| 1. |
- Ahlström, Christoffer, et al.
(författare)
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Optimus Pråm - Semi-submersible wind farm installation vessel for Blekinge Offshore
- 2014
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- In Sweden the government is investing lots of resources in order to meet the energy need with clean and renewable alternatives. Since wind is an unlimited source of energy the exploitations of wind farms is of great interest. This report describes a conceptual design of an innovative offshore wind turbine installation vessel for inland sea conditions, with highest possible energy efficiency and environmental friendly performance in every detail. The customer, Blekinge Offshore, main requirement is to receive a concept with an as low installation cost as possible.The final concept Optimus Pråm includes one installation vessel, which is a semi-submersible barge, and one support vessel that supply the installation vessel with power and propulsion. The power is distributed from the support vessel to the installation vessel through a power cable. The installation vessel will be self-propelled during the installation phase using electrical motors and thrusters.The installation vessel shall be able to handle gravity foundations and fully assembled wind turbines, transported vertically to the installation site. Foundations and windmills will be fully assembled in Karlshamn port before transit to site. During transit the installation and support vessel are connected to each other in all motions except pitch. This almost total fixed connection makes the two vessels acts like one, which gives the joint vessel excellent manoeuvrability. When installing foundations, the installation vessel and the support vessel disconnect. The installation vessel places the foundation at the planned location by ballasting until the foundation has reached the seabed. After de-ballasting the installation vessel and support vessel connects again and transit back to the harbour. When installing wind turbines the two vessels are kept connected and makes highly accurate positioning for the installation possible
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| 2. |
- Korkmaz, Kadir Burak, 1989, et al.
(författare)
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A Validation Study of Full-Scale CFD Simulation for Sea Trial Performance Prediction of Ships
- 2023
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Ingår i: World Congress in Computational Mechanics and ECCOMAS Congress. - 2696-6999.
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Konferensbidrag (refereegranskat)abstract
- Shipping is a critical component of global trade but also accounts for a substantial portion of global greenhouse gas emissions. Recognising this issue, the International Maritime Organisation (IMO) has implemented new measures aimed at determining the energy efficiency of all ships and promoting continuous improvements, such as the Energy Efficiency Existing Ship Index (EEXI). As Computational Fluid Dynamics (CFD) can be used to calculate the EEXI value, RISE-SSPA1 and Flowtech have developed a CFD-based method for predicting full-scale ship performance with SHIPFLOW v7.0, which meets the new requirements of IMO. The method is validated through an extensive comparison study that examines the delivered power and propeller rotation rate between full-scale CFD predictions and high-quality sea trials using 14 common cargo ships of varying sizes and types. The comparison between the CFD predictions and 59 sea trials shows that both delivered power and RPM can be predicted with satisfactory accuracy, with an average comparison error of about 4% and 2%, respectively. The numerical methods used in this study differ significantly from the majority of the state-of-the-art CFD codes, highlighting their potential for future applications in ship performance prediction. Thorough validation with a large number of sea trials is essential to establish confidence in CFD-based ship performance prediction methods, which is crucial for the credibility of the EEXI framework and its potential to contribute to shipping decarbonisation.
