A pre-swirl fin (PSF), pre-swirl duct (PSD) and wake-equalizing duct (WED) energy-saving devices ... more A pre-swirl fin (PSF), pre-swirl duct (PSD) and wake-equalizing duct (WED) energy-saving devices (ESD) are designed for the Duisburg Test Case (DTC). To this aim, a simulation-based design optimization method, combining RANSE analyses (ship resistance) with BEM calculations (unsteady propeller performances) in a simplified optimization process realized through a parametric description of ESD geometries, was employed. Fully resolved RANSE analyses were used to validate the outcomes of this affordable design process, which identifies devices capable of saving energy in the delivered power for this type of challenging test case by up to 2.6%. Comparisons with model-scale calculations, furthermore, permit us to discuss the influence of each appendage in different flowfields (model- and full-scale, as well as under the action of the simplified or the resolved propeller) and the reliability of the full-scale extrapolation methods recently proposed for these types of devices.
International Journal of Naval Architecture and Ocean Engineering, 2021
The problem of predicting a ship's form factor and associated scale effects has been subject ... more The problem of predicting a ship's form factor and associated scale effects has been subject to many investigations in recent years. In this study, an attempt is made to investigate whether the form factor is influenced by a change in the ship's speed by numerically modelling a geosim series of the KCS hull with the aid of a RANS solver. The turbulence dependence of the problem is also studied by altering the closure model among three widely used approaches (the k-ω, k-ω SST, and k-e models). The results show that at very low speeds (Froude numbers in the range of 0.02~0.06) the numerical model predicts changes in the form factor of a ship between 10% and 20%, depending on the turbulence model and scale factor. As the speed is increased further, the form factor exhibits little change, usually in the range of 1% or less. Simulations where the Reynolds number is changed by approximately two orders of magnitude, achieved by altering the value of viscosity, confirmed that the form factor is Froude-dependent only for low speeds, predicting essentially identical values for two high speed cases.
The hydrodynamics of surface piercing struts and pile-like structures in general presents some ve... more The hydrodynamics of surface piercing struts and pile-like structures in general presents some very complex fluid dynamics phenomena that are worth investigating. Among them there are the forward wave pile-up at stagnation, the wave breaking with flow reversal like that observed in Bidone-type hydraulic jumps, flow separation caused by interactions of steep free-surface waves and the turbulent wall boundary layer. Such a type of flow structures plays a key role in several engineering applications, ranging from naval architecture to civil and ocean engineering. The hydrodynamic analysis of different surface-piercing struts in tandem configuration has been done in the framework of a Smoothed Particle Hydrodynamic approach available through the open-source software DualSPHysics, developed to exploit the GP-GPU architecture to speed up the computation. A numerical wave tank has been set-up to carry out calm water tests. Beyond the influence of the forward speed, the analysis has focused...
This paper addresses the problem of the numerical evaluation of the forces exerted by rudder/prop... more This paper addresses the problem of the numerical evaluation of the forces exerted by rudder/propeller complex; in particular, considering the common framework of RANS computations, different possible approximations of the propeller effect are taken into account, starting from the simplest uniform actuator disk and moving successively to an actuator disk with radial distributions of axial and tangential forces and then to a set of unsteady body forces, computed by a panel method, representative of the rotating pressure field of the propeller. All the results, in terms of global mean forces on the rudder and of fluctuating components and flow field, are compared to the full RANS computations and to the experimental results in model scale for the same configuration. The comparison of the results allows to identify the merits and the shortcomings of the different approaches, in order to select the best ones for the various possible applications, having in mind the necessity to keep the...
Pressure pulses evaluation is a current issue in highperformance propeller design. Usually, it ha... more Pressure pulses evaluation is a current issue in highperformance propeller design. Usually, it has been addressed experimentally and numerically but in most cases the analysis has been limited to the verification of a given geometry identified at the end of a traditional design loop. A more direct inclusion of pressure pulses evaluation in the design procedure, for instance by very attractive multi-objective optimization approaches, could be beneficial, especially if higher fidelity codes may be exploited. Among the others, BEM represent an acceptable compromise between computational costs and accuracy, allowing to better considering propeller geometry. However, the direct computation of pressure pulses by means of BEM may be not always reliable, especially in correspondence to heavy cavitation. Hence, further validations are needed, in particular when the influence of geometrical characteristics rarely taken into account, such as rake distribution, are considered. Cavitation tunnel...
PARTICLES VI : proceedings of the VI International Conference on Particle-Based Methods : fundamentals and applications, 2019
The hydrodynamic forces generated by the water moving inside a U-shaped tank are predicted by usi... more The hydrodynamic forces generated by the water moving inside a U-shaped tank are predicted by using the open-source Smoothed Particle Hydrodynamic (SPH) solver DualSPHysics. In particular the study focuses on the roll moment prediction of the U-tank undergoing forced roll motion at different frequencies. The sensitivity of the hydrodynamic prediction with respect to variations of particle resolution density is investigated by a systematic set of numerical simulations. Results of the SPH simulations are validated by comparison against available experimental data on a particular U-tank shape and discussed both in terms of roll moment amplitude and phase lag with respect to the imposed motion.
In this paper, we propose a Simulation-Based Design Optimization (SBDO) approach for the design o... more In this paper, we propose a Simulation-Based Design Optimization (SBDO) approach for the design of a Pre-Duct type Energy Saving Device (ESD). Pre-Ducts reduce the wake losses, contribute to a better interactions between the propeller and the hull and generate, in the end, generate an additional thrust. An integrated design approach, based on a parametric description of the duct geometry and on RANSE calculations together managed by an optimization algorithm, is developed to this aim, i.e. to maximize the thrust delivered by a Wake Equalizing Duct (WED). The Japan Bulk Carrier test case, for which experimental data regarding the effectiveness of WED is available in the literature, is considered as a reference. Results from the design activity show sensible improvements of the overall propulsive efficiency when the Pre-Duct design is tailored to the actual hull wake shape thanks to the flexibility provided by the fully automated design approach proposed in this paper
The 9th Conference on Computational Methods in Marine Engineering (Marine 2021), 2022
The potential impact of ships underwater radiated noise (URN) on marine fauna has become an impor... more The potential impact of ships underwater radiated noise (URN) on marine fauna has become an important issue. The most dominant noise source on a propeller-driven vessel is propeller cavitation, and the accurate prediction of its noise signature is fundamental for the design process. In this work, we investigate the potential of using low-computational-cost methods for the prediction of URN from cavitating marine propellers that can be conveniently implemented within the design process. We compare computational and experimental results on a subset of the Meridian standard propeller series, behind different severities of axial wake, for a total of 432 experiments.
Shape optimization and sensitivity can now be considered a standard to design efficient ships and... more Shape optimization and sensitivity can now be considered a standard to design efficient ships and new unconventional hull forms. There might be very different strategies to achieve such a process, depending on many circumstances, both operational (e.g. available time windows for computations) and methodological (e.g. available numerical methods). As in most of the engineering cases, the best trade-off between accuracy of the solution and the time required to achieve it is searched. When using medium-fidelity methods e.g. Boundary Element Methods (BEMs) for wave resistance and seakeeping, population based optimization algorithm can still be a viable way to achieve a design solution (see e.g. Vernengo et al., 2015 or Vernengo and Brizzolara, 2017). However, when the solution of the quantity of interest becomes more demanding, alternative methods of searching through the design space are needed. In this perspective, a surrogate model based approach for hull form sensitivity analysis is...
