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New hierarchical vector basis functions for quadrilateral cells are introduced, and the matrix condition numbers associated with their use are compared to those of existing vector basis families to assess the relative linear independence of the functions. Scale factors are employed to improve the condition numbers. In addition, the proper use of subsets of these families to transition from one order to another (as needed for adaptive p-refinement) without exciting spurious modes is considered.

The torsional stresses in straight round bars with periodic U-shaped shallow grooves are calculated numerically (boundary elements) taking advantage of a computationally efficient thermal analogy. Neuber’s theory is scrutinized, which equates the stress concentration factor in the periodic notch to the stress concentration factor in the single notch of like profile and lower depth. (Corrected depth = original depth times a depth reduction factor, which is a function of the depth-to-pitch aspect ratio of the periodic notch.) The results disclose a depth correction function in close agreement with Neuber’s theory for ideally sharp notches. For a wide range of rounded notches, which are more likely to occur in practice, the paper shows that Neuber’s depth correction grossly overestimates the stresses. By modifying the expression of the depth correction factor, however, Neuber’s conceptual equivalence works well for engineering purposes. Comparison with former results by the authors indicates that the optimal depth correction function is different for notches affected by shear stresses (as in this paper) or by normal stresses.

Electro- and Magneto-Encephalography are precious tools for studying brain activity, notably due to their time resolution and their non invasive nature. Acquisitions are done on the exterior of the head (scalp electrodes for EEG, and magnetometers for MEG); in order to recover the sources responsible of the measured signal, an inverse problem must be solved, for which accurate solutions of the forward problem must be available. This requires a good modeling of the head tissues, and an appropriate representation of this electrophysiological model within numerical methods such as the BEM or FEM. In this thesis we focus on this dual problem of modeling and numerical resolution, notably to handle the skull region which must often be considered anisotropic or highly inhomogeneous in clinical applications, and for the white matter anisotropy which surrounds the sources in the brain. In this thesis we first see the common numerical solvers for solving the forward problem, and expose their strengths and weaknesses. Then, a dual point of view for solving the forward problem using any numerical method is exposed; which is the adjoint method of our forward problem. Its application within a BEM framework is given. Later using a domain decomposition (DD) framework, we present different coupling procedures of the main methods BEM and FEM, in order to get both methods advantages regarding the resolution of the forward problem (notably for handling the skull). This is done within a DD framework, which appears to be interesting in many points. Finally, we propose a new method for dealing with locally anisotropic or inhomogeneous conductivities using a BEM., L'électro- et la magnéto-encéphalographie sont deux techniques très utiles pour observer l'activité électrique du cerveau de par leur résolution temporelle et leur caractère non invasif. Les mesures sont faites sur la surface extérieure de la tête (électrodes pour l'EEG et magnétomètres pour la MEG); afin de retrouver les sources responsables du signal mesuré, un problème inverse de localisation doit être résolu. Celui-ci requiert une bonne résolution du problème direct, ce qui demande une bonne modélisation des tissus de la tête, ainsi qu'une représentation fidèle de ce modèle électro-physiologique par une méthode numérique comme la FEM ou la BEM. Dans cette thèse, nous nous intéressons au choix critique d'un modèle et de sa représentation par une méthode numérique notamment pour prendre en compte l'inhomogénéité de la conductivité du crâne et celle de la matière blanche qui est proche des sources. Après avoir mis en évidence les avantages et inconvénients des méthodes courantes, nous exposons une méthode duale de résolution du problème direct: c'est la méthode adjointe applicable quel que soit la méthode numérique choisie. Puis en utilisant une approche de décomposition de domaine nous formulons plusieurs méthodes de couplage de méthodes numériques visant à tirer parti de leurs avantages dans des sous domaines. Cela permet de coupler la BEM avec la FEM, et implique de nombreux aspects intéressants notamment pour une bonne prise en compte du crâne. Finalement, nous proposons une nouvelle méthode permettant de traiter des conductivités localement anisotropes ou inhomogènes avec la BEM.

Prikazuju se osnovne postavke, dokazi i postupci metode rubnih elemenata (MRE). Iz literature je korišten objavljeni program za proračun naprezanja i deformacija uz podzemne prostorije, pri čemu je obuhvaćeno ravninsko stanje deformacija za elastični kontinuum. Program je proširen predprocesorom za interaktivno zadavanje ulaznih podataka i postprocesorom za grafički prikaz rezultata. Radni dio programa je također proširen, tako da se u proračun stanja naprezanja i deformacija mogu uključiti utjecaji različitih podgradnih sistema za podzemne prostorije, posebno: slojevi mlaznog betona, čelični lukovi te pasivna i prednapregnuta sidra, Razvoj ove numeričke metode je vrlo aktualan u novije vrijeme, a posebno će bili aktualna primjena na materijale s nelinearnim svojstvima. Metoda je brža od ostalih numeričkih metoda, i predstavlja efikasnu dopunu tih metoda., This paper includes main theses, proofs, and procedures of Boundary Element Method (BEM). The computer program. announced in 1981, for the calculation of stresses and strains around underground opening was used, comprising plane strain state for elastic continuum. Preprocessor with interactive input and postprocessor for graphic presentation of the results have been added to the program. In the main program the influences of various support systems for underground rooms were added, especially: shotcrete layers, steel arches and passive and prestressed bolts. This numerical method has been under current development, especially for materials with nonlinear behaviour The method is faster than other numerical methods and represents an efficient supplementation to them.

It is presented in this paper a three-dimensional Boundary Element Method (BEM) implementation of the Energy Domain Integral for the fracture mechanical analysis of three-dimensional interface cracks in transversely isotropic bimaterials. The J-integral is evaluated using a domain representation naturally compatible with the BEM, in which the stresses, strains and derivatives of displacements at internal points are evaluated using their appropriate boundary integral equations. Several examples are solved and the results compared with those available in the literature to demonstrate the efficiency and accuracy of the implementation to solve straight and curved crack-front problems. Fil: Larrosa, Nicolás Oscar. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentina. Universidad de Sevilla; España Fil: Ortiz, J. E.. Universidad de Sevilla; España Fil: Cisilino, Adrian Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Mar del Plata. Instituto de Investigación en Ciencia y Tecnología de Materiales (i); Argentina. Universidad Nacional de Mar del Plata. Facultad de Ingeniería; Argentina

Electronic components have large geometric scale factors, and involve materials with very different thermal conductivities. Experience shows that in this context, the boundary element method is a good choice for thermal simulation in steady state. In transient regime, the temporal dimension adds a number of difficulties. Among these are typically higher computation time and stability criteria, or more generally the links between spatial and temporal discretizations. More specifically, a current issue in electronics is to measure the impact of highly localized phenomena, such as switching or short circuit on the overall thermal component. This is then coupled space-time scales, ensuring in particular the changes of scale without loss of information. In the first part of this work, we propose to use the transient boundary element method to address this problem. We combine first integral formulations and various optimization techniques to reduce the computational cost of the method. We then reuse this work to develop a multi-scale approach, and generalize the boundary element method for nonlinear materials. A second part is devoted to developing an alternative method, to reduce computation time more significantly while retaining a boundary element basis. This is a proper generalized decomposition method, which builds a separate representation of the solution within a non-incremental strategy. We study the convergence of the algorithm on different test cases, providing techniques for dealing with non-homogeneous boundary conditions and initial data, and nonlinear source terms., Les composants électroniques présentent des facteurs d'échelle géométrique importants, et font intervenir des matériaux aux conductivités thermiques très différentes. L'expérience montre que dans ce cadre, la méthode des éléments de frontière est un choix judicieux pour la simulation thermique en régime permanent. En régime transitoire, la dimension temporelle ajoute un certain nombre de difficultés. Parmi celles-ci figurent classiquement l'augmentation des temps de calcul et les critères de stabilité, ou d'un manière plus générale les liens entre discrétisations spatiale et temporelle. Plus spécifiquement, un des enjeux actuels en électronique est de mesurer l'impact de phénomènes très localisés, comme des commutations ou des courts-circuits, sur la thermique globale d'un composant. Il s'agit alors de coupler différentes échelles espace-temps, en assurant en particulier des changements d'échelle sans perte d'information. Dans la première partie de ce travail, on propose d'utiliser la méthode des éléments de frontière transitoire pour répondre à cette problématique. On combine tout d'abord différentes formulations intégrales et des techniques d'optimisation pour réduire le coût de la méthode. On réutilise ensuite ce travail pour développer une approche multi-échelles, et généraliser la méthode des éléments de frontière aux matériaux non linéaires. Une seconde partie est consacrée au développement d'une méthode alternative, visant à réduire les temps de calcul de manière plus significative tout en conservant une base éléments de frontière. Il s'agit d'une méthode de décomposition propre généralisée, qui permet de construire une représentation à variables séparées de la solution de manière non incrémentale. On étudie la convergence de l'algorithme sur différents cas de test, en proposant des techniques pour traiter des conditions aux limites et initiales non homogènes, ainsi que des termes sources non linéaires.

