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The development of alternative fuels, such as lower cost refinery fuels, solar fuels, heavy fuel oils, represents one of the main directions of internal combustion engine research. These modern fuels require a new modelling framework capable of predicting their multi-component behaviour in engine-like conditions since droplet evaporation of such fuel involves physical processes which are significantly more complex than in a fuel that can be approximated by one component. Therefore, the topic of this research project is the development of a numerical model capable of predicting the dynamic behaviour of multi- component fuels in dense sprays. In the model, the method of classes will be used in the Eulerian framework, where each dispersed phase is characterised by its droplet size, velocity and concentration of components. In the current method, the poly-dispersed nature of the spray is handled using the method of classes in the Euler-Euler framework, where each dispersed phase is characterised by its droplet size and velocity. This approach treats every droplet class as a different phase in the calculation. Therefore, every size class has its momentum and continuity equation, but the mixture pressure is shared among all phases. The individual size classes undergo breakup and coalescence, which are implemented as mass source/sink terms in phase continuity equations and momentum source/sink terms in the phase momentum equation.

An extensive campaign of model and full scale experimental tests and numerical computations is being undertaken within the framework of the Project “SOPHYA - Seakeeping Of Planing Hull YAchts”, co-financed by Friuli-Venezia Giulia Region in the field of joint industrial and academic research. The project is aimed at the prediction and optimization of the hydrodynamic performances of a 65 ft motoryacht by MonteCarlo Yachts SpA in calm water and in waves. In this paper, selected results of the numerical computations for the calm water case, conducted jointly by HyMOLab-University of Trieste and by the University of Zagreb, are presented. RANS, Volume-of-Fluid and Level Set simulations are carried out in combination with an automatic mesh-generation tool, developed in this project within the OpenFOAM/foam–extend frameworks. The numerical results are compared with experimental data obtained within the project at the towing tank of the University of Naples.

This study presents the progress towards resolving the atomization pattern of an idealized fire sprinkler by using volume of fluid (VOF) modeling. Numerical modeling has been applied to understanding the atomization behavior of an idealized sprinkler geometry consisting of a 9.5 mm inner diameter cylindrical nozzle and a flat, 25.4 mm diameter disk with a liquid flow rate of 0.71 L/s. The simulations have been performed with foam -extend-4.1 (a community driven fork of the OpenFOAM CFD software), using the ghost fluid scheme and the isoAdvector scheme for interfacial reconstruction. In order to achieve efficient computations and adequately resolve the flow, a newly implemented adaptive mesh refinement (AMR) scheme has been used. Comparisons of the liquid sheet breakup behavior in the near vicinity of the disk are shown for various AMR criteria. The computational efficiency is analyzed. This study represents a first step towards using AMR coupled with VOF modeling to adequately obtain injection patterns, and provides a path to subsequently simulate realistic sprinkler geometries.

A numerical environment for efficient assessment of ship resistance using CFD is presented in this paper. Predicting ship resistance in calm water with the Naval Hydro Pack can be performed within a few hours, including grid generation, computation and post–processing of results. Being able to rapidly predict ship resistance renders CFD a cost-effective design tool, since a hull form designer can evaluate multiple variants of hull geometry quickly. The process of setting up, running and post-processing is accelerated by automating the process to a high level, significantly decreasing the number of manual work effort. In this paper the capabilities of the Naval Hydro Pack are demonstrated by calculating steady resistance for three different benchmark hull forms, where time for pre- processing, processing and post-processing is reported. On average, it took two and a half hours to obtain steady state results per hull form, including set–up, computational time and data analysis. Results are validated against available experimental data s

This paper serves as an overview of the numerical modelling technology within the Naval Hydro Pack, a software package specifically designed for efficient simulations of various marine hydrodynamic problems. The Naval Hydro Pack is based on foam-extend, a community driven fork of the OpenFOAM software. The goal of this paper is to provide an overview of numerical models required for free surface flows in marine hydrodynamics, where we intend to openly discuss drawbacks and advantages of each of our methods.