The following paper has as objective questioning the legitimacy of state's paternalistic interven... more The following paper has as objective questioning the legitimacy of state's paternalistic interventions on individual autonomy by using institutional-criminal instruments. In this path, the paper aims to understand in which cases the State is allowed to interfere in private individual lives under the justification of being promoting a well or avoiding a harm and, as well, in which cases such interference is abusive of individuals self-determination. Into this analysis, the work will study the current concepts of paternalism, the theoretical classifications on paternalistic interventions which will be useful to demonstrate admissible and inadmissible species of paternalism and Joel Feinberg and Gerald Dworkin's antipaternalistic theories. Following, this subject will be analyzed in association with the implications of juridical-criminal goods involved in conflicts between autonomy, human vulnerabilities and paternalism, specially regarding to the (un)availability of those goods. In the end, the work intends to define legitimation criteria for paternalistic interventions inserted in criminal laws, which superimpose themselves on the individual autonomy, in order to harmonize constitutional values of respect for autonomy, protection of vulnerable individuals and the Criminal Law functions of exclusive protection of juridical goods.
Two types of numerical simulations for the hydrodynamic solution of water entry problems are perf... more Two types of numerical simulations for the hydrodynamic solution of water entry problems are performed and systematically compared in order to highlight their peculiarities: a viscous Unsteady Reynolds Averaged Navier-Stokes (URANS) based on Volume of Fluid (VoF) approach and a meshless Smooth Particle Hydrodynamics (SPH) solver. In both cases open-source software have been chosen. The numerical solutions from the two proposed CFD methods are veried against experimental measurements. The systematic analysis is performed considering a prescribed motion of the wedge aiming to a better understanding of the effect of the model set-up on the prediction of both local and global eld variables. Even if a bothcodes shows a high ability to capture the global physics of the problem, due to the strongly non-linear dynamic of the body- ow interactions involved in impact problems, the local pressure peaks can be hardly predicted if the numerical method is not suitably tuned for the specific problem. Finally the two approaches are performed also for a free falling simulation, comparing the numerical predictions to the available experimental drop tests results
Marine propellers design requirements are always more pressing and the application of unusual pro... more Marine propellers design requirements are always more pressing and the application of unusual propulsive configurations, like ducted propellers with decelerating nozzles, may represent a valuable alternative to fulfil stringent design constraints. If accelerating duct configurations were realized mainly to increase the propeller efficiency in highly-loaded conditions, decelerating nozzles sustains the postponing of the cavitating phenomena that reflects into reduction of vibrations and radiated noise. The design of decelerating nozzle, unfortunately, is still challenging. No extensive systematic series are available and the design relies on few measurements. On the other hand, viscous flow solvers appear as reliable and accurate tools for the prediction of complex flow fields. Hence, in the present paper the opportunity to use CFD as a part of a design procedure based on optimization, by combining a parametric description of the geometry, the OpenFOAM solver and a genetic type algor...
In this paper, the underlay cognitive radio network over mix fading environment is presented and ... more In this paper, the underlay cognitive radio network over mix fading environment is presented and investigated. A cooperative cognitive system with a secondary source node S, a secondary destination node D, secondary relay node Relay, and a primary node P are considered. In this model system, we consider the mix fading environment in two scenarios as Rayleigh/ Nakagami-m and Nakagami-m/Rayleigh Fading channels. For system performance analysis, the closed-form expression of the system outage probability (OP) and the integral-formed expression of the ergodic capacity (EC) are derived in connection with the system's primary parameters. Finally, we proposed the Monte Carlo simulation for convincing the correctness of the system performance.
Abstract We propose a Simulation-Based Design Optimization (SBDO) approach for the design of an E... more Abstract We propose a Simulation-Based Design Optimization (SBDO) approach for the design of an Energy Saving Device (ESD) based on the Wake Equalizing Duct (WED) concept. Pre-Ducts, like Wake Equalizing Ducts, reduce the wake losses, improve the propeller-hull interaction and generate an additional thrust. An integrated design approach, relying on a parametric description of the duct geometry of the WEDs and on a RANSE method, managed by a global convergence optimization algorithm, is developed to maximize the delivered thrust. The Japan Bulk Carrier (JBC) test case, for which model scale experimental data on the effectiveness of the WED are available in the literature, is considered as a baseline. Results obtained by using the adaptive, fully automated proposed design framework highlight significant improvements of the overall propulsive efficiency when the Pre-Duct design is tailored to the actual hull wake shape. In addition, off-design conditions are considered to verify the robustness of the proposed designs with respect to variations of the working point and discuss the opportunity of a robust optimization process.
A pre-swirl fin (PSF), pre-swirl duct (PSD) and wake-equalizing duct (WED) energy-saving devices ... more A pre-swirl fin (PSF), pre-swirl duct (PSD) and wake-equalizing duct (WED) energy-saving devices (ESD) are designed for the Duisburg Test Case (DTC). To this aim, a simulation-based design optimization method, combining RANSE analyses (ship resistance) with BEM calculations (unsteady propeller performances) in a simplified optimization process realized through a parametric description of ESD geometries, was employed. Fully resolved RANSE analyses were used to validate the outcomes of this affordable design process, which identifies devices capable of saving energy in the delivered power for this type of challenging test case by up to 2.6%. Comparisons with model-scale calculations, furthermore, permit us to discuss the influence of each appendage in different flowfields (model- and full-scale, as well as under the action of the simplified or the resolved propeller) and the reliability of the full-scale extrapolation methods recently proposed for these types of devices.
International Journal of Naval Architecture and Ocean Engineering, 2021
The problem of predicting a ship's form factor and associated scale effects has been subject ... more The problem of predicting a ship's form factor and associated scale effects has been subject to many investigations in recent years. In this study, an attempt is made to investigate whether the form factor is influenced by a change in the ship's speed by numerically modelling a geosim series of the KCS hull with the aid of a RANS solver. The turbulence dependence of the problem is also studied by altering the closure model among three widely used approaches (the k-ω, k-ω SST, and k-e models). The results show that at very low speeds (Froude numbers in the range of 0.02~0.06) the numerical model predicts changes in the form factor of a ship between 10% and 20%, depending on the turbulence model and scale factor. As the speed is increased further, the form factor exhibits little change, usually in the range of 1% or less. Simulations where the Reynolds number is changed by approximately two orders of magnitude, achieved by altering the value of viscosity, confirmed that the form factor is Froude-dependent only for low speeds, predicting essentially identical values for two high speed cases.
The hydrodynamics of surface piercing struts and pile-like structures in general presents some ve... more The hydrodynamics of surface piercing struts and pile-like structures in general presents some very complex fluid dynamics phenomena that are worth investigating. Among them there are the forward wave pile-up at stagnation, the wave breaking with flow reversal like that observed in Bidone-type hydraulic jumps, flow separation caused by interactions of steep free-surface waves and the turbulent wall boundary layer. Such a type of flow structures plays a key role in several engineering applications, ranging from naval architecture to civil and ocean engineering. The hydrodynamic analysis of different surface-piercing struts in tandem configuration has been done in the framework of a Smoothed Particle Hydrodynamic approach available through the open-source software DualSPHysics, developed to exploit the GP-GPU architecture to speed up the computation. A numerical wave tank has been set-up to carry out calm water tests. Beyond the influence of the forward speed, the analysis has focused...
This paper addresses the problem of the numerical evaluation of the forces exerted by rudder/prop... more This paper addresses the problem of the numerical evaluation of the forces exerted by rudder/propeller complex; in particular, considering the common framework of RANS computations, different possible approximations of the propeller effect are taken into account, starting from the simplest uniform actuator disk and moving successively to an actuator disk with radial distributions of axial and tangential forces and then to a set of unsteady body forces, computed by a panel method, representative of the rotating pressure field of the propeller. All the results, in terms of global mean forces on the rudder and of fluctuating components and flow field, are compared to the full RANS computations and to the experimental results in model scale for the same configuration. The comparison of the results allows to identify the merits and the shortcomings of the different approaches, in order to select the best ones for the various possible applications, having in mind the necessity to keep the...
