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Wave-induced loads on the ship hull are of significant interest for many reasons. These loads, however, are highly nonlinear in realistic wave conditions and consequently difficult to predict. In this paper, we analysed and compared wave-induced loads acting on a container vessel in regular head waves computed with a newly developed weakly nonlinear potential theory-based code and a flow solver based on the Reynolds-averaged Navier-Stokes Equations. We investigated both long and short waves with moderate steepness. Initially, the vessel was completely fixed and the ship motions were suppressed, then the vessel was free to heave and pitch motion. We compared time-histories of the computed wave-induced longitudinal and vertical global forces as well as the pitch moment and we deeply analysed nonlinear effects by applying a Fourier transformation and comparing the corresponding harmonic amplitude up to the fourth order. Our results demonstrated satisfactory agreement between the two numerical methods, especially when the ship was free to heave and pitch. Additionally, the results provided detailed information about the capabilities and limitations of the weakly nonlinear potential theory-based approach. [ABSTRACT FROM AUTHOR]

The paper discusses the length to beam (L/B) ratio effects on ship resistance at three different Froude numbers using unsteady RANSE simulation. First, the JBC ship model was used as an initial hull form for verification and validation of predicted ship resistance results with measured data, and then the influence of the L/B ratio on ship resistance was carried out. Ship hull forms with different L/B ratios were produced from the initial one by using the Lackenby method. The numerical results obtained show the L/B ratio’s effect on ship resistance. Increases of the L/B ratio led to gradual reduction of the total ship resistance and vice versa. Analysis of the changing of the resistance components indicates that the pressure resistance changes are considerably larger than the frictional one. Finally, the paper analyses the difference in the flow field around the hull of the ship with variation of the L/B ratio to fully understand the physical phenomenon in the change of ship resistance at different L/B parameters.

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. [ABSTRACT FROM AUTHOR]

The hydrodynamic interaction effects between ships are significantly pronounced in restricted waters, and this may potentially threaten the safety of ships, especially given that ship dimensions and waterway traffic have kept increasing. Although there has been a good amount of research on ship hydrodynamic interactions, the study of the effect of the propeller on the ship's hydrodynamic interaction is very limited. In this paper, a series of RANSE-based numerical simulations are carried out to study the characteristics of the propeller in near-field interaction between ships without speed. The hydrodynamic forces and moment acting on the ship are calculated and analyzed. Through the analysis of the characteristics of the flow field and the behavioral pattern of the hydrodynamic forces, it is found that the propeller has a significant influence on the pressure distribution on the hull as well as on the hydrodynamic interaction forces. The maximum lateral force acting on the interacting ship could reach 0.58 times the standard thrust of a KP458 propeller (the revolution is 594 rpm and the velocity coefficient is 0.25 in open water). [ABSTRACT FROM AUTHOR]

This paper deals with the results of studying the effect of trim on the performance of series cargo ship 12500DWT in full scale at two operating conditions by using the RANSE method. The Body Force Propeller method is used to simulate a rotating propeller behind the ship. The numerical predicted results at the ballast condition were verified and validated with sea trial data. The ship’s engine power curves for different trim conditions at two operating conditions were carried out to produce a data source to evaluate the effect of trim on the performance of the 12500DWT cargo ship. The results indicate that if the ship operates under optimum trim conditions, this can decrease the ship’s engine power in a range from 2.5 to 4.5% depending on different loading conditions and ship speeds. Finally, the paper also provides detailed differences in flow around the ship due to trim variation to explain the physical phenomenon of changing ship performance.

