This paper is a study of some of the basic properties of the metric half-space topology, a topology on a set which is derived from a metric on the set. In the first it is found that in a complete inner product space, the metric half-space topology is the same as one defined in terms of linear functionals on the space. In the second it is proven that in Rn the metric half-space topology is the same as the usual metric topology. In the third theorem it is shown that in a certain sense the nature of the metric halfspace topology generated by a norm on the space determines whether the norm is quadratic, that is to say, whether or not there exists an inner product on the space with the property that |x|^2=(x,x) for all x in the space.

A Thurston map whose postcritical set consists of exactly four points and for which the local degree at each of its critical points is 2 is called textit{nearly Euclidean}. These maps were specified to parse Thurston's combinatorial characterization of rational functions. We determine an extension of the half-space theorem which provides an open hyperbolic half-space such that the negative reciprocal of any fixed slope value is excluded from the boundary of the half-space. / Master of Science

Size-dependent material responses observed at fine length scales are receiving growing attention due to the need in the modeling of very small sized mechanical structures. The conventional continuum theories do not suffice for accurate descriptions of the exact material behaviors in the fine-scale regime due to the lack of inherent material lengths. A number of new theories/models have been propounded so far to interpret such novel phenomena. In this dissertation a few enriched-continuum theories - the adhesive contact mechanics, surface elasticity and strain gradient elasticity - are employed to study the mechanical behaviors of a semi-infinite solid induced by the boundary forces. A unified treatment of axisymmetric adhesive contact problems is developed using the harmonic functions. The generalized solution applies to the adhesive contact problems involving an axisymmetric rigid punch of arbitrary shape and an adhesive interaction force distribution of any profile, and it links existing solutions/models for axisymmetric non-adhesive and adhesive contact problems like the Hertz solution, Sneddon's solution, the JKR model, the DMT model and the M-D model. The generalized Boussinesq and Flamant problems are examined in the context of the surface elasticity of Gurtin and Murdoch (1975, 1978), which treats the surface as a negligibly thin membrane with material properties differing from those of the bulk. Analytical solution is derived based on integral transforms and use of potential functions. The newly derived solution applies to the problems of an elastic half-space (half-plane as well) subjected to prescribed surface tractions with consideration of surface effects. The newly derived results exhibit substantial deviations from the classical predictions near the loading points and converge to the classical ones at a distance far away from those points. The size-dependency of material responses is clearly demonstrated and material hardening effects are predicted. The half-space contact problems are also studied using the simplified strain gradient elasticity theory which incorporates material microstructural effects. The solution is obtained by taking advantage of the displacement functions of Mindlin (1964) and integral transforms. Significant discrepancy between the current and the classical solutions is seen to exist in the immediate vicinity of the loading area. The discontinuity and singularity exist in classical solution are removed, and the stress and displacement components change smoothly through the solid body.

No description available.

Foundation uplift is the partial separation of a shallow foundation from soil due to excessive load eccentricity. Foundation uplift can significantly change the seismic response of slender structures, and frames as well. In literature, different support models for foundations are employed in order to simulate foundation uplift in seismic analysis of structures. One of the most widely used models is the Winkler model which assumes distributed tensionless springs beneath a shallow foundation. In this study, two simple algorithms are developed in order to compute static and dynamic response of foundations on tensionless supports. Any formula given in literature for calculation of foundation impedance coefficients can be easily introduced in these algorithms. Hence, the use of Winkler model is critically evaluated through comparisons with the response of a foundation on elastic halfspace. For that purpose, available impedance formulas given for a shallow rectangular foundation on elastic halfspace are used. It is concluded that, the coupling between vertical displacement and rocking of foundation is very significant during uplift. Therefore, the accuracy of Winkler model in uplift v simulation is limited, since the model cannot simulate vertical and rocking response of a shallow foundation concurrently with a single spring coefficient.