Pressure pulses evaluation is a current issue in highperformance propeller design. Usually, it ha... more Pressure pulses evaluation is a current issue in highperformance propeller design. Usually, it has been addressed experimentally and numerically but in most cases the analysis has been limited to the verification of a given geometry identified at the end of a traditional design loop. A more direct inclusion of pressure pulses evaluation in the design procedure, for instance by very attractive multi-objective optimization approaches, could be beneficial, especially if higher fidelity codes may be exploited. Among the others, BEM represent an acceptable compromise between computational costs and accuracy, allowing to better considering propeller geometry. However, the direct computation of pressure pulses by means of BEM may be not always reliable, especially in correspondence to heavy cavitation. Hence, further validations are needed, in particular when the influence of geometrical characteristics rarely taken into account, such as rake distribution, are considered. Cavitation tunnel...
PARTICLES VI : proceedings of the VI International Conference on Particle-Based Methods : fundamentals and applications, 2019
The hydrodynamic forces generated by the water moving inside a U-shaped tank are predicted by usi... more The hydrodynamic forces generated by the water moving inside a U-shaped tank are predicted by using the open-source Smoothed Particle Hydrodynamic (SPH) solver DualSPHysics. In particular the study focuses on the roll moment prediction of the U-tank undergoing forced roll motion at different frequencies. The sensitivity of the hydrodynamic prediction with respect to variations of particle resolution density is investigated by a systematic set of numerical simulations. Results of the SPH simulations are validated by comparison against available experimental data on a particular U-tank shape and discussed both in terms of roll moment amplitude and phase lag with respect to the imposed motion.
In this paper, we propose a Simulation-Based Design Optimization (SBDO) approach for the design o... more In this paper, we propose a Simulation-Based Design Optimization (SBDO) approach for the design of a Pre-Duct type Energy Saving Device (ESD). Pre-Ducts reduce the wake losses, contribute to a better interactions between the propeller and the hull and generate, in the end, generate an additional thrust. An integrated design approach, based on a parametric description of the duct geometry and on RANSE calculations together managed by an optimization algorithm, is developed to this aim, i.e. to maximize the thrust delivered by a Wake Equalizing Duct (WED). The Japan Bulk Carrier test case, for which experimental data regarding the effectiveness of WED is available in the literature, is considered as a reference. Results from the design activity show sensible improvements of the overall propulsive efficiency when the Pre-Duct design is tailored to the actual hull wake shape thanks to the flexibility provided by the fully automated design approach proposed in this paper
The 9th Conference on Computational Methods in Marine Engineering (Marine 2021), 2022
The potential impact of ships underwater radiated noise (URN) on marine fauna has become an impor... more The potential impact of ships underwater radiated noise (URN) on marine fauna has become an important issue. The most dominant noise source on a propeller-driven vessel is propeller cavitation, and the accurate prediction of its noise signature is fundamental for the design process. In this work, we investigate the potential of using low-computational-cost methods for the prediction of URN from cavitating marine propellers that can be conveniently implemented within the design process. We compare computational and experimental results on a subset of the Meridian standard propeller series, behind different severities of axial wake, for a total of 432 experiments.
Shape optimization and sensitivity can now be considered a standard to design efficient ships and... more Shape optimization and sensitivity can now be considered a standard to design efficient ships and new unconventional hull forms. There might be very different strategies to achieve such a process, depending on many circumstances, both operational (e.g. available time windows for computations) and methodological (e.g. available numerical methods). As in most of the engineering cases, the best trade-off between accuracy of the solution and the time required to achieve it is searched. When using medium-fidelity methods e.g. Boundary Element Methods (BEMs) for wave resistance and seakeeping, population based optimization algorithm can still be a viable way to achieve a design solution (see e.g. Vernengo et al., 2015 or Vernengo and Brizzolara, 2017). However, when the solution of the quantity of interest becomes more demanding, alternative methods of searching through the design space are needed. In this perspective, a surrogate model based approach for hull form sensitivity analysis is...
The following paper has as objective questioning the legitimacy of state's paternalistic interven... more The following paper has as objective questioning the legitimacy of state's paternalistic interventions on individual autonomy by using institutional-criminal instruments. In this path, the paper aims to understand in which cases the State is allowed to interfere in private individual lives under the justification of being promoting a well or avoiding a harm and, as well, in which cases such interference is abusive of individuals self-determination. Into this analysis, the work will study the current concepts of paternalism, the theoretical classifications on paternalistic interventions which will be useful to demonstrate admissible and inadmissible species of paternalism and Joel Feinberg and Gerald Dworkin's antipaternalistic theories. Following, this subject will be analyzed in association with the implications of juridical-criminal goods involved in conflicts between autonomy, human vulnerabilities and paternalism, specially regarding to the (un)availability of those goods. In the end, the work intends to define legitimation criteria for paternalistic interventions inserted in criminal laws, which superimpose themselves on the individual autonomy, in order to harmonize constitutional values of respect for autonomy, protection of vulnerable individuals and the Criminal Law functions of exclusive protection of juridical goods.
Two types of numerical simulations for the hydrodynamic solution of water entry problems are perf... more Two types of numerical simulations for the hydrodynamic solution of water entry problems are performed and systematically compared in order to highlight their peculiarities: a viscous Unsteady Reynolds Averaged Navier-Stokes (URANS) based on Volume of Fluid (VoF) approach and a meshless Smooth Particle Hydrodynamics (SPH) solver. In both cases open-source software have been chosen. The numerical solutions from the two proposed CFD methods are veried against experimental measurements. The systematic analysis is performed considering a prescribed motion of the wedge aiming to a better understanding of the effect of the model set-up on the prediction of both local and global eld variables. Even if a bothcodes shows a high ability to capture the global physics of the problem, due to the strongly non-linear dynamic of the body- ow interactions involved in impact problems, the local pressure peaks can be hardly predicted if the numerical method is not suitably tuned for the specific problem. Finally the two approaches are performed also for a free falling simulation, comparing the numerical predictions to the available experimental drop tests results
Marine propellers design requirements are always more pressing and the application of unusual pro... more Marine propellers design requirements are always more pressing and the application of unusual propulsive configurations, like ducted propellers with decelerating nozzles, may represent a valuable alternative to fulfil stringent design constraints. If accelerating duct configurations were realized mainly to increase the propeller efficiency in highly-loaded conditions, decelerating nozzles sustains the postponing of the cavitating phenomena that reflects into reduction of vibrations and radiated noise. The design of decelerating nozzle, unfortunately, is still challenging. No extensive systematic series are available and the design relies on few measurements. On the other hand, viscous flow solvers appear as reliable and accurate tools for the prediction of complex flow fields. Hence, in the present paper the opportunity to use CFD as a part of a design procedure based on optimization, by combining a parametric description of the geometry, the OpenFOAM solver and a genetic type algor...
In this paper, the underlay cognitive radio network over mix fading environment is presented and ... more In this paper, the underlay cognitive radio network over mix fading environment is presented and investigated. A cooperative cognitive system with a secondary source node S, a secondary destination node D, secondary relay node Relay, and a primary node P are considered. In this model system, we consider the mix fading environment in two scenarios as Rayleigh/ Nakagami-m and Nakagami-m/Rayleigh Fading channels. For system performance analysis, the closed-form expression of the system outage probability (OP) and the integral-formed expression of the ergodic capacity (EC) are derived in connection with the system's primary parameters. Finally, we proposed the Monte Carlo simulation for convincing the correctness of the system performance.
Abstract We propose a Simulation-Based Design Optimization (SBDO) approach for the design of an E... more Abstract We propose a Simulation-Based Design Optimization (SBDO) approach for the design of an Energy Saving Device (ESD) based on the Wake Equalizing Duct (WED) concept. Pre-Ducts, like Wake Equalizing Ducts, reduce the wake losses, improve the propeller-hull interaction and generate an additional thrust. An integrated design approach, relying on a parametric description of the duct geometry of the WEDs and on a RANSE method, managed by a global convergence optimization algorithm, is developed to maximize the delivered thrust. The Japan Bulk Carrier (JBC) test case, for which model scale experimental data on the effectiveness of the WED are available in the literature, is considered as a baseline. Results obtained by using the adaptive, fully automated proposed design framework highlight significant improvements of the overall propulsive efficiency when the Pre-Duct design is tailored to the actual hull wake shape. In addition, off-design conditions are considered to verify the robustness of the proposed designs with respect to variations of the working point and discuss the opportunity of a robust optimization process.
