| A ship subjected to wind and wave forces perform motions in six degrees of freedom,i.e. surge, sway, heave, roll, pitch and yaw. There are numerous reasons for trying tocontrol and reduce the motions of a ship. Excessive motions can interfere with theactivities of the crew or passengers, reduce the combat readiness of naval vessels, cause theloss of containers on cargo vessels, and reduce the operational parameters of various ships.The roll motion is the most critical one because it is lightly damped and therefore prone todynamic magnification, in particular in the resonance frequency range.Ship-roll stabilization has therefore received considerable attention; it is still a majorsubject of interest to ship designers and naval architects. Among a wide variety of roll-damping devices, anti-roll tanks are appreciated for their simplicity, low cost and action atlow or even zero speed. To reduce the cost of the study and design of these systems, theship anti-rolling tank test platform was created.Ship anti-rolling tank test platform is a specific-designed synthesis system, which isimportant equipment for the study and design of the anti-rolling tank. Up to now, there isno equipment with so many functions like this one in China. This platform is used toimitate the ship’s movement in the sea wave, based on our knowledge of the tank’smovement and the anti-rolling effect to get the reliable experiment data for the fieldequipping of the real ship tank.Since the fast change of the amplitude and frequency of the sea wave moment calls forhigh performance of the control system, the electro-hydraulic servo system featuring highaccuracy and fast respond is employed. The quality of the anti-rolling tank experimentplatform mainly depends on two aspects: one is the reasonable selection of the keyassembly parts used in the electro-hydraulic servo system, for example, the type selectionand parameter calculation of the servo amplifier, actuating cylinder and moment sensor;the other aspect deals with the control strategy. So, for a given ship type with fixed keyassembly parts, the anti-rolling quality depends on its control strategy.The main purpose of the future study is to analyze the most relevant properties of theship anti-rolling tank test platform and to make an analysis of the control strategies that may be used for the control of these types of system. The idea is to evaluate, throughdetailed simulation, several types of controllers.In this thesis, the classical feedback controller (PID) is described as a benchmark forthe other controllers. Then, a Pole Placement Controller is going to be examined. Also,some new advanced strategies as nonlinear and intelligent control techniques are includedin the analysis. Among nonlinear techniques, a sliding mode control has attracted aconsiderable attention to elaborate this work; because it provides a systematic approach tothe problem of maintaining stability and consistent performance in the face of modelingimprecision and disturbances. On the other hand, Fuzzy Controller, which is one of themost useful intelligent techniques, is chosen to be analyzed. This latter which uses fuzzysets and fuzzy inference to derive control laws in which no precise model of the plantsexists.To assess the performance of the proposed controllers, several simulations have beenperformed with different desired inputs. The inputs have been selected in order to give thebest approximation of the ship rolling motion in various sea conditions. Basing on theseconditions, the inputs are divided into two sets: firstly, the ship rolls motion in regularwaves. Secondly, the ship rolls motion in irregular waves.This report concludes that the use of sliding mode and fuzzy logic controllers give abest results comparing to the PID controller in different conditions. |
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