Yüzer Araçlarda Dinamik Konumlandırma Sistemlerinde Bileşen Seçiminin Sistemin Çalışmasına Etkisi Bakımından Önemi

Abstract

Gemi inşa sanayii, denizcilik gereksinimlerine; bu gereksinimler ise ulusal ve uluslar arası ticarete göre şekillenmektedir. Günümüzde enerji sektörünün, zorlu deniz koşullarında platformlar vasıtası ile açık denizde gerçekleşen faaliyetleri, yeni gemi tiplerinin ve yeni gemi ana ve yardımcı sistemlerinin gelişmelerini sağlamıştır. Bu gemi tiplerinden başlıcaları, yüzer üretim, depolama ve nakil araçları (FPSO’lar), çapa toplama gemileri, platform destek gemileri, boru yerleştirme gemileri, sismik gemiler, çevre kirliliği önleme gemileri, yangın söndürme gemileri, ikamet gemileri vb. olup, bu gemiler malzeme veya insan transferi yapan, uzay veya sabit bir noktaya göreceli olarak mümkün mertebe konumunu koruyabilecek özelliklerde olmaları gerekmektedir. Zor deniz koşullarında, gemilerin ve yüzer araçların kumandasının insan kabiliyetine mahkum kalmadan konumunu koruması, rota izlemesi ve çevresel faktörlerden daha az etkilenmesi amacıyla, günümüz gemilerinde kullanılan ve geliştirilmeye devam eden dinamik konumlandırma sistemleri mevcuttur. Bu sistemler, kendi karmaşık matematik yapılarının yanısıra, birlikte çalıştığı bileşenlerle bir bütün olarak gemideki görevlerini yerine getirmektedir. Bu nedenle ekipman donatımı, geminin amacı ve çalıştığı bölgeler dikkate alınarak yapılmalıdır. İlk yatırım maliyetlerinin yüksek olması, değişiklik veya dönüşüm yapılmasının fiziksel imkansızlıkları/zorlukları sebebiyle, tasarım aşamasında en başında doğru kararların verilmesi büyük önem taşımaktadır. Tez kapsamında, gemiler için dinamik konumlandırma sisteminin bileşenleri ele alınmış, bileşenler tanıtılarak haklarında ayrıntılı bilgiler verilmiş, bileşenlerin birbiriyle ilişkisi araştırılmıştır. Özellikle tahrik unsurları ve güç kaynakları gibi doğrudan sistemin ekonomik ömrüne etki eden bileşenlerin somut verilerle değerlendirilebilmesi için, sanal gemilerin parametrik incelenmesi fikrinden hareketle bileşenlerin karşılaştırması ve önem derecelerinin saptanması için bir bilgisayar kodu yazılmış ve verilerle sonuçlar yorumlanmıştır. Dinamik konumlandırma sistemi bileşenleri ana hatlarıyla dört temel başlık olan referans sistemleri, kontrol sistemleri, tahrik sistemleri ve güç kaynakları olarak ele alınmıştır. Bu tez, ticari gemiler için hangi dinamik konumlandırma sisteminin seçilmesi gerektiğini ortaya koyması açısından Türkiye de hazırlanmış ilk yüksek lisans tezi özelliğindedir ve dinamik konumlandırma sistemleri barındıracak gemi tasarımı yapacak veya genel olarak bu sistemlerin programlanması/geliştirilmesinde rol alacak mühendislere önemli kolaylıklar sağlayacağına inanılmaktadır.

