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

Contributions to discrete-time methods for room acoustic simulation

The sound field distribution in a room is the consequence of the acoustic properties of radiating sources and the position, geometry and absorbing characteristics of the surrounding boundaries in an enclosure (boundary conditions). Despite there existing a consolidated acoustic wave theory, it is very difficult, nearly impossible, to find an analytical expression of the sound variables distribution in a real room, as a function of time and position. This scenario represents as an inhomogeneous boundary value problem, where the complexity of source properties and boundary conditions make that problem extremely hard to solve. Room acoustic simulation, as treated in this thesis, comprises the algebraical approach to solve the wave equation, and the way to define the boundary conditions and source modeling of the scenario under analysis. Numerical methods provide accurate algorithms for this purpose and among the different possibilities, the use of discrete-time methods arises as a suitable solution for solving those partial differential equations, particularized by some specific constrains. Together with the constant growth of computer power, those methods are increasing their suitability for room acoustic simulation. However, there exists an important lack of accuracy in the definition of some of these conditions so far: current frequency-dependent boundary conditions do not comply with any physical model, and directive sources in discrete-time methods have been hardly treated. This thesis discusses about the current state-of-the-art of the boundary conditions and source modeling in discrete-time methods for room acoustic simulation, and it contributes some algorithms to enhance boundary condition formulation, in a locally reacting impedance sense, and source modelling in terms of directive sources under a defined radiation pattern. These algorithms have been particularized to some discrete-time methods such as the Finite Difference Time Domain and the Digital Waveguide Mesh.Escolano Carrasco, J. (2008). Contributions to discrete-time methods for room acoustic simulation [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/8309Palanci

Urban Sound Planning - An attempt to bridge the gap

Cities are constantly between transition and adaptation, where current urban development needs a consistent strategic solution capable of understanding and including the relationships between urban form, environment and urban life. Awareness of the quality of the urban environment is leading the vision on the resilience and sustainability of the built environment, highlighting the importance of a multidisciplinary urban framework. One of the main concerns is the negative impact of outdoor noise due to road traffic. Europe and other parts of the world are experiencing a chronic traffic congestion problem and the environmental impact is overwhelming, where it is estimated that traffic-related noise (including road, rail and air traffic) in Western Europe causes the loss of at least one million years of healthy life each year, where the dominating source is road traffic. The aim of this thesis is to overcome negative aspects arising from a late intervention by including urban sound planning as an opportunity for the built environment. This means including the experience and wellbeing of users, avoiding poor patches in the urban configuration and economical burden. The present work is committed to the development of tools to control, communicate and design the sound environment on a level beyond today\u27s solutions, capable of being included in the early stages of the planning process through a holistic approach. The document is seen as a contribution to both professional practice and academic fields. In this sense, this thesis is an attempt to bridge the gap between future urban practice and the current situation in cities regarding the sound environment, through the role of sound urban planning. This is materialised from a variety of tools and approaches aimed at different spatial scales, times in planning, problems and opportunities, and fields of knowledge and contexts. First, the study goes through the urban sound planning idea and its opportunities and strategies. Thereafter, an overview highlights the threats and opportunities of urban sound planning implementation. Therefrom, the study goes into more detail about the strategies to address urban sound planning. As a starting point, the importance of the quiet side and the implementation of an engineering method as a powerful tool in urban development is investigated, obtaining accurate results in relation to measurements. In an attempt to study time variations of traffic within cities and their relevance with respect to noise emission (normally overlooked in current noise mapping calculations), a microscopic road traffic modelling tool is developed, giving useful output for noise level predictions as function of time. Time-pattern analysis opens the possibility of testing traffic configurations and exploring a wide variety of results in the form of descriptors such as statistical indicators, calm periods and noise events, and outcomes such as difference and contribution maps. The study extends to the evaluation of the effects of spatial heterogeneity (considered a key strategy to increase liveability of spaces) on the environmental performance and resilience capacity of the transportation system. For instance, the study of noise pollution and its economic impact gives ideas on the urban transformation possibilities when anticipatory and trans-disciplinary processes are pursued. The last study looks at the understanding and relevance of the sound environment in the use of common space. The intention is to identify suitable activities when certain sound environments and spatial characteristics are present (and vice versa), in an attempt to provide opportunities in the anticipatory design of public spaces. The studies presented use real case scenarios as a test bench not only for implementation, but mainly for the development of tools. The resulting tools developed in the thesis are: SWOT analysis of urban sound planning approach; Qside implementation model; Dynamic traffic noise assessment; Analysis matrix of indicators regarding urban form (diversity), transportation and the sound environment, studying the performance and resilience capacity; and Questionnaire about the study of common public spaces, activities and the sound environment