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Sökning: WFRF:(Tezdogan Tahsin)

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1.
  • Andersson, Jennie, 1986, et al. (författare)
  • Ship-scale CFD benchmark study of a pre-swirl duct on KVLCC2
  • 2022
  • Ingår i: Applied Ocean Research. - : Elsevier Ltd. - 0141-1187 .- 1879-1549. ; 123
  • Tidskriftsartikel (refereegranskat)abstract
    • 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. © 2022 The Authors
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2.
  • Korkmaz, Kadir Burak, et al. (författare)
  • CFD based form factor determination method
  • 2021
  • Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 220
  • Tidskriftsartikel (refereegranskat)abstract
    • The 1978 ITTC Power Prediction method is used to predict the propulsive power of ships through towing tank testing. The form factor approach and its determination in this method have been questioned. This paper investigates the possibility to improve the power predictions by introducing Combined CFD/EFD Method where the experimental determination of form factor is replaced by double body RANS computations applied for open cases KVLCC2 and KCS, including first-time published towing tank tests of KVLCC2 at ballast condition including an experimental uncertainty analysis specifically derived for the form factor. Computations from nine organisations and seven CFD codes are compared to the experiments. The form factor predictions for both hulls in design loading condition compared well with the experimental results in general. For the KVLCC2 ballast condition, majority of the form factors were under-predicted while staying within the experimental uncertainty. Speed dependency is observed with the application of ITTC57 line but it is reduced with the Katsui line and nearly eliminated by numerical friction lines. Comparison of the full-scale viscous resistance predictions obtained by the extrapolations from model scale and direct full-scale computations show that the Combined CFD/EFD Method show significantly less scatter and may thus be a preferred approach.
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