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}
}
Crepier, P.
Ship Resistance Prediction: Verification And Validation Exercise On Unstructured Grids Conference
VII International Conference on Computational Methods in Marine Engineering (MARINE2017), 2017.
@conference{Crepier2017,
title = {Ship Resistance Prediction: Verification And Validation Exercise On Unstructured Grids},
author = {Crepier, P.},
url = {http://www.marin.nl/web/Publications/Publication-items/Ship-Resistance-Prediction-Verification-And-Validation-Exercise-On-Unstructured-Grids.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering (MARINE2017)},
abstract = {The prediction of the resistance of a ship is, together with the propeller performance prediction, part of the key aspects during the design process of a ship, as it partly ensures the quality of the power-prediction. Body fitted structured grids for ship simulations can be rather challenging and time consuming to build, especially when dealing with appended ship geometries. For this reason, unstructured hexahedral trimmed grids are more and more used. Such grids can be build by various CFD package such as CD-Adapcos Star CCM+, NUMECAs Hexpress grid generator or OpenFOAMSs SnappyHexMesh. Although their use is increasing or even already adopted, the numerical uncertainty of these simulations seems to be a well-kept secret.
In the study presented, an attempt at quantifying the numerical uncertainty of the resistance for the combination of the RANS Solver ReFRESCO [1] with grids generated using the commercial package Hexpress is made. The studied case is the flow around the bare-hull KVLCC2 at model scale Reynolds number. Extensive verification and validation on the same test case has already been published for the combination of ReFRESCO and structured grids by Pereira et al. [2].
The method to generate grids as geometrically similar as possible is presented, and the uncertainty analysis by L. Ec¸a and M. Hoekstra [3] is performed on the integral results obtained.
The simulations are performed using the k − ω SST, k − ω TNT and the k −√kL turbulence models. The velocity fields calculated in the propeller plane are compared to the measured ones and to the results obtained by Pereira et al. [2] on structured grids.
The results show that the differences with the experimental results are in the same range as the differences obtained with structured grids. The numerical uncertainties are, however, higher. They are also strongly dependent on the turbulence model used, like for structured grids, and are spread between 1.3% and 12%.
Concerning the wake flow details, not all features present in the experimental results are obtained and, compared to structured grids, the flow features are smoothed. The wake flow is also influenced by the turbulence modelling and needs to be adressed in more detail.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
In the study presented, an attempt at quantifying the numerical uncertainty of the resistance for the combination of the RANS Solver ReFRESCO [1] with grids generated using the commercial package Hexpress is made. The studied case is the flow around the bare-hull KVLCC2 at model scale Reynolds number. Extensive verification and validation on the same test case has already been published for the combination of ReFRESCO and structured grids by Pereira et al. [2].
The method to generate grids as geometrically similar as possible is presented, and the uncertainty analysis by L. Ec¸a and M. Hoekstra [3] is performed on the integral results obtained.
The simulations are performed using the k − ω SST, k − ω TNT and the k −√kL turbulence models. The velocity fields calculated in the propeller plane are compared to the measured ones and to the results obtained by Pereira et al. [2] on structured grids.
The results show that the differences with the experimental results are in the same range as the differences obtained with structured grids. The numerical uncertainties are, however, higher. They are also strongly dependent on the turbulence model used, like for structured grids, and are spread between 1.3% and 12%.
Concerning the wake flow details, not all features present in the experimental results are obtained and, compared to structured grids, the flow features are smoothed. The wake flow is also influenced by the turbulence modelling and needs to be adressed in more detail.
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}
}
J. Liu, Quadvlieg; Hekkenberg, R.
Impacts of the rudder profile on manoeuvring performance of ships Journal Article
In: Ocean Engineering, 2016, vol. 124, pp. 226-240, 2016.
