reproduction, were investigated. Both particles filled the digestive tract of daphnids and adults within 24 h of exposure at all the tested concentrations. Ingested P\u3bcPs remained in the digestive tract even after 96 h in a clean medium. For both particles, an overall increase in body size of adults was noted at the end of the exposure to the highest tested concentrations, accompanied by a significant increase in swimming activity, in terms of distance moved and swimming velocity, and by an alteration of the phototactic behavior. A significant increase in the mean number of offspring after the exposure to the highest P\u3bcPs concentrations of different size was recorded. Polystyrene \u3bcPs can affect behavioral traits of D. magna leading to potentially harmful consequences on population dynamics of this zooplanktonic species
Predicting PCB concentrations in cow milk: validation of a fugacity model in high-mountain pasture conditions
A fugacity model reported in the literature was applied to a high - altitude pasture in the Italian Alps. The model takes into account three compartments (digestive tract, blood and fat tissues) in unsteady-state conditions using food as the contamination source. Disregarding biotransformation inside cow tissues, the predicted concentrations of 14 polychlorinated biphenyls (PCBs) in milk were in good agreement with the observed data, especially for congeners known for their resistance to biotransformation (e.g., CB-138 and 153). In contrast, the predicted concentrations were clearly overestimated for congeners with high biotransformation susceptibilities.
Therefore data measured in milk and faeces were used to calculate the first-order-biotransformation rate constants in dairy cows. The PCB absorption efficiency observed for pasture conditionswas lower than that observed in the cowshed. The final version of the model included biotransformation and observed PCB absorption andwas able to predict PCB concentrations in cow milkwith mean differences between the predicted and measured data below \ub120% for most congener
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