Modeling fluid-structure and soil-structure interaction problems covers several research fields dealing with multiple aspects such as : unbounded geometry of soil media and in some cases of retained fluid, viscous and radiation dissipative effects, application of seismic loading, choice of the basic variables, algebraic properties of the resulting coupled system, ... etc. In this work, different numerical models of soil-structure and fluid-structure coupling have been studied. The truncation boundaries of the soil and of the fluid domains have been considered by using infinite elements whose performances were compared to those of radiation conditions. The problem of the free coupled vibrations of the fluid-structure systems has been solved by introducing efficient symmetrization techniques. In addition, a new symmetric boundary element formulation is proposed. It allows to produce a positive definite and symmetric matrix and therefore to conduct to an algebraic system similar to the one obtained from finite element discretization. The produced matrix called "equivalent stiffness matrix" can easily be assembled or coupled to finite element matrices. All of the applications which have been done in order to compare models or to validate the developed programs were built in the case of concrete gravity dams, which constitute typical coupled fluid- soil-structure problems; La modélisation des problèmes d'interactions sol-structure et fluide-structure couvre plusieurs domaines de recherche très actifs qui traitent une multitude d'aspects tels que la géométrie non bornée du sol et dans certains cas du fluide stocké, les effets dissipatifs visqueux et radiatifs, l'application du chargement sismique, le choix des variables de base, les propriétés algébriques des systèmes d'équations résultant du couplage,... etc. Dans le présent travail, différents modèles numériques de couplage sol-structure et fluide-structure ont été examinés. Les limites de troncature géométrique du sol et du fluide on été traitées avec des éléments infinis dont les performances ont été comparées à celles des conditions de radiations. Le problème de vibrations libres couplées des systèmes fluide-structure a été résolu en introduisant de nouvelles techniques de symétrisation efficaces. De plus, une nouvelle formulation symétrique en éléments de frontière a été proposée. Cette formulation permet de produire une matrice symétrique définie positive et aboutit ainsi à un système algébrique similaire à celui qui découle de la discrétisation en éléments finis. La matrice bâtie dite "raideur équivalente" peut facilement être assemblée ou couplée avec les matrices de la formulation en éléments finis. Toutes les applications qui ont servi soit à comparer des modèles soit à valider les programmes développés, ont été effectué es dans le cas des barrages poids en béton. Ce cas constitue un problème de couplage fluide-sol-structure typique

Τα δομικά στοιχεία των μηχανολογικών κατασκευών υπόκεινται σε επαναλαμβανόμενες κυκλικές καταπονήσεις, από τις οποίες δημιουργούνται και διαδίδονται ρωγμές. Οι καταπονήσεις αυτές, οι οποίες προκαλούν κόπωση στις κατασκευές, μπορεί να είναι είτε καθαρά μηχανικές είτε θερμικές ή να προκύπτουν σα συνδυασμός θερμικής και μηχανικής φόρτισης. Τυπικές περιπτώσεις θερμικών και θερμομηχανικών φορτίσεων εμφανίζονται σε κατασκευές, όπως σωλήνες κυκλωμάτων ψύξης, πιεστικά δοχεία, συνιστώσες ηλεκτρικών κυκλωμάτων, θάλαμοι μηχανών εσωτερικής καύσης και πτερύγια στροβιλοκινητήρων. Η κυκλική μεταβολή του θερμικού φορτίου στις προαναφερθείσες περιπτώσεις, συνιστά συνθήκες θερμικής κόπωσης. Επίσης, λόγω της σχετικά υψηλής συχνότητας του φορτίου η θερμοκρασία παρουσιάζει έντονη μεταβολή στο χώρο και στο χρόνο. Ο προσδιορισμός της διάρκειας ζωής ενός δομικού στοιχείου κατά τη φάση του σχεδιασμού μπορεί να γίνει με τη βοήθεια πειραματικών διαδικασιών. Τα πειράματα όμως κόπωσης είναι δαπανηρά και χρονοβόρα και προφανώς απαιτούνται περισσότερες από μια πειραματικές δοκιμές. Οπότε, είναι εύλογο να υπάρχουν υπολογιστικά εργαλεία που να δίνουν τη δυνατότητα στο μηχανικό να εκτιμήσει την διάρκεια ζωής ή τη σοβαρότητα της βλάβης ενός εξαρτήματος. Τα περισσότερα υπολογιστικά μοντέλα αναφέρονται σε καθαρά μηχανικές καταπονήσεις. Έτσι υπάρχει πρόσφορο έδαφος για την ανάπτυξη υπολογιστικών εργαλείων για την ανάλυση προβλημάτων θερμικής και θερμομηχανικής κόπωσης. Τέτοιου είδους εργαλεία θα πρέπει να λαμβάνουν υπόψη το κλείσιμο των ρωγμών, που συμβαίνει λόγω των θερμικών παραμορφώσεων, διότι είναι δυνατόν να επηρεάζεται τοπικά το θερμοκρασιακό πεδίο. Επομένως, χρειάζεται επαναληπτική διαδικασία για τον προσδιορισμό του θερμικού και τασικού πεδίου που αλληλεπιδρούν. Είναι προφανές ότι η ανάλυση της θερμικής κόπωσης εξελίσσεται σε συνθέτη διαδικασία, που θα πρέπει να συμπεριλαμβάνει τον υπολογισμό της κατανομής της θερμοκρασίας, την τοπική επίδραση του άκρου της ρωγμής στο τασικό πεδίο καθώς και την επαφή των επιφανειών της ρωγμής. Η μέθοδος των συνοριακών στοιχείων είναι ικανή να αντιμετωπίζει τέτοιου είδους τοπικές επιδράσεις. Η παρούσα διατριβή επικεντρώνεται στην ανάπτυξη υπολογιστικού εργαλείου βασισμένου στα συνοριακά στοιχεία, για την πρόβλεψη της διάδοσης ρωγμών και την εκτίμηση της διάρκειας ζωής, εξαρτημάτων υπό θερμική και θερμομηχανική κόπωση. Έμφαση δίνεται σε περιπτώσεις που το θερμικό φορτίο προκαλεί κλείσιμο της ρωγμής και σε περιπτώσεις διεπιφανειακών ρωγμών, όπου το θερμοκρασιακό πεδίο επηρεάζεται από την θερμική αντίσταση ανάμεσα στις επιφάνειες της ρωγμής. Στο πρώτο κεφάλαιο γίνεται βιβλιογραφική ανασκόπηση σε εργασίες που εστιάζουν σε φαινόμενα κόπωσης και διάδοσης ρωγμών, καθώς και στην ανάπτυξη υπολογιστικών μοντέλων για την πρόβλεψη της διάδοσης ρωγμών. Επιπλέον, προσδιορίζεται λεπτομερώς το αντικείμενο της παρούσας διατριβής και εξηγείται η συνεισφορά της και τα καινοτόμα σημεία της. Στο δεύτερο κεφάλαιο περιγράφεται η ιδιόμορφη συμπεριφορά του άκρου της ρωγμής, δίνονται οι διατυπώσεις των μεγεθών θραύσης που χρησιμοποιούνται στην ανάλυση της κόπωσης και αναφέρονται τρόποι με τους οποίους μελετάται η διάδοση ρωγμών. Στο τρίτο κεφάλαιο περιγράφονται λεπτομερώς οι ολοκληρωτικές συνοριακές διατυπώσεις για την επίλυση προβλημάτων θερμοελαστικότητας. Στο τέταρτο κεφάλαιο περιγράφονται οι υπολογιστικές διαδικασίες που ακολουθούνται στην παρούσα εργασία για τον προσδιορισμό του πεδίου θερμοκρασιών και μετατοπίσεων, καθώς και ο τρόπος που προσομοιώνεται η διάδοση ρωγμής. Στο πέμπτο κεφάλαιο παρατίθενται τα αποτελέσματα που προέκυψαν από τις αναλύσεις για διάφορες περιπτώσεις, ενώ στο έκτο κεφάλαιο εξάγονται συμπεράσματα και διατυπώνονται προτάσεις για μελλοντική έρευνα. The prediction of fatigue life is essential for the integrity and reliability of a structure when designing engineering components that undergo cyclic loading. In most cases, the mechanical cyclic loads are taken into account in order to evaluate the life and damage tolerance of structures with existing cracks. However, there exists a category of structures that experience severe thermal cycling that acts alongside the mechanical loads. Such structures include cooling system pipes, pressure vessels, pistons and combustion chambers of internal combustion engines, gas turbine blades and components of electrical circuits. Interfacial crack growth is of paramount importance when designing components that are protected by thermal barrier coatings in order to increase their endurance and efficiency. These types of structures are exposed to very intense thermo-mechanical cycling, which gradually causes delamination and eventually leads to spallation of the coating Numerical simulations, via the finite element method, are a common trend, when analysing the endurance of coated components. However, important aspects such as the heat exchange between the contacting faces and friction are not taken into account in fracture assessments of these components. The boundary element method is very attractive for crack-growth analyses because only the boundary is meshed, rather than the whole domain of the problem. In the present thesis, the boundary integral equations of uncoupled, time-dependent thermo-elasticity are employed to account for the time-varying nature of the thermal load. Our study discusses the influence of crack closure on quasi-static, sub-critical crack extension in the presence of thermo-mechanical cyclic loading. Appropriate thermal and mechanical boundary conditions are imposed on the numerical model to account for the contact state. The validity of the code to compute the temperature distribution under thermal cycling is checked through analytical solutions. Afterwards, a pure mode-I and mixed mode fracture problems in homogeneous material are analysed and the results are compared to other boundary element solutions. The singularity resulting from tractions and heat flux around the crack tip is effectively captured by singular quarter-point elements, while the fracture magnitudes can be computed using appropriate traction formulas. In these problems, the fatigue life is evaluated in terms of load cycle when the crack closure is considered. The number of cycles required for an existing crack to grow a certain length can be empirically predicted using the Paris’ law. The crack extension angle is evaluated by means of the maximum circumferential stress. The results are discussed, clearly indicating the impact of crack closure on fatigue life evaluation. The main conclusion is that crack closure should be incorporated into the analysis whenever the contact effect is inevitable. Otherwise, the fatigue life may be underestimated, leading to a conservative design. Finally, the sub-domain boundary element procedure is applied to interfacial cracks where the crack closure is more pronounced. Specifically, a case of a thermal barrier coating system is investigated. The thermal resistance between the contacting crack faces is incorporated into the procedure and it is assumed to be dependent on the contact pressure. If crack closure due to thermal distortion takes place, then the displacement and traction field may affect the heat flux between the crack faces, and the thermal and mechanical parts of the problem will need to be solved repeatedly until thermo-mechanical convergence is achieved. The results suggest that there are significant effects on the behaviour of stably growing cracks and the evaluation of failure capacity, emanating from crack closure, the amount of thermal resistance and the phase angle between the mechanical and thermal loads.

