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Roberto Verzicco, Università degli Studi di Roma ‘Tor Vergata’, Gran Sasso Science Institute, L’Aquila, and University of Twente, Enschede,Marco D. de Tullio, Politecnico di Bari,Francesco Viola, Gran Sasso Science Institute, L’Aquila
Major techniques for enhancing the bandwidth of magnetoelectric (ME) dipoles available in the literature are reviewed and discussed. Designs with single-input port and differential input ports are reported. Hopefully, it can help the readers to appreciate the beauty of these interesting designs and inspire innovative designs for future applications.
Roberto Verzicco, Università degli Studi di Roma ‘Tor Vergata’, Gran Sasso Science Institute, L’Aquila, and University of Twente, Enschede,Marco D. de Tullio, Politecnico di Bari,Francesco Viola, Gran Sasso Science Institute, L’Aquila
As the textbook is concerned with the application of immersed boundary methods for complex flow simulations, some general preliminary considerations are necessary in order to make the book self-consistent.
Basic concepts about fluids, their governing equations and the fundamentals relating to numerical integration are introduced and discussed.
Using a simple numerical example of the flow around a square cylinder, the relation between spatial numerical resolution and smallest flow scale is introduced and explained in connection with the successive requirements of immersed boundary methods.
A final discussion of the concepts of verification and validation of a numerical model closes the chapter.
Roberto Verzicco, Università degli Studi di Roma ‘Tor Vergata’, Gran Sasso Science Institute, L’Aquila, and University of Twente, Enschede,Marco D. de Tullio, Politecnico di Bari,Francesco Viola, Gran Sasso Science Institute, L’Aquila
In this chapter, techniques for size reduction of the magnetoelectric dipole available in the literature are reviewed. The relative advantages of employing the folded patch technique, dielectric-loaded method, and the metamaterial-loaded approach are compared. Designs with single-input port and differential input ports are also reviewed. Hopefully, possible new techniques will be achieved by readers after reviewing all these interesting designs.
Roberto Verzicco, Università degli Studi di Roma ‘Tor Vergata’, Gran Sasso Science Institute, L’Aquila, and University of Twente, Enschede,Marco D. de Tullio, Politecnico di Bari,Francesco Viola, Gran Sasso Science Institute, L’Aquila
When the flow and immersed object dynamics are two-way coupled, the problem is a fluid-structure interaction and additional changes are necessary to implement immersed boundary methods. Depending on the coupling between flow and structure solvers (loose or strong), the nature of the structure (rigid or deformable body) and the specific solution algorithms, several possibilities are available and this chapter aims at providing insights to guide the choice.
The performance of the basic linearly polarized magnetoelectric dipole is reviewed in detail to prepare the readers to appreciate other sophisticated designs in the chapters to follow. A new equivalent circuit of the antenna is given, which is different from the previous one proposed in the literature. The current density distributions on the antenna surfaces are provided to help understand the operating principle of the magnetoelectric antenna. The effect of ground plane size and sidewall height on the radiation patterns is given. Finally, a design guideline is suggested.
Substantial amount of work on the development of ME dipoles has been published by the originator’s group and other researchers and scholars over the past decade. It is now the appropriate time to review those findings and put those useful designs into appropriate perspectives. After providing the necessary background in understanding the importance of the ME dipoles in this introductory chapter, the detailed design guideline and performance of various ME dipoles with different characteristics will be presented and discussed in the chapters to follow.
Roberto Verzicco, Università degli Studi di Roma ‘Tor Vergata’, Gran Sasso Science Institute, L’Aquila, and University of Twente, Enschede,Marco D. de Tullio, Politecnico di Bari,Francesco Viola, Gran Sasso Science Institute, L’Aquila
Roberto Verzicco, Università degli Studi di Roma ‘Tor Vergata’, Gran Sasso Science Institute, L’Aquila, and University of Twente, Enschede,Marco D. de Tullio, Politecnico di Bari,Francesco Viola, Gran Sasso Science Institute, L’Aquila
This chapter is devoted to numerical examples and applications intended as tutorials for the interested reader. The possibility to download and use a computer code together with the book is given, and some of the described examples can be replicated using the provided code. The examples are of increasing complexity and they range from simple two-dimensional flows up to complex three-dimensional problems with fluid-structure interaction.
A detailed description of the computer code is also included in order to allow the readers to quickly get acquainted with the method and allow them to modify it according to their needs.
The inertial migration of neutrally buoyant spherical particles in viscoelastic fluids flowing through square channels is experimentally and numerically studied. In the experiments, using dilute aqueous solutions of polymers with various concentrations that have nearly constant viscosities, we measured the distribution of suspended particles in downstream cross-sections for the Reynolds number ($\textit{Re}$) up to 100 and the elasticity number ($El$) up to 0.07. There are several focusing patterns of the particles, such as four-point focusing near the centre of the channel faces on the midlines for low $\textit{El}$ and/or high $\textit{Re}$, four-point focusing on the diagonals for medium $\textit{El}$, single-point focusing at the channel centre for relatively high $\textit{El}$ and low $\textit{Re}$, and five-point focusing near the four corners and the channel centre for high $\textit{El}$ and very low $\textit{Re}$. Among these focusing patterns, various types of particle distributions suggesting the presence of a new equilibrium position located between the midline and the diagonal, and multistable states of different equilibrium positions were observed. In general, as $\textit{El}$ increases from 0 at a constant $\textit{Re}$, the particle focusing positions shift from the midline to the diagonal in the azimuthal direction first, and then inward in the radial direction to the channel centre. These focusing patterns and their transitions were numerically well reproduced based on a FENE-P model with measured values of viscosity and relaxation time. Using the numerical results, the experimentally observed focusing patterns of particles are elucidated in terms of the fluid elasticity-induced lift and the wall-induced elastic lift.
