OPTIMAL CONTROL OF AN UNDERSEA GLIDER IN A SYMMETRIC PULL-UP

Summary An undersea glider is a winged autonomous undersea vehicle which modulates its buoyancyto rise or sink and moves its center of mass to control pitch and roll attitude. By properlyphasing buoyancy and pitch control, an undersea glider rectifies the vertical motion causedby changes in buoyancy into forward motion caused by the lift force on the fixed wing. Thecharacteristic “porpoising” motion is useful in oceanographic surveys and the propulsionmethod is extremely efficient – undersea gliders routinely operate for months without humanintervention. Glider efficiency could be improved even further by addressing the phenomenonof “stall” (loss of lift) when a glider transitions from downward to upward flight. Becausethe stall phenomenon occurs asymmetrically over the vehicle’s wing, it can cause directionalerrors which must be corrected at a corresponding energetic cost. This paper describes theformulation of a point mass model and its dynamic equations of motion. An optimal controlformulationwas designed usingangleofattackandbuoyancy ascontrols toinvestigate controlscheduling methods for avoiding stall in a symmetric pull-up. The calculations were repeatedusing three different numerical solution techniques for comparison of the methodologies andresults. The model was updated to include longitudinal rigid body dynamics and changedthe control to the rate of change of the longitudinal center of gravity location. This modelallowed for the inclusion of added mass effects due to fluid displacement.i