Propagation of Sonic Booms in Urban Landscapes

Open Access
- Author:
- Riegel, Kimberly A
- Graduate Program:
- Acoustics
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- December 13, 2011
- Committee Members:
- Victor Ward Sparrow, Dissertation Advisor/Co-Advisor
Ute Poerschke, Committee Member
David Carl Swanson, Committee Member
Anthony A Atchley, Committee Member - Keywords:
- Sonic Boom
Ray Tracing
Radiosity
Acoustics
Urban Environment - Abstract:
- A combined ray tracing/radiosity method for propagation of sonic booms was developed. The method was developed modularly so that complexity can be added and the radiosity part of the model can be turned off. The method is a high frequency approximation and models the shocks of the sonic boom most accurately. The model was compared to an image theory and a stochastic ray tracing model to validate its overall accuracy. This validation showed good agreement. The model was then used to simulate environments that were measured during the 2009 Sonic Booms On Big Structures (SonicBOBS) NASA experiment on Edwards AirForce Base. These environments were used for further validation to determine the accuracy when applied to a realistic sonic boom event. The Environmental Management (EM) building, a single building with surface irregularities, was examined. Facade features, diffusion and surface absorption were varied to determine their impact. The EM building showed good comparison to the measured data. The model was then used to simulate an environment with multiple buildings. This did not show good agreement between the simulated and measured data even for microphones that were not affected by the presence of additional buildings. The reason for this is the location of the multiple building environment on the edge of the boom carpet. It is concluded that the ray tracing/radiosity method is not valid for locations near the edge of the carpet. With these limitations in mind this model can successfully used to propagate sonic booms around buildings. The impact of absorption was shown to be minimal for a single building. The loss of energy to diffuse reflections reduced the amount of specularly reflected energy significantly. The complexity of the facade features did not improve the accuracy of the results enough to warrant the additional computation time and memory required. The method was then applied to an urban canyon environment. The perceived loudness (PLdB) on the sidewalk, the shape of the signal, and the pressure loading on the building wall were all examined. It was found that the PLdB increases as much as 7 dB from an environment with no buildings. While this increases the impact on people it does not drastically increase the impact over a single building environment. The PLdB can also be zero if it falls in a shadow zone. There was no observable trend between the parameters varied, building height, canyon width, initial boom elevation angle and azimuthal angle and the sound level. Varying diffusion did have a significant effect on both the signal shape and the PLdB on the sidewalk. Diffusion could significantly reduce the impact on people at the ground level.