Understanding the power requirements of autonomous underwater systems, Part I: An analytical model for optimum swimming speeds and cost of transport

Many marine species exhibit capabilities that would be desirable for manmade systems operating in the maritime environment. However, without detracting from the potential, if bioinspiration is to prove beneficial, it is important to have a consistent set of metrics that allow fair comparison, without bias, when comparing the performance of engineered and biological systems. In this study we focus on deriving an unbiased metric of performance applicable to marine animals and engineered subsea vehicles for one of the most fundamental of properties; that of the energy cost of locomotion. We present a rational analytical model of the physics behind the total energy cost of locomotion applicable to both biological and engineered autonomous underwater marine systems. This model proposes the use of an equivalent spheroid efficiency as a fair metric to compare engineered and biological systems. The model is then utilised to identify how changes in mass, speed, spheroid efficiency and hotel load impact the performance of the system.