Dissertations / Theses on the topic 'Non-linear FEM analyse'

Le crissement de frein est une nuisance sonore qui représente des coûts importants pour l'industrie automobile. Il tire son origine dans des phénomènes complexes à l'interface frottante entre les plaquettes de frein et le disque. L'analyse de stabilité reste aujourd'hui la méthode privilégiée dans l'industrie pour prédire la stabilité d'un système de frein malgré ses aspects sur- et sous-prédictifs.Afin de construire un système de frein robuste, il est nécessaire de trouver la technologie qui permette de limiter les instabilités malgré certains paramètres incertains présents dans le système. Ainsi, l'un des objectifs de la thèse est de développer une méthode permettant de traiter et de propager l'incertitude et la variabilité de certains paramètres dans le modèle éléments finis de frein avec des coûts numériques abordables.Dans un premier temps, l'influence d'un premier groupe de paramètres correspondant à des contacts internes au système a été étudiée afin de mieux comprendre les phénomènes physiques mis en jeu et leurs impacts sur le phénomène de crissement. Une approche basée sur l'utilisation d'un algorithme génétique a été également mise en place afin d'identifier le jeu de paramètres le plus défavorable en terme de propension au crissement sur le système.Dans un second temps, différentes méthodes de méta-modélisation ont été proposées afin de prédire la stabilité du système de frein en fonction de différents paramètres qui peuvent être des paramètres de conception ou des paramètres incertains liés à l'environnement du système.Dans un troisième temps, une méthode d'analyse non-linéaire complémentaire de l'analyse de stabilité a été proposée et développée. Elle se base sur le suivi de la stabilité d'une solution vibratoire approchée et permet d'identifier les modes instables présents dans la réponse dynamique du système. Cette méthode a été appliquée sur un modèle simple avant d'illustrer sa faisabilité sur le modèle éléments finis de frein complet
Brake squeal is a noise nuisance that represents significant costs for the automotive industry. It originates from complex phenomena at the frictional interface between the brake pads and the disc. The stability analysis remains the preferred method in the industry today to predict the stability of a brake system despite its over- and under-predictive aspects.In order to build a robust brake system, it is necessary to find the technology that limits instabilities despite some uncertain parameters present in the system. Thus, one of the main objectives of the PhD thesis is to develop a method to treat and propagate the uncertainty and variability of some parameters in the finite element brake model with reasonable numerical costs.First, the influence of a first group of parameters corresponding to contacts within the system was studied in order to better understand the physical phenomena involved and their impacts on the squealing phenomenon. An approach based on the use of a genetic algorithm has also been implemented to identify the most unfavourable set of parameters in terms of squeal propensity on the brake system.In a second step, different meta-modelling methods were proposed to predict the stability of the brake system with respect to different parameters that may be design parameters or uncertain parameters related to the environment of the brake system.In a third step, a non-linear analysis method complementary to the stability analysis was proposed and developed. It is based on the tracking of the stability of an approximate vibrational solution and allows the identification of unstable modes present in the dynamic response of the system. This method was applied to a simple academic model before demonstrating its feasibility on the complete industrial brake finite element model under study

