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The Ffowcs-Williams and Hawkings acoustic analogy was exploited to reconstruct the acoustic signature of a tip-loaded propeller with winglets across a range of working conditions, from design toward higher loads. Results of Large-Eddy Simulations, conducted on a computational grid consisting of about 5 × 109 points, were utilized. For decreasing values of the advance coefficient, that is for increasing rotational speeds of the propeller, the rise of the values of acoustic pressure was found faster than linear, approximating a logarithmic growth. This result was verified in line with the behavior by the turbulent fluctuations on the surface of the propeller and in its wake system, which were the major sources of the loading and quadrupole components of sound, respectively. The former was the leading one on the propeller plane and at radial coordinates away from the wake system, while the latter was higher at smaller radial coordinates in the vicinity of the wake system. In addition, increasing loads on the propeller blades resulted in an outward shift of the boundary of the computational domain where the lead of the acoustic signature switched from the non-linear sources within the wake to the linear ones on the propeller surface.

In this chapter, CFD computations for a steady turn manoeuvre are compared to experiments performed in the QinetiQ rotating arm basin. The validation data provided to the group consists of forces and moments measured on the appended hull during the turn. As for the other chapters, a huge amount of data is collected given the number of institutions, computational codes and turbulence models or grid methodologies. The comparison between the CFD and the experiments is then the largest collaborative validation database known to date and provides the state of the art for CFD methodologies on submarines in complex manoeuvres. The validation exercise concludes that the dominant forces and moments Y , K and M are predicted consistently with the experiments but that more accurate information on the uncertainties in the measurements is needed to strengthen the conclusions. It is also concluded that the discrepancies observed in the comparisons are originating from the presence (or absence) of stall on the aft control surfaces. These differences in the local flows around the control surfaces are mostly attributed to the turbulence models and, as concluded in the previous chapters, the complete knowledge of the implementation of the models is found necessary to understand the results. Further validation studies on this turning manoeuvre would require aft control surfaces dedicated measurements of forces and wall shear stress to fully validate the computational methodologies. The analysis of the flow variables in the vortices confirms previous conclusions in the variability of the results due to the differences in the local grid refinements, and experimental data is necessary to achieve validation of the numerical prediction of these flow features.

The flow around the rotor of an axial turbine, operating in the wake of an upstream one, is resolved using large-eddy simulation on a cylindrical grid consisting of 3.8 billion points. Three distances from the upstream rotor are considered, ranging from 6 to 10 diameters. The inflow boundary conditions for the simulation of the downstream rotor were generated by a precursor simulation of the upstream one. The impact on the dynamics of the tip vortices and the statistics at their core is compared across cases. Results demonstrate the strong sensitivity of the tip vortices shed by the downstream rotor to the disturbance produced by the wake of the upstream one. The onset of their instability moves very close to the rotor plane and is almost independent of the distance between the upstream and downstream rotors, at least in the range of simulated distances. This makes the development of the wake of the downstream rotors, driven by the instability of the tip vortices, much faster and very similar across distances from the upstream one. The results explain the phenomena of performance stabilization of downstream turbines in linear arrays, recently reported in the literature.

Il presente rapporto sintetizza le attività di ottimizzazione numerica svolte all'interno della commessa 01CT19 per la Marina Militare Italiana

The acoustic analogy is adopted to reconstruct the sound generated by a system consisting of a hydrofoil and a downstream propeller. The data from high-fidelity large-eddy simulations with the hydrofoil at angles of incidence of [Formula: see text], and [Formula: see text] were generated using a cylindrical grid consisting of 1.7 × 109 points. The results of the analysis demonstrate the following: (i) the strong influence by the incidence of the hydrofoil on the acoustic signature of the system; (ii) the leading role of the non-linear component of sound at small radial coordinates in the vicinity of the wake, especially moving away from the propeller plane; (iii) the leading role of the linear component of sound from the surface of the propeller moving away along the radial direction; (iv) the importance of the shear between the wakes shed by the hydrofoil and the propeller in accelerating the process of instability of the coherent structures and reinforcing the non-linear sources of sound; and (v) the strong, complex directivity of sound at small radial coordinates, as a consequence of the interaction between the wakes from the hydrofoil and the propeller.

Large-eddy simulations on a cylindrical grid consisting of 5 × 109 points are reported on both conventional and winglets propellers with and without a downstream shaft. Comparisons are focused on the influence by the hub vortex on the process of instability of the tip vortices. They demonstrate that in straight ahead conditions, this influence is actually quite limited for both propellers. The presence of the hub vortex at the wake core results in only a slight upstream shift of the instability of the tip vortices. Meanwhile, the development of the instability of the hub vortex is always delayed, compared to that of the tip vortices, and the former keeps coherent further downstream of their breakup. The results of this study highlight that the hub vortex is not a major source of instability of the tip vortices. Therefore, simplified configurations with no hub vortex, often adopted in the literature, can also provide a good approximation of the process of instability of the tip vortices shed by actual propellers. In contrast, the instability of the tip vortices could be the trigger of that of the hub vortex, whose development is slower. Therefore, experimental and computational studies aimed at analyzing the dynamics of the hub vortex should be designed accordingly, extending to further downstream distances.

