Buoyancy Glider Sawtooth

What is modelled

A 52 kg glider with 17 kg of added mass moves in the vertical plane. Pumping oil into an external bladder changes its displaced volume and so its net buoyancy. The wings turn that vertical force into forward motion.

Equations

• Net buoyancy B = ρ g ΔV, with ΔV the bladder volume change.
• Lift L = ½ ρ v2 S CL(α), drag D = ½ ρ v2 Ad, C_L = 3.35 α clipped at 1.12.
• RK4 integration of translation; the bladder and pitch actuators are rate limited.
• Battery E = Photel t + Ppump tpump.

Checks run in the page

• At steady glide the hydrodynamic force balances net buoyancy.
• The energy ledger for 200 s.
• Archimedes force for a given bladder volume.
• Depth and battery invariants of the live run.

Honest simplifications

Constant density, a fixed lift slope and a smooth current profile; no thermocline, biofouling or compressibility. This is an educational model, not a navigation tool.

• Increase the glide pitch: the glider sinks faster but covers less distance per cycle.
• Reduce the buoyancy engine stroke and watch the speed and battery use per kilometre.
• Pick Shallow profile in a current and see the surface current sweep the track sideways.