Abstract

Animal borne data loggers are powerful tools that provide researchers with valuable insight into the behaviour and ecology of free-ranging marine animals. Despite their usefulness, the addition of a tag inevitably alters the forces acting on a swimming body and can increase the energetic cost of swimming. Computational Fluid Dynamics (CFD) tools offer a powerful means of assessing tag impact and a number of previous works have employed CFD to this end but have typically been based on a range of simplifying assumptions. Chief amongst these simplifications is that animals can be modelled as rigid bodies with a simple tag induced drag increase used as the primary measure of tag impact. Additionally, relatively little work has been conducted to validatethe results of such models.The main aims of this work were to determine how accurately CFD models based on the ’rigid body’ assumption can capture tag induced changes in the forces acting on a body and also to determine whether a self-propelled model of active swimming, a type of CFD model yet to be used in tag impact assessment, could yield more biologically relevant estimates of tag impact. Using case study bodies based on an anatomically correct harp seal (Pagophilus groenlandicus) and a commercially available tag, both types of model have been developed and validated in this thesis.Results suggest that the rigid body model is likely to under-predict the drag-impact imposed by a tag by around 16%, validation work indicates this is due to inaccurate prediction of the body surface pressure distribution in regions experiencing separated flow.The self-propelled model predicted that the addition of the tag reduced the swim speed achieved by the harp seal model during rectilinear motion by 0.72% while increasing the required output power by 1.45% when compared to the untagged body. Consequently the locomotory Cost of Transport increased by 2.15% when wearing a tag. An interesting observation was that the locomotory Cost of Transport values predicted by the self-propelled CFD model were in reasonable agreement with a published allometric scaling law relating body mass to Cost of Transport. This suggests that self-propelled models may yield both useful comparative and absolute estimates of tagimpact, particularly if the recommendations made at the end of this thesis are implemented.This work constitutes the first attempt to quantify tag impact using a self-propelled swimming model and also, to the best of my knowledge, the first study to attempt to determine the accuracy with which rigid body models can capture the change in forces generated by a tag. This combination of studies provides researchers with useful guidance in how CFD may be used to aid future tag design and development work.

Keywords

CFD, Marine mammal, Tagging, Tag impact, Self-propelled

Document Type

Thesis

Publication Date

2025

Embargo Period

2025-02-04

Creative Commons License

Creative Commons Attribution-NonCommercial 4.0 International License
This work is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License

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