Large-Eddy Simulations are reported, dealing with an axial-flow hydrokinetic turbine operating in the wake of an upstream one. Computations were conducted on a cylindrical grid consisting of 3.8 × 109 points, using an Immersed-Boundary methodology. The performance of the downstream turbine was negatively affected by the wake of the upstream one and substantially dependent on its distance. Results demonstrated a faster wake development, compared to the case of the same turbine operating in isolated conditions within a uniform flow, due to the faster instability of the tip vortices, induced by the perturbation of the inflow conditions by the wake of the upstream turbine. In contrast with the turbine performance, the process of wake recovery was found rather insensitive to the distance from the upstream turbine. In comparison with the case of the isolated turbine, the role of radial turbulent transport just downstream of the instability of the tip vortices was found especially important in accelerating the process of wake recovery at the outer radii, providing a significant contribution together with radial advection. Further downstream, the contribution by turbulent transport was verified reinforced also within the wake core, where instead momentum replenishment by radial advection was rather limited.

Large-eddy simulations of a propeller operating upstream of a hydrofoil at incidence were conducted on a cylindrical grid consisting of almost 4 × 109 points. This manuscript, focused on the interaction between the tip and hub vortices shed by the propeller with the downstream hydrofoil, is part of a broader study, including the analysis of the boundary layer on the hydrofoil [A. Posa and R. Broglia, “Flow over a hydrofoil at incidence immersed within the wake of a propeller,” Phys. Fluids 33, 125108 (2021)] and the downstream development of the wake of the overall system [A. Posa and R. Broglia, “Development of the wake shed by a system composed of a propeller and a rudder at incidence,” Int. J. Heat Fluid Flow 94, 108919 (2022)]. The results demonstrate a substantial influence by the orientation of the hydrofoil on the propeller wake. The pressure and suction side branches of the tip vortices experience outward and inward spanwise shifts across the hydrofoil, respectively. However, these shifts are affected significantly by the angle of incidence. As a result, the propeller wake undergoes an overall contraction on the suction side of the hydrofoil, promoting higher levels of shear and turbulence and a faster growth of the boundary layer thickness. The opposite occurs on the pressure side of the hydrofoil, producing eventually a strong asymmetry of the overall wake. Also the evolution of the hub vortex is substantially affected. It splits into two branches, shifting across the span of the hydrofoil in the direction opposite to the tip vortices. As the incidence angle of the hydrofoil grows, the branch of the hub vortex populating its pressure side becomes larger than the one on its suction side, developing a higher shear with the hydrofoil boundary layer and the suction side branches of the tip vortices.

Large-Eddy Simulations are reported on the INSEAN E1658 propeller, upstream of a NACA0020 hydrofoil, to mimic the interaction of the propeller wake with a downstream rudder. The same three values of advance coefficient as in an earlier validation study on the INSEAN E1658 propeller in open-water conditions are considered. Results demonstrate that the wake of the propeller is dramatically modified by the presence of the hydrofoil. Each tip vortex and the hub vortex are split into two branches, experiencing a significant spanwise displacement across the hydrofoil, which occurs towards opposite directions for tip and hub vortices. These phenomena trigger higher levels of turbulence, compared to the open-water configuration, due to an increased interaction involving the coherent structures populating the propeller wake and the boundary layer on the hydrofoil. A strong anti-symmetry of the overall wake is produced by the spanwise shift on the two sides of the

The design of efficient seagoing vessels is key to a sustainable blue growth. Computer simulations are routinely used to explore different designs, but a reliable analysis must take into account the unavoidable uncertainties that are intrinsic to the maritime environment. We investigated two ways of performing this analysis in an effective, CPU-time parsimonious way.

This paper is aimed at studying the hydrodynamic noise generated by a marine propeller in open water conditions. The hydrodynamic field is computed by means of high-fidelity Large Eddy Simulations (LES), coupled with an Immersed-Boundary (IB) approach; these results have been already presented in Posa et al. (2019a), including a complete validation assessment. LES is especially well suited for investigating radiated noise, since all the large energy-carrying structures of the flow are fully resolved with no turbulence modeling. The acoustic field is estimated using the acoustic analogy by suitable formulations of the Ffowcs-Williams and Hawkings (FW-H) equation. In particular, in this paper the analysis is performed using both the porous formulation and the direct formulation of the FW-H equation. For the latter, as a preliminary stage only the linear terms (i.e. those coming from the surface integral over the blade surfaces) are estimated; the analysis of the contribution from the non-linear quadrupole term through the use of volume integrals (i.e. the contribution from the wake of the propeller in the direct formulation) which is mainly responsible for the contribution from the wake is left to future developments.

This extended abstract is a summary of [4], where a comparison of two methods for the forward uncertainty quantification (UQ) of complex industrial problems is presented. Specifically, the performance of Multi-Index Stochastic Collocation (MISC) and adaptive multi-fidelity Stochastic Radial Basis Functions (SRBF) surrogates is assessed for the UQ of a rollon/roll-off passengers ferry advancing in calm water and subject to two operational uncertainties, namely the ship speed and draught. The CFD simulations needed by both methods are performed by a multi-grid Reynolds Averaged Navier-Stokes solver.

