Guilherme Vaz Thomas Lloyd, Douwe Rijpkema
Fifth International Symposium on Marine Propulsors smp’17, 2017.
@conference{Lloyd2017,
title = {Computational fluid dynamics prediction of marine propeller cavitation including solution verification},
author = {Thomas Lloyd, Guilherme Vaz, Douwe Rijpkema, Antoine Reverberi},
url = {http://www.marin.nl/web/Publications/Publication-items/Computational-fluid-dynamics-prediction-of-marine-propeller-cavitation-including-solution-verification.htm},
year = {2017},
date = {2017-06-01},
booktitle = {Fifth International Symposium on Marine Propulsors smp’17},
abstract = {This paper analyses the effect of grid refinement on computational fluid dynamics simulations of cavitating propeller flow. Refinement is made both globally, using geometrically similar grids, and locally, by applying adaptive grid refinement. The test case is the E779A propeller operating in uniform inflow conditions in a cavitation tunnel. This allows more computationally efficient steady simulations to be made, permitting a grid uncertainty analysis not previously seen for cavitating flow computations. Unsteady simulations are also presented in order to compare two turbulence modelling approaches. Differences in the discretisation uncertainty in terms of propeller thrust and torque were found to be small between wetted and cavitating flow conditions, although the order of convergence for the cavitating case is lower. Overall the largest effect of grid refinement is found to be in the tip vortex region, where differences in the predicted cavity extents are significant between grids. The use of adaptive grid refinement allows improved capture of tip vortex cavitation with fewer total grid cells, although the cavity extent is limited by increasing eddy viscosity when using RANS. Application of DDES reduces this influence somewhat, motivating further study into the potential of scale-resolving simulations in combination with adaptive grid refinement for vortex cavitation prediction.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
J. Baltazar, Rijpkema; Bosschers, J.
Prediction of the Open-Water Performance of Ducted Propellers With a Panel Method Conference
Fifth International Symposium on Marine Propulsors (SMP), Espoo, Finland, 2017.
@conference{Baltazar2017b,
title = {Prediction of the Open-Water Performance of Ducted Propellers With a Panel Method},
author = {Baltazar, J., Rijpkema, D.R., Falcão de Campos, J.A.C. and Bosschers, J.},
url = {http://www.marin.nl/web/Publications/Publication-items/Prediction-of-the-OpenWater-Performance-of-Ducted-Propellers-With-a-Panel-Method.htm},
year = {2017},
date = {2017-06-01},
booktitle = {Fifth International Symposium on Marine Propulsors (SMP), Espoo, Finland},
abstract = {In the present work, a comparison between the results obtained by a panel code with a RANS code is made to obtain a better insight on the viscous effects of the ducted propeller and on the limitations of the inviscid flow model, especially near bollard pull conditions or low advance ratios, which are important in the design stage. The analysis is carried out for propeller Ka4-70 operating inside duct 19A. From the comparison, several modelling aspects are studied for improvement of the inviscid (potential) flow solution. Finally, the experimental open-water data is compared with the panel method and RANS solutions. A strong influence of the blade wake pitch, especially near the blade tip, on the ducted propeller force predictions is seen. A reduction of the pitch of the gap strip is proposed for improvement of the performance prediction at low advance ratios.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Guilherme Vaz, Thomas Lloyd; Gnanasundaram, Arun
Improved Modelling Of Sheet Cavitation Dynamics On Delft Twistll Hydrofoil Conference
VII International Conference on Computational Methods in Marine Engineering, 2017.
