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Several communities are currently working on Wave Energy Converters (WECs); all of them have highlighted the need of experimental open-source benchmark test cases, they are fundamental to validate the different numerical algorithms that are used to model WECs. Outside the WeCANet community, the need for publicly available experimental data has been underlined by the ITTC specialist committee on hydrodynamics modelling of marine renewable energy devices [1]; it is an objective of the Marinet2 project, in the framework of this project some round robin experimental tests are underway and some experimental data are made available in the OES TASK 10. The wide variety of WEC devices and the shortage of available data leave space to new multi campaignstests. While the development of the WECs technology also asks for the introduction of experimental round robin tests on arrays. The wave basin n.2 at CNR-INM well suits the study of WECs in open sea. In fact, it has already been used for several experimental campaigns related to WECs [2],[3],[4]. Its dimensions (length = 220 m, breadth = 9.0 m, water depth = 3.5 m) allow for a reduced blockage effect and it can even host arrays of small scale devices.

This research activity represents the logical continuation of the work documented in [1] and [2] on water on deck and parametric roll for an FPSO in regular waves. Here the same numerical method, based on a domain-decomposition strategy, is used to examine the platform with bilge keels, both without and with mooring-line system. It is found that bilge keels with length 40% of the ship length and with breadth the 3% of the ship breadth limit effectively the roll when instability is promoted by vertical bow motions in waves. In these conditions also the amount of the shipped water is substantially reduced. Large roll induced by the coupling with the lateral motions seems to be less well counteracted and remains close to Iff for steepness kA >= 0.2. This value is often set as maximum allowed amplitude for FPSOs in normal operational conditions. Also the effect on the shipped water is limited in this case. Increasing the bilge-keels breadth is confirmed to be beneficial but the combination of the mooring system with dynamic positioning appears needed for a proper control of the roll motion in the worst examined cases.

Objective: To evaluate the family history of epilepsy in first degree relatives of probands with epilepsy. Methods: A sample of 10787 patients with epilepsy with complete information about first degree relatives (parents, siblings and offspring) was selected from the database of the Episcreen Project, the largest Italian observational study on epilepsy. Family history was assessed by: (1) prevalence estimates of epilepsy among proband's relatives, (2) modified cumulative risks (MCR), adjusted using proband's age as censoring time in life tables, (3) standardised morbidity ratios (SMR), using a sub-group of symptomatic epilepsies as control group. Results: Patients (9.1%) had a family history of epilepsy. The overall prevalence of epilepsy among first degree relatives was 2.6%. Idiopathic generalised epilepsies had the highest prevalence (5.3%). Cryptogenetic epilepsies had a lower prevalence (2.1%) than idiopathic epilepsies, but higher then symptomatic epilepsies (1.5%), both in generalised and focal forms (3.8% vs. 2.0% and 1.8% vs. 1.3%). A similar tendency was detected using MCR and SMR, with the higher values of risks/ratios for idiopathic and generalised epilepsies. Probands with idiopathic generalised epilepsies were highly concordant with respect to their relatives' type of epilepsy. Considering other strata factors, risks were higher in proband's epilepsies with an onset less then 14 years of age, while sex played no definite role in differentiating the family history. Conclusions: The Episcreen model permits a variety of stratification factors to measure family risk, including age at onset, epilepsy localisation and aetiology with a large sample of more than 10000 probands and 1065/40544 relatives affected and classified.

The multi-fluid SPH formulation by [1] is studied in the context of engineering flows encountered in the offshore industry where bubbly flows are of importance in some production processes. These particular flows being dominated by viscous and surface tension effects, the considered formulation includes models of these physical effects. This model is then used to simulate viscous incompressible bubbly flows of increasing complexity. These flows include the merging of two bubbles, the separation process in a bubbly flow in a closed tank and then in a simplified separator. Results are compared to numerical solutions when available. The influence of the Bond number on these interfacial flow evolutions is investigated in detail.Copyright © 2013 by ASME

The design process of a device for energy harvesting from sea waves is a complex task, which involves many different stages ranging from the initial mathematical models to an extensive field testing. Scale models are a crucial tool to asses the real world device performance and to validate the mathematical models used in the design process. This paper describes the first laboratory campaign of the scale model of an Inertial Sea Wave Energy Converter (ISWEC). The experiments were carried out in the wave tank of INSEAN (The Italian ship model basin, Rome) between February and April 2012. ISWEC uses a gyroscope to create an internal inertial reaction able to harvest wave power without exposing mechanical parts to the harsh oceanic environment. As for other WECs, the theoretically optimal control of ISWEC should be able to adjust the dynamic parameters of the PTO, such as the spring constant and energy absorbing damping, to maximize the energy absorption. The aim of this manuscript is to explore the effect of PTO control parameters on energy production for a given incoming wave