The goal of the HOLISHIP project is to implement a design synthesis process as an alternative to the traditional design spiral approach. This objective can be reached by integrating all ship design tools (hull form design, hydrodynamic assessment, structural design, machinery etc.) into a new design platform. The HOLISHIP platform shall take care of geometry modelling, providing the necessary data for each tool, exchange of data between the tools, the inter-dependencies of tool results and much more. The platform will also implement a holistic optimisation ramework, taking all relevant aspects of the respective design phase into account. In an early stage simple methods like regression formulae will be used, in later stages of the design process more sophisticated and accurate methods will be applied. The work packages of Cluster 1 (WP 1 to 6) have two purposes in the project. First, they must ensure that the tools are able to cover all practical requirements regarding the application in the design process. In HOLISHIP this means that the tools must be suitable to be used in the application case work packages of Cluster 3 (WP 9 to 17) . The Cluster 1 work packages will therefore carry out validation work and add missing features - where needed - to their tools. The second aspect is that the tools must be prepared to be integrated into the HOLISHIP Cluster 2 platforms (WP 7 and to some extent WP 8). The required input data and formats of output results must be well-defined and the tools must be capable to be executed without graphical user interface (often referred to as batch mode). While adding a batch mode to a numerical tool is usually not associated with a significant development effort, adapting or creating new file formats (which can be processed by the HOLISHIP platform) may prove a substantial task. The work carried out in WP 3 in this respect ensures that all related requirements and preconditions regarding the necessary hydrostatic-stability and hydrodynamic software tools in the HOLISHIP project are met and are ready for use with the commencement of the Application Case studies.

Closed-loop flow control is aimed at altering a natural flow state into a more desirable state, which is chosen depending on control objectives. The control input is usually an electric signal, which has to be converted to a physical quantity by means of an actuator. A new and original technology using non-thermal surface plasmas has witnessed a significant growth in interest in recent years, as they: have no moving parts; exhibit an extremely fast time-response; are characterised by low mass and low input power. These surface dielectric barrier discharge (DBD) actuators are used to accelerate the near-wall flow, thus modifying the velocity profile within the boundary layer. In this paper, we focus on the robust feedback control of the flow separation using plasma actuators. Our objective is to solve the problem of directly controlling the unsteady flow separation using real-time velocity measurements, which are available in realistic applications. We propose this flow separation problem as a practical application of the new theoretical results in Marino and Tomei, Automatica, 60(8):2213–2218, 2015, [4]. The aim of this paper is to show how, despite the high complexity of the system, a simple robust output regulator is sufficient to effectively suppress the flow separation along an aerofoil, using two actuator/sensor pairs. Accurate two-dimensional (laminar flow) and three-dimensional (turbulent flow) numerical simulations of incompressible flows on a NACA0012 at Reynolds \(Re=20{,}000\) are performed in order to illustrate the effectiveness of the proposed approach. In the two-dimensional case a robust, fast flow reattachment is achieved, along with both stabilisation and increase/reduction of the lift/drag, respectively. The control system shows good dynamic performances, as the angle of attack is varied. For the three-dimensional test, a Large Eddy Simulation (LES) approach has been chosen for the modelling of the turbulence dynamics, whereas the eddy viscosity is calculated according to the well established classical Smagorinsky model.

For the first time a comprehensive investigation has been carried out to quantify the possible effects of dredging a navigable canal on the hydrogeological system underlying a coastal lagoon. The study is focused on the Venice Lagoon, Italy, where the port authority is planning to open a new 10m deep and 3km long canal to connect the city passenger terminal to the central lagoon inlet, thus avoiding the passage of large cruise ships through the historic center of Venice. A modeling study has been developed to evaluate the short (minutes), medium (months), and long (decades) term processes of water and pollutant exchange between the shallow aquifer system and the lagoon, possibly enhanced by the canal excavation, and ship wakes. An in-depth characterization of the lagoon subsurface along the channel has supported the numerical modeling. Piezometer and sea level records, geophysical acquisitions, laboratory analyses of groundwater and sediment samples (chemical analyses and ecotoxicity testing), and the outcome of 3-D hydrodynamic and computational fluid dynamic (CFD) models have been used to set up and calibrate the subsurface multi-model approach. The numerical outcomes allow us to quantify the groundwater volume and estimate the mass of anthropogenic contaminants (As, Cd, Cu, Cr, Hg, Pb, Se) likely leaked from the nearby industrial area over the past decades, and released into the lagoon from the canal bed by the action of depression waves generated by ships. Moreover, the model outcomes help to understand the effect of the hydrogeological layering on the propagation of the tidal fluctuation and salt concentration into the shallow brackish aquifers underlying the lagoon bottom., Facultad de Ciencias Naturales y Museo, Centro de Investigaciones Geológicas

The goal of the HOLISHIP project is to implement a design synthesis process as an alternative to the traditional design spiral approach. This objective can be reached by integrating all ship design tools (hull form design, hydrodynamic assessment, structural design, machinery etc.) into a new design platform. The HOLISHIP platform shall take care of geometry modelling, providing the necessary data for each tool, exchange of data between the tools, the inter-dependencies of tool results and much more. The platform will also implement a holistic optimisation ramework, taking all relevant aspects of the respective design phase into account. In an early stage simple methods like regression formulae will be used, in later stages of the design process more sophisticated and accurate methods will be applied. The work packages of Cluster 1 (WP 1 to 6) have two purposes in the project. First, they must ensure that the tools are able to cover all practical requirements regarding the application in the design process. In HOLISHIP this means that the tools must be suitable to be used in the application case work packages of Cluster 3 (WP 9 to 17) . The Cluster 1 work packages will therefore carry out validation work and add missing features - where needed - to their tools. The second aspect is that the tools must be prepared to be integrated into the HOLISHIP Cluster 2 platforms (WP 7 and to some extent WP 8). The required input data and formats of output results must be well-defined and the tools must be capable to be executed without graphical user interface (often referred to as batch mode). While adding a batch mode to a numerical tool is usually not associated with a significant development effort, adapting or creating new file formats (which can be processed by the HOLISHIP platform) may prove a substantial task. The work carried out in WP 3 in this respect ensures that all related requirements and preconditions regarding the necessary hydrostatic-stability and hydrodynamic software tools in the HOLISHIP project are met and are ready for use with the commencement of the Application Case studies.