ECCOMAS MARINE 2021 - 9th Conference on Computational Methods in Marine Engineering
The potential impact of ships underwater radiated noise (URN) on marine fauna has become an impor... more The potential impact of ships underwater radiated noise (URN) on marine fauna has become an important issue. The most dominant noise source on a propeller-driven vessel is propeller cavitation, and the accurate prediction of its noise signature is fundamental for the design process. In this work, we investigate the potential of using low-computational-cost methods for the prediction of URN from cavitating marine propellers that can be conveniently implemented within the design process. We compare computational and experimental results on a subset of the Meridian standard propeller series, behind different severities of axial wake, for a total of 432 experiments.
5th International Conference on Maritime Technology and Engineering - MARTECH 2020, 2020
The interest in Energy Saving Devices (ESD) has grown significantly during the last years. Recent... more The interest in Energy Saving Devices (ESD) has grown significantly during the last years. Recent regulations, like the IMO EEOI (Energy Efficiency Operational Indicator) and EEDI (Energy Efficiency Design Index), impose further restrictions on emissions for both new designs and existing vessels. Moreover, these regulations encourage the development and the application of efficient, unconventional, propulsive solutions to fulfil these new requirements. The paper presents a design approach, based on the paradigm of optimization applied to Propeller Boss Cap Fin (PBCF) energy saving devices for ducted propellers. PBCF, indeed, were extensively studied in the case of conventional propellers, but nowadays there are only very few researches regarding the combination of these devices with unconventional propulsors, such as ducted propellers. Since the particular functioning of propellers inside nozzles can influence significantly the entire flow field aft the propeller, normally exploited by the PBCF for energy losses recovery, ad-hoc design procedures are required. By using a combination of RANSE analyses, a parametric description of the PBCF blade and an optimization algorithm, the paper illustrates the results of the design of PBCFs for propellers operating both in accelerating and decelerating nozzles, discussing the effectiveness of such kind of devices in case of ducted propellers.
VIII International Conference on Computational Methods in Marine Engineering, 2019
Propeller optimisation is always the focus of the propeller design process, as such process is ai... more Propeller optimisation is always the focus of the propeller design process, as such process is aimed at finding the best compromise between often conflicting objectives accounting for many design constraints. The use of optimization algorithms combined with blade shape modification techniques has been proposed by a number of research groups in the past few years and has proved to have a potential for practical applications, but integration in the everyday propeller design process is still beyond to be so consolidated. In the past one and a half year, CETENA, University of Genoa and the Fincantieri's Naval Vessels Business unit have teamed to set up a propeller optimization software environment to be used by Fincantieri's propeller designers in their everyday design work. A specification of the optimisation environment was worked out based on an analysis of the current design process, in order for the new procedures and tools to allow continuity of current practices while offering new possibilities in the comparative investigation of design variants and the identification of the very best design solution. The resulting optimisation environment integrates different software tools and consists of three main components linked by JAVA script architecture: a software tool for blade shape modification and definition (1), a BEM code for the evaluation of the propeller performance (2) and the open-source software DAKOTA to guide the optimisation (3). The software suite has been setup such as to be compatible with both Windows and Linux operating systems, in order to take advantage of all available computational resources, from single Windows workstations to the company's cluster, which operates under Linux. An ad-hoc '2D modeler' has been developed by the University of Genoa to model and modify the propeller design table, while a 3D modeller has been developed by CETENA to generate the 3D propeller description suitable for CFD RANS computations, starting from the 2D 296 propeller design curves. The propeller performance is evaluated using CRS BEM code PROCAL and the CRS Empirical Tip Vortex model. Measures of merit usually include: the propeller efficiency, pressure coefficients at specific locations on the blade back and face sides and, for an hydro-acoustic optimization, also the tip vortex induced pressure. The paper will provide details of the setup of the optimization environment focusing on an industrial application to design by optimization a naval propeller. The specific needs of the final users of the optimization suite will be highlighted and the expected benefits will be discussed, related to the time frame of the design process and the possibility of performing thorough investigations of design variants.
VIII International Conference on Computational Methods in Marine Engineering, 2019
The multi-fidelity machine learning framework proposed in this paper leverages a probabilistic ap... more The multi-fidelity machine learning framework proposed in this paper leverages a probabilistic approach based on Gaussian Process modeling for the formulation of stochas-tic response surfaces capable of describing propeller performance for different mission profiles. The proposed multi-fidelity techniques will help coping with the scarcity of high-fidelity measurements by using lower-fidelity numerical predictions. The existing correlation of the multi-fidelity data sets is used to infer high-fidelity measurements from lower fidelity numerical predictions. The probabilistic formulations embedded in Gaussian Process regressions gives the unique opportunity to learn the target functions describing propeller performance at different operating conditions, while quantifying the uncertainty associated to that specific prediction. While the multi-fidelity autoregressive scheme allows to construct high accurate response surfaces using only few experimental data, Uncertainty Quantification (UQ) provides an important metric to asses the quality of the learning process. We demonstrate the capability of the proposed framework to predict the performance of a controllable pitch propeller using few experimental data coming from towing tank experiments and many medium-fidelity predictions obtained using an in-house developed BEM, validated and verified in many previous studies.
Sixth International Symposium on Marine Propulsors, 2019
In this paper, we propose a Simulation-Based Design Optimization (SBDO) approach for the design o... more In this paper, we propose a Simulation-Based Design Optimization (SBDO) approach for the design of a Pre-Duct type Energy Saving Device (ESD). Pre-Ducts reduce the wake losses, contribute to a better interactions between the propeller and the hull and generate, in the end, generate an additional thrust. An integrated design approach, based on a parametric description of the duct geometry and on RANSE calculations together managed by an optimization algorithm, is developed to this aim, i.e. to maximize the thrust delivered by a Wake Equalizing Duct (WED). The Japan Bulk Carrier test case, for which experimental data regarding the effectiveness of WED is available in the literature , is considered as a reference. Results from the design activity show sensible improvements of the overall propul-sive efficiency when the Pre-Duct design is tailored to the actual hull wake shape thanks to the flexibility provided by the fully automated design approach proposed in this paper.
Fifth International Symposium on Marine Propulsors, 2017
Pressure pulses evaluation is a current issue in high-performance propeller design. Usually, it h... more Pressure pulses evaluation is a current issue in high-performance propeller design. Usually, it has been addressed experimentally and numerically but in most cases the analysis has been limited to the verification of a given geometry identified at the end of a traditional design loop. A more direct inclusion of pressure pulses evaluation in the design procedure, for instance by very attractive multi-objective optimization approaches, could be beneficial, especially if higher fidelity codes may be exploited. Among the others, BEM represent an acceptable compromise between computational costs and accuracy, allowing to better considering propeller geometry. However, the direct computation of pressure pulses by means of BEM may be not always reliable, especially in correspondence to heavy cavitation. Hence, further validations are needed, in particular when the influence of geometrical characteristics rarely taken into account, such as rake distribution, are considered. Cavitation tunnel test, BEM and RANS calculations (monitoring cavitation extent and pressure pulses) have been consequently carried out for two propellers, designed for the same functioning conditions with different rake distributions. This allows analyzing capabilities and limitations of these numerical approaches in the light of their possible application in a design by optimization procedure.