This paper deals with the novel design methodology of modular passenger ships aimed for operation in the Mediterranean Sea. It actually outlines aims and methods of an ongoing long-term competitive Installation research project funded by the Croatian Science Foundation (CSF) which is based on the modular concept enabling the change of the ship production paradigm from the classical all-in-one approach to a parallel manufacture of different components by highly specialized producers and a final assembly done by the local shipyard. The target vessel is considered as made of independent modules which can be combined together to achieve different characteristics in terms of ship dimensions, carrying capacity, operability, comfort, fuel consumption and energy efficiency. Within the project, an analysis of the market needs and of the corresponding ship requirements is being performed for different navigation regions in the Mediterranean Sea. Then, the preliminary concepts based on that analysis are being proposed, while the final concepts will be developed taking into account all important aspects of ship design: resistance and propulsion, seakeeping, structural aspects, ship habitability, simplified manufacturing processes as well as environmentally friendly energy solutions. Through this project several optimized modular passenger vessels will be proposed depending on the selected design criteria sets. In this sense it is expected that the project will result in a number of concepts fitting to the market needs with reduced production costs, higher level of comfort for crew and passengers, reduced fuel consumption as well as lower environmental impact.

Full scale turning circle manoeuvre is simulated using the Finite Volume (FV) based CFD software called the Naval Hydro Pack, which is based on foam-extend. Results are directly compared to sea trial measurements for two propeller rotation rates. Two different approaches for modelling the free surface are investigated: as single–phase flow model with a simplified linearised free surface method, and a two–phase numerical model with Volume of Fluid (VOF) method for interface capturing. The comparison in terms of accuracy, computational time and robustness between the two methods is presented. In both approaches the propeller is modelled using the actuator disc model, while the moving rudder is handled using the overset grid technology. A newly developed publicly available open–source overset library based on foam-extend is used.

Harmonic Balance (HB) method is applied to the problems of surface gravity waves in the Naval Hydro pack in foam–extend, which enables time–spectral simulations of wave diffraction. HB transforms a transient problem into a set of coupled steady state equations by assuming a temporally periodic flow.

In this paper a detailed validation and verification of seakeeping simulations using Computational Fluid Dynamics (CFD) software OpenFOAM is presented. For the DSYHS #44 sailing boat, different head wave conditions for a fixed Froude number are simulated and the results are compared to experimental data. For the KRISO Container Ship (KCS), a large number of incident wave cases is considered at design Froude number. Incident wave parameters and direction of wave propagation with respect to ship’s heading are varied. The results for the total resistance, heave, pitch and roll are compared to experimental data. All simulations are conducted on three different grids in order to assess numerical uncertainties.

This paper presents an efficient method for simulating extreme wave loads using Higher Order Spectral (HOS) method and Computati onal Fluid Dynamics (CFD) in OpenFOAM. HOS is capable of nonlinear propagation of arbitrary wave spectrum, while being computationally effective. CFD enables fully nonlinear two-phase, turbulent flow solution with vorticity effects at the cost of increased CPU time. In this work the coupling of HOS and CFD is briefly presented and numerical simulations depicting the capabilities of the coupling are shown.

An overview of validation and verification studies of seakeeping simulations is given in this work. A detailed validation and verification study is performed for KRISO Container Ship (KCS) hull for design Froude number in head waves and oblique waves for various wave parameters and eading angles. Grid and periodic convergence tudies are performed for all cases, and the results are compared to experimental measurements. In addition, zero speed and low Froude number seakeeping results for regular and irregular head and oblique waves are presented for the Duisburg Test Case (DTC) container ship model. Enhanced body motion–fluid flow coupling is used in the latter simulations resulting in significant reduction of the required CPU time. Solution decomposition SWENSE (SpectralWave Explicit Navier–Stokes Equations) [1, 2] method is used for wave modelling with implicit relaxation zones, while embedded free surface model [3, 4] is employed for accurate interface representation. The methodology is implemented within the Naval Hydro pack based on foam–extend. For KCS hull five head waves cases are presented with varying wave parameters, where the total resistance, heave and pitch motions are reported. For oblique cases, five headings are simulated with the model free to pitch, roll and heave. All simulations are performed for design Froude number Fr = 0:26. Periodic uncertainty is assessed using moving window FFT (Fast Fourier Transform), as shown on an example of periodic convergence on Figure 1: the time domain signal is shown on the left and the periodic convergence throughout successive periods is shown on the right. Figure 2 shows the comparison of total resistance harmonics with experimental results for different wave parameters for head waves cases. It can be observed that results for head waves agree well with the experimental data. For the DTC hull a total of 17 seakeeping cases are simulated. Six regular head waves cases are conducted for low Froude number Fr = 0:056 with different wave parameters, and an irregular JONSWAP spectrum head waves case. For the oblique wave cases, a total of ten conditions are simulated with different parameters and heading angles. All regular wave cases are performed on three grids to perform a grid convergence study amounting to a total of 49 simulations.