This report presents the progress of the activities pursued within Work Package "WP2 - CFD Computations in Manoeuvring", task "WE23: CFD analysis of the stabilized phase of the turning circle", whose final goal is the analysis of the flow field around the Horizon frigate in steady turning manoeuvre. The analysis will be performed for the steady phase of the manoeuvre, propeller effects will be taken into account by means of a generalised unsteady hybrid RANS/BEM methodology. Two different conditions will be studied, corresponding to the full scale trials 15 degrees rudder starboard and 25 degrees rudder starboard manoeuvres (approaching speed 18knots). These operative conditions were already analysed by using an interactive simplified propeller model. The results will allow for a direct comparison between the two models and for an analysis of unsteady phenomena produced by the propeller operation.

Coherent structures play a dominant role in affecting the wake features of submarine propellers. Large-Eddy Simulation (LES) is especially well suited for investigating such influence, since the large energy-carrying structures of the flow are fully resolved with no turbulence modeling. However, detailed validations with experiments are rather limited in the literature, especially for the forward mode of operation, due to the challenges associated to both computations and experiments of this class of flows. Here the focus will be especially on the comparison of present LES computations of a notional seven-bladed propeller in open-water conditions with Particle Image Velocimetry (PIV) results, to assess carefully the capability of LES to capture the flow physics. A comparison across three values of advance coefficient will be also presented, based on the full three-dimensional fields from computations, in order to illuminate the influence of this parameter on flow features and wake coherence.

Large-Eddy Simulation, with an Immersed-Boundary method, is adopted to analyze the wake of a notional submarine propeller, using a cylindrical grid composed of about 840 million nodes. The accuracy of the overall approach is validated by comparisons with available measurements. Three different load conditions are investigated, allowing an assessment of the sensitivity to the rotational speed. Results demonstrate that tip and hub vortices are the main coherent structures. However, several additional vortices are produced across the span of the propeller blades. The evolution of turbulent kinetic energy in the propeller wake is substantially affected by coherent structures. The highest values occur at the axis and at outer radii, due to the hub and the tip vortices, respectively. In addition, downstream evolution of turbulence associated to the tip vortices is not monotonic. In contrast, fluctuations at the wake axis, originating mainly from instability of the hub vortex, keep decreasing starting from the near wake.

In the present paper a stability analysis of the porpoising problem for a luxury yacht is proposed. The approach is based on a linearization of the sink and pitch motions of the boat around the center of gravity (CG. The stability coefficients, usually calculated by means of simplified approaches, are now evaluated through unsteady RANS simulations, in order to perform a deeper and more close to reality investigation of this problem. Two in-house numerical codes have been employed, both based on a finite volume method with a level set approach, in order to cross-check the results for the lowest speed. A total number of four speeds, spanning from 18 to 34 knots, has been studied and an encouraging porpoising analysis is finally discussed.

This report presents the status of the activities pursued within Work Package "WP2 - CFD Computations in Manoeuvring", task "WE22: CFD simulations of the turning-circle manoeuvre", whose final goal is the analysis of the flow field around the Horizon frigate in steady turning manoeuvre. As agreed within the consortium, the analysis was performed for the steady phase of the manoeuvre and the study will include free surface effects. Two different conditions were studied, corresponding to the full scale trials 15 degrees rudder starboard and 25 degrees rudder starboard manoeuvres (approaching speed 18knots).

This report refers to the work that has be done within the Job Order 12-OCT-2015 Phase-2: ''Numerical simulation of lowercase with the propeller and free surface''. Numerical analysis has been performed on the same lowercase geometry provided by FluidTechno Co., Ltd and analyzed in the Phase-1. The geometry has been provided in form of CAD-IGES file. The activity regards the numerical simulations of the flow field around the lowercase, mimicking the experimental campaign carried out in the CNR-INSEAN towing tank "U. Pugliese". For this set of computations the model scale is 2.50, propeller effects are not considered, whereas free surface effects are taken into considerations. This configuration and operative conditions have been already tested and reported previously; three speeds have been tested, namely: 4m/s, 7m/s and 10m/s. Topic of this report is an additional simulation performed with a very fine grid around the surface. This simulation was intended only for an accurate definition of the wave pattern, surface data as well as integral quantities (local and global hydrodynamic loads) are not expected to have any significant change (verification reports a difference in hydrodynamic loads bounded by 2%). Only one speed has been tested, the selected speed is 7m/s. As usual, results are reported in terms of total resistance. Since the focus of this report is the development of the free-surface, example of flow field analysis is mainly given in terms of wave pattern. Verification and validation (i.e. the analysis of the convergence properties and the estimation of both the numerical uncertainty and the comparison error) have been assessed following a widespread adopted procedure. Simulations have been carried out on wall resolved grids (i.e. no wall functions have been used), which count for about 3.5 millions of grid volumes for the description of the lowercase, about 2.1 millions for the background grid (these two parts are the same used in the previous tests) and about 12.6 millions of control volume for the accurate description of the free surface evolution. Therefore, a total of about 18.2 millions of grid points have been used for the discretization of half of the geometry/physical domain (being the configuration symmetrical about the vertical longitudinal plane, no transverse flow or lateral asymmetry has expected to take place). Overlapping grid approach have been used to accurately represent the geometry of the lowercase. Numerical computations have been carried out by means of the Xnavis solver, which is a general purpose unsteady Reynolds averaged Navier-Stokes (uRaNS) solver developed at CNR-INSEAN. For the sake of completeness, the theoretical model adopted at CNR-INSEAN is briefly described in the following, a detailed discussion have been reported in the phase one report.

