Selected developments in computational electromagnetics for radio engineering

This thesis deals with the development and application of two simulation methods commonly used in radio engineering, namely the Finite-Difference Time-Domain method (FDTD) and the Finite Element Method (FEM). The main emphasis of this thesis is in FDTD. FDTD has become probably the most popular computational technique in radio engineering. It is a well established, fairly accurate and easy-to-implement method. Being a time-domain method, it can provide wide-band information in a single simulation. It simulates physical wave propagation in the computational volume, and is thus especially useful for educational purposes and for gaining engineering insight into complicated wave interaction and coupling phenomena. In this thesis, numerical dispersion taking place in the FDTD algorithm is analyzed, and a novel dispersion reduction procedure is described, based on artificial anisotropy. As a result, larger cells can be used to obtain the same accuracy in terms of dispersion error. Simulation experiments suggest that typically the dispersion reduction allows roughly doubling the cell size in each coordinate direction, without sacrificing the accuracy. The obtainable advantage is, however, dependent on the problem. In the open literature, a few other procedures are also presented to reduce the dispersion error. However, the rather dominating effect of unequal grid resolution along different coordinate directions has been neglected in previous studies. The so-called Perfectly Matched Layer (PML) has proven to be a very useful absorbing boundary condition (ABC) in FDTD simulations. It is reliable, works well in wide frequency band and is easy to implement. The most notable deficiency of PML is that it enlarges the computational volume - in open 3-D structures easily by a factor of two. However, due to its advantages, PML has become a standard ABC. In this thesis, the operation of PML in FDTD has been studied theoretically, and some interesting properties of it not known before are uncovered. For example, it is shown that, surprisingly, PML can absorb perfectly (i.e. with zero reflection) plane waves propagating towards almost arbitrary given direction at given frequency. Optimizing the conductivity profile allows reduction of the PML thickness. A typical application of the FDTD method is the design of a mobile handset antenna. An improved coaxial probe model has been developed for antenna simulations. The well-known resistive voltage source (RVS) model has also been discussed. A reference plane transformation is proposed to correct the simulated input impedance. A popular thin-wire model in 2-D FDTD is discussed, and it is shown to be based on erroneous reasoning. The error has been corrected by a simple procedure, and the corrected model has been demonstrated to simulate infinite long thin wires much better than the commonly used model. A novel way to implement singular basis functions in FEM is discussed. It is shown theoretically and demonstrated by examples that if a waveguide propagation mode contains field singularities, then explicit inclusion of singularities in finite element analysis is crucial in order to obtain accurate cut-off wavenumbers.reviewe

An Unfitted Higher-Order Discontinuous Galerkin Method for Incompressible Two-Phase Flow with Moving Contact Lines

The author presents an unfitted discontinuous Galerkin method for incompressible two-phase flow applicable to dynamic regimes with significant surface tension. The method is suitable for simulations in complex geometries and a recursive algorithm is proposed, which allows the generation of piecewise linear sub-triangulations re- solving both the domain boundaries and the interface between the two immiscible phases. Hence, discontinuous finite element spaces can be employed to capture the irregularities in the solution along the interface, i.e. the jump in the pressure field and in the velocity derivatives. While the sub-triangulation is based on a linear Cartesian cut-cell approach, its resolution is decoupled from the resolution of the finite element mesh thus enabling the application of higher-order finite element spaces. The time development of the two subdomains is realized by level set methods and an unfitted discretization for the solution of the corresponding equations is described. Multiple approaches for the numerical treatment of surface tension in the context of unfitted discretizations are discussed and compared. Furthermore, these methods are extended to allow simulations with contact lines taking into account the occurrence of microscopic deformations of the contact angle. All proposed methods are verified by numerical test simulations in two and three dimensions