Fifth International Symposium on Marine Propulsors, 2017
The design of a propeller for a high-speed craft is addressed by using a multi-objective numerica... more The design of a propeller for a high-speed craft is addressed by using a multi-objective numerical optimization approach. By combining a fast and reliable Boundary Elements Method, a viscous flow solver based on the RANSE approximation, a parametric 3D description of the blade and a genetic algorithm, the new propeller shape is designed to improve the propulsive efficiency, reduce the cavitation extension, increase the cavitation inception speed and maximize, at the same time, the ship speed. Rather than by constraining the propeller delivered thrust, indeed, the proposed procedure works together with an engine-propeller matching algorithm that, each time a new propeller is defined, identifies the achievable maximum speed and the resulting engine functioning point that turn in additional goals for the optimization. A set of optimal propellers, obtained through the design by optimization based on potential flow calculations, are preliminary selected for additional viscous analyses in order to further validate the results of the BEM calculations and provide a deeper insight into the complex flow fields of high-speed propellers useful for choosing the optimal geometry. The improvements observed at the cavitation tunnel and the substantial increase of the maximum ship speed during sea trials on a high-speed craft provided by Azimut|Benetti prove the reliability of the design procedure.
ABSTRACT In the present work, an analysis of a CP CLT propeller, functioning in stationary and no... more ABSTRACT In the present work, an analysis of a CP CLT propeller, functioning in stationary and non-stationary conditions, is presented. Results of model tests at the cavitation tunnel of the University of Genoa, in correspondence to different advance coefficients, cavitation number and inflow wake, are presented, and used in order to compare with numerical results obtained with different numerical approaches. In particular, an in-house potential Panel Code, a commercial RANSE solver (StarCCM+) and an open source RANSE code (OpenFoam) are employed for the analysis of steady and unsteady cavitation characteristics, allowing to clearly underline merits and shortcomings of the different numerical approaches. Particular attention is given to the complex phenomena related to the tip region where the influence of the endplate is more pronounced.
This paper addresses the problem of the prediction of propellers induced pressures; to this aim n... more This paper addresses the problem of the prediction of propellers induced pressures; to this aim numerical and experimental results (both in model and full scale) in correspondence to different functioning conditions for a fast twin screw ship are reported. Numerical results were obtained by means of two different BEM codes and, only for specific cases, of a RANSE solver. Experiments were carried out both in model scale at cavita-tion tunnel and in full scale
In this work, the analysis of the Kriso Container Ship (KCS) test case using the OpenFOAM RANS so... more In this work, the analysis of the Kriso Container Ship (KCS) test case using the OpenFOAM RANS solver is proposed. Both ship resistance in calm water, propeller open water performances, self-propulsion calculations are proposed and the numerical results are validated by a comparison with the model scale experiments shared in literature and through workshops. The analyses are carried out applying the open source tools, from pre-to post-processing, available in the OpenFOAM environment, namely snappyHexMesh for the generation of the computational mesh, simpleFoam, pimpleDyMFoam, LTSInterFoam for the solution of the various hydrodynamic problems and Paraview for the post-processing of the results. The comparison with the experimental measurements, finally, demonstrates the maturity of these solvers for a reliable and, from an engineering point of view, accurate prediction of some of the peculiar characteristics of the flow ships and propellers are subjected to.
A numerical investigation of the impact of the speed reduction achieved by pitch or propeller Rev... more A numerical investigation of the impact of the speed reduction achieved by pitch or propeller Revolutions Per Minute (RPM) variations on propeller performances is proposed. A test case is selected from the European Project AQUO, for which experimental data are available. Numerical self-propulsion analyses are carried out to assess the off-design propeller functioning conditions of the propeller. Results, in terms of self-propulsion points and predicted pressure pulses in the various conditions under investigation (design speed at design pitch, reduced speed at reduced pitch and at reduced RPM), are compared with the available experimental measurements. On the basis of the predicted pressure pulses and cavitation volumes, conclu-sions are drawn about the acoustic impact of different strategies for realizing off-design operative conditions and on the possibility of ranking them by numerical methods.
In the last years the application of Computational Fluid Dynamics (CFD) methods experienced an ex... more In the last years the application of Computational Fluid Dynamics (CFD) methods experienced an exponential growth: the increase of the computational performances and the generalization of the Navier-Stokes equation to more complex physical problems made possible the solution of complex problems like free surfaces flows. The physical complexity of the planing hulls flows (i.e. the formation of jet sprays, the large pressure gradients in the stagnation area on the bottom, the sharp flow separation on the chines) poses some issues on the possibility of numerically predict the global hydrodynamic parameters (hull resistance, dynamic attitude) of planing hulls and on the confidence that can be expected on the numerical results. In last decade commercial RANS software have been successfully applied for the prediction of the planing hull characteristics with reasonable correlation with the available experimental measurements. Recently the interest in Open Source approaches, also for the solution of engineering problems, has rapidly grow: in this work, as a consequence, a set of calculations on a systematic series standard hull shape has been carried out, adopting from pre-to post-processing (and, of course, for the numerical solution) only Open Source tools, in order to compare and validate, through the available experimental measurements, the results calculated by a RANS solver and to define the optimal simulation strategy to include this kind of tools in the usual design loop.
This paper addresses the problem of the numerical evaluation of the forces exerted by rudder/prop... more This paper addresses the problem of the numerical evaluation of the forces exerted by rudder/propeller complex; in particular, considering the common framework of RANS computations, different possible approximations of the propeller effect are taken into account, starting from the simplest uniform actuator disk and moving successively to an actuator disk with radial distributions of axial and tangential forces and then to a set of unsteady body forces, computed by a panel method, representative of the rotating pressure field of the propeller. All the results, in terms of global mean forces on the rudder and of fluctuating components and flow field, are compared to the full RANS computations and to the experimental results in model scale for the same configuration. The comparison of the results allows to identify the merits and the shortcomings of the different approaches, in order to select the best ones for the various possible applications, having in mind the necessity to keep the computational efforts to a reasonable level during the design phases.
A major source of the underwater radiated noise from ships is represented by propulsion systems
a... more A major source of the underwater radiated noise from ships is represented by propulsion systems and by propellers in particular. The main noise-generating mechanism within ship propellers is cavitation, associated to the growing and collapse of vapour bubbles resulting from the unsteady hydrodynamic pressure field generated on the blades. The control of propeller underwater radiated noise is therefore strictly related to the control of cavitation phenomena, which are responsible for a larger part of the radiation. The activity within work package 2 of the collaborative project AQUO (Achieve QUiter Oceans by shipping noise footprint reduction, www.aquo.eu) of the 7th FP of the EU focuses on this aspect, which is analysed both from the experimental and numerical viewpoint. The present paper reports motivations, aims and achievements of such activity in the first year of the project.
The paper deals with self-propulsion problem, i.e. the solution of the flow around a hull that ad... more The paper deals with self-propulsion problem, i.e. the solution of the flow around a hull that advances at uniform speed due to the action of the propeller. Two different approaches are presented and compared in the paper: an approximated approach, using the classical actuator disk theory to represent the time averaged fluid dynamic action of the propeller through body forces in the RANSE solver; a viscous-inviscid coupled solution, in which the hull viscous flow is solved through RANSE, the propeller hydrodynamics in the wake of the hull through an unsteady panel method and the two solutions are matched via unsteady body forces. Main differences between the two approaches are presented also in quantitative sense. The very good results obtained with the proposed V.I. coupled method make it an ideally fast and robust tool to be used for ship self-propulsion characteristics evaluation in ship routine design activities.