HOLISHIP WP 3 addresses hydrodynamic and hydrostatic analysis and optimisation of ships and other maritime assets. A significant number of numerical tools to predict and optimise both the stability and hydrodynamic performance of maritime products shall be prepared for use in integrated design platforms. The CFD tools to be used comprise methods for the prediction of ship resistance and power demand, the assessment of manoeuvrability properties and the seakeeping behaviour of the product. They range from very simple statistical analysis tools suitable for a very early design stage (concept design) to highly sophisticated software packages able to accurately predict specific properties during later project phases (contract design). In today's practice the use of such tools is often time consuming and only loosely integrated with other design processes. The prime objective of WP 3 is hence to adapt a number of promising stability and CFD tools and make them fit for use in the integrated design platforms which will be developed in WPs 7 and 8.

We address the problem of controlling the unsteady flow separation over an aerofoil, using plasma actuators. Despite the complexity of the dynamics of interest, we show how the problem of controlling flow separation can be formulated as a simple output regulation problem, so that a simple control strategy may be used. Different configurations are tested, in order to identify optimal positions of the actuator/sensor pairs along the aerofoil, as well as the corresponding references for the available real-time velocity measurements. A multi-objective deterministic particle swarm optimization algorithm is applied to identify the set of non dominated configurations considering as objectives the time-averaged input signal and the drag-to-lift ratio. Accurate numerical simulations of incompressible flows around a NACA0012 profile at Reynolds $Re=20,000$ and angle of attack 15° illustrate the effectiveness of the proposed approach, in the presence of complex nonlinear dynamics, which are neglected in the control design. Fast flow reattachment is achieved, along with both stabilisation and increase/reduction of the lift/drag, respectively. A major advantage of the presented method is that the chosen controlled outputs can be easily measured in realistic applications.

Grazie alla disponibilità di architetture HPC, l'utilizzo di tecniche CFD per l'analisi fluidodinamica in ambiente navale è diventata di uso quasi comune. Al CNR-INSEAN nel corso degli ultimi decenni si è sviluppato un codice di calcolo parallelo per simulazioni RANS non stazionarie che viene quotidianamente utilizzato sia per scopi di ricerca che scopi commerciali. Il codice è utilizzato per analisi di problematiche quali, ad esempi, la manovrabilità, la tenuta a mare e studi fluidodinamici su propulsori; inoltre il codice è stato accoppiato ad algoritmi di ottimizzazione e a solutori per la predizione del rumore acustico. L'intervento fornirà una visione globale delle applicazioni più importanti, non solo in ambito navale, oltre ad una descrizione delle tecniche numerico/matematico ed algoritmiche sviluppate nel codice di calcolo.

Simulation based design methodologies are replacing the costly and time-consuming build-and-test paradigm for the design of naval vehicles. On the one hand, accurate high-fidelity simulations are required to guarantee the accuracy of the solution and ensure adequate design decisions. On the other hand, high-quality experiments are needed to validate high-fidelity simulations, ensuring the reliability of the computational tools. In real-world applications, all the relevant parameters are affected by uncertainty and its assessment is necessary to provide the required confidence intervals of all relevant variables used for validation. Here a high-fidelity uncertainty quantification (UQ) of a high-speed catamaran is presented, with focus on (a) the validation methods for ship response in irregular waves and (b) the validation of a stochastic regular wave UQ method. The approach includes a priori CFD simulations by URANS, followed by the ex post facto EFD campaign. The validation variables are the wave elevation, x-force, heave and pitch motions, vertical acceleration of the bridge and vertical velocity of the flight deck. Time series value is addressed as primary variable, whereas the mean-crossing wave height is indicated as secondary variable. Bootstrap methods are applied to estimate validation values and 95% confidence intervals for expected value (EV), standard deviation (SD), mode, and quantiles. Additionally, validation values and confidence intervals for time series EV and SD are evaluated by classical time series theory, based on the sample variance, size, and autocovariance function. The regular wave UQ method evaluates EV of force and SD of pitch, acceleration, and velocity, as relevant merit factors for design optimization. The present work extends the EFD and CFD studies presented in earlier work with the aim of achieving high-quality rigorous statistical validation. Both EFD and CFD data are provided with a larger run length and a larger number of encounter waves. New EFD data address the dynamic part of the force, which was one of the limitations of earlier work. The CFD simulations include a larger number of runs without significant self-repetition, which was also a limitation of earlier studies.