Research on metamaterials has been growing ever since the first experimental realization of double negative media. The theory of transformation optics provides people with a perfect tool to make use of vast possibilities of the constitutive parameters for metamaterials. A lot of fascinating designs have been brought to us by transformation optics, with invisibility cloaks being the most intensely studied. The present thesis aims to develop the basic theory of transformation optics, and utilize it to design invisibility cloaks for various applications. After the background description of this field, the theory of transformation optics is first introduced. Formulas of transformation medium parameters and transformed fields are derived with every detail explained, so that the working knowledge of transformation optics can be grasped with minimal prerequisite mathematics. Proof of form invariance of full Maxwell’s equations with sources is presented. Design procedure of transformation optics is then demonstrated by creating perfect invisibility cloaks. The introduction to basic theory is followed by discussions on our works included in our published papers. As our first application, a method of designing two-dimensional reduced cloaks of complex shapes is proposed to relieve the difficulty of singularity occurring in perfect cloaks. The simple and intuitive method is the first way to design two-dimensional reduced cloaks of shapes other than cylindrical. Elliptical and bowtie shaped reduced cloaks are presented to verify the effectiveness of the method. Prominent scattering reduction is observed for both examples. Considering the practical realization, transformations continuous in the whole space must be the identity operation outside certain volume, and thus they can only manipulate fields locally. Discontinuous transformations are naturally considered to break the limitation. We study the possible reflections from such a transformation medium due to a discontinuous transformation by a new concept of inverse transformation. This way, the reflection falls into the framework of transformation optics as well. A necessary and sufficient condition for no reflection is derived as a special case. Unlike the invisibility realized by perfect cloaks, cloaking an object over a dielectric half-space has advantages in some particular applications. Starting from a perfect cloak, a half-space cloak is designed to achieve this. In our design, two matching strips embedded in the dielectric ground are used to induce proper reflection in the upper air space, so that the reflected field is the same as that from the bare dielectric ground. Cloaks obtained from singular transformations and even reduced models all have null principal value in their material parameters, making invisibility inherently very narrowband. In contrast, a carpet cloak designed by only coordinate deformation does not have the narrowband issue, and can perform well in a broad spectrum. The invisibility accomplished by the carpet cloak is also for the half-space case as our previous design. In this part, we extend the original version of a carpet cloak above a PEC sheet to a general dielectric ground. / QC 20110415

Die zerstörungsfreie Ultraschallprüfung von akustisch anisotropen Werkstoffen stellt auch heute noch eine Herausforderung dar. Die Gefügestruktur in solchen Materialien beeinflusst die Wellenausbreitung derart, dass es zum einen zu starken Streuungen durch die großflächigen Korngrenzen und zum anderen, aufgrund der akustischen Anisotropie, zu einer Richtungsabhängigkeit der Schallgeschwindigkeiten kommt. In den vergangenen Jahren wurden bereits Lösungsansätze zur mathematischen Modellierung der Schallausbreitung in anisotropen Materialien vorgestellt. Diese basieren in der Regel auf FEM- bzw. FIT- Algorithmen, die durch die Diskretisierung des gesamten Volumens einen hohen Rechenaufwand erfordern und in der täglichen Prüfpraxis aufgrund ihrer Komplexität bei der Parametrierung nur bedingt einsetzbar sind. Aus diesem Grund wird hier ein Ansatz zur Schallfeldberechnung gewählt, der auf die praktische Anwendung von Gruppenstrahler-Prüfköpfen zugeschnitten ist. Während sich andere Verfahren auf einzelne Wellenanteile und monofrequente Lösungen beschränken, um den Rechenaufwand zu reduzieren, können mit diesem Ansatz die reale Signalform des Prüfkopfes sowie alle auftretenden Wellenanteile in homogenen transversalisotropen Medien