The purpose of this study case is to assess the total resistance and investigate the fluid flow around a scale model catamaran varying distance between the diametral planes of the two hulls. This study is focused on accurately determining the total resistance encountered by the catamaran while it moves through water and, additionally, on understanding how the fluid flow behaves around the vessel with these design variables. [ABSTRACT FROM AUTHOR]

This study presents a comprehensive Computational Fluid Dynamics (CFD) analysis of an 18-meter motor yacht featuring a trawler hull design with a swim platform. The investigation explores the hydrodynamic performance of the yacht across three distinct drafts and six varying speeds. [ABSTRACT FROM AUTHOR]

This paper proposes a fast multigrid algorithm to simulate the non-linear motion of ships in both intact and damaged conditions. The simulations of ship motions in waves are known to require much time to calculate due to the strong non-linear interactions between ship and waves. To improve the calculation efficiency while retaining the accuracy, a prediction-correction strategy was designed to accelerate the simulation through three sets of locally refined meshes. The flow field was first estimated in a coarse mesh and then mapped to a locally refine mesh for further higher-fidelity corrections. A partitioned radial basis function (PRBF) method is proposed to interpolate and reconstruct the flow field for the refined mesh. A new two-phase flow solver was developed with a fast multigrid algorithm based on the Reynolds-averaged Navier–Stokes equations (RANSE). The new solver was applied to study the non-linear behavior of a damaged ship in beam waves and the effect of damaged compartments on ship rolling motion. Validation against the solution with the original method of single set meshes and experimental data indicates that the proposed algorithm yields satisfactory results while saving 30–40% of the computational time. [ABSTRACT FROM AUTHOR]

The hydrodynamic interaction effects between ships are significantly pronounced in restricted waters, and this may potentially threaten the safety of ships, especially given that ship dimensions and waterway traffic have kept increasing. Although there has been a good amount of research on ship hydrodynamic interactions, the study of the effect of the propeller on the ship’s hydrodynamic interaction is very limited. In this paper, a series of RANSE-based numerical simulations are carried out to study the characteristics of the propeller in near-field interaction between ships without speed. The hydrodynamic forces and moment acting on the ship are calculated and analyzed. Through the analysis of the characteristics of the flow field and the behavioral pattern of the hydrodynamic forces, it is found that the propeller has a significant influence on the pressure distribution on the hull as well as on the hydrodynamic interaction forces. The maximum lateral force acting on the interacting ship could reach 0.58 times the standard thrust of a KP458 propeller (the revolution is 594 rpm and the velocity coefficient is 0.25 in open water).

This study intends to develop a Computational Fluid Dynamics space exploration framework, which creates a bridge between the NAPA software and OpenFOAM 9 simulation software. With the use of the Free Form Deformation function implemented in NAPA, iterations of the KCS hull were automatically generated by changing the length of the bulb. The newly created versions of the model were further analyzed with numerical investigations to determine the ship resistance simulation using RANS equations. The optimization process and the data transfer between the two software packages are monitored by the Dakota optimization software. [ABSTRACT FROM AUTHOR]

The purpose of this study was to determine the total resistance and investigate the flow around a full-scale kayak. Utilizing Computational Fluid Dynamics (CFD), it was determined how the presence of a rudder affects the kayak’s hydrodynamic performance. To analyse the flow, computational fluid dynamics based on the RANS-VOF solver were employed. The fluid volume approach and the k-ω turbulence model were used in two-phase steady flow simulations around the kayak hulls. [ABSTRACT FROM AUTHOR]

This paper proposes a fast multigrid algorithm to simulate the non-linear motion of ships in both intact and damaged conditions. The simulations of ship motions in waves are known to require much time to calculate due to the strong non-linear interactions between ship and waves. To improve the calculation efficiency while retaining the accuracy, a prediction-correction strategy was designed to accelerate the simulation through three sets of locally refined meshes. The flow field was first estimated in a coarse mesh and then mapped to a locally refine mesh for further higher-fidelity corrections. A partitioned radial basis function (PRBF) method is proposed to interpolate and reconstruct the flow field for the refined mesh. A new two-phase flow solver was developed with a fast multigrid algorithm based on the Reynolds-averaged Navier–Stokes equations (RANSE). The new solver was applied to study the non-linear behavior of a damaged ship in beam waves and the effect of damaged compartments on ship rolling motion. Validation against the solution with the original method of single set meshes and experimental data indicates that the proposed algorithm yields satisfactory results while saving 30–40% of the computational time.