Proceedings of the YIC 2021 - VI ECCOMAS Young Investigators Conference

The 6th ECCOMAS Young Investigators Conference YIC2021 will take place from July 7th through 9th, 2021 at Universitat Politècnica de València, Spain. The main objective is to bring together in a relaxed environment young students, researchers and professors from all areas related with computational science and engineering, as in the previous YIC conferences series organized under the auspices of the European Community on Computational Methods in Applied Sciences (ECCOMAS). Participation of senior scientists sharing their knowledge and experience is thus critical for this event.YIC 2021 is organized at Universitat Politécnica de València by the Sociedad Española de Métodos Numéricos en Ingeniería (SEMNI) and the Sociedad Española de Matemática Aplicada (SEMA). It is promoted by the ECCOMAS.The main goal of the YIC 2021 conference is to provide a forum for presenting and discussing the current state-of-the-art achievements on Computational Methods and Applied Sciences,including theoretical models, numerical methods, algorithmic strategies and challenging engineering applications.Nadal Soriano, E.; Rodrigo Cardiel, C.; Martínez Casas, J. (2022). Proceedings of the YIC 2021 - VI ECCOMAS Young Investigators Conference. Editorial Universitat Politècnica de València. https://doi.org/10.4995/YIC2021.2021.15320EDITORIA

CAD-integrierte Isogeometrische Analyse und Entwurf leichter Tragwerke

Isogeometric methods are extended for the parametric design process of complex lightweight structures. Three novel methods for the coupling of different structural elements are proposed: rotational coupling, implicit geometry description, and frictionless sliding contact. Moreover, the necessary steps for the integration of the numerical analysis, including pre- and post-processing, in CAD are investigated. It is possible to base several different analyses on each other in order to parametrically represent a construction process with multiple steps.Die isogeometrischen Methoden werden zur Anwendung im parametrischen Entwurfsprozess von komplexen Leichtbaustrukturen erweitert. Hierzu werden drei neue Methoden zur Kopplung unterschiedlicher Strukturelemente vorgeschlagen: Rotationskopplung, implizite Geometriebeschreibung und reibungsfreier Gleitkontakt. Ferner werden die nötigen Schritte zur Einbindung von Pre- und Postprocessing für numerische Simulationen in CAD untersucht. Mehrere unterschiedliche Analysen können auf einander folgen und werden verlinkt, um den Aufbauprozess in mehreren Schritten vollparametrisch abzubilden

GiD 2008. 4th Conference on advances and applications of GiD

The extended use of simulation programs has leaned on the advances in user-friendly interfaces and in the capability to generate meshes for any generic complex geometry. More than ten years of development have made Gid grow to become one of the more popular pre ans postprocessing systems at international level. The constant dialogue between the GiD development team and the users has guided the development of giD to cover the pre-post needs of many disciplines in science and engineering. Following gthis philosophy, the biannual GiD Conference has become an important forum for discussion and interchange of experiences among the GiD community. This monograph includes the contributions of the participants to the fourth edition of the GiD Conference held in the island of Ibiza from 8-9 May 2008

Workshop on the Integration of Finite Element Modeling with Geometric Modeling

The workshop on the Integration of Finite Element Modeling with Geometric Modeling was held on 12 May 1987. It was held to discuss the geometric modeling requirements of the finite element modeling process and to better understand the technical aspects of the integration of these two areas. The 11 papers are presented except for one for which only the abstract is given

SOLID-SHELL FINITE ELEMENT MODELS FOR EXPLICIT SIMULATIONS OF CRACK PROPAGATION IN THIN STRUCTURES

Crack propagation in thin shell structures due to cutting is conveniently simulated using explicit finite element approaches, in view of the high nonlinearity of the problem. Solidshell elements are usually preferred for the discretization in the presence of complex material behavior and degradation phenomena such as delamination, since they allow for a correct representation of the thickness geometry. However, in solid-shell elements the small thickness leads to a very high maximum eigenfrequency, which imply very small stable time-steps. A new selective mass scaling technique is proposed to increase the time-step size without affecting accuracy. New ”directional” cohesive interface elements are used in conjunction with selective mass scaling to account for the interaction with a sharp blade in cutting processes of thin ductile shells