Abstract
Abstract. Physalia physalis, also called the bluebottle in Australia, is a colonial animal resembling a jellyfish that is well known to beachgoers for the painful stings delivered by its tentacles. Despite being a common occurrence, the origin of the bluebottle before reaching the coastline is not well understood, and neither is the way it drifts at the surface of the ocean. Previous studies used numerical models in combination with simple assumptions to calculate the drift of this species, excluding complex drifting dynamics. In this study, we provide a new parameterization for Lagrangian modelling of the bluebottle by considering the similarities between the bluebottle and a sailboat. This allows us to compute the hydrodynamic and aerodynamic forces acting on the bluebottle and use an equilibrium condition to create a generalized model for calculating the drifting speed and course of the bluebottle under any wind and ocean current conditions. The generalized model shows that the velocity of the bluebottle is a linear combination of the ocean current velocity and the wind velocity scaled by a coefficient (“shape parameter”) and multiplied by a rotation matrix. Adding assumptions to this generalized model allows us to retrieve models used in previous literature. We discuss the sensitivity of the model to different parameters (shape, angle of attack and sail camber) and explore different cases of wind and current conditions to provide new insights into the drifting dynamics of the bluebottle.
Highlights
Physalia physalis (Fig. 1), called the Indo-Pacific Portuguese man o’ war or the bluebottle (Physalia utriculus, a synonym), is well known on the east coast of Australia for stinging tens of thousands of beachgoers each year (Daw et al, 2020)
We have added the ocean background current to an existing theoretical model of aerodynamic and hydrodynamic forces acting on a bluebottle
We solve for an equilibrium condition to create a generalized vector model for the speed and course of the bluebottle
Summary
Physalia physalis (Fig. 1), called the Indo-Pacific Portuguese man o’ war or the bluebottle (Physalia utriculus, a synonym), is well known on the east coast of Australia for stinging tens of thousands of beachgoers each year (Daw et al, 2020). Totton and Mackie (1960) performed their own experiments and observed that in light winds (about 4 m s−1) the PMW balances itself at approximately 40◦ to the wind (angle of attack), resulting in a completely different course of about 45◦ relative to the wind In another experiment, Shannon and Chapman (1983) found that left- and right-handed specimens would separate by about 40◦ in force 7–8 winds (14–21 m s−1). Ferrer and González (2020) improved on the model from Ferrer and Pastor (2017) by analysing the same beaching event but incorporating dimorphism and different drift angles relative to the wind direction They found different regions of origin depending on the drifting angle considered and concluded that the PMWs were likely right-handed. We compare our results to previous studies and discuss some variables that were not included in the model (Sect. 6)
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
