Control of Autonomous Underwater Vehicles in Stratified Fluids and Near Surface Operations
Abstract
Background Submarine hull hydrodynamics and propeller performance are generally well-characterized in open water conditions. Techniques for depth, speed, and heading control in open water are thus well understood and straightforward to automate on unmanned platforms. However, when operating near the surface, in the presence of obstacles, or in stratified flows with steep density gradients, there can be significant additional interactions between hull, propulsor, and control surfaces and the surrounding fluid. These poorly modeled interactions can result in undesirable behaviors, including loss of depth control and breaching. Control problems are especially acute when operating at slow speeds, as dive planes and rudders require forward speed in order to maintain control authority. NSWC-Carderock has a long term responsibility for maintaining subject matter expertise in dynamic modeling and control of underwater vehicles. NSWCCarderock is also charged with advancing the current state of the art in submarine hydrodynamics, control, and autonomy. The proposed effort is designed to address both of these needs. Over the course of this effort, we will introduce students seeking Bachelors, Masters, and Ph.D. degrees to fundamental principles of underwater vehicle modeling, simulation and control through hands-on experimental research, enhanced course offerings, and direct involvement with research efforts performed in collaboration with NSWC-Carderock engineers. Project Goals (Technical) The technical goals of this effort will be to develop adaptive depth control strategies for overactuated underwater vehicles in stratified flow and to characterize the nonlinear depth dynamics of cross-body internal and external thrusters near the surface. To meet the first goal, we will validate a ‘complementary allocation’ approach to the control of over-actuated underwater vehicles, in order to reduce hull drag, control effort, and propulsion power for vehicles operating in fluids with varying density. To meet the second goal, we will develop and validate reduced order models of unintended depth forcing due to thruster jet wake effects during maneuvering with cross body thrusters. Project Goals (Recruitment and Training) Training and recruitment for the Naval laboratories is the primary purpose of the NEEC. The proposed effort is designed to train selected high quality students while maximizing their exposure to NSWC-Carderock staff and facilities. The recruitment goal for this effort will be to facilitate offers of full time employment at NSWC to at least one student per year. Undergraduate and graduate students who participate in the effort will be trained to perform vehicle hydrodynamic and maneuvering tests, and to process, analyze, and interpret the resulting data. They will also learn to script unmanned underwater vehicle (UUV) missions and troubleshoot UUV operations. The graduate student will additionally be able to quantify hydrodynamic forces acting on maneuvering UUVs, create dynamic simulations of maneuvering UUVs, and design and test UUV control algorithms in simulation and experiment.
Document Details
- Document Type
- DoD Grant Award
- Publication Date
- Jul 29, 2020
- Source ID
- N001741910019
Entities
People
- Stephen Licht
Organizations
- United States Navy
- University of Rhode Island