Study On Fin Stabilizer Of All Speed Based On Lift Feedback

Subject to marine environment disturbances such as ocean wave, ocean wind and oceancurrent, ship sailing on the sea would inevitably show a variety of forced motions. Among allmotions in the six degree of freedom, roll is almost the most harmful one. Severe rollingwould seriously degrade the vessel’s seaworthiness, equipment’s safeness, crew’s comfort andweapon’s performance. Researchers have invented hundreds of anti-rolling devices forreducing the roll of ships. The most widely used anti-rolling devices are fin stabilizer andanti-rolling tank nowadays. In the past, for stabilizing the ships moving in all speed, the bestchoice was to equip the ship with both fin stabilizer and anti-rolling tank where anti-rollingtank is employed when moving in zero and low speed, and fin stabilizer is employed whenmoving in middle and high speed (or both anti-rolling tank and fin stabilizer). However,anti-rolling tank does not only occupy the valuable cabin space but also dissatisfies thedamping effect. Furthermore, it is economical costive since it requires maintenance of the twosets of system simultaneously.The general fin stabilizer can only be applied in middle and high speed condition resultedfrom the restriction of lift generating mechanism, where lift force is approximatelyproportional to the square of the speed, and would produce little stable moment at low speed.If fins can produce sufficient lift force that meets the ship stabilization requirement at lowspeed, then fin stabilizer can be applied in conditions with zero and low speed. Combinedwith general fin stabilizer that applied at middle and high speed, the improved fin stabilizercan be applied at all speed conditions, zero, low, middle and high. Another shortcoming ofgeneral fin stabilizer lies in that fact that fin angle is used as the feedback signal of servosystem ignoring the nonlinear and uncertainty between lift force and fin angle, and this factblocked the further improvement of stabilization effect. Using the lift force on the fin insteadof the fin angle as the feedback signal of servo system, the above problem will be overcomed.Since that the technology of general high speed fin stabilizer with fin angle feedback hasalready been mature, the remained key research topics on all speed fin stabilizer now includethe zero and low speed fin stabilizer, force feedback technology, and the switching principlebetween the conditions of low speed and middle speed. A new lift generating mechanism wasdiscussed at first. Then the different structure form that can produce lift force at zero speedwas analyzed. Longitudinal flapping structure was employed as fin type of the all speed application. Next, the lift force model at low speed was established, which will be morepractical significance. At last the unknown parameters in the model were determined byhydrodynamic test, and the effectiveness of lift model was verified through experiments.Lift and lift maintenance time were limited, and they are a pair of contradiction for thespecial working mode in zero and low speed. Therefore, research on how to increase the liftof longitudinal flapping structure fin in zero and low speed was performed. The effects of finshaft position, aspect ratio and fin type on lift were discussed. Taking into account of the allspeed working requirement, the parallelogram fins with flap was applied in fin stabilizer.Experiments were carried out on camber deformation and area deformation. Experimentresults demonstrate the correctness of the theoretical analysis.The sole challenge in lift force feedback technology is lift measuring, because that manyfactors should be taken into account, such as the installation, decoupling, maintenance, costsand other factors of force sensor. Noticing the shortcomings of lift measurement methods ofSperry, Rolls-Royce and Mitsubishi Heavy Industries, by analyzing the drawbacks of ordinaryfin angle feedback fin stabilizer, a lift measurement method based on square ness micro driveproposed by Harbin Engineering University was adopted. The specific implementation formand mechanical structure were discussed and the problems of lift feedback at all speedworking condition were analyzed, so the combined feedback based on fin angle and lift forcewere adopted in this paper.According to the control characteristics of zero/low speed and middle/high speed, variouscontrol methods were employed. Taking stabilization moment maximum consumption wavedisturbance moment as the goal, in zero and low speed, and through the wavelet transformand mean-generating function period extrapolation to forecast the roll state of ship, nonlinearprogramming was applied according to the forecasted results to determine the optimalparameters of the control sequence, and the nonlinear and multi mapping problem weresolved. The nonlinear equation of ship roll was transformed into a linear time-varying systemby T-S model, in middle and high speed, and the online identification of ship roll equationwas applied to solve the uncertainty problem. The stall problem was solved in lift-feedbackfin stabilizer at severe sea conditions by employing controller constrained condition. Aswitching strategy between low speed and high speed was designed for a certain type of shipparameters and roll reduction requirements. Simulation results show that the control strategycan meet the requirements of all-speed stabilizer.