Ship-scale CFD benchmark study of a pre-swirl duct on KVLCC2

Installing an energy saving device such as a pre-swirl duct (PSD) is a major investment for a ship owner and prior to an order a reliable prediction of the energy savings is required. Currently there is no standard for how such a prediction is to be carried out, possible alternatives are both model-scale tests in towing tanks with associated scaling procedures, as well as methods based on computational fluid dynamics (CFD). This paper summarizes a CFD benchmark study comparing industrial state-of-the-art ship-scale CFD predictions of the power reduction through installation of a PSD, where the objective was to both obtain an indication on the reliability in this kind of prediction and to gain insight into how the computational procedure affects the results. It is a blind study, the KVLCC2, which the PSD is mounted on, has never been built and hence there is no ship-scale data available. The 10 participants conducted in total 22 different predictions of the power reduction with respect to a baseline case without PSD. The predicted power reductions are both positive and negative, on average 0.4%, with a standard deviation of 1.6%-units, when not considering two predictions based on model-scale CFD and two outliers associated with large uncertainties in the results. Among the variations present in computational procedure, two were found to significantly influence the predictions. First, a geometrically resolved propeller model applying sliding mesh interfaces is in average predicting a higher power reduction with the PSD compared to simplified propeller models. The second factor with notable influence on the power reduction prediction is the wake field prediction, which, besides numerical configuration, is affected by how hull roughness is considered

Anti Roll Tanks in Pure Car and Truck Carriers

This is a master thesis conducted at KTH Centre for Naval Architecture in collaboration with Wallenius Marine AB. Rolling motions is something that is undesired in all kinds of seafaring. In terms of propulsion resistance, comfort and route planning it would be desirable to reduce these motions. This thesis is an investigation on how different roll stabilising systems affect the performance of an 8000 unit PCTC vessel, special emphasis is put on investigating the performance of anti roll tanks. The ship in question has a recorded incidence of parametric rolling and the ability of the tanks to countervail this phenomenon is also investigated. The tank and fin stabilising systems are relatively equal when it comes to roll damping performance related to changes in the required forward propulsion power. The tanks however, have a higher potential for improvements, addition of features such as heeling systems and parametric roll prevention systems. The tank performance is also independent of the speed of the ship. The tanks are easier to retrofit and do not require the ship to be put in dry dock during installation. The conclusion of this thesis is that a combined anti roll and heeling system should be installed but that a further study has to be made on the performance of active rudder stabilisation. It is shown that passive tanks are efficient at preventing parametric rolling in some sea states. A proposal is made for a further study on a control system that could achieve the same performance for all sea states.HTML clipboard Detta är ett examensarbete utfört på KTH Marina System i samarbete med Wallenius Marine AB. Rullningsrörelser är något som är oönskat i all form av sjöfart. Framsteg kan göras i både framdrivningsmotstånd, komfort och ruttplanering om dessa rörelser kunde minskas. Detta examensarbete består av en undersökning hur olika system för rulldämpning påverkar prestandan hos ett 8000 enheters PCTC-fartyg. Speciell vikt har lagts vid att undersöka prestandan hos antirulltankar. Det undersökta fartyget har en dokumenterad incident med parametrisk rullning och tankarnas förmåga att motverka detta fenomen undersöks. Tank- och fenstabilisatorer är i princip likvärdiga vad det gäller dämpningsprestanda relaterat till erforderliga ändringar i framdrivningseffekten. Tankarna har dock en större potential för förbättring och tillägg av ytterligare inslag som krängningshämmare och system för motverkan av parametrisk rullning. Tankarnas prestanda är också oberoende av fartygets fart. Tankarna är lättare att installera i efterhand och kräver inte att fartyget läggs i torrdocka under installationen. Slutsatsen av detta arbete är att en kombinerad antirull- och krängningshämmande tank bör installeras men att en vidare studie måste göras på prestandan hos aktiva roderstabiliseringssystem. Det visas att passiva tankar kan motverka parametrisk rullning i vissa sjötillstånd. Ett förslag om en vidare studie på reglersystem som skulle kunna ge samma prestanda vid alla sjötillstånd ges.