This study presents the numerical investigation for the flow around the propeller of the ONR Tumblehome combatant in open water and for the flow around the same ship in the case of self-propulsion with actuator disk method. Computational Fluid Dynamics based on RANS-VOF solver have been used in order to analyse the flow. The free surface treatment is multi-phase flow approach, incompressible and nonmiscible flow phases are modelled through the use of conservation equations for each volume fraction of phase. Accuracy involves close attention to the physical modelling, particularly the effects of turbulence, as well as the numerical discretization. [ABSTRACT FROM AUTHOR]

The tumblehome hull adopts some novelty designs such as low-tumblehome freeboard and wave-piercing bow. The new form design makes the ship have many special hydrodynamic performances. Especially the green water of tumblehome hull is different from that of hulls with flare free board. Green water is a strong nonlinear phenomenon of ship-wave interaction, the variation of free surface of liquid is complicated, and there are still some difficulties to solve green water problems well with numerical simulation method. In this paper firstly the motion responses of the tumblehome hull was calculated based on 3D potential theory, and then the dam-break flow model was used to calculate green water height and pressure distribution. According to the result of numerical simulation, some typical working conditions are chosen for 3D CFD simulation using RANS method. The results of numerical simulation methods are compared with the experimental results measured in towing tank. The influence of different ship form parameters and wave parameters to the green water of tumblehome hull is analyzed, and some regularities of green water on tumblehome hull in regular waves are summarized.

In this study, the numerical investigation of ship motions and added resistance at constant forward velocity of KVLCC2 model is presented. Finite volume CFD code is used to calculate three dimensional, incompressible, unsteady RANS equations. Numerical computations show that reliable numerical results can be obtained in head waves. In the numerical analyses, body attached mesh method is used to simulate the ship motions. Free surface is simulated by using VOF method. The relationship between the turbulence viscosity and the velocities are obtained through the standard k − ε turbulence model. The numerical results are examined in terms of ship resistance, ship motions and added resistance. The validation studies are carried out by comparing the present results obtained for the KVLCC2 hull from the literature. It is shown that, ship resistance, pitch and heave motions in regular head waves can be estimated accurately, although, added resistance can be predicted with some error.

The paper presents the results of numerical simulations of propeller open water characteristics by using RANSE method with rotating reference frame approach. The effects of grid type, mesh density and turbulence models on simulation results are analyzed. The well-known Potsdam Propeller PPTC test case is used to verify and validate the accuracy of case studies. At the end, the assessment and recommendation for choosing grid type and turbulence model from the point of view of the level of accuracy are given. The solver used in this study is the commercial package Star-CCM+from SIEMENS. [ABSTRACT FROM AUTHOR]

Ships operate in seaways, but ship manoeuvrability is usually studied in calm water conditions, thus ignoring the effects of wave on the ship hydrodynamic behaviour. So, the assessment of surface ship manoeuvrability in wave environment is more realistic and accurate than its estimation in calm water condition. In the present study, captive dynamic ship model tests are numerically simulated in a computational fluid dynamics environment in regular head sea waves and the hydrodynamic derivatives are derived from the estimated force/moment time series using the Fourier series expansion method. These derivatives and wave excitation forces are fitted in the manoeuvring equations of motion and are solved to simulate the ship standard manoeuvres in head sea waves. Parameters of these definitive manoeuvres in wave condition are compared with those in still-water condition. [ABSTRACT FROM AUTHOR]

