Subjective assessments of noise from aircraft flight operations require time histories of acoustic pressure at listener positions. Synthesized sound has an advantage over recordings by allowing the examination of proposed aircraft, flight procedures, and other conditions or configurations for which recordings are unavailable. Previous work by the authors [J. Acoust. Soc. Am. 113, 2245 (2003); 114, 2340 (2003); 116 2515 (2004)] focused on the development of a two-stage process for simulating flyover noise. The first stage entailed synthesizing the time histories at the flying source based on predictions of the source directivity. A second real-time rendering stage entailed propagation to a listener position on the ground, with binaural playback over headphones. More recently, loudspeaker based rendering was implemented for three-dimensional presentation in the NASA Langley Exterior Effects Room [J. Acoust. Soc. Am. 128, 2482 (2010); POMA 9, 015004 (2010)]. This paper discusses recent developments to the synthesis and rendering stages, including a new technique for sample-based synthesis of rotary wing sources, improvements to fan noise synthesis, and enhancements to ground plane simulation.

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The Exterior Effects Room (EER), located at the NASA Langley Research Center, is a facility built for psychoacoustic studies of aircraft community noise. Recently, the EER was significantly upgraded to allow for simulation of aircraft flyovers in a 3-D audio and visual environment. The upgrade included installation of 27 satellite and 4 subwoofer loudspeakers that are driven by a real-time audio server. The audio server employs an implementation of the vector base amplitude panning method to position virtual sources at arbitrary azimuth and elevation angles in the EER. Real-time application of filters, time delays, and gains are required to compensate for installation effects, including those associated with the irregular room geometry, colorization due to varying loudspeaker installations, and crossover filtering. The authors previously showed [J. Acoust. Soc. Am., 127, 1969 (2010)] that color compensation and crossover filtering could be achieved for satellite and subwoofer loudspeakers. However, the resulting FIR filters were too long (32 768 taps) to implement in real-time. The focus of this work is on the development of reduced-length surrogate IIR filters and on the measurement of the acoustic performance of the installed real-time system.

Robust design strategies continue to be relevant during concept-stage complex system design to minimize the impact of uncertainty in system performance due to uncontrollable external failure events. Historical system failures such as the 2003 North American blackout and the 2011 Arizona-Southern California Outages show that decision making, during a cascading failure, can significantly contribute to a failure's magnitude. In this paper, a scalable, model-based design approach is presented to optimize the quantity and location of decision-making agents in a complex system, to minimize performance loss variability after a cascading failure, regardless of where the fault originated in the system. The result is a computational model that enables designers to explore concept-stage design tradeoffs based on individual risk attitudes (RA) for system performance and performance variability, after a failure. The IEEE RTS-96 power system test case is used to evaluate this method, and the results reveal key topological locations vulnerable to cascading failures, that should not be associated with critical operations. This work illustrates the importance of considering decision making when evaluating system level tradeoffs, supporting robust design.