Objective
Amphibious Uncrewed Ground Vehicles (AUGV) are an alternative platform for waterborne sensing that show promise for operation in the very shallow water and surf-zone subaqueous portions of the coastal profile, which can also be used on the adjacent sub-aerial shorelines. Prior operations and testing with AUGV by the project team have demonstrated evidence that waves and currents can at times lift AUGV, that there are slopes that may lead to vehicle instabilities, and substrates in which AUGV are immobilized, however, no prior work has explicitly quantified these operational constraints, and so it is unclear if these are solvable challenges through further platform development or unavoidable limitations of an AUGV. For this SEED work the project team will demonstrate the ability to develop a field and numerical testing framework which can be used to quantify effects on AUGV maneuverability due to vehicle-hydrodynamic and vehicle-seabed interaction, which is believed to present the first order controls on performance in a variety of benthic environments and is critical for determining the operational envelope and future research directions for AUGV.
Technical Approach
This research develops a framework to integrate field and numerical testing to explore AUGV maneuverability as a function of vehicle geometry, vehicle mass properties, sediment properties, seabed topography, and the environmental conditions. The field efforts will provide insight into AUGV operation in varying wave and current conditions, as well as different seabed types, taking precise measurements of vehicle traction and settlement processes. Field efforts will examine vehicle kinematics, track slippage, sinkage, or other immobilizing mechanics. The measurements from the field efforts will be used to inform and validate numerical modeling efforts which will focus on two areas: (1) the effects of hydrodynamics on vehicle motion using a coupling of a phase-resolved wave model (SWASH: Zijlema, 2011) and a Computational Fluid Dynamics model that is capable of FluidStructure Interaction, and (2) track-sediment modeling, simulate the soil-water-structure interaction between the tracks and the seabed to understand operability in a range of substrate types. Deliverables will include demonstration of the field and numerical analysis framework in two environments and synthesis in a final report of initial results and next steps.
Benefits
This work is intended to demonstrate what could be done with a combined modeling and field effort for vehicular mobility in the coastal environment. Follow-on work will continue the existing line of efforts, building performance curves of AUGV maneuverability (quantified as effects on vehicle mobility and localization) as a function of vehicle geometry, mass properties, sediment properties (such as grain size, undrained strength, etc.), seabed topography, and the environmental conditions (wave height, period, etc.) – information which will inform SERDP’s future investment in this technology. (Anticipated Project Completion - 2025)
References:
Zijlema, M., G. Stelling, and P. Smit. 2011. SWASH: An operational public domain code for simulating wave fields and rapidly varied flows in coastal waters. Coastal Engineering, 58(10):992-1012. doi.org/10.1016/j.coastaleng.2011.05.015.