Page 343 - Offshore Electrical Engineering Manual

330 CHAPTER 1 Notes on Dynamic Positioning and Ballast Control

INTEGRATED CONTROL SYSTEMS

Sophisticated computer-based Integrated Automation System (IAS) provide a super-
visory control, alarm and data acquisition functions and integrate the control and
monitoring systems into one single system. IAS is based on distributed processing
units (DPUs) in which the various process parameters are controlled via input/output
field stations, located in different places of the vessel. Man–machine interface for
the vessel management system (VMS) are multiple redundant operator station that
include the following functions:

1. power management system
2. alarm and monitoring system
3. auxiliary control systems
4. ballast automation systems
5. propulsion control systems including thruster control
6. DP systems including joystick system.

Operator stations allow control and monitoring vessel equipment including and
are receiving process alarms. It is possible to change limits or parameters on one
operator station and that information is automatically updated in all relevant operator
stations. All data are displayed on custom-made process mimics. All monitoring and
automation functions are carried out by the DPUs. Communication between operator
stations is via redundant local area networks (Fig. 6.1.1).

PROPULSION REDUNDANCY

The automation should include an algorithm/truth table which decides whether the pro-
pulsion setup is still viable as a DP system when a propulsion device has failed. One bow
thruster by itself is obviously not viable, but the system may be a mixture of conven-
tional propeller and rudder, azimuth thrusters and tunnel bow thrusters, so depending on
which device fails, and on its relative position, the DP system may or may not be viable.

BALLAST CONTROL SYSTEMS
The movement of heavy fluids aboard a floating vessel such as an FPSO or semi-
submersible has a pronounced effect on the attitude of that vessel in the water,
which must be counteracted by filling and emptying built-in ballast tanks with
water (Figs 6.1.2 and 6.1.3).

FLOATING PRODUCTION, STORAGE AND OFFLOADING UNITS

If too much weight flows to one side or another, the vessel tends to list that way and,
in extreme cases, may be in danger of capsizing, particularly if the vessel is lightly