berücksichtigt werden. Durch entsprechende Optimierungen im Berechnungsalgorithmus lässt sich das gesamte vierdimensionale Schallfeld eines Gruppenstrahler-Prüfkopfes im Halbraum in kürzester Zeit berechnen. Die analytische Lösung der Wellengleichung für den Halbraum in Form einer Greenschen Funktion wird dabei in eine Gleichung umgeformt, die hier als vierdimensionale Punktrichtwirkung bezeichnet wird. Dieser Modellansatz ermöglicht es, die Parameter eines Gruppenstrahlersystems in der praktischen Anwendung zu überprüfen und durch iterative Rechnungen zu optimieren. Mit Hilfe einer einfach zu handhabenden Visualisierungstechnik ist es möglich diesen Modellansatz mit realen Schallfeldmessungen zu vergleichen. Dazu werden mit elektrodynamischen Sonden die einzelnen Komponenten des dreidimensionalen Vektors der Teilchenverschiebung an der Oberfläche von Festkörpern abgetastet. Die an den Messpunkten ermittelten Zeitfunktionen des Verschiebungsvektors werden dann dem berechneten Zeitverlauf der Wellenausbreitung gegenübergestellt. Die berechneten und gemessenen Schallfelder stimmen in der Phasenlage und im Amplitudenverlauf gut überein. Die Ergebnisse zeigen, dass mit dem verwendeten Rechenmodell alle in der Realität auftretenden Wellenanteile vollständig berücksichtigt werden und dreidimensionale Problemstellungen aus der Praxis mit diesem Modell korrekt berechnet werden können. / The non-destructive ultrasonic testing of acoustic anisotropic materials is an important challenge. The texture of these materials causes a strong scattering of the sound wave by the extensive grain boundaries and a direction dependent sound velocity by the acoustic anisotropy. Several approaches for the modelling of the sound propagation in anisotropic materials were presented in the last years. These approaches are normally based on FEM or FIT algorithms using a discretisation of the complete volume. Their calculation needs extensive time and a very complex parameterisation. Thus these algorithms are not suitable in practice of ultrasonic testing. In this work an approach is presented that is optimised for the application of phased array transducers. The new approach considers the real frequency spectrum of the transducer as well as all occurring wave modes in homogeneous transversely isotropic media, whereas other approaches are limited to solutions for single wave modes and single frequencies to reduce the calculation effort. The appropriate optimisations of the mathematical algorithm allow the fast calculation of the complete four-dimensional transient wave field of a phased array transducer in the half-space. The Green’s functions are derived by an analytical solution of the elastodynamic wave equation for the half-space. These functions will be transformed into an equation which will be referred to in this work as four-dimensional directivity pattern. This approach allows the verification of the parameters of a phased array system and their optimisation by iterative calculations in the practical application. To get accurate results in these calculations, the experimental verification of the applied mathematical model for the wave propagation is an essential task. The technique presented in this work applies electrodynamic probes, which provides a simple use. The probes can detect the particle displacement at a solid surface in all three spatial directions. The measured time-functions of the wave field will be compared with the calculated time-functions. They show a good accordance in the phase and the amplitude. This confirms that the applied mathematical model considers completely all in practice occurring wave modes. The results further show that three-dimensional problems in practice can be calculated correctly with this model.

Στην παρούσα εργασία, πραγματοποιείται η μελέτη του φαινομένου της δυναμικής αλληλεπίδρασης εδάφους-κατασκευής όταν αυτή θεμελιώνεται επί εύκαμπτων, επιφανειακών θεμελιώσεων με ή χωρίς πασσάλους. Η μέχρι σήμερα μελέτη της αλληλεπίδρασης εδάφους-κατασκευής έχει περιορισθεί κυρίως σε επιφανειακά, άκαμπτα ή εύκαμπτα θεμέλια και επιφανειακές ή βαθιές, άκαμπτες θεμελιώσεις επί πασσάλων. Ο συνδυασμός εύκαμπτων θεμελιώσεων, επιφανειακών ή βαθιών, και πασσαλώσεων, κοινή πρακτική σε πλείστες κατασκευές, δεν έχει μελετηθεί λόγω της περιπλοκότητας του φαινομένου και των σχετικών αβεβαιοτήτων όσον αφορά στα δεδομένα του προβλήματος. Συνεπώς, η κρισιμότητα των διαφόρων παραμέτρων, και των πολλαπλών