The experimental studies performed on the behaviour of very thick concrete beams subjected to static loads have revealed that the shear mechanisms play an important role in the overall response and failure behaviour. The aim of this thesis is to recommend suitable design methods for thick concrete beams subjected to off-centre static concentrated load according Eurocode 2 by using non-linear finite element analysis (NLFEA). To achieve this task, Abaqus/Explicit has been used by employing constitutive material models to capture the material non-linearity and stiffness degradation of concrete. Concrete damaged plasticity model and perfect plasticity model has been used for concrete and steel respectively. Three dilation angles (30º, 38º and 45º) and fracture energy from FIB 1990 (76 N/m) and FIB 2010 (142 N/m) has been used to investigate their influence on the finite element model. The dilation angle of 38º and FIB 2010 fracture energy was adopted as the suitable choice that reasonably matched with the experimental results. In verifying and calibrating the finite element model, the experimental results of the thick reinforced concrete beam conducted by the American Concrete Institute have been used. Three design approaches in the ultimate and serviceability limit state according to Eurocode 2 recommendations have been used namely; the beam method, strut and tie method and shell element method. Using the reinforcement detailing of the hand calculations of beam method and strut and tie method and linear finite element analysis of shell element method, non-linear finite element models have been pre-processed and analysed in Abaqus/Explicit. During the post-processing, the results have been interpreted and compared between the three design methods. The results under consideration are hand-calculated load at 0.3 mm crack width, FE-load at 0.3 mm crack width, amount of reinforcement and FE-failure load. The comparison of the results between the three design approaches (beam method, strut and tie method and shell element method) indicates that strut and tie method is better design approach, because it is relatively economic with regards to the quantity of reinforcement bars, has the higher load capacity and has a higher load at crack width of 0.3 mm crack width.
De experimentella studier som utförts på tjocka betongbalkar som utsätts för statisk last har visat att skjuvning spelar en viktig roll i brottmekanismen. Syftet med detta examensarbete är att rekommendera lämpliga dimensioneringsmetoder för tjock betongbalkar utsatt for statisk koncentrerad last enligt Eurokod 2 med hjälp av ickelinjära finita element metod. Abaqus/Explicit användes genom att utnyttja konstitutiva materialmodeller för att fånga materialens icke-linjäritet och minskad styvhet. Tre dilatationsvinklar (30°, 38° och 45°) och två brottenergi från FIB 1990 (76 N/m) och FIB 2010 (142 N/m) tillämpas för att kontrollera deras inverkan på FE-modellerna. Dilatationsvinkel med 38° och FIB 2010 med högre brottenergi valdes i de icke-linjära finita elementanalyserna. Kontroll av FE-modellerna är baserad på ”American Concret Institutes” experimentella resultat på de tjocka betongbalkarna. Handberäkningar av tjocka betongbalkar har utförts i brott- och bruksgränstillstånd med tre dimensioneringsmetoder i Eurokod 2 nämligen balk metoden, fackverksmetoden och linjära-FE skalelementmetoden. Jämförelse har gjorts för de olika dimensioneringsmetoderna, genom att använda de armeringsdetaljer av handberäkningar i de verifierade och kalibrerade icke linjära FE-modellerna i Abaqus/Explicit. Resultaten i fråga är last för 0.3 mm handberäknad sprikvidd, FE-last för 0.3 mm sprikvidd, armeringsmängd och FE-brottlast. Jämförelse av resultaten mellan de tre dimensioneringsmetoder (balkmetod, fackverksmetod och skalelementmetod) visar att fackverksmetod är bättre design metod, eftersom det är relativt ekonomiskt med avseende på armeringsmängd, har högre lastkapacitet och last på 0.3 mm sprickvidd.

Le travail s’inscrit dans le cadre d’une collaboration entre le Pôle Ameublement FCBA et le Laboratoire MSME de l’UPEM. L’objectif était de mettre au point un outil de simulation permettant à FCBA de mener une étude de validation (tenue aux tests normalisés) avant la fabrication du meuble. Ce travail était supporté par les fonds collectifs de la profession ameublement. Il a donné lieu à des développements dans le domaine de l’identification du comportement anisotrope du bois par analyse d’images couplée à la méthode des éléments finis, d’une approche multi-échelle pour identifier le comportement des liens entre éléments de meuble et d’un programme éléments finis utilisant l’approche « poutres » pour réaliser une étude statistique du comportement du meuble prenant en compte la dispersion du comportement du bois. Chaque étape a été validée expérimentalement. La simulation par éléments finis s’est focalisée sur une application « lits superposées en bois massif » pour laquelle un code à base de poutres a été développé dans l’environnement Matlab afin de pouvoir y implanter :• une théorie élastique anisotrope via des poutres de Timoshenko pour prendre en compte l’effet des déformations dues aux faibles rigidités transversales du bois en regard de la rigidité longitudinale ;• des éléments de connexion ponctuels représentant la contribution des composants de quincaillerie (vis, écrou noyé, tourillon…) et les effets locaux 3D aux liaisons entre poutres ;• la possibilité de prendre en compte les incertitudes sur les paramètres matériau d’une poutre à l’autre en fonction de l’orientation des planches, de la densité du bois etc… via une simulation de Monte-Carlo
The work joins within the framework of a collaboration between the Pole Furnishing FCBA and the Laboratory MSME of the UPEM. The objective was to finalize(to work out) a tool of simulation allowing FCBA to lead a study of validation (held the normalized(standardized) tests) before the manufacturing of the piece of furniture

Permanent magnets synchronous reluctance (PMSynRel) motors are attractive due to their high torque density and because a lower quantity of permanent magnets is necessary in comparison with other permanent magnet machines. This thesis deals with the analysis of PMSynRel machines using a finite element method (FEM) and reluctance networks. First, a PMSynRel machine model is built in order to carry out simulations using a finite element method package. The effect of different design parameters such as the combination of the number of poles and slots, the number of flux barriers or the number of magnets can be studied since the implementation provides the possibility to change those variables. Next, a reluctance networks model, aimed to enable lower computation times than corresponding finite element models, is implemented for analysing the flux density distributions along the air gap of the machine disregarding the magnetic influence of the rotor. Finally, the results are compared with FEM simulations. It is concluded that the agreement reached is satisfactory in most of the cases analysed.