@conference{Vaz2017,
title = {Improved Modelling Of Sheet Cavitation Dynamics On Delft Twistll Hydrofoil},
author = {Guilherme Vaz, Thomas Lloyd and Arun Gnanasundaram},
url = {http://www.marin.nl/web/Publications/Publication-items/Improved-Modelling-Of-Sheet-Cavitation-Dynamics-On-Delft-Twistll-Hydrofoil.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering},
abstract = {In this paper, unsteady viscous-flow cavitation predictions for a 3D hydrofoil are performed using three different approaches: 1) a pure RANS method; 2) a RANS method including an eddy-viscosity “Reboud” correction; 3) a DDES Scale-Resolving-Simulation approach. Both wetted and cavitating flow conditions are analysed and compared with experimental data. The accuracy of these approaches is scrutinised in terms of integral quantities, cavity dynamics, different background principles, and the influence of grid refinement. Low numerical uncertainties have been obtained for wetted flow conditions, but a somewhat large deviation on the wing loading has been observed when compared with experimental results. For the cavitating flow case, the RANS calculations do not accurately simulate the cavity dynamics. The RANSReboud correction improves the fidelity of the calculations at increased numerical demands and decreased robustness. The DDES approach leads to improved dynamics, slightly less accurate cavity shedding mechanism, at lower computational cost. The cavity extents are underpredicted for all methods and conditions used, when compared with the available experimental data.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Thomas P. Scholcz, Christian H. J. Veldhuis
Multi-Objective Surrogate Based Hull-Form Optimization Using High-Fidelity RANS Computations Conference
VII International Conference on Computational Methods in Marine Engineering (MARINE 2017), 2017.
@conference{Scholcz2017,
title = {Multi-Objective Surrogate Based Hull-Form Optimization Using High-Fidelity RANS Computations},
author = {Thomas P. Scholcz, Christian H.J. Veldhuis},
url = {http://www.marin.nl/web/Publications/Publication-items/MultiObjective-Surrogate-Based-HullForm-Optimization-Using-HighFidelity-RANS-Computations.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering (MARINE 2017)},
abstract = {RANS-based optimization procedures for ship design become increasingly complex and require the development of more efficient optimization techniques. The four phases of the design procedure are: shape parameterization, global sensitivity analysis, multi-objective optimization and design review. The dimensions of the design space can be mitigated by a smart choice for the shape parameterization and by screening and ranking the design variables in the global sensitivity phase. Subsequently, Surrogate Based Global Optimization (SBGO) is used to reduce the cost of the multi-objective optimization phase. For a practical application it is shown that the computational time reduces from two weeks to only a day when using SBGO instead of applying a Multi-Objective Genetic Algorithm (MOGA) directly to the solver. The design review phase is then used to verify and further develop the optimal design. Here, we focus on automatic ship design techniques which comprises the first three steps of the design procedure. Accelerating the ship design process is subject of ongoing research at the Maritime Research Institute Netherlands, making it useful for practical applications with turnaround times of only a few weeks.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
THOMAS LLOYD CARLO NEGRATO, TOM VAN TERWISGA; BENSOW, RICKARD
NUMERICAL STUDY OF CAVITATION ON A NACA0015 HYDROFOIL: SOLUTION VERIFICATION Conference
VII International Conference on Computational Methods in Marine Engineering, 2017.
@conference{NEGRATO2017,
title = {NUMERICAL STUDY OF CAVITATION ON A NACA0015 HYDROFOIL: SOLUTION VERIFICATION},
author = {CARLO NEGRATO, THOMAS LLOYD, TOM VAN TERWISGA, GUILHERME VAZ AND RICKARD BENSOW},
url = {http://www.marin.nl/web/Publications/Publication-items/Numerical-Study-Of-Cavitation-On-A-NACA0015-Hydrofoil-Solution-Verification.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering},
abstract = {The present paper analyses a series of Computational Fluid Dynamic simulations of the cavitating flow around a two-dimensional NACA0015 foil. The foil is placed at 6◦ angle of attack and the cavitation number is 1.1. Two mesh designs, namely a block-structured topology and an unstructured topology, are compared; additionally, grid refinements and time step refinements are carried out. Solution Verification is addressed with calculation of the discretization error and the numerical uncertainty. The numerical uncertainty for the average lift coefficient is found to be large, up to 15%. The reason is the difficulty of achieving a grid independent solution: with very fine meshes, the flow shifts from an attached, oscillating sheet cavity pattern to a regime dominated by shedding of cavity clouds. On the other hand, neither the time resolution nor the choice of grid topology influence largely the flow pattern; instead, they only lead to differences in the maximum and minimum cavity size.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Ana Lu´ısa Rocha, Lu´ıs E¸ca; Vaz, Guilherme
VII International Conference on Computational Methods in Marine Engineering, 2017.