U ovom radu su prikazane mogućnosti brzih i točnih simulacija pomorstvenosti broda u programskom paketu Naval Hydro u sklopu programa računalne dinamike fluida (eng. “Computational Fluid Dynamics”, CFD) otvorenog koda foam-extend. Naval Hydro je programski paket specijaliziran za modeliranje dvofaznog, viskoznog i turbulentnog strujanja na velikim prostornim skalama. U programu se koristi eksplicitan tretman propagacije valova što olakšava modeliranje valova uz smanjenje numeričke greške difuzije i disperzije. Dodatnom spregom jednadžbe tlaka i jednadžbi gibanja krutog tijela omogućeno je korištenje manjeg broja iteracija algoritma, što znatno smanjuje vrijeme proračuna. Da bi se prikazala brzina proračuna u odnosu na uobičajene CFD proračune pomorstvenosti, napravljena je komparativna studija između uobičajenih postavki simulacija broda na valovima i postavki za minimizaciju proračunskog vremena, te su rezultati uspoređeni sa eksperimentom. Smanjenje vremena proračuna umanjuje i točnost rezultata, međutim ovaj pristup može biti vrlo koristan za optimizaciju brodske forme s obzirom na otpor na valovima.

The Harmonic Balance Method (HBM) for temporally periodic, non–linear, turbulent, free surface flows is presented in this work. The methodology is primarily targeted to efficient simulations related to wave–structure interaction in naval and offshore hydrodynamics. Transient flows in marine hydrodynamics are often periodic, e.g. due to ocean waves (wave propagation and diffraction, seakeeping of a ship) and rotating propellers. Such flows often have well–defined base frequency: wave frequency or rotational frequency of the propeller. In fully non–linear, two–phase state–of–the–art CFD algorithms, such flows are almost exclusively resolved in time domain. Transient simulations usually require a large number of periods in order to achieve harmonically steady (purely oscillatory) solution. Due to its spectral decomposition, HBM allows us to efficiently model flow effects up to a specified order, without performing a fully transient simulation. Hence, a substantial performance improvement is expected, with almost negligible decrease in accuracy for flows with a well–defined base frequency. Due to the steady–state mathematical formulation of the HBM, authors believe that the method is highly suitable for adjoint optimisation regarding seakeeping of marine objects in the ship–building industry. This suitability has been recently confirmed by Huang and Ekici [1], who developed an adjoint shape optimisation tool based on the HBM for turbomachinery applications. The HBM [2] has been originally developed to tackle periodic single–phase turbomachinery flows in an efficient way. This paper presents an extension of the single-phase HBM [3, 4] to two–phase free surface flows, comparing the results and computational efficiency with a transient solution. The implementation is carried out in a second– order accurate, polyhedral Finite Volume framework developed within foam-extend, a community driven fork of the OpenFOAM software. In the HBM, a transient governing equation set is replaced with a specified number of coupled steady state problems, each represented by an equation for a unique time instant. The method simulates a periodic flow by evaluating the temporal derivative via spectral decomposition, yielding flow solution at discrete instants in time simultaneously. Multi–mode transformation from a transient to a set of coupled steady state problems is achieved by a Fourier transform, assuming temporally periodic flow. The accuracy of the model is controlled by a specified number of harmonics to allow efficient capturing of higher order flow effects. Generally, specified number of harmonics n, yields solutions at 2n + 1 discrete time instants (n for real and imaginary parts and 1 for the mean component). As an example, HBM simulation with n = 1 yields solution at t = 1=3T ; 2=3T and T, where T is the specified period. As a post processing step, the three solutions for n = 1 can be used to transform the results into frequency domain, up to first order. In the present study, HBM is applied to Navier-Stokes equations and Level Set interface capturing equation, yielding a coupled set of two-phase flow equations for discrete instants of time within one period. In addition, SWENSE decomposition is used to facilitate incident wave propagation. Preliminary results are presented for a 2D free–surface flow over a ramp, Figure 1, where the inlet free surface height, h1 is set to 1 m. ~U is the periodic inlet velocity with mean value ~U0 = (6 ; 0 ; 0), first order amplitude ~U1 = (1 ; 0 ; 0) and frequency f = 0:5 Hz. Density ratio of water and air is 1000, and the CFD domain extends 1 m above the initial free surface position. Gravity is set to ~g = (0 ; 9:81 ; 0), where the periodic inlet velocity causes non–linear wave propagation, where non–linear higher order effects are more pronounced after the ramp. HBM simulations are performed with 1 and 2 harmonics, where the periodically steady state solution is achieved within 800 iterations. In contrast, transient simulation is run for 10 periods, totalling 8000 time steps with time step size of 0.0025 s. Wave gauges are positioned at 2, 4, 6 and 8 m from the inlet, and the comparison of results is briefly shown in Figure 2, where the HBM solution (obtained as a steady state solution for one period) is extended to all periods. HBM results show good agreement with transient simulation results, where the HBM simulation with 2 harmonics captures second order effects, yielding better overall agreement with the transient solution. CPU time for the transient simulation (10 periods) is 5067 s, while the HBM CPU times are 271 and 488 s, for 1 and 2 harmonics, respectively. Considering that the transient simulations regarding more complex flows (seakeeping of a ship) require more than 10 periods in order to get correct periodically averaged results, a considerable speed up factor may be expected. Additional validation and verification cases regarding wave propagation and diffraction are going to be performed, assessing the trade–off between accuracy and CPU efficiency of the presented approach compared to transient simulations.