Shipbuilding industry is formed through the maritime requirements and these requirements are formed by the national and international trade. Nowadays the activities of the energy sector taking place in the off-shore, around rigs, platforms and harsh sea conditions lead to new ship types and developments of new main and auxiliary systems on ships. Significant ship types of this purpose can be counted as floating production, storage and offloading units (FPSO’s), anchor handling vessels, seismic research vessels, pollution prevention ships (oil recovery ships), fire-fighting ships, accomodation ships, platform supply vessels, pipe laying vessels, etc. and they require features as to keep steady relative to a spatial or terrestrial reference point because they are oftenly subject to human or material transfer. Recently there are dynamic positioning systems present and even being developed for such vessels, in order to keep them in a specified position, route and avoid them from being affected by the environmental factors in the difficult sea conditions without being convicted to the abilities of persons. These systems try to fulfill their purpose on one hand with their complex mathematic structures and on the other hand with the components they work together as a whole. For this reason, component selection is to be made taking into consideration the purpose of the ship and areas where the ship will work. Due to high initial investment costs, physical impossibilities/difficulties of changes or conversions, great importance should be given to the right decisions at the beginning of the design phase. This thesis consists of five sections, from which the first is the Introduction, where the idea and main methods of position keeping is described. Three methods have been taken into account as most common, respectively jack-up systems, anchoring systems, which are more basic systems and lastly the dynamic positioning systems, which constitute more complex computer systems, enabling great maneouvring for the vessels. The first two systems, due to their nature, have constraints, the length of the legs of the jack-up barge and the chains of the anchor are defining the maximum sea depth they can be used. Moreover these systems are only available to work over a sea bed without obstructions. In the contrary, the dynamic positioning systems keep their position with the thrusters and they have no depth limit in the sea. They produce a high flexibility, because their position can easily be changed by a new command onto the computer, without the need of long time to retract legs or an anchor handling vessel to help collect the anchor. Components of dynamic positioning systems on ships have been taken into consideration and described with detailed information and the interaction between different components has been researched in the second section of the thesis. Components of the system are taken into account basically on four main subjects, namely reference systems, control systems, thrust systems and power systems. All the individual components of these subjects have been evaluated in accordance with their complexity, operational requirements, dependence to exterior references and effects of weather and other environmental factors. Radar based and DGPS reference systems are dependent on terrestrial equipment, however the acoustic and taut-wire systems operate only with their equipment, however these systems require areas where the equipment are not to be damaged or affected by environmental factors. They also do not work with an ultimate coordinate system however they can fix a reference system on each operation and keep their position relatively. The type and number of control system components will be determined in accordance with the DP class of the vessel and comfort of the operator requested. Therefore their criteria relevant to the dynamic positioning system are less and these systems are designed in an economical point of view compared to the material quality and furtherly to meet statutory regulations and classification society rules. The section continues with statutory requirements and class rules, in the examples of Norwegian Maritime Administration classification of ships operations requiring the dynamic positioning systems and Italian Classification Society RINA (Registro Italiano Navale) classification of equipment used on these systems. There are four principle classes defined for these ships, shortly semi automatic systems (not classified), automatic systems without backup (Class 1), with backup of active components (Class 2) and with a backup of physical separation of the equipment (Class 3). Equipment classes are determined in the design phase in accordance with the operations the vessel will be involved throughout its life. A computer code has been developed in Excel and VBA to provide an occasion to compare components on virtual ships and to discuss the results. The program aims to calculate the behaviour of a vessel with defined power systems, thrust systems and control parameters, from a point to another target point and direction. The calculation works by a step by step movement of the ship in three phases. In the first phase, the vessel turns its direction to the target point. Complying an accuracy defined in the program, the program shifts to the second phase, where the vessel moves towards the target and respectively to the third phase, where the vessel finally reached the target position and turns around to comply the target direction. In each step, thruster requirements, power demands and resulting consumption from all engines are cumulatively calculated. Section three of the thesis has all the details of the program and the parametric analysis, which is carried out to evaluate the systems, which are based on equipment capacity and effect the economic life of the vessel. The analysis has been conducted with eight virtual ships to compare two different parameters, from which one is the generator set power and the next is the Diff parameter of the control system, which regulates the behaviour of thrusters when approaching the target. The results of eight different ships have been presented in results graphs in section four, which enables the evaluation of the said parameters. The results have shown for ships with all other parameters completely equivalent and only generator powers different, that the less power led the generators under load continuously and further need of shaft alternators to cover the required power by thrusters. Too much capacity led to the non use of the second generator and the only one generator being heavily loaded. Intermediate generator powers led to the most economic results. The next parametric analysis showed that less number for approaching parameter Diff, resulted in the vessel to behave aggressive to approach the target before slowing down to catch the target, which led to more consumption on short time to aggressively stop the vessel on target and even in some cases led the vessel to miss the target and make more effort to catch back. In the contrary, too high parameters led the vessel to slow down very early and resulted in a long and less economic approach to target. Repeatingly the intermediate values chosen have shown more economic results. The program has been developed as an introductory code to evaluate the required components and therefore missed several features explained in the thesis with their reasons. These exclusions can be listed in four main subjects: 1) Program assumes the actual and target positions of the vessel are certain points and the processing of the data received from the reference systems has not been programmed. 2) The effects of the environmental factors have been neglected, because they have been considered to have an equal effect on each vessel in the parametric analysis. For this reason, processing of data such as wind/sea flow measurement and their effect on the ship have not been programmed. 3) It is deemed that each ship in water will have different behaviour and each thrust component power demand and their reaction on the vessel will be variable, main assumptions explained in the section 3.3 have been made and the Diff and Chng parameters have been taken equal for each different thrust component. This leads to certain results at certain power demands and the need of mathematical model correction via a Kalman Filter is avoided. In fact, while applying the program to a real application, each thrust component should be defined separately by the values obtained from manufacturers, so that the forces and moments can be calculated acting on the ship at each unit power of the said thrust component. Furthermore the parameters should be defined for each thrust unit, defining how fast the thruster can react when sudden demands for power occur. 4) In dynamic positioning systems, it is possible to follow various algorhytms to reach a target position and keep that position. For instance, one method would be using the side thrusters in same direction together with the propulsion propellers to move towards the target without changing its ahead direction. Another method, obtained in this thesis, would be turning to the target in advance, approaching using propulsion propellers and lastly turning in position to keep the direction as targeted. These algorhytms are various and is matter of choice for the engineer designing the system. The program has been developed so far to support naval architects who are intending to design ships equipped with those systems or develope the dynamic positioning systems. In conclusion, section five summarizes the component selection and the results of the parametric analysis. This thesis, being the first to be written on the subject in Turkey, has made very clear with the computer program results, that selection of systems is not based on cheap/less capacity is economic or expensive/high capacity is unfeasable. All components are to be taken very carefully into account in the design phase of these vessels preferably with mathematic and/or physical models to estimate and evaluate the behaviour of the vessel under several position-keeping scenarios.