Connecting the fluid free-surface with the interior acoustic field
Abstract
"The aim of this proposed research is to connect observations of water surface effects in a complex flow (composed of ocean water, bubbles, and benthos) to a predictive knowledge of the acoustically relevant properties underneath, enabling an operationally-useful understanding of the shallow-water environment. Understanding or predicting an acoustic field requires fundamental knowledge of: (a) whether scatterers are present; (b) basic properties of the scatterers; (c) in cases where the scattering is very strong, knowledge of the coherent aspects including correlation in scatterer position. We hypothesize that observations of free surface perturbations of flows can inform important aspects of this acoustic problem, namely the knowledge that scatterers are present and measures of the coherent fluctuations in the scatterers themselves.We propose to study the connection between free-surface perturbations and the interior acoustic field using alaboratory case study of submerged aquatic vegetation. Under a constant current, a seagrass meadow can develop a flow instability that causes large-amplitude, synchronous waving of the meadow; the vortex structures that drive this phenomenon can also leave a periodic signature at the water surface. We will seed model seagrass blades with microbubbles and collect measurements of the acoustic field, coherent vegetation motion, and free-surface slope under a variety of experimental conditions. Measurements will then be compared with predictive acoustic models using experimental knowledge of both the scatterers and the fluid flow. The aim is to develop improved models for clustered scatterers, and tie these into models for the free-surface signature of the scatterers. While the case study proposed here uses submerged aquatic vegetation in order to leverage the PIs previous work, the results will be broadly applicable to other scenarios with preferentially concentrated scatterers and fluid surface signatures, such as river fronts, breaking waves, and subsurface gas seeps."
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Aug 05, 2021
- Source ID
- N000142112659
Entities
People
- Tracy Mandel
Organizations
- Office of Naval Research
- United States Navy
- University System of New Hampshire