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Studio termo-fluidodinamico di sistemi di abbattimento della temperatura dei gas di scarico per applicazioni navali
No full textQuesta tesi di dottorato è focalizzata sull'analisi CFD (Computational Fluid Dynamics)
di un eduttore navale, con l'obiettivo di migliorarne le prestazioni e sviluppare strategie
per la riduzione delle emissioni termiche. Nella prima fase, viene condotta un'analisi
parametrica approfondita per valutare l'influenza di variabili geometriche e operative
sull'efficienza del dispositivo, individuando una configurazione ottimale come
riferimento.
La seconda parte esplora la fattibilità dell'uso di spray d'acqua all'interno dell'eduttore per ridurre le emissioni termiche, utilizzando il modello DPM (Discrete Phase Model)
accoppiato alla modellazione dell'evaporazione. Le simulazioni CFD consentono di
valutare l’efficacia della soluzione proposta.
Infine, la terza sezione affronta l'analisi termica del sistema attraverso simulazioni di
scambio termico coniugato (CHT), considerando anche l'uso della modellazione tramite
shell conduction, per lo studio della conduzione termica nelle superfici solide, al fine di
ottimizzare ulteriormente il comportamento termico dell'eduttore.This PhD thesis focuses on the CFD (Computational Fluid Dynamics) analysis of a naval
eductor-diffuser, aiming to enhance its performance and develop strategies for thermal
emission reduction. In the first phase, a detailed parametric analysis is conducted to
evaluate the influence of geometric and operational variables on device efficiency,
identifying an optimal configuration as a reference.
The second part investigates the feasibility of applying water sprays within the eductor to
reduce thermal emissions, using the Discrete Phase Model (DPM) coupled with
evaporation modeling. CFD simulations are employed to assess the effectiveness of this
approach.
Finally, the third section presents a thermal analysis of the system through conjugate heat transfer (CHT) simulations, also evaluating the use of shell conduction modeling for the thermal conduction in solid surfaces, to further optimize the eductor’s thermal
performance
Axiomatic/Asymptotic Analysis of Refined Layer-Wise Theories for Composite and Sandwich Plates
Full text linkThis paper deals with layer-wise (LW) models for composite and sandwich plates. Refined layer-wise models are built according to the Carrera Unified Formulation (CUF) which has been developed over the last decade for beams, plate and shell theories. CUF allows the hierarchical implementation of refined models based on any-order expressions of the unknown variables. In this paper, displacement variables are expanded along the layer thickness through Legendre polynomials. Comparisons with previous analysis based on Equivalent Single Layer (ESL) approaches are given. The effect of each term of the expansion on the accuracy of stress/displacement components for the static response of composite and sandwich plates is analyzed. Ineffective terms are discarded from the expansion in order to save computational cost. The reduced models obtained, which are denoted as mixed axiomatic/asymptotic models, are as accurate as full expansion models. Numerical analysis is restricted to closed-form solutions via Navier-type solutions. A number of problems related to laminated and sandwich structures are solved and related reduced models are built by varying geometrical, lay-up and mechanical parameters. Results show that in some cases (in particular those related to sandwich plates) reduced layer-wise models can save up to 50% of the degrees-of-freedom of the full models without significant accuracy losses. It is found that the significant terms related to reduced models are very much subordinated to the problems considered and that from that point of view the use of a framework that can generate any theory, such as CUF, appears very suitable to build reduced models for plate
Static aeroelastic response of wing-structures accounting for in-plane cross-section deformation
Full text linkIn this paper, the aeroelastic static response of flexible wings with arbitrary cross-section geometry via a coupled CUF-XFLR5 approach is presented. Refined structural one-dimensional (1D) models, with a variable order of expansion for the displacement field, are developed on the basis of the Carrera Unified Formulation (CUF), taking into account cross-sectional deformability. A three-dimensional (3D) Panel Method is employed for the aerodynamic analysis, providing more accuracy with respect to the Vortex Lattice Method (VLM). A straight wing with an airfoil cross-section is modeled as a clamped beam, by means of the finite element method (FEM). Numerical results present the variation of wing aerodynamic parameters, and the equilibrium aeroelastic response is evaluated in terms of displacements and in-plane cross-section deformation. Aeroelastic coupled analyses are based on an iterative procedure, as well as a linear coupling approach for different free stream velocities. A convergent trend of displacements and aerodynamic coefficients is achieved as the structural model accuracy increases. Comparisons with 3D finite element solutions prove that an accurate description of the in-plane cross-section deformation is provided by the proposed 1D CUF model, through a significant reduction in computational cost
Best theory diagram for metallic and laminated composite plates
Full text linkBest theory diagrams (BTDs) are reported in this article for the static analysis of metallic and laminated composite plates. A BTD is a curve that provides the minimum number of unknown variables of a structural theory for a fixed error. The error is related to a given variable with respect to an exact or quasi-exact solution. The theories that belong to the BTD have been obtained by means of the axiomatic/asymptotic technique, and a genetic algorithm has been employed to obtain the BTD. The Carrera Unified Formulation (CUF) has been employed to obtain refined models, since the CUF can generate automatically, and in a unified manner, any type of plate model. Equivalent single layer (ESL) and layer-wise (LW) kinematics are discussed. Closed-form, Navier-type solutions have been employed, and attention has therefore been restricted to simply-supported plates. The influence of various geometries, material properties, and layouts has been considered, and their influence on the BTD has been evaluated. Furthermore, some known theories have been evaluated and compared with the BTD curve. The results suggest that the BTD and the CUF can be considered as tools to evaluate the accuracy of any structural theory against a reference solution in a systematic manne