In February 2021, in San Pio delle Camere, on the Navelli plateau south-east of L'Aquila, a masonry building collapsed suddenly, after repair work had just begun on the damage caused by the 2009 earthquake. The current study, after a detailed examination of all the design documentation and the comparison of the post-earthquake damage with the results of the analysis on the model, finding an excellent correspondence, went to research the possible causes of the structural collapse, which occurred in static conditions. The masonry texture was then analysed, consisting of unworked natural stones of medium-small size bound by poor quality mortar, parameterising the mechanical characteristics with in situ tests, the Masonry Quality Index and the values proposed in NTC 2018. Then, the analysis of the global model lead to the verification of the complexity of the aggregate induced greater pressures, and consequent deformations, precisely in the walls from which the collapse originated. With these assumptions, and from the evidence of the presence of a modest void in an internal facing, the study of the local mechanism was deepened, arriving at the presumption of the possible minimum dimensions of such a cavity and how this, even if minimal, could have been the cause if concomitant with the degradation of the bonding mortar induced by the absence of maintenance and the loss of even minimal resistance capacities.

This thesis is in the field of non-linear partial differential equations (PDE), focusing on problems which show some type of phase-transition. A single phase Hele-Shaw flow models a Newtoninan fluid which is being injected in the space between two narrowly separated parallel planes. The time evolution of the space that the fluid occupies can be modelled by a semi-linear PDE. This is a problem within the field of free boundary problems. In the multi-phase problem we consider the time-evolution of a system of phases which interact according to the principle that the joint boundary which emerges when two phases meet is fixed for all future times. The problem is handled by introducing a parameterized equation which is regularized and penalized. The penalization is non-local in time and tracks the history of the system, penalizing the joint support of two different phases in space-time. The main result in the first paper is the existence theory of a weak solution to the parameterized equations in a Bochner space using the implicit function theorem. The family of solutions to the parameterized problem is uniformly bounded allowing us to extract a weakly convergent subsequence for the case when the penalization tends to infinity. The second problem deals with a parameterized highly oscillatory quasi-linear elliptic equation in divergence form. As the regularization parameter tends to zero the equation gets a jump in the conductivity which occur at the level set of a locally periodic function, the obstacle. As the oscillations in the problem data increases the solution to the equation experiences high frequency jumps in the conductivity, resulting in the corresponding solutions showing an effective global behaviour. The global behavior is related to the so called homogenized solution. We show that the parameterized equation has a weak solution in a Sobolev space and derive bounds on the solutions used in the analysis for the case when the regularization is lost. Surprisingly, the limiting problem in this case includes an extra term describing the interaction between the solution and the obstacle, not appearing in the case when obstacle is the zero level-set. The oscillatory nature of the problem makes standard numerical algorithms computationally expensive, since the global domain needs to be resolved on the micro scale. We develop a multi scale method for this problem based on the heterogeneous multiscale method (HMM) framework and using a finite element (FE) approach to capture the macroscopic variations of the solutions at a significantly lower cost. We numerically investigate the effect of the obstacle on the homogenized solution, finding empirical proof that certain choices of obstacles make the limiting problem have a form structurally different from that of the parameterized problem.

QC 20180222

Published Article
The simulation of an exhaust manifold's thermal behaviour is an important concern for various reasons. Amongst them is the need to minimise catalyst light-offtime as significant exhaust emissions are generated within this period. Modelling such behaviour is not simplistic as it is governed by complex interactions between exhaust gas flow and the manifold itself. Computational fluid dynamics (CFD) is a powerful tool for such simulations. However its applicability for transient simulations is limited by high central processing unit (CPU) demands. The present study proposes an alternative computational method to assess and rank the relative impact of the manifold's thermal properties on its exterior temperature. The results show that stainless steel manifolds potentially minimise heat loss from the exhaust gas when compared with their cast iron counterparts. This may result in an increase in thermal energy being available to heat the catalyst.