The representation and the variation of hull shapes are two challenging problems in naval archite... more The representation and the variation of hull shapes are two challenging problems in naval architecture due to the complexity of the geometry and to the need to ensure the fairness of the surfaces. Conventional CAD techniques are widely used to accurately describe the hull shape. However, they are rather complex to be easily used to generate hull shape variations due to the great number of variables involved. We propose a study to highlight the pro and cons of the application of space reduction techniques, usually referred to as Reduced Order Models (ROMs), to create a parametric model for both global and local hull shape variations. A geometric transformation relying on the Proper Orthogonal Decomposition (POD) method is applied on top of a combined subdivision surface-Free Form Deformation (FFD) approach conceived for modeling and variation of hull shapes. The analysis focuses on highlighting the geometric meaning of the new POD basis functions and on how this model affects the variability of the explored design space. Two studies are developed in order to show possible applications of this technique. In the first one a new set of selection criteria for the POD modes based on geometric considerations are proposed to use it on uncorrelated geometric domains. In the latter the large-dimensional space of the so-called Design Velocities (DV), related to the shape sensitivity, is reduced by using the POD approach to create a new transformation of the hull shape.
Ducted propellers are unconventional systems that are usually adopted for ship propulsion. These ... more Ducted propellers are unconventional systems that are usually adopted for ship propulsion. These devices have recently been studied with medium-fidelity computational fluid dynamics code (based on the potential flow hypothesis) with promising results. However, these tools, even though they provide a good prediction of the forces and moments generated by the blades and the duct, are not able to provide insight into the flow field characteristics due to their crude flow approximations. On the contrary, modern high-fidelity viscous-based computational fluid dynamics codes could give a better description of the near and far-field flow of these particular devices. In the present paper, forces and the most significant features of the flow field around two ducted propellers are analyzed by means of both experimental and computational fluid dynamics approaches. In particular, accelerating and decelerating ducts are considered, and we demonstrate the ability of the adopted solver to accurately predict the performance and the flow field for both types. These results, in particular for the less-studied decelerating duct, designate CFD as a useful tool for reliable designs.
Wake equalizing duct (WED) Hydrodynamic shape optimization Reynolds averaged navier stokes (RANS)... more Wake equalizing duct (WED) Hydrodynamic shape optimization Reynolds averaged navier stokes (RANS) Simulation based design optimization (SBDO) Japab bulk carrier (JBC) A B S T R A C T We propose a Simulation-Based Design Optimization (SBDO) approach for the design of an Energy Saving Device (ESD) based on the Wake Equalizing Duct (WED) concept. Pre-Ducts, like Wake Equalizing Ducts, reduce the wake losses, improve the propeller-hull interaction and generate an additional thrust. An integrated design approach, relying on a parametric description of the duct geometry of the WEDs and on a RANSE method, managed by a global convergence optimization algorithm, is developed to maximize the delivered thrust. The Japan Bulk Carrier (JBC) test case, for which model scale experimental data on the effectiveness of the WED are available in the literature, is considered as a baseline. Results obtained by using the adaptive, fully automated proposed design framework highlight significant improvements of the overall propulsive efficiency when the Pre-Duct design is tailored to the actual hull wake shape. In addition, off-design conditions are considered to verify the robustness of the proposed designs with respect to variations of the working point and discuss the opportunity of a robust optimization process.
Achieving a reliable and accurate numerical prediction of the self-propulsion performance of a sh... more Achieving a reliable and accurate numerical prediction of the self-propulsion performance of a ship is still an open problem that poses some relevant issues. Several CFD methods, ranging from boundary element methods (BEM) to higher-fidelity viscous Reynolds averaged Navier-Stokes (RANS) based solvers, can be used to accurately analyze the separate problems, i.e. the open water propeller and the hull calm water resistance. However, when the fully-coupled self-propulsion problem is considered, i.e. the hull advancing at uniform speed propelled by its own propulsion system, several complexities rise up. Typical flow simplifications adopted to speed-up the simulations of the single analysis (hull and propeller separately) lose their validity requiring a more complex solver to tackle the fully-coupled problem. The complexity rises up further when considering a maneuver condition. This aspect increases the computational burden and, consequently, the required time which becomes prohibitive in a preliminary ship design stage. The majority of the simplified methods proposed in literature to include propeller effects, without directly solve the propeller flow, in a high-fidelity viscous solver are not able to provide all the commonly required self-propulsion coefficients. In this work, a new method to enrich the results from a body force based approach is proposed and investigated, with the aim to reduce as much as possible the computational burden without losing any useful result. This procedure is tested for validation on the KCS hull form in self-propulsion and maneuver conditions.
A computational framework for hydrodynamic shape optimization of complex ship hull form is propos... more A computational framework for hydrodynamic shape optimization of complex ship hull form is proposed and applied to improve the calm water performance of the KRISO Container Ship (KCS). The framework relies on three key features: a novel shape morphing method based on a combination of subdivision surfaces and free form deformations, a robust three dimensional viscous computational fluid dynamic solver based on the openFOAM open-source libraries and a Gaussian process-response surface method (GP-RSM) based on ordinary Kriging model which has been created to speed-up the evaluation of the quantity of interest (QoI) of the design process. The accuracy of the hydrodynamic solver is proven by comparing the obtained results against available experimental measurements. A preliminary sensitivity analysis on the mesh size has been carried out aiming at reducing the computational burden required by the CFD predictions. Three GP-RSMs have been trained relying on increasing number of hull designs. Each surrogate model has been cross-validated by both leave-one-out and k-fold techniques. The behaviours of these multi-dimensional surfaces have been analyzed in details by sampling the investigated design space with 10 7 points according to a Full-Factorial algorithm, highlighting the regions of maximum deviation with respect to the resistance of the reference hull. The three optimum designs provided by the corresponding GP-RSM models have been verified by using high-fidelity CFD simulations with a refined mesh configuration. Calm water resistance, wave patterns and pressure distributions over the selected hull surfaces have been discussed in the light of the generated shape variations.
A proper orthogonal decomposition (POD)-based method is proposed to reduce the dimensions of the ... more A proper orthogonal decomposition (POD)-based method is proposed to reduce the dimensions of the design space for the shape optimisation of marine propellers. The effectiveness of the proposed approach is proven in the case of the INSEAN-E779A propeller, which blade shape is modified to maximise efficiency while reducing suction side cavitation. The 23-dimensions design space defined by the conventional shape representation is reduced by the POD method to 5, 12 and 15 dimensions, retaining up to the 98% of the geometric variance of the original space. A multi-objective optimisation algorithm drives the simulation-based design optimisation (SBDO) process in the new design spaces using BEM for the hydrodynamic predictions. Finally, optimal designs are verified using RANSE to assess the correlation between the performance improvements, the dimensionality reduction and the corresponding geometric variance. The effectiveness of the proposed POD-SBDO framework is discussed with respect to a design by optimisation process relying on the conventional parametric representation of the blade geometry.
A B S T R A C T Marine propellers design requirements are always more pressing and the applicatio... more A B S T R A C T Marine propellers design requirements are always more pressing and the application of unusual propulsive configurations, like ducted propellers with decelerating nozzles, may represent a valuable alternative to fulfill stringent design constraints. Accelerating duct configurations were realized mainly to increase the propeller efficiency in the case of highly-loaded functioning. The use of decelerating nozzles sustains the postponing of the cavitating phenomena that, in turn, reflects into a reduction of vibrations and radiated noise. The design of decelerating nozzle, unfortunately, is still challenging. The complex interaction between the propeller and the nozzle, both in terms of global flow feature and local (tip located) phenomena, is not yet fully understood. No extensive systematic series, as in the case of accelerating configurations, are available and the design still relies on few measurements and data. On the other hand, viscous flow solvers appear as reliable and accurate tools for the prediction of complex flow fields and their application for the calculation of ducted propeller performance and nozzle flow was almost successful. Hence, using CFD as a part of a design procedure based on optimization, by combining a parametric description of the geometry, a RANSE solver (OpenFOAM) and a genetic type algorithm (the modeFrontier optimization environment), is the obvious step towards an even more reliable ducted propeller design. An actuator disk model is adopted to include efficiently the influence of the propeller on the flow around the duct; this allows avoiding the weighting of the computational effort that is necessary for the calculations of the thousands of geometries needed for the indirect design by optimization. Design improvements, in model scale, are measured by comparing, by means of dedicated fully resolved RANSE calculations, the performance of the optimized geometries with those of conventional shapes available in literature. For both nozzle typologies, dedicated shapes reducing the risk of cavitation and increasing the delivered thrust are obtained, showing the opportunity of customized nozzle design out of usual systematic series. In addition, by analyzing the results of the optimization histories, appropriate design criteria are derived for both accelerating and decelerating nozzle shapes.
