ABSTRACT Floating Production Storage and Offloading (FPSO) vessels for offshore operations use a Dynamic Positioning system (DP), which includes a controller to correct the position variation of the FPSO subject to internal and external disturbances. Most of these positioning systems use a classic Proportional Integral Derivative controllers (PID) and their deferent variants, where the control law is determined adjusting three control gains: proportional, integral and derivative, usually heuristic techniques are employed to determine the control gains. In this study we propose a theoretical tuning procedure in order to determine the control gains in a simple way, analyzing the boundary conditions in the matrices of the FPSO dynamic model, as well as the relation they have with the control gains for the FPSO motion in an adjust domain. In order to guarantee the semi-global stability of the closed-loop system, a stability proof in the Lyapunov sense is carried out. The theoretical results were validated in numerical simulations using Matlab. These results show that the methodology presented in this work is highly satisfactory for the control gain selection in the trajectory tracking control problem for FPSO motion. INTRODUCTION A Floating Production, Storage and Offloading (FPSO) system is considered in this paper. In the last two decades FPSOs have been the dominant offshore platforms used in oil and gas fields. Fig. 1 shows the Ta'Kuntah FPSO, which was the first FPSO operated in the Cantarell Field in the Gulf of Mexico. A FPSO can be operated in deep water and sometimes must perform maneuvering movements and marine activities with other vessels as shown in Fig. 2 (Tamuri, 2009), these activities involve huge risks due to the environmental random forces presence, affecting the normal operation and sometimes causing severe accidents (Moan, 2002) and lack stability (Chen, 2008). In offshore basically there are two ways to maintain the FPSO position, the first is by Mooring Positioning (MP) and the second by Dynamic Positioning (DP) (Sorensen, 1996; Sorensen, 1997). In DP the principal advantage is the immediate positioning on a required set point, in other hand the MP systems are limited to operate about 500m (Veksler, 2016).

ABSTRACT: An adaptive operation of a disturbance accommodating controller(DAC) depending on the seastate number for roll motion of a ship is suggested. DAC suggested in this paper assumes the shape of the disturbance, i. e. the wave slope excitation as a harmonic signal that consists of two sine waves of different frequencies and the dynamic model of this kind of disturbance is adopted in the controller to estimate the disturbance from the measurement of roll and to generate the control force to counteract exactly the estimated disturbance. Frequencies of the disturbance model used in the controller are selected so that the energy of the roll response in each seastate is to be minimized. Pole placement technique is combined to enhance the performance of DAC. A necessity of an adaptation scheme i. e. tuning the suggested DAC according to the varying sea environment is also shown by the results of the performance assessment of DAC's with different sets of design frequencies optimized for each seastate. INTRODUCTION Major developments of ship motion theories have been said to be attributed to two important foundations : the development of strip theory and the treatment of ship motions in irregular waves as the ‘black box’ eletronic filter. "The signal received by the filter contains a number of different frequency components and these are amplified or attenuated to produce some modified output signal according to the characteristics of the filter. Extendng the latter idea further into modeling the wave elevation or the wave slope as a filter of the white noise lets us adopt the stochastic control theory in suppressing the unwanted ship motions (Sgobbo and Parsons, 1999) or enhancing the estimation of the state-variables of ship motions in irregular waves (Reid et al., 1984; Triantafyllou and Athans, 1981).

ABSTRACT: In this paper, by dividing a multivariable system into single inputoutput systems by a decoupling technique and adding feedback control loops to each single input-output system, the author has tried to design an automatic control system to satisfy our specifications for control system design, as specified in the body of the paper. A rational and clear design of a multivariable control system is proposed. The fundamental characteristics of the control system are shown analytically, and examined by computer simulation. This control system combining decoupling and PI action feedback controls shows good tracking and disturbance control ability and is effective and useful during the approach and berthing maneuvers. INTRODUCTION Systems are generally multivariable, usually with coupling systems as shown in the top figure of Fig. 1. If the system can be divided so as to have an input-output relation of one-to-one correspondence as shown in the bottom figure of Fig. 1, it will be easier to design the control system. It is also important that the control system not only be able to perform the desired task, but that it also be able to compensate for disturbances. Ships are multivariable systems. Every input that is fed into a shipsystem has an effect on every output in the ship-system. Both functions must be factored into any control system. As an example, selecting the propeller and bow and stern thrusters as final control elements and ship speed, lateral shift displacement and heading angle as controlled variables, the author divides the multivariable system into three single input-output systems by use of a decoupling technique, and adds feedback control loops to each single input-output system. Furthermore, a rational and clear design method of the control system that satisfies our specifications for control system design is proposed.

ABSTRACT: Current control system for fully-submerged hydrofoil based on optimal feedback control has several problems, such as it has no good performance of contouring waves and it cannot reduce the effect of wave disturbance. In this paper, the longitudinal control system for fully-submerged hydrofoil based on optimal preview servo system was proposed to settle the problems of current control system. The proposed control system is composed of feedback control input and feedforward control input which are calculated by using future information of reference input and wave disturbance. And also, in order to design the proposed control system, the necessary prediction range of future information and the weight function in performance index are determined. Finally the validity of the proposed control system is confirmed by simulation. The research results show that the proposed control system has good performance of contouring waves in the follow sea and reduce the effect of wave disturbance. And also the research results show that the proposed control system is effective to settle the problems of current control system for fully-submerged hydrofoil. INTRODUCTION Fully-submerged hydrofoil is essentially configured to provide good ride quality and speed performance since it is free from water (Weist and Mitchell, 1976). And the control system is efficient to stabilize or to argument stability of the hydrofoil. The current automatic control system (ACS) of hydrofoil is designed by optimal feedback gain theory, inertial sensor signals and ultrasonic sensor signals. And this includes platform and contour mode selection and manual input of fore foil depth by human operator. The contour mode is to keep foil depth in waves to avoid cresting and exposing of foil. And the manual input of fore foil depth is performed to strengthen contouring waves (Saito and Kuroi, 1989; Saito and Ikebuchi, 1990).

ABSTRACT: Based on the proper description of the condition at infinity for nonlinear surface wave diffraction In physical sense, the high order asymptotic solution as well as the Inhomogeneous boundary condition at infinity for second order surface wave diffraction are obtained. It contributes a complete and rational mathematical model towards the problem, and clarifies the controversy rising among a lot of works about it. I. INTRODUCTION Stokes perturbation expansion has been recognized as an effective method valid for the solution of mild nonlinear sun-ace wave diffraction. The first order wave diffraction theory, i.e., the linear diffraction theory, based on the expansion, is complete and rational in Its mathematical formulation. However, for the diffraction problems of second order and higher orders, the free surface boundary condition is inhomogeneous. The right-hand side inhomogeneous term is recognized as pressure disturbance distributed infinitely on the free surface. Consequently, the question is how to properly define the boundary condition at infinity for the surface wave diffraction problems of second order and higher orders to be consistent with this kind of pressure disturbance. In the context of second order problem, a lot of papers have been published previously [1-5, 7-13]. However, even for the wave diffraction against a vertical cylinder, many solutions of second order problem obtained by different authors exhibit obvious differences, which are partly affected by distinct forms of boundary condition at infinity presented In those papers. II. PHYSICAL CONDITION AT INFINITY FOR SECOND ORDER DIFFRACTION PROBLEM Essentially, the surface wave diffraction phenomenon is the wave motion generated by some active disturbance at infinity and existing in the flow field where some structures of large scale is located. For the nonlinear surface wave diffraction problem, we can't define the physical condition at infinity of assuming an active disturbance source at Infinity.