The aim of the project is to develop a model, which is going to be used for mass reduction of a standard profile of aluminium seat rails in Aircraft structure. Using nonlinear analysis including plasticity and material failure laws the effect of changes in geometry vs. ultimate load is analysed (ABAQUS 6.11). First, the non-linear model used is validated with experimental testing: Boundary conditions and material properties are adjusted based on load displacement curves, strain gauges information and failure patterns. Less than 1% deviation is achieved between simulation and testing. An inclusion of material imperfection led to a 5% improvement of the results. Using the validated algorithm, a mass reduction is performed via geometry variation
Ziel der Studie ist es ein adäquates Simulationsmodell zu entwickeln, welches zur Gewichtsreduzierung einer Standardprofil Aluminium Sitzschiene im Flugzeug verwendet werden kann. In einer nichtlinearen Analyse unter Berücksichtigung der Plastizität des Materials und von Materialfehlern wird die Auswirkung der Geometrieänderungen auf die maximale Traglast analysiert (ABAQUS 6.11). Zunächst wird das nicht-lineare Modell mit experimentell ermittelten Daten überprüft: Randbedingungen und Materialeigenschaften werden basierend auf Lastverschiebungskurven, Informationen von Dehnungsmessstreifen und Versagensmustern angepasst. Dabei wurden weniger als 1% Abweichung zwischen Simulation und Test erzielt. Die Berücksichtigung von Materialfehlern führte zu einer 5%-igen Verbesserung der Ergebnisse. Mit dem validierten Modell wird abschließend eine Gewichtsreduzierung mittels Geometrievariation durchgeführt

This doctoral thesis presents a structural analysis of the Paderno d’Adda Bridge, an impressive iron arch viaduct built in 1889 and located in Lombardia region (Italy). The thesis falls in the context of a research activity started at University of Bergamo since 2005, that is still ongoing and aims to perform an evaluation of the present state of conservation of the bridge. In fact, the bridge is currently still in service and its important position in the context of transport network will soon lead to questions about its future destination, with particular attention to the evaluation of the residual performance capacity. To this end, an inelastic structural analysis of the Paderno d’Adda bridge has been performed, up to failure. This analysis has been conducted through an autonomous computer code of a 3D frame structure that runs in the MATLAB environment and has been developed within the classical frame of Limit Analysis and Theory of Plasticity. The algorithm has been developed applying the “exact” and stepwise holonomic step-by-step analysis method. It has shown very much able to track the limit structural behaviour of the bridge, by reaching convergence with smooth runs up to the true limit load and corresponding collapse displacements. The main characteristic ingredients of its elastoplastic FEM formulation are: beam finite elements; perfectly plastic joints (as an extension of classical plastic hinges); piece-wise linear yield domains; “exact” time integration. In the algorithm, the following original features have been implemented: treatment of mutual connections by static condensation and Gaussian elimination; determination of the tangent stiffness formulation through Gaussian elimination. These peculiar contributions are presented in detail in this thesis.

In the automobile industry, there is a big push for the automotive car manufacturers to base engineering decisions on the results of Computer Aided Engineering (CAE) solutions, and to transform the prototyping and testing, from a costly iterative process to a final verification and validation step. The variability in components material properties and environmental conditions together with the lack of knowledge about the underlying physics of complex systems often make it impractical to make reliable predictions based on only deterministic CAE models. One such area is the CAE modelling of cast aluminium components. These cast aluminium components have gained a huge relevance in the automobile industries due to their commendable mechanical properties. The advantage of the cast aluminium alloys are being a well-established alloy system in manufacturing processes, their functional integrity and relatively low weight. However, the presence of pores and micro-voids obtained during the manufacturing process constitutes a specific material behaviour and establishes a challenge in modelling of the cast materials. Furthermore, the low ductility of the materialdemands for the advanced numerical model to predict the failure. The main focus of this master thesis work is to investigate modelling technique of a cast aluminium alloy component, a spring tower, for a drop tower test and validate the predicted behaviour with the physical test results. Volvo Car Corporation currently uses a material model provided by MATFEM for cast aluminium parts which are explored in this thesis work, to validate the material model for component level testing. The methodology used to achieve this objective was to develop a boundary condition to perform component level tests in the drop tower and to correlate these with the obtained results found by using various modelling techniques in the explicit solver LS-DYNA. Therefore, precise and realistic modelling of the drop tower is crucial because the simulation results can be influenced by major design changes. A detailed finite element model for the spring tower has been developed from the observations made during the physical testing. The refined model showed good agreement with the existing model for the spring tower and observations from physical tests.

