|Robust Adaptive Dynamic Surface Control Based on Structural Reliability for a Turret-moored Floating Production Storage and Offloading Vessel
Yulong Tuo, Yuanhui Wang*, Simon X. Yang, Mohammad Biglarbegian, and Mingyu Fu
International Journal of Control, Automation, and Systems, vol. 16, no. 4, pp.1648-1659, 2018
Abstract : "For floating production storage and offloading (FPSO) vessels, a dynamic positioning controller is necessary
because using only a mooring system is not possible to keep the ship within a predefined region. Position
control of the FPSO vessel is extremely challenging due to model uncertainties and unknown control coefficients.
This paper develops a new robust adaptive positioning controller consisting of several components: adaptive law,
dynamic surface control (DSC) technology, sigmoid tracking differentiator (STD), Nussbaum gain function, and
structural reliability index. Model uncertainties can be estimated by the adaptive law derived from the Lyapunov
theory. The DSC technology is used to eliminate repeated differentiation by introducing first-order filtering of the
virtual control. The chattering-free STD with the characteristics of global fast convergence can estimate the derivatives
of model uncertainties that are difficult to calculate directly. Therefore, the DSC and STD techniques make
the proposed controller simpler to compute and easier to implement in engineering practice. Most of the traditional
controllers require the information about the control coefficients to guarantee the stability of the closed-loop system
while the Nussbaum gain function can remove the requirement for a priori knowledge of the sign of control
coefficients. The capacity of the mooring system can be fully utilized to position the FPSO vessel by adjusting the
structural reliability index on the premise of ensuring the safety of mooring lines, and hence less control effort is
needed for the positioning controller. Simulations using two sets of system parameters demonstrate the proposed
controller’s effectiveness. In addition, a qualitative comparison with the adaptive backstepping controller shows
that our proposed controller is computationally more efficient and does not require a priori knowledge of the sign
of control coefficients. A quantitative comparison with robust adaptive controller without the structural reliability
shows that less control effort is needed using our proposed controller."
Adaptive dynamic surface control, Nussbaum gain, positioning for ships, structural reliability index.