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Grants: ONR Awards N000141712690 and N000141612216, NSF CMMI-1462825
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Autonomous marine vehicles (AMVs) are typically deployed for long periods of time in the ocean to monitor different physical, chemical, and biological processes. Given their limited
energy budgets, it makes sense to consider motion plans that leverage the dynamics of the surrounding flow field so as to minimize energy usage for these vehicles. This project focuses on developing suitable graph search based techniques to compute energy and/or time optimal
paths for AMVs in two- and three-dimensional time-varying flows (2D+1 and 3D+1). This project has contributed novel techniques that can capture the kinematic actuation
constraints on the vehicles in our cost functions, generate optimal paths in different homotopy classes, and employ an adaptive discretization scheme to construct the search graph. Our current efforts are focused on how best to leverage coherent structure information into our strategies.
This work is a collaboration between Dr. Subhrajit Bhattacharya at Lehigh University.
This work leverages the complimentary mobility and sensing capabilities of a network of heterogeneous robots that operate in remote oceanic environments, to efficiently collect information and effectively manage the volume of data collected. We consider the deployment of minimally actuated active drifters or similarly power-constrained mobile sensors. The active drifters periodically offload their sensory information to more capable robotic vehicles routed in a coordinated fashion through the drifter ensemble. Different from their passive counterparts, active drifters can adapt, albeit in a limited fashion, their sampling strategies to maximize information gain. When coupled with more capable autonomous surface, underwater, or even remotely operated vehicles (ASVs, AUVs, or ROVs), active drifters can significantly increase the spatial sampling reach of ASVs, AUVs, and ROVs. On the other hand, ASVs, AUVs, and ROVs can complement the sensing capabilities of active drifters since they have larger sensor payloads and reach regions not easily accessible to the active drifters due to actuation limitations. However, due to their severely limited power budgets, active drifters
must have the ability to plan and execute energy aware motion control and coordination strategies for data harvesting and rendezvous with AVUs and ASVs for data exchange and upload.
This work focuses on developing motion planning and control strategies for teams of mobile sensors with limited actuation capabilities or power budgets, i.e., active drifters, to harvest data and rendezvous with other autonomous vehicles. The proposed paradigm maximizes the impact of small, power constrained mobile sensors by leveraging the surrounding environmental dynamics to reduce their energy requirements. The objectives of this work are:
- To develop energy-aware motion control strategies for synchronous rendezvous by leveraging the dynamics of the fluidic environment;
- To synthesize distributed synchronous rendezvous strategies for a set of moving rendezvous
points whose motions are dictated by surrounding flow field;
- To develop a stochastic modeling and control framework where the individual average behavior can be specified and tuned to achieve the desired collective targets; and
- To validate the proposed strategies using the multi-robot Coherent Structure Testbed (mCoSTe).
Success of these endeavors will improve the autonomy and energy efficiency of various marine
platforms, directly affect the human’s abilities to navigate the oceans, increase the energy-efficiency of existing robotic sensor networks, and provide greater situational awareness for marine, coastal, and littoral applications. The research focuses on developing a general stochastic control framework for coordinated energy-aware motion planning and navigation that are important for power constrained unmanned systems. The expected outcomes include:
- Energy aware motion planning and control strategies for minimally actuated autonomous vehicles with limited power budgets;
- New stochastic control tools to enable large collectives of autonomous sensing resources to rendezvous in dynamic environments; and
- A novel modeling, control, and analysis framework for coordinating large collectives of collaborating autonomous unmanned systems subject to energy constraints.
Geophysical fluid dynamics (GFD) is the study of natural large-scale fluid flows, such as oceans, the atmosphere, and rivers. GFD flows are naturally stochastic and aperiodic, yet exhibit coherent structure. Coherent structures are important because they enable the estimation of the underlying geophysical fluid dynamics. While these transport controlling structures in GFD flows are inherently complicated and unsteady, their understanding is necessary for the design of robust underwater vehicle control and the prediction of various physical, chemical, and biological processes that in GFD flows. Nevertheless, the data sets that describe GFD flows are often finite-time and of low resolution and most transport controlling features in fluids are unstable and non-stationary, this renders the problem of “mapping” these features using teams of autonomous vehicles highly challenging.
The goals of this project are to overcome the theoretical and technical challenges and develop a general mathematical and control framework for distributed autonomous sensing and tracking of geophysical fluid dynamics in 2D space over time (2D+1) and in 3D space over time (3D+1). The key idea exploits the capability of the team to cover large regions in physical space to increase the spatio-temporal sampling resolution of the flow field. The data will then be processed in a distributed fashion by the team to obtain a global description of the flow dynamics that can be maintained and updated in real time. Objectives of this work include:
- Identifying and evaluating key kinematic features that control transport in oceanic surface flows of greatest relevance to autonomous vehicle navigation and control;
- Synthesizing distributed sensing and tracking strategies for a class of transport controlling features in 2D, 2D+1, 3D, and 3D+1 flows;
- Developing a general mathematical and control framework for teams of autonomous vehicles that leverages key transport controlling features in oceanic flows for improved navigation and monitoring of dynamic and uncertain environments;
- Developing a new control and coordination framework that leverages the disparate sensing, mobility, and computational capabilities within a heterogeneous teams of mobile robots for ocean monitoring;
- Experimentally validate the proposed strategies via a proof-of-concept robotic system with simulated and realistic flow data.
Grants: (ONR) Awards No. N000141211019 and No. N000141310731, NSF IIS-253917, NSF CMMI-1462825, NSF IIS-1724399.
Two Robots Straddling a Manifold in the Multi-Robot (MR) Tank
Two robots driving on opposite sides of the stable manifold of saddle point in an actual time-invariant flow created in the MR tank. The robots are obtaining measurements of the flow field using their onboard flow sensors which are capable of measuring both the speed and direction of the current relative to the robot’s movements. Global position for the robots are provided using an external OptiTrack motion capture system.
Tracking Lagrangian Coherent Structures
Three-robot manifold/LCS tracking strategy validated on a periodic wind-driven double-gyre model, experimental data, and actual ocean data.
Full simulation run three robots tracking the LCS off the coast of Santa Barbara, CA.