Acoustic modelling of bat pinnae utilising the TLM method

This thesis describes the numerical modelling of bioacoustic structures, the focus being the outer ear or pinnae of the Rufous Horseshoe bat (Rhinolophus rouxii). There have been several novel developments derived from this work including: • A method of calculating directionality based on the sphere with a distribution of measuring points such that each lies in an equal area segment. • Performance estimation of the pinna by considering the directionality of an equivalent radiating aperture. • A simple synthetic geometry that appears to give similar performance to a bat pinna. The outcome of applying the methods have yielded results that agree with measurements, indeed, this work is the first time TLM has been applied to a structure of this kind. It paves the way towards a greater understanding of bioacoustics and ultimately towards generating synthetic structures that can perform as well as those found in the natural world

13th Annual Review of Progress in Applied Computational Electromagnetics at the Naval Postgraduate School, Monterey, CA, March 17-21, 1997, Conference Proceedings Volumes I & II

Includes Volumes 1 &

Modeling EMI Resulting from a Signal Via Transition Through Power/Ground Layers

Signal transitioning through layers on vias are very common in multi-layer printed circuit board (PCB) design. For a signal via transitioning through the internal power and ground planes, the return current must switch from one reference plane to another reference plane. The discontinuity of the return current at the via excites the power and ground planes, and results in noise on the power bus that can lead to signal integrity, as well as EMI problems. Numerical methods, such as the finite-difference time-domain (FDTD), Moment of Methods (MoM), and partial element equivalent circuit (PEEC) method, were employed herein to study this problem. The modeled results are supported by measurements. In addition, a common EMI mitigation approach of adding a decoupling capacitor was investigated with the FDTD method

Investigation of charged aerosol transport and deposition in human airway models

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.Several theoretical and experimental studies of charged aerosol deposition in human airways have been reported. These studies suggest that higher charge values on particles lead to improve deposition efficiency in the human lung, especially in the alveolar region. Most of the previous numerical studies in realistic 3D geometrical models have been investigated only for uncharged particles. Hence, this research was aimed at numerically investigating aerosol transport and deposition by including the effect of electrostatic forces (both space and image charge forces). The numerical models that have been developed and presented in this thesis, treat the aerodynamics and electrodynamics as a coupled problem and successfully integrate both mechanisms. The physical model of the human lung used for this research consists of three sub-models: a 3D bifurcation airway model, a 3D reconstructed airway model representing the tracheobronchial region, and a 2D alveolar airway model representing the alveolar region. The airflow dynamics in these geometrical models were carried out using a Computational Fluid Dynamic software (CFD) with given boundary conditions related to corresponding breathing conditions. The space charge force was calculated using the Particle Mesh (PM) method, and the image charge force was computed using the mesh configuration. Both airflow dynamics and electrodynamics are integrated in the newly developed software, and the particle trajectories are then calculated. The numerical study of electrostatic forces is primarily focused on the submicron particle. The numerical study in the 3D tubular airway model gives a better understanding of parameters affecting the predicted deposition efficiency. The numerical study in the 3D tubular airway model focuses on the transport and deposition of particles near the branching regions between the parent and daughter tubes, where airflow profile is significantly altered, and secondary airflow also arises. Many charged particles are deposited near the carinae by the strong skewed axial velocity and image charge force. The space charge will influence the deposition efficiency if the number concentration of particles is high. Similarly, the charged particles in the 3D reconstructed airway model tends to have the deposition pattern near the branching regions, depending on the local airflow and charge value. In the 2D alveolar model, the image charge force can improve deposition efficiency. The outcome of this research clearly shows how the electrostatic forces play an important role in aerosol transport and deposition in human airways. The integrated numerical model provides a valuable tool for respiratory clinicians and the pharmaceutical industry to study the complex mechanism of drug aerosol deposition in human airways. Although this model is adequate for the intended purpose, it can be further improved by extending this work to develop a complete 3D model of entire human airways incorporating the full breathing cycle. Such a model would require extensive computing facilities, nevertheless it would be an enormous benefit to develop a better treatment for respiratory diseases.Financial support obtained from the Overseas Research Students Awards Scheme (ORS)and System Engineering department

