2,357 research outputs found

    Dynamical system analysis of ignition phenomena using the tangential stretching rate concept

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    We analyze ignition phenomena by resorting to the stretching rate concept formerly introduced in the study of dynamical systems. We construct a Tangential Stretching Rate (TSR) parameter by combining the concepts of stretching rate with the decomposition of the local tangent space in eigen-modes. The main feature of the TSR is its ability to identify unambiguously the most energetic scale at a given space location and time instant. The TSR depends only on the local composition of the mixture, its temperature and pressure. As such, it can be readily computed during the post processing of computed reactive flow fields, both for spatially homogeneous and in-homogenous systems. Because of the additive nature of the TSR, we defined a normalized participation index measuring the relative contribution of each mode to the TSR. This participation index to the TSR can be combined with the mode amplitude participation Index of a reaction to a mode – as defined in the Computational Singular Perturbation (CSP) method – to obtain a direct link between a reaction and TSR. The reactions having both a large participation index to the TSR and a large CSP mode amplitude participation index are those contributing the most to both the explosive and relaxation regimes of a reactive system. This information can be used for both diagnostics and for the simplification of kinetic mechanisms. We verified the properties of the TSR with reference to three nonlinear planar models (one for isothermal branched-chain reactions, one for a non-isothermal, one-step system, and for non-isothermal branched-chain reactions), to one planar linear model (to discuss issues associated with non-normality), and to test problems involving hydro-carbon oxidation kinetics. We demonstrated that the reciprocal of the TSR parameter is the proper characteristic chemical time scale in problems involving multi-step chemical kinetic mechanisms, because (i) it is the most relevant time scale during both the explosive and relaxation regimes and (ii) it is intrinsic to the kinetics, that is, it can be identified without the need of any ad hoc assumption

    On the Assessment of an Unstructured Finite-Volume DES/LES Solver for Turbomachinery Applications

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    Improvements in mean flow and performances simulation in turbomachinery has brought research to focus more demanding topics like turbulence effects on turbines. Although overall performances are well predicted by Unsteady-RANS, other phenomena such as aerodynamic noise or transition need more accurate prediction of turbulent flow features. Thus different kinds of equation modeling other than URANS are needed to cope with this issue. The success of Detached-Eddy Simulation and Large-Eddy Simulation applications in reproducing physical behavior of flow turbulence is well documented in literature. Despite that, LES simulations are still computationally very expensive and their use for investigating industrial configurations requires a careful assessment of both numerical and closure modeling techniques. Moreover LES solvers are usually developed on a structured mesh topology for sake of simplicity of high-order schemes implementation. Application to complex geometries like those of turbomachinery is therefore difficult. The present work addresses this issue considering the feasibility of converting an operative in-house URANS solver, widely validated for applicative purposes, into higher resolution DES and LES, in order to face turbulence computation of turbomachinery technical cases. The solver presents a 3D unstructured finite-volume formulation, which is kept in LES approach in order to handle complex geometries and it is developed to perform unsteady simulations on turbine stages. Preliminary assessment of the solver has been performed to evaluate and improve the accuracy of the convective fluxes discretization on an inviscid bump test case. First a DES-based approach has been implemented, as it is less computationally challenging and numerically demanding than LES. A square cylinder test case has been assessed and compared with experiments. Then, a pure LES with a Smagorinsky sub-grid scale model has been evaluated on the test case of incompressible periodic channel flow in order to assess the capability of the solver to correctly sustain a time developing turbulent field

    EXPERIMENTAL AND NUMERICAL INVESTIGATION OF ASYMMETRICAL BEHAVIOUR OF RUDDER / PROPELLER FOR TWIN SCREW SHIPS

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    the present work addresses the asymmetrical functioning of rudder/propeller complex of twin screw/twin rudders ships. A series of free running model test results are analysed, with the aid of some simplified numerical calculations. this analysis allows to show the asymmetrical propeller loading during manoeuvres and the considerably different rudder functioning. A possible simplified model to include these effects in manoeuvring simulators is proposed and discussed, allowing to define the needs for future research activities to further improve the understanding of the different phenomena shown

    TRAMPLE: the transmembrane protein labelling environment

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    TRAMPLE () is a web application server dedicated to the detection and the annotation of transmembrane protein sequences. TRAMPLE includes different state-of-the-art algorithms for the prediction of signal peptides, transmembrane segments (both beta-strands and alpha-helices), secondary structure and fast fold recognition. TRAMPLE also includes a complete content management system to manage the results of the predictions. Each user of the server has his/her own workplace, where the data can be stored, organized, accessed and annotated with documents through a simple web-based interface. In this manner, TRAMPLE significantly improves usability with respect to other more traditional web servers

    Effects of P4 Antagonist RU486 on VEGF and Its Receptors' Signaling during the In Vivo Transition from the Preovulatory to Periovulatory Phase of Ovarian Follicles

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    The development of an adequate blood vessel network is crucial for the accomplishment of ovarian follicle growth and ovulation, which is necessary to support the proliferative and endocrine functions of the follicular cells. Although the Vascular Endothelial Growth Factor (VEGF) through gonadotropins guides ovarian angiogenesis, the role exerted by the switch on of Progesterone (P4) during the periovulatory phase remains to be clarified. The present research aimed to investigate in vivo VEGF-mediated mechanisms by inducing the development of periovulatory follicles using a pharmacologically validated synchronization treatment carried out in presence or absence of P4 receptor antagonist RU486. Spatio-temporal expression profiles of VEGF, FLT1, and FLK1 receptors and the two major MAPK/ERKs and PI3K/AKT downstream pathways were analyzed on granulosa and on theca compartment. For the first time, the results demonstrated that in vivo administration of P4 antagonist RU486 inhibits follicular VEGF receptors' signaling mainly acting on the theca layer by downregulating the activation of ERKs and AKTs. Under the effect of RU486, periovulatory follicles' microarchitecture did not move towards the periovulatory stage. The present evidence provides new insights on P4 in vivo biological effects in driving vascular and tissue remodeling during the periovulatory phase
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