@article{Liu2016,
title = {Impacts of the rudder profile on manoeuvring performance of ships},
author = {Liu, J., Quadvlieg, F.H.H.A. and Hekkenberg, R.},
url = {http://www.marin.nl/web/Publications/Papers/Impacts-of-the-rudder-profile-on-manoeuvring-performance-of-ships.htm},
doi = {10.1016/j.oceaneng.2016.07.064},
year = {2016},
date = {2016-09-01},
journal = {Ocean Engineering, 2016},
volume = {124},
pages = {226-240},
abstract = {The profile of a ship rudder influences the forces it generates, which in turn influence the manoeuvring performance of a ship. Thus, rudder forces and moments should be calculated considering the profile. Instead of an empirical estimation of the rudder normal force coefficient, this paper applies a RANS method to determine the hydrodynamic characteristics of various profiles, i.e. lift and drag coefficients. The RANS method is validated with a classic NACA 0012 profile and applied to 9 profiles from the NACA series, the wedge-tail series, and the IFS series. Furthermore, the 2D open-water RANS results are corrected for the effects of the propeller slipstream and the rudder aspect ratio. New regression formulas of the normal force coefficients are proposed for the tested profiles. These formulas are then integrated into a standard MMG model. Taking the KVLCC2 tanker as a reference ship, the manoeuvring model is validated with free-running tests executed by MARIN. Finally, the manoeuvring performance of the reference ship with various rudder profiles are quantified with turning and zigzag manoeuvres. The simulation results confirm that the wedge-tail series is most effective (largest manoeuvring forces) while the NACA series is most efficient (highest lift to drag ratio) among the tested profiles. The IFS series achieves a balance of effectiveness and efficiency.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
L. Eça, Vaz; Abreu, H.
Validation: What, Why And How Conference
OMAE ASME 35th International Conference on Ocean, Offshore and Arctic Engineering, Busan, South Korea, 2016.
@conference{Eça2016,
title = {Validation: What, Why And How},
author = {Eça, L., Vaz, G., Koop, A., Pereira, F. and Abreu, H.},
url = {http://www.marin.nl/web/Publications/Papers/Validation-What-Why-And-How.htm},
year = {2016},
date = {2016-06-19},
booktitle = {OMAE ASME 35th International Conference on Ocean, Offshore and Arctic Engineering, Busan, South Korea},
pages = {OMAE2016-54005},
abstract = {Offshore and Naval engineering have relied on physical models, i.e. experimental fluid dynamics (EFD), for several decades. Although the role of experiments in engineering is still unquestionable, some of the limitations of physical models, as for example domain size (blockage and scale effects), can be addressed using mathematical models, i.e. computational fluid dynamics (CFD). However, to gain confidence in the use of CFD it is fundamental to determine the modelling accuracy, i.e. to determine the difference between the “physical reality” and the selected mathematical model. The quantification of the modelling error is the goal of Validation. It must be emphasized that Validation applies to the mathematical model (and not the code) and is performed for selected flow quantities (the so-called quantities of interest).
Ideally, Validation would be performed comparing an exact measurement of the “physical reality” with the exact solution of the selected mathematical model. However, exact measurements do not exist and mathematical models for turbulent flows do not have analytical solutions. Therefore, procedures must be developed to take into account experimental and numerical uncertainties. Furthermore, the exact values of the flow parameters as for example Reynolds number, fluid viscosity or inlet turbulence quantities are often unknown, which leads to the so-called parameter uncertainty that also has to be dealt within the assessment of the modelling error.
The main goal of this paper is to demonstrate that the very popular designation of ”code X is validated” is meaningless without saying what is the mathematical model embedded in the code, what are the quantities of interest for the specific application and what is the Validation uncertainty imposed by the experimental, numerical and parameter uncertainties. Furthermore, we also illustrate that Validation is not a pass or fail exercise. A modelling error of 10% may be acceptable for a given application, whereas 1% may not be enough for a different one.
