Virtual Tether Search: A self-constraining search algorithm for swarms in an open ocean

Underwater robotic swarms have more challenging operating conditions when compared to their ground counterparts. One such major limitation is vastness of the oceanic environment, which significantly increases the possibility of losing swarm members. Although swarms can tolerate losses, if care is not taken in the design of swarm-level behaviors, they can cause a complete failure of the mission. An additional design factor for such systems is, therefore, the spatial constrained-ness of the swarm. Virtual Tether Search (VTS) has been developed to address this concern. Robots use a virtual tether attached to the drop-off location along with dead-reckoning to stay within a maximum-radius distance from that location. Constrained Spiral Flocking (CSF), a previously developed algorithm, Robotic Particle Swarm Optimization (R-PSO), and Simple Sweeping (SSW) are compared to VTS and pros and cons of each algorithm are highlighted. VTS is shown to have a superior behavior in terms of omni-directionality and loss-prevention at the expense of relatively slow, but guaranteed convergence.