Conceptual and Control System Design of a Lagrangian Float

Abstract: Lagrangian floats are autonomous drifting buoys that ideally behave identicalto the surrounding water particles in the water column. Existing examples ofLagrangian floats are often costly and heavy, carrying expensive sensor anddata collection equipment, which prevents their scalability to larger fleets orbroader usage. There is significant oceanographic benefit to be expected fromthe deployment of a larger group of Lagrangian floats operating together tosample the environment during mission times of weeks or months, such asthe tracing of interval waves. The development of such a fleet of Lagrangianfloats realistically requires a scalable and low cost design, focused rather on asimple mechanical and low weight structure as opposed to elaborate sensingequipment. Therefore, the aim of this thesis is to firstly develop a designtool that allows user-friendly dimensioning of a Lagrangian float accordingto necessary conditions of feasibility. Secondly, this thesis presents a controlmechanism to autonomously adjust the float’s buoyancy. The control shouldfacilitate two operational modes: keeping a target depth in the presence ofdisturbances or uncertainties, and profiling the water column over a longperiod of time while neither consuming excessive energy nor risking the loss ofsignificant data collection. Future work will entail the mechanical realizationof the suggested prototype as well as improved nonlinear or adaptive controltechniques ideally tailored for internal wave trajectory following.