The study of the interactions between a gas cavity, the surrounding liquid and the nearby structures in the acoustic regime is very appealing because it involves several physical phenomena and it is of practical interest in different contexts: from the underwater explosions, to medical applications, to erosion of propellers. In Lingeman et al. (2009), the implosion of micro-bubbles close to human tissues has been studied in the case ultrasounds are used as a technique to remove calculi in human bodies. In Dular et al. 2009, it is shown that the cavitational bubble collapse can cause a shock wave associated with erosion damage on solid surfaces in hydraulic machinery. Although there are many practical studies associated with micro-bubble explosions most of the results are for military purposes in the case of underwater explosions of mines close to ships and offshore structures. There, it is necessary both to predict structural effects and to try to improve the design of the mentioned structures. To this purpose, physical tests were performed along the years and theories were developed (Cole 1948). Because of this availability of information, the first application of the present work focuses on underwater explosions for which most of the data useful for comparative purposes is available. Nonetheless, it is important to notice that all the above described problems are characterized by: 1) bubble oscillations with the generation and/or interaction with acoustic waves, 2) interaction of the acoustic waves with the surrounding structures, 3) reflection of the waves and 4) their interaction with the bubble. All these phenomena evolve within the so-called "acoustic phase", because compressibility is important for both water and gas phases. The study, here summarized, covers most of the points described above, some other results connected with this are referred into Colicchio et al. (2013). The following stage, where compressibility becomes unimportant for water and it is an issue only for the gaseous phase, has already been described in Colicchio et al. (2011).

A 3D Domain-Decomposition (DD) strategy has been developed to deal with violent wave-ship interactions involving water-on-deck and slamming occurrence. It couples a linear potential flow seakeeping solver with a Navier–Stokes method. The latter is applied in an inner domain where slamming, water-on-deck, and free surface fragmentation may occur, involving important flow nonlinearities. The field solver combines an approximated projection method with a level set technique for the free surface evolution. A hybrid strategy, combining the Eulerian level set concept to Lagrangian markers, is used to enforce more accurately the body boundary condition in case of high local curvatures. Main features of the weak and the strong coupling algorithms are described with special focus on the boundary conditions for the inner solver. Two ways of estimating the nonlinear loads by the Navier–Stokes method are investigated, on the basis of an extrapolation technique and an interpolation marching cubes algorithm, respectively. The DD is applied for the case of a freely floating patrol ship in head sea regular waves and compared against water-on-deck experiments in terms of flow evolution, body motions, and pressure on the hull. Improvement of the solver efficiency and accuracy is suggested. This is the pre-peer reviewed version of the following article: [3D domain decomposition for violent wave-ship interactions], which has been published in final form at [http://onlinelibrary.wiley.com/doi/10.1002/nme.4523/abstract]. This article may be used for non-commercial purposes in accordance with Wiley Terms and Conditions for Self-Archiving.

The gas-cavity problem with initially high pressure, evolving in a surrounding liquid, and interacting with a near body, is a very interesting research topic because it involves several physical phenomena and is of practical interest in different contexts. For instance, underwater explosions represent an important issue for ships and offshore structures. Therefore it is necessary to predict structural effects and try to improve vessel design. To this purpose, physical tests were performed along the years and theories were developed (Cole 1948). Another important application is in medical field. Implosion of micro-bubbles with ultrasound in biological flows is used within a noninvasive technique to remove calculi in human bodies (Lingeman et al. 2009). Here we first focus on the first application. When an underwater explosion occurs, a chemical reaction and a detonation process cause the formation of a hot gas with high pressure and the release of a shock wave traveling in the surrounding fluid. Then a superheated, spherical, bubble is formed which will first expand while the high pressure reduces in time and propagates in the surrounding liquid. Eventually the bubble starts to oscillate and affect the local pressure. In the first stage (shock wave) both the gas and the surrounding liquid behave as compressible, in the later stages (gas bubble) the acoustic wave will disappear and the water can be considered incompressible. The interaction of this two-phase fluid with a body will then depend on the vicinity of the body from the explosion zone and by the presence or not of other boundaries, e.g. the sea floor, the free surface.

