Abstract
Fin-angle feedback control is usually used in conventional fin stabilizers, and its actual anti-rolling effect is difficult to reach theoretical design requirements. Primarily, lift of control torque is a theoretical value calculated by static hydrodynamic characteristics of fin. However, hydrodynamic characteristics of fin are dynamic while fin is moving in waves. As a result, there is a large deviation between actual value and theoretical value of lift. Firstly, the reasons of deviation are analyzed theoretically, which could avoid a variety of interference factors and complex theoretical derivations. Secondly, a new device is designed for direct measurement of actual lift, which is composed of fin-shaft combined mechanism and sensors. This new device can make fin-shaft not only be the basic function of rotating fin, but also detect actual lift. Through analysis using stiffness matrix of Euler-Bernoulli beam, displacement of shaft-core end is measured instead of lift which is difficult to measure. Then quantitative relationship between lift and displacement is defined. Three main factors are analyzed with quantitative relationship. What is more, two installation modes of sensors and a removable shaft-end cover are proposed according to hydrodynamic characteristics of fin. Thus the new device contributes to maintenance and measurement. Lastly, the effectiveness and accuracy of device are verified by contrasting calculation and simulation on the basis of actual design parameters. And the new measuring lift method can be proved to be effective through experiments. The new device is achieved from conventional fin stabilizers. Accordingly, the reliability of original equipment is inherited. The alteration of fin stabilizers is minor, which is suitable for engineering application. In addition, the flexural properties of fin-shaft are digitized with analysis of stiffness matrix. This method provides theoretical support for engineering application by carrying out finite element analysis with computers.
Highlights
The undesirable motion of ships at sea is induced by the action of environmental disturbances: waves, wind and current
A new device is designed for measuring lift, which is improved based on actual fin stabilizers and method of Sperry Marine [27,28,29]
The relationship between lift and fin angle is not linear according to dynamic hydrodynamic characteristics of fin stabilizers obtained from water tank experiments
Summary
The undesirable motion of ships at sea is induced by the action of environmental disturbances: waves, wind and current. Lift-feedback control of fin stabilizers is still an emerging research. Specialized measuring device is designed according to specific characteristics of fin stabilizers. Research Institute of ship anti-rolling and control proposes a measuring lift method using bearing load [18, 19]. A new device is designed for measuring lift, which is improved based on actual fin stabilizers and method of Sperry Marine [27,28,29]. Kc denotes control torque of fin stabilizers. The key factor of roll reduction is the accuracy of control torque induced by fin stabilizers. Measuring actual disturbance torque accurately and effectively is a difficult problem. The difficult point of fin stabilizers is how to measure actual lift accurately
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