This thesis discusses the process of modeling a 21,000 seat fan-shaped auditorium using methods of geometric acoustics. Two commercial geometric acoustics software packages were used in the research: CATT-Acoustic™ 8.0 and EASE™ 4.1. The process first included creating preliminary models of the hall using published absorption coefficients for its surfaces and approximate scattering coefficients based on current best-known techniques. A detailed analysis determined the minimum numbers of rays needed in both packages to produce reliable results with these coefficient values. It was found that 100,000 rays were needed for CATT™ and 500,000 rays were needed for EASE™. Analysis was also done to determine whether the model was sensitive to the scattering coefficients of the seating areas. It was found that most acoustic parameters were not significantly affected by scattering coefficient variation. The models were subsequently refined by including measured absorption coefficients of dominant surfaces in the hall: the seats, audience and suspended absorptive panels. Comparisons were made between measurements made in the hall and results from the computer models with impulse responses, acoustic parameters, and auralizations. The results have shown that the models have been successful at representing characteristics of the hall at some positions but less successful at representing them at other positions. Comparisons have shown that positions on the rostrum were especially difficult positions to model in this hall. Significant differences were not found between the preliminary models and the refined models. There was not significant evidence showing that either the EASE™ or the CATT™ model was more successful in accurately representing the acoustical conditions of the hall. The results from this research suggest that more work must be done to improve the modeling capabilities of these packages for this application.

This thesis presents a procedure to optimise the shape of a coaxial transducer ultrasonic flow meter. The technique uses separate numerical simulations of the fluid flow and the ultrasound propagation within a meter duct. A new flow meter geometry has been developed, having a significantly improved (smooth and monotonic) calibration curve. In this work the complex fluid flow field and its influence on the propagation of ultrasound in a cylindrical flow meter duct is investigated. A geometric acoustics (ray tracing) propagation model is applied to a flow field calculated by a commercial Computational Fluid Dynamics (CFD) package. The simulation results are compared to measured calibration curves for a variety of meter geometries having varying lengths and duct diameters. The modelling shows reasonable agreement to the calibration characteristics for several meter geometries over a Reynolds number range of 100...100000 (based on bulk velocity and meter duct diameter). Various CFD simulations are validated against flow visualisation measurements, Laser Doppler Velocimetry measurements or published results. The thesis includes software to calculate the acoustic ray propagation and also to calculate the optimal shape for the annular gap around the transducer housings in order to achieve desired flow acceleration. A dimensionless number is proposed to characterise the mean deflection of an acoustic beam due to interaction with a fluid flow profile (or acoustic velocity gradient). For flow in a cylindrical duct, the 'acoustic beam deflection number' is defined as M g* (L/D)^2, where: M is the Mach Number of the bulk velocity; g* is the average non-dimensionalised velocity gradient insonified by the acoustic beam (g* is a function of transducer diameter - typically g* = 0.5...4.5); L is the transducer separation; and D is the duct diameter. Large values of this number indicate considerable beam deflection that may lead to undesirable wall reflections and diffraction effects. For a single path coaxial transducer ultrasonic flow meter, there are practical limits to the length of a flow meter and to the maximum size of a transducer for a given duct diameter. The 'acoustic beam deflection number' characterises the effect of these parameters.