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| 3. |
- Korkmaz, Kadir Burak, 1989
(författare)
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Assessment of Experimental, Computational, and Combined EFD/CFD Methods for Ship Performance Prediction
- 2023
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- In today’s highly competitive market, alongside increasingly stringent regulatory requirements, the precise prediction of ship performance has assumed paramount importance for both design verification and operational evaluations. This thesis addresses the need for a comprehensive assessment of Experimental Fluid Dynamics (EFD), Computational Fluid Dynamics (CFD), and their combination to enhance the accuracy of performance predictions. Moreover, it explores the potential of combined EFD/CFD methods in improving power predictions by either replacing or complementing certain aspects of the existing methodology, while also introducing novel methods. The investigation identifies the Prohaska method as a prominent source of uncertainty in the ITTC-78 method. As an alternative, the CFD-based form factor method is meticulously examined, employing various codes and numerical approaches. The findings robustly establish the applicability and accuracy of the CFD-based form factor method, even when subjected to diverse numerical approaches and computational grids. Furthermore, best practice guidelines are derived for double-body RANS computations, ensuring compatibility with experimental form factors. Another debated issue within the ITTC-78 method is the very concept of form factor. This study conclusively affirms the Reynolds number dependence in form factors when the ITTC-57 line is employed. However, the numerical friction lines derived in this research, effectively eliminates these scale effects. Additionally, this study addresses conditions with flow separation, which renders the conventional form factor approach inadequate. A two form factor method (2−k method) is proposed to address instances of separated flow, complemented by an empirical correction formula for vessels with deep transom submergence and wetted transom flow. Furthermore, this thesis delves into the exploration of direct full-scale CFD computations for ship performance prediction. Extensive validation studies, encompassing numerous test cases and sea trials, are conducted to compare the accuracy of full-scale CFD computations with EFD based, and combined EFD/CFD methods. This thesis quantifies, for the first time in the literature, the difference in accuracy between fully computational and extrapolation-based methods using a large number of test cases and sea trials. The results indicate that while the prediction accuracy of full-scale CFD computations for power and RPM is lower than the other methods, the discrepancy is not substantial. Conversely, the investigations underscore that the combined EFD/CFD methods stand as the most accurate prediction method. Consequently, this thesis recommends incorporating combined EFD/CFD methods into the recommended procedures, as it offers immediate improvements to the existing ship performance prediction methods.
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| 4. |
- Korkmaz, Kadir Burak, et al.
(författare)
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CFD based form factor determination method
- 2021
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Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 220
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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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| 5. |
- Korkmaz, Kadir Burak, 1989, et al.
(författare)
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CFD PREDICTIONS INCLUDING VERIFICATION AND VALIDATION OF RESISTANCE, PROPULSION AND LOCAL FLOW FOR THE JAPAN BULK CARRIER (JBC) WITH AND WITHOUT AN ENERGY SAVING DEVICE
- 2015
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Ingår i: Proceedings, Tokyo 2015 Workshop on CFD in Ship Hydrodynamics. ; 3
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- This paper presents the results of verification and validation (V&V) studies for resistance and self-propulsion simulations together with investigations of the local flow on the JAPAN Bulk Carrier (JBC) with and without an energy saving device (ESD). Computations are reported for all JBC test cases proposed by the Tokyo 2015 Workshop. In total, four V&V studies are presented for Case1.1a, Case1.2a, Case1.5a and Case1.6a using five systematically refined grids in each study. Local flow predictions for Case1.3a, Case1.4a, Case1.7a and Case1.8a are shown using the finest grids of the grid convergence studies. Resistance predictions using the finest grids are within 1% of the measured data both with and without the ESD. The predicted gain in delivered power is the same as in the measurements: 6.0%, although there is an under prediction of the effective wake in both cases
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| 6. |
- Korkmaz, Kadir Burak, 1989
(författare)
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Improved Power Predictions of Ships Using Combined CFD/EFD Methods for the Form Factor
- 2020
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Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Performance prediction of a ship is one of the most important tasks during the design phase. Once the design is finalized, the speed attained at a certain power consumption has to be verified with the most accurate prediction as it is specified at the contract of a new ship order and also required by the legal authorities. Considering the current commercial tendencies and the requirements enforced by legal authorities, towing tank testing and the extrapolation methods recommended by the International Towing Tank Conference (ITTC) are used and regarded as a highly accurate power prediction methodology for common cargo vessels. However, some aspects of this methodology have been questioned such as the scale effects on the form factor and its determination method. It is argued in this thesis that if a part of the Experimental Fluid Dynamics (EFD) based measure or the extrapolation procedure causes higher uncertainty than the numerical uncertainty and modelling errors of a Computational Fluid Dynamics (CFD) application, the corresponding part of the performance prediction method can be replaced or supplemented by CFD. In this study, the possibility to improve the power predictions by the introduction of a combined CFD/EFD Method was investigated by replacing the experimental determination of the form factor with double body computations based on the Reynolds-Averaged Navier-Stokes (RANS) equations, i.e. CFD based form factors. As a result of a joint, study where the double body simulations performed with seven different CFD codes, the CFD based form factors compared well with the experimentally determined form factors. Additionally, the standard deviations of the CFD based form factors were similar to the experimental uncertainty of the form factors even though the abundance of unsystematically varied methods and grids. Following the Quality Assurance Procedure proposed by the ITTC, a best practice guideline has been derived for the CFD based form factor determination method by applying systematic variations to the CFD set-ups. After the verification and validation of the CFD based form factor method in model scale, the full scale speed-power-rpm relations between large number of speed trials and full scale predictions were investigated using the CFD based form factors in combination to the ITTC-57 line and the numerical friction lines. It is observed that the usage of CFD based form factors improves the predictions in general and no deterioration in the prediction accuracy is noted within the limits of this study. Therefore, the combination of EFD and CFD is expected to provide immediate improvements to the 1978 ITTC Performance Prediction Method.