Abstract Economic pressures and regulatory obligations have brought about a great interest in improving ship propulsion efficiency. This has motivated and directed research to improve the hydrodynamic performance of a vessel thus seeking the development and generation of optimised designs. When analysing flow characteristics of a vessel, particular attention is given to analysing its wake field and stern flow characteristics. For the detailed analysis of the wake flow field, a Wake Analysis Tool (WAT) was developed within the programming environment of a commercial CAE tool. The WAT is based on a framework that enables easy interaction to an external CFD solver reading flow field properties from a generic csv file. The wake flow field is visualised and analysed in schematic form according to the standard and customized (i.e. the British Ship Research Association criteria) wake analyses. By coupling the CAE tool with a commercial flow solver, an example was given how to use the wake tool in a fully automated simulation process. Finally, the wake tool was used to analyse the nominal propeller wake flow of the Japan Bulk Carrier (JBC) thus showing how it can be efficiently applied to a set of numerical results. Graphical abstract Image 10314 Highlights • Introduction of the functionality of a custom-developed propeller Wake Analysis Tool. • Tool extension that includes the B.S.R.A. criteria assessment. • Tool integration into a software chain to perform an automated design study. • Automated analysis of Japan Bulk Carrier wake field at different speeds and drafts. • Numerical Results Verification and Validation for JBC baseline conditions. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The tumblehome hull adopts some novelty designs such as low-tumblehome freeboard and wave-piercing bow. The new form design makes the ship have many special hydrodynamic performances. Especially the green water of tumblehome hull is different from that of hulls with flare free board. Green water is a strong nonlinear phenomenon of ship-wave interaction, the variation of free surface of liquid is complicated, and there are still some difficulties to solve green water problems well with numerical simulation method. In this paper firstly the motion responses of the tumblehome hull was calculated based on 3D potential theory, and then the dam-break flow model was used to calculate green water height and pressure distribution. According to the result of numerical simulation, some typical working conditions are chosen for 3D CFD simulation using RANS method. The results of numerical simulation methods are compared with the experimental results measured in towing tank. The influence of different ship form parameters and wave parameters to the green water of tumblehome hull is analyzed, and some regularities of green water on tumblehome hull in regular waves are summarized. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

The design of pumpjet propulsors (PJP) is addressed through a simulation-based design optimization approach built on a parametric description of the main geometrical characteristics of the system, a RANSE solver with mixing plane interface capabilities and a genetic algorithm. Both Rotor/Stator (PJP-R/S) and Stator/Rotor (PJP-S/R) configurations are considered and optimal designs from a multi-objective optimization process aimed at maximizing the propulsive efficiency at the lowest possible cavitation inception index are compared to a reference ducted propeller with decelerating nozzle (Gaggero et al., 2012), which served as baseline during the design. Detached Eddy Simulations (DES) were finally carried out to highlight, in addition to the performance improvements provided by the PJPs, also the influence of the rotor/stator/nozzle interactions on the vortical structures shed by the propulsor. • Pumpjets are efficient propulsors, especially for high-speed vessels. • A pre- or a post-stator stage is used to induce pre-swirl or extract additional thrust respectively. • SBDO using RANSE calculations represent a feasible design alternative for this type of propulsors. • A complex interaction between blade tip vortex and vortical structures from stator and nozzle is observed using DES analyses. • Such interaction has a detrimental effect on the stability of the trailing vortical wake of the propulsor. [ABSTRACT FROM AUTHOR]

The effects of SO2 emission, which is one of the most important emission gases caused by ships passing through Strait of Istanbul are investigated numerically by means of environmental effects. The numerical analyses are performed by using a commercial CFD (Computational Fluid Dynamics) code solving RANSE (Reynolds Averaged Navier- Stokes Equations). A 100 meters heighted air zone over the Strait of Istanbul is modeled in 3-D and analyses are carried out for unsteady and steady cases and different wind directions. SO2 emission distributions at different heights are obtained. The numerical results gathered by statistical data provide a basis for the authorities in taking precautions, setting up regulations and applying the related regulations of MARPOL Annex VI. The method used for emission estimation in Strait of Istanbul can also give short-term predictions for different scenarios. [ABSTRACT FROM AUTHOR]