Les capacités de résistance de l'argilite Callovo-Oxfordian (COx), qui est une roche hôte potentielle pour le dépôt souterrain profond de déchets radioactifs de haute activité en France, sont étudiées. À une échelle microscopique, des micros pores peuvent être observés dans la matrice. Une première étape d'homogénéisation a été réalisée afin d'évaluer le critère de résistance de la matrice. L'analyse microstructurale de ce matériau à quelques centaines d'échelle, référencée échelle échelle mésoscopique, montre une matrice argileuse et une distribution aléatoire d'inclusions minérales (quartz et calcite).Dans le but de déterminer le domaine de résistance à l'argilite COx, un premier outil numérique a été développé dans le contexte du comportement élastoplastique de la matrice. Plusieurs modèles morphologiques du volume élémentaire représentatif ont été considérés, et soumis à un chargement incrémental dans des conditions périodiques jusqu'à la charge limite. A la suite de ce calcul élastoplastique, un point de la frontière du domaine de résistance est obtenu. Ce dernier est alors obtenu par des calculs élastoplastiques successifs.Une alternative aux simulations élastoplastique directes, des approches cinématiques et statiques du calcul à la rupture sont réalisées. Une méthode du type éléments finis basée sur la construction d'un champ de contrainte (dans l'approche statique) et d'un champ de vitesse (dans l'approche cinématique) est développé dans un outil numérique permettant de calculer une limite inférieure et une limite supérieure de domaine de résistance
The strength capacities of Callovo-Oxfordian (COx) argillite which is a potential host rock for the deep underground repository of high-level radioactive waste in France are investigated. At a micro-scale, micro-pores can be observed in the matrix. A first strength homogenization step has been performed in order to evaluate the matrix strength criteria. The microstructure analysis of this material at some hundreds of micromet scale, referred at meso-scale, shows a clay matrix and a random distribution of mineral inclusions (quartz and calcite).Aiming to the determination of COx argillite strength domain, an FEM numerical tool has been developed in the context of the elastoplastic behavior of the matrix. Several morphological patterns of the representative elementary volume have been considered and subjected to an incremental loading in periodic conditions until collapse occurs. As a result of such elastoplastic calculation, one point of the boundary of the strength domain is obtained. The latter then could be reached by successive elastoplastic calculations.As an alternative to direct elastoplastic simulations, kinematic and static approaches of limit analysis are performed. The stress-based (static approach) and the velocity-based (kinematic approach) finite element method are used to develop a numerical tool able to derive a lower bound and upper bound of strength domain, respectively

Possibilities of modeling non-linear behavior of concrete within standard room temperatures and increased fire-load values using FEM software ANSYS are studied. Temperature dependences of material models are considered. Fire resistance of reinforced concrete and concrete-steel composite construction is analyzed. Fire loads are defined in accordance with relevant standards. Non-linear structural transient analyses are calculated after temperatures were determined by transient thermal analyses. Results obtained from analyses of simple reinforced concrete structure are compared with approach of isotherm 500 °C method.