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| 7. |
- Korkmaz, Kadir Burak, 1989, et al.
(författare)
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Investigations for CFD Based Form Factor Methods
- 2019
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Ingår i: Numerical Towing Tank Symposium.
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Konferensbidrag (refereegranskat)abstract
- In this study, the form factor concept has been investigated by analyzing the results obtained from the simulations performed on KVLCC2 and KCS hulls. Grid dependence studies, sensitivity analysis of loading conditions and varying grid setups have been performed with SHIPFLOW code. Extrapolation of viscous resistance to full scale has been performed with ITTC57 line and numerical friction lines.
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| 8. |
- Korkmaz, Kadir Burak, 1989, et al.
(författare)
-
Investigations on experimental and computational trim optimisation methods
- 2023
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Ingår i: Ocean Engineering. - : Elsevier Ltd. - 0029-8018 .- 1873-5258. ; 288
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Tidskriftsartikel (refereegranskat)abstract
- Shipping is vital for global trade but also emits significant greenhouse gases. To address this issue, various measures have been proposed, including improved ship design, alternative fuels, and improved operational practices. One such cost-effective operational measure is trim optimisation, which involves operating the ship at the hydrodynamically optimal forward and aft draughts. This study focuses on investigating the trim trends of a RoPax vessel using experimental fluid dynamics (EFD) and computational fluid dynamics (CFD) methods. The trim trends are derived in resistance and self-propelled modes. Multiple CFD methods are examined, along with different extrapolation techniques for experimental results. Uncertainty assessment is conducted for the experimental data, and a verification and validation study is performed. Furthermore, the predictions are compared with real operational data. The findings reveal that determining trim trends solely in towed mode is inadequate due to the profound influence of the operating propeller. Some of the investigated CFD methods demonstrate good agreement with the model test results in self-propelled mode, while others exhibit limitations. By selecting appropriate models and configurations, this study demonstrates that trim trends can be determined with sufficient precision, as evidenced by the comparison between ship operational data and predictions from EFD and CFD methods.
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| 9. |
- Korkmaz, Kadir Burak, 1989, et al.
(författare)
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Numerical Friction Lines for CFD Based Form Factor Determination Method
- 2019
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Ingår i: 8th International Conference on Computational Methods in Marine Engineering, MARINE 2019. - : International Center for Numerical Methods in Engineering. - 9788494919435 ; , s. 694-705
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Konferensbidrag (refereegranskat)abstract
- In this study, frictional resistance coefficients of an infinitely thin 2D plate have been computed at 14 Reynolds numbers (between log(10)(Rn) = 6.25 to 9.5) in sets of five geometrically similar structured grids in order to perform reliable grid dependence studies. Additional grid dependency studies have been performed by using 5 sets of grids which have the same number of cells in all directions but varying first cell sizes normal to the flat plate at log(10)(Rn) = 6.25. Average y(+) values for each grid set for the finest grid varies between 0.0075 and 0.5 (from set 1 to 5 respectively) while none of the simulations exceeded average y+ value of 1. All simulations were performed with the direct application of the no-slip condition at walls. Therefore, no wall functions were used. Two turbulence models have been used for the investigations: k - omega SST and EASM. Extensive grid dependence studies have been performed with two different CFD codes SHIPFLOW and FINE (TM)/MARINE, using the same grids. Special attention was paid to the transition from laminar to turbulent flow at the lowest Reynolds number since laminar part can cover a significant part of the plate. At log(10)(Rn) = 6.25 for both CFD codes, laminar flow and transition to turbulent flow was distinctive even though no transition models were applied. Significant dependency on y+ has been observed with FINE (TM)/MARINE on friction resistance coefficient. On the other hand, SHIPFLOW exhibited less sensitivity to the first cell size variation, hence, revealed smaller numerical uncertainties in general. To ensure a numerical uncertainty of frictional resistance component below 1%, average y(+) < 0.016 have been used for generating the data points of friction line with SHIPFLOW for each turbulence model. Data points of 14 Reynolds number have been transformed into numerical friction lines by applying curve fits. Obtained friction lines are compared with ITTC57 line, Schoenherr, Hughes, Toki, Katsui, Grigson lines and two numerical friction lines.
