Abstract This paper considers the control system design problem of a barge type surface vessel。 The main role of a barge ship is to carry and supply cargo and materials to floating units and other marine locations。 To carry out this job, the barge ship has to be positioned in a specified area。 Although thrust systems are installed on the ship, in general, the mooring winch system with cable is used。 Therefore, this paper proposes a single type mooring winch system and a method of designing a control system。 We propose a mathematical model of the vessel winch control system, and the reliability of the control system is verified by numerical calculations and experiments。 In addi- tion, a cable model is constructed from the experimental data to identify the characteristic of cable motion, which is unknown in general and considered as an uncertainty。 Based on these results, a robust control system is designed, and its control performance evaluated by simulation and experiment show that the proposed approach works well。95138

Keywords: Barge type surface vessel; Dynamic positioning system (DPS); Mooring winch; Mathematical model; Robust  control

1。 Introduction

Fixed or floating units are frequently positioned at a particu- lar spot in the ocean and stationary conditions must be main- tained depending on their purpose and use。 Ships either stand by inside the harbor or dock at the quay along the bank。 The drill ship and its special purpose marine equipment such as rigs, FPSO, and barges maintain a steady position on the ocean’s surface for a long time to extract deep sea natural resources。 To move from one marine location to another ma- rine location, these fixed or floating units either use their own self-propelling apparatus or they use the passive method of being towed by tugboats。 In some cases such as FPSOs and drill ships that are engaged in extracting materials and the floating units that are supporting the extraction works, their stationary position has to be limited to within the error margin of several meters。 When fixed position control is required, in general, the side thruster and the mooring winch are used as the two basic position control systems。 The mooring winch system installs a proper number of winches on the marine surface structures and moving units, and the winches are oper- ated to control the posture and position of the floating units by controlling the tension of the ropes。 This is a topic that has been studied by many researchers throughout the world。 Re- search  on  this  topic  has  been  limited  mostly  to theoretical

research on mechanics and dynamics of winch designing [1-9]。 For example, Fossen and Amao [1] presented a model for the mooring system based on analyzing cable dynamics with higher-order, and extended results about dynamic positioning (DP) was obtained by Berntsen et al。 [2]。 These studies ad- dress the dynamic positioning of surface vessels moored to the seabed via a turret-based spread mooring system, an operation referred to as position mooring。 While the mooring system keeps the surface vessel in place most of the time, thruster assistance is needed in severe weather conditions to avoid mooring line failure。 In Refs。 [1, 2], the authors conceptually presented a controller for thruster-assisted positioning of moored  vessels。  They  focused  on  the  structural   reliability

problem of mooring lines。

However, this paper proposes a mooring winch control sys- tem and applies it to the development of a mooring system for vessels。 In exact words, the authors are considering the vessel motion control system design problem by controlling the mooring lines without thruster assistance。

Since a winch control system has to be constructed before constructing a mooring system that controls the vessel mo- tions, this paper deals with the problems involved with con- structing a position control system for the barge ship on which the mooring winch system is installed。 We focus on the cable motions which are induced by vessel moving, wave distur- bance and other environmental situations。 After analyzing the dynamic characteristics of the mooring cable, including the motion characteristics of the barge ship on which it is installed, a mathematical model is built for the mooring winch   system。