Anti Roll Tanks in Pure Car and Truck Carriers

This is a master thesis conducted at KTH Centre for Naval Architecture in collaboration with Wallenius Marine AB. Rolling motions is something that is undesired in all kinds of seafaring. In terms of propulsion resistance, comfort and route planning it would be desirable to reduce these motions. This thesis is an investigation on how different roll stabilising systems affect the performance of an 8000 unit PCTC vessel, special emphasis is put on investigating the performance of anti roll tanks. The ship in question has a recorded incidence of parametric rolling and the ability of the tanks to countervail this phenomenon is also investigated. The tank and fin stabilising systems are relatively equal when it comes to roll damping performance related to changes in the required forward propulsion power. The tanks however, have a higher potential for improvements, addition of features such as heeling systems and parametric roll prevention systems. The tank performance is also independent of the speed of the ship. The tanks are easier to retrofit and do not require the ship to be put in dry dock during installation. The conclusion of this thesis is that a combined anti roll and heeling system should be installed but that a further study has to be made on the performance of active rudder stabilisation. It is shown that passive tanks are efficient at preventing parametric rolling in some sea states. A proposal is made for a further study on a control system that could achieve the same performance for all sea states.HTML clipboard Detta är ett examensarbete utfört på KTH Marina System i samarbete med Wallenius Marine AB. Rullningsrörelser är något som är oönskat i all form av sjöfart. Framsteg kan göras i både framdrivningsmotstånd, komfort och ruttplanering om dessa rörelser kunde minskas. Detta examensarbete består av en undersökning hur olika system för rulldämpning påverkar prestandan hos ett 8000 enheters PCTC-fartyg. Speciell vikt har lagts vid att undersöka prestandan hos antirulltankar. Det undersökta fartyget har en dokumenterad incident med parametrisk rullning och tankarnas förmåga att motverka detta fenomen undersöks. Tank- och fenstabilisatorer är i princip likvärdiga vad det gäller dämpningsprestanda relaterat till erforderliga ändringar i framdrivningseffekten. Tankarna har dock en större potential för förbättring och tillägg av ytterligare inslag som krängningshämmare och system för motverkan av parametrisk rullning. Tankarnas prestanda är också oberoende av fartygets fart. Tankarna är lättare att installera i efterhand och kräver inte att fartyget läggs i torrdocka under installationen. Slutsatsen av detta arbete är att en kombinerad antirull- och krängningshämmande tank bör installeras men att en vidare studie måste göras på prestandan hos aktiva roderstabiliseringssystem. Det visas att passiva tankar kan motverka parametrisk rullning i vissa sjötillstånd. Ett förslag om en vidare studie på reglersystem som skulle kunna ge samma prestanda vid alla sjötillstånd ges.

An Investigation into the Logistical and Economical Benefits of using Offshore Thermal Power in a Future CCS Scheme

Carbon Capture and Storage (CCS) is an increasingly popular scheme to mitigate CO2 emissions from large point sources (IPCC 2005). Thermal power plants account for a large portion of the world's total CO2 emissions and are therefore the most attractive target for CCS. For a typical thermal power plant; the process would involve capturing the CO2, transporting it to a suitable location for storage and storing it in a manner that will ensure minimal leakage over a very long period of time. Due to public concerns and protests regarding storage onshore, offshore geological storage of CO2 is most likely to be used for future projects (Winden et al. 2011). The successful implementation of CCS thus depends on the feasibility of capturing the CO2, transporting it to an offshore site and injecting it deep beneath the seabed. Pilot projects such as the Sleipner rig in Norway have already proven the feasibility of using offshore geological storage and post combustion technology for capturing CO2 can also be considered mature. No long distance, large scale transportation solutions for CO2 has yet been proven to work with satisfactory results. Transportation of CO2 is thus identified as an area where breakthroughs could lead to forward leaps in mitigating greenhouse gas emissions. This paper presents a study on a possible future way of solving CO2 transportation issues associated with the use of CCS. Geological storage locations are located in the sedimentary basins which is where oil and gas reserves are also found. The issue of transporting CO2 from an onshore power plant to an offshore storage site can thus be compared to the issue of transporting natural gas from an offshore extraction site to an onshore power plant or production facility. This is conventionally done using either ships or pipelines. This paper investigates the cost competitiveness of using the third alternative of Gas To Wire (GTW) where the gas is combusted offshore. This eliminates the need for transportation altogether and the concept has already been proven to be attractive for exploiting certain gas fields. It is shown here that the concept is even more attractive in a scenario where CCS is used since it eliminates two transportation issues. In this study, the transportation cost of natural gas and CO2 is compared to the costs of sub-sea High Voltage Direct Current (HVDC) electrical cables and is shown to be higher. Pipelines have a large potential to be the most economical way of transporting CO2 to most prospective storage sites in the future (Winden et al. 2011) and will therefore be used to represent a conventional method of CO2 transportation in this study. For comparison, the alternative of transporting by ship or using a pipeline-ship combination will also be presented briefly. Initial studies show that the reduction in transportation costs compared to all conventional methods would more than offset the increased costs of operating a power plant offshore. It is also shown that the gains in transportation cost will decrease the Levelised Cost Of Energy (LCOE) for an example scenario located in Western Australia. This work has been carried out as a part of the Lloyd's Register Educational Trust Collegium of 2011. (C) 2013 The Authors. Published by Elsevier Ltd. Open access under CC BY-NC-ND license. Selection and/or peer-review under responsibility of GHGT11sciescopu

Investigation of an offshore thermal power plant with carbon capture as an alternative to CO2 transportation

Carbon Capture and Storage (CCS) technology is considered to be one option to reduce CO2 emissions in order to mitigate climate change. Conventional CCS technology has its own complexities including high costs and risks for storing CO2. This paper introduces the concept of an Offshore Thermal Power Plant with CCS (OTPPC), which eliminates the needs for transporting CO2 and therefore reduces the complexities of the whole system. A general design selection process for the OTPPC is established. A case study is carried out to demonstrate the application of the OTPPC. The cost-effectiveness of this concept is evaluated by calculating the Levelised Cost Of Energy (LCOE) for both the OTPPC and conventional CCS technology for an onshore power plant with the assumption that CCS is necessary