A nonlinear six degree-of-freedom dynamic model is presented for a marine surface vessel. The formulation closely follows the current literature on ship modeling. It considers the effects of inertial forces, wave excitations, retardation forces, nonlinear restoring forces, wind and current loads along with linear viscous damping terms. The capability of the model is shown through its prediction of the ship response during a turning-circle maneuver. The ship model is used herein as a test bed to assess the performance of the proposed controller. The present study assumes that the ship is fully actuated and all state variables of the system are available through measurements. A nonlinear robust controller, based on the sliding mode methodology, has been designed based on a reduced-order version of the ship model. The latter accounts only for the surge, sway and yaw motions of the ship. The initial simulation results, generated based on the reduced-order model of the marine vessel, demonstrate robust performance and good tracking characteristics of the controller in the presence of structured uncertainties and external disturbances. Furthermore, they illustrate the adverse effects of the physical limitations of the propulsion system on the controlled response of the ship. Next, the same controller is implemented on the six degree-of-freedom model of the ship. The simulation results reveal tracking characteristics of the controller that are similar to those observed in the initial results, in spite of significantly larger modeling uncertainties.
No abstract
A robust nonlinear controller has been designed to control the surge speed and the heading angle of a marine surface vessel. The control actions are carried out through the propeller and the rudder. Moreover, a nonlinear observer has been devised to accurately estimate the surge speed and the yaw angle and their time derivatives. Both the controller and the observer are designed based on a reduced-order model of the ship. However, their performances have been assessed on a six degree-of-freedom ship model, which accounts for the wave excitation, retardation forces, nonlinear restoring forces, wind and sea-current resistive loads. Furthermore, the model accounts for the physical limitations of both the rudder and the ship propulsion system. The simulation results demonstrate the capability of the integrated controller-observer system in providing a good tracking characteristic of the ship in spite of significant modeling imprecision and environmental disturbances.
Diesel engines have to meet stringent emissions standards without penalties in performance and fuel economy. This necessitated the use of elaborate after treatment devices to reduce the tail pipe emissions. In order to decrease the demand on the after treatment devices, there is a need to reduce the emissions in the formation stage during combustion. This requires a precise control of the phasing of the combustion process. Currently, diesel engines are controlled by pre-set open loop schedules that require extensive, time consuming and costly laboratory tests and calibration tasks to meet the production target goals which are stricter than the emission standards. Such goals are set as a safe guard against the deterioration during engine life cycle. This paper presents an incremental fuzzy logic controller that adjusts the combustion phasing as per desired targets to meet production goals over the engine life period. An ion current/ glow plug sensor and its circuit are used to produce a signal indicative of different combustion parameters. Signal conditioning and filtering are applied to improve the quality of ion current. The algorithm developed in this paper optimizes the ion current feed back to increase its reliability for stable engine control while maintaining fast controller response, and high accuracy. Experiments are carried out on a four cylinder, turbo-charged, 4.5L heavy duty diesel engine equipped with a common rail injection system and an open ECU. The response of the controller is evaluated from experimental data obtained by running the engine under different steady, and transient operating conditions. The results demonstrate the ability of the closed-loop control system in achieving the desired combustion phasing.
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