1,720,968 research outputs found
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
A ML strategy for the identification of optimal LPT design region and related blade shape
No full textThis work presents a machine-learning (ML) strategy for the identification of the design region that guarantees minimum losses for Low Pressure Turbine (LPT) blades, allowing the definition of the optimal blade shape. The data-driven procedure is twofold. Firstly, an advanced loss-correlation model (M1) that describes the LPT efficiency as a function of the main flow and geometrical parameters, also accounting for unsteady effects, has been trained from a numerical database. Then, a second model (M2) has been tuned to interpret the corresponding blade geometries. Proper Orthogonal Decomposition (POD) has been applied to formally decompose the blade shape into modes and coefficients. The modes provide basis functions, while the coefficients give the weights that, depending on the combination of the design parameters, define the blade shape. Gaussian Process (GP) and Cross-Validation techniques have been used for tuning both M1 and M2. Once properly tuned, the overall procedure provides the loss-correlation model (M1) for the identification of the design region that is expected to minimize losses, and the geometrical model (M2) for a quick definition of the corresponding optimal blade shape. The procedure can be extended to other engineering applications where own efficiency and geometrical data are available
FINITE ELEMENT SIMULATION OF MULTILAYER METAL CYLINDER HEAD GASKETS
No full textABAQUS gasket elements are an efficient and flexible tool to study gasket applications. Nevertheless the usage of the ABAQUS gasket elements is not limited to gasket analysis,
but it provides an effective improvement in structural analysis. The results point out that both the predicted contact pressure and the predicted stress distribution depend on the mesh
topology. Several combinations of mesh dimension and topology are investigated. The purpose is the definition of a calculation methodology and the demonstration of the
application potentiality. Complex models analysis highlights that the set methodology constitutes a very effective tool for the design and optimization of gasket, cylinder head and
cylinder block. At last a particular case is studied and a structural improvement to resolve the problem of the low seal was obtained by FEM; the modifications were introduced in the
layout and the test on the modified component confirmed the calculation previsions. The qualitative and quantitative indications provided by the calculation are confirmed by the
experimental results, whether in condition of cold assembly (color film paper approach) or in condition of hot working (test to motor bench)
TUNING OF AN ALGEBRAIC MODEL FOR SEPARATED FLOWS BY MEANS OF BAYESIAN LASSO
No full textIn this work, machine learning techniques are exploited to train a new model based on Pope’s tensorial bases, where the common definition of the turbulent viscosity is extended to define the Reynolds stress tensor as an expansion of strain-rate and rotation tensors. Specifically, a Sparse Bayesian approach has been implemented to provide new expressions for the turbulent eddy viscosities appearing in the Pope’s formulation. An experimental dataset acquired with Time-Resolved Particle Image Velocimetry has been used to tune the present model. Data provide the mean flow and the Reynolds stress distributions of different separation bubbles evolving on a flat plate with applied variable adverse pressure gradients, reproducing in some extent the diffusion that characterize the rear suction side of turbine blades. The model has been tuned with different independent conditions of flow Reynolds number and free-stream turbulence intensity. Then, two additional flow conditions have been adopted to cross-validate and test the generated model. The adoption of the Sparse Bayesian approach allows the direct identification of the leading predictors, i.e., flow features, exploiting the main characteristics of the transition scenario (here, the transition process induced by flow separation). Specifically, the correlations here tuned may contribute to improve the capability of RANS solvers in the prediction of transitional flows
Analisi della Separazione di un Booster da un Velivolo UAV (Store Separation Analysis of a Booster from an UAV)
Full text linkIn questo lavoro viene presentato un modello numerico in grado di simulare le fasi di sgancio di un booster dallo UAV (Unmanned Aerial Vehicle) al quale è inizialmente vincolato. Il lavoro è stato condotto in collaborazione con Selex Galileo secondo i suoi obiettivi industriali.
Il modello numerico è stato sviluppato in ambiente FLUENT (ANSYS), dove è possibile risolvere tramite calcolo CFD le equazioni fondamentali della fluidodinamica nel tempo. Per gli scopi del lavoro, il calcolo CFD è stato risolto su griglia dinamica non strutturata.
Un’apposita routine (UDF – User Define Function), in grado di calcolare la dinamica del booster come corpo rigido, è stata scritta e compilata nel modello CFD. Tale routine è in grado di fornire il moto del booster nei sei gradi di libertà (6DoF – 6-Degrees of Freedom), prelevando le azioni aerodinamiche sul booster dal calcolo CFD e risolvendo le equazioni fondamentali del moto (Newton-Euler).
L’uso di una mesh dinamica permette al domino di calcolo di modificarsi ed essere nuovamente discretizzato al fine di tener conto degli spostamenti del booster.
Sono qui presentati i risultati ottenuti per un dato assetto di volo. Tali risultati rappresentano una prima verifica della procedura di sgancio in vista dei futuri test sperimentali
A New Empirical Correlation for Transition in Both Short and Long Separation Bubbles
No full textWith the aim of improving the predicting capability of current correlation-based transition models, a new correlation for transition in separated flows is presented, which is based only on local quantities. The peak value of the vorticity-based Reynolds number at the detachment position has been chosen as a local indicator of the boundary layer state. As largely discussed in the literature, this facilitates the implementation of transition models into modern numerical schemes, characterized by parallel execution and unstructured grids. The current experimental database consists of a total amount of almost 90 flow conditions concerning a flat plate boundary layer developing under variable Reynolds number, free-stream turbulence intensity and adverse pressure gradient. The typical operating conditions of low-pressure turbine profiles have been reproduced. Due to the wide range of Reynolds numbers tested, the bursting process of the laminar separation bubble has been observed. Using the present database, a proportionality coefficient between the momentum-thickness and the vorticity-based Reynolds numbers at the separation position has been computed, which is found to be the same for both short and long bubbles. This provides the link between local and integral quantities of the boundary layer. Then, the vorticity-based Reynolds number is adopted as main ingredient of a correlation for the prediction of the transition onset in separated boundary layers. The influence of other factors such as the free-stream turbulence and the streamwise pressure gradient has been also considered. The present work is thought to improve the code ability in predicting the profile losses and the blade loading distribution n in case of separated flows, for both short and long bubble states
Local correlations for predicting the transition process in separated flows tuned with a large experimental database
No full textThis work provides new correlations based on local variables for characterizing the transition process developing in the case of separated flows. The goal is to improve the capability of correlation-based transition models through the use of local variables. This may indeed simplify the implementation of the correlations into modern numerical codes, especially dealing with parallel computation and unstructured meshes. A large experimental database considering about 90 different flow conditions has been used to tune the present correlations. The database accounts for the variation of the flow Reynolds number, the free-stream turbulence intensity and the adverse pressure gradient affecting the boundary layer developing over a flat plate. The parameter variation induces the formation of both short and long laminar separation bubbles. The vorticity Reynolds number, based on the second invariant of the vorticity tensor, has been used as the main local variable for the activation of the transition process. Since it is proportional to the momentum thickness Reynolds number at the separation position, the vorticity Reynolds number (local) can be used in place of its counterpart based on the momentum thickness (integral), which is the variable usually adopted for activation of transition. Then, correlations providing a critical threshold for the vorticity Reynolds number promoting transition are tuned, for both short and long bubbles. These may be used into transition models to directly provide the location where the turbulence production needs to be activated. The proposed correlations have been validated using a second database not adopted for tuning and finally tested with data concerning a separated flow case in a low-pressure turbine cascade
A design-space minimum sampling strategy based on proper-orthogonal-decomposition projection
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