The Tulip in the Swan

As the frequency of rocket launches increases, accurately predicting their noise is necessary to assess structural, environmental, and societal impacts. NASA’s Space Launch System (SLS) is a challenging vehicle to model because it has both solid-fuel rocket boosters and liquid-fueled engines that contribute to its thrust at launch. This paper discusses measured aeroacoustic properties of this super heavy-lift rocket in the context of supersonic jet theory and measurements of other rockets. Using four measured aeroacoustic properties: directivity, spectral peak frequency, maximum overall sound pressure level, and overall sound power level, an equivalent rocket based on merged plumes is created for SLS. With the constraint that the effective thrust and mass flow rates should match those of the actual vehicle, a method using weighted averages of the disparate plume parameters successfully reproduces SLS’s desired aeroacoustic properties, yielding a relatively simple model for the complex vehicle.

Because their high-intensity sound fields pose hearing loss risk to personnel and increased community annoyance, high-performance military aircraft noise remains an important area of study. To help address these concerns, Brigham Young University has been analyzing noise from a T-7A-installed F404 engine. This paper presents an overview of key findings related to source characteristics and radiation properties and their connection to current jet noise models – both qualitative and quantitative. Included are three-source similarity spectrum decompositions, a sound power and acoustic efficiency analysis, an examination of convective Mach number effects on the radiated directivity, and holography and beamforming-based source description. This paper summarizes new understanding of tactical jet noise radiation characteristics.

For the past several years, Space Exploration Technologies Corporation (SpaceX) has been propulsively landing first stage rocket boosters for reuse. Because the boosters return at supersonic speeds, they produce a sonic boom. As the landing cadence continues to increase, it is important to understand these sonic booms and how they propagate to the surrounding areas. This abstract reports on measurements made of the SpaceX Transporter-8 launch and landing of a Falcon-9 rocket at Vandenberg Space Force Base. A unique triple-boom shape is preserved over propagation distances as close as 300 m and as far as 25 km from the landing pad. At distances greater than about 1 km, the sonic boom peak overpressure exceeds the launch peak pressure. Additionally, sound exposure metrics indicate that the sonic boom itself is comparable to the rest of the launch noise. Conclusions from these results include that sonic booms should be considered alongside launch noise when considering sound exposure and that there remain several mysteries regarding the propagation of these unique triple booms.

Many material properties can be traced back to properties of their grain boundaries. Grain boundary energy (GBE), as a result, is a key quantity of interest in the analysis and modeling of microstructure. A standard method for calculating grain boundary energy is molecular dynamics (MD); however, on-the-fly MD calculations are not tenable due to the extensive computational time required. Lattice matching (LM) is a reduced-order method for estimating GBE quickly; however, it has only been tested against a relatively limited set of data, and does not have a suitable means for assessing error. In this work, we use the recently published dataset of Homer et al. (2022) to assess the performance of LM over the full range of GB space, and to equip LM with a metric for error estimation. LM is used to generate energy estimates, along with predictions of facet morphology, for each of the 7,304 boundaries in the Homer dataset. The relative and absolute error of LM, based on the reported MD data, is found to be 5%-8%. An essential part of the LM method is the faceting relaxation, which corrects the expected energy by convexification across the compact space (S2) S 2) of boundary plane orientations. The original Homer dataset did not promote faceting, but upon extended annealing, it is shown that facet patterns similar to those predicted by LM emerge.

Due to the difficulty and expense of underwater field trials, a high-fidelity underwater simulator is a necessity for testing and developing algorithms. To fill this need, we present HoloOcean, an open-source underwater simulator, built upon Unreal Engine 4 (UE4). HoloOcean comes equipped with multiagent support, various sensor implementations of common underwater sensors, and simulated communications support. Due to being built upon UE4, new environments are straightforward to add, enabling easy extensions to be built. HoloOcean is controlled via a simple Python interface, allowing simple installation via pip, and requiring few lines of code to execute simulations. Each agent is equipped with various control schemes and dynamics that can be customized via the Python interface. Also included is a novel sonar sensor framework that leverages an octree representation of the environment for efficient and realistic sonar imagery generation. In addition, to improve the authenticity of the imaging sonar simulation, we use a novel cluster-based multipath ray-tracing algorithm, various probabilistic noise models, and properties of reflecting surfaces. We also leverage the sonar simulation framework to simulate sidescan, single-beam, and multibeam profiling sonars.