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2010, Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2010, Bu çalışmada, 154 kV hava hattı silikon kauçuk izolatör “Electro” programı ile modellenmiş; bu izolatörün üzerinde alternatif ve darbe gerilim şartlarında oluşan elektrik alan şiddetleri ve elektrik potansiyel değerleri incelenmiştir. Benzetimlerde izolatör etrafındaki korona halkası yerleşiminin izolatör üzerinde oluşan elektrik alan şiddeti ve potansiyel değerlerine etkisi incelenmiştir. İncelemelerde 3 temel unsur göz önünde tutulmuştur. Bunlar, korona halkasının izolatör alt ucundan yüksekliği, halka çapı ve et kalınlığı unsurlarıdır. Ayrıca program yardımıyla izolatör üzerine su halkaları yerleştirilerek oluşan alan şiddeti ve potansiyel değerleri, temiz durum değerleri ile karşılaştırılmıştır. Günümüzde darbe geriliminde oluşan anlık değerler deneysel yöntemler ile ölçülememektedir. Darbe gerilimi anında oluşan anlık değerleri ancak sayısal yöntemler ile elde edebilmekteyiz. Kullanılan bilgisayar programının çözüm tekniğindeki kısıtlamalardan dolayı, alternatif gerilim benzetimlerinde her iki yöntemin de kullanılabilmesine rağmen benzetimler sınır elemanları yöntemi ile darbe gerilimi benzetimlerinde ise sadece sonlu elemanlar yöntemi ile gerçekleştirilmiştir. Çalışmanın birinci bölümünde konu hakkında giriş yapılmış, ikinci bölümünde ise elektrik alan ifadeleri, sonlu elemanlar yöntemi ve sınır elemanları yöntemi hakkında genel bilgiler verilmiştir. Ayrıca model üzerinde alternatif gerilim kullanılarak hem sonlu elemanlar hem de sınır elemanları yöntemleri ile benzetim yapılıp, her iki yöntem ile ulaşılan sonuçlar karşılaştırılmıştır. Üçüncü bölümde ise kullanılan izolatörün modellemesinin nasıl yapıldığı ve benzetim sonuçlarında kullanılan bölgelerin tanımlamaları yapılmıştır. Dördüncü bölümde alternatif gerilim altında yapılan benzetim sonuçları verilmiştir. Beşinci bölümde ise darbe gerilimi ile yapılan benzetimlerin sonuçları verilmiştir. Çalışmanın sonucu olarak alternatif ve darbe gerilim benzetim sonuçları kullanılarak korona halkasının izolatör performansını en üst seviyeye çıkaracak yerleşimi belirlenmeye çalışılmıştır., In this study, 154 kV overhead line silicone rubber insulator is modelled with a computer program named Electro and electrical field and electrical potential values occurred under alternative and impulse voltage signals are investigated. In these analysis; the impact of the corona ring location to the electrical field and electrical potential values occurred on the insulator according to the corona ring diameter, height from energised end and tube diameter is also studied. Beside of these, electrical field and electrical potential values are analyzed in the existence of water rings on the insulator. It is not possible to determine exact values of electrical field and potentials with today’s experimental techniques. These values can only be determined by analytical techniques. In this study, in spite of the fact that both techniques can be used for alternative signal simulations, we prefer to use boundary element methods for alternative signal solutions. For the impulse signal simulations, we use finite elements method due to the methodological limitations of the software. In the first section of the study, a general introduction to the topic is made. In the second section, electrical field definitions, finite elements method and boundary elements method is briefly explained. Beside of these, the results of the boundary elements and finite element methods are compared by using alternative voltage signal upon the same model. In the third section, the method of modelling of the insulator is explained and critical areas used in the simulation results are defined. Simulation results under alternative voltage signal are enlisted in the fourth section. In the fifth section, simulation results done by impulse signal are mentioned. As the result of the study, the location of corona ring which leads the highest performance of insulator is concluded by using alternative and impulse signal simulation results., Yüksek Lisans, M.Sc.