To this end, we present the application of the ASME V&V 20 Validation procedure for local set points and the metric for multiple set points to several practical test cases: prediction of transition from laminar to turbulent regime for the flow over a flat plate; flow around a circular cylinder; flow around the KVLCC2 tanker and current loads in shallow water for a LNG carrier. In most of these exercises, parameter uncertainty is assumed to be zero, which is an assumption often required for the so-called practical calculations due to the computational effort required to address it. Nonetheless, as an illustration of its application, the flow over the flat plate includes parameter uncertainty for the specification of the inlet turbulence quantities.},
keywords = {},
pubstate = {published},
tppubtype = {conference}
}
Ideally, Validation would be performed comparing an exact measurement of the “physical reality” with the exact solution of the selected mathematical model. However, exact measurements do not exist and mathematical models for turbulent flows do not have analytical solutions. Therefore, procedures must be developed to take into account experimental and numerical uncertainties. Furthermore, the exact values of the flow parameters as for example Reynolds number, fluid viscosity or inlet turbulence quantities are often unknown, which leads to the so-called parameter uncertainty that also has to be dealt within the assessment of the modelling error.
The main goal of this paper is to demonstrate that the very popular designation of ”code X is validated” is meaningless without saying what is the mathematical model embedded in the code, what are the quantities of interest for the specific application and what is the Validation uncertainty imposed by the experimental, numerical and parameter uncertainties. Furthermore, we also illustrate that Validation is not a pass or fail exercise. A modelling error of 10% may be acceptable for a given application, whereas 1% may not be enough for a different one.
To this end, we present the application of the ASME V&V 20 Validation procedure for local set points and the metric for multiple set points to several practical test cases: prediction of transition from laminar to turbulent regime for the flow over a flat plate; flow around a circular cylinder; flow around the KVLCC2 tanker and current loads in shallow water for a LNG carrier. In most of these exercises, parameter uncertainty is assumed to be zero, which is an assumption often required for the so-called practical calculations due to the computational effort required to address it. Nonetheless, as an illustration of its application, the flow over the flat plate includes parameter uncertainty for the specification of the inlet turbulence quantities.
2017
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}
}
Crepier, P.
Ship Resistance Prediction: Verification And Validation Exercise On Unstructured Grids Conference
VII International Conference on Computational Methods in Marine Engineering (MARINE2017), 2017.
Abstract | Links | BibTeX | Tags: CFD, Double-body, KVLCC2, Unstructured grid, Validation, verification
@conference{Crepier2017,
title = {Ship Resistance Prediction: Verification And Validation Exercise On Unstructured Grids},
author = {Crepier, P.},
url = {http://www.marin.nl/web/Publications/Publication-items/Ship-Resistance-Prediction-Verification-And-Validation-Exercise-On-Unstructured-Grids.htm},
year = {2017},
date = {2017-05-01},
booktitle = {VII International Conference on Computational Methods in Marine Engineering (MARINE2017)},
abstract = {The prediction of the resistance of a ship is, together with the propeller performance prediction, part of the key aspects during the design process of a ship, as it partly ensures the quality of the power-prediction. Body fitted structured grids for ship simulations can be rather challenging and time consuming to build, especially when dealing with appended ship geometries. For this reason, unstructured hexahedral trimmed grids are more and more used. Such grids can be build by various CFD package such as CD-Adapcos Star CCM+, NUMECAs Hexpress grid generator or OpenFOAMSs SnappyHexMesh. Although their use is increasing or even already adopted, the numerical uncertainty of these simulations seems to be a well-kept secret.
In the study presented, an attempt at quantifying the numerical uncertainty of the resistance for the combination of the RANS Solver ReFRESCO [1] with grids generated using the commercial package Hexpress is made. The studied case is the flow around the bare-hull KVLCC2 at model scale Reynolds number. Extensive verification and validation on the same test case has already been published for the combination of ReFRESCO and structured grids by Pereira et al. [2].
The method to generate grids as geometrically similar as possible is presented, and the uncertainty analysis by L. Ec¸a and M. Hoekstra [3] is performed on the integral results obtained.
The simulations are performed using the k − ω SST, k − ω TNT and the k −√kL turbulence models. The velocity fields calculated in the propeller plane are compared to the measured ones and to the results obtained by Pereira et al. [2] on structured grids.
The results show that the differences with the experimental results are in the same range as the differences obtained with structured grids. The numerical uncertainties are, however, higher. They are also strongly dependent on the turbulence model used, like for structured grids, and are spread between 1.3% and 12%.