Propeller modeling approaches for off–design operative conditions, 2019
In adverse situations, such as maneuvering and motion in waves, severe variations of the propelle... more In adverse situations, such as maneuvering and motion in waves, severe variations of the propeller inflow may be experienced, resulting in an increase of propeller thrust and torque and in the generation of in-plane loads. This may cause undesired hull-vibratory loads, stress of the propulsive system and even affect somehow the ship dynamic response. Thus, a reliable prediction of these phenomena during design phases is necessary to comply with the increasingly stringent constraints on safety at sea, propulsive efficiency, vibration and noise pollution. In the present work, the capabilities of a propeller solver based on a potential, boundary element method, routinely used in the optimization process of the propulsive device, to analyze the propeller performance under different maneuvering conditions are considered. After a first validation against simulations considering a simple oblique flow, the analysis is broadened to a propeller operating in the wake field of a twin screw ship in different maneuvering conditions, for which experimental results from free running tests in model scale are available. The solver is compared also to a steady blade element approach in order to achieve an overview of the respective pros and cons in view of their inclusion in simulations.
The effect of laminar to turbulent flow transition plays an important role for the prediction of ... more The effect of laminar to turbulent flow transition plays an important role for the prediction of model scale performance, which is of utmost interest for the development of scaling approaches entirely based on Computational Fluid Dynamics calculations. The recent inclusion of transition models (either based on local correlations, like the γ−Reθ , or on the concept of kinetic laminar energy, like the k−kL −ω) inmany RANS codes fosters their application for improving the model scale prediction of propeller performance. In the present work the numerical results using the well-established SST k − ω and the k − kL − ω turbulence models available in OpenFOAM are presented and compared with towing tank experiments for three test case propellers. The influence of turbulence parameters (i.e. turbulence intensity and turbulent viscosity ratio at inlet) is discussed, at first for the ERCOFTAC T3A flat plate validation case, through which useful guidelines for propeller performance predictions using transition sensitive turbulence models are derived. By using these relationships, a significant improvement of numerical predictions of propeller forces is achieved, with discrepancies with respect to model scale measurements appreciably reduced if compared to usual fully turbulent calculations. At the same time the limitations of the adopted transitional model are discussed based on the systematic analyses carried out for three test cases.
Correct evaluation of rudder performance is a key issue in assessing ship maneuverability. This p... more Correct evaluation of rudder performance is a key issue in assessing ship maneuverability. This paper presents a simplified approach based on a viscous flow solver to address propeller and rudder interactions. Viscous flow solvers have been applied to this type of problems, but the large computational requests limit (or even prevent) their application at a preliminary ship design stage. Based on this idea, a simplified approach to include the propeller effect in front of the rudder is considered to speed up the solution. Based on the concept of body forces, this approach enables sufficiently fast computation for a preliminary ship design stage, thereby maintaining its reliability. To define the limitations of the proposed procedure, an extensive analysis of the simplified method is performed and the results are compared with experimental data presented in the literature. Initially, the reported results show the capability of the body-force approach to represent the inflow field to the rudder without the full description of the propeller, also with regard to the complex bollard pull condition. Consequently, the rudder forces are satisfactorily predicted at least with regard to the lift force. However, the drag force evaluation is more problematic and causes higher discrepancies. Nevertheless, these discrepancies may be accepted due to their lower influence on the overall ship maneuverability performance.
In this paper, we present our analysis of the non-cavitating and cavitating unsteady performances... more In this paper, we present our analysis of the non-cavitating and cavitating unsteady performances of the Potsdam Propeller Test Case (PPTC) in oblique flow. For our calculations, we used the Reynolds-averaged Navier-Stokes equation (RANSE) solver from the open-source OpenFOAM libraries. We selected the homogeneous mixture approach to solve for multiphase flow with phase change, using the volume of fluid (VoF) approach to solve the multiphase flow and modeling the mass transfer between vapor and water with the Schnerr-Sauer model. Comparing the model results with the experimental measurements collected during the Second Workshop on Cavitation and Propeller Performance – SMP'15 enabled our assessment of the reliability of the open-source calculations. Comparisons with the numerical data collected during the workshop enabled further analysis of the reliability of different flow solvers from which we produced an overview of recommended guidelines (mesh arrangements and solver setups) for accurate numerical prediction even in off-design conditions. Lastly, we propose a number of calculations using the boundary element method developed at the University of Genoa for assessing the reliability of this dated but still widely adopted approach for design and optimization in the preliminary stages of very demanding test cases.
A B S T R A C T The present paper is focused on an experimental investigation of pressure pulses ... more A B S T R A C T The present paper is focused on an experimental investigation of pressure pulses and radiated noise for two alternative designs of a propeller of a high-speed craft. The propellers have been designed in the context of a research project starting from two different rake distributions (forward rake to increase thrust and efficiency, backward rake to reduce cavitation), using different techniques (traditional lifting line / lifting surface and optimization algorithm coupled with a panel code), leading thus to rather different geometries. Propellers have been tested through cavitation tunnel experiments. The activity represents an interesting case study for this kind of measurement in presence of rather large cavitation extensions. The effects of cavitation on different components of pressure pulses and noise are investigated for the different rake distributions adopted. Results clearly shows the effects of this geometrical characteristic on cavitation and pressure pulses pointing out that, in some cases, propeller hydrodynamic performances may determine pressure pulses intensity more than cavitation extensions. A simplified numerical approach, adopting stationary RANS calculations, for the evaluation of the effects of propeller geometry, has been proposed. Results show a good correlation with measurements allowing to have an insight into the phenomenon and confirming the effect of the rake.
The present paper deals with the side effects of propellers cavitation, i.e. pressure pulses and ... more The present paper deals with the side effects of propellers cavitation, i.e. pressure pulses and radiated noise. These effects are gaining more and more importance for commercial ships for different reasons. Pressure pulses significantly affect comfort onboard, thus their reduction is of utmost importance for all ships carrying passengers. As regards the underwater radiated noise, in the last decade interest has shifted from navy applications to commercial ships, due to the concern for the rising background noise in the oceans. The propellers, generating noise directly in water, represent one of the main contributions to the overall underwater noise emitted from ships. Due to the complexity of the mechanisms of propeller noise generation, different complementary strategies have to be followed to properly analyze the problem, ranging from induced pressure pulses to broadband noise and cavitation. In the present work, part of the activities carried out in the framework of the collaborative EU FP7 project AQUO (Achieve QUieter Oceans by shipping noise footprint reduction, www.aquo.eu) are reported. The paper presents the investigations carried out on a specific test case represented by a single screw research vessel , which is analyzed with three different strategies: numerical calculations, model scale investigations and full-scale measurements.
The design of a propeller for a high-speed craft is addressed by using a multi-objective numerica... more The design of a propeller for a high-speed craft is addressed by using a multi-objective numerical optimization approach. By combining a fast and reliable Boundary Elements Method (BEM), a viscous flow solver based on the RANSE approximation, a parametric 3D description of the blade and a genetic algorithm , the new propeller shape is designed to improve the propulsive efficiency, reduce the cavitation extension, increase the cavitation inception speed and maximize, at the same time, the ship speed. Rather than by constraining the propeller delivered thrust, indeed, the proposed procedure works together with an engine-propeller matching algorithm that, each time a new propeller is defined, identifies the achievable maximum ship speed and the resulting engine functioning point that turn in additional goals for the multi-objective optimization. A set of optimal propellers, obtained through the design by optimization based on potential flow calculations (via the Boundary Elements Method), are selected for additional viscous analyses (RANSE calculations) in order to further validate the results of the BEM calculations and provide a deeper insight into the complex flow fields of high speed propellers. Among this subset of optimal configurations, a final geometry is selected to verify the reliability of the design procedure by means of dedicated cavitation tunnel tests and full-scale measurements on a high-speed craft provided by Azimut|Benetti.
