Modelling, Simulation and Controller Design for Hydraulically Actuated Ship Fin Stabilizer Systems

MATEC Web of Conferences 4 2 , 0 1 0 0 3 (2016 ) DOI: 10.1051/ m atecconf/ 2016 4 2 0 1 0 0 3  C Owned by the authors, published by EDP Sciences, 2016 Modelling, Simulation and Controller Design for Hydraulically Actuated Ship Fin Stabilizer Systems 1 2 1 1 Alper Zihnioglu , Melek Ertogan , G. Tansel Tayyar , C. Safak Karakas , and Seniz Ertugrul 3 1 Naval Architecture and Marine Engineering, Istanbul Technical University, Turkey Maritime Faculty-Marine Engineering, Istanbul Technical University, Turkey 3 Mechanical Engineering, Istanbul Technical University, Turkey 2 Abstract. In general, hydraulic systems that are used for ship fin stabilizers and rudders, are modelled as first or second order of linear equations to obtain only system’s delay and overshoot for controlling purposes. This approach assumes the hydraulic system is well designed and contains no faults. It’s an easy and quick way to focus on control subject. However, limits and capacities of hydraulic components cannot be examined carefully with this approach. Due to this deficiency, expensive over-engineered or inadequate hydraulic systems can be designed. For this reason, an interdisciplinary study was done in Istanbul Technical University. The purpose of the study is to parametrically model hydraulic system of a ship motion reduction active fin stabilizer system with fins, ship roll dynamics and controllers in detail, so every property of the system can be observed in a simulation environment via non-linear equations. With the help of parametric modelling, every component can be changed and resized easily, including the ship, fins, hydraulic components and controllers. Results obtained from simulation are verified with full scale sea trials using a ship named Volcano71. 1 Introduction A ship’s active fin stabilizers is an important piece of ship equipment that reduces roll motion, thus allowing better cruising experience for the people onboard and extending the service life of installed components on the ship. This equipment is hydraulically powered, because hydraulic units can have high power in small volumes making them indispensable for onboard usage. Hydraulic systems for stabilizers are generally proportional valve controlled types with constant displacement or variable displacement pumps equipped with constant speed electric motors. In recent years, there have been great interest in variable speed pump control systems [1], which offer high energy efficiency. These systems do not provide precision position control of a fin stabilizer system. Therefore, valve controlled systems are still a good choice for this kind of application. Energy efficiency can still be obtained by pressure compensated variable displacement pumps. Rudder and fin stabilizer systems were represented by two saturating blocks and first order time delay for controlling purposes in [2]. Saturating blocks are used for limiting the desired angle and the angle rate. Delay is used to match main servo, since it is responsible for most of the delay between desired and actual rudder or fin angles. Although this is an approximately accurate assumption, there is no information about dynamic behavior of hydraulic system. To overcome this, nonlinear modelling approach was adopted for a real hydraulic fin system, installed on a motor yacht named Volcano71 . Environmental loads such as winds, waves and currents, cause a vessel to move in six degrees of freedom. These axes were standardized by SNAME (The Society of Naval Architects and Marine Engineers) in 1950. To model ship motions in detail; one needs hydrodynamic calculations of a ship that is to be modelled. These hydrodynamic calculations are made by using special naval architecture software to obtain mass, added mass, coriolis, damping and RAO (Response Amplitude Operator) matrices. This kind of work incorporates different disciplines and therefore takes too much time. Instead of this, a one degree of freedom model was used by calibrating unknown equation coefficients with known values of displacement, GM and natural roll period. Then this equation was used to obtain environmental moments as a result of experimental roll values. Fin moments were calculated in the same way by combining both theoretical and experimental results. In the simulation, different types of controllers for hydraulic and roll motion reduction control systems were studied. The results of the simulation were verified by the real-time data from the full-scale experiments. The hydraulic controller on real system was a PID type, on the other hand roll motion reduction controller was PDD2 type. This paper, therefore, describes detailed modelling, This is an Open Access article distributed under the terms of the Creative Commons Attribution License 4.0, which permits XQUHVWULFWHGXVH distribution, and reproduction in any medium, provided the original work is properly cited. Article available at http://www.matec-conferences.org or http://dx.doi.org/10.1051/matecconf/20164201003 MATEC Web of Conferences simulations and controller design of hydraulically actuated fin stabilizer systems. 2 MODELLING OF HYDRAULIC SYSTEM AND SHIP ROLL MOTION 2.1 Non-linear hydraulic modelling Figure 2. This curve for a certain pump speed The hydraulic system of the ship’s roll motion reduction active fin stabilizer was modelled as non-linear system. Its cost effectiveness during the initial design process became the main motivation for this approach. The hydraulic system was made of 2 asymmetric cylinders; 2 four way three position critically centered proportional valves, 2 driver cards for proportional valves, 2 potentiometers, 1 pressure compensated variable displacement pump, 1 pressure relief valve, filters, a tank and power supply. The hydraulic system scheme is given in Figure 1. 2.1.2 Accumulator model In hydraulic systems, accumulators are used for both preventing pressure surge and providing easy pressure build up owing to the oil reserve inside. Equations given (2) - (4) were used for the modelling. An isentropic polytrophic process is assumed in these equations.

















(2) (3)












(4)











2.1.3 Pressure Relief Valve To mathematically model the pressure relief valve, the mass of spool, the friction coefficient between spool and the valve body, the valve spring coefficient need to be known. This kind of detailed information is not given in manufacturer’s catalogue. Instead, pressure flow curves are given. By using these curves with tables and adding a bias block in a simulation, desired set pressure and flow rates were obtained. In Figure 3, an example pressureflow curve for a pressure relief valve is shown. Figure 1. Hydraulic system scheme While constructing the non-linear model, assumptions were made as follows: oil temperature is constant, pump speed is constant, hydraulic components are rigid, pump pressure-flow curve is ideal. Pump, accumula (...truncated)