| The ballast water system is a vitality system among all the ship systems. By controlling the perfusion and discharge of water tank, the ballast water system can adjust the sink-and-float state of a ship, and ensure the safe and smooth operation of a ship. In the meantime, because of possessing some excellent characteristics, such as compact structure, large flow coefficient, and easily realizing the fluid transport at large flow and diameter, butterfly valve is widely used in the ballast water system. In this thesis, the butterfly valve(DN250) was chosen as the research object. In view of the deficiency of the traditional switch control system, we developed a electro-hydraulic proportional control system to control the continuous opening angle of butterfly valve. In the meanwhile, the genetic algorithm was employed to optimize the dynamic performance of this system. The flow field characteristic and reasonable opening angle of butterfly valve were analyzed and discussed. All the work and related conclusions obtained in this thesis are summarized as follows:Firstly, in view of the deficiency of existing hydraulic on-off control system for the marine butterfly valve, we studied the overall design scheme for this project, and analyzed the functional requirements and important technical parameters of the electro-hydraulic proportional control system. Base on the overall design scheme, the mathematical model of this system was established, and the transfer function was obtained by analyzing the mathematical model, then the related parameters affecting the dynamic performance of the system were discussed.Secondly, by using software AMESim, the comparative analysis was respectively studyed on the dynamic performance of this system with three kinds of situations, which are Non-PID control, General PID control and PID control with genetic algorithm optimization. The results show that: 1) After optimizing with genetic algorithm, the operation of this system is much stabler and smoother; 2) The opening time of butterfly valve is 25.2s, the opening angle is 90.015°, and the maximum deviation obtained is 0.017°, which are satisfied with the functional requirements of this electro-hydraulic proportional control system.Finally, by using software FLUENT, the flow characteristics at constant rate and steady flow of butterfly valve(DN250) at different opening angles were numerically simulated and analyzed. In the meantime, the influences of the flow resistance coefficient, relative flow rate coefficient and hydrodynamic torque coefficient on the opening angle of butterfly valve were discussed. The results indicate that when the opening angle is: a) less than 30 degree, the flow field will incur relatively big flow resistance coefficient and flow disturbance to bring about large amounts of energy dissipation, which are of no benefit to the butterfly valve for long-term and efficient operation; b) greater than 60 degree, the flow resistance coefficient is small, the flow shape is smooth, and the energy dissipation induced is very low, which are beneficial to promote the butterfly valve’s work efficiency; c) equal to 70 degree, the hydrodynamic torque coefficient reaches its peak value, which is 0.193. So 70 degree could be the preferred opening angle when the butterfly valve is working.In summary, based on the ballast water system, an electro-hydraulic proportional control system used to control the continuous-opening of butterfly valve was developed, and the optimized dynamic performance of this system was studied. In the meanwhile, by analyzing the characteristics of the flow field, the reasonable work opening angle of butterfly valve was discussed. The results obtained in this thesis can provide theoretical basis for the design and research on the hydraulic control system of butterfly valve used in marine. |
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