The assessment of current distribution induced along complex grounding systems has been undertaken using the corresponding antenna model and the set of Pocklington integro-differential equations for curved wires. The set of Pocklington equations is numerically handled via the Galerkin-Bubnov scheme of the Indirect Boundary Element Method (GB-IBEM) featuring the isoparametric elements. Some illustrative numerical results for the current distribution are presented in the paper.

The terminology "wave boundary elements" relates to boundary elements enriched in the Partition of Unity sense by a multiple plane wave basis for the analysis of the propagation of short wavelength waves. This paper presents a variant of this approach in which the plane wave basis is selected adaptively according to an error indicator. The error indicator is residual based, and exhibits useful local and global properties. Model improvement in each adaptive iteration is carried out by the addition of new plane waves with no h-refinement. The convergence properties of the scheme are demonstrated.

An important cause of sound radiation from a submarine in the low frequency range is fluctuating forces at the propeller. The forces arise from the operation of the propeller in a non-uniform wake and are transmitted from the propeller to the submarine hull through both the shaft and the fluid. The sound radiated from the submarine is due to the combination of sound radiation caused by hull and propeller vibrations as well as dipole sound radiation from the propeller. To improve the stealth of a submarine, the radiated sound power can be reduced using passive and active noise and vibration control mechanisms. In this thesis, dynamic models of a submarine hull and propeller/shafting system are developed. To reduce the radiated sound fields, passive control is introduced using a hydraulic vibration attenuation device known as a resonance changer, which is implemented in the propeller/shafting system. Active control techniques are implemented using either tuned actuators or a control moment. To initially obtain the structural and acoustic responses of a submarine hull, an analytical model and fully coupled finite element/boundary element model are developed, for a simplified physical model of the hull. The submerged body under axial excitation is modelled as a ring-stiffened cylindrical shell with finite rigid end closures and separated by bulkheads into a number of compartments. Lumped masses are located at each end to maintain a condition of neutral buoyancy. In the low frequency range, only the axial hull modes in accordion motion and axial vibration of the propeller/shafting system are examined, which gives rise to an axisymmetric case. The frequency responses, axial and radial responses of the cylinder and the radiated sound pressure from both the analytical and computational models are compared. A dynamic model of the propeller/shafting system developed computationally and including the resonance changer is then coupled to the FE/BE model of the hull which is subject to both structural excitation from the propeller/shafting system and acoustic excitation from the propeller. The influence of tailcone properties on the structural and acoustic responses of the submarine are investigated. Passive control is implemented to attenuate the hull responses using a resonance changer. It is demonstrated that the performance of the resonance changer is negatively influenced at frequencies above the fundamental axial resonance of the hull by the effect of forces transmitted through the fluid. When the resonance changer is optimised to minimise excitation of the hull via the propeller shaft, the increased axial movement of the propeller results in an additional sound field that excites the submarine hull in a similar manner to the fluid forces that arise directly from the hydrodynamic mechanism. Cost functions that represent the submarine radiated sound power are developed, where the virtual stiffness, damping and mass of the resonance changer were chosen as design parameters. The minima of the cost functions are found by applying gradient based optimisation techniques. The adjoint operator is employed to calculate the sensitivity of the cost function to the design parameters. The influence of sound radiation due to propeller vibration on the optimisation of the resonance changer is investigated. The influence of the reduction in amplitude for higher harmonics of the blade passing frequency on the control performance is also examined. Different active control strategies are investigated, in which active control is applied to the propeller/shafting system and/or to the submarine hull. Active vibration control and discrete structural acoustic sensing based on the far field radiated sound power were considered in the development of the cost functions. In addition, the performance of a of a combined passive and active control system is investigated. Significant reduction of radiated sound power is achieved when an active control system using tuned actuators is combined with a resonance changer. The structural responses of a model scale, free flooded submarine tailcone are investigated computationally and experimentally. The tailcone is represented by a thin-walled conical shell attached to a stiff plate. The stiff plate represents the pressure hull end plate of the submarine and is subject to axial excitation correlated to propeller forces. Good agreement between the computational and experimental results are found for the tailcone in air as well as for the submerged tailcone.

The Green’s function $G(y,x)$ of the Poisson equation $−∆u = p$ in $Ω$, $u = 0$ on $Γ$ allows to write the solution $u(x)$ in terms of an influence function$$u(x) =\int_Ω G(y,x)p(y)dΩ_y$$.

The stress concentrations produced by tensile loading of elastic solids with periodic notches are addressed. The criterion suggested by Neuber, which likens the periodic notch to a single notch of similar shape but smaller depth, is evaluated. According to Neuber, the depth reduction factor only depends on the ratio between the depth and pitch of the periodic notch, regardless of its particular shape. This work benchmarks the criterion against many axially loaded flat plates and round bars with periodic V-notches, which are analysed by means of the boundary element method. The investigation highlights a strong disparity between Neuber's predictions and numerical findings. However, upon slight adjustment of the depth reduction factor with respect to Neuber's proposal, a satisfactory agreement is achieved. The good correlation holds true both for shallow notches (notched semi-infinite plate) and for deep notches (notched plates or bars of finite width), which were not covered in Neuber's work. Excellent correspondence is also found for the stress concentration around an infinite row of equispaced circular holes loaded longitudinally, a solution taken from the literature as a test case. These results lead to the conclusion that Neuber's criterion, supplemented with the newly disclosed depth reduction factor, can be applied to periodic notches of whatever geometry under normal stresses.

