A computational methodology for the hydrodynamic analysis of horizontal axis marine current turbines is presented. The approach is based on a boundary integral equation method for inviscid flows originally developed for marine propellers and adapted here to describe the flow features that characterize hydrokinetic turbines. To this purpose, semi-analytical trailing wake and viscous-flow correction models are introduced. A validation study is performed by comparing hydrodynamic performance predictions with two experimental test cases and with results from other numerical models in the literature. The capability of the proposed methodology to correctly describe turbine thrust and power over a wide range of operating conditions is discussed. Viscosity effects associated to blade flow separation and stall are taken into account and predicted thrust and power are comparable with results of blade element methods that are largely used in the design of marine current turbines. The accuracy of numerical predictions tend to reduce in cases where turbine blades operate in off-design conditions.

This paper presents a novel theoretical and computational methodology for the generation of an onset turbulent field with prescribed properties in the numerical simulation of an arbitrary viscous flow. The methodology is based on the definition of a suitable distribution of volume force terms in the right–hand side of the Navier–Stokes equations. The distribution is represented by harmonic functions that are randomly variable in time and space. The intensity of the distribution is controlled by a simple PID strategy in order to obtain that the generated turbulent flow matches a prescribed turbulence intensity. A further condition is that a homogeneous isotropic flow is es- tablished downstream of the region where volume force terms are imposed. Although it is general, the proposed methodology is primarily intended for the computational modelling of hydrokinetic turbines in turbulent flows representative of tidal or riverine installations. A first numerical applica- tion is presented by considering the injection of homogeneous and isotropic turbulence with 16% intensity into a uniform unbounded flow. The analysis of statistical properties as auto-correlation, power spectral density, probability density functions, demonstrates that the generated flow tends to achieve satisfactory levels of stationarity and isotropy, whereas the simple control strategy used determines overestimated turbulent intensity levels.

An experimental study is carried out in a cavitation tunnel on a propeller operating downstream of a non-uniform wake. The goal of this work is to establish quantitative correlations between the near pressure field and the cavitation pattern that takes place on the propeller blades. The pressure field is measured at the walls of the test section and in the near wake of the propeller, and is combined with quantitative high-speed image recording of the cavitation pattern. Through simple harmonic analysis of the pressure data and image processing techniques that allow to retrieve the cavitation extension and volume, we discuss the potential sources that generate the pressure fluctuations. Time correlations are unambiguously established between pressure peak fluctuations and cavitation collapse events, based upon the Rayleigh collapse time. Finally, we design a model to predict the cavitation-induced pressure fluctuations from the derivation of the cavitation volume acceleration. This simple model demonstrates a remarkable agreement with the actual pressure field.

BACKGROUND AND OBJECTIVES. Rod-Cone Dystrophies (RCDs) are genetically determined retinal dystrophies, resulting in nyctalopia, visual field progressive reduction and visual acuity decay in the late stages. Retinitis Pigmentosa (RP) is the most described type. All modes of transmission can be identified in RP, with the autosomal dominant form (ADRP) accounting for about 20% of cases. To date, over 30 genes have been related to ADRP, with RP1 gene estimated to be involved in 5-10% of cases. In a cohort of patients affected by RCD and sharing the same geographic origin from Palermo province in Western Sicily, we identified a prevalent causative variant in the RP1 gene (NM_006269.2; c.2219C>G, p.Ser740*). Objective of our study was to analyse clinical and molecular data of this population and define the entity and the meaning of this finding. MATERIALS AND METHODS. Eighty-four patients with a diagnosis of RCD or RP underwent deep phenotyping, pedigree definition and molecular characterization, mostly by Next Generation Sequencing (NGS). All potentially pathogenic variants have been confirmed through direct sequencing and familial segregation. Statistical evaluation of resulting data has been performed. RESULTS. In 28 probands we identified a pathogenic variant (p.Ser740*) in the RP1 gene that resulted significantly prevalent. Some patients, after careful interviewing, were found to share the same pedigree; we ultimately defined 20 family groups with no traceable consanguinity. CONCLUSIONS. The high prevalence of the p.Ser740* variant in RP patients from Western Sicily unveils the presence of a founder effect, which has implications for the molecular diagnosis of RCD in patients coming from this Italian region. This variant can be primarily searched in RP affected subjects displaying compatible mode of transmission and phenotype, with an advantage in terms of costs and analysis time. Moreover, given its high prevalence, RP1 p.Ser740* variant could represent a potential candidate for the development of therapeutic strategies based on gene editing or translational read-through therapy for suppression of nonsense variants.