@conference{Rocha2017,
title = {ON THE NUMERICAL CONVERGENCE PROPERTIES OF THE CALCULATION OF THE FLOW AROUND THE KVLCC2 TANKER IN UNSTRUCTURED GRIDS},
author = {Ana Lu´ısa Rocha, Lu´ıs E¸ca and Guilherme Vaz},
url = {http://www.marin.nl/web/Publications/Publication-items/On-The-Numerical-Convergence-Properties-Of-The-Calculation-Of-The-Flow-Around-The-KVLCC2-Tanker-In-Unstructured-Grids.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering},
abstract = {This paper addresses the estimation of numerical errors in the calculation of the flow around the KVLCC2 tanker at model scale Reynolds number in unstructured grids. The flow solution is based on the Reynolds-Averaged Navier-Stokes equations supplemented by the k − ω SST two-equation eddy-viscosity model using the so-called double-body approach, i.e. free surface effects are neglected. Grid refinement studies are performed for sets of grids generated with the open source code SnappyHexMesh and with the HEXPRESSTM grid generator. Definition of grid refinement ratio in unstructured grids and its consequences for the estimation of numerical errors is discussed. Friction and pressure resistance coefficients and mean velocity components at the propeller plane are compared with reference solutions obtained in nearly-orthogonal multi-block structured grids with the same flow solver ReFRESCO.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
F.S. Pereira, Eça; Vaz, G.
Verification and Validation exercises for the flow around the KVLCC2 tanker at model and full-scale Reynolds numbers Journal Article
In: Ocean Engineering, vol. 129, no. DOI: 10.1016/j.oceaneng.2016.11.005, pp. 133-148, 2017.
@article{Pereira2017,
title = {Verification and Validation exercises for the flow around the KVLCC2 tanker at model and full-scale Reynolds numbers},
author = {Pereira, F.S., Eça, L. and Vaz, G.},
url = {http://www.marin.nl/web/Publications/Publication-items/Verification-and-Validation-exercises-for-the-flow-around-the-KVLCC2-tanker-at-model-and-fullscale-Reynolds-numbers.htm},
year = {2017},
date = {2017-01-02},
booktitle = {Ocean Engineering},
journal = {Ocean Engineering},
volume = {129},
number = {DOI: 10.1016/j.oceaneng.2016.11.005},
pages = {133-148},
abstract = {This paper presents the quantification of numerical and modelling errors for the solution of the flow around the KVLCC2 tanker at model-scale Reynolds number. Numerical errors are also quantified for full-scale Reynolds number simulations to address the numerical accuracy of the prediction of scale-effects. The calculations are performed with the solver ReFRESCO using fourteen distinct Reynolds-Averaged Navier-Stokes (RANS) equations models. The quantities of interest for the Validation exercises at model-scale are the resistance coefficient and the velocity and turbulence kinetic energy fields at the propeller plane. Modelling errors are estimated using the ASME V & V20 procedure which requires numerical and experimental data with their respective uncertainties. Numerical uncertainties are dominated by the contribution of the discretization error, which is determined by grid refinement studies. Scale-effects are also assessed for the wake-fraction and formfactor. The outcome shows that quantifying modelling errors is not a trivial exercise that depends on the quality and details of simulations and experiments. Nonetheless, it is also evident that a quantitative evaluation of modelling errors is more reliable than traditional graphical comparisons of simulations and experiments. Fullscale results show scale-effects larger than numerical uncertainties that are illustrated for the form-factor and wake-fraction.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Gerco; Hooijmans Hagesteijn, Patrick; van der Meij
Proceedings of the ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering, OMAE2016, Busan, South Korea, 2016.
