  We extend source seeking algorithms, in the absence of position and velocity
measurements, and with tuning of the surge input, from velocity-actuated
(unicycle) kinematic models to force-actuated generic Euler-Lagrange dynamic
underactuated models. In the design and analysis, we employ a symmetric product
approximation, averaging, passivity, and partial-state stability theory. The
proposed control law requires only real-time measurement of the source signal
at the current position of the vehicle and ensures semi-global practical
uniform asymptotic stability (SPUAS) with respect to the linear motion
coordinates for the closed-loop system. The performance of our source seeker
with surge force tuning is illustrated with both numerical simulations and
experiments of an underactuated boat.