This Chapter deals with the experimental survey of the flow field around a catamaran advancing in steady drift. The survey was aimed at investigating the dynamics of the keel vortices with particular emphasis on the mechanisms underlying their generation, detachment, evolution and destabilization. Detailed flow measurements were undertaken by Stereo-PIV (S-PIV) at selected cross planes along and downstream of the catamaran. The test matrix consists of two Froude numbers (Fr=0.4 and 0.5) and two drift angles (6° and 9°). In the experiments, the model was kept fixed at the dynamical values of trim and sinkage, as measured in a previous Planar Motion Mechanism (PMM) test campaign. The major topological and kinematical features of the keel vortices are highlighted through the analysis of the mean and fluctuating components of the velocity and vorticity field. A conditional average technique was used to investigate the interaction between the keel-vortex and free-surface in the wake of the model.

Nel presente rapporto tecnico di ricerca vengono presentate e descritte le attività svolte per la caratterizzazione idrodinamica dello USWATH progettato realizzato nell'ambito della linea SP1_LI2_WP1_UO1 del progetto RITMARE. In particolare, il progetto di base (baseline USWATH design) è stato studiato per mezzo di simulazione numeriche CFD (URANS) al fine di caratterizzare le forze idrodinamiche in tutto il range di utilizzo previsto e per valutare gli effetti di interferenza tra i due scafi e tra i gli strut dei singoli scafi.

This chapter presents CFD validation efforts for the high-speed, multihull Delft Catamaran 372 advancing in calm water with steady drift angles. Available experimental data include hydrodynamic loads (from BSHC), sinkage and trim measurements (from BSHC and CNR-INSEAN), and stereo-PIV measurements of the velocity field on several transverse planes (from CNR-INSEAN). Three organizations have conducted RANS or DES simulations by using their own codes: CNR-INSEAN using Xnavis; IIHR, The University of Iowa using CFDShip-Iowa and CNRS/ECN using ISIS. Computations have been made using different grid strategies (structured grid with overlapping, unstructured grid with or without an automatic grid refinement), several turbulence models (the isotropic one equation Spalart-Allmaras model, the anisotropic two equations STT k? and EARSM models, and DES simulations) and different free surface approaches (single phase level set and volume of fluid). Comparisons are made in terms of integral quantities (i.e. hydrodynamics loads and vehicle attitudes), local quantities in separated vortex core (i.e. axial vorticity, axial velocity, position of the vortex and TKE), planar data (velocity field, axial vorticity field and TKE on selected planes) and wave patterns. Discussions and comparisons on the onset and progression of the vortical structures separated from the two hulls will be presented. In general computational results have shown that the main features of the separated flow field are well captured by all the computations. No large differences between submissions can be inferred from the cross planar fields; effects of turbuence model and grid resolution have been investigated by the core vortex analysis. Grid resolution effects are dominant in the onset region; only very refined grids (total of order of 100M of grid points or using an automatic grid refinement technique) are able to provide field quantities closer to EFD data. Turbulence model effects are dominant in the progression of the main vortices, with DES simulations and RANS based on non-isotropic models, proved to be superior (stronger and less dissipated vortices) than one equation isotropic models. In terms of hydrodynamic loads, a general good agreement between the submissions has been observed, with the standard deviation on the resistance prediction of about 3.5%; similar differences between CFD have been seen for the lateral force prediction, whereas larger discrepancy is observed for the yaw moment estimation (about 7%). The comparison with measured data revels a rather large overall error (of the order of 15%); however, it has to be pointed out that EFD values where collected for different conditions and a larger model; reference values have been obtained by an interpolation procedure on speed/drift plane, whereas no Reynolds number correction was considered. Differences due to grid resolution and the model adopted for the description of the free surface have been also observed; very fine grids are required to capture wave breaking and rebounds phenomena. Both single phase Level Set and Volume of Fluids approaches are able to capture wave induced vortices; the VOF method shows the formation of foam close to the free surface region and a consequent dissipation of the vortices, whereas the single phase level set provides a long life vortices. The different behaviour is supposed due to the interaction with the underline turbulence model (i.e. the production of turbulent viscosity close to the free surface), rather than the free surface approach itself.

The flow field generated by the towing of a semidisplacement hull, free to heave and pitch, is numerically investigated in the velocity range 18 - 34 Kn. The effect of an imposed roll angle have been studied for 4o , 6o and 8o and for three velocities (namely: 20, 24 and 28 Kn). The numerical code adopted is the in-house developed Xnavis, which is a general purpose unsteady RANS based solver; the solver is based on a Finite Volume approach together with a Chimera technique for overlapping grids and a Level Set approach to handle the air/water interface. The generated wave pattern shows many interesting features with an evident wave plunging near the hull bow, while the stern remains completely dry for velocities over 30 Kn. The numerical outcomes are discussed in terms of forces and attitudes.