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| 10. |
- Korkmaz, Kadir Burak, 1989, et al.
(författare)
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Scaling of wetted-transom resistance for improved full-scale ship performance predictions
- 2022
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Ingår i: Ocean Engineering. - : Elsevier BV. - 0029-8018 .- 1873-5258. ; 266
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Tidskriftsartikel (refereegranskat)abstract
- Determining a ship's propulsive power is a critical stage in the design phase in which the evaluation of the stern plays a crucial role. Different flow regimes can be observed depending on the position and shape of the transom. This paper investigates the wetted-transom flow characteristics and their implications on the 1978 ITTC Performance Prediction Method. In the case of flow separation, such as the wetted-transom flow, the current ITTC-78 procedure does not provide an alternative method. Therefore, two alternative methods were proposed based on the investigations of CFD computations on seven hull forms. The firstly proposed method is a combined EFD&CFD method called the two form factor method. It requires CFD computations in model and full-scale, and it can handle any case of flow separation, including the wetted-transom flow. The second proposed method is an empirical correction formula for the hulls with a wetted-transom flow. Finally, the full-scale speed-power relations between the speed trials and the full-scale predictions from the two alternative methods and the standard ITTC-78 method were presented. It is observed that the two suggested methods considerably improve the correlation between the predictions and the speed trials.
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| 11. |
- Korkmaz, Kadir Burak, 1989, et al.
(författare)
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Verification and Validation of CFD Based Form Factors as a Combined CFD/EFD Method
- 2021
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Ingår i: Journal of Marine Science and Engineering. - : MDPI AG. - 2077-1312. ; 9:1, s. 1-30
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Tidskriftsartikel (refereegranskat)abstract
- Predicting the propulsive power of ships with high accuracy still remains a challenge. Well established practices in the 1978 ITTC Power Prediction method have been questioned such as the form factor approach and its determination method. This paper investigates the possibility to improve the power predictions by the introduction of a combined CFD/EFD Method where the experimental determination of form factor is replaced by double body RANS computations. Following the Quality Assurance Procedure proposed by ITTC, a best practice guideline has been derived for the CFD based form factor determination method by applying systematic variations to the CFD set-ups. Following the verification and validation of the CFD based form factor method in model scale, the full scale speed-power-rpm relations between large number of speed trials and full scale predictions using the CFD based form factors in combination with ITTC-57 line and numerical friction lines are investigated. It is observed that the usage of CFD based form factors improves the predictions in general and no deterioration is noted within the limits of this study. Therefore, the combination of EFD and CFD is expected to provide immediate improvements to the 1978 ITTC Performance Prediction Method.
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| 12. |
- Korkmaz, Kadir Burak, 1989, et al.
(författare)
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Virtual captive tests as a new tool for early maneuvering performance assessment
- 2018
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Ingår i: SNAME Maritime Convention, SMC 2018.
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Konferensbidrag (refereegranskat)abstract
- Maneuverability is an important aspect of ship performance, and often evaluated in late stages of ship design process. In order to include maneuvering assessment in the early design stage, virtual captive test (VCT) method have been developed as a new tool for early maneuvering performance assessment. In this study, a destroyer hull form with complex appendages and a MR tanker have been analyzed with VCT. Hydrodynamic coefficients were compared to the captive model tests for both hulls and maneuvering simulations of the destroyer hull form is presented in comparison to model tests.
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