Roberto Verzicco, Università degli Studi di Roma ‘Tor Vergata’, Gran Sasso Science Institute, L’Aquila, and University of Twente, Enschede,Marco D. de Tullio, Politecnico di Bari,Francesco Viola, Gran Sasso Science Institute, L’Aquila
This chapter begins with a motivation to use computational models in scientific and technical applications. An overview of the advantages and drawbacks of numerical simulations with respect to laboratory experiments is given and advancements in various fields are discussed.
After this general introduction, a historical overview of the subject is presented and the present state of the art is discussed. In particular, it is shown that immersed boundary methods are being used in all fields of computational science and the number of scientific publications per year has been increasing with a constant acceleration over the past two decades: This has resulted in an exploding research field in which a reference textbook is still missing.
Finally, the objective of the book and the plan of the various chapters is given.
Roberto Verzicco, Università degli Studi di Roma ‘Tor Vergata’, Gran Sasso Science Institute, L’Aquila, and University of Twente, Enschede,Marco D. de Tullio, Politecnico di Bari,Francesco Viola, Gran Sasso Science Institute, L’Aquila
Various feeding techniques and antenna structures for achieving dual-polarized and circularly polarized ME dipoles will be reviewed. Since some circularly polarized ME dipoles can be developed from dual-polarized ME dipoles, these two classes of ME dipoles are considered and reviewed together here.
A partial differential equation governing the evolution of the joint probability distribution of multicomponent flow observations, drawn randomly from one or more control volumes, is derived and applied to examples involving irreversible mixing. Unlike local probability density methods, this work adopts an integral perspective by regarding a control volume as a sample space with an associated probability distribution. A natural and general definition for the boundary of such control volumes comes from the magnitude of the gradient of the sample space distribution, which can accommodate Eulerian or Lagrangian frames of reference as particular cases. The formulation exposes contributions made by uncertain or stochastic boundary fluxes and internal cross-gradient mixing in the equation governing the observables’ joint probability distribution. Advection and diffusion over a control volume’s boundary result in source and drift terms, respectively, whereas internal mixing, in general, corresponds to the sign-indefinite diffusion of probability density. Several typical circumstances for which the corresponding diffusion coefficient is negative semidefinite are identified and discussed in detail. The framework is a natural setting for examining available potential energy, the incorporation of uncertainty into bulk models, and establishing a link with the Feynman–Kac formula and Kolmogorov equations that are used to analyse stochastic processes.
The development of linearly polarized magnetoelectric (ME) dipoles operated at lower microwave frequencies is reviewed. Magnetoelectric dipoles can be fabricated at low costs, as they are purely made of metal plates at a few GHz range. Designs with modified L-shaped probe feeds for various purposes are first presented. Magnetoelectric dipoles with modified dipole shapes and feeds for enabling the antennas to be d.c. grounded are summarized. The aperture coupling technique was widely applied for the designs of microstrip antennas. Magnetoelectric dipoles with aperture-coupled feeds were also proposed in the literature. Their characteristics are presented. Differentially fed ME dipoles are also reviewed. The performance of ME dipoles for MIMO systems is discussed, which is of topical interest for 5G applications. Some recent applications of linearly polarized ME dipoles in different array environments are also presented.
Roberto Verzicco, Università degli Studi di Roma ‘Tor Vergata’, Gran Sasso Science Institute, L’Aquila, and University of Twente, Enschede,Marco D. de Tullio, Politecnico di Bari,Francesco Viola, Gran Sasso Science Institute, L’Aquila
This study is devoted to the analysis of capillary oscillations of a gas bubble in a liquid with an insoluble surfactant adsorbed on the surface. The influence of the Gibbs elasticity, the viscosities of the liquid and gas, as well as the shear and dilatational surface viscosities, on the damping of free oscillations is examined. Dependences of the frequency shift and the damping rate on the parameters of the problem are determined. In the limit of small viscosities and neglecting the surfactant surface diffusion, a simplified dispersion relation is obtained, which includes finite parameters of surface viscosities and Gibbs elasticity. From this relation, conditions are identified under which the damping of capillary oscillations can occur with a small frequency. Numerical solutions of the full dispersion relation demonstrate that a non-oscillatory regime is impossible for the considered configuration. An additional mode associated with Gibbs elasticity is discovered, characterized as a rule by low natural frequency and damping rate. Approximate relations for the complex natural frequency of bubble oscillations in a low-viscosity liquid in the presence of a surfactant are derived, including an estimate of the contribution of the gas inside the bubble to viscous dissipation. An original Lagrangian–Eulerian method is proposed and used to perform direct numerical simulations based on the full nonlinear Navier–Stokes equations and natural boundary conditions at the interface, accounting for shear and dilatational viscosities. The numerical data on the damping process confirm the results of the linear theory.
Roberto Verzicco, Università degli Studi di Roma ‘Tor Vergata’, Gran Sasso Science Institute, L’Aquila, and University of Twente, Enschede,Marco D. de Tullio, Politecnico di Bari,Francesco Viola, Gran Sasso Science Institute, L’Aquila
As IBMs have gained popularity, their use has expanded to multiphysics problems in which the Navier-Stokes equations are only one among many other possibilities. In this chapter, a list of advanced applications is described in which IBMs are used to solve heat transfer, phase change and chemical reaction problems. These examples are intended as suggestions to extend the application of immersed boundary methods to complex physics problems.