Dynamic model of scuba diver buoyancy

• Mathematical dynamic model of a diver with compressible BCD's was presented and simulated.
• Diver's vertical motion, compressible BCDs' volume and pneumatic valves volume flow dynamics were studied.
• The models have shown nonlinearities of a BCD's volume and pneumatic valves volume flows versus depth and the BCD's volume.
• Simulation models are validated with experimental BCD's tests and show excellent agreement.

Divers commonly use buoyancy vests for maintenance and changing depth. They do this by manually actuating two pneumatic valves that cause the jacket's volume to expand or shrink, thus changing its buoyancy. Divers desire for a device that would automatically modify or maintain depth has been present since the beginning of modern diving using a buoyancy vest. The need arises mainly when diving: where poor visibility is present; when both hands are needed for the job; during amateur dives; where decompression procedures are needed; to limit the maximum ascending speed; during a safety stop procedure; automatic ascending when a diver's life functions are critical but nevertheless using the same technology for changing depth in small modern submarines and submarine-like vessels. A prerequisite for successful buoyancy control is definitely knowledge of the system's behaviour based on mathematical modelling. This paper proposes a detailed dynamic model of a diver with all its accessories. The accuracy of the model was validated by comparing simulation results with the measurement results of various experiments.