αλληλεπιδράσεων τους, στη σεισμική απόκριση των κατασκευών παραμένει εν πολλοίς άγνωστη. Στόχος της εργασίας είναι η ανάπτυξη ενός διακριτού προσομοιώματος για τον εδαφικό ημιχώρο, το οποίο θα δύναται να χρησιμοποιηθεί για την δυναμική ανάλυση εύκαμπτων θεμελίων με ή χωρίς πασσάλους. Σε αυτή την μελέτη χρησιμοποιείται αποκλειστικά η μέθοδος των πεπερασμένων στοιχείων (ΜΠΣ), για την διακριτοποίηση της κατασκευής, του εδάφους και του συστήματος θεμελίωσης. Ειδικότερα, με τη χρήση του πακέτου πεπερασμένων στοιχείων ACS SASSI, διακριτοποιείται ο εδαφικός ημιχώρος και υπολογίζεται το πεδίο μετακινήσεων της επιφάνειας του ημιχώρου για διάφορες συχνότητες που αντιστοιχούν σε συνήθεις σεισμικές διεγέρσεις. Με γνωστό το πεδίο μετακινήσεων, υπολογίζονται οι δυναμικές δυσκαμψίες του ημιχώρου συναρτήσει της συχνότητας και της απόστασης από το σημείο φόρτισης και δημιουργείται ένα νέο διακριτό προσομοίωμα που αντικαθιστά το έδαφος, με βάση το μητρώο δυναμικών δυσκαμψιών. Τέλος με κατάλληλη αδιαστατοποίηση, προκύπτουν κλειστές εκφράσεις για τα στοιχεία του μητρώου δυναμικών δυσκαμψιών, που παρέχουν το επιπλέον πλεονέκτημα ότι είναι ανεξάρτητες της συχνότητας διέγερσης και έτσι γίνεται εφικτή η απευθείας ανάλυση συστημάτων αλληλεπίδρασης εδάφους – κατασκευής στο πεδίο του χρόνου. Το προτεινόμενο προσομοίωμα του ελαστικού ημιχώρου επεκτείνεται στην περίπτωση του μεμονωμένου πασσάλου σε εδαφικό ημιχώρο. Το διακριτό προσομοίωμα που αναπτύχθηκε προηγουμένως είναι κατάλληλο για εισαγωγή σε πρόγραμμα πεπερασμένων στοιχείων γενικού σκοπού ( όπως π.χ. ANSYS, SAP2000, ABAQUS ) και μπορεί να χρησιμοποιηθεί για κάθε είδος επιφανειακής εύκαμπτης ή άκαμπτης θεμελίωσης ανεξαρτήτου γεωμετρίας, υποκαθιστώντας τον ελαστικά γραμμικό εδαφικό ημιχώρο. Με αυτό τον τρόπο γίνεται εφικτή η επίλυση οποιουδήποτε συστήματος αλληλεπίδρασης εδάφους – κατασκευής. Η ακρίβεια και αποτελεσματικότητα του προτεινόμενου προσομοιώματος για τον εδαφικό ημιχώρο, γίνεται φανερή από μια σειρά συγκρίσεων με αποτελέσματα παλαιοτέρων δημοσιεύσεων για άκαμπτα και εύκαμπτα θεμέλια και κατασκευών με ή χωρίς πασσάλους. / During the last decades the problem of dynamic soil-structure interaction (SSI), has received considerable attention due to the large number of installations and structures sensitive to dynamic excitations such as multistory buildings, bridges, nuclear reactors, platforms etc. In fact every structure that lies on a deformable soil medium, experiences the effects of dynamic SSI. Although the phenomenon is thoroughly studied for a variety of soil-structure systems the main research effort has been focused on the dynamic behavior of rigid foundations. The assumption of foundation rigidity is so popular because it simplifies the solution procedure. In contrast, the dynamic analysis of flexible foundations adds more parameters to the problem, by requiring the discretization of both the soil medium and the foundation itself. In this work, the main goal is the study of the dynamic response of flexible foundations (e.g. mat foundations, raft foundations) and the development of a new discrete model for the analysis of soil-foundation-structure systems, which incorporates the effects of foundation flexibility. The problem under consideration consists of determining the dynamic response of the surface of the soil medium idealized as a linear elastic, isotropic half space. To this end the Finite element Method (FEM) is utilized throughout this work. The FEM computer code ACS SASSI is used to simulate the half space. Using the dynamic response of half space surface due to a unit harmonic load, calculated at a dense network of surface nodal points, the impedances of the half space are computed. Using these values a simplified, frequency independent discrete impedance matrix is constructed. Results of the above analysis are presented for a range of frequencies and half-space material properties, in easy to use graphs. This model is expanded to incorporate the case of a single flexible pile embedded on a homogenous half space. The above discrete model can easily be imported to any standard general purpose FEM code (e.g., ANSYS, SAP2000), where the solution of the soil-structure system can be obtained for a variety of soil-structure systems. The main advantages of this model are 1) Accurate, easy and fast discretization of the soil medium 2) No limitation exist due to foundation type or geometry 3) Analyses can be performed both in frequency and time domain.