@conference{Hagesteijn2016,
title = {Correlation allowances in model tests results: A delicate balance between performance, accuracy and commercial interests?},
author = {Hagesteijn, Gerco; Hooijmans, Patrick; van der Meij, Karola},
url = {http://www.marin.nl/web/Publications/Papers/Correlation-allowances-in-model-tests-results-A-delicate-balance-between-performance-accuracy-and-commercial-interests.htm},
year = {2016},
date = {2016-06-19},
booktitle = {Proceedings of the ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering, OMAE2016, Busan, South Korea},
abstract = {Model tests at ballast and design draught are used to
convert the sea trial results from the ballast trial draught to the
contractual design draught. Correlation allowances in model test
results and their effect on the trial performance prediction are of
major importance. Nowadays it is not only typical to verify the
contract speed but also the EEDI certification requires a
verification of the speed power performance of the vessel. The
use of a to favorable CA-value may lead to attractive
performance figures, but also leads to higher fuel consumption
figures than expected. Furthermore the design point of the
propeller is affected, which leads to a too low light running
margin and in some cases to erosive cavitation.
During a study, large spreading in the values of the
correlation allowances for design draughts have been found for
merchant vessels tested at different model test institutes, but at
ballast trial draught the spreading is much less. Can it happen
that some institutes select favorable correlations allowances on
the basis of inaccurate trial data of shipyards? Or should we
accept a large spreading in correlation allowances and have
these indeed been confirmed by sea trials at design draught?
This paper will present a discussion using the experience of a
large full scale trial database as well as the accuracy of model
and full scale tests.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
convert the sea trial results from the ballast trial draught to the
contractual design draught. Correlation allowances in model test
results and their effect on the trial performance prediction are of
major importance. Nowadays it is not only typical to verify the
contract speed but also the EEDI certification requires a
verification of the speed power performance of the vessel. The
use of a to favorable CA-value may lead to attractive
performance figures, but also leads to higher fuel consumption
figures than expected. Furthermore the design point of the
propeller is affected, which leads to a too low light running
margin and in some cases to erosive cavitation.
During a study, large spreading in the values of the
correlation allowances for design draughts have been found for
merchant vessels tested at different model test institutes, but at
ballast trial draught the spreading is much less. Can it happen
that some institutes select favorable correlations allowances on
the basis of inaccurate trial data of shipyards? Or should we
accept a large spreading in correlation allowances and have
these indeed been confirmed by sea trials at design draught?
This paper will present a discussion using the experience of a
large full scale trial database as well as the accuracy of model
and full scale tests.
Veldhuis, Christian; van der Ploeg, Auke
Improved hull optimisation using PARNASSOS Explorer Journal Article
In: MARIN Report, no. 109, pp. 20-21, 2013.
@article{Veldhuis2013,
title = {Improved hull optimisation using PARNASSOS Explorer},
author = {Christian Veldhuis and Auke van der Ploeg},
url = {http://www.marin.nl/extra/marin-bladermodules/html/109/#20},
year = {2013},
date = {2013-08-01},
journal = {MARIN Report},
number = {109},
pages = {20-21},
abstract = {MARIN’s inhouse RANS optimisation tool PARNASSOS Explorer is helping the industry discover more about the optimal hull form in order to improve performance and save energy.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
2017
Guilherme Vaz Thomas Lloyd, Douwe Rijpkema
Fifth International Symposium on Marine Propulsors smp’17, 2017.
Abstract | Links | BibTeX | Tags: adaptive grid refinement, cavitation, DDES, RANS, verification
@conference{Lloyd2017,
title = {Computational fluid dynamics prediction of marine propeller cavitation including solution verification},
author = {Thomas Lloyd, Guilherme Vaz, Douwe Rijpkema, Antoine Reverberi},
url = {http://www.marin.nl/web/Publications/Publication-items/Computational-fluid-dynamics-prediction-of-marine-propeller-cavitation-including-solution-verification.htm},
year = {2017},
date = {2017-06-01},
booktitle = {Fifth International Symposium on Marine Propulsors smp’17},
abstract = {This paper analyses the effect of grid refinement on computational fluid dynamics simulations of cavitating propeller flow. Refinement is made both globally, using geometrically similar grids, and locally, by applying adaptive grid refinement. The test case is the E779A propeller operating in uniform inflow conditions in a cavitation tunnel. This allows more computationally efficient steady simulations to be made, permitting a grid uncertainty analysis not previously seen for cavitating flow computations. Unsteady simulations are also presented in order to compare two turbulence modelling approaches. Differences in the discretisation uncertainty in terms of propeller thrust and torque were found to be small between wetted and cavitating flow conditions, although the order of convergence for the cavitating case is lower. Overall the largest effect of grid refinement is found to be in the tip vortex region, where differences in the predicted cavity extents are significant between grids. The use of adaptive grid refinement allows improved capture of tip vortex cavitation with fewer total grid cells, although the cavity extent is limited by increasing eddy viscosity when using RANS. Application of DDES reduces this influence somewhat, motivating further study into the potential of scale-resolving simulations in combination with adaptive grid refinement for vortex cavitation prediction.},