Concerning the wake flow details, not all features present in the experimental results are obtained and, compared to structured grids, the flow features are smoothed. The wake flow is also influenced by the turbulence modelling and needs to be adressed in more detail.},
keywords = {CFD, Double-body, KVLCC2, Unstructured grid, Validation, verification},
pubstate = {published},
tppubtype = {conference}
}
In the study presented, an attempt at quantifying the numerical uncertainty of the resistance for the combination of the RANS Solver ReFRESCO [1] with grids generated using the commercial package Hexpress is made. The studied case is the flow around the bare-hull KVLCC2 at model scale Reynolds number. Extensive verification and validation on the same test case has already been published for the combination of ReFRESCO and structured grids by Pereira et al. [2].
The method to generate grids as geometrically similar as possible is presented, and the uncertainty analysis by L. Ec¸a and M. Hoekstra [3] is performed on the integral results obtained.
The simulations are performed using the k − ω SST, k − ω TNT and the k −√kL turbulence models. The velocity fields calculated in the propeller plane are compared to the measured ones and to the results obtained by Pereira et al. [2] on structured grids.
The results show that the differences with the experimental results are in the same range as the differences obtained with structured grids. The numerical uncertainties are, however, higher. They are also strongly dependent on the turbulence model used, like for structured grids, and are spread between 1.3% and 12%.
Concerning the wake flow details, not all features present in the experimental results are obtained and, compared to structured grids, the flow features are smoothed. The wake flow is also influenced by the turbulence modelling and needs to be adressed in more detail.
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
J. Liu, Quadvlieg; Hekkenberg, R.
Impacts of the rudder profile on manoeuvring performance of ships Journal Article
In: Ocean Engineering, 2016, vol. 124, pp. 226-240, 2016.
Abstract | Links | BibTeX | Tags: KVLCC2, Manoeuvring simulations, RANS methods, Rudder profiles, Ship manoeuvrability
@article{Liu2016,
title = {Impacts of the rudder profile on manoeuvring performance of ships},
author = {Liu, J., Quadvlieg, F.H.H.A. and Hekkenberg, R.},
url = {http://www.marin.nl/web/Publications/Papers/Impacts-of-the-rudder-profile-on-manoeuvring-performance-of-ships.htm},
doi = {10.1016/j.oceaneng.2016.07.064},
year = {2016},
date = {2016-09-01},
journal = {Ocean Engineering, 2016},
volume = {124},
pages = {226-240},
abstract = {The profile of a ship rudder influences the forces it generates, which in turn influence the manoeuvring performance of a ship. Thus, rudder forces and moments should be calculated considering the profile. Instead of an empirical estimation of the rudder normal force coefficient, this paper applies a RANS method to determine the hydrodynamic characteristics of various profiles, i.e. lift and drag coefficients. The RANS method is validated with a classic NACA 0012 profile and applied to 9 profiles from the NACA series, the wedge-tail series, and the IFS series. Furthermore, the 2D open-water RANS results are corrected for the effects of the propeller slipstream and the rudder aspect ratio. New regression formulas of the normal force coefficients are proposed for the tested profiles. These formulas are then integrated into a standard MMG model. Taking the KVLCC2 tanker as a reference ship, the manoeuvring model is validated with free-running tests executed by MARIN. Finally, the manoeuvring performance of the reference ship with various rudder profiles are quantified with turning and zigzag manoeuvres. The simulation results confirm that the wedge-tail series is most effective (largest manoeuvring forces) while the NACA series is most efficient (highest lift to drag ratio) among the tested profiles. The IFS series achieves a balance of effectiveness and efficiency.},
keywords = {KVLCC2, Manoeuvring simulations, RANS methods, Rudder profiles, Ship manoeuvrability},
pubstate = {published},
tppubtype = {article}
}
L. Eça, Vaz; Abreu, H.
Validation: What, Why And How Conference
OMAE ASME 35th International Conference on Ocean, Offshore and Arctic Engineering, Busan, South Korea, 2016.