Efficient Light and Sound Propagation in Refractive Media with Analytic Ray Curve Tracer

Refractive media is ubiquitous in the natural world, and light and sound propagation in refractive media leads to characteristic visual and acoustic phenomena. Those phenomena are critical for engineering applications to simulate with high accuracy requirements, and they can add to the perceived realism and sense of immersion for training and entertainment applications. Existing methods can be roughly divided into two categories with regard to their handling of propagation in refractive media; first category of methods makes simplifying assumption about the media or entirely excludes the consideration of refraction in order to achieve efficient propagation, while the second category of methods accommodates refraction but remains computationally expensive. In this dissertation, we present algorithms that achieve efficient and scalable propagation simulation of light and sound in refractive media, handling fully general media and scene configurations. Our approaches are based on ray tracing, which traditionally assumes homogeneous media and rectilinear rays. We replace the rectilinear rays with analytic ray curves as tracing primitives, which represent closed-form trajectory solutions based on assumptions of a locally constant media gradient. For general media profiles, the media can be spatially decomposed into explicit or implicit cells, within which the media gradient can be assumed constant, leading to an analytic ray path within that cell. Ray traversal of the media can therefore proceed in segments of ray curves. The first source of speedup comes from the fact that for smooth media, a locally constant media gradient assumption tends to stay valid for a larger area than the assumption of a locally constant media property. The second source of speedup is the constant-cost intersection computation of the analytic ray curves with planar surfaces. The third source of speedup comes from making the size of each cell and therefore each ray curve segment adaptive to the magnitude of media gradient. Interactions with boundary surfaces in the scene can be efficiently handled within this framework in two alternative approaches. For static scenes, boundary surfaces can be embedded into the explicit mesh of tetrahedral cells, and the mesh can be traversed and the embedded surfaces intersected with by the analytic ray curve in a unified manner. For dynamic scenes, implicit cells are used for media traversal, and boundary surface intersections can be handled separately by constructing hierarchical acceleration structures adapted from rectilinear ray tracer. The efficient handling of boundary surfaces is the fourth source of speedup of our propagation path computation. We demonstrate over two orders-of-magnitude performance improvement of our analytic ray tracing algorithms over prior methods for refractive light and sound propagation. We additionally present a complete sound-propagation simulation solution that matches the path computation efficiency achieved by the ray curve tracer. We develop efficient pressure computation algorithm based on analytic evaluations and combine our algorithm with the Gaussian beam for fast acoustic field computation. We validate the accuracy of the simulation results on published benchmarks, and we show the application of our algorithms on complex and general three-dimensional outdoor scenes. Our algorithms enable simulation scenarios that are simply not feasible with existing methods, and they have the potential of being extended and complementing other propagation methods for capability beyond handling refractive media.Doctor of Philosoph

Biomechanical Soft Tissue Modeling - Techniques, Implementation and Application

The reaction of soft tissue to applied forces can be calculated with biomechanical simulation algorithms. Several modeling approaches exist. A scheme is suggested which allows the classification of arbitrary modeling approaches with respect to the degree of physical realism contained in the model (physical and descriptive models). Besides well known approaches like mass-spring, finite element, particle models and others the ChainMail algorithm is investigated. Where ChainMail in its original formulation lacked the capability to model inhomogeneous material, it is exceptionally stable and converges in one step to a valid configuration. In this thesis ChainMail is generalized to the Enhanced ChainMail algorithm which is capable to model inhomogeneous, volumetric objects and is fast enough for real time simulations. While now in principle being able to simulate and visualize an object in real time, a software architecture is required to team up simulation and visualization. As visualization and simulation have so far evolved independently, they work with different data structures. Multiplicity of data representations leads to the problems of data consistency and high memory consumption. A software architecture is developed which provides a universal data structure for several simulation and visualization approaches. The versatility of the developed architecture is demonstrated by two medical simulations. The first is the simulation of an intra-ocular surgery, which makes heavy use of Virtual Reality techniques. Designed as a training and educational tool the simulator EyeSi relies on descriptive real time ti me tissue simulation and visualization. The second deals with the simulation of decompressive craniotomy. The medical problem requires a physical model as the project's goal is to provide exact predictions on tissue behavior to support surgeons in surgery planning