Investigation of magnus effect roll stabilizer system

Abstract

Different systems have been designed to reduce rolling motions in marine vehicles. Each of these systems gives efficient results under certain boundary conditions. Today, marine vehicles have started to do new and different tasks. New missions have brought new constraints for marine vessels, and different roll reduction systems have to be designed for these constraints. Magnus effect roll stabilizer system continues to be developed as an alternative system for different maritime missions. Within the scope of the thesis, components of magnus effect roll stabilizing system were examined, and the design ranges in which it was efficient were explained. In Chapter 1, the operation of the system, the flow problem araund rotating cylinder and the development process of the roll stabilizer systems are explained. Magnus effect roll stabilizer system basically consists of two components. The first component of the system is the cylinder whose rotation direction and speed can be controlled, and the second component is the electric motor that provides the movement of the cylinders. Magnus lifting force is obtained by controlling the movement of the cylinder in the fluid area. With this force, the amplitude of the roll motion is reduced. The forced roll motion is mathematically modeled by a second order inhomogeneous differantial equation. The wave force, which is the primary cause of motion, and the Magnus force exerted by the roll damping system are represented on the right side of the differential equation. Magnus force changes direction in the same period as the roll motion, reducing the roll amplitude of the vessel. In Chapter 2, mathematical model of the roll motion is examined. In Chapter 3, the variation of the Magnus force depending on the parameters was examined by CFD analysis. According to Kutta – Joukowski lifting theory, the parameters affecting the Magnus lift force are shown. Fluent software was used for CFD analysis. Analyzes were performed at 1,2 m/s and 1,72 m/s fluid velocities for a 250 mm long and 50 mm diameter cylinder. The cylinder was rotated in the fluid at speed range of 800 – 2000 rpm. The turbulence model was made according to k – w theory. Layered mesh was modeled around the cylinder wall up to a certain level according to the y+ value. Fluid field is modeled with a rectangular mesh. As a result of the analysis, the lift force values created by the cylinder at a different rotation speeds were found. Experimental study was performed to evaluate the accuracy of the results obtained by CFD analysis. Model towing test was carried out in Ata Nutku Ship Model Laboratory and the lift force values created by the cylinders were found. Roll stabilizer system we produced as a prototype was mounted on a 2,65 m full length boat model. Model boat was moved at 1,2 m/s and 1,72 m/s velocities as in CFD analysis. At these speed values, the transverse waves created by the model boat are very few, depending on the Froude number. In this way, the Magnus lift force, which inclines the boat, is calculated more accurately. At each speed value, cylinders were rotated in the same rotation speed but in the opposite direction, and the instant heel angle values of the boat were transferred to the computer with the help of android device. Lift force values were calculated based on the model boat inclination angle values. The graphs of the data we obtained from numerical analysis and experimental study were drawn. Both towing tests were performed at different speeds but at the same cylinder rotational speeds. Lift force increased in direct proportion to the the icrease in speed. An increase in the lifting force was observed when the cylinder rotation speed was increased up to 1400 rpm. After this value, the increase in the rotational speed of the cylinder did not cause a change in the lifting force. Within the scope of the thesis, operation of Magus effect roll stabilizer system has been investigated computationally and experimentally according to the parameters. The results obtained were found to be operating conditions where the roll stabilizer system was efficient. In the recommendations section, changes that can be made to increase the efficiency of the roll stabilizer system are explained.