We present new finite element methods for Helmholtz and Maxwell equations on general three-dimensional polyhedral meshes, based on domain decomposition with boundary elements on the surfaces of the polyhedral volume elements. The methods use the lowest-order polynomial spaces and produce sparse, symmetric linear systems despite the use of boundary elements. Moreover, piecewise constant coefficients are admissible. The resulting approximation on the element surfaces can be extended throughout the domain via representation formulas. Numerical experiments confirm that the convergence behavior on tetrahedral meshes is comparable to that of standard finite element methods, and equally good performance is attained on more general meshes., {"references":["R.A. Adams. Sobolev spaces, volume 65 of Pure and Applied Mathematics.\nAcademic Press [a subsidiary of Harcourt Brace Jovanovich\nPublishers], New York-London, 1975.","M. Bebendorf. Approximation of boundary element matrices. Numerische\nMathematik, 86, pp. 565-589, 2000.","F. Brezzi, K. Lipnikov, and M. Shashkov. Convergence of the mimetic\nfinite difference method for diffusion problems on polyhedral meshes.\nSIAM Journal on Numerical Analysis, 43, pp. 1872-1896 (electronic),\n2005.","A. Buffa, and S.H. Christiansen. The electric field integral equation on\nLipschitz screens: definitions and numerical approximation. Numerische\nMathematik, 94, pp. 229-267, 2003.","A. Buffa and P. Ciarlet, Jr. On traces for functional spaces related to\nMaxwell-s equations. I. An integration by parts formula in Lipschitz\npolyhedra. Mathematical Methods in the Applied Sciences, 24, pp. 9-30,\n2001.","A. Buffa and P. Ciarlet, Jr. On traces for functional spaces related\nto Maxwell-s equations. II. Hodge decompositions on the boundary\nof Lipschitz polyhedra and applications. Mathematical Methods in the\nApplied Sciences, 24, pp. 31-48, 2001.","A. Buffa, M. Costabel, and C. Schwab. Boundary element methods for\nMaxwell-s equations on non-smooth domains. Numerische Mathematik,\n92, pp. 679-710, 2002.","A. Buffa, M. Costabel, and D. Sheen. On traces for H(curl, ╬®) in\nLipschitz domains. Journal of Mathematical Analysis and Applications,\n276, pp. 845-867, 2002.","A. Buffa and R. Hiptmair. Galerkin boundary element methods for\nelectromagnetic scattering. Topics in computational wave propagation,\nvolume 31 of Lecture Notes in Computational Science and Engineering,\npp. 83-124. Springer, Berlin, 2003.\n[10] A. Buffa and R. Hiptmair. A coercive combined field integral equation\nfor electromagnetic scattering. SIAM Journal on Numerical Analysis, 42,\npp. 621-640 (electronic), 2004.\n[11] A. Buffa and R. Hiptmair. Regularized combined field integral equations.\nNumerische Mathematik, 100, pp. 1-19, 2005.\n[12] A. Buffa, R. Hiptmair, T. von Petersdorff, and C. Schwab. Boundary element\nmethods for Maxwell transmission problems in Lipschitz domains.\nNumerische Mathematik, 95, pp. 459-485, 2003.\n[13] M. Costabel. Boundary integral operators on Lipschitz domains: elementary\nresults. SIAM Journal on Mathematical Analysis, 19, pp. 613-626,\n1988.\n[14] V. Dolean, H. Fol, S. Lanteri, and R. Perrussel. Solution of the timeharmonic\nMaxwell equations using discontinuous Galerkin methods.\nJournal of Computational and Applied Mathematics, 218, pp. 435-445,\n2008.\n[15] S. Erichsen and S.A. Sauter. Efficient automatic quadrature in 3-d\nGalerkin BEM. Computer Methods in Applied Mechanics and Engineering,\n157, pp. 215-224, 1998. Seventh Conference on Numerical Methods\nand Computational Mechanics in Science and Engineering (NMCM 96)\n(Miskolc).\n[16] W. Hackbusch A sparse matrix arithmetic based on H-matrices. I. Introduction\nto H-matrices. Computing. Archives for Scientific Computing,\n62, pp. 89-108, 1999.\n[17] R. Hiptmair. Coupling of finite elements and boundary elements in\nelectromagnetic scattering. SIAM Journal on Numerical Analysis, 41, pp.\n919-944 (electronic), 2003.\n[18] R. Hiptmair and P. Meury. Stabilized FEM-BEM coupling for Helmholtz\ntransmission problems. SIAM Journal on Numerical Analysis, 44, pp.\n2107-2130 (electronic), 2006.\n[19] P. Houston, I. Perugia, A. Schneebeli, and D. Sch┬¿otzau. Interior penalty\nmethod for the indefinite time-harmonic Maxwell equations. Numerische\nMathematik, 100, pp. 485-518, 2005.\n[20] P. Houston, I. Perugia, A. Schneebeli, and D. Sch┬¿otzau. Mixed discontinuous\nGalerkin approximation of the Maxwell operator: the indefinite\ncase. M2AN. Mathematical Modelling and Numerical Analysis, 39, pp.\n727-753, 2005.\n[21] G.C. Hsiao, O. Steinbach, and W.L. Wendland. Domain decomposition\nmethods via boundary integral equations. Journal of Computational and\nApplied Mathematics, 125, pp. 521-537, 2000. Numerical analysis 2000,\nVol. VI, Ordinary differential equations and integral equations.\n[22] J.M. Hyman and M. Shashkov. Mimetic discretizations for Maxwell-s\nequations. Journal of Computational Physics, 151, pp. 881-909, 1999.\n[23] Y. Kuznetsov, K. Lipnikov, and M .Shashkov. The mimetic finite\ndifference method on polygonal meshes for diffusion-type problems.\nComputational Geosciences, 8, pp. 301-324, 2005.\n[24] K. Lipnikov, M. Shashkov, and D. Svyatskiy. The mimetic finite difference\ndiscretization of diffusion problem on unstructured polyhedral\nmeshes. Journal of Computational Physics, 211, pp. 473-491, 2006.\n[25] W. McLean. Strongly elliptic systems and boundary integral equations.\nCambridge University Press, Cambridge, 2000.\n[26] P. Monk. Finite element methods for Maxwell-s equations, Numerical\nMathematics and Scientific Computation. Oxford University Press, New\nYork, 2003.\n[27] O. Steinbach. Numerical approximation methods for elliptic boundary\nvalue problems. Finite and boundary elements. Springer, New York, 2008.\nTranslated from the 2003 German original."]}

Made available in DSpace on 2013-09-27T14:52:53Z (GMT). No. of bitstreams: 1 WOS000268277100004.pdf: 257892 bytes, checksum: cadcfe973fa5763a872cdcecc5fddebc (MD5) Previous issue date: 2009-01-01 Made available in DSpace on 2013-09-30T19:23:49Z (GMT). No. of bitstreams: 1 WOS000268277100004.pdf: 257892 bytes, checksum: cadcfe973fa5763a872cdcecc5fddebc (MD5) Previous issue date: 2009-01-01 Submitted by Vitor Silverio Rodrigues (vitorsrodrigues@reitoria.unesp.br) on 2014-05-20T15:34:18Z No. of bitstreams: 1 WOS000268277100004.pdf: 257892 bytes, checksum: cadcfe973fa5763a872cdcecc5fddebc (MD5) Made available in DSpace on 2014-05-20T15:34:18Z (GMT). No. of bitstreams: 1 WOS000268277100004.pdf: 257892 bytes, checksum: cadcfe973fa5763a872cdcecc5fddebc (MD5) Previous issue date: 2009-01-01 Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) In this work, non-linear analyses of reinforced concrete plates are performed by using a BEM formulation, based on Kirchhoff's theory, which has already proved to be a robust technique to deal with plate problems. The non-linear behavior of concrete is modeled by the Mazars model, which is based on continuum damage mechanics (CDM) and has an easy parametric identification, while the reinforcement is governed by the uniaxial elasto-plastic model with constant hardening. Initially, the different types of damage models and their parametric identification are discussed and the Mazars model is presented. Then the BEM formulation is discussed, which is based on the initial moment technique, where the remaining domain integrals are evaluated by approaching the initial moment field over internal cells. The stress distribution over the plate thickness is obtained by using a Gauss scheme in which the adopted criterion is verified in each Gauss point defined along the plate. Then, the internal values of moments are approached by numerical integrals along the plate thickness. Finally, some numerical examples of reinforced concrete plates are analyzed, where the potentiality of the Mazars model is verified despite the difficulties of the parametric identification. Universidade Federal de Goiás (UFG), BR-75700000 Catalao, Goias, Brazil Univ Estadual Paulista, Fac Engn Ilha Solteira, São Paulo, Brazil Univ Estadual Paulista, Fac Engn Ilha Solteira, São Paulo, Brazil

In this work, non-linear analyses of reinforced concrete plates are performed by using a BEM formulation, based on Kirchhoff’s theory, which has already proved to be a robust technique to deal with plate problems. The non-linear behavior of concrete is modeled by the Mazars model, which is based on continuum damage mechanics (CDM) and has an easy parametric identification, while the reinforcement is governed by the uniaxial elasto-plastic model with constant hardening. Initially, the different types of damage models and their parametric identification are discussed and the Mazars model is presented. Then the BEM formulation is discussed, which is based on the initial moment technique, where the remaining domain integrals are evaluated by approaching the initial moment field over internal cells. The stress distribution over the plate thickness is obtained by using a Gauss scheme in which the adopted criterion is verified in each Gauss point defined along the plate. Then, the internal values of moments are approached by numerical integrals along the plate thickness. Finally, some numerical examples of reinforced concrete plates are analyzed, where the potentiality of the Mazars model is verified despite the difficulties of the parametric identification In this work, non-linear analyses of reinforced concrete plates are performed by using a BEM formulation, based on Kirchhoff’s theory, which has already proved to be a robust technique to deal with plate problems. The non-linear behavior of concrete is modeled by the Mazars model, which is based on continuum damage mechanics (CDM) and has an easy parametric identification, while the reinforcement is governed by the uniaxial elasto-plastic model with constant hardening. Initially, the different types of damage models and their parametric identification are discussed and the Mazars model is presented. Then the BEM formulation is discussed, which is based on the initial moment technique, where the remaining domain integrals are evaluated by approaching the initial moment field over internal cells. The stress distribution over the plate thickness is obtained by using a Gauss scheme in which the adopted criterion is verified in each Gauss point defined along the plate. Then, the internal values of moments are approached by numerical integrals along the plate thickness. Finally, some numerical examples of reinforced concrete plates are analyzed, where the potentiality of the Mazars model is verified despite the difficulties of the parametric identification.