In this paper, an in-depth study of SPH method, in its original weakly compressible version, is achieved on dedicated 2D and 3D free-surface flow test cases. These rather critical prototype problems shall constitute suitable test cases to get through when building a free-surface SPH model. The present work aims at investigating various numerical aspects of this method, often little mentioned in literature. In particular, a great care is paid to the dynamic part of the solution, which is critical to the local hydrodynamic load prediction. The role of numerical errors in the development of acoustic frequencies in the pressure signals is discussed, as well as the influence of the choice of the sound velocity. On the shown test problems, it is also evidenced that some numerical tools are crucial to ensure the robustness and accuracy of the standard SPH method. The convergence of our model is heuristically proved on these nonlinear prototype tests, showing at the same time the very satisfactory level of accuracy reached. Through these tests, some other numerical specificities of the SPH method are discussed, such as the self-redistribution of the particles occurring during the Lagrangian evolution. A higher order model is also proposed, and its advantages and drawbacks are discussed.

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The SPH model in his weakly compressible formulation is applied to simulate viscous flows at low and intermediate Reynolds numbers (10 < Re < 1000) around a cylinder. It is well know in the literature that this kind of problem represents a challenge for the proposed numerical model. To overcome these drawbacks, here a proper ghost-fluid technique is proposed to deal with blunt bodies in viscous fluids. The no-slip condition on the body surface is implemented combining the technique proposed by Takeda et al. (1994) with the one proposed by De Leffe et al. (2011). The global loads on bodies are efficiently evaluated in the ghost fluid framework. Making use of a weakly compressible approach, additional issues have to be addressed for the sound waves. An in-depth validation of the model is performed comparing the numerical outcome with experiments data from the literature and other numerical references. In particular the solver is validated on the prediction of: drag and lift coefficients, wake length and shape and angle of separation (low Reynolds number), shedding frequency and minimum and maximum angles of separation (intermediate Reynolds number). The influence of the domain size is discussed in order to avoid wall side effects and at the same time to limit the computational costs. Convergence of the numerical solutions have been checked for both global and local quantities choosing appropriate Reynolds-cell number for the different test cases.

Greco et al. (2011) tried to identify the proper numerical choices for the development of a three-dimensional DomainDecomposition (DD) strategy. It aims to study the violent interaction of FPSO ships with head-sea regular waves. The present work represents a contribution in this direction. The under development DD solver combines a Boundary Element Method (BEM) for the global linear seakeeping analysis in frequency domain with a Navier-Stokes (NS) method for the flow investigation in an inner sea region containing the forward portion of the vessel. In this region, water shipping and slamming events can be caused by the liquid-structure interactions, while it is assumed that the rest of the fluid domain can be suitably described by the linear potential-flow solver. Within the NS solver, a Projection method is adopted with a finite-difference scheme on an Eulerian grid and a Predictor-Corrector scheme for the time evolution. The solver is accurate to the second order. The evolution of the free surface is captured by means of a Level-Set (LS) technique updating in time the normal distance (with-sign) from the water-air interface. Moreover the influence of the air on the water is neglected and the velocity field is smoothly extended from the liquid to the gas domain. The non-slip bodyboundary condition is enforced through a hybrid Eulerian-Lagrangian approach combining the body LS function ?body (positive in the fluid) with point markers moving with the body and initially defined on a uniform grid four times finer than the minimum mesh size in the computational grid and within a band across the body surface six times larger than the maximum mesh size of the computational grid. The body points evolve in time carrying with them their distance from the body surface and this allows a more accurate estimate of ?body on the Eulerian grid by interpolation from the markers. The coupling between the outer and inner solvers is implemented as a weak and a strong strategy. In the former case, the information travels from the outer to the inner solver but not vice versa; in the latter, the information travels back and fourth. The NS solver needs initial and boundary conditions in terms of velocity, pressure and free surface elevation in the fluid and the body-boundary condition along the solid surface. The seakeeping solver feels the nonlinearities and possible viscous effects predicted in the inner domain through local and global loads acting on the ship portion inside this region. The rest of the ship hull is assumed to be subjected to the loads provided by the potential-flow outer solver. For a freely-floating vessel, the inner-domain global loads are introduced in the body-motion equations, so that the ship motion can be affected by the inner-flow features that can alter the flow pattern in the inner domain in return.