keywords = {adaptive grid refinement, cavitation, DDES, RANS, verification},
pubstate = {published},
tppubtype = {conference}
}
J. Baltazar, Rijpkema; Bosschers, J.
Prediction of the Open-Water Performance of Ducted Propellers With a Panel Method Conference
Fifth International Symposium on Marine Propulsors (SMP), Espoo, Finland, 2017.
Abstract | Links | BibTeX | Tags: Ducted Propeller, Gap Strip Pitch., Panel Method, RANS
@conference{Baltazar2017b,
title = {Prediction of the Open-Water Performance of Ducted Propellers With a Panel Method},
author = {Baltazar, J., Rijpkema, D.R., Falcão de Campos, J.A.C. and Bosschers, J.},
url = {http://www.marin.nl/web/Publications/Publication-items/Prediction-of-the-OpenWater-Performance-of-Ducted-Propellers-With-a-Panel-Method.htm},
year = {2017},
date = {2017-06-01},
booktitle = {Fifth International Symposium on Marine Propulsors (SMP), Espoo, Finland},
abstract = {In the present work, a comparison between the results obtained by a panel code with a RANS code is made to obtain a better insight on the viscous effects of the ducted propeller and on the limitations of the inviscid flow model, especially near bollard pull conditions or low advance ratios, which are important in the design stage. The analysis is carried out for propeller Ka4-70 operating inside duct 19A. From the comparison, several modelling aspects are studied for improvement of the inviscid (potential) flow solution. Finally, the experimental open-water data is compared with the panel method and RANS solutions. A strong influence of the blade wake pitch, especially near the blade tip, on the ducted propeller force predictions is seen. A reduction of the pitch of the gap strip is proposed for improvement of the performance prediction at low advance ratios.},
keywords = {Ducted Propeller, Gap Strip Pitch., Panel Method, RANS},
pubstate = {published},
tppubtype = {conference}
}
Guilherme Vaz, Thomas Lloyd; Gnanasundaram, Arun
Improved Modelling Of Sheet Cavitation Dynamics On Delft Twistll Hydrofoil Conference
VII International Conference on Computational Methods in Marine Engineering, 2017.
Abstract | Links | BibTeX | Tags: cavitation, DDES, Delft Foil, RANS, Reboud-correction, ReFRESCO
@conference{Vaz2017,
title = {Improved Modelling Of Sheet Cavitation Dynamics On Delft Twistll Hydrofoil},
author = {Guilherme Vaz, Thomas Lloyd and Arun Gnanasundaram},
url = {http://www.marin.nl/web/Publications/Publication-items/Improved-Modelling-Of-Sheet-Cavitation-Dynamics-On-Delft-Twistll-Hydrofoil.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering},
abstract = {In this paper, unsteady viscous-flow cavitation predictions for a 3D hydrofoil are performed using three different approaches: 1) a pure RANS method; 2) a RANS method including an eddy-viscosity “Reboud” correction; 3) a DDES Scale-Resolving-Simulation approach. Both wetted and cavitating flow conditions are analysed and compared with experimental data. The accuracy of these approaches is scrutinised in terms of integral quantities, cavity dynamics, different background principles, and the influence of grid refinement. Low numerical uncertainties have been obtained for wetted flow conditions, but a somewhat large deviation on the wing loading has been observed when compared with experimental results. For the cavitating flow case, the RANS calculations do not accurately simulate the cavity dynamics. The RANSReboud correction improves the fidelity of the calculations at increased numerical demands and decreased robustness. The DDES approach leads to improved dynamics, slightly less accurate cavity shedding mechanism, at lower computational cost. The cavity extents are underpredicted for all methods and conditions used, when compared with the available experimental data.},
keywords = {cavitation, DDES, Delft Foil, RANS, Reboud-correction, ReFRESCO},
pubstate = {published},
tppubtype = {conference}
}
Thomas P. Scholcz, Christian H. J. Veldhuis
Multi-Objective Surrogate Based Hull-Form Optimization Using High-Fidelity RANS Computations Conference
VII International Conference on Computational Methods in Marine Engineering (MARINE 2017), 2017.