PurposeThe purpose of this paper is to present a hybrid numerical simulation approach for the calculation of potential and electric field distribution considering charge and dielectric constant.Design/methodology/approachEach numerical method has its own advantages and disadvantages. The idea is to overcome the disadvantages of the corresponding numerical method by coupling with other numerical methods. An augmented finite element method (FEM), linear FEM and boundary element method are used with an efficient coupling.FindingsThe simulation model of microstructured devices is not so simple. During the simulation various types of problems will occur. It is found that by using several numerical methods these problems can be overcome and the calculation can be performed efficiently.Research limitations/implicationsThe present approach can be applied in 2D cases. But, in 3D cases the calculation of augmented FEM in a spherical coordinate becomes quite elaborate.Practical implicationsThe proposed hybrid numerical simulation approach can be applied for the simulation of the electrostatic force microscope (EFM) which is a very high‐resolution measuring tool in nanotechnology. This approach can be applied also to other micro‐electro‐mechanical systems.Originality/valueSince the scanning process of the EFM is dynamic, it requires the updating of the FEM mesh in each calculation time step. In the present paper, the mesh updating is achieved by an arbitrary Lagrangian‐Eulerian (ALE) method. The proposed numerical approach can be applied for the simulation of the EFM including this remeshing algorithm ALE.

In eukaryotes the genome adopts a non-random spatial organisation, which is important for gene regulation. However, very little is known about the driving forces behind nuclear organisation. In the simple model eukaryote fission yeast, Schizosaccharomyces pombe, it has been known for a long time that transcriptionally repressed heterochromatin localise to the nuclear membrane (NM); the centromeres attaches to spindle pole body (SPB), while the telomeres are positioned at the NM on the opposite side of the nucleus compared to the SPB. Studies presented in this thesis aimed at advancing our knowledge of nuclear organisation in Schizosaccharomyces pombe. We show that the heterochromatic mating-type region localises to the NM in the vicinity of the SPB. This positioning was completely dependent on Clr4, a histone methyl transferase crucial for the formation of heterochromatin. Additional factors important for localisation were also identified: the chromo domain protein Swi6, and the two boundary elements IR-L and IR-R surrounding this locus. We further identify two other chromo domain proteins; Chp1 and Chp2, as crucial factors for correct subnuclear localisation of this region. From these results we suggest that the boundary elements together with chromodomain proteins in balanced dosage and composition cooperate in organising the mating-type chromatin. Gene regulation can affect the subnuclear localisation of genes. Using nitrogen starvation in S. pombe as a model for gene induction we determined the subnuclear localisation of two gene clusters repressed by nitrogen: Chr1 and Tel1. When repressed these loci localise to the NM, and this positioning is dependent on the histone deacetylase Clr3. During induction the gene clusters moved towards the nuclear interior in a transcription dependent manner. The knowledge gained from work presented in this thesis, regarding nuclear organisation in the S. pombe model system, can hopefully aid to a better understanding of human nuclear organisation.

Eukaryotic genomes have complex spatial organization in the nucleus. The factors and the mechanisms involved in this organization remain an enigma. Among the many proteins implicated in such a role, the ubiquitous Zn-finger protein CTCF stands out. Here we summarize the evidence placing CTCF in the enviable position of a master organizer of the genome. CTCF can form loops in cis, and can bridge sequences located on different chromosomes in trans. The thousands of CTCF binding sites, identified in recent genome-wide localization studies, and their distribution along the genome further support a crucial role of CTCF as a chromatin organizer.

A numerical tool for the design of foam-like microstructures with customized heat conduction properties is presented in this paper. The spatial variation of the local material properties is achieved via the optimization of the spatial distribution of the gas cells. A Genetic Algorithm (GA) is used for this purpose. Although very effective and versatile GAs are computationally expensive. This problem is tackled in two ways here: a Fast Multipole Boundary Element Method algorithm is used for the thermal analysis of the microstructures, and the GA is implemented in parallel using a cluster of PCs. Two examples illustrate the performance of the developped implementation. Fil: Dondero, Marco. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Cisilino, Adrian Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Rodriguez Carranza, A.. Universidad Nacional de Trujillo.; Perú Fil: Stavroulakis, G.. Technical University of Crete; Grecia

En este trabajo se estudió el comportamiento de muros de mampostería construidos con elementos de borde en los dos extremos; cada elemento de borde armado con varillas de 5/8" localizadas en dos celdas y estribos de 3/8" cada dos hiladas colocadas dentro de unidades especiales. Embebido en el mortero de pega se coloca un marco en platina de 5/8" de ancho y 1/8" de espesor. Todas las celdas del muro se rellenaron con mortero. Los muros se diseñaron por el método de la resistencia última, siguiendo los lineamientos de las Normas Colombianas de Diseño y Construcción Sismo Resistente NSR98, pero no se colocó refuerzo a cortante. Se construyeron tres muros a escala natural (1.50 m de base y 2.30 m de alto), y se ensayaron ante carga monotónica. En los ensayos se encontró que las fallas eran por cortante, con muy poco daño en los elementos de borde. Sin embargo, la resistencia de los muros fue mucho mayor a la esperada, indicando que los elementos de borde incrementan la resistencia del muro. En investigaciones anteriores se había encontrado resultados similares, tanto para cargas monotónicas, como para cargas cíclicas. / Abstract. This work research the behavior of masonry walls built whit boundary elements at both end, made up two 5/8" rod steel inside external brick cells, and 3/8" steel stirrups each two courses, inside special units. In the mortar join, a welded piece 5/8"x1/8" flat steel profile. All brick cells were filled whit mortar. The walls are designed by ultimate resistance method, following Normas Colombianas de Diseño y Construcción Sismo Resistente NSR98 specifications, but without shear reinforcement. Three walls were building in natural scale (1.50m width by 2.3 m tall) and tested to monotonic loads. It was found that walls to be cracked by shear strength, whit little damage in boundary elements. However, walls strength´s were bigger than. Earliest researches found similar results, so much monotonic loads so that cyclic loads. Especialista en estructuras Otra

El Método de los Elementos Finitos y el Método de los Elementos de Contorno son las herramientas numéricas más utilizadas para análisis en mecánica de sólidos. Cada uno de estos métodos tiene sus ventajas y desventajas en diferentes casos. El MEF es adecuado para análisis de dominios finitos con materiales no homogeneos y comportamiento no lineal, mientras que MEC ofrece ventajas en el análisis de dominios infinitos con materiales homogéneos y comportamiento lineal. En este trabajo se presenta un acople iterativo del método de los elementos finitos y el método de los elementos de contorno. El dominio del problema es dividido en dos subdominios, donde cada subdominio es analizado por separado y sólo la información en la interfase es comunicada entre los dos subdominios. El ensamble y análisis de un sistema de ecuaciones general es evitado, obteniéndose ventaja de las características de las matrices, ya que el sistema de ecuaciones en el método de los elementos finitos es simétrico.Los resultados numéricos obtenidos concuerdan satisfactoriamente con resultados obtenidos por otros autores. The Finite Element Method and the Boundary Element Method are the most used numerical tools for solid mechanics analysis. Each one of these methods has advantages and drawbacks in different cases. FEM is well suited for finite domains with inhomogeneous materials and non linear behaviour while BEM offers advantages when dealing with infinite domains displaying homogeneous materials and linear behaviour. An iterative coupling of the Finite Element Method and the Boundary Element Method is presented. The domain of the problem is divided in two subdomains, where each subdomain is analyzed separately and only the interface information is exchanged between both subdomains. The assembly and solution of a general equation system is avoided, thus obtaining full advantage of the matrices characteristics, since the system of equations is symmetric in FEM. Numerical results compare well with other available numerical results.