Abstract | Links | BibTeX | Tags: a circular cylinder, a flat plate, CFD, EFD, KVLCC2, LNG carrier, Validation
@conference{Eça2016,
title = {Validation: What, Why And How},
author = {Eça, L., Vaz, G., Koop, A., Pereira, F. and Abreu, H.},
url = {http://www.marin.nl/web/Publications/Papers/Validation-What-Why-And-How.htm},
year = {2016},
date = {2016-06-19},
booktitle = {OMAE ASME 35th International Conference on Ocean, Offshore and Arctic Engineering, Busan, South Korea},
pages = {OMAE2016-54005},
abstract = {Offshore and Naval engineering have relied on physical models, i.e. experimental fluid dynamics (EFD), for several decades. Although the role of experiments in engineering is still unquestionable, some of the limitations of physical models, as for example domain size (blockage and scale effects), can be addressed using mathematical models, i.e. computational fluid dynamics (CFD). However, to gain confidence in the use of CFD it is fundamental to determine the modelling accuracy, i.e. to determine the difference between the “physical reality” and the selected mathematical model. The quantification of the modelling error is the goal of Validation. It must be emphasized that Validation applies to the mathematical model (and not the code) and is performed for selected flow quantities (the so-called quantities of interest).
Ideally, Validation would be performed comparing an exact measurement of the “physical reality” with the exact solution of the selected mathematical model. However, exact measurements do not exist and mathematical models for turbulent flows do not have analytical solutions. Therefore, procedures must be developed to take into account experimental and numerical uncertainties. Furthermore, the exact values of the flow parameters as for example Reynolds number, fluid viscosity or inlet turbulence quantities are often unknown, which leads to the so-called parameter uncertainty that also has to be dealt within the assessment of the modelling error.
The main goal of this paper is to demonstrate that the very popular designation of ”code X is validated” is meaningless without saying what is the mathematical model embedded in the code, what are the quantities of interest for the specific application and what is the Validation uncertainty imposed by the experimental, numerical and parameter uncertainties. Furthermore, we also illustrate that Validation is not a pass or fail exercise. A modelling error of 10% may be acceptable for a given application, whereas 1% may not be enough for a different one.
To this end, we present the application of the ASME V&V 20 Validation procedure for local set points and the metric for multiple set points to several practical test cases: prediction of transition from laminar to turbulent regime for the flow over a flat plate; flow around a circular cylinder; flow around the KVLCC2 tanker and current loads in shallow water for a LNG carrier. In most of these exercises, parameter uncertainty is assumed to be zero, which is an assumption often required for the so-called practical calculations due to the computational effort required to address it. Nonetheless, as an illustration of its application, the flow over the flat plate includes parameter uncertainty for the specification of the inlet turbulence quantities.},
keywords = {a circular cylinder, a flat plate, CFD, EFD, KVLCC2, LNG carrier, Validation},
pubstate = {published},
tppubtype = {conference}
}
Ideally, Validation would be performed comparing an exact measurement of the “physical reality” with the exact solution of the selected mathematical model. However, exact measurements do not exist and mathematical models for turbulent flows do not have analytical solutions. Therefore, procedures must be developed to take into account experimental and numerical uncertainties. Furthermore, the exact values of the flow parameters as for example Reynolds number, fluid viscosity or inlet turbulence quantities are often unknown, which leads to the so-called parameter uncertainty that also has to be dealt within the assessment of the modelling error.
The main goal of this paper is to demonstrate that the very popular designation of ”code X is validated” is meaningless without saying what is the mathematical model embedded in the code, what are the quantities of interest for the specific application and what is the Validation uncertainty imposed by the experimental, numerical and parameter uncertainties. Furthermore, we also illustrate that Validation is not a pass or fail exercise. A modelling error of 10% may be acceptable for a given application, whereas 1% may not be enough for a different one.
To this end, we present the application of the ASME V&V 20 Validation procedure for local set points and the metric for multiple set points to several practical test cases: prediction of transition from laminar to turbulent regime for the flow over a flat plate; flow around a circular cylinder; flow around the KVLCC2 tanker and current loads in shallow water for a LNG carrier. In most of these exercises, parameter uncertainty is assumed to be zero, which is an assumption often required for the so-called practical calculations due to the computational effort required to address it. Nonetheless, as an illustration of its application, the flow over the flat plate includes parameter uncertainty for the specification of the inlet turbulence quantities.