Efficient Navigation of a Robotic Fish Swimming Across the Vortical Flow Field

TL;DR

This paper introduces a deep reinforcement learning algorithm with LSTM architecture to enable a robotic fish to efficiently navigate complex vortical flow fields, demonstrating robustness and adaptability in hydrodynamic environments.

Contribution

The study presents a novel DRL-based navigation method that effectively handles partial observations and complex fluid-structure interactions in vortical flows.

Findings

Robotic fish successfully navigates to target across vortical flows.

Algorithm leverages vortex-induced velocity and pressure differences.

Robust navigation from various initial positions.

Abstract

Navigating efficiently across vortical flow fields presents a significant challenge in various robotic applications. The dynamic and unsteady nature of vortical flows often disturbs the control of underwater robots, complicating their operation in hydrodynamic environments. Conventional control methods, which depend on accurate modeling, fail in these settings due to the complexity of fluid-structure interactions (FSI) caused by unsteady hydrodynamics. This study proposes a deep reinforcement learning (DRL) algorithm, trained in a data-driven manner, to enable efficient navigation of a robotic fish swimming across vortical flows. Our proposed algorithm incorporates the LSTM architecture and uses several recent consecutive observations as the state to address the issue of partial observation, often due to sensor limitations. We present a numerical study of navigation within a Karman vortex street, created by placing a stationary cylinder in a uniform flow, utilizing the immersed boundary-lattice Boltzmann method (IB-LBM). The aim is to train the robotic fish to discover efficient navigation policies, enabling it to reach a designated target point across the Karman vortex street from various initial positions. After training, the fish demonstrates the ability to rapidly reach the target from different initial positions, showcasing the effectiveness and robustness of our proposed algorithm. Analysis of the results reveals that the robotic fish can leverage velocity gains and pressure differences induced by the vortices to reach the target, underscoring the potential of our proposed algorithm in enhancing navigation in complex hydrodynamic environments.