2013/2014
Gli alti livelli di comfort che sono richiesti oggigiorno a bordo di navi da crociera e mega-yachts, portano i progettisti a concentrare la loro attenzione sul problema del rumore strutturale. I motori diesel quattro tempi che sono installati a bordo nave come motori principali o diesel generatori, sono tra le principali sorgenti di rumore strutturale. Per questa ragione, al fine di ridurre l’energia vibrazionale generata da queste sorgenti e trasmessa, tramite le strutture nave, ai locali alloggio, i motori diesel sono sospesi mediante elementi resilienti. Tali elementi resilienti disaccoppiano la sorgente di rumore e vibrazioni (motore diesel) dal mezzo di propagazione (le strutture nave) e isolano dunque la sorgente dalle strutture riceventi. I livelli di rumore strutturale misurati alle fondazioni del motore diesel dipendono dai livelli di velocità misurati sulla sorgente (cioè ai piedi del motore diesel), dai livelli di impedenza meccanica degli elementi resilienti e dai livelli di mobilità meccanica delle fondazioni del motore diesel. Il single-point approach è un approccio semplificato per la previsione dei livelli di rumore strutturale che trascura l’interazione tra elementi resilienti. Secondo tale teoria, al fine di ridurre il rumore strutturale trasmesso attraverso gli elementi resilienti alle strutture nave, si deve ridurre l’impedenza meccanica degli elementi resilienti così come la mobilità meccanica delle fondazioni del motore diesel. In altre parole, si devono aumentare la rigidezza dinamica degli elementi resilienti così come l’impedenza meccanica delle fondazioni del motore diesel. Ad oggi, l’impedenza meccanica degli elementi resilienti può essere ricavata solo mediante prove sperimentali in laboratorio, mentre la mobilità meccanica del motore diesel è solitamente misurata quando la nave è in costruzione. Dunque non vi è la possibilità di predire, in fase progettuale, il rumore strutturale dovuto ai motori diesel. In questa tesi, viene presentata una procedura per la simulazione del rumore strutturale dovuto a motori diesel marini. La procedura si basa su test sperimentali e simulazioni numeriche. Nella prima parte della tesi sono richiamate le basi teoriche necessarie per l’esecuzione delle procedure numeriche e delle prove sperimentali. Sono dunque presentati i risultati delle analisi numeriche per simulare la mobilità delle fondazioni dei motori diesel marini. I risultati delle analisi FEM sono stati validati mediante confronto dei risultati delle analisi numeriche con i dati ottenuti da una campagna di misure eseguite a bordo nave. Successivamente sono presentati i risultati di una serie di prove eseguite per collaudare una nuova macchina sperimentale per misurare l’impedenza meccanica degli elementi resilienti. Lo scopo del collaudo era definire una procedura per l’utilizzo della macchina e per l’esecuzione di prove sperimentali in accordo alla ISO 10846, che è considerata normativa di riferimento per questo tipo di prove. Si è dunque proceduto con l’esecuzione di prove sperimentali eseguite su un elemento resiliente per motori diesel marini. Le prove sono state eseguite a differenti carichi statici. I risultati di queste prove sperimentali sono stati utilizzati per settare un modello numerico che simuli il comportamento non-lineare del componente in gomma del resiliente. I risultati ottenuti sia dalle prove sperimentali sia dalle simulazioni numeriche sono stati utilizzati per predire il rumore strutturale generato dai motori diesel, in accordo al single-point approach. I risultati ottenuti dall’applicazione del metodo sono stati confrontati con misure eseguite a bordo e sono stati discussi per evidenziare vantaggi e svantaggi dell’applicazione del metodo. Le procedure numeriche per la simulazione del comportamento dinamico del resiliente e della fondazione costituiscono un primo passo per l’ottimizzazione del sistema di isolazione del motore diesel marino.
The high level of comfort that is required today on board cruise vessels and mega-yachts, leads the designers to focus their attention on structure-borne noise issues. Four-stroke diesel engines that are installed on board as main diesel engines for the propulsion system and as gen-sets, are usually the main sources of structure-borne noise. For this reason, the diesel engines are usually resiliently mounted in order to reduce the vibration energy generated by these sources and transmitted through the ship structures to the accommodation areas. These mounts decouple the noise and vibration source (diesel engine) from the means of wave propagation (ship structures) and so, they isolate the source from the receiving structures. The structure-borne noise levels measured at the diesel engine foundation depend on the velocity levels measured at the source (diesel engine feet), on the mechanical impedance levels of the resilient mounts and on the mechanical mobility levels of the diesel engine foundation. The simplified theory of the single-point approach neglects the interaction among the resilient mounts. According to this theory, to decrease the structure-borne noise transmitted through the resilient mounts towards the ship structures, the mechanical impedance of the resilient mounts as well as the mechanical mobility of the diesel engine foundation are to be lowered. In other words the dynamic stiffness of the resilient mounts has to be decreased and the mechanical impedance of the diesel engine foundation has to be increased. To date, the mechanical impedance of real resilient mounts can only be obtained by laboratory tests and the mechanical mobility of the diesel engine foundation is usually measured when the ship is under construction, so it is not available for predictive analyses. In the thesis, a procedure for simulating the structure-borne noise generated by marine diesel engine is discussed. The procedure is based on both experimental tests and numerical simulations. In the first part of the thesis, some notes on the theoretical background are presented. Then, the results of FE analyses for simulating the mechanical mobility of a diesel engine foundation are shown. The FE models have been validated by the results of a measurement campaign carried out on board a ship. Then, the results of a series of tests performed to tune a new test rig, designed and built up at the University of Trieste for measuring the mechanical impedance of resilient mounts, are discussed. The campaign for tuning the test rig has been carried out in order to set an experimental procedure that allows achieving results in compliance with the ISO 10846 Standard, which is a sound reference for this kind of tests. As a case study, a large resilient mount for marine diesel engines has been tested to achieve its mechanical impedance curve at different static pre-loads. The outcomes of the experimental tests have been used for tuning the best numerical model of the resilient mount that properly takes into account the nonlinear behaviour of the rubber core. The data of the experimental tests carried out on board ships as well as in laboratory and the outcomes of numerical simulations have been used to predict the structure-borne noise according to the single-point approach. The outcomes achieved by the application of the method have been compared with on board measurements and pros and cons of the method are widely discussed. Moreover, the numerical procedures for the simulation of the dynamic behaviour of the resilient mount and the diesel engine foundation, pave the way for the optimization of the decoupling system of marine diesel engines.
XXVII Ciclo
1982

