Simplified trawl system modeling and design of a depth control system using fuzzy logic

This paper describes a simplified mathematical model of a mid-water trawl s ystem developed to help and understand the dynamic behavior of trawl, and t o design the depth control system of the mid-water trawl operation. The equ ations of the motion for the vertically moved trawl system were obtained us ing Lagrange's equation with respect to the variables of the displacement o f the trawler, the length of the trawl warp, the angle of the warp to the h orizon, and the angle of the hand rope to the horizon. These equations were modified as simplified types. A fuzzy logic controller was designed to control the depth of a mid-water t rawl net. The fuzzy controller calculates the tension of the trawl warp to be changed, based on the depth error between desired depth and actual depth of the trawl net and the ratio of changes in the depth error. The error an d error change are calculated every second of sampling time. The control in put, i.e., the desirable tension of the trawl warp is determined. by infere nce from the linguistic control rules, which is usually carried out by crew experienced in controlling the depth of the trawl net during manual operat ion. Computer simulations indicated that the calculated motion of the trawl syst em using the simplified mathematical model agreed reasonably with those of the original model and actual trawl system obtained from field experiments, and the proposed fuzzy controller rapidly followed the desired depth witho ut steady-state error. (C) 2001 Elsevier Science B.V. All fights reserved.