Motivée par le développement de diverses applications déployant des antennes près d'une interface, comme les systèmes militaires UGS, les réseaux corporels sans fil BAN et la surveillance environnementale impliquant des capteurs au sol, cette thèse porte sur la modélisation de la propagation des ondes électromagnétiques près d'une interface. Tout d'abord, la méthode classique de l'optique géométrique est confrontée à des formules approchées fournies par Norton et par Bannister. Cette étude met en évidence les cas où l'optique géométrique ne décrit pas correctement la propagation près de la surface. Pour une compréhension plus exhaustive, les fonctions de Green de ce type de propagation, présentées sous forme d'intégrales de Sommerfeld, sont évaluées à la lumière de la méthode de la plus grande pente. Cette évaluation permet d'extraire trois équations importantes pour la propagation près d'une interface. La première est la condition essentielle pour que la proximité au sol puisse profiter au bilan de liaison grâce à l'excitation d'une composante de l'onde diffractée qui se propage près de l'interface. Les deux autres identifient des distances critiques qui bornent le début et la fin de la zone présentant un affaiblissement de trajet amélioré. L'ensemble de ces trois équations permet d'évaluer le rôle de certains paramètres physiques, notamment les propriétés électromagnétiques du sol, la fréquence de travail et la hauteur des antennes. Cette thèse inclut également les pistes pratiques envisagées pour une démonstration de faisabilité de l'amélioration d'une liaison sans fil par la proximité des antennes à l'interface. La couverture du sol ayant une importance prépondérante, nous présentons des recherches préliminaires sur la réalisation et la caractérisation d'un matériau approprié pour ce type de propagation. Dans un axe de recherche parallèle, cette thèse évalue également l'exactitude et la pertinence d'une nouvelle formulation théorique pour la propagation près du sol. Cette formulation dite « de Schelkunoff » suscite des controverses dans la communauté scientifique / Motivated by the development of various applications deploying antennas near an interface, such as military systems (UGS), wireless body area networks (BAN) and environmental monitoring involving ground sensors, this thesis deals with the near-ground wave propagation modelling. First, the results of the geometrical optics are confronted with the approximations provided by Norton and Bannister. This study reveals the cases where geometrical optics does not correctly describe the wave propagation near the surface. For a more comprehensive understanding, Green's functions of this type of propagation, presented as Sommerfeld integrals, are evaluated using the steepest descent technique. This evaluation offers the possibility to extract three important equations for near-ground wave propagation. The first one presents the essential condition under which the link budget can benefit from the ground proximity through the excitation of a diffracted wave component propagating near the interface. The other two equations identify critical distances indicating the beginning and the end of the zone with an improved path loss. All these three equations highlight the role of certain physical parameters, in particular the electromagnetic properties of the ground, the working frequency and the heights of the antennas. This thesis also includes the practical solutions that can be considered to demonstrate the feasibility of improving a wireless link by the proximity of the antennas to the interface. Since floor coating is of major importance, we present preliminary research on the realisation and characterisation of a suitable material for this type of propagation. In a parallel research axis, this thesis also evaluates the accuracy and relevance of a new theoretical formulation for near-ground propagation. The "so-called Schelkunoff" formulation has become a controversial issue in the scientific community