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This paper presents CFD validation efforts for the high-speed, multihull Delft Catamaran 372 advancing in calm water with steady drift angles. Available experimental data include hydrodynamic loads (from BSHC), sinkage and trim measurements (from BSHC and CNR-INSEAN), and stereo-PIV measurements on several transverse planes (from CNR-INSEAN). Three organizations from three countries have conducted unsteady Reynolds averaged Navier Stokes (URANS) or Detached Eddy Simulations (DES) by using their own codes: CNR-INSEAN using Xnavis; IIHR, The University of Iowa using CFDShip-Iowa and CNRS/ECN using ISIS. Computations have been made using different grid strategies (structured grid with overlap, unstructured grid with or without an automatic mesh refinement (AMR)), several turbulence models (the isotropic one equation Spalart-Allmaras model, the anisotropic two equations Shear Stress Transport (SST) k and Explicit Algebraic Reynolds Stress Model (EARSM) models, and Detached Eddy Simulations) and different free surface approaches (single phase level set (LS) and volume of fluid (VoF)). Comparisons are made in terms of hydrodynamics loads, local quantities in separated vortex cores (i.e. axial vorticity, axial velocity, position of the vortex and turbulent kinetic energy (TKE)), planar data (velocity field, axial vorticity field and TKE on selected planes) and wave patterns. Discussions and comparisons on the onset and progression of the separated vortical structures are presented. In general computational results have shown that the main features of the separated flow field are well captured by all the computations. No large differences between submissions can be inferred from the cross planar fields; effects of grid resolution and turbulence model have been investigated by the vortex analysis. Grid resolution effects are dominant in the onset region; only very refined grids (total of order of 100M of grid points or using an AMR technique) are able to provide field quantities closer to EFD data. Turbulence model effects are dominant in the progression of the main vortices, with DES simulations and RANS based on non-isotropic models proved to be superior (stronger and less dissipated vortices) than one equation isotropic models. In terms of hydrodynamic loads, a general good agreement between the submissions has been observed (standard deviation on the resistance prediction of about 3.5%). Similar differences between CFD have been seen for the lateral force prediction, whereas larger discrepancy is observed for the yaw moment estimation (about 7%). The comparison with measured data reveals a rather large overall error (of the order of 15%). However, EFD values where collected for different conditions and a larger model; reference values have been obtained by an interpolation procedure on speed/drift plane, whereas no Reynolds number correction was considered. Differences due to grid resolution and the model adopted for the description of the free surface have been also investigated; very fine grids are required to capture wave breaking and rebounds phenomena. Both single phase LS and VoF approaches are able to capture wave induced vortices, some differences are seen in their progression; the VOF method shows the formation of foam close to the free surface region, whereas the LS provides a long life vortices.

In this paper numerical computations dedicated to the analysis of the maneuvering behavior of a fully appended submarine are presented. The work presented here is part of the CNR-INSEAN activities scheduled in the framework of a joint Italian and Norwegian MoDs project, with the partnership of MARINTEK, under the egida of the European Defence Agency. The aim of the numerical work is to exploit the effect of cruciform and X rudder configuration on the turning qualities of the submarine in two operation conditions, namely open water and snorkeling depth. In this paper, the free running turning circle maneuver is analyzed; predictions are achieved by an in-house CFD solver.

This technical report concerns with results for the submarine advancing with prescribed sinusoidal motions, mimic the classical maneuvering tests usually performed in the towing tank (Planar Motion Mechanism) for the maneuvering analysis of marine vessel. Numerical computations have been carried out by means of the Xnavis solver, which is a general purpose Unsteady RANS solver developed at CNR-INSEAN. For the sake of completeness, the theoretical model adopted at CNR-INSEAN is described and related assumptions and limits are discussed; the solution algorithm is outlined and the main features of the developed solver are firstly described. In the following sections the grids used, the parameters of the numerical simulations and results will be described.

In this technical report the results of the turning circle simulations carried out by means of the CNR-INSEAN general purpose CFD solver ?Navis are presented. The turning qualities of the cross and X-rudder configurations are investigated both in deep water and close to the free surface at the reference speed Fn = 0.21. Numerical results are presented for two grid refinement levels and the results of the cross-rudder configurations are further validated with respect to free running model tests performed at QinetiQ (Submotion I project) and numerical simulations obtained by simplified mathematical models by Cetena and Marintek.

In this technical report the results of the turning circle simulations carried out by means of the CNR--INSEAN general purpose CFD solver XNavis are presented. The turning qualities of the cross and X--rudder configurations are investigated both in deep water and close to the free surface at the reference speed Fn=0.21. Numerical results are presented for two grid refinement levels and the results of the cross--rudder configurations are further validated with respect to free running model tests performed at QinetiQ (Submotion I project) and numerical simulations obtained by simplified mathematical models by Cetena and Marintek.

In this technical report the results of the appendages-moving simulations carried out by means of the CNR--INSEAN general purpose CFD solver XNavis are presented. Cross and X--rudder configurations are investigated at the reference speed Re=6.65 10^6, for a movement of the appendages which are typical for a bow up/down and turn manoeuvres. Numerical results are presented for medium and fine mesh, allowing an estimation of the numerical uncertainty. Moreover, results are compared with the results of the experimental activities performed at CNR-INSEAN. The presented results are used as a numerical validation for the results described into the report WP-2.4

In this paper numerical computations dedicated to the analysis of the maneuvering behavior of a fully appended submarine are presented. The work presented here is part of the CNR-INSEAN activities scheduled in the framework of a joint Italian and Norwegian MoDs project, with the partnership of MARINTEK, under the egida of the European Defence Agency. The aim of the numerical work is to exploit the effect of cruciform and X rudder configuration on the course stability qualities of the submarine in two operation conditions, namely open water and close to the free surface.