In this work, the design and the analysis of the performance of an improved tip loaded propeller geometry are proposed. Based on the experimental data and on the numerical results collected at SISTEMAR and at the University of Genoa in the case of Contracted and Tip Loaded (CLT) propellers, a new tip loaded propeller geometry is devised in order to mitigate some of the downsides of the CLT geometries increasingly adopted to improve full-scale propeller efficiency. The modified tip loaded propeller, i.e. a mix between a tip rake and a Contracted and Tip Loaded propeller, is designed via an optimization strategy using a Boundary Elements Method (BEM), a custom parametric description of the unconventional blade geometry and an optimization algorithm (of genetic type) within the modeFRONTIER environment. The reliability of the design process and of the improvements achievable with the modified tip loaded propeller are extensively verified with dedicated RANSE calculations. At first, the accuracy of the BEM, adopted for the design by optimization, is verified in terms of predicted propeller performance in order to assess its applicability for the analysis of modified tip geometries and check its confidence with respect to the allowable modifications of the blade shape. As a second step, viscous calculations are adopted to confirm the improvements of the newly designed geometries, in terms of both cavitation and predicted velocity field downstream the propeller, as a result of a better adaptation of the end plate geometry to the incoming flow. Finally, a set of unsteady calculations, by using the unsteady BEM, is carried out to verify the amplitude of the induced pressure pulses and, by comparing these numerical results with the available measurements and calculations in the case of a reference CLT propeller, to confirm the effectiveness of the modified propeller tip shape. [ABSTRACT FROM AUTHOR]

The numerical study of manoeuvrability of surface ships necessitates the determination of the hydrodynamic derivatives in the equations of motion. Standard manoeuvring tests are simulated to evaluate the ship's manoeuvring qualities. This paper deals with the estimation of linear, nonlinear and roll-coupled hydrodynamic derivatives of a container ship by numerically simulating static and dynamic tests at different roll angles using a RANSE solver. The mathematical model suitable for the nonlinear roll-coupled steering model for high-speed container ships is considered here. In order to include the effect of roll on the ship, the roll-dependent derivatives are estimated by using static and dynamic tests numerically performed at discrete heel angles. Standard definitive manoeuvres such as turning circle and zig-zag tests are numerically simulated by solving the equations of motion and the results are verified with those obtained by using experimental values. [ABSTRACT FROM PUBLISHER]

In present work, a design by optimization of contracted and tip-loaded (CLT) propellers is proposed and implemented. The design approach is based on a parametric description of the propeller blade, derived from the usual design table by using B-Spline parametric curves, and an in-house developed Panel Method/Boundary Element Method (BEM) aimed to evaluate the performance (including cavitation) of the propellers selected by a genetic optimization algorithm. The modeFRONTIER optimization environment drives the entire design process. A preliminary sensitivity study is carried out to evaluate the effect of the discretization meshes for BEM and RANSE calculations. Based on this analysis, Boundary Element Method and RANSE results over the parent propeller, in terms of both open water propeller performance, unsteady cavitation and induced pressure pulses, are compared with the available experimental measurements in order to validate the adopted design approach. Finally, to assess the reliability of the design by optimization, a set of optimized geometries, selected on the basis of the fulfillment of the design objectives, are checked by means of dedicated RANSE calculations. [ABSTRACT FROM AUTHOR]

The analysis of yacht hulls performance using RANSE based free surface simulations has become an accepted approach over the last decade. Access to this technology has been eased by the development of user-friendly software and by the increase of computational power. Results are widely accepted as superior to previous non-viscous approaches and have to compete with towing tank results in terms of accuracy. However, many practical applications suffer from a numerical smearing of the free surface interface between air and water which can be described as numerical ventilation. This problem occurs when the intersection between bow and calm water surface forms an acute angle and is further pronounced if the stem is rounded or blunt. It is therefore especially linked to sailing yacht applications. The problem manifests itself as a non-physical suction of the air–water mixture under the yacht hull, causing a significant under-prediction of viscous resistance. While this is the easily observable appearance of the problem, a second issue is its effect on wave resistance. It can be shown that wave damping is significantly increased, causing a prediction of wave resistance which is also too low. The paper provides a review of the Volume-of-Fluid method. It discusses the resultant implications for practical applications. A remedy to circumvent the problem is described and its impact on the accuracy of the result is shown. Simulations on an identical appended hull with and without interface smearing are compared. Effects on free surface visualization and numerical accuracy are shown. The paper finishes with a thorough verification and validation of a fully appended yacht in accordance with ITTC standards. [ABSTRACT FROM AUTHOR]