Topological optimization provides a powerful framework to obtain the optimal domain topology for several engineering problems. The topological derivative is a function which characterizes the sensitivity of a given problem to the change of its topology, like opening a small hole in a continuum or changing the connectivity of rods in a truss. A numerical approach for the topological optimization of 2D linear elastic problems using boundary elements is presented in this work. The topological derivative is computed from strain and stress results which are solved by means of a standard boundary element analysis. Models are discretized using linear elements and a periodic distribution of internal points over the domain. The total potential energy is selected as cost function. The evaluation of the topological derivative is performed as a post-processing procedure. Afterwards, material is removed from the model by deleting the internal points and boundary nodes with the lowest values of the topological derivate. The new geometry is then remeshed using a weighted Delaunay triangularization algorithm capable of detecting "holes" at those positions where internal points and boundary points have been removed. The procedure is repeated until a given stopping criterion is satisfied. The proposed strategy proved to be flexible and robust. A number of examples are solved and results are compared to those available in the literature. © 2007 Elsevier Ltd. All rights reserved. Fil: Carretero Neches, L.. Universidad de Sevilla; España Fil: Cisilino, Adrian Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina

Made available in DSpace on 2014-06-11T19:25:21Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-05-15Bitstream added on 2014-06-13T18:53:17Z : No. of bitstreams: 1 konda_dh_me_ilha.pdf: 2260135 bytes, checksum: 7b50e08a2458da851841fed8236b0b31 (MD5) Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) Esse trabalho trata da análise linear de flexão de pavimentos de edifícios utilizando o Método dos Elementos de Contorno. A formulação de placas baseada nas hipóteses de Reissner, que possibilita a análise de placas finas e moderadamente espessas, é estendida a fim de se modelar pavimentos de edifícios. Nesse modelo, o pavimento é representado por uma placa composta de sub-regiões, sendo cada subregião a representação de uma placa ou viga. Assim, a viga é modelada por uma subregião de pequena largura e maior rigidez. As equações integrais dos deslocamentos são deduzidas utilizando-se o Método dos Resíduos Ponderados. Inicialmente as variáveis são definidas ao longo das interfaces e contorno externo da placa. Então, a fim de reduzir o número de graus de liberdade do problema, apresenta-se um modelo alternativo onde as variáveis ao longo das interfaces são escritas em função dos valores nos eixos das vigas. A validação da formulação proposta é feita através de exemplos, cujos resultados numéricos são comparados com valores previstos analiticamente ou com valores obtidos numericamente a partir de um software comercial baseado no Método dos Elementos Finitos. This work deals with linear bending analysis of building floor structures by the Boundary Element Method. The plate formulation based on Reissner’s hypothesis, which can be used either for thin or thick plates, is extended to model building floor structures which is represented by a zoned plate, where each sub-region defines a slab or a beam. The beams are modelled as narrow sub-regions with larger thickness. The integral equations are derived by applying the weighted residual method to each subregion and summing them to obtain the equation for the whole body. Initially the values are defined on the interfaces and external boundary. Then, in order to reduce further the degrees of freedom, the interfaces values are translated to the the beam axis. The accuracy of the proposed model is confirmed by several numerical examples whose results are compared with the analytical solution if it exists or with a wellknown finite element code.

A three-dimensional boundary element method (BEM) implementation of the interaction integral methodology for the numerical analysis of mixed-mode three-dimensional thermoelastic crack problems is presented in this paper. The interaction integral is evaluated from a domain representation naturally compatible with the BEM, since stresses, strains, temperatures and derivatives of displacements and temperatures at internal points can be evaluated using the appropriate boundary integral equations. Several examples are analysed and the results compared with those available in the literature to demonstrate the efficiency and accuracy of the implementation to solve straight and curved crack-front problems. Fil: Balderrama, R.. Universidad Central de Venezuela; Venezuela Fil: Cisilino, Adrian Pablo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Mar del Plata. Instituto de Investigaciones en Ciencia y Tecnología de Materiales. Universidad Nacional de Mar del Plata. Facultad de Ingeniería. Instituto de Investigaciones en Ciencia y Tecnología de Materiales; Argentina Fil: Martinez, M.. Universidad Central de Venezuela; Venezuela

Orientador: Paulo Sollero Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Mecanica Resumo: Este trabalho apresenta uma ferramenta para análise de sub-domínios utilizando o Método dos Elementos de Contorno 3D (MEC3D). Para a implementação são considerados elementos retangulares, quadráticos e contínuos, isto é, os nós compartilham graus de liberdade e assim, há a necessidade de uma formulação adequada para o tratamento de quinas entre as sub-regiões. As matrizes [H] e [G] são calculadas independentemente do programa de sub-regiões. Isto permite um tratamento computacional eficiente, tendo em vista que atualmente os microcomputadores contam com mais de um processador, viabilizando a computação paralela. Também é apresentada a implementação e o estudo da solução fundamental para anisotropia plena utilizando a Transformada de Radon. Esta formulação é especialmente atraente devido a sua simplicidade de programação, entretanto, ela apresenta uma integral numérica no núcleo do problema o que compromete sua aplicação em problemas de grande porte. Assim, são propostas estratégias para a melhoria do desempenho computacional, como um esquema de interpolação para obtenção das funções de deslocamento e forças de superfície. Abstract: This work presents a tool for sub-domains analysis using the 3D Boundary Element Method (BEM3D). For its implementation are considered rectangular, quadratic and continuous elements, which means that the nodes share degrees of freedom and so, a proper formulation to deal with corners and edges between the sub regions is required. The matrices [H] and [G] are computed independent of the sub regions program. This makes possible an efficient computational treatment, since the actual computers have more than on processor, and parallel computing is used. Also presents the implementation and the study of the fundamental solution for anisotropic elasticity using the Radon Transform. This formulation is especially attractive due to its simplicity for computational implementations, but it requires a numerical integration in the kernel and then, some strategies are proposed to improve the computational performance. Mestrado Mecânica dos Sólidos e Projeto Mecânico Mestre em Engenharia Mecânica

The paper deals with a frequency domain analysis of a log-periodic dipole array (LPDA) antenna using boundary element analysis. The mathematical model is based on the set of corresponding coupled Pocklington integro-differential equations. Once the current distribution along the wires is obtaining, it is possible to determine the radiation characteristics of LPDA. The set of coupled Pocklington integro-differential equations is handled via the Galerkin-Bubnov scheme of the Indirect Boundary Element Method (GB-IBEM). The field irradiated by LPDA is also assessed using BEM formalism.

Modern offshore wind turbines are flexible structures with natural frequencies near the excitation frequencies related to wave and wind-induced loads. In order to obtain a reliable prediction of the structural response, the dynamic stiffness of the foundation must be evaluated accurately. This paper concerns the analysis of bucket foundations with focus on torsional motion and coupled horizontal sliding and rocking. The frequency-dependent stiffness is found by means of a three-dimensional coupled boundary-element/finite-element scheme. Comparisons are made with known analytical and numerical solutions, finding that the present boundary-element-finite-element model provides accurate results. The influence of the soil properties as well as the skirt length of the foundation is analysed, and each dynamic stiffness component is computed as function of a non-dimensional frequency. Modern offshore wind turbines are flexible structures with natural frequencies near the excitation frequencies related to wave and wind-induced loads. In order to obtain a reliable prediction of the structural response, the dynamic stiffness of the foundation must be evaluated accurately. This paper concerns the analysis of bucket foundations with focus on torsional motion and coupled horizontal sliding and rocking. The frequency-dependent stiffness is found by means of a three-dimensional coupled boundary-element/finite-element scheme. Comparisons are made with known analytical and numerical solutions, finding that the present boundary-element-finite-element model provides accurate results. The influence of the soil properties as well as the skirt length of the foundation is analysed, and each dynamic stiffness component is computed as function of a non-dimensional frequency.