Abstract | Links | BibTeX | Tags: Hull-form, Multi-level, Multi-objective, optimization, RANS, Surrogate
@conference{Scholcz2017,
title = {Multi-Objective Surrogate Based Hull-Form Optimization Using High-Fidelity RANS Computations},
author = {Thomas P. Scholcz, Christian H.J. Veldhuis},
url = {http://www.marin.nl/web/Publications/Publication-items/MultiObjective-Surrogate-Based-HullForm-Optimization-Using-HighFidelity-RANS-Computations.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering (MARINE 2017)},
abstract = {RANS-based optimization procedures for ship design become increasingly complex and require the development of more efficient optimization techniques. The four phases of the design procedure are: shape parameterization, global sensitivity analysis, multi-objective optimization and design review. The dimensions of the design space can be mitigated by a smart choice for the shape parameterization and by screening and ranking the design variables in the global sensitivity phase. Subsequently, Surrogate Based Global Optimization (SBGO) is used to reduce the cost of the multi-objective optimization phase. For a practical application it is shown that the computational time reduces from two weeks to only a day when using SBGO instead of applying a Multi-Objective Genetic Algorithm (MOGA) directly to the solver. The design review phase is then used to verify and further develop the optimal design. Here, we focus on automatic ship design techniques which comprises the first three steps of the design procedure. Accelerating the ship design process is subject of ongoing research at the Maritime Research Institute Netherlands, making it useful for practical applications with turnaround times of only a few weeks.},
keywords = {Hull-form, Multi-level, Multi-objective, optimization, RANS, Surrogate},
pubstate = {published},
tppubtype = {conference}
}
THOMAS LLOYD CARLO NEGRATO, TOM VAN TERWISGA; BENSOW, RICKARD
NUMERICAL STUDY OF CAVITATION ON A NACA0015 HYDROFOIL: SOLUTION VERIFICATION Conference
VII International Conference on Computational Methods in Marine Engineering, 2017.
Abstract | Links | BibTeX | Tags: cavitation, Discretization Error, NACA0015 foil, RANS, verification
@conference{NEGRATO2017,
title = {NUMERICAL STUDY OF CAVITATION ON A NACA0015 HYDROFOIL: SOLUTION VERIFICATION},
author = {CARLO NEGRATO, THOMAS LLOYD, TOM VAN TERWISGA, GUILHERME VAZ AND RICKARD BENSOW},
url = {http://www.marin.nl/web/Publications/Publication-items/Numerical-Study-Of-Cavitation-On-A-NACA0015-Hydrofoil-Solution-Verification.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering},
abstract = {The present paper analyses a series of Computational Fluid Dynamic simulations of the cavitating flow around a two-dimensional NACA0015 foil. The foil is placed at 6◦ angle of attack and the cavitation number is 1.1. Two mesh designs, namely a block-structured topology and an unstructured topology, are compared; additionally, grid refinements and time step refinements are carried out. Solution Verification is addressed with calculation of the discretization error and the numerical uncertainty. The numerical uncertainty for the average lift coefficient is found to be large, up to 15%. The reason is the difficulty of achieving a grid independent solution: with very fine meshes, the flow shifts from an attached, oscillating sheet cavity pattern to a regime dominated by shedding of cavity clouds. On the other hand, neither the time resolution nor the choice of grid topology influence largely the flow pattern; instead, they only lead to differences in the maximum and minimum cavity size.},
keywords = {cavitation, Discretization Error, NACA0015 foil, RANS, verification},
pubstate = {published},
tppubtype = {conference}
}
Ana Lu´ısa Rocha, Lu´ıs E¸ca; Vaz, Guilherme
VII International Conference on Computational Methods in Marine Engineering, 2017.