Droop-Nose Leading Edge (DNLE) morphing wings are one of the most promising devices in order to achieve aerodynamic drag and noise reduction during take-off and landing phases. An accurate design of these structures could lead to the decrease of aircraft fuel consumption in the perspective of reaching a greener aviation, following the objectives indicated by Flightpath 2050 issued by the E.U. However, due to the challenges related to the realization of this technology and TRL reached, DNLE are more likely implemented in Unmanned Aerial Systems (UAS) for testing and evaluation purposes. In the present study, an optimization methodology for the DNLE composite laminate skin and morphing mechanism structure is proposed and applied to a study case represented by the UAS-S45 aircraft. The work starts from the morphing leading edge structure developed by the LARCASE laboratory at ETS Montreal. The results showed that by means of the optimization strategy adopted, the force required on the actuator mechanism is 88% lower than the original design. A significant improvement on the profile smoothness along its section and in the spanwise direction in morphing conditions has been obtained too. However, further investigations are still needed in order to achieve a more appropriate morphing shape. Despite this, it appears from the results obtained that the proposed methodology can be useful to tackle the DNLE design problem in an effective and efficient way. What developed in this work has been conceived to support the investigation of DNLE in the small leading edge profiles typical of the UAS. In this way, an easier procedure for the set up of the design flow, and a decrease in the computational effort for the optimization process can be obtained. An experimental validation of the results obtained is currently being performed at ETS, and future development regards the assessment of the errors of the numeric procedure herein presented respect to real data.

The focus of this thesis is developing optical fibre Bragg grating (FBG) pressure sensors with enhanced sensitivity for use in a low (gauge) pressure range (0 - 50 kPa) together with understanding observed non-linear behaviour. To appreciate the behaviour of FBG sensor spectra, it is necessary to understand geometrical and material properties of FBGs. The thesis is an in-depth investigation of the behaviour of FBGs including their manufacturing and fabrication process details. A new computational approach has been introduced to simulate FBG structures based on how the FBG fabrication process produces changes in refractive index. There are various numerical analysis methods existing for analysing fibre Bragg grating structures and their spectral properties. Although computation design and simulations are used extensively in engineering problems, current computational approaches do not combine FBGs formation and their resultant spectra. In this study, this has been addressed by developing a simple Finite Element Analysis (2-D) model using the Wave Optics module in COMSOL Multiphysics simulation software. The 2-D model was developed considering the phase mask method commonly used to fabricate FBGs. It simulates a complex grating structure which is useful for manufacturers and researchers. The 2-D model then creates a unit cell of a grating structure which is able to be implemented within an optical fibre. The model allows users to decide the length of the grating by selecting the number of unit cells required. By changing the geometrical parameter of a unit cell of the 2-D phase mask structure, it was possible to demonstrate formation of complex grating structures. There have been many studies reported for ideal gratings; however, much less attention and research has been given to the spectra produced by these complex FBG structures. Therefore, this study specially focuses on complex grating structures and their spectral behaviour. The developed 2-D model successfully reproduced observed complex grating structures arising with the use of multiple phase masks orders, with theoretically acceptable results for the spectrum produced. Furthermore, the 2-D model of the phase-mask method was also able to produce tilted gratings by changing the incident angle of light on the phase mask. Therefore, this FEA approach provides insight into not only complex FBG structures but also tilted FBGs using a simple computational tool which will be useful in further research to understand the behaviour of a variety of FBG structures. For this study, material properties of standard single mode fibre (SMF-28) was considered. However, the model is able to simulate any optical fibre used in FBG fabrication by changing the material properties. The thesis also considers the understanding of FBG pressure sensors and observed non-linear behaviour. Therefore, a thorough literature review was carried out to find the influence of structural and material properties of optical fibres and FBGs which is believed to be the cause of non-linear behaviour. It investigates in depth the birefringence effect on fibres due to point load and distributed load on FBGs using the Structural Mechanics and Wave Optics module in COMSOL software. Many research studies have employed a plane strain assumption for structural mechanics problems; however, they do not clearly explain the true nature of FBGs under stress generalized strain. This study overcomes that problem by introducing proper mathematical equations to develop 3-D behaviour in a 2-D computational model. The behaviour of a distributed load on FBGs was discussed in detail with the help of the computational model. It provides new information about an asymmetric peak produced as a result of birefringence effects. The research proposes a new FBG uniform pressure sensor using a 2-D computational model. It was designed in simulation by adding a polymer material to the cladding of an SMF-28 by reducing the cladding diameter. In this study, polymers of PDMS and PTFE were chosen to further investigate the pressure enhancement in the suggested pressure range. The results show similar pressure sensitivity for both materials. Both materials are highly capable of enhancing pressure sensitivity in the range of 0 – 50 kPa. The suggested pressure range is most suitable for biomedical application. The positive results of the current study lend credibility for using the envisaged sensor for commercial use.