Higher Order Spectral (HOS) method for nonlinear surface wave propagation is implemented in OpenFOAM. HOS is a pseudo–spectral method for solving nonlinear free surface boundary conditions up to arbitrary order of nonlinearity. Time relaxation scheme is used to enable initialization using linear solution. Linear initialization enables propagation of arbitrary input spectrum. Use of Fast Fourier Transform (FFT) reduces CPU time, making this method favourable for coupling with CFD. The method is implemented as a wave theory in the Naval Hydro pack, using existing FFT and time integration algorithms. Implemented code is validated on both regular and irregular wave propagation. Development of higher modes for a regular wave initialized with linear solution is compared with the work by Dommermuth. Nonlinear propagation of irregular input spectra is compared with viscous simulation results by Lupieri et al. Finally, development of Benjamin–Feir instability on regular wave propagation is observed.

Off–shore structure design often relies on accurate assessment of higher–order forces because of ringing phenomena. In this work, calculation of higher–order forces on a vertical surface piercing cylinder is carried out by a decomposition CFD model. The model is based on Spectral Wave Explicit Navier–Stokes Equations (SWENSE) [1], allowing efficient coupling of arbitrary potential flow solutions with fully non–linear, viscous, two–phase CFD model. The domain is decomposed with implicit relaxation zones [2], preventing wave reflection. Implicitly redistanced Level Set method [3] is used for interface capturing, where additional explicit redistancing is not necessary. The validation of the method is performed on two sets of test cases. First, mesh and time refinement studies are carried out for a case with intermediately steep (ka = 0.12) incoming wave train. Second, a set of waves with different frequencies are simulated, keeping the wave steepness constant, ka = 0.06. Higher–order forces up to fourth order are compared with fully non–linear potential flow results [4]. A discussion on strong second order behaviour of vorticity effects in the vicinity of the cylinder is presented.

Validation and verification of a KCS model in head seas is presented in this paper for five wave conditions. Validation is performed by comparing added resistance, heave and pitch motions with experimental data. Numerical model is verified via grid refinement studies, assessing grid uncertainty for each test case. Periodic uncertainty by means of moving window FFT is introduced and assessed. The decomposition model is based on SWENSE (Spectral Wave Explicit Navier-Stokes Equations) method and implicit relaxation zones. Jump conditions at the interface are used to obtain interface-corrected interpolation schemes for density and pressure, embedding the free surface into two single-phase equations for water and air. The method fully resolves issues with parasitic air velocities and ensures one-cell-sharp jump of dynamic pressure and density across the free surface. Implicitly redistanced Level Set equation is used for interface capturing, while the k-omega SST model is used for turbulence. The method is implemented in the Naval Hydro pack based on foam-extend, a fork of the open source software OpenFOAM.