Die zerstörungsfreie Ultraschallprüfung von akustisch anisotropen Werkstoffen stellt auch heute noch eine Herausforderung dar. Die Gefügestruktur in solchen Materialien beeinflusst die Wellenausbreitung derart, dass es zum einen zu starken Streuungen durch die großflächigen Korngrenzen und zum anderen, aufgrund der akustischen Anisotropie, zu einer Richtungsabhängigkeit der Schallgeschwindigkeiten kommt. In den vergangenen Jahren wurden bereits Lösungsansätze zur mathematischen Modellierung der Schallausbreitung in anisotropen Materialien vorgestellt. Diese basieren in der Regel auf FEM- bzw. FIT- Algorithmen, die durch die Diskretisierung des gesamten Volumens einen hohen Rechenaufwand erfordern und in der täglichen Prüfpraxis aufgrund ihrer Komplexität bei der Parametrierung nur bedingt einsetzbar sind. Aus diesem Grund wird hier ein Ansatz zur Schallfeldberechnung gewählt, der auf die praktische Anwendung von Gruppenstrahler-Prüfköpfen zugeschnitten ist. Während sich andere Verfahren auf einzelne Wellenanteile und monofrequente Lösungen beschränken, um den Rechenaufwand zu reduzieren, können mit diesem Ansatz die reale Signalform des Prüfkopfes sowie alle auftretenden Wellenanteile in homogenen transversalisotropen Medien berücksichtigt werden. Durch entsprechende Optimierungen im Berechnungsalgorithmus lässt sich das gesamte vierdimensionale Schallfeld eines Gruppenstrahler-Prüfkopfes im Halbraum in kürzester Zeit berechnen. Die analytische Lösung der Wellengleichung für den Halbraum in Form einer Greenschen Funktion wird dabei in eine Gleichung umgeformt, die hier als vierdimensionale Punktrichtwirkung bezeichnet wird. Dieser Modellansatz ermöglicht es, die Parameter eines Gruppenstrahlersystems in der praktischen Anwendung zu überprüfen und durch iterative Rechnungen zu optimieren. Mit Hilfe einer einfach zu handhabenden Visualisierungstechnik ist es möglich diesen Modellansatz mit realen Schallfeldmessungen zu vergleichen. Dazu werden mit elektrodynamischen Sonden die einzelnen Komponenten des dreidimensionalen Vektors der Teilchenverschiebung an der Oberfläche von Festkörpern abgetastet. Die an den Messpunkten ermittelten Zeitfunktionen des Verschiebungsvektors werden dann dem berechneten Zeitverlauf der Wellenausbreitung gegenübergestellt. Die berechneten und gemessenen Schallfelder stimmen in der Phasenlage und im Amplitudenverlauf gut überein. Die Ergebnisse zeigen, dass mit dem verwendeten Rechenmodell alle in der Realität auftretenden Wellenanteile vollständig berücksichtigt werden und dreidimensionale Problemstellungen aus der Praxis mit diesem Modell korrekt berechnet werden können. / The non-destructive ultrasonic testing of acoustic anisotropic materials is an important challenge. The texture of these materials causes a strong scattering of the sound wave by the extensive grain boundaries and a direction dependent sound velocity by the acoustic anisotropy. Several approaches for the modelling of the sound propagation in anisotropic materials were presented in the last years. These approaches are normally based on FEM or FIT algorithms using a discretisation of the complete volume. Their calculation needs extensive time and a very complex parameterisation. Thus these algorithms are not suitable in practice of ultrasonic testing. In this work an approach is presented that is optimised for the application of phased array transducers. The new approach considers the real frequency spectrum of the transducer as well as all occurring wave modes in homogeneous transversely isotropic media, whereas other approaches are limited to solutions for single wave modes and single frequencies to reduce the calculation effort. The appropriate optimisations of the mathematical algorithm allow the fast calculation of the complete four-dimensional transient wave field of a phased array transducer in the half-space. The Green’s functions are derived by an analytical solution of the elastodynamic wave equation for the half-space. These functions will be transformed into an equation which will be referred to in this work as four-dimensional directivity pattern. This approach allows the verification of the parameters of a phased array system and their optimisation by iterative calculations in the practical application. To get accurate results in these calculations, the experimental verification of the applied mathematical model for the wave propagation is an essential task. The technique presented in this work applies electrodynamic probes, which provides a simple use. The probes can detect the particle displacement at a solid surface in all three spatial directions. The measured time-functions of the wave field will be compared with the calculated time-functions. They show a good accordance in the phase and the amplitude. This confirms that the applied mathematical model considers completely all in practice occurring wave modes. The results further show that three-dimensional problems in practice can be calculated correctly with this model.