Dissertação de mestrado em Structural Analysis of Monuments and Historical Construction
The Castle of Arbeteta, Guadalajara (Spain) is strategically located on top of the cliff rocks with a drawbridge as its only entrance. The castle has undergone various changes in over the time of centuries. It was once a two storey structure, of which only the ruins of the external walls exist. The castle is in a continuous state of degradation due to abandonment. Currently, there is an ongoing intervention project where a new use is going to be given to the castle. This will inevitably alter the current state of the existing structure. Preliminary inspection works and a detailed archaeological survey was carried out which specified the phases of construction of different sections of the castle. However, there is still need of a better characterization of the stone masonry walls and their structural behaviour. The main research question of the present thesis deals with the possible influence of the construction evolution of the castle on its structural behaviour. The thesis thus try to link two commonly separated and hermetic fields from the conservation projects: archaeological survey and structural analysis. For that matter, a non-destructive campaign consisting of indirect sonic tests and dynamic identification, which aimed at a thorough characterization of all the structural elements was planned. The campaign was carefully planned according to an archaeological research previously carried out. Secondly, a numerical model was made to analyse the structural behaviour of the castle, based upon photogrammetry model and the same archaeological survey. The experimental data collected through indirect sonic tests and dynamic identification was used to calibrate the model.. The results of the thesis show that indeed taking into account the archaeological findings improved our knowledge on the structural behaviour of the castle and has to be taken into account before carrying out a rigorous structural analysis.
O castelo de Arbeteta, em Guadalajara (Espanha) está estratégicamente situado no topo de um penhasco rocoso que tem uma ponte levadiça como unico acesso. O castelo tem sido submetido a muitos cambios e alterações estruturais durante estes séculos. Num momento da sua história, o castelo era uma estrutura de dois andares, dos que agora só as ruinas das paredes de alvenaria de pedra exteriores ainda existem. O castelo está agora num processo de degradação continuo devido ao seu abandono. No momento, existe um projeto de intervenção no castelo e um novo uso vai ser proposto no castelo. Esto vai alterar inevitavelmente o estado atual da estrutura existente. Inspeções preliminares do castelo e um levantamento arqueologico detalhado foram realizados e ajudaram a identificar as diferentes fases de construção nas diferentes partes do castelo. Contudo, uma melhor caracterização das paredes de alvenaria de pedras é necessária, para ajudar a compreender melhor o seu comportamento estrutural. Esta investigação estuda principalmente a possível influência da evolução estrutural do castelo no seu comportamento estrutural. A tese portanto trata de ligar dois campos necessários nos projetos de conservação que estão normalmente separados e muito compartimentados: o levantamento arqueologico e a análise estrutural. Com este objetivo, uma campaha de ensaios experimentais não destrutivos que incluiu ensaios sónicos indireitos e ensaios de identificação dinâmica foi planejada e destinada a caracterizar em detalhe todos os elementos estruturais do castelo. A campanha foi planejada cuidadosamente de acordo à investigação arqueologica previamente realizada. Numa segunda parte do trabalho, um modelo numerico foi preparado para analisar o comportamento estrutural do castelo, baseado no modelo fotogrametrico e no levantamento arqueologico. Os resultados experimentais recoletados dos ensaios sonicos e dinamicos foram usados para calibrar o modelo numérico. A tese mostra que, de fato, a consideração das descobertas arqueologicas melhoraram o entendimento do comportamento estrutural do castelo e tem de ser tidos em conta antes de realizar um análise estrutural rigoroso.