MIXED AXIOMATIC/ASYMPTOTIC ANALYSES OF REFINED LAYER-WISE AND EQUIVALENT SINGLE LAYER PLATE/SHELL MODELS FOR COMPOSITE STRUCTURES
No full textOn the effectiveness of higher-order terms in layer-wise shell models
No full textRefined layer-wise theories for shell and plate models are presented and discussed in this paper. Higher-order models are obtained through the Unified Formulation (UF) developed by the first author over the last decade. The effectiveness of each higher-order term is evaluated through the so-called mixed axiomatic/asympthotic approach (MAAA). MAAA has been recently developed and can be seen as a tool to build reduced refined models against full expansion theories. The development of reduced models is carried out through the investigation of the effectiveness of each unknown variable on the solution for a given problem. Reduced models are then built for various structural cases, such as thin and thick shells, layered shells and sandwiches. Results show the enhanced capabilities of MAAA and UF to develop refined layer-wise models with reduced computational costs
Best Theory Diagrams for multilayered plates considering multifield analysis
Full text linkThis work presents the best theory diagrams (BTDs) for multilayered plates involved in multifield problems (mechanical, thermal and electrical). A BTD is a curve that reports the minimum number of terms of a refined model for a given accuracy. The axiomatic/asymptotic technique is employed in order to detect the relevant terms, and the error is computed with respect to an exact or quasi-exact solution. The models that belong to the BTDs are constructed by means of a genetic algorithm and the Carrera Unified Formulation (CUF). The CUF defines the displacement field as an expansion of the thickness coordinate. The governing equations are obtained in terms of few fundamental nuclei, whose form does not depend on the particular expansion order that is employed. The Navier closed-form solution has been adopted to solve the equilibrium equations. The analyses herein reported are related to plates subjected to multifield loads: mechanical, thermal and electrical. The aim of this study is to evaluate the influence of the type of the load in the definition of the BTDs. In addition, the influence of geometry, material parameters and displacement/stress components are considered. The results suggest that the BTD and the CUF can be considered as tools to evaluate any structural theory against a reference solution. In addition, it has been found that the BTD definition is influenced to a great extent by the type of load
Evaluation of mixed theories for laminated plates through the axiomatic/asymptotic method
Full text linkThis paper proposes variable kinematic, mixed theories for laminated plates built via the asymptotic/axiomatic method (AAM). This method has been recently developed and successfully applied to develop refined theories for multilayered plates and shells. The AAM evaluates the accuracy of each unknown variables of a structural model. The present paper extends the AAM to mixed theories based on the Reissner Mixed Variational Theorem (RMVT). The displacement and transverse stress fields are modeled by means of the Carrera Unified Formulation (CUF), and expansions up to the fourth-order are employed. Equivalent Single Layer (ESL) and Layer Wise (LW) schemes are adopted, and closed-form Navier-type solutions are considered.
The AAM is exploited to determine the set of active terms of a refined plate model. The inactive terms are then discarded. The effectiveness of each variable is evaluated with respect to an LW, fourth-order mixed model. Reduced models are built for different thickness ratios, stacking sequences and displacement/stress variables.
The results suggest that reduced models with significantly less unknown variables than full models can be built with no accuracies penalties. Such models are problem dependent, and full models should be preferred in the case of thick, asymmetric plates
Results on best theories for metallic and laminated shells including Layer-Wise models
Full text linkThis paper deals with Best Theory Diagrams (BTDs) for metallic and laminated shells. The BTD is a curve that is defined over a 2D reference frame in which the horizontal axis indicates the error of a shell model with respect to a reference solution whereas the vertical axis indicates the number of displacement variables of the model. The best reduced model is a refined model that offers the lowest possible error for a given number of variables. The relevant terms of a model are detected by means of the axiomatic/asymptotic method (AAM), and the error is related to a given variable with respect to an exact or quasi-exact solution. In this work, a genetic algorithm has been used to obtain the BTD. The Carrera Unified Formulation (CUF) has been employed to build the refined models. The CUF makes it possible to generate automatically, and in a unified manner, any plate or shell models. Equivalent Single Layer (ESL) and Layer Wise (LW) refined models have been considered. The governing equations for shells have been obtained through the Principle of Virtual Displacements (PVD), and Navier-type closed form solutions have been considered. BTDs have been constructed by considering the influence of several parameters, such as various geometries, material properties, layouts, different displacement/stress components and loadings. The accuracies of some well-known theories have been evaluated and compared with BTD reduced models. The results suggest that, since the BTD depends on the problem characteristics to a great extent, the systematic adoption of the CUF and the AAM can be considered as a powerful tool to evaluate the accuracy of any structural theory against a reference solution for any structural proble
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