The Lattice Boltzmann Method (LBM) has been introduced about 20 years ago (see [1] and [2]), but only the recent development of a multiple-relaxation-time (MRT) collision model [3] has allowed its application to a wide range of Reynolds numbers. The comparison of its results with those obtained with a DNS incompressible-flow spectral element solver has also shown that it can correctly capture the details of the fluid turbulence [4], preserving its basic features of simplicity, flexibility and intrinsic parallelism. For these last features and for its enhanced suitability to deal with viscous flows, the LBM starts to be appealing to deal with high vorticity generated in water and its interaction with the both the solid and deformable boundaries as the air-water interface. For moving vehicles, e.g. submarines and airplanes, vorticity generation and its interaction with the downstream body part can cause boundary layer separation and transition to turbulence with a dramatic effect on the unsteady forces [5]. Here, we present the application of the MRT Lattice Boltzman model to a variety of fluid-body interaction dealing with vorticity generation and dissipation. The vorticity is either generated in 2D or 3D lid driven cavity. The computed flow features are widely compared with data available in literature. In particular, the velocity, vorticity and pressure evolution are analyzed versus the same quantities obtained with Navier-Stokes solutions or in the experiments. The results show convergence and accuracy of the LBM solver. Finally, the 3D problem of a vortex ring impacting on a flat wall is analyzed. The effects of the interaction with the solid boundary are highlighted: dissipation at low Reynolds (Re) numbers, instabilities at high Re.

This research activity represents an additional step toward a three-dimensional Domain-Decomposition strategy for violent wave-ship interaction involving water-on-deck and slamming phenomena. The focus is on FPSO ships and on head-sea waves and vessel without forward speed. The compound solver under development aims to couple a global 3D linear seakeeping solver with an inner 3D single-phase (water) Navier-Stokes (NS) method in a region containing the forward portion of the vessel. The NS solver is characterized by a Projection method with a finite-difference scheme on an Eulerian grid. The Level-Set (LS) technique is applied to step in time the free surface and combined with point markers to enforce adequately the body-boundary condition within a hybrid Eulerian-Lagrangian approach. This requires a much finer discretization than the computational grid around the body to preserve its geometrical details in time. As time goes on, the markers move in a Lagrangian fashion and then the LS function is estimated on the Eulerian grid by interpolation from the markers locations. Previous efforts have been documented for instance in Greco et al. (2009)) and Colicchio et al. (2010). Here some of the challenges and the possible solutions for the development of the inner 3D NS solver are discussed. The stress is on the boundary conditions.

The diffusive weakly-compressible SPH scheme described in Antuono et al.[1] (hereinafter denoted as Delta-SPH model) has been challenged in the analysis of impacts against structures generated by dam-break flows. Specifically, the 3D SPHERIC benchmarks number 1 and 2 have been studied as well as a novel 2D test case characterized by complex solid boundary profiles. In all the test cases the solid boundaries have been modelled through the boundary particle technique described in Colagrossi et al.[2] and a free-slip condition has been imposed along the solid profiles. For the SPHERIC benchmarks, the numerical results have been validated through comparison with the experimental data already available in the literature. Conversely, the new test case has been compared with the numerical results obtained through a Navier-Stokes Level-Set scheme. Finally, a brief insight on viscous effects has been provided for the latter test case. All test cases proved that the Delta-SPH scheme with the boundary particle technique is an accurate and robust solver for the prediction of the global fluid evolution and the local loads against structures.

The present analysis is a part of a research activity aimed to develop a numerical method reliable and efficient for seakeeping problems with water-on-deck occurrence. Highlighting the need for efficient solutions, the Domain-Decomposition (DD) algorithm was chosen. A two-dimensional DD strategy has already been developed and assessed by comparison against experimental data and other numerical results for fluid dynamic problems similar to the one of interest. Its details can be found for instance in Colicchio et al. (2006) and Greco et al. (2007) and have been documented also at previous workshops. A preliminary 3D analysis was obtained combining a weakly-nonlinear potential flow solver for the external seakeeping problem with an in-deck shallow-water approximation to handle the water-on-deck events (see i.e. Greco et al. 2009). This has the advantage of being very efficient but has limitation in terms of validity because the nonlinearities involved in the water-ship interactions are accounted for only partially. Just to mention, the water run-up is not properly described when high-speed jets are formed and the plunging-wave phase, which usually characterizes the initial stages of the water shipping, is not captured.