A presentation describing a decomposition model for naval hydrodynamics based on SWENSE approach, implicitly redistanced Level Set method. The model is validated and verified with various wave propagation sensitivity studies and wave diffraction on a circular cylinder.

In this paper validation and verification of a KCS model in oblique seas is presented for five headings. Validation is performed by comparing added resistance, heave, roll and pitch motions with experimental data. For each test case, grid refinement study is carried out and the corresponding grid uncertainty is calculated. Periodic uncertainty using moving window FFT is calculated. The decomposition model is based on SWENSE (Spectral Wave Explicit Navier--Stokes Equations) method and implicit relaxation zones, with embedded free surface approach via implicit interface-- corrected interpolation schemes. The method provides one--cell-- sharp jump of dynamic pressure and density across the free surface for arbitrary polyhedral grids. Implicitly redistanced Level Set equation is used for interface capturing, while the k-omega SST model is used for turbulence. The method is implemented in the Naval Hydro pack, based on foam--extend, a fork of the open source software OpenFOAM.

This paper presents detailed validation and verification study for the KCS in calm water conditions. Validation is performed by comparing the resistance, sinkage and trim with experimental data for six Froude numbers, while verification is performed for each case by assessing grid and iterative uncertainties. A single set of governing equations for water and air is used where jump conditions at the free surface are used to discretise discontinuous density and dynamic pressure fields. Volume of Fluid (VOF) method is used for interface capturing, and the k-omega SST model is used for turbulence modelling. Ship motion is solved with quaternion based six degrees-of-freedom (6 DOF) rigid body motion equations. The method is implemented in the Naval Hydro pack based on foam-extend, a community driven fork of OpenFOAM software.

Added resistance of ships in waves is one of increasingly important problems in naval engineering due to energy efficiency regulations. In this work, validation of the Naval Hydro pack in OpenFOAM is performed by conducting simulations of a KRISO container ship (KCS) in calm water and head waves. Steady resistance and dynamic sinkage and trim at different Froude numbers are compared to experimental data. Mesh refinement study has been carried out for design Froude number in order to asses numerical uncertainty. Seakeeping simulations of the ship in head waves are carried out for a number of different wave parameters at design Froude number. Heave, pitch and added resistance are compared with experimental results. All simulations are performed with fully non–linear, turbulent, two–phase CFD solver. Wave modelling is performed using Spectral Wave Explicit Navier–Stokes Equations (SWENSE) [1] with implicit relaxation zones [2] that are used to prevent wave reflection. In addition to the validation runs, 3-D freak wave simulation encountering a KCS has been performed using the SWENSE solver coupled with a directional Higher Order Spectrum (HOS) [3] method for nonlinear wave propagation.

Due to the general slow convergence of steady-state incompressible solvers, coupled ap- proaches are attractive alternatives. Such implicit solvers are well suited within the ex- isting generic block matrix format available with foam-extend. In this work, new implicit discretisation operators as well as assembling tools and matrix solvers are described and combined in the new solver pUCoupledFoam. To preserve the transparency and clarity of the current segregated solvers, all needed block discretisation operators must be generically implemented and kept within the gen- eral framework of foam-extend. The block coefficients must also be assembled fully auto- matically, avoiding ugly and error prone code which is intrinsically difficult to extend. However, for the implementation of the coupled pressure-velocity algorithm, there was a lack of implicit divergence and gradient operators, Due to the mapping from scalar to vector and from vector to scalar, for the implicit gradient and divergence operators respectively, these schemes are not supported within the standard scalar or vector matrix formats. The implicit block matrix discretisation of the the gradient operator, allows computing the implicit contribution from the pressure to the velocity. On the other hand, the implicit discretisation of the divergence operator computes the contribution from the velocity to the pressure. The discretised operators are automatically assembled in the block matrix system using existing and new block matrix coefficient insertion tools. All insertion tools are generic and templated on the type of solution variable (scalar/vector). which is realised by a combination of an implicit Laplacian and an explicit computation of the divergence of a surface normal gradient. Again, such an interpolation is achieved fully with operators and block matrix tools, without any discretization or assembly by hand in the solver. The block matrix is solved by current Krylov space solvers or by the newly implemented block algebraic multigrid (AMG) solver, released with foam-extend-3.0. All solvers are fully parallelised and templated on the size and type. To characterize the performance of the method and the implementation, the new code (pUCoupledFoam) is compared to the existing segregated incompressible solver (simpleFoam). A sample, single CPU investigation of the convergence rate per time is given for a laminar pitzDaily case in Figure 1. The results show a substantial increase in the convergence rate, in particular for the pressure equation. Out of the applied block matrix solvers, the AMG solver results in the best convergence rate per elapsed CPU time. Similar conver- gence results will be presented for the parallelised problem to additionally determine the scaling of the solver. The full source code of the coupled pressure-velocity solver will be released in the upcom- ing release of foam-extend-3.1.