The paper deals with the self-propulsion problem, i.e. the solution of the flow around the hull t... more The paper deals with the self-propulsion problem, i.e. the solution of the flow around the hull that advances at uniform speed due to the action of its own propeller. A coupled BEM/RANS approach, previously proposed for a simpler case with only rudder and propeller, has been extensively analysed to highlight the strength and the weakness of the method. The proposed analyses consider the influence of different turbulence modelling, the role of the interpolating algorithm for the inclusion of body forces into the RANS domain, a mesh and simulation time step sensitivity study and the influence of the extrap-olation procedure for the definition of the effective wake to the propeller in the light of the lightest and the most affordable computational setup for daily accurate calculations. At first, the well-known Kriso Container Ship (KCS) test case is considered. This ship has been widely investigated in the context of different research projects and a large amount of data (both measurements and numerical calculations) is available to validate the solution approach and to highlight the benefits, as well as the weaknesses, of the proposed coupled BEM/RANS approach versus established but computationally demanding calculations based only on RANS simulations. Once the approach has been developed and validated via the KCS test case, calculations have been repeated in the case of completely different ships, in order to evaluate its general applicability and to test the robustness and the reliability of the proposed procedure.
A spatial non uniform inflow is the usual inflow to which a marine propeller is subjected to. Ins... more A spatial non uniform inflow is the usual inflow to which a marine propeller is subjected to. Inside a ship wake, in inclined shaft condition, in tandem/contra rotating configurations, the spatial non uniformity of the incoming flow on the propeller plane leads to the unsteadiness responsible of thrust and torque fluctuations, induced pressures, cavitation and the associated noise. Any design method and, moreover, each analysis tool should be able to treat these phenomena, to carry out a more consistent ship oriented propeller design and to better understand the flow features and the performances of an already designed propeller. In the present work two different numerical approaches, a commercial RANS solver and a in house developed Panel Method, are addressed and applied for the analysis of marine propellers subjected to an oblique inflow, showing, through the comparison with the experimental measures, their capabilities and their limitations.
Accurate and reliable numerical predictions of propeller performance are a fundamental aspect for... more Accurate and reliable numerical predictions of propeller performance are a fundamental aspect for any analysis and design of a modern propeller. Prediction of cavitation and of cavity extension is another important task, since cavitation is one of the crucial aspects that influences efficiency in addition to propagated noise and blade vibration and erosion. The validation of the numerical tools that support the design process, including open-source codes, is, consequently, essential. The public availability of measurements and observations which cover not only usual thrust and torque in open water conditions (including cavitation) but also unsteady functioning with pressure pulse measurements in the case of the Potsdam Propeller Test Case certainly represents an extremely useful source of information and an excellent chance for verification and validation purposes. In the present work, the prediction of the Potsdam Propeller Test Case propeller performance using the OpenFOAM computational fluid dynamics package is proposed. After a preliminary validation and calibration of the OpenFOAM native Schnerr–Sauer interphase mass transfer model for cavitating flow, based on the experimental results on a 2D NACA66Mod hydrofoil, open water propeller performance and cavitation predictions are carried out. The OpenFOAM results are finally compared both with the available experimental measurements and with calculations carried out with StarCCM+ and with a proprietary boundary element method code, in order to assess the accuracy and the overall capabilities of the open-source tools (from meshing to post-processing) available in the OpenFOAM package. The comparison, in addition to assessing the accuracy of the open-source approach, is aimed to verify its advantages and drawbacks with respect to widely used solvers and to further verify the reliability of traditional boundary element method approaches that are still widely adopted for design and optimization (thanks to their extremely higher computational efficiency) in a very demanding test case.
SUMMARY In recent years, the application of Computational Fluid Dynamics (CFD) methods experience... more SUMMARY In recent years, the application of Computational Fluid Dynamics (CFD) methods experienced an exponential growth: the increase of the computational performances and the generalization of the Navier-Stokes equation to more complex physical problems made possible the solution of complex problems like free surfaces flows. The physical complexity of planing hulls flows poses some issues in the ability to numerically predict the global hydrodynamic parameters (hull resistance, dynamic attitude) of these configurations and on the expected confidence on the numerical results. In the last decade, commercial RANS software have been successfully applied for the prediction of the planing hull characteristics with reasonable correlation to the available experimental measurements. Recently, moreover, the interest in Open Source approaches, also for the solution of engineering problems, has rapidly grow. In this work, a set of calculations on a systematic series standard hull shape has been carried out, adopting from pre-to post-processing only Open Source tools. The comparison and the validation, through the available experimental measurements, of the computed results will define an optimal simulation strategy to include this kind of tools in the usual design loop.
In the context of the low speed and high drift angles manoeuvres, a limited number of experimenta... more In the context of the low speed and high drift angles manoeuvres, a limited number of experimental test cases are available in open literature. Consequently, the ability to reliably predict the hull forces (and the related hydrodynamic coefficients) via computational fluid dynamics calculations may represent a significant added value to further tune or to generate new simplified hull forces models to be employed in a manoeuvring code. Even if some applications can be found in the literature for selected cases and conditions, as those considered in the present work, a more systematic comparison is mandatory to confirm the reliability of these numerical approaches. In light of this, in the present work a systematic application of the open-source viscous-based flow solver OpenFOAM to predict forces at low-speed manoeuvring conditions for two ship test cases (the KCS and the KVLCC) is presented. The proposed numerical setup, specifically designed to be applied in the early ship design stage (limiting computational effort), shows a satisfactory accuracy to cope with the strong off-design conditions related to these specific ship operative conditions. Keywords Slow speed manoeuvrability · CFD viscous code · OpenFOAM · CFD verification and validation
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Papers by Diego Villa
and by propellers in particular. The main noise-generating mechanism within ship propellers is cavitation,
associated to the growing and collapse of vapour bubbles resulting from the unsteady hydrodynamic
pressure field generated on the blades. The control of propeller underwater radiated noise is therefore strictly
related to the control of cavitation phenomena, which are responsible for a larger part of the radiation. The activity
within work package 2 of the collaborative project AQUO (Achieve QUiter Oceans by shipping noise
footprint reduction, www.aquo.eu) of the 7th FP of the EU focuses on this aspect, which is analysed both from
the experimental and numerical viewpoint. The present paper reports motivations, aims and achievements of
such activity in the first year of the project.
scale performance, which is of utmost interest for the development of scaling approaches entirely based
on Computational Fluid Dynamics calculations. The recent inclusion of transition models (either based on
local correlations, like the γ−Reθ , or on the concept of kinetic laminar energy, like the k−kL
−ω) inmany
RANS codes fosters their application for improving the model scale prediction of propeller performance.
In the present work the numerical results using the well-established SST k − ω and the k − kL
− ω
turbulence models available in OpenFOAM are presented and compared with towing tank experiments for
three test case propellers. The influence of turbulence parameters (i.e. turbulence intensity and turbulent
viscosity ratio at inlet) is discussed, at first for the ERCOFTAC T3A flat plate validation case, through
which useful guidelines for propeller performance predictions using transition sensitive turbulence models
are derived. By using these relationships, a significant improvement of numerical predictions of propeller
forces is achieved, with discrepancies with respect to model scale measurements appreciably reduced if
compared to usual fully turbulent calculations. At the same time the limitations of the adopted transitional
model are discussed based on the systematic analyses carried out for three test cases.