Abstract | Links | BibTeX | Tags: KVLCC2, Numerical Error, RANS, Unstructured Grids
@conference{Rocha2017,
title = {ON THE NUMERICAL CONVERGENCE PROPERTIES OF THE CALCULATION OF THE FLOW AROUND THE KVLCC2 TANKER IN UNSTRUCTURED GRIDS},
author = {Ana Lu´ısa Rocha, Lu´ıs E¸ca and Guilherme Vaz},
url = {http://www.marin.nl/web/Publications/Publication-items/On-The-Numerical-Convergence-Properties-Of-The-Calculation-Of-The-Flow-Around-The-KVLCC2-Tanker-In-Unstructured-Grids.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering},
abstract = {This paper addresses the estimation of numerical errors in the calculation of the flow around the KVLCC2 tanker at model scale Reynolds number in unstructured grids. The flow solution is based on the Reynolds-Averaged Navier-Stokes equations supplemented by the k − ω SST two-equation eddy-viscosity model using the so-called double-body approach, i.e. free surface effects are neglected. Grid refinement studies are performed for sets of grids generated with the open source code SnappyHexMesh and with the HEXPRESSTM grid generator. Definition of grid refinement ratio in unstructured grids and its consequences for the estimation of numerical errors is discussed. Friction and pressure resistance coefficients and mean velocity components at the propeller plane are compared with reference solutions obtained in nearly-orthogonal multi-block structured grids with the same flow solver ReFRESCO.},
keywords = {KVLCC2, Numerical Error, RANS, Unstructured Grids},
pubstate = {published},
tppubtype = {conference}
}
F.S. Pereira, Eça; Vaz, G.
Verification and Validation exercises for the flow around the KVLCC2 tanker at model and full-scale Reynolds numbers Journal Article
In: Ocean Engineering, vol. 129, no. DOI: 10.1016/j.oceaneng.2016.11.005, pp. 133-148, 2017.
Abstract | Links | BibTeX | Tags: KVLCC2, Modelling error, Numerical Error, RANS, Turbulence modelling
@article{Pereira2017,
title = {Verification and Validation exercises for the flow around the KVLCC2 tanker at model and full-scale Reynolds numbers},
author = {Pereira, F.S., Eça, L. and Vaz, G.},
url = {http://www.marin.nl/web/Publications/Publication-items/Verification-and-Validation-exercises-for-the-flow-around-the-KVLCC2-tanker-at-model-and-fullscale-Reynolds-numbers.htm},
year = {2017},
date = {2017-01-02},
booktitle = {Ocean Engineering},
journal = {Ocean Engineering},
volume = {129},
number = {DOI: 10.1016/j.oceaneng.2016.11.005},
pages = {133-148},
abstract = {This paper presents the quantification of numerical and modelling errors for the solution of the flow around the KVLCC2 tanker at model-scale Reynolds number. Numerical errors are also quantified for full-scale Reynolds number simulations to address the numerical accuracy of the prediction of scale-effects. The calculations are performed with the solver ReFRESCO using fourteen distinct Reynolds-Averaged Navier-Stokes (RANS) equations models. The quantities of interest for the Validation exercises at model-scale are the resistance coefficient and the velocity and turbulence kinetic energy fields at the propeller plane. Modelling errors are estimated using the ASME V & V20 procedure which requires numerical and experimental data with their respective uncertainties. Numerical uncertainties are dominated by the contribution of the discretization error, which is determined by grid refinement studies. Scale-effects are also assessed for the wake-fraction and formfactor. The outcome shows that quantifying modelling errors is not a trivial exercise that depends on the quality and details of simulations and experiments. Nonetheless, it is also evident that a quantitative evaluation of modelling errors is more reliable than traditional graphical comparisons of simulations and experiments. Fullscale results show scale-effects larger than numerical uncertainties that are illustrated for the form-factor and wake-fraction.},
keywords = {KVLCC2, Modelling error, Numerical Error, RANS, Turbulence modelling},
pubstate = {published},
tppubtype = {article}
}
2016
Gerco; Hooijmans Hagesteijn, Patrick; van der Meij
Proceedings of the ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering, OMAE2016, Busan, South Korea, 2016.