Three dimensional (3D) flow past an Autonomous Underwater Vehicle (AUV) is simulated using a Computational Fluid Dynamics (CFD) approach at a Reynolds (Re) number of 2.09* 106. A non-linear k-ε (NLKE) turbulence model is used for solving the Reynolds Averaged Navier-Stokes equations (RANSE). The effect of control surfaces over the flow, the flow interaction between hull and appendages at various Angles of Attack (AoA) and the effect of the symmetry plane is studied. Flow structure, variation of flow variables and force distribution for various AoA are presented and discussed in detail. [ABSTRACT FROM AUTHOR]

An important application of optimization of a ship is the minimization of calm-water resistance for a given displacement. In this work, an innovative flow solver that combines free-surface effects with a viscous solution allows for an accurate drag prediction with fast turnaround times ideally suited for an optimization study. A large number of geometrical-design variables are considered in early-stage design; thus, in this article, different techniques are examined to reduce the curse of dimensionality. Different methods such as multivariate analysis are used to optimize the hull with respect to resistance over a range of different speeds for a given displacement. [ABSTRACT FROM AUTHOR]

A transpiration velocity based partial sheet cavitation model has previously been successfully validated when implemented within potential flow codes. The model is independent from any solver and permits to estimate the cavity length based on the subcavitating pressure distribution. This paper presents its implementation within a Reynolds Averaged Navier–Stokes Equations solver. In order to compare the results of the implementation, experimental measurements on a 2D hydrofoil and potential flow code results are used. Several stages are covered. First the geometries of the cavitation sheets computed with the potential flow code are imposed with a slippery boundary condition on its surface into the RANSE simulation. The results obtained are in very good agreement with the previous validated results. In the second stage, the Volume of Fluid module is activated and water vapour is ejected from the foil surface and the transpiration velocities are computed with the potential flow code. The results are similar but the length of the cavitation closure is much shorter. Finally, the model is fully implemented within the RANSE solver. The transpiration velocities are computed using the model from the subcavitating pressure distribution. They are then applied on the foil surface as water vapour. The results are quasi-identical to the results obtained when the transpiration velocities are taken from the potential flow code. The paper proves the feasibility of modelling the cavitation sheet using transpiration velocities and VOF within a RANSE solver. [ABSTRACT FROM AUTHOR]

The flow around the gap of a semi-spade rudder was simulated as part of an effort to minimize gap cavitation. Simulations were performed for various devices aimed at controlling the gap flow in two-dimensional and three-dimensional domains using the Reynolds-averaged Navier-Stokes equations. A significant difference in the pressure field near the gap in two- and three-dimensional computations was found. In particular, the pressure field of the gap, where the local flow is dominant, and that of the main flow from the propeller were compared. Finally, a remedy for the gap cavitation that occurs between the horn and the rudder was introduced. [ABSTRACT FROM AUTHOR]

Principles of RANSE-based (Reynolds Averaged Navier-Stokes Equations) numerical modelling of a flow around the tanker model hull are introduced with the application of the CD-adapco STAR-CCM+ (Computational Continuum Mechanics) software package in the field of ship hydrodynamics. The numerical model used in simulation is drawn up through base parameters and methods of geometrical and mathematical modelling. Results of two numerical simulations performed at design and ballast loading conditions are presented and a comparison with available experimental data is made. Some aspects of further improvements of the presented numerical model are pointed out. [ABSTRACT FROM AUTHOR]

This paper presents the results of study effect of trim on resistance of US Navy Combatant DTMB 5415 model at three different drafts and two Froude numbers by using unsteady RANSE method in conjunction with towing tank tests. Firstly, the numerical results at zero trim condition were verified and validated with experimental data. Then, a series of resistance curves for different trim conditions at different drafts and speeds were performed to produce data source to evaluate the influence of trim on ship resistance. Results denote that the changing tendency of total ship resistance at different trim conditions varying with speed and draft combinations, and the variation of pressure resistance component due to trim is considerably larger than frictional resistance component. Finally, the paper provides details of flow characteristics around ship like wave patterns on free surface, pressure distribution and skin friction on the hull surface, and free water surface in order to explain the physical phenomenon of changing ship resistance at different trim condition. [ABSTRACT FROM AUTHOR]