The hydrodynamic flow around three given profiles has been studied with a series of two-dimensional simulations performed at three advancing speeds, namely 5, 10 and 12 kn. Particular attention has been paid in capturing the vortex shedding phenomenon. The hydrodynamic performances in terms of drag and lift coefficients, as well as the Strouhal number, have been computed through numerical simulations of the turbulent flow around the profiles, using an unsteady Reynolds Averaged Navier-Stokes (uRaNS) numerical code, developed at CNR-INSEAN. The Chimera approach has allowed to exploit the overlapping grid approach, which ensures a correct evaluation of the near field, as well as of the wake evolution. The validation of the approach has been carried out through the study of the turbulent flow around a circular cylinder and the comparisons with experiments and other available numerical simulations.

The turning circle manoeuvre of a naval supply vessel (characterized by a block coefficient CB ~ 0.60) is simulated by the integration of the unsteady Reynolds-Averaged Navier Stokes equations coupled with the equations of rigid body motion with six degree of freedom. The model is equipped with all the appendages, and it is characterised by an unusual single rudder/twin screws configuration. This arrangement causes poor directional stability qualities, which makes the prediction of the trajectory a challenging problem. As already shown in previous works, the treatment of the in-plane loads exerted by the propellers is of paramount importance; to this aim each propeller is simulated by an actuator disk model, properly modified to account for oblique flow effects. The main goal of the present paper is to assess the capability of the CFD tool to accurately predict the trajectory of the ship and to analyse the complex flow field around a vessel performing a turning manoeuvre. Distribution of forces and moments on the main hull, stern appendages and rudder are analysed in order to gain a deeper insight into the dynamic behaviour of the vessel. Validation is provided by the comparison with experimental data from free running tests.

The 35° turning circle manoeuver of the KVLCC2 is simulated numerically by means of the globally second order accurate finite volume solver ?navis. To this purpose, the Reynolds averaged Navier-Stokes equations and the Euler equation are coupled to predict the rigid body motions; the solver adopt a Chimera approach to deal with the relative motions of grid blocks. The effect of the propeller is modelled by the Hough and Ordway actuator disk properly modified to account for the propeller side force.

In this paper a coupled experimental and numerical activity dedicated to the analysis of the maneuvering behavior of a fully appended submarine is presented. The work presented here is part of the CNR-INSEAN activities scheduled in the framework of a joint Italian and Norwegian MoDs project, with the partnership of MARINTEK, under the egida of the European Defence Agency. The aim of the experimental work is mostly the collection of valuable data set for CFD benchmarking and the hydrodynamic characterization of the aft planes. Tests were carried out for two different stern appendage layouts (namely a cruciform and a X rudder configuration), allowing a comparison of the maneuverability capabilities between the two configurations. CFD studies were mainly devoted to the analysis of the flow field around the submarine and to collect hydrodynamic coefficients required by an in-house System Based Maneuvering solver. The latter has been used to perform two free running, self-propelled, maneuvers on the vertical plane.

The turning circle maneuver of a self-propelled tanker like ship model is numerically simulated by means of the unsteady RANS solver Xnavis developed at CNR-INSEAN. The focus is on the analysis of the maneuvering behavior of the ship with two different stern appendages configurations; a twin screw with a single rudder and a twin screw, twin rudder with a central skeg. Validation of the predicted trajectory and the kinematical parameters is provided by comparison with experimental data from free running tests. Maneuvering abilities of the two configurations are discussed.

The turning circle maneuver of a self-propelled tanker like ship model is numerically simulated through the integration of the unsteady Reynolds averaged Navier-Stokes (uRaNS) equations coupled with the equations of the motion of a rigid body. The solution is achieved by means of the unsteady RANS solver Xnavis developed at CNR-INSEAN. The focus here is on the analysis of the maneuvering behavior of the ship with two different stern appendages configurations; namely, a twin screw with a single rudder and a twin screw, twin rudder with a central skeg. Each propeller is taken into account by a model based on the actuator disk concept; anyhow, in order to correctly capture the turning maneuvering behavior of the model, a suitable model which takes into account for oblique flow effects has to be considered. Results from a preliminary verification assessment are discussed; validation of the predicted trajectory and the kinematical parameters is provided by comparison with experimental data from free running tests. Maneuvering abilities of the two configurations are discussed; in order to better understand the different behavior of the two configurations, an in depth analysis of the force and moments on the hull and on the individual appendages is provided.

In this paper the maneuvering behavior of a fully appended submarine in the vertical plane is analyzed by means of combined use of a CFD solver and System Based Maneuvering based model. CFD is extremely useful for characterizing the submarine dynamic response in terms of hydrodynamic coefficients, whereas system based mathematical model is a fast tool for executing a free running, self-propelled, maneuver. Present approach can be very useful for analyzing submarine control system strategies adopted during critical operations, like rising and diving.

In this work the numerical simulations of a submarine in straight ahead motion with the appendages at several prescribed deflection angles are performed. Due to the complex geometry involved (the presence of moving appendages), these simulations are rather demanding form the point of view of both grid generation and accuracy of the numerical method. In order to analyze these aspects, the numerical solutions are computed by means of an unsteady Reynolds averaged Navier-Stokes equations solver, which is particularly effective because of the high order discretization schemes adopted. From the point of view of mesh construction, a dynamic overset grid technique is used, where each geometrical element of the whole geometry is discretized with a set of block-structured body-conformal mesh with partial overlapping (Chimera approach). In the present paper, the details of the method and numerical results for several deflection angles of the bow and stern planes are presented.