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MAROFF-2-Maritim virksomhet og offsh-2

Improving Performance in Real Sea

Alternative title: Forbedring av skipsytelse i realistiske sjøtilstander

Awarded: NOK 12.0 mill.

When a ship is moving forward in waves it will experience an increase in resistance in waves. Traditionally, ship designs are optimized for calm water performance. However, this condition does not reflect the real condition the vessel will experience at sea. The International Maritime Organization (IMO) has established the Energy Efficiency Design Index (EEDI) as the most important policy measure to reduce greenhouse gas emissions from shipping. The current implementation of the EEDI is based on calm-water conditions. Depending on the type and size, vessels are not allowed to exceed a threshold for emitted CO2. However, when vessels operate under real-sea conditions with effects of wind and waves, the emissions are higher than assumed for a given speed according to the calculations following the EEDI. This is due to the fact that the required power in real sea exceeds the power requirement in calm water conditions. Hence, calm water optimization, currently applied by the EEDI, does not necessarily produce the ship with the lowest energy consumption over its lifetime, leading to increased fuel consumption and raising a safety concern for the operation of the vessel in extreme weather conditions. To better address the IMO 2050 greenhouse gas reduction target, robust and more accurate analyses of ships in realistic operating conditions are needed with emphasis on the prediction of added resistance in waves. The overall goal of the current project is the introduction of more accurate numerical tools to study ship seakeeping performance in real-sea conditions. The proposed project will develop high-resolution tools and couple high-resolution modelling with efficient wave modelling to evaluate the added resistance problem in realistic sea states in more detail. At SINTEF Ocean, the numerical tool for the prediction of the seakeeping qualities of ships with forward speed, accounting for three-dimensional effects, was further developed. As additional feature, responses in waves at finite water depth was developed. This numerical tool is intended for use by the industry in an early design phase, and efficient computational performance is a main consideration. At NTNU, the PhD student and the PostDoc have commenced their research. The focus of the first year has been on using high-resolution hydrodynamic models of ships in waves. As a first step, standard benchmark cases were used to validate the new immersed boundary-based algorithm. The results have been presented at a conference. The new approach enables the calculation of large ship motions using computational fluid dynamics (CFD) solvers without complex overset-mesh strategies. A major feature of the seakeeping problem with forward speed is the complicated wave pattern formed by the ship's motions and wave reflection in waves. The calculation of forces on the body requires that the pressure created by the interaction of the moving ship hull with the waves around it is obtained on the hull surface correctly. Traditionally, this seakeeping problem is solved by a so-called boundary element method where only the wetted surface of the hull is included in the mathematical description. A fundamental mathematical component of this boundary element method is the Green function. Without forward speed, efficient formulations for this Green function exist and several efficient codes are used within the offshore industry. With forward speed, however, the Green function is much more complex and difficult to calculate, and this inhibits practical use. For the development of a robust industry-standard seakeeping code, a simplified formulation where the forward speed terms in the free-surface condition are dropped, seems favourable. This approach has been chosen for the present development, as it allows for efficient calculations using available formulations for the zero-speed Green function.

In order to reduce the climate footprint of the maritime transport sector, a major improvement is required in the form of reduced energy requirements and increased efficiency at sea. This can be achieved through improved design and production of sea-going vessels. When vessels operate under real sea conditions with effects of wind and waves, the emissions are higher due to assumption of calm water conditions in the design phase. With the advances in computational methods and computational power, high-resolution numerical simulations can be carried out to overcome the limitations of the current standards of practice. The proposed project will develop high resolution tools and couple high resolution modelling with efficient wave modelling to evaluate the added resistance problem in realistic sea states in more detail. The relevance of the proposed project is in accordance to the prioritised thematic area: Digitalisation of the maritime industry — Design and production. In the Norwegian context, a national infrastructure to serve the needs of the maritime and offshore industry through the establishment of the Ocean Space Centre in Trondheim is approved. This facility will provide large opportunities for testing new concepts and designs under realistic conditions. Concurrent to this development, investment in improving the digital infrastructure will further accentuate the gains from operating modern large-scale model testing facilities. This introduces the concept of a digital twin to a large experimental facility that will provide a tool carry out parametric and feasibility studies, visualise model tests and configure the physical modelling as a preliminary process before starting model testing to evaluate design parameters in a focused manner. The proposed project is relevant to the priority research area listed in the Maroff programme, to the development of the Ocean Space Centre and also training researchers for future development in the field.

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MAROFF-2-Maritim virksomhet og offsh-2