41 research outputs found
Parameterized macromodeling of passive and active dynamical systems
L'abstract è presente nell'allegato / the abstract is in the attachmen
System- and Data-Driven Methods and Algorithms
An increasing complexity of models used to predict real-world systems leads to the need for algorithms to replace complex models with far simpler ones, while preserving the accuracy of the predictions. This two-volume handbook covers methods as well as applications. This first volume focuses on real-time control theory, data assimilation, real-time visualization, high-dimensional state spaces and interaction of different reduction techniques
Finite difference and finite volume methods for wave-based modelling of room acoustics
Wave-based models of sound propagation can be used to predict and synthesize sounds as they would
be heard naturally in room acoustic environments. The numerical simulation of such models with traditional
time-stepping grid-based methods can be an expensive process, due to the sheer size of listening
environments (e.g., auditoriums and concert halls) and due to the temporal resolution required by audio
rates that resolve frequencies up to the limit of human hearing. Finite difference methods comprise a
simple starting point for such simulations, but they are known to suffer from approximation errors that
may necessitate expensive grid refinements in order to achieve sufficient levels of accuracy. As such, a
significant amount of research has gone into designing finite difference methods that are highly accurate
while remaining computationally efficient.
The problem of designing and using accurate finite difference schemes is compounded by the fact
that room acoustics models require complex boundary conditions to model frequency-dependent wall
impedances over non-trivial geometries. The implementation of such boundary conditions in a numerically
stable manner has been a challenge for some time. Stable boundary conditions for finite difference
room acoustics simulations have been formulated in the past, but generally they have only been useful
in modelling trivial geometries (e.g., idealised shoebox halls). Finite volume methods have recently
been shown to be a viable solution to the problem of complex boundary conditions over non-trivial
geometries, and they also allow for the use of energy methods for numerical stability analyses. Finite
volume methods lend themselves naturally to fully unstructured grids and they can simplify to the types
of grids typically used in finite difference methods. This allows for room acoustics simulation models
that balance the simplicity of finite difference methods for wave propagation in air with the detail of
finite volume methods for the modelling of complex boundaries.
This thesis is an exploration of these two distinct, yet related, approaches to wave-based room acoustic
simulations. The overarching theme in this investigation is the balance between accuracy, computational
efficiency, and numerical stability. Higher-order and optimised schemes in two and three spatial
dimensions are derived and compared, towards the goal of finding accurate and efficient finite difference
schemes. Numerical stability is analysed using frequency-domain analyses, as well as energy techniques
whenever possible, allowing for stable and frequency-dependent boundary conditions appropriate for
room acoustics modelling. Along the way, the use of non-Cartesian grids is investigated, geometric
relationships between certain finite difference and finite volume schemes are explored, and some problems
associated to staircasing effects at boundaries are considered. Also, models of sound absorption
in air are incorporated into these numerical schemes, using physical parameters that are appropriate for
room acoustic scenarios
Update On Hearing Loss
Update on Hearing Loss encompasses both the theoretical background on the different forms of hearing loss and a detailed knowledge on state-of-the-art treatment for hearing loss, written for clinicians by specialists and researchers. Realizing the complexity of hearing loss has highlighted the importance of interdisciplinary research. Therefore, all the authors contributing to this book were chosen from many different specialties of medicine, including surgery, psychology, and neuroscience, and came from diverse areas of expertise, such as neurology, otolaryngology, psychiatry, and clinical and experimental audiology