Made available in DSpace on 2014-06-11T19:25:22Z (GMT). No. of bitstreams: 0 Previous issue date: 2007-12-07Bitstream added on 2014-06-13T19:12:02Z : No. of bitstreams: 1 denipotti_gj_me_ilha.pdf: 1071673 bytes, checksum: 6d761992a1a3009f2f3628701a9ccbe8 (MD5) Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) Este trabalho trata da inclusão de pilares numa formulação do Método dos Elementos de Contorno para análise linear de pavimentos de edifícios. Inicialmente é apresentada a formulação para análise do pavimento sujeito à flexão simples, onde o pavimento é modelado por uma placa composta por sub-regiões de diferentes rigidezes, sendo cada sub-região a representação de uma viga ou laje. Nesse modelo as forças de superfície são eliminadas das interfaces e todas as sub-regiões são representadas por suas superfícies médias. Então, a fim de reduzir o número de graus de liberdade do problema, aproximam-se os deslocamentos ao longo da largura da viga, obtendo-se um novo modelo em que as variáveis ficam definidas ao longo dos eixos das vigas ao invés de seus contornos. Em seguida, introduz-se o efeito de membrana nessa formulação para que se possa fazer a análise do pavimento sujeito à flexão composta, isto é, representando todas as sub-regiões por uma mesma superfície de referência. Nesse modelo considera-se aproximação linear para as forças de membrana ao longo da largura das vigas. Finalmente, estendem-se essas formulações para análise de pavimentos de edifícios com pilares, através da inclusão de pontos do domínio com carregamentos prescritos, que são escritos em termos das reações do pilar sobre a placa. Os esforços de flexão do pilar sobre a placa são escritos em termos da tensão uniformemente distribuída sobre a seção transversal do pilar e os esforços de membrana são escritos em termos de linhas de carga atuando na seção transversal do pilar. This work deals with the inclusion of columns in a formulation of the Boundary Element Method (BEM) for linear analysis of building floors structures. Initially it is presented the BEM formulation for analyzing building floors subjected to simple bending, where the floor is modeled by a plate divided into sub-regions of different rigidities, being each sub-region the representation of either a beam or slab. In this model the tractions are eliminated on the interfaces and all the sub-regions are represented by their middle surfaces. Then, in order to reduce the number of degrees of freedom, some approximations for the displacements are adopted along the beam width, leading to a model where the values are defined on the beam axis, instead of its boundaries. Then the membrane effects are introduced into this formulation in order to represent all sub-regions by a same reference surface. In this model are assumed linear approximation for the in-plane tractions along the beam cross section. Finally, those formulations are extended in order to consider columns in the plate domain. This is done by considering domain points with prescribed loadings which are written in terms of the column reactions on the plate. The columns bending reactions are written in terms of a stress uniformly distributed over the column cross section and the membrane forces are written in terms of loading lines acting in the column cross section.

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An overview of the main theoretical aspects of finite-element and boundary-element modelling of the response to moving loads is given. The moving loads represent sources of noise and vibration generated by moving vehicles, and the analysis describes the propagation of the disturbances generated in soil. A finite-element time-domain analysis in convected coordinates with a simple upwind scheme is presented, including a special set of boundary conditions permitting the passage of outgoing waves in the convected coordinate system. The modification of frequency-dependent damping to convected coordinates is described, and the convected formulation of boundary elements is presented and used for illustrating the effect of ‘high-speed' motion. Finally, a procedure for the coupling of a local finiteelement model with a boundary-element model of an exterior, or open, domain is described. The paper uses recent results from the Danish research programme ‘Damping Mechanisms in Dynamics of Structures and Materials' as a basis for a general discussion and review of the recent literature on the subject. An overview of the main theoretical aspects of finite-element and boundary-element modelling of the response to moving loads is given. The moving loads represent sources of noise and vibration generated by moving vehicles, and the analysis describes the propagation of the disturbances generated in soil. A finite-element time-domain analysis in convected coordinates with a simple upwind scheme is presented, including a special set of boundary conditions permitting the passage of outgoing waves in the convected coordinate system. The modification of frequency-dependent damping to convected coordinates is described, and the convected formulation of boundary elements is presented and used for illustrating the effect of ‘high-speed' motion. Finally, a procedure for the coupling of a local finiteelement model with a boundary-element model of an exterior, or open, domain is described. The paper uses recent results from the Danish research programme ‘Damping Mechanisms in Dynamics of Structures and Materials' as a basis for a general discussion and review of the recent literature on the subject.

An original approach to solve domain decomposition problems by the symmetric Galerkin boundary element method is developed. The approach, based on a new variational principle for such problems, yields a fully symmetric system of equations. A natural property of the proposed approach is its capability to deal with nonconforming discretizations along straight and curved interfaces, allowing in this way an independent meshing of non-overlapping subdomains to be performed. Weak coupling conditions of equilibrium and compatibility at an interface are obtained from the critical point conditions of the energy functional. Equilibrium is imposed through local traction (Neumann) boundary conditions prescribed on a subdomain situated at one side of the interface, and compatibility is imposed through local displacement (Dirichlet) boundary conditions prescribed on the other subdomain situated at the opposite side of the interface. No additional unknowns such as Lagrange multipliers are introduced. An SGBEM code for 2D elastic domain decomposition problems has been implemented. The effectiveness of the approach developed is documented by numerical examples involving non-matching linear boundary element meshes at the interfaces, where the accuracy is analyzed by comparing the numerical results obtained versus the analytical solutions and by evaluating the convergence rate of the error in the (discretized) integral L2-norm and maximum-normfor h-refinements of boundary element meshes. Finally, a theoretical analysis of a problem with an interior and an exterior subdomain is introduced to explain the observed behaviour of numerical results.

The present work deals with the application of the traction hypersingular boundary integral equation to approximate the stress tensor along the boundary, by making use of unit vectors that differ from the normal at the boundary. It is proved that special care is required in the evaluation of the free terms, in order to avoid insidious and unexpected errors. Copyright © 2007 John Wiley & Sons, Ltd.

28th World Conference on Boundary Elements and other Mesh Reduction Methods (from 5/10/2006 to 5/12/2006), Skiathos, Greece, available, unclassified, unlimited

This paper is intended to present wavelet Galerkin schemes for the boundary element method. Wavelet Galerkin schemes employ appropriate wavelet bases for the discretization of boundary integral operators. This yields quasisparse system matrices which can be compressed to O(N_J) relevant matrix entries without compromising the accuracy of the underlying Galerkin scheme. Herein, O(N_J) denotes the number of unknowns. The assembly of the compressed system matrix can be performed in O(N_J) operations. Therefore, we arrive at an algorithm which solves boundary integral equations within optimal complexity. By numerical experiments we provide results which corroborate the theory.

We considered a nonlinear parabolic equation in a bounded domain of R 2 coupled with the Laplace equation in the corresponding exterior region. This kind of problems appears in the modelling of quasi-stationary electromagnetic fields. We chose a regular artificial boundary containing the nonlinear region in its interior. Then, we applied a symmetric FEM-BEM coupling procedure including a parameterization of the artificial boundary. We used the backward Euler method for the time discretization and an exact triangulation of the finite element domain. Assuming that the nonlinear operator is strongly monotone and Lipschitz-continuous, we proved convergence and obtained optimal error estimates for the solution of the discrete problem. Finally, we proposed a fully discrete scheme with quadrature formulas of low order and, under some additional conditions on the nonlinearity, proved that the order of convergence remains optimal.

The elastic maximum equivalent stress in a pin-loaded, straight- or taper-shanked, round-ended lug subject to inclined loading is investigated using the finite element and the boundary element methods, and, partly, photoelasticity. The influence of the load direction, of the ratio between the bore diameter and lug width, and of the shank taper angle are particularly addressed. In addition, the effects of the axial length of the lug trunk and, partially, of the initial clearance between the lug bore and pin are numerically examined in the presence of a loading variously inclined to the lug axis. An interpolating expression for the maximum equivalent stress as a function of the ratio between the bore diameter and lug width, taper angle, and load inclination angle is proposed.

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