Abstract | Links | BibTeX | Tags: allowance, analysis, correlation, extrapolation, merchant, prediction, RANS
@conference{Hagesteijn2016,
title = {Correlation allowances in model tests results: A delicate balance between performance, accuracy and commercial interests?},
author = {Hagesteijn, Gerco; Hooijmans, Patrick; van der Meij, Karola},
url = {http://www.marin.nl/web/Publications/Papers/Correlation-allowances-in-model-tests-results-A-delicate-balance-between-performance-accuracy-and-commercial-interests.htm},
year = {2016},
date = {2016-06-19},
booktitle = {Proceedings of the ASME 2016 35th International Conference on Ocean, Offshore and Arctic Engineering, OMAE2016, Busan, South Korea},
abstract = {Model tests at ballast and design draught are used to
convert the sea trial results from the ballast trial draught to the
contractual design draught. Correlation allowances in model test
results and their effect on the trial performance prediction are of
major importance. Nowadays it is not only typical to verify the
contract speed but also the EEDI certification requires a
verification of the speed power performance of the vessel. The
use of a to favorable CA-value may lead to attractive
performance figures, but also leads to higher fuel consumption
figures than expected. Furthermore the design point of the
propeller is affected, which leads to a too low light running
margin and in some cases to erosive cavitation.
During a study, large spreading in the values of the
correlation allowances for design draughts have been found for
merchant vessels tested at different model test institutes, but at
ballast trial draught the spreading is much less. Can it happen
that some institutes select favorable correlations allowances on
the basis of inaccurate trial data of shipyards? Or should we
accept a large spreading in correlation allowances and have
these indeed been confirmed by sea trials at design draught?
This paper will present a discussion using the experience of a
large full scale trial database as well as the accuracy of model
and full scale tests.},
keywords = {allowance, analysis, correlation, extrapolation, merchant, prediction, RANS},
pubstate = {published},
tppubtype = {conference}
}
convert the sea trial results from the ballast trial draught to the
contractual design draught. Correlation allowances in model test
results and their effect on the trial performance prediction are of
major importance. Nowadays it is not only typical to verify the
contract speed but also the EEDI certification requires a
verification of the speed power performance of the vessel. The
use of a to favorable CA-value may lead to attractive
performance figures, but also leads to higher fuel consumption
figures than expected. Furthermore the design point of the
propeller is affected, which leads to a too low light running
margin and in some cases to erosive cavitation.
During a study, large spreading in the values of the
correlation allowances for design draughts have been found for
merchant vessels tested at different model test institutes, but at
ballast trial draught the spreading is much less. Can it happen
that some institutes select favorable correlations allowances on
the basis of inaccurate trial data of shipyards? Or should we
accept a large spreading in correlation allowances and have
these indeed been confirmed by sea trials at design draught?
This paper will present a discussion using the experience of a
large full scale trial database as well as the accuracy of model
and full scale tests.
2013
Veldhuis, Christian; van der Ploeg, Auke
Improved hull optimisation using PARNASSOS Explorer Journal Article
In: MARIN Report, no. 109, pp. 20-21, 2013.
Abstract | Links | BibTeX | Tags: CFD, Explorer, improve performance, PARNASSOS, RANS, save engergy
@article{Veldhuis2013,
title = {Improved hull optimisation using PARNASSOS Explorer},
author = {Christian Veldhuis and Auke van der Ploeg},
url = {http://www.marin.nl/extra/marin-bladermodules/html/109/#20},
year = {2013},
date = {2013-08-01},
journal = {MARIN Report},
number = {109},
pages = {20-21},
abstract = {MARIN’s inhouse RANS optimisation tool PARNASSOS Explorer is helping the industry discover more about the optimal hull form in order to improve performance and save energy.},
keywords = {CFD, Explorer, improve performance, PARNASSOS, RANS, save engergy},
pubstate = {published},
tppubtype = {article}
}