Ovaj rad prikazuje mogućnosti primjene programskog paketa NavalHydro u programu OpenFOAM na probleme određivanja valnih opterećenja u brodogradnji. Diskretizacija Navier-Stokesovih jednadžbi se provodi metodom kontrolnih volumena, dok se za praćenje slobodne površine koristi „Volume of Fluid“ metoda. Paket NavalHydro prilagođen je provođenju proračuna gdje su prisutni značajni utjecaji slobodne površine, što ga čini pogodnim za određivanje valnih opterećenja. U ovom radu je prikazan proračun opterećenja vertikalnog cilindra uslijed nailaska harmonijskih valova. Rezultati su uspoređeni s eksperimentalnim podacima. Uz to je prikazana simulacija ekstremnog vala (eng. „freak wave“), koja pokazuje mogućnost određivanja opterećenja uslijed ovakvih pojava.

The subject of this paper is the application of OpenFOAM software in marine hydrodynamics. Mathematical model for two phase flows using the Volume of Fluid method is briefly presented. Finite volume method is used for equation discretization. The simulation results of steady state resistance in calm seas are compared with experimental data for two hull forms. Seakeeping simulations are also presented. Since OpenFOAM supports mesh motion, it can be used for forced oscillation simulations. As an example, results of harmonic sway motion with forward speed are presented. Finally, the seakeeping simulation of ship advancing in head waves with constant forward speed is presented.

Ovaj rad prikazuje pregled primjene NavalHydro paketa u programu OpenFOAM za simulacije viskoznih, turbulentnih, dvofaznih strujanja sa slobodnom površinom. Za praćenje slobodne površine se koristi "Volume of Fluid" metoda, te se numerički proračuni vrše metodom kontrolnih volumena. Programski paket NavalHydro omogućava različite vrsta simulacija vezane za brodsku hidrodinamiku, kao i za ostala područja gdje postoje dominantna strujanja sa slobodnom površinom. U ovom radu su ukratko prikazani primjeri otpora broda na mirnom moru, kao i gibanje broda kao krutog tijela na valovima. Također je prikazana simulacija kolapsa brane u kojoj vodeni val udara nepomičan, kruti stup.

This paper presents numerical simulation of wave loads on static offshore structures. The Naval Hydro Pack in OpenFOAM is used. Two phase free surface flow model is used with Volume of Fluid (VOF) [2] and Level Set (LS) method [1] for interface capturing. Govern- ing equations are discretized using the Finite Volume Method. Pressure-velocity coupling is obtained by PIMPLE algorithm, a combination of SIMPLE and PISO algorithm. The method is validated with three test cases. In first simulation truncated vertical cylinder immersed in water is exposed to incoming waves. Forces on cylindrical column are calculated. Data is compared with experimental results from [3]. In the second test case a simulation of 3D dam break impacting on a square cross section column is conducted and results are compared to experimental data. The third test case describes freak wave initialization and simulation. Finally it is concluded that CFD simulations for given cases give acceptably accurate results.

This paper presents numerical simulation of wave loads on static offshore structures. The Naval Hydro Pack in OpenFOAM is used. Two phase free surface flow model is used with Volume of Fluid and Level Set method for interface capturing. Governing equations are discretized using the Finite Volume Method. Wave modelling with relaxation zones is described. Simulation of 3D dam break with fixed square column is carried out. Results are compared with corresponding experimental data. Next, a method for freak wave initialization using wave focusing is given. Wave components are